Zang-Sie Hung1 Je-Lueng Shie6 Yi-Hung Chen7 and Min-Hao Yuan17
1Graduate Institute of Environmental Engineering National Taiwan University Taipei 106 Taiwan2Department of Cosmetic Science and Application Lan Yang Institute of Technology Yilan 261 Taiwan3Department of Chemical Engineering National Taiwan University Taipei 106 Taiwan4Department of Environmental Science and Engineering Tunghai University Taichung 407 Taiwan5Chemical Engineering Division Institute of Nuclear Energy Research Atomic Energy Council Lungtan Taoyuan 325 Taiwan6Department of Environmental Engineering National Ilan University Yilan 260 Taiwan7Department of Chemical Engineering and Biotechnology National Taipei University of Technology Taipei 106 Taiwan
Correspondence should be addressed to Ching-Yuan Chang cychang3ntuedutw
Received 10 November 2014 Revised 23 May 2015 Accepted 10 June 2015
Academic Editor Zulin Zhang
Copyright copy 2015 Dar-Ren Ji et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
Dimethyl phthalate (DMP) was treated via wet oxygen oxidation process (WOP) The decomposition efficiency 120578DMP of DMPand mineralization efficiency 120578TOC of total organic carbons were measured to evaluate the effects of operation parameters on theperformance of WOP The results revealed that reaction temperature 119879 is the most affecting factor with a higher 119879 offering higher120578DMP and 120578TOC as expected The 120578DMP increases as rotating speed increases from 300 to 500 rpm with stirring enhancement of gasliquid mass transfer However it exhibits reduction effect at 700 rpm due to purging of dissolved oxygen by overstirring Regardingthe effects of pressure 119875
119879 a higher 119875
119879provides more oxygen for the forward reaction with DMP while overhigh 119875
119879increases
the absorption of gaseous products such as CO2and decomposes short-chain hydrocarbon fragments back into the solution thus
hindering the forward reaction For the tested 119875119879of 241 to 345MPa the results indicated that 241MPa is appropriate A longer
reaction time of course gives better performance At 500 rpm 483K 241MPa and 180min the 120578DMP and 120578TOC are 93 and 36respectively
1 Introduction
Phthalic acid esters (PAEs) including dimethyl phthalate(DMP) aremajor plasticizer to improve themechanical prop-erties of polymersThese polymers in turnwere used formak-ing tableware such as forks spoons dishes cups and lunch-boxes In fact the PAEs are added via noncovalent bondingwith the polymers It means PAEs are easily released to thehot soup heated food and oily contents from the tablewareand are orally ingested daily [1 2]
PAEs are endocrine disrupter substances (EDSs) tooTheir derivatives exhibit the similar structure with endocrineof human and other animals thus inducing the possibility of
cancer of human and the sex development of maleThe worstinfluence of EDSs to the ecosystem would be extinction forendanger species [3 4]
Although PAEs can be effectively removed from the aque-ous phase by adsorption [5] which also has been applied totreat other EDSs [6 7] it needs the regeneration of exhaustedadsorbent and the post treatment of concentrated regener-ation solution Activated sludge based biological sewagetreatment system needs 20 d to reach 71 mineralizationefficiency and is not beneficial to deal with toxic DMP It wasbiodegraded to monomethyl phthalate (MMP) and phthalicacid (PA) after treatment of 25 d [8ndash10] Some advanced solu-tions were proposed such as photolysis [11ndash13] photocatalysis
Hindawi Publishing Corporatione Scientific World JournalVolume 2015 Article ID 164594 8 pageshttpdxdoiorg1011552015164594
2 The Scientific World Journal
[11ndash15] electrochemical [16 17] and oxidant-added oxidation[11 14 18 19] methods Most of these treatments need postbi-ological process to further mineralize the decomposed com-pounds The unconsumed oxidant residue needs to be neu-tralized for matching the effluent standard [14 15] Processesof wet air oxidation (WAP) and wet oxygen oxidation (WOP)with (CWAP and CWOP) and without catalysts have beensuccessfully employed for oxidation treatments [20ndash30] Forexample in a study on the treatment of high-strength indus-trial wastewater Lin and Ho [27] reported that the chemicaloxygen demand (COD) removal efficiencies (120578COD) viaWAPWOP and CWAP with CuSO
4catalyst were 65 73 and 75
respectively at 473K 3MPa 300 rpm 1 Lmin gas flow rateand 2 h The application of WAP and WOP has the advan-tages avoiding the posttreatment of unwanted residual oxi-dant species and no need for the recovery and regener-ation of catalyst compared with oxidant-added oxidationand catalytic oxidation respectively The abundant dissolvedoxygen left can improve the performance of regular biologicalsewage system if needed [18] Moreover WOP gives 120578CODonly slightly less than catalytic oxidation while higher thanWAP This study thus employed WOP to treat the DMP-containing aqueous solution
2 Experimental Materials and Methods
21 Materials DMP with purity of 995 was supplied byHayashi Pure Chemical Industries Ltd (Osaka Japan) Themobile phase of high performance liquid chromatography(HPLC) was composed as acetonitrile (CH
3CN) DI water =
1 1 where acetonitrile of 100 purity was from J T BakerPhillipsburg NJThe solvent for apparatus cleaning is acetone(C3H4O)with purity of 995 byMallinckrodt Chemicals St
Louis MD The reagents for measurement of total organiccarbon (TOC) were (1) carrier gas 9999 N
2from San
Fu Chemical Co Ltd Taipei Taiwan (2) oxidant sodiumperoxydisulfate Na
2S2O8(99 purity) fromNacalai Tesque
Kyoto Japan (3) standard solution anhydrous potassiumbiphthalate KHP C
8H5KO4(990 purity) from Riedel-de
Haen Seelze Germany The reaction gas O2(9999 purity)
and air (O2 N2=20 80 9999purity)were purchased from
San Fu Chemical Co Ltd Taipei Taiwan
22 Methods The pressurized autoclave reaction system isshown in Figure 1 A 1 L bench top reactor is used It is madeof stainless steel 316 and equipped with a stirring rotor(DC-2RT44 Hsing-Tai Machinery Ind Co Taipei Taiwan)pressure display module and K-type thermal couple Thetemperature of heater (Model-TC-10A Macro FortunateTaipei Taiwan) is controlled with temperature controller(Model-BMW-500 Newlab Instrument Co Taipei Taiwan)Mass flow controller of Model 5850E manufactured byBrooks (Hatfield PA) is employed to control the gas flow rateThe bearing is cooled by cooling water from circulating bath(Model-B403 Firstek Scientific Taipei Taiwan) The uppercap of vessel has six holes with five for two sampling valvesthermal couple pressure gauge and release valve while onefor spare port The experiments were batch type with volume
Table 1 Operation parameters and range of WOP
Parameter of operation Operation rangeRotation speed Nr rpm 300 500 700Temperature 119879 K 463 473 483Pressure 119875
119879 MPa 241 267 310 345
Working gas of O2 Pure O2
of liquid of DMP solution (119881119871) of 400mL The sampling
valves are connected to cooling coilThe pressured vapor wascaptured to the coil and then cooled while keeping the pres-sure of the reactor After 5mL liquor was sampled the nonco-llected cooled liquid was conducted back to the reactor
The initial concentration (1198620) of DMP solution was
100mgL The concentrations of DMP of samples (119862) wereanalyzed by high performance liquid chromatography(HPLC Viscotek Model 500 Houston TX) while those oftotal organic carbon (TOC) were analyzed by TOC analyzer(Model 1010 OI Analytical NY) The column of HPLC is516C-18 of 25 cm times 46mm with ID 5120583m (Supelco IncBellefonte PA) The TOC analyzer uses nondispersive infra-red (NDIR) detector with carrier gas of N
2 oxidative agent
of 10 sodium peroxydisulfate solution and TOC standardsolution of anhydrous potassium biphthalate The precisionof experimental data was indicated in figures by error barwith standard deviation (120590
119899minus1) above and below the average
valueThe batchWOPprocess was performed in two stagesThe
first is heating stage The DMP-containing solution whichwas prebubbled by N
2to purge out the residual oxygen
was filled into the autoclave reactor and then heated fromroom temperature 283K to the set reaction temperature (119879)without any oxidant The tested temperatures were 463 473and 483K The initial time (119905) was noted as 0
119894 while the
final time of the first stage as 0119891 In the second stage the
working gas O2was introduced into the reactor at 119905 = 0
119891
to the desired operation pressure (119875119879) to continue the oxygen
oxidation reactionThe major operation parameters of batch WOP were
examined including (1) the stirring speed (Nr) (2) reactiontemperature 119879 and (3) operation pressure 119875
119879 The initial
pH value (pH0) was not adjusted while reflected by the 119862
0
Values of parameters are listed in Table 1 referring to thoseof others [27 29] For example Lin and Ho [27] performedthe experiments with Nr = 100ndash400 rpm 119875
119879= 25ndash50MPa
and119879 = 423ndash513 KThey reported that (1) 300 rpm and 3MPawere appropriate and (2)119879was themost important operationvariable with marginal enhancing effect for 119879 above 498KThe present study extended Nr to 500ndash700 rpm while itemployed 119875
119879and 119879 in the proper ranges of those of Lin and
Ho [27]
3 Results and Discussion
31 Effects of Rotation Speeds Nr Figure 2 illustrate thevariation of decomposition efficiency of DMP (120578DMP) withreaction time 119905 at various rotation speeds (Nr = 300 500
The Scientific World Journal 3
(1) Gas cylinder
1
4
3
2
8
9
10
56
500rpm
EV 210 mACV 210
7
(9) Temperature controller(5) Rotor
(2) Net (10) Circulating bath(6) Sampling port
(3) Reactor (7) Thermal probe
(4) Cooling loop (8) Heater
N2 O2
Figure 1 Schematic diagram of wet oxygen oxidation system
and 700 rpm) Other conditions are reaction temperature 119879= 473K and operation pressure 119875
119879= 241MPa As expected
more DMP is decomposed with longer 119905 giving higher 120578DMPThe 120578DMP is 66 78 and 66 at 119905 = 180min for Nr = 300500 and 700 rpm respectively In general a good gas liquidmixing assists the reaction Thus an increase of Nr from 300to 500 rpm increases the gas liquid mass transfer and offersa higher 120578DMP However the dissolved oxygen needed forreaction may be tripped or purged out from liquid to gas asfurther increasing the Nr say to 700 rpm reducing the 120578DMPThe Nr of 500 rpm leads to better increasing trend of 120578DMP
It is noted that although the effects of Nr of low rpm saybelow 300 rpm on the system performance were not inves-tigated in this study its qualitative effects may be realizedreferring to the work of Lin and Ho [27] dealing with thetreatment of high-strength industrial wastewaterThey exam-ined the effects of Nr from 100 to 400 rpm on the chemicaloxygen demand removal efficiencies 120578COD indicating appar-ently significant effect asNr below 300 rpmAnNr of 300 rpm
was thus adopted for their further experimentsThis thus jus-tified the adoption of 500 rpm for the followed experimentsof the present study assuring the good mixing
The effect of reaction time on the pH value of DMP-containing solution during WOP at different Nr is depictedin Figure 3 The decrease of pH value as oxidation decompo-sition takes place indicates the formation of acidic productsAlthough the decompositions are significant from 60 to180min as shown in Figure 2 the pH value stays nearly thesame at about 4 after 60min This might be due to the causethat some intermediate acidic products from the decompo-sition of DMP are further broken down to small acidic frag-ments of low solubility being released to gas phase leavingthe pH value of liquid essentially not altered for 119905 longerthan 60min The negligible effect of Nr on pH value as Nris sufficiently high as 300 rpm or higher might be attributedto the balance of enhancement of gas liquid mass transferand the purge of small acidic fragments by rotation stir-ring
4 The Scientific World Journal
0102030405060708090
100
Time (min)18012060
300500700
0i 0f
120578D
MP
()
Figure 2 Time variation of decomposition efficiency of DMP(120578DMP) via WOP at various rotating speeds Nr ◻ and Nr =300 500 and 700 rpm 119862
0= 100mg Lminus1 119881
119871= 400mL 119879 = 473K
and 119875119879= 241MPa Working gas after time = 0
119891is O2 Mean and
Standard deviation (SD 119899 minus 1method) at 119905 = 0119891 148 plusmn 28
18012060
300500700
123456789
10
Time (min)
pH
0i 0f
Figure 3 Time variation of pH value for the decomposition of DMPviaWOP at various Nr ◻ and Nr = 300 500 and 700 rpm 119862
0
= 100mg Lminus1 119881119871= 400mL 119879 = 473K and 119875
119879= 241MPa Working
gas after time = 0119891is O2 Mean and Standard deviation (SD 119899 minus 1
method) at 119905 = 0119891 44 plusmn 01
32 Effects of Reaction Temperature 119879 Figures 4 and 5 showthe time variations of 120578DMP and 120578TOC at reaction temperatures119879 of 463 473 and 483K for the case with Nr = 500 rpm and119875119879= 241MPa In the heating period from 0
119894to 0119891without
oxidant DMP underwent mainly the hydrothermal decom-position accompanied with slight mineralization The 120578DMPis 17 for 463 and 473K while 45 for 483K at the end ofheating periodwith no oxygenThedecomposition ofDMP isvery vigorous at high temperature But the 120578TOC is lower than10 for all three temperatures because of the oxidant lackWith the presence of oxygen the 120578DMP was greatly enhanced
0102030405060708090
100
18012060Time (min)
463K473K483K
0i 0f
120578D
MP
()
Figure 4 Time variation of 120578DMP via WOP at various temperatures119879 ◻ and I 119879 = 463 473 and 483K 119862
0= 100mg Lminus1 119881
119871=
400mL 119875119879= 241MPa and Nr = 500 rpmWorking gas after time =
0119891is O2
05
101520253035404550
18012060Time (min)
463K473K483K
0i 0f
120578TO
C(
)
Figure 5 Time variation ofmineralization efficiency ofDMP (120578TOC)
via WOP at various 119879 ◻ and I 119879 = 463 473 and 483K 1198620=
100mg Lminus1119881119871= 400mL119875
119879= 241MPa andNr = 500 rpmWorking
gas after time = 0119891is O2
while 120578TOC moderately improved The results indicated thelow reactivity of acidic product fragments with oxygen Asexpected both 120578DMP and 120578TOC increased as reaction time andtemperature increasedAt119879=483K and 119905= 180min the 120578DMPand 120578TOC were 93 and 36 respectively
Figure 6 demonstrates the variation of pH value withtime at various temperatures As in Figure 3 the pH valuedecreased with time while it levels off at a longer timedepending on the temperature for example at 60min forhigher temperatures of 473 and 483K while at 120min forlower temperature of 464K Thus a higher temperature casepromotes the decomposition reaction generally lowering and
The Scientific World Journal 5
123
4
7
89
10
pH
18012060Time (min)
463K473K483K
0i 0f
56
Figure 6 Time variation of pH value for the decomposition ofDMPvia WOP at various 119879 ◻ and I 119879 = 463 473 and 483K 119862
0=
100mg Lminus1119881119871= 400mL119875
119879= 241MPa andNr = 500 rpmWorking
gas after time = 0119891is O2 Mean and Standard deviation (SD 119899 minus 1
method) at 119905 = 0119894 56 plusmn 03
0102030405060708090
100
241 276310 345
18012060Time (min)
0i 0f
120578D
MP
()
Figure 7 Time variation of 120578DMP via WOP at various pressures ◻ + and times 119875
119879= 241 276 310 and 345MPa 119862
0= 100mg Lminus1 119881
119871
= 400mL 119879 = 483K and Nr = 500 rpm Working gas after time =0119891is O2 Mean and Standard deviation (SD 119899 minus 1method) at 119905 =
0119891 382 plusmn 53
leveling the pH value faster than the lower temperature caseFor 483K the pHvalue decreases to a leveling value of around4 after 60min
33 Effects of Operation Pressure 119875119879 Figures 7 and 8 present
the 120578DMP and 120578TOC versus time at 119875119879of 241 276 310 and
345MPa with Nr = 500 rpm and 119879 = 483K Both 120578DMP and120578TOC increase with time as expected The oxygen was filledto reach the desired pressure right after heating period thatis at 119905 = 0
119891 There is no oxidant in the time period from 0
119894to
0119891 The DMP is hydrothermally decomposed in heating
0
10
20
30
40
50
241 276310 345
18012060Time (min)
0i 0f
120578TO
C(
)
Figure 8 Time variation of 120578TOC via WOP at various pressures I + and times 119875
119879= 241 276 310 and 345MPa 119862
0= 100mg Lminus1 119881
119871
= 400mL 119879 = 483K and Nr = 500 rpm Working gas after time =0119891is O2 Mean and Standard deviation (SD 119899 minus 1method) at 119905 =
0119891 15 plusmn 13
period giving 120578DMP of around 33 to 45 The DMP is onlyslightly mineralized with low 120578TOC of about 03 to 31 Inthe presence of oxygen both 120578DMP and 120578TOC are enhancedas decomposition and mineralization proceed The oxidativedecomposition of DMP essentially consists of two-stagereversible reactions as illustrated in Figure 10 which isdiscussed in the next sectionThedecomposition ofDMPandintermediates to short-chain aliphatic acid and then CO
2are
proposed by referring to the mechanism for the ozonationof DMP with UV and catalyst presented by Chang et al[11] An increase of oxygen as well as temperature enhancesthe forward reactions toward mineralization way while theaccumulation of CO
2reversely inhibits the mineralization
according to LeChatelierrsquos principle [31]Thus sufficient oxy-genwith satisfactorily high119875
119879is needed to ensure the forward
oxidative decomposition reaction of DMP For example 119875119879
at 241MPa yields 120578DMP and 120578TOC of 93 and 36 at 180minrespectively Although higher 119875
119879with more oxygen favors
the forward decomposition reaction of DMP by oxygenthe absorption of accumulated gaseous products such asCO2and decomposed short-chain hydrocarbon fragments
in the closed reaction system increases as 119875119879increases The
reabsorption of gaseous products back into the solution thusinhibits the forward reaction Hence as indicated in Figures7 and 8 119875
119879of 241MPa is more appropriate than those of 276
to 345MPaFigure 9 plots pH value versus time at various 119875
119879 The
reduction of pHvalue in hydrothermal decomposition periodis more vigorous than that in the oxidative decompositionperiod The trend is similar to that of Figure 3 previouslydiscussed The increase of 119875
119879higher than 241MPa exhibits
negligible effect on the pH value The pH value levels offindicating the limited oxidative mineralization to CO
2and
the gas liquid absorption balance of acidic compounds ofCO2
and decomposed short-chain hydrocarbon fragments
6 The Scientific World Journal
Table 2 Comparison with some results of others for the decomposition of DMP via various methods
Study Method Result
Bauer et al [1] Anaerobic process in field municipal landfillleachates
DMP was completely hydrolysis to phthalic acidbut no cleavage for aromatic ring at different pHvalues
Wang et al [16]Electro-Fenton methods by electrodes traditionalgraphite cathode (G) carbon nanotube sponge(CNTS) and graphite gas diffusion electrode(GDE)
120578TOC G 15 GDE 35 CNTS 75
Souza et al [17] Electrochemical oxidation on F-doped Ti120573-PbO2anode in filter press reactor
DMP was completely decomposed underelectrolyte Na2SO4 and low current densities(10mA) 120578TOC = 25
Chang et al [11]
Catalytic ozonation (OZ) in high-gravity rotatingpacked bed (HG) with catalyst (Pt-Al2O3) andultraviolet (UV) (mix of UV-C UV-B and UV-Awith 200ndash280 280ndash315 and 315ndash400 nm and withintensities of 373 159 and 399Wmminus2)
120578DMP at 50min near 100 for Pt-OZ andUV-Pt-OZ120578TOC at 1 h 45 (OZ) 56 (UV-OZ) 57(Pt-OZ) 68 (UV-Pt-OZ)
Chen et al [13]Photocatalytic degradation using magneticpoly(methyl methacrylate) (mPMMA) and UV254 nm
120578DMP at 4 h 55ndash100 via TiO2mPMMA (C1)68ndash100 via Pt-TiO2mPMMA (C2)120578TOC at 4 h 75ndash375 via C1 11ndash64 via C2
Chen et al [19] Photocatalytic ozonation using TiO2 Al2O3 andTiO2Al2O3 catalysts
120578DMP at 30min 2ndash22 without O3 90ndash100 withO3 120578TOC 16ndash93 32ndash97 at 1 4 h
Chen et al [12] Photocatalysis using magnetic Pt-TiO2mPMMA UV 185 nm contributes better removal efficiencythan UV 254 nm
This study Wet oxygen oxidation 120578DMP and 120578TOC are 93 and 36 at Nr = 500 rpm119879 = 483K 119875
119879= 241MPa and 119905 = 180min
12
345
678
910
pH
241 276310 345
18012060Time (min)
0i 0f
Figure 9 Time variation of pH value for decomposition of DMPvia WOP at various pressures I + and times 119875
119879= 241 276 310
and 345MPa 1198620= 100mg Lminus1 119881
119871= 400mL 119879 = 483K and Nr =
500 rpm Working gas after time = 0119891is O2 Mean and Standard
deviation (SD 119899 minus 1 method) at 119905 = 0119894 52 plusmn 02 and at 119905 = 0
119891 41 plusmn
02
It is noted that the 119875119879was the sum of partial pressures
of oxygen (119875O2) and water vapor (119875WV) The saturation 119875WV
varies with temperature and is about 23MPa at 483K [27]Setting 119875
119879at 241 and 345MPa gave 119875O2
of 011 and 115MParespectively for supplying the oxygen for mineralizationreaction Referring to the study of Lin and Ho [27] using
25MPa as the lowest setting at 473K this analysis thus didnot employ 119875
119879lower than 241MPa at 483K
34 Mechanism of Two-Stage Decomposition of DMP viaWOP In this test the reactions are involved in componentsof DMP oxygen intermediate products and ultimate endproducts of CO
2and H
2OThe intermediates are the decom-
posed short-chain hydrocarbon fragmentswhich are acidic asreflected by the low pH value Accordingly the mechanism oftwo-stage decomposition of DMP via WOP may be depictedin Figure 10 In the heating stage without oxygen DMP isessentially hydrothermally decomposed to acidic fragmentslowering the pH value with significant 120578DMP while forminglittle CO
2with low 120578TOC With the introduction of oxygen
in the second stage oxidation of DMP and its decomposedfragments takes place destructing them into short-chainacids such as aliphatic acids or more completely to CO
2
and H2O The produced CO
2 however was kept within the
closed-batch reaction system in this studyThe stoichiometry equation for the forward oxidation
reaction of DMP can expressed as follows
C10H10O4 + 105O2 997888rarr 10CO2 + 5H2O (1)
For complete mineralization of DMP each mole DMP con-sumes 105 moles of O
2while producing 10 moles of CO
2
The CO2partial pressure contributed from the complete
mineralization of DMP is about 0045MPa by consuming0047MPa O
2 This reaction reduces the total pressure
slightly In fact the oxygen is not a limited factor because
The Scientific World Journal 7
Hydrothermolysis
DMPN2
298ndash483K
O2 O2
483K 483K
Short-chainaliphatic acid CO2 + H2O
Wet oxidation
intermediatesDMP +
Figure 10 Two stages for the decomposition of DMP via WOP
the minimum pressure applied is 241MPa exceeding theneed However the mineralization of reaction (1) is hinderedby the accumulation of product CO
2in the closed-batch
reaction system It forces the backward reaction of reaction(1) according to Le Chatelierrsquos principle [31] The equilibriumbalance of the forward and backward reaction thus limits thecomplete mineralization of DMP A release of CO
2gas out
from the reaction system would certainly assist approachingthe complete mineralization of DMP
35 Comparison with Results of Others Comparison of theresults of this study with others is illustrated in Table 2 Thepresent WOP can reach 120578DMP of 93 as high as the advancedmethods (AMs) of electrochemical oxidation photocatalyticdegradation and photocatalytic ozonationThe 120578TOC ofWOPof 36 is lower than those of the aforementioned AMs atsome conditions however comparable at other conditionsIt is noted that the WOP simply uses oxygen with demandof the thermal energy while other AMs need to employchemical agents catalysts and ozone along with electric orUV energies Thus the WOP is comparatively simple toapplyThe discrepancy of incomplete mineralization ofWOPmay be consummated with the postbiological treatment ifnecessary [20] The predecomposition of DMP by WOPcertainly greatly enhances the followed biological processing
4 Conclusions
This study treated the toxic endocrine disrupter substance(EDC) of DMP via wet oxidation using oxygen (WOP)without other oxidant additives being beneficial to thesubsequent biological process if necessary while avoiding thetreatment of unwanted oxidant residuesTheWOP effectivelydecomposed the DMP indicating its feasible application forthe treatment of other EDCs
Among the three factors investigated namely rotationspeed Nr reaction temperature 119879 and operation pressure 119875
119879
the effects of 119879 are most significant The proper conditionsfound are at 483K 241MPa and 500 rpm The 120578DMP and120578TOC of 93 and 36 respectively can be achieved at180minThe produced CO
2kept in the closed-batch reaction
system seems to resist the further mineralization reactionfrom intermediates The application of sequential releaseof CO
2while addition of O
2to improve the 120578TOC is thus
suggested
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors are grateful for the financial supports of thisresearch provided by theMinistry of Science and Technology(formerly the National Science Council) of Taiwan
References
[1] M J Bauer R Herrmann A Martin and H Zellmann ldquoChe-modynamics transport behaviour and treatment of phthalicacid esters in municipal landfill leachatesrdquo Water Science andTechnology vol 38 no 2 pp 185ndash192 1998
[2] M Zhang S Liu H Zhuang and Y Hu ldquoDetermination ofdimethyl phthalate in environment water samples by a highlysensitive indirect competitive ELISArdquoApplied Biochemistry andBiotechnology vol 166 no 2 pp 436ndash445 2012
[3] J P Sumpter ldquoEndocrine disrupters in the aquatic environmentan overviewrdquo Acta Hydrochimica et Hydrobiologica vol 33 no1 pp 9ndash16 2005
[4] C A Staples D R Peterson T F Parkerton and W J AdamsldquoThe environmental fate of phthalate esters a literature reviewrdquoChemosphere vol 35 no 4 pp 667ndash749 1997
[5] W Den H C Liu S F Chan K T Kin and C Huang ldquoAdsorp-tion of phthalate esters with multiwalled carbon nanotubesand its applicationrdquo Journal of Environmental Engineering andManagement vol 16 no 4 pp 275ndash282 2006
[6] A J Kumar andCNamasivayam ldquoUptake of endocrine disrup-tor bisphenol-A onto sulphuric acid activated carbon developedfrom biomass equilibrium and kinetic studiesrdquo SustainableEnvironment Research vol 24 no 1 pp 73ndash80 2014
[7] M F N Secondes V Naddeo F J Ballesteros and V BelgiornoldquoAdsorption of emerging contaminants enhanced by ultrasoundirradiationrdquo Sustainable Environment Research vol 24 no 5 pp349ndash355 2014
[8] DW Liang T Zhang H H P Fang and J He ldquoPhthalates bio-degradation in the environmentrdquo Applied Microbiology andBiotechnology vol 80 no 2 pp 183ndash198 2008
[9] D LWu B L Hu P Zheng andQMahmood ldquoAnoxic biodeg-radation of dimethyl phthalate (DMP) by activated sludge cul-tures under nitrate-reducing conditionsrdquo Journal of Environ-mental Sciences vol 19 no 10 pp 1252ndash1256 2007
[10] D L Wu Q Mahmood L L Wu and P Zheng ldquoActivatedsludge-mediated biodegradation of dimethyl phthalate underfermentative conditionsrdquo Journal of Environmental Sciences vol20 no 8 pp 922ndash926 2008
[11] C-C Chang C-Y Chiu C-Y Chang et al ldquoCombined pho-tolysis and catalytic ozonation of dimethyl phthalate in a high-gravity rotating packed bedrdquo Journal of Hazardous Materialsvol 161 no 1 pp 287ndash293 2009
8 The Scientific World Journal
[12] Y-H Chen L-L Chen and N-C Shang ldquoPhotocatalytic deg-radation of dimethyl phthalate in an aqueous solution with Pt-doped TiO
2-coated magnetic PMMAmicrospheresrdquo Journal of
Hazardous Materials vol 172 no 1 pp 20ndash29 2009[13] Y-H Chen N-C Shang L-L Chen et al ldquoPhotodecomposi-
tion of dimethyl phthalate in an aqueous solution withUV radi-ation using novel catalystsrdquo Desalination and Water Treatmentvol 52 no 16ndash18 pp 3377ndash3383 2014
[14] Y Jing L Li Q Zhang P Lu P Liu and X Lu ldquoPhotocatalyticozonation of dimethyl phthalate with TiO
[15] W Jiang J A Joens D D Dionysiou and K E OrsquoShea ldquoOpti-mization of photocatalytic performance of TiO
2coated glass
microspheres using response surface methodology and theapplication for degradation of dimethyl phthalaterdquo Journal ofPhotochemistry and Photobiology A Chemistry vol 262 pp 7ndash13 2013
[16] Y Wang Y Liu T Liu et al ldquoDimethyl phthalate degradationat novel and efficient electro-Fenton cathoderdquo Applied CatalysisB Environmental vol 156-157 pp 1ndash7 2014
[17] F L Souza J M Aquino K Irikura D W Miwa M ARodrigo and A J Motheo ldquoElectrochemical degradation of thedimethyl phthalate ester on a fluoride-doped Ti120573-PbO
2
anoderdquo Chemosphere vol 109 pp 187ndash194 2014[18] F Charest and E Chornet ldquoWet oxidation of active carbonrdquo
Canadian Journal of Chemical Engineering vol 54 no 6 pp190ndash196 1976
[19] Y-H Chen D-C Hsieh and N-C Shang ldquoEfficient miner-alization of dimethyl phthalate by catalytic ozonation usingTiO2Al2O3catalystrdquo Journal of Hazardous Materials vol 192
no 3 pp 1017ndash1025 2011[20] M J Dietrich T L Randall and P J Canney ldquoWet air oxidation
of hazardous organics in wastewaterrdquo Environmental Progressvol 4 no 3 pp 171ndash177 1985
[21] S Imamura H Kinunaka andN Kawabata ldquoThewet oxidationof organic compounds catalyzed by Co-Bi complex oxiderdquoBulletin of the Chemical Society of Japan vol 55 no 11 pp 3679ndash3680 1982
[22] M M Ito K Akita and H Inoue ldquoWet oxidation of oxygen-and nitrogen-containing organic compounds catalyzed bycobalt(III) oxiderdquo IndustrialsampEngineeringChemistry Researchvol 28 no 7 pp 894ndash899 1989
[23] J Levec M Herskowitz and J M Smith ldquoActive catalyst foroxidation of acetic-acid solutionsrdquo AIChE Journal vol 22 no5 pp 919ndash920 1976
[24] L X Li P S Chen andE FGloyna ldquoGeneralized kinetic-modelfor wet oxidation of organic-compoundsrdquo AIChE Journal vol37 no 11 pp 1687ndash1697 1991
[25] W H Li J L Huang H Wang A J Qi and J Xie ldquoTreatmentof acrylic acid waste water by catalytic wet oxidationrdquo Journalof Jilin Institute of Chemical Technology vol 24 no 3 pp 3ndash62007
[26] S H Lin and Y F Wu ldquoCatalytic wet air oxidation of phenolicwastewatersrdquo Environmental Technology vol 17 no 2 pp 175ndash181 1996
[27] S H Lin and S J Ho ldquoTreatment of high-strength industrialwastewater by wet air oxidationmdasha case studyrdquoWaste Manage-ment vol 17 no 1 pp 71ndash78 1997
[28] H Lin Sheng and S J Ho ldquoKinetics of wet air oxidation ofhigh-strength industrial wastewaterrdquo Journal of EnvironmentalEngineering vol 123 no 9 pp 852ndash858 1997
[29] V S Mishra V V Mahajani and J B Joshi ldquoWet air oxidationrdquoIndustrial and Engineering Chemistry Research vol 34 no 1 pp2ndash48 1995
[30] A Sadana and J R Katzer ldquoCatalytic oxidation of phenol inaqueous solution over copper oxiderdquo Industrial and EngineeringChemistry vol 13 no 2 pp 127ndash134 1974
[31] P W Atkins ldquoPrinciples of chemical equilibriumrdquo in The Ele-ments of Physical Chemistry chapter 7 Oxford University PressOxford UK 3rd edition 1993
[11ndash15] electrochemical [16 17] and oxidant-added oxidation[11 14 18 19] methods Most of these treatments need postbi-ological process to further mineralize the decomposed com-pounds The unconsumed oxidant residue needs to be neu-tralized for matching the effluent standard [14 15] Processesof wet air oxidation (WAP) and wet oxygen oxidation (WOP)with (CWAP and CWOP) and without catalysts have beensuccessfully employed for oxidation treatments [20ndash30] Forexample in a study on the treatment of high-strength indus-trial wastewater Lin and Ho [27] reported that the chemicaloxygen demand (COD) removal efficiencies (120578COD) viaWAPWOP and CWAP with CuSO
4catalyst were 65 73 and 75
respectively at 473K 3MPa 300 rpm 1 Lmin gas flow rateand 2 h The application of WAP and WOP has the advan-tages avoiding the posttreatment of unwanted residual oxi-dant species and no need for the recovery and regener-ation of catalyst compared with oxidant-added oxidationand catalytic oxidation respectively The abundant dissolvedoxygen left can improve the performance of regular biologicalsewage system if needed [18] Moreover WOP gives 120578CODonly slightly less than catalytic oxidation while higher thanWAP This study thus employed WOP to treat the DMP-containing aqueous solution
2 Experimental Materials and Methods
21 Materials DMP with purity of 995 was supplied byHayashi Pure Chemical Industries Ltd (Osaka Japan) Themobile phase of high performance liquid chromatography(HPLC) was composed as acetonitrile (CH
3CN) DI water =
1 1 where acetonitrile of 100 purity was from J T BakerPhillipsburg NJThe solvent for apparatus cleaning is acetone(C3H4O)with purity of 995 byMallinckrodt Chemicals St
Louis MD The reagents for measurement of total organiccarbon (TOC) were (1) carrier gas 9999 N
2from San
Fu Chemical Co Ltd Taipei Taiwan (2) oxidant sodiumperoxydisulfate Na
2S2O8(99 purity) fromNacalai Tesque
Kyoto Japan (3) standard solution anhydrous potassiumbiphthalate KHP C
8H5KO4(990 purity) from Riedel-de
Haen Seelze Germany The reaction gas O2(9999 purity)
and air (O2 N2=20 80 9999purity)were purchased from
San Fu Chemical Co Ltd Taipei Taiwan
22 Methods The pressurized autoclave reaction system isshown in Figure 1 A 1 L bench top reactor is used It is madeof stainless steel 316 and equipped with a stirring rotor(DC-2RT44 Hsing-Tai Machinery Ind Co Taipei Taiwan)pressure display module and K-type thermal couple Thetemperature of heater (Model-TC-10A Macro FortunateTaipei Taiwan) is controlled with temperature controller(Model-BMW-500 Newlab Instrument Co Taipei Taiwan)Mass flow controller of Model 5850E manufactured byBrooks (Hatfield PA) is employed to control the gas flow rateThe bearing is cooled by cooling water from circulating bath(Model-B403 Firstek Scientific Taipei Taiwan) The uppercap of vessel has six holes with five for two sampling valvesthermal couple pressure gauge and release valve while onefor spare port The experiments were batch type with volume
Table 1 Operation parameters and range of WOP
Parameter of operation Operation rangeRotation speed Nr rpm 300 500 700Temperature 119879 K 463 473 483Pressure 119875
119879 MPa 241 267 310 345
Working gas of O2 Pure O2
of liquid of DMP solution (119881119871) of 400mL The sampling
valves are connected to cooling coilThe pressured vapor wascaptured to the coil and then cooled while keeping the pres-sure of the reactor After 5mL liquor was sampled the nonco-llected cooled liquid was conducted back to the reactor
The initial concentration (1198620) of DMP solution was
100mgL The concentrations of DMP of samples (119862) wereanalyzed by high performance liquid chromatography(HPLC Viscotek Model 500 Houston TX) while those oftotal organic carbon (TOC) were analyzed by TOC analyzer(Model 1010 OI Analytical NY) The column of HPLC is516C-18 of 25 cm times 46mm with ID 5120583m (Supelco IncBellefonte PA) The TOC analyzer uses nondispersive infra-red (NDIR) detector with carrier gas of N
2 oxidative agent
of 10 sodium peroxydisulfate solution and TOC standardsolution of anhydrous potassium biphthalate The precisionof experimental data was indicated in figures by error barwith standard deviation (120590
119899minus1) above and below the average
valueThe batchWOPprocess was performed in two stagesThe
first is heating stage The DMP-containing solution whichwas prebubbled by N
2to purge out the residual oxygen
was filled into the autoclave reactor and then heated fromroom temperature 283K to the set reaction temperature (119879)without any oxidant The tested temperatures were 463 473and 483K The initial time (119905) was noted as 0
119894 while the
final time of the first stage as 0119891 In the second stage the
working gas O2was introduced into the reactor at 119905 = 0
119891
to the desired operation pressure (119875119879) to continue the oxygen
oxidation reactionThe major operation parameters of batch WOP were
examined including (1) the stirring speed (Nr) (2) reactiontemperature 119879 and (3) operation pressure 119875
119879 The initial
pH value (pH0) was not adjusted while reflected by the 119862
0
Values of parameters are listed in Table 1 referring to thoseof others [27 29] For example Lin and Ho [27] performedthe experiments with Nr = 100ndash400 rpm 119875
119879= 25ndash50MPa
and119879 = 423ndash513 KThey reported that (1) 300 rpm and 3MPawere appropriate and (2)119879was themost important operationvariable with marginal enhancing effect for 119879 above 498KThe present study extended Nr to 500ndash700 rpm while itemployed 119875
119879and 119879 in the proper ranges of those of Lin and
Ho [27]
3 Results and Discussion
31 Effects of Rotation Speeds Nr Figure 2 illustrate thevariation of decomposition efficiency of DMP (120578DMP) withreaction time 119905 at various rotation speeds (Nr = 300 500
The Scientific World Journal 3
(1) Gas cylinder
1
4
3
2
8
9
10
56
500rpm
EV 210 mACV 210
7
(9) Temperature controller(5) Rotor
(2) Net (10) Circulating bath(6) Sampling port
(3) Reactor (7) Thermal probe
(4) Cooling loop (8) Heater
N2 O2
Figure 1 Schematic diagram of wet oxygen oxidation system
and 700 rpm) Other conditions are reaction temperature 119879= 473K and operation pressure 119875
119879= 241MPa As expected
more DMP is decomposed with longer 119905 giving higher 120578DMPThe 120578DMP is 66 78 and 66 at 119905 = 180min for Nr = 300500 and 700 rpm respectively In general a good gas liquidmixing assists the reaction Thus an increase of Nr from 300to 500 rpm increases the gas liquid mass transfer and offersa higher 120578DMP However the dissolved oxygen needed forreaction may be tripped or purged out from liquid to gas asfurther increasing the Nr say to 700 rpm reducing the 120578DMPThe Nr of 500 rpm leads to better increasing trend of 120578DMP
It is noted that although the effects of Nr of low rpm saybelow 300 rpm on the system performance were not inves-tigated in this study its qualitative effects may be realizedreferring to the work of Lin and Ho [27] dealing with thetreatment of high-strength industrial wastewaterThey exam-ined the effects of Nr from 100 to 400 rpm on the chemicaloxygen demand removal efficiencies 120578COD indicating appar-ently significant effect asNr below 300 rpmAnNr of 300 rpm
was thus adopted for their further experimentsThis thus jus-tified the adoption of 500 rpm for the followed experimentsof the present study assuring the good mixing
The effect of reaction time on the pH value of DMP-containing solution during WOP at different Nr is depictedin Figure 3 The decrease of pH value as oxidation decompo-sition takes place indicates the formation of acidic productsAlthough the decompositions are significant from 60 to180min as shown in Figure 2 the pH value stays nearly thesame at about 4 after 60min This might be due to the causethat some intermediate acidic products from the decompo-sition of DMP are further broken down to small acidic frag-ments of low solubility being released to gas phase leavingthe pH value of liquid essentially not altered for 119905 longerthan 60min The negligible effect of Nr on pH value as Nris sufficiently high as 300 rpm or higher might be attributedto the balance of enhancement of gas liquid mass transferand the purge of small acidic fragments by rotation stir-ring
4 The Scientific World Journal
0102030405060708090
100
Time (min)18012060
300500700
0i 0f
120578D
MP
()
Figure 2 Time variation of decomposition efficiency of DMP(120578DMP) via WOP at various rotating speeds Nr ◻ and Nr =300 500 and 700 rpm 119862
0= 100mg Lminus1 119881
119871= 400mL 119879 = 473K
and 119875119879= 241MPa Working gas after time = 0
119891is O2 Mean and
Standard deviation (SD 119899 minus 1method) at 119905 = 0119891 148 plusmn 28
18012060
300500700
123456789
10
Time (min)
pH
0i 0f
Figure 3 Time variation of pH value for the decomposition of DMPviaWOP at various Nr ◻ and Nr = 300 500 and 700 rpm 119862
0
= 100mg Lminus1 119881119871= 400mL 119879 = 473K and 119875
119879= 241MPa Working
gas after time = 0119891is O2 Mean and Standard deviation (SD 119899 minus 1
method) at 119905 = 0119891 44 plusmn 01
32 Effects of Reaction Temperature 119879 Figures 4 and 5 showthe time variations of 120578DMP and 120578TOC at reaction temperatures119879 of 463 473 and 483K for the case with Nr = 500 rpm and119875119879= 241MPa In the heating period from 0
119894to 0119891without
oxidant DMP underwent mainly the hydrothermal decom-position accompanied with slight mineralization The 120578DMPis 17 for 463 and 473K while 45 for 483K at the end ofheating periodwith no oxygenThedecomposition ofDMP isvery vigorous at high temperature But the 120578TOC is lower than10 for all three temperatures because of the oxidant lackWith the presence of oxygen the 120578DMP was greatly enhanced
0102030405060708090
100
18012060Time (min)
463K473K483K
0i 0f
120578D
MP
()
Figure 4 Time variation of 120578DMP via WOP at various temperatures119879 ◻ and I 119879 = 463 473 and 483K 119862
0= 100mg Lminus1 119881
119871=
400mL 119875119879= 241MPa and Nr = 500 rpmWorking gas after time =
0119891is O2
05
101520253035404550
18012060Time (min)
463K473K483K
0i 0f
120578TO
C(
)
Figure 5 Time variation ofmineralization efficiency ofDMP (120578TOC)
via WOP at various 119879 ◻ and I 119879 = 463 473 and 483K 1198620=
100mg Lminus1119881119871= 400mL119875
119879= 241MPa andNr = 500 rpmWorking
gas after time = 0119891is O2
while 120578TOC moderately improved The results indicated thelow reactivity of acidic product fragments with oxygen Asexpected both 120578DMP and 120578TOC increased as reaction time andtemperature increasedAt119879=483K and 119905= 180min the 120578DMPand 120578TOC were 93 and 36 respectively
Figure 6 demonstrates the variation of pH value withtime at various temperatures As in Figure 3 the pH valuedecreased with time while it levels off at a longer timedepending on the temperature for example at 60min forhigher temperatures of 473 and 483K while at 120min forlower temperature of 464K Thus a higher temperature casepromotes the decomposition reaction generally lowering and
The Scientific World Journal 5
123
4
7
89
10
pH
18012060Time (min)
463K473K483K
0i 0f
56
Figure 6 Time variation of pH value for the decomposition ofDMPvia WOP at various 119879 ◻ and I 119879 = 463 473 and 483K 119862
0=
100mg Lminus1119881119871= 400mL119875
119879= 241MPa andNr = 500 rpmWorking
gas after time = 0119891is O2 Mean and Standard deviation (SD 119899 minus 1
method) at 119905 = 0119894 56 plusmn 03
0102030405060708090
100
241 276310 345
18012060Time (min)
0i 0f
120578D
MP
()
Figure 7 Time variation of 120578DMP via WOP at various pressures ◻ + and times 119875
119879= 241 276 310 and 345MPa 119862
0= 100mg Lminus1 119881
119871
= 400mL 119879 = 483K and Nr = 500 rpm Working gas after time =0119891is O2 Mean and Standard deviation (SD 119899 minus 1method) at 119905 =
0119891 382 plusmn 53
leveling the pH value faster than the lower temperature caseFor 483K the pHvalue decreases to a leveling value of around4 after 60min
33 Effects of Operation Pressure 119875119879 Figures 7 and 8 present
the 120578DMP and 120578TOC versus time at 119875119879of 241 276 310 and
345MPa with Nr = 500 rpm and 119879 = 483K Both 120578DMP and120578TOC increase with time as expected The oxygen was filledto reach the desired pressure right after heating period thatis at 119905 = 0
119891 There is no oxidant in the time period from 0
119894to
0119891 The DMP is hydrothermally decomposed in heating
0
10
20
30
40
50
241 276310 345
18012060Time (min)
0i 0f
120578TO
C(
)
Figure 8 Time variation of 120578TOC via WOP at various pressures I + and times 119875
119879= 241 276 310 and 345MPa 119862
0= 100mg Lminus1 119881
119871
= 400mL 119879 = 483K and Nr = 500 rpm Working gas after time =0119891is O2 Mean and Standard deviation (SD 119899 minus 1method) at 119905 =
0119891 15 plusmn 13
period giving 120578DMP of around 33 to 45 The DMP is onlyslightly mineralized with low 120578TOC of about 03 to 31 Inthe presence of oxygen both 120578DMP and 120578TOC are enhancedas decomposition and mineralization proceed The oxidativedecomposition of DMP essentially consists of two-stagereversible reactions as illustrated in Figure 10 which isdiscussed in the next sectionThedecomposition ofDMPandintermediates to short-chain aliphatic acid and then CO
2are
proposed by referring to the mechanism for the ozonationof DMP with UV and catalyst presented by Chang et al[11] An increase of oxygen as well as temperature enhancesthe forward reactions toward mineralization way while theaccumulation of CO
2reversely inhibits the mineralization
according to LeChatelierrsquos principle [31]Thus sufficient oxy-genwith satisfactorily high119875
119879is needed to ensure the forward
oxidative decomposition reaction of DMP For example 119875119879
at 241MPa yields 120578DMP and 120578TOC of 93 and 36 at 180minrespectively Although higher 119875
119879with more oxygen favors
the forward decomposition reaction of DMP by oxygenthe absorption of accumulated gaseous products such asCO2and decomposed short-chain hydrocarbon fragments
in the closed reaction system increases as 119875119879increases The
reabsorption of gaseous products back into the solution thusinhibits the forward reaction Hence as indicated in Figures7 and 8 119875
119879of 241MPa is more appropriate than those of 276
to 345MPaFigure 9 plots pH value versus time at various 119875
119879 The
reduction of pHvalue in hydrothermal decomposition periodis more vigorous than that in the oxidative decompositionperiod The trend is similar to that of Figure 3 previouslydiscussed The increase of 119875
119879higher than 241MPa exhibits
negligible effect on the pH value The pH value levels offindicating the limited oxidative mineralization to CO
2and
the gas liquid absorption balance of acidic compounds ofCO2
and decomposed short-chain hydrocarbon fragments
6 The Scientific World Journal
Table 2 Comparison with some results of others for the decomposition of DMP via various methods
Study Method Result
Bauer et al [1] Anaerobic process in field municipal landfillleachates
DMP was completely hydrolysis to phthalic acidbut no cleavage for aromatic ring at different pHvalues
Wang et al [16]Electro-Fenton methods by electrodes traditionalgraphite cathode (G) carbon nanotube sponge(CNTS) and graphite gas diffusion electrode(GDE)
120578TOC G 15 GDE 35 CNTS 75
Souza et al [17] Electrochemical oxidation on F-doped Ti120573-PbO2anode in filter press reactor
DMP was completely decomposed underelectrolyte Na2SO4 and low current densities(10mA) 120578TOC = 25
Chang et al [11]
Catalytic ozonation (OZ) in high-gravity rotatingpacked bed (HG) with catalyst (Pt-Al2O3) andultraviolet (UV) (mix of UV-C UV-B and UV-Awith 200ndash280 280ndash315 and 315ndash400 nm and withintensities of 373 159 and 399Wmminus2)
120578DMP at 50min near 100 for Pt-OZ andUV-Pt-OZ120578TOC at 1 h 45 (OZ) 56 (UV-OZ) 57(Pt-OZ) 68 (UV-Pt-OZ)
Chen et al [13]Photocatalytic degradation using magneticpoly(methyl methacrylate) (mPMMA) and UV254 nm
120578DMP at 4 h 55ndash100 via TiO2mPMMA (C1)68ndash100 via Pt-TiO2mPMMA (C2)120578TOC at 4 h 75ndash375 via C1 11ndash64 via C2
Chen et al [19] Photocatalytic ozonation using TiO2 Al2O3 andTiO2Al2O3 catalysts
120578DMP at 30min 2ndash22 without O3 90ndash100 withO3 120578TOC 16ndash93 32ndash97 at 1 4 h
Chen et al [12] Photocatalysis using magnetic Pt-TiO2mPMMA UV 185 nm contributes better removal efficiencythan UV 254 nm
This study Wet oxygen oxidation 120578DMP and 120578TOC are 93 and 36 at Nr = 500 rpm119879 = 483K 119875
119879= 241MPa and 119905 = 180min
12
345
678
910
pH
241 276310 345
18012060Time (min)
0i 0f
Figure 9 Time variation of pH value for decomposition of DMPvia WOP at various pressures I + and times 119875
119879= 241 276 310
and 345MPa 1198620= 100mg Lminus1 119881
119871= 400mL 119879 = 483K and Nr =
500 rpm Working gas after time = 0119891is O2 Mean and Standard
deviation (SD 119899 minus 1 method) at 119905 = 0119894 52 plusmn 02 and at 119905 = 0
119891 41 plusmn
02
It is noted that the 119875119879was the sum of partial pressures
of oxygen (119875O2) and water vapor (119875WV) The saturation 119875WV
varies with temperature and is about 23MPa at 483K [27]Setting 119875
119879at 241 and 345MPa gave 119875O2
of 011 and 115MParespectively for supplying the oxygen for mineralizationreaction Referring to the study of Lin and Ho [27] using
25MPa as the lowest setting at 473K this analysis thus didnot employ 119875
119879lower than 241MPa at 483K
34 Mechanism of Two-Stage Decomposition of DMP viaWOP In this test the reactions are involved in componentsof DMP oxygen intermediate products and ultimate endproducts of CO
2and H
2OThe intermediates are the decom-
posed short-chain hydrocarbon fragmentswhich are acidic asreflected by the low pH value Accordingly the mechanism oftwo-stage decomposition of DMP via WOP may be depictedin Figure 10 In the heating stage without oxygen DMP isessentially hydrothermally decomposed to acidic fragmentslowering the pH value with significant 120578DMP while forminglittle CO
2with low 120578TOC With the introduction of oxygen
in the second stage oxidation of DMP and its decomposedfragments takes place destructing them into short-chainacids such as aliphatic acids or more completely to CO
2
and H2O The produced CO
2 however was kept within the
closed-batch reaction system in this studyThe stoichiometry equation for the forward oxidation
reaction of DMP can expressed as follows
C10H10O4 + 105O2 997888rarr 10CO2 + 5H2O (1)
For complete mineralization of DMP each mole DMP con-sumes 105 moles of O
2while producing 10 moles of CO
2
The CO2partial pressure contributed from the complete
mineralization of DMP is about 0045MPa by consuming0047MPa O
2 This reaction reduces the total pressure
slightly In fact the oxygen is not a limited factor because
The Scientific World Journal 7
Hydrothermolysis
DMPN2
298ndash483K
O2 O2
483K 483K
Short-chainaliphatic acid CO2 + H2O
Wet oxidation
intermediatesDMP +
Figure 10 Two stages for the decomposition of DMP via WOP
the minimum pressure applied is 241MPa exceeding theneed However the mineralization of reaction (1) is hinderedby the accumulation of product CO
2in the closed-batch
reaction system It forces the backward reaction of reaction(1) according to Le Chatelierrsquos principle [31] The equilibriumbalance of the forward and backward reaction thus limits thecomplete mineralization of DMP A release of CO
2gas out
from the reaction system would certainly assist approachingthe complete mineralization of DMP
35 Comparison with Results of Others Comparison of theresults of this study with others is illustrated in Table 2 Thepresent WOP can reach 120578DMP of 93 as high as the advancedmethods (AMs) of electrochemical oxidation photocatalyticdegradation and photocatalytic ozonationThe 120578TOC ofWOPof 36 is lower than those of the aforementioned AMs atsome conditions however comparable at other conditionsIt is noted that the WOP simply uses oxygen with demandof the thermal energy while other AMs need to employchemical agents catalysts and ozone along with electric orUV energies Thus the WOP is comparatively simple toapplyThe discrepancy of incomplete mineralization ofWOPmay be consummated with the postbiological treatment ifnecessary [20] The predecomposition of DMP by WOPcertainly greatly enhances the followed biological processing
4 Conclusions
This study treated the toxic endocrine disrupter substance(EDC) of DMP via wet oxidation using oxygen (WOP)without other oxidant additives being beneficial to thesubsequent biological process if necessary while avoiding thetreatment of unwanted oxidant residuesTheWOP effectivelydecomposed the DMP indicating its feasible application forthe treatment of other EDCs
Among the three factors investigated namely rotationspeed Nr reaction temperature 119879 and operation pressure 119875
119879
the effects of 119879 are most significant The proper conditionsfound are at 483K 241MPa and 500 rpm The 120578DMP and120578TOC of 93 and 36 respectively can be achieved at180minThe produced CO
2kept in the closed-batch reaction
system seems to resist the further mineralization reactionfrom intermediates The application of sequential releaseof CO
2while addition of O
2to improve the 120578TOC is thus
suggested
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors are grateful for the financial supports of thisresearch provided by theMinistry of Science and Technology(formerly the National Science Council) of Taiwan
References
[1] M J Bauer R Herrmann A Martin and H Zellmann ldquoChe-modynamics transport behaviour and treatment of phthalicacid esters in municipal landfill leachatesrdquo Water Science andTechnology vol 38 no 2 pp 185ndash192 1998
[2] M Zhang S Liu H Zhuang and Y Hu ldquoDetermination ofdimethyl phthalate in environment water samples by a highlysensitive indirect competitive ELISArdquoApplied Biochemistry andBiotechnology vol 166 no 2 pp 436ndash445 2012
[3] J P Sumpter ldquoEndocrine disrupters in the aquatic environmentan overviewrdquo Acta Hydrochimica et Hydrobiologica vol 33 no1 pp 9ndash16 2005
[4] C A Staples D R Peterson T F Parkerton and W J AdamsldquoThe environmental fate of phthalate esters a literature reviewrdquoChemosphere vol 35 no 4 pp 667ndash749 1997
[5] W Den H C Liu S F Chan K T Kin and C Huang ldquoAdsorp-tion of phthalate esters with multiwalled carbon nanotubesand its applicationrdquo Journal of Environmental Engineering andManagement vol 16 no 4 pp 275ndash282 2006
[6] A J Kumar andCNamasivayam ldquoUptake of endocrine disrup-tor bisphenol-A onto sulphuric acid activated carbon developedfrom biomass equilibrium and kinetic studiesrdquo SustainableEnvironment Research vol 24 no 1 pp 73ndash80 2014
[7] M F N Secondes V Naddeo F J Ballesteros and V BelgiornoldquoAdsorption of emerging contaminants enhanced by ultrasoundirradiationrdquo Sustainable Environment Research vol 24 no 5 pp349ndash355 2014
[8] DW Liang T Zhang H H P Fang and J He ldquoPhthalates bio-degradation in the environmentrdquo Applied Microbiology andBiotechnology vol 80 no 2 pp 183ndash198 2008
[9] D LWu B L Hu P Zheng andQMahmood ldquoAnoxic biodeg-radation of dimethyl phthalate (DMP) by activated sludge cul-tures under nitrate-reducing conditionsrdquo Journal of Environ-mental Sciences vol 19 no 10 pp 1252ndash1256 2007
[10] D L Wu Q Mahmood L L Wu and P Zheng ldquoActivatedsludge-mediated biodegradation of dimethyl phthalate underfermentative conditionsrdquo Journal of Environmental Sciences vol20 no 8 pp 922ndash926 2008
[11] C-C Chang C-Y Chiu C-Y Chang et al ldquoCombined pho-tolysis and catalytic ozonation of dimethyl phthalate in a high-gravity rotating packed bedrdquo Journal of Hazardous Materialsvol 161 no 1 pp 287ndash293 2009
8 The Scientific World Journal
[12] Y-H Chen L-L Chen and N-C Shang ldquoPhotocatalytic deg-radation of dimethyl phthalate in an aqueous solution with Pt-doped TiO
2-coated magnetic PMMAmicrospheresrdquo Journal of
Hazardous Materials vol 172 no 1 pp 20ndash29 2009[13] Y-H Chen N-C Shang L-L Chen et al ldquoPhotodecomposi-
tion of dimethyl phthalate in an aqueous solution withUV radi-ation using novel catalystsrdquo Desalination and Water Treatmentvol 52 no 16ndash18 pp 3377ndash3383 2014
[14] Y Jing L Li Q Zhang P Lu P Liu and X Lu ldquoPhotocatalyticozonation of dimethyl phthalate with TiO
[15] W Jiang J A Joens D D Dionysiou and K E OrsquoShea ldquoOpti-mization of photocatalytic performance of TiO
2coated glass
microspheres using response surface methodology and theapplication for degradation of dimethyl phthalaterdquo Journal ofPhotochemistry and Photobiology A Chemistry vol 262 pp 7ndash13 2013
[16] Y Wang Y Liu T Liu et al ldquoDimethyl phthalate degradationat novel and efficient electro-Fenton cathoderdquo Applied CatalysisB Environmental vol 156-157 pp 1ndash7 2014
[17] F L Souza J M Aquino K Irikura D W Miwa M ARodrigo and A J Motheo ldquoElectrochemical degradation of thedimethyl phthalate ester on a fluoride-doped Ti120573-PbO
2
anoderdquo Chemosphere vol 109 pp 187ndash194 2014[18] F Charest and E Chornet ldquoWet oxidation of active carbonrdquo
Canadian Journal of Chemical Engineering vol 54 no 6 pp190ndash196 1976
[19] Y-H Chen D-C Hsieh and N-C Shang ldquoEfficient miner-alization of dimethyl phthalate by catalytic ozonation usingTiO2Al2O3catalystrdquo Journal of Hazardous Materials vol 192
no 3 pp 1017ndash1025 2011[20] M J Dietrich T L Randall and P J Canney ldquoWet air oxidation
of hazardous organics in wastewaterrdquo Environmental Progressvol 4 no 3 pp 171ndash177 1985
[21] S Imamura H Kinunaka andN Kawabata ldquoThewet oxidationof organic compounds catalyzed by Co-Bi complex oxiderdquoBulletin of the Chemical Society of Japan vol 55 no 11 pp 3679ndash3680 1982
[22] M M Ito K Akita and H Inoue ldquoWet oxidation of oxygen-and nitrogen-containing organic compounds catalyzed bycobalt(III) oxiderdquo IndustrialsampEngineeringChemistry Researchvol 28 no 7 pp 894ndash899 1989
[23] J Levec M Herskowitz and J M Smith ldquoActive catalyst foroxidation of acetic-acid solutionsrdquo AIChE Journal vol 22 no5 pp 919ndash920 1976
[24] L X Li P S Chen andE FGloyna ldquoGeneralized kinetic-modelfor wet oxidation of organic-compoundsrdquo AIChE Journal vol37 no 11 pp 1687ndash1697 1991
[25] W H Li J L Huang H Wang A J Qi and J Xie ldquoTreatmentof acrylic acid waste water by catalytic wet oxidationrdquo Journalof Jilin Institute of Chemical Technology vol 24 no 3 pp 3ndash62007
[26] S H Lin and Y F Wu ldquoCatalytic wet air oxidation of phenolicwastewatersrdquo Environmental Technology vol 17 no 2 pp 175ndash181 1996
[27] S H Lin and S J Ho ldquoTreatment of high-strength industrialwastewater by wet air oxidationmdasha case studyrdquoWaste Manage-ment vol 17 no 1 pp 71ndash78 1997
[28] H Lin Sheng and S J Ho ldquoKinetics of wet air oxidation ofhigh-strength industrial wastewaterrdquo Journal of EnvironmentalEngineering vol 123 no 9 pp 852ndash858 1997
[29] V S Mishra V V Mahajani and J B Joshi ldquoWet air oxidationrdquoIndustrial and Engineering Chemistry Research vol 34 no 1 pp2ndash48 1995
[30] A Sadana and J R Katzer ldquoCatalytic oxidation of phenol inaqueous solution over copper oxiderdquo Industrial and EngineeringChemistry vol 13 no 2 pp 127ndash134 1974
[31] P W Atkins ldquoPrinciples of chemical equilibriumrdquo in The Ele-ments of Physical Chemistry chapter 7 Oxford University PressOxford UK 3rd edition 1993
Figure 1 Schematic diagram of wet oxygen oxidation system
and 700 rpm) Other conditions are reaction temperature 119879= 473K and operation pressure 119875
119879= 241MPa As expected
more DMP is decomposed with longer 119905 giving higher 120578DMPThe 120578DMP is 66 78 and 66 at 119905 = 180min for Nr = 300500 and 700 rpm respectively In general a good gas liquidmixing assists the reaction Thus an increase of Nr from 300to 500 rpm increases the gas liquid mass transfer and offersa higher 120578DMP However the dissolved oxygen needed forreaction may be tripped or purged out from liquid to gas asfurther increasing the Nr say to 700 rpm reducing the 120578DMPThe Nr of 500 rpm leads to better increasing trend of 120578DMP
It is noted that although the effects of Nr of low rpm saybelow 300 rpm on the system performance were not inves-tigated in this study its qualitative effects may be realizedreferring to the work of Lin and Ho [27] dealing with thetreatment of high-strength industrial wastewaterThey exam-ined the effects of Nr from 100 to 400 rpm on the chemicaloxygen demand removal efficiencies 120578COD indicating appar-ently significant effect asNr below 300 rpmAnNr of 300 rpm
was thus adopted for their further experimentsThis thus jus-tified the adoption of 500 rpm for the followed experimentsof the present study assuring the good mixing
The effect of reaction time on the pH value of DMP-containing solution during WOP at different Nr is depictedin Figure 3 The decrease of pH value as oxidation decompo-sition takes place indicates the formation of acidic productsAlthough the decompositions are significant from 60 to180min as shown in Figure 2 the pH value stays nearly thesame at about 4 after 60min This might be due to the causethat some intermediate acidic products from the decompo-sition of DMP are further broken down to small acidic frag-ments of low solubility being released to gas phase leavingthe pH value of liquid essentially not altered for 119905 longerthan 60min The negligible effect of Nr on pH value as Nris sufficiently high as 300 rpm or higher might be attributedto the balance of enhancement of gas liquid mass transferand the purge of small acidic fragments by rotation stir-ring
4 The Scientific World Journal
0102030405060708090
100
Time (min)18012060
300500700
0i 0f
120578D
MP
()
Figure 2 Time variation of decomposition efficiency of DMP(120578DMP) via WOP at various rotating speeds Nr ◻ and Nr =300 500 and 700 rpm 119862
0= 100mg Lminus1 119881
119871= 400mL 119879 = 473K
and 119875119879= 241MPa Working gas after time = 0
119891is O2 Mean and
Standard deviation (SD 119899 minus 1method) at 119905 = 0119891 148 plusmn 28
18012060
300500700
123456789
10
Time (min)
pH
0i 0f
Figure 3 Time variation of pH value for the decomposition of DMPviaWOP at various Nr ◻ and Nr = 300 500 and 700 rpm 119862
0
= 100mg Lminus1 119881119871= 400mL 119879 = 473K and 119875
119879= 241MPa Working
gas after time = 0119891is O2 Mean and Standard deviation (SD 119899 minus 1
method) at 119905 = 0119891 44 plusmn 01
32 Effects of Reaction Temperature 119879 Figures 4 and 5 showthe time variations of 120578DMP and 120578TOC at reaction temperatures119879 of 463 473 and 483K for the case with Nr = 500 rpm and119875119879= 241MPa In the heating period from 0
119894to 0119891without
oxidant DMP underwent mainly the hydrothermal decom-position accompanied with slight mineralization The 120578DMPis 17 for 463 and 473K while 45 for 483K at the end ofheating periodwith no oxygenThedecomposition ofDMP isvery vigorous at high temperature But the 120578TOC is lower than10 for all three temperatures because of the oxidant lackWith the presence of oxygen the 120578DMP was greatly enhanced
0102030405060708090
100
18012060Time (min)
463K473K483K
0i 0f
120578D
MP
()
Figure 4 Time variation of 120578DMP via WOP at various temperatures119879 ◻ and I 119879 = 463 473 and 483K 119862
0= 100mg Lminus1 119881
119871=
400mL 119875119879= 241MPa and Nr = 500 rpmWorking gas after time =
0119891is O2
05
101520253035404550
18012060Time (min)
463K473K483K
0i 0f
120578TO
C(
)
Figure 5 Time variation ofmineralization efficiency ofDMP (120578TOC)
via WOP at various 119879 ◻ and I 119879 = 463 473 and 483K 1198620=
100mg Lminus1119881119871= 400mL119875
119879= 241MPa andNr = 500 rpmWorking
gas after time = 0119891is O2
while 120578TOC moderately improved The results indicated thelow reactivity of acidic product fragments with oxygen Asexpected both 120578DMP and 120578TOC increased as reaction time andtemperature increasedAt119879=483K and 119905= 180min the 120578DMPand 120578TOC were 93 and 36 respectively
Figure 6 demonstrates the variation of pH value withtime at various temperatures As in Figure 3 the pH valuedecreased with time while it levels off at a longer timedepending on the temperature for example at 60min forhigher temperatures of 473 and 483K while at 120min forlower temperature of 464K Thus a higher temperature casepromotes the decomposition reaction generally lowering and
The Scientific World Journal 5
123
4
7
89
10
pH
18012060Time (min)
463K473K483K
0i 0f
56
Figure 6 Time variation of pH value for the decomposition ofDMPvia WOP at various 119879 ◻ and I 119879 = 463 473 and 483K 119862
0=
100mg Lminus1119881119871= 400mL119875
119879= 241MPa andNr = 500 rpmWorking
gas after time = 0119891is O2 Mean and Standard deviation (SD 119899 minus 1
method) at 119905 = 0119894 56 plusmn 03
0102030405060708090
100
241 276310 345
18012060Time (min)
0i 0f
120578D
MP
()
Figure 7 Time variation of 120578DMP via WOP at various pressures ◻ + and times 119875
119879= 241 276 310 and 345MPa 119862
0= 100mg Lminus1 119881
119871
= 400mL 119879 = 483K and Nr = 500 rpm Working gas after time =0119891is O2 Mean and Standard deviation (SD 119899 minus 1method) at 119905 =
0119891 382 plusmn 53
leveling the pH value faster than the lower temperature caseFor 483K the pHvalue decreases to a leveling value of around4 after 60min
33 Effects of Operation Pressure 119875119879 Figures 7 and 8 present
the 120578DMP and 120578TOC versus time at 119875119879of 241 276 310 and
345MPa with Nr = 500 rpm and 119879 = 483K Both 120578DMP and120578TOC increase with time as expected The oxygen was filledto reach the desired pressure right after heating period thatis at 119905 = 0
119891 There is no oxidant in the time period from 0
119894to
0119891 The DMP is hydrothermally decomposed in heating
0
10
20
30
40
50
241 276310 345
18012060Time (min)
0i 0f
120578TO
C(
)
Figure 8 Time variation of 120578TOC via WOP at various pressures I + and times 119875
119879= 241 276 310 and 345MPa 119862
0= 100mg Lminus1 119881
119871
= 400mL 119879 = 483K and Nr = 500 rpm Working gas after time =0119891is O2 Mean and Standard deviation (SD 119899 minus 1method) at 119905 =
0119891 15 plusmn 13
period giving 120578DMP of around 33 to 45 The DMP is onlyslightly mineralized with low 120578TOC of about 03 to 31 Inthe presence of oxygen both 120578DMP and 120578TOC are enhancedas decomposition and mineralization proceed The oxidativedecomposition of DMP essentially consists of two-stagereversible reactions as illustrated in Figure 10 which isdiscussed in the next sectionThedecomposition ofDMPandintermediates to short-chain aliphatic acid and then CO
2are
proposed by referring to the mechanism for the ozonationof DMP with UV and catalyst presented by Chang et al[11] An increase of oxygen as well as temperature enhancesthe forward reactions toward mineralization way while theaccumulation of CO
2reversely inhibits the mineralization
according to LeChatelierrsquos principle [31]Thus sufficient oxy-genwith satisfactorily high119875
119879is needed to ensure the forward
oxidative decomposition reaction of DMP For example 119875119879
at 241MPa yields 120578DMP and 120578TOC of 93 and 36 at 180minrespectively Although higher 119875
119879with more oxygen favors
the forward decomposition reaction of DMP by oxygenthe absorption of accumulated gaseous products such asCO2and decomposed short-chain hydrocarbon fragments
in the closed reaction system increases as 119875119879increases The
reabsorption of gaseous products back into the solution thusinhibits the forward reaction Hence as indicated in Figures7 and 8 119875
119879of 241MPa is more appropriate than those of 276
to 345MPaFigure 9 plots pH value versus time at various 119875
119879 The
reduction of pHvalue in hydrothermal decomposition periodis more vigorous than that in the oxidative decompositionperiod The trend is similar to that of Figure 3 previouslydiscussed The increase of 119875
119879higher than 241MPa exhibits
negligible effect on the pH value The pH value levels offindicating the limited oxidative mineralization to CO
2and
the gas liquid absorption balance of acidic compounds ofCO2
and decomposed short-chain hydrocarbon fragments
6 The Scientific World Journal
Table 2 Comparison with some results of others for the decomposition of DMP via various methods
Study Method Result
Bauer et al [1] Anaerobic process in field municipal landfillleachates
DMP was completely hydrolysis to phthalic acidbut no cleavage for aromatic ring at different pHvalues
Wang et al [16]Electro-Fenton methods by electrodes traditionalgraphite cathode (G) carbon nanotube sponge(CNTS) and graphite gas diffusion electrode(GDE)
120578TOC G 15 GDE 35 CNTS 75
Souza et al [17] Electrochemical oxidation on F-doped Ti120573-PbO2anode in filter press reactor
DMP was completely decomposed underelectrolyte Na2SO4 and low current densities(10mA) 120578TOC = 25
Chang et al [11]
Catalytic ozonation (OZ) in high-gravity rotatingpacked bed (HG) with catalyst (Pt-Al2O3) andultraviolet (UV) (mix of UV-C UV-B and UV-Awith 200ndash280 280ndash315 and 315ndash400 nm and withintensities of 373 159 and 399Wmminus2)
120578DMP at 50min near 100 for Pt-OZ andUV-Pt-OZ120578TOC at 1 h 45 (OZ) 56 (UV-OZ) 57(Pt-OZ) 68 (UV-Pt-OZ)
Chen et al [13]Photocatalytic degradation using magneticpoly(methyl methacrylate) (mPMMA) and UV254 nm
120578DMP at 4 h 55ndash100 via TiO2mPMMA (C1)68ndash100 via Pt-TiO2mPMMA (C2)120578TOC at 4 h 75ndash375 via C1 11ndash64 via C2
Chen et al [19] Photocatalytic ozonation using TiO2 Al2O3 andTiO2Al2O3 catalysts
120578DMP at 30min 2ndash22 without O3 90ndash100 withO3 120578TOC 16ndash93 32ndash97 at 1 4 h
Chen et al [12] Photocatalysis using magnetic Pt-TiO2mPMMA UV 185 nm contributes better removal efficiencythan UV 254 nm
This study Wet oxygen oxidation 120578DMP and 120578TOC are 93 and 36 at Nr = 500 rpm119879 = 483K 119875
119879= 241MPa and 119905 = 180min
12
345
678
910
pH
241 276310 345
18012060Time (min)
0i 0f
Figure 9 Time variation of pH value for decomposition of DMPvia WOP at various pressures I + and times 119875
119879= 241 276 310
and 345MPa 1198620= 100mg Lminus1 119881
119871= 400mL 119879 = 483K and Nr =
500 rpm Working gas after time = 0119891is O2 Mean and Standard
deviation (SD 119899 minus 1 method) at 119905 = 0119894 52 plusmn 02 and at 119905 = 0
119891 41 plusmn
02
It is noted that the 119875119879was the sum of partial pressures
of oxygen (119875O2) and water vapor (119875WV) The saturation 119875WV
varies with temperature and is about 23MPa at 483K [27]Setting 119875
119879at 241 and 345MPa gave 119875O2
of 011 and 115MParespectively for supplying the oxygen for mineralizationreaction Referring to the study of Lin and Ho [27] using
25MPa as the lowest setting at 473K this analysis thus didnot employ 119875
119879lower than 241MPa at 483K
34 Mechanism of Two-Stage Decomposition of DMP viaWOP In this test the reactions are involved in componentsof DMP oxygen intermediate products and ultimate endproducts of CO
2and H
2OThe intermediates are the decom-
posed short-chain hydrocarbon fragmentswhich are acidic asreflected by the low pH value Accordingly the mechanism oftwo-stage decomposition of DMP via WOP may be depictedin Figure 10 In the heating stage without oxygen DMP isessentially hydrothermally decomposed to acidic fragmentslowering the pH value with significant 120578DMP while forminglittle CO
2with low 120578TOC With the introduction of oxygen
in the second stage oxidation of DMP and its decomposedfragments takes place destructing them into short-chainacids such as aliphatic acids or more completely to CO
2
and H2O The produced CO
2 however was kept within the
closed-batch reaction system in this studyThe stoichiometry equation for the forward oxidation
reaction of DMP can expressed as follows
C10H10O4 + 105O2 997888rarr 10CO2 + 5H2O (1)
For complete mineralization of DMP each mole DMP con-sumes 105 moles of O
2while producing 10 moles of CO
2
The CO2partial pressure contributed from the complete
mineralization of DMP is about 0045MPa by consuming0047MPa O
2 This reaction reduces the total pressure
slightly In fact the oxygen is not a limited factor because
The Scientific World Journal 7
Hydrothermolysis
DMPN2
298ndash483K
O2 O2
483K 483K
Short-chainaliphatic acid CO2 + H2O
Wet oxidation
intermediatesDMP +
Figure 10 Two stages for the decomposition of DMP via WOP
the minimum pressure applied is 241MPa exceeding theneed However the mineralization of reaction (1) is hinderedby the accumulation of product CO
2in the closed-batch
reaction system It forces the backward reaction of reaction(1) according to Le Chatelierrsquos principle [31] The equilibriumbalance of the forward and backward reaction thus limits thecomplete mineralization of DMP A release of CO
2gas out
from the reaction system would certainly assist approachingthe complete mineralization of DMP
35 Comparison with Results of Others Comparison of theresults of this study with others is illustrated in Table 2 Thepresent WOP can reach 120578DMP of 93 as high as the advancedmethods (AMs) of electrochemical oxidation photocatalyticdegradation and photocatalytic ozonationThe 120578TOC ofWOPof 36 is lower than those of the aforementioned AMs atsome conditions however comparable at other conditionsIt is noted that the WOP simply uses oxygen with demandof the thermal energy while other AMs need to employchemical agents catalysts and ozone along with electric orUV energies Thus the WOP is comparatively simple toapplyThe discrepancy of incomplete mineralization ofWOPmay be consummated with the postbiological treatment ifnecessary [20] The predecomposition of DMP by WOPcertainly greatly enhances the followed biological processing
4 Conclusions
This study treated the toxic endocrine disrupter substance(EDC) of DMP via wet oxidation using oxygen (WOP)without other oxidant additives being beneficial to thesubsequent biological process if necessary while avoiding thetreatment of unwanted oxidant residuesTheWOP effectivelydecomposed the DMP indicating its feasible application forthe treatment of other EDCs
Among the three factors investigated namely rotationspeed Nr reaction temperature 119879 and operation pressure 119875
119879
the effects of 119879 are most significant The proper conditionsfound are at 483K 241MPa and 500 rpm The 120578DMP and120578TOC of 93 and 36 respectively can be achieved at180minThe produced CO
2kept in the closed-batch reaction
system seems to resist the further mineralization reactionfrom intermediates The application of sequential releaseof CO
2while addition of O
2to improve the 120578TOC is thus
suggested
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors are grateful for the financial supports of thisresearch provided by theMinistry of Science and Technology(formerly the National Science Council) of Taiwan
References
[1] M J Bauer R Herrmann A Martin and H Zellmann ldquoChe-modynamics transport behaviour and treatment of phthalicacid esters in municipal landfill leachatesrdquo Water Science andTechnology vol 38 no 2 pp 185ndash192 1998
[2] M Zhang S Liu H Zhuang and Y Hu ldquoDetermination ofdimethyl phthalate in environment water samples by a highlysensitive indirect competitive ELISArdquoApplied Biochemistry andBiotechnology vol 166 no 2 pp 436ndash445 2012
[3] J P Sumpter ldquoEndocrine disrupters in the aquatic environmentan overviewrdquo Acta Hydrochimica et Hydrobiologica vol 33 no1 pp 9ndash16 2005
[4] C A Staples D R Peterson T F Parkerton and W J AdamsldquoThe environmental fate of phthalate esters a literature reviewrdquoChemosphere vol 35 no 4 pp 667ndash749 1997
[5] W Den H C Liu S F Chan K T Kin and C Huang ldquoAdsorp-tion of phthalate esters with multiwalled carbon nanotubesand its applicationrdquo Journal of Environmental Engineering andManagement vol 16 no 4 pp 275ndash282 2006
[6] A J Kumar andCNamasivayam ldquoUptake of endocrine disrup-tor bisphenol-A onto sulphuric acid activated carbon developedfrom biomass equilibrium and kinetic studiesrdquo SustainableEnvironment Research vol 24 no 1 pp 73ndash80 2014
[7] M F N Secondes V Naddeo F J Ballesteros and V BelgiornoldquoAdsorption of emerging contaminants enhanced by ultrasoundirradiationrdquo Sustainable Environment Research vol 24 no 5 pp349ndash355 2014
[8] DW Liang T Zhang H H P Fang and J He ldquoPhthalates bio-degradation in the environmentrdquo Applied Microbiology andBiotechnology vol 80 no 2 pp 183ndash198 2008
[9] D LWu B L Hu P Zheng andQMahmood ldquoAnoxic biodeg-radation of dimethyl phthalate (DMP) by activated sludge cul-tures under nitrate-reducing conditionsrdquo Journal of Environ-mental Sciences vol 19 no 10 pp 1252ndash1256 2007
[10] D L Wu Q Mahmood L L Wu and P Zheng ldquoActivatedsludge-mediated biodegradation of dimethyl phthalate underfermentative conditionsrdquo Journal of Environmental Sciences vol20 no 8 pp 922ndash926 2008
[11] C-C Chang C-Y Chiu C-Y Chang et al ldquoCombined pho-tolysis and catalytic ozonation of dimethyl phthalate in a high-gravity rotating packed bedrdquo Journal of Hazardous Materialsvol 161 no 1 pp 287ndash293 2009
8 The Scientific World Journal
[12] Y-H Chen L-L Chen and N-C Shang ldquoPhotocatalytic deg-radation of dimethyl phthalate in an aqueous solution with Pt-doped TiO
2-coated magnetic PMMAmicrospheresrdquo Journal of
Hazardous Materials vol 172 no 1 pp 20ndash29 2009[13] Y-H Chen N-C Shang L-L Chen et al ldquoPhotodecomposi-
tion of dimethyl phthalate in an aqueous solution withUV radi-ation using novel catalystsrdquo Desalination and Water Treatmentvol 52 no 16ndash18 pp 3377ndash3383 2014
[14] Y Jing L Li Q Zhang P Lu P Liu and X Lu ldquoPhotocatalyticozonation of dimethyl phthalate with TiO
[15] W Jiang J A Joens D D Dionysiou and K E OrsquoShea ldquoOpti-mization of photocatalytic performance of TiO
2coated glass
microspheres using response surface methodology and theapplication for degradation of dimethyl phthalaterdquo Journal ofPhotochemistry and Photobiology A Chemistry vol 262 pp 7ndash13 2013
[16] Y Wang Y Liu T Liu et al ldquoDimethyl phthalate degradationat novel and efficient electro-Fenton cathoderdquo Applied CatalysisB Environmental vol 156-157 pp 1ndash7 2014
[17] F L Souza J M Aquino K Irikura D W Miwa M ARodrigo and A J Motheo ldquoElectrochemical degradation of thedimethyl phthalate ester on a fluoride-doped Ti120573-PbO
2
anoderdquo Chemosphere vol 109 pp 187ndash194 2014[18] F Charest and E Chornet ldquoWet oxidation of active carbonrdquo
Canadian Journal of Chemical Engineering vol 54 no 6 pp190ndash196 1976
[19] Y-H Chen D-C Hsieh and N-C Shang ldquoEfficient miner-alization of dimethyl phthalate by catalytic ozonation usingTiO2Al2O3catalystrdquo Journal of Hazardous Materials vol 192
no 3 pp 1017ndash1025 2011[20] M J Dietrich T L Randall and P J Canney ldquoWet air oxidation
of hazardous organics in wastewaterrdquo Environmental Progressvol 4 no 3 pp 171ndash177 1985
[21] S Imamura H Kinunaka andN Kawabata ldquoThewet oxidationof organic compounds catalyzed by Co-Bi complex oxiderdquoBulletin of the Chemical Society of Japan vol 55 no 11 pp 3679ndash3680 1982
[22] M M Ito K Akita and H Inoue ldquoWet oxidation of oxygen-and nitrogen-containing organic compounds catalyzed bycobalt(III) oxiderdquo IndustrialsampEngineeringChemistry Researchvol 28 no 7 pp 894ndash899 1989
[23] J Levec M Herskowitz and J M Smith ldquoActive catalyst foroxidation of acetic-acid solutionsrdquo AIChE Journal vol 22 no5 pp 919ndash920 1976
[24] L X Li P S Chen andE FGloyna ldquoGeneralized kinetic-modelfor wet oxidation of organic-compoundsrdquo AIChE Journal vol37 no 11 pp 1687ndash1697 1991
[25] W H Li J L Huang H Wang A J Qi and J Xie ldquoTreatmentof acrylic acid waste water by catalytic wet oxidationrdquo Journalof Jilin Institute of Chemical Technology vol 24 no 3 pp 3ndash62007
[26] S H Lin and Y F Wu ldquoCatalytic wet air oxidation of phenolicwastewatersrdquo Environmental Technology vol 17 no 2 pp 175ndash181 1996
[27] S H Lin and S J Ho ldquoTreatment of high-strength industrialwastewater by wet air oxidationmdasha case studyrdquoWaste Manage-ment vol 17 no 1 pp 71ndash78 1997
[28] H Lin Sheng and S J Ho ldquoKinetics of wet air oxidation ofhigh-strength industrial wastewaterrdquo Journal of EnvironmentalEngineering vol 123 no 9 pp 852ndash858 1997
[29] V S Mishra V V Mahajani and J B Joshi ldquoWet air oxidationrdquoIndustrial and Engineering Chemistry Research vol 34 no 1 pp2ndash48 1995
[30] A Sadana and J R Katzer ldquoCatalytic oxidation of phenol inaqueous solution over copper oxiderdquo Industrial and EngineeringChemistry vol 13 no 2 pp 127ndash134 1974
[31] P W Atkins ldquoPrinciples of chemical equilibriumrdquo in The Ele-ments of Physical Chemistry chapter 7 Oxford University PressOxford UK 3rd edition 1993
Figure 2 Time variation of decomposition efficiency of DMP(120578DMP) via WOP at various rotating speeds Nr ◻ and Nr =300 500 and 700 rpm 119862
0= 100mg Lminus1 119881
119871= 400mL 119879 = 473K
and 119875119879= 241MPa Working gas after time = 0
119891is O2 Mean and
Standard deviation (SD 119899 minus 1method) at 119905 = 0119891 148 plusmn 28
18012060
300500700
123456789
10
Time (min)
pH
0i 0f
Figure 3 Time variation of pH value for the decomposition of DMPviaWOP at various Nr ◻ and Nr = 300 500 and 700 rpm 119862
0
= 100mg Lminus1 119881119871= 400mL 119879 = 473K and 119875
119879= 241MPa Working
gas after time = 0119891is O2 Mean and Standard deviation (SD 119899 minus 1
method) at 119905 = 0119891 44 plusmn 01
32 Effects of Reaction Temperature 119879 Figures 4 and 5 showthe time variations of 120578DMP and 120578TOC at reaction temperatures119879 of 463 473 and 483K for the case with Nr = 500 rpm and119875119879= 241MPa In the heating period from 0
119894to 0119891without
oxidant DMP underwent mainly the hydrothermal decom-position accompanied with slight mineralization The 120578DMPis 17 for 463 and 473K while 45 for 483K at the end ofheating periodwith no oxygenThedecomposition ofDMP isvery vigorous at high temperature But the 120578TOC is lower than10 for all three temperatures because of the oxidant lackWith the presence of oxygen the 120578DMP was greatly enhanced
0102030405060708090
100
18012060Time (min)
463K473K483K
0i 0f
120578D
MP
()
Figure 4 Time variation of 120578DMP via WOP at various temperatures119879 ◻ and I 119879 = 463 473 and 483K 119862
0= 100mg Lminus1 119881
119871=
400mL 119875119879= 241MPa and Nr = 500 rpmWorking gas after time =
0119891is O2
05
101520253035404550
18012060Time (min)
463K473K483K
0i 0f
120578TO
C(
)
Figure 5 Time variation ofmineralization efficiency ofDMP (120578TOC)
via WOP at various 119879 ◻ and I 119879 = 463 473 and 483K 1198620=
100mg Lminus1119881119871= 400mL119875
119879= 241MPa andNr = 500 rpmWorking
gas after time = 0119891is O2
while 120578TOC moderately improved The results indicated thelow reactivity of acidic product fragments with oxygen Asexpected both 120578DMP and 120578TOC increased as reaction time andtemperature increasedAt119879=483K and 119905= 180min the 120578DMPand 120578TOC were 93 and 36 respectively
Figure 6 demonstrates the variation of pH value withtime at various temperatures As in Figure 3 the pH valuedecreased with time while it levels off at a longer timedepending on the temperature for example at 60min forhigher temperatures of 473 and 483K while at 120min forlower temperature of 464K Thus a higher temperature casepromotes the decomposition reaction generally lowering and
The Scientific World Journal 5
123
4
7
89
10
pH
18012060Time (min)
463K473K483K
0i 0f
56
Figure 6 Time variation of pH value for the decomposition ofDMPvia WOP at various 119879 ◻ and I 119879 = 463 473 and 483K 119862
0=
100mg Lminus1119881119871= 400mL119875
119879= 241MPa andNr = 500 rpmWorking
gas after time = 0119891is O2 Mean and Standard deviation (SD 119899 minus 1
method) at 119905 = 0119894 56 plusmn 03
0102030405060708090
100
241 276310 345
18012060Time (min)
0i 0f
120578D
MP
()
Figure 7 Time variation of 120578DMP via WOP at various pressures ◻ + and times 119875
119879= 241 276 310 and 345MPa 119862
0= 100mg Lminus1 119881
119871
= 400mL 119879 = 483K and Nr = 500 rpm Working gas after time =0119891is O2 Mean and Standard deviation (SD 119899 minus 1method) at 119905 =
0119891 382 plusmn 53
leveling the pH value faster than the lower temperature caseFor 483K the pHvalue decreases to a leveling value of around4 after 60min
33 Effects of Operation Pressure 119875119879 Figures 7 and 8 present
the 120578DMP and 120578TOC versus time at 119875119879of 241 276 310 and
345MPa with Nr = 500 rpm and 119879 = 483K Both 120578DMP and120578TOC increase with time as expected The oxygen was filledto reach the desired pressure right after heating period thatis at 119905 = 0
119891 There is no oxidant in the time period from 0
119894to
0119891 The DMP is hydrothermally decomposed in heating
0
10
20
30
40
50
241 276310 345
18012060Time (min)
0i 0f
120578TO
C(
)
Figure 8 Time variation of 120578TOC via WOP at various pressures I + and times 119875
119879= 241 276 310 and 345MPa 119862
0= 100mg Lminus1 119881
119871
= 400mL 119879 = 483K and Nr = 500 rpm Working gas after time =0119891is O2 Mean and Standard deviation (SD 119899 minus 1method) at 119905 =
0119891 15 plusmn 13
period giving 120578DMP of around 33 to 45 The DMP is onlyslightly mineralized with low 120578TOC of about 03 to 31 Inthe presence of oxygen both 120578DMP and 120578TOC are enhancedas decomposition and mineralization proceed The oxidativedecomposition of DMP essentially consists of two-stagereversible reactions as illustrated in Figure 10 which isdiscussed in the next sectionThedecomposition ofDMPandintermediates to short-chain aliphatic acid and then CO
2are
proposed by referring to the mechanism for the ozonationof DMP with UV and catalyst presented by Chang et al[11] An increase of oxygen as well as temperature enhancesthe forward reactions toward mineralization way while theaccumulation of CO
2reversely inhibits the mineralization
according to LeChatelierrsquos principle [31]Thus sufficient oxy-genwith satisfactorily high119875
119879is needed to ensure the forward
oxidative decomposition reaction of DMP For example 119875119879
at 241MPa yields 120578DMP and 120578TOC of 93 and 36 at 180minrespectively Although higher 119875
119879with more oxygen favors
the forward decomposition reaction of DMP by oxygenthe absorption of accumulated gaseous products such asCO2and decomposed short-chain hydrocarbon fragments
in the closed reaction system increases as 119875119879increases The
reabsorption of gaseous products back into the solution thusinhibits the forward reaction Hence as indicated in Figures7 and 8 119875
119879of 241MPa is more appropriate than those of 276
to 345MPaFigure 9 plots pH value versus time at various 119875
119879 The
reduction of pHvalue in hydrothermal decomposition periodis more vigorous than that in the oxidative decompositionperiod The trend is similar to that of Figure 3 previouslydiscussed The increase of 119875
119879higher than 241MPa exhibits
negligible effect on the pH value The pH value levels offindicating the limited oxidative mineralization to CO
2and
the gas liquid absorption balance of acidic compounds ofCO2
and decomposed short-chain hydrocarbon fragments
6 The Scientific World Journal
Table 2 Comparison with some results of others for the decomposition of DMP via various methods
Study Method Result
Bauer et al [1] Anaerobic process in field municipal landfillleachates
DMP was completely hydrolysis to phthalic acidbut no cleavage for aromatic ring at different pHvalues
Wang et al [16]Electro-Fenton methods by electrodes traditionalgraphite cathode (G) carbon nanotube sponge(CNTS) and graphite gas diffusion electrode(GDE)
120578TOC G 15 GDE 35 CNTS 75
Souza et al [17] Electrochemical oxidation on F-doped Ti120573-PbO2anode in filter press reactor
DMP was completely decomposed underelectrolyte Na2SO4 and low current densities(10mA) 120578TOC = 25
Chang et al [11]
Catalytic ozonation (OZ) in high-gravity rotatingpacked bed (HG) with catalyst (Pt-Al2O3) andultraviolet (UV) (mix of UV-C UV-B and UV-Awith 200ndash280 280ndash315 and 315ndash400 nm and withintensities of 373 159 and 399Wmminus2)
120578DMP at 50min near 100 for Pt-OZ andUV-Pt-OZ120578TOC at 1 h 45 (OZ) 56 (UV-OZ) 57(Pt-OZ) 68 (UV-Pt-OZ)
Chen et al [13]Photocatalytic degradation using magneticpoly(methyl methacrylate) (mPMMA) and UV254 nm
120578DMP at 4 h 55ndash100 via TiO2mPMMA (C1)68ndash100 via Pt-TiO2mPMMA (C2)120578TOC at 4 h 75ndash375 via C1 11ndash64 via C2
Chen et al [19] Photocatalytic ozonation using TiO2 Al2O3 andTiO2Al2O3 catalysts
120578DMP at 30min 2ndash22 without O3 90ndash100 withO3 120578TOC 16ndash93 32ndash97 at 1 4 h
Chen et al [12] Photocatalysis using magnetic Pt-TiO2mPMMA UV 185 nm contributes better removal efficiencythan UV 254 nm
This study Wet oxygen oxidation 120578DMP and 120578TOC are 93 and 36 at Nr = 500 rpm119879 = 483K 119875
119879= 241MPa and 119905 = 180min
12
345
678
910
pH
241 276310 345
18012060Time (min)
0i 0f
Figure 9 Time variation of pH value for decomposition of DMPvia WOP at various pressures I + and times 119875
119879= 241 276 310
and 345MPa 1198620= 100mg Lminus1 119881
119871= 400mL 119879 = 483K and Nr =
500 rpm Working gas after time = 0119891is O2 Mean and Standard
deviation (SD 119899 minus 1 method) at 119905 = 0119894 52 plusmn 02 and at 119905 = 0
119891 41 plusmn
02
It is noted that the 119875119879was the sum of partial pressures
of oxygen (119875O2) and water vapor (119875WV) The saturation 119875WV
varies with temperature and is about 23MPa at 483K [27]Setting 119875
119879at 241 and 345MPa gave 119875O2
of 011 and 115MParespectively for supplying the oxygen for mineralizationreaction Referring to the study of Lin and Ho [27] using
25MPa as the lowest setting at 473K this analysis thus didnot employ 119875
119879lower than 241MPa at 483K
34 Mechanism of Two-Stage Decomposition of DMP viaWOP In this test the reactions are involved in componentsof DMP oxygen intermediate products and ultimate endproducts of CO
2and H
2OThe intermediates are the decom-
posed short-chain hydrocarbon fragmentswhich are acidic asreflected by the low pH value Accordingly the mechanism oftwo-stage decomposition of DMP via WOP may be depictedin Figure 10 In the heating stage without oxygen DMP isessentially hydrothermally decomposed to acidic fragmentslowering the pH value with significant 120578DMP while forminglittle CO
2with low 120578TOC With the introduction of oxygen
in the second stage oxidation of DMP and its decomposedfragments takes place destructing them into short-chainacids such as aliphatic acids or more completely to CO
2
and H2O The produced CO
2 however was kept within the
closed-batch reaction system in this studyThe stoichiometry equation for the forward oxidation
reaction of DMP can expressed as follows
C10H10O4 + 105O2 997888rarr 10CO2 + 5H2O (1)
For complete mineralization of DMP each mole DMP con-sumes 105 moles of O
2while producing 10 moles of CO
2
The CO2partial pressure contributed from the complete
mineralization of DMP is about 0045MPa by consuming0047MPa O
2 This reaction reduces the total pressure
slightly In fact the oxygen is not a limited factor because
The Scientific World Journal 7
Hydrothermolysis
DMPN2
298ndash483K
O2 O2
483K 483K
Short-chainaliphatic acid CO2 + H2O
Wet oxidation
intermediatesDMP +
Figure 10 Two stages for the decomposition of DMP via WOP
the minimum pressure applied is 241MPa exceeding theneed However the mineralization of reaction (1) is hinderedby the accumulation of product CO
2in the closed-batch
reaction system It forces the backward reaction of reaction(1) according to Le Chatelierrsquos principle [31] The equilibriumbalance of the forward and backward reaction thus limits thecomplete mineralization of DMP A release of CO
2gas out
from the reaction system would certainly assist approachingthe complete mineralization of DMP
35 Comparison with Results of Others Comparison of theresults of this study with others is illustrated in Table 2 Thepresent WOP can reach 120578DMP of 93 as high as the advancedmethods (AMs) of electrochemical oxidation photocatalyticdegradation and photocatalytic ozonationThe 120578TOC ofWOPof 36 is lower than those of the aforementioned AMs atsome conditions however comparable at other conditionsIt is noted that the WOP simply uses oxygen with demandof the thermal energy while other AMs need to employchemical agents catalysts and ozone along with electric orUV energies Thus the WOP is comparatively simple toapplyThe discrepancy of incomplete mineralization ofWOPmay be consummated with the postbiological treatment ifnecessary [20] The predecomposition of DMP by WOPcertainly greatly enhances the followed biological processing
4 Conclusions
This study treated the toxic endocrine disrupter substance(EDC) of DMP via wet oxidation using oxygen (WOP)without other oxidant additives being beneficial to thesubsequent biological process if necessary while avoiding thetreatment of unwanted oxidant residuesTheWOP effectivelydecomposed the DMP indicating its feasible application forthe treatment of other EDCs
Among the three factors investigated namely rotationspeed Nr reaction temperature 119879 and operation pressure 119875
119879
the effects of 119879 are most significant The proper conditionsfound are at 483K 241MPa and 500 rpm The 120578DMP and120578TOC of 93 and 36 respectively can be achieved at180minThe produced CO
2kept in the closed-batch reaction
system seems to resist the further mineralization reactionfrom intermediates The application of sequential releaseof CO
2while addition of O
2to improve the 120578TOC is thus
suggested
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors are grateful for the financial supports of thisresearch provided by theMinistry of Science and Technology(formerly the National Science Council) of Taiwan
References
[1] M J Bauer R Herrmann A Martin and H Zellmann ldquoChe-modynamics transport behaviour and treatment of phthalicacid esters in municipal landfill leachatesrdquo Water Science andTechnology vol 38 no 2 pp 185ndash192 1998
[2] M Zhang S Liu H Zhuang and Y Hu ldquoDetermination ofdimethyl phthalate in environment water samples by a highlysensitive indirect competitive ELISArdquoApplied Biochemistry andBiotechnology vol 166 no 2 pp 436ndash445 2012
[3] J P Sumpter ldquoEndocrine disrupters in the aquatic environmentan overviewrdquo Acta Hydrochimica et Hydrobiologica vol 33 no1 pp 9ndash16 2005
[4] C A Staples D R Peterson T F Parkerton and W J AdamsldquoThe environmental fate of phthalate esters a literature reviewrdquoChemosphere vol 35 no 4 pp 667ndash749 1997
[5] W Den H C Liu S F Chan K T Kin and C Huang ldquoAdsorp-tion of phthalate esters with multiwalled carbon nanotubesand its applicationrdquo Journal of Environmental Engineering andManagement vol 16 no 4 pp 275ndash282 2006
[6] A J Kumar andCNamasivayam ldquoUptake of endocrine disrup-tor bisphenol-A onto sulphuric acid activated carbon developedfrom biomass equilibrium and kinetic studiesrdquo SustainableEnvironment Research vol 24 no 1 pp 73ndash80 2014
[7] M F N Secondes V Naddeo F J Ballesteros and V BelgiornoldquoAdsorption of emerging contaminants enhanced by ultrasoundirradiationrdquo Sustainable Environment Research vol 24 no 5 pp349ndash355 2014
[8] DW Liang T Zhang H H P Fang and J He ldquoPhthalates bio-degradation in the environmentrdquo Applied Microbiology andBiotechnology vol 80 no 2 pp 183ndash198 2008
[9] D LWu B L Hu P Zheng andQMahmood ldquoAnoxic biodeg-radation of dimethyl phthalate (DMP) by activated sludge cul-tures under nitrate-reducing conditionsrdquo Journal of Environ-mental Sciences vol 19 no 10 pp 1252ndash1256 2007
[10] D L Wu Q Mahmood L L Wu and P Zheng ldquoActivatedsludge-mediated biodegradation of dimethyl phthalate underfermentative conditionsrdquo Journal of Environmental Sciences vol20 no 8 pp 922ndash926 2008
[11] C-C Chang C-Y Chiu C-Y Chang et al ldquoCombined pho-tolysis and catalytic ozonation of dimethyl phthalate in a high-gravity rotating packed bedrdquo Journal of Hazardous Materialsvol 161 no 1 pp 287ndash293 2009
8 The Scientific World Journal
[12] Y-H Chen L-L Chen and N-C Shang ldquoPhotocatalytic deg-radation of dimethyl phthalate in an aqueous solution with Pt-doped TiO
2-coated magnetic PMMAmicrospheresrdquo Journal of
Hazardous Materials vol 172 no 1 pp 20ndash29 2009[13] Y-H Chen N-C Shang L-L Chen et al ldquoPhotodecomposi-
tion of dimethyl phthalate in an aqueous solution withUV radi-ation using novel catalystsrdquo Desalination and Water Treatmentvol 52 no 16ndash18 pp 3377ndash3383 2014
[14] Y Jing L Li Q Zhang P Lu P Liu and X Lu ldquoPhotocatalyticozonation of dimethyl phthalate with TiO
[15] W Jiang J A Joens D D Dionysiou and K E OrsquoShea ldquoOpti-mization of photocatalytic performance of TiO
2coated glass
microspheres using response surface methodology and theapplication for degradation of dimethyl phthalaterdquo Journal ofPhotochemistry and Photobiology A Chemistry vol 262 pp 7ndash13 2013
[16] Y Wang Y Liu T Liu et al ldquoDimethyl phthalate degradationat novel and efficient electro-Fenton cathoderdquo Applied CatalysisB Environmental vol 156-157 pp 1ndash7 2014
[17] F L Souza J M Aquino K Irikura D W Miwa M ARodrigo and A J Motheo ldquoElectrochemical degradation of thedimethyl phthalate ester on a fluoride-doped Ti120573-PbO
2
anoderdquo Chemosphere vol 109 pp 187ndash194 2014[18] F Charest and E Chornet ldquoWet oxidation of active carbonrdquo
Canadian Journal of Chemical Engineering vol 54 no 6 pp190ndash196 1976
[19] Y-H Chen D-C Hsieh and N-C Shang ldquoEfficient miner-alization of dimethyl phthalate by catalytic ozonation usingTiO2Al2O3catalystrdquo Journal of Hazardous Materials vol 192
no 3 pp 1017ndash1025 2011[20] M J Dietrich T L Randall and P J Canney ldquoWet air oxidation
of hazardous organics in wastewaterrdquo Environmental Progressvol 4 no 3 pp 171ndash177 1985
[21] S Imamura H Kinunaka andN Kawabata ldquoThewet oxidationof organic compounds catalyzed by Co-Bi complex oxiderdquoBulletin of the Chemical Society of Japan vol 55 no 11 pp 3679ndash3680 1982
[22] M M Ito K Akita and H Inoue ldquoWet oxidation of oxygen-and nitrogen-containing organic compounds catalyzed bycobalt(III) oxiderdquo IndustrialsampEngineeringChemistry Researchvol 28 no 7 pp 894ndash899 1989
[23] J Levec M Herskowitz and J M Smith ldquoActive catalyst foroxidation of acetic-acid solutionsrdquo AIChE Journal vol 22 no5 pp 919ndash920 1976
[24] L X Li P S Chen andE FGloyna ldquoGeneralized kinetic-modelfor wet oxidation of organic-compoundsrdquo AIChE Journal vol37 no 11 pp 1687ndash1697 1991
[25] W H Li J L Huang H Wang A J Qi and J Xie ldquoTreatmentof acrylic acid waste water by catalytic wet oxidationrdquo Journalof Jilin Institute of Chemical Technology vol 24 no 3 pp 3ndash62007
[26] S H Lin and Y F Wu ldquoCatalytic wet air oxidation of phenolicwastewatersrdquo Environmental Technology vol 17 no 2 pp 175ndash181 1996
[27] S H Lin and S J Ho ldquoTreatment of high-strength industrialwastewater by wet air oxidationmdasha case studyrdquoWaste Manage-ment vol 17 no 1 pp 71ndash78 1997
[28] H Lin Sheng and S J Ho ldquoKinetics of wet air oxidation ofhigh-strength industrial wastewaterrdquo Journal of EnvironmentalEngineering vol 123 no 9 pp 852ndash858 1997
[29] V S Mishra V V Mahajani and J B Joshi ldquoWet air oxidationrdquoIndustrial and Engineering Chemistry Research vol 34 no 1 pp2ndash48 1995
[30] A Sadana and J R Katzer ldquoCatalytic oxidation of phenol inaqueous solution over copper oxiderdquo Industrial and EngineeringChemistry vol 13 no 2 pp 127ndash134 1974
[31] P W Atkins ldquoPrinciples of chemical equilibriumrdquo in The Ele-ments of Physical Chemistry chapter 7 Oxford University PressOxford UK 3rd edition 1993
Figure 6 Time variation of pH value for the decomposition ofDMPvia WOP at various 119879 ◻ and I 119879 = 463 473 and 483K 119862
0=
100mg Lminus1119881119871= 400mL119875
119879= 241MPa andNr = 500 rpmWorking
gas after time = 0119891is O2 Mean and Standard deviation (SD 119899 minus 1
method) at 119905 = 0119894 56 plusmn 03
0102030405060708090
100
241 276310 345
18012060Time (min)
0i 0f
120578D
MP
()
Figure 7 Time variation of 120578DMP via WOP at various pressures ◻ + and times 119875
119879= 241 276 310 and 345MPa 119862
0= 100mg Lminus1 119881
119871
= 400mL 119879 = 483K and Nr = 500 rpm Working gas after time =0119891is O2 Mean and Standard deviation (SD 119899 minus 1method) at 119905 =
0119891 382 plusmn 53
leveling the pH value faster than the lower temperature caseFor 483K the pHvalue decreases to a leveling value of around4 after 60min
33 Effects of Operation Pressure 119875119879 Figures 7 and 8 present
the 120578DMP and 120578TOC versus time at 119875119879of 241 276 310 and
345MPa with Nr = 500 rpm and 119879 = 483K Both 120578DMP and120578TOC increase with time as expected The oxygen was filledto reach the desired pressure right after heating period thatis at 119905 = 0
119891 There is no oxidant in the time period from 0
119894to
0119891 The DMP is hydrothermally decomposed in heating
0
10
20
30
40
50
241 276310 345
18012060Time (min)
0i 0f
120578TO
C(
)
Figure 8 Time variation of 120578TOC via WOP at various pressures I + and times 119875
119879= 241 276 310 and 345MPa 119862
0= 100mg Lminus1 119881
119871
= 400mL 119879 = 483K and Nr = 500 rpm Working gas after time =0119891is O2 Mean and Standard deviation (SD 119899 minus 1method) at 119905 =
0119891 15 plusmn 13
period giving 120578DMP of around 33 to 45 The DMP is onlyslightly mineralized with low 120578TOC of about 03 to 31 Inthe presence of oxygen both 120578DMP and 120578TOC are enhancedas decomposition and mineralization proceed The oxidativedecomposition of DMP essentially consists of two-stagereversible reactions as illustrated in Figure 10 which isdiscussed in the next sectionThedecomposition ofDMPandintermediates to short-chain aliphatic acid and then CO
2are
proposed by referring to the mechanism for the ozonationof DMP with UV and catalyst presented by Chang et al[11] An increase of oxygen as well as temperature enhancesthe forward reactions toward mineralization way while theaccumulation of CO
2reversely inhibits the mineralization
according to LeChatelierrsquos principle [31]Thus sufficient oxy-genwith satisfactorily high119875
119879is needed to ensure the forward
oxidative decomposition reaction of DMP For example 119875119879
at 241MPa yields 120578DMP and 120578TOC of 93 and 36 at 180minrespectively Although higher 119875
119879with more oxygen favors
the forward decomposition reaction of DMP by oxygenthe absorption of accumulated gaseous products such asCO2and decomposed short-chain hydrocarbon fragments
in the closed reaction system increases as 119875119879increases The
reabsorption of gaseous products back into the solution thusinhibits the forward reaction Hence as indicated in Figures7 and 8 119875
119879of 241MPa is more appropriate than those of 276
to 345MPaFigure 9 plots pH value versus time at various 119875
119879 The
reduction of pHvalue in hydrothermal decomposition periodis more vigorous than that in the oxidative decompositionperiod The trend is similar to that of Figure 3 previouslydiscussed The increase of 119875
119879higher than 241MPa exhibits
negligible effect on the pH value The pH value levels offindicating the limited oxidative mineralization to CO
2and
the gas liquid absorption balance of acidic compounds ofCO2
and decomposed short-chain hydrocarbon fragments
6 The Scientific World Journal
Table 2 Comparison with some results of others for the decomposition of DMP via various methods
Study Method Result
Bauer et al [1] Anaerobic process in field municipal landfillleachates
DMP was completely hydrolysis to phthalic acidbut no cleavage for aromatic ring at different pHvalues
Wang et al [16]Electro-Fenton methods by electrodes traditionalgraphite cathode (G) carbon nanotube sponge(CNTS) and graphite gas diffusion electrode(GDE)
120578TOC G 15 GDE 35 CNTS 75
Souza et al [17] Electrochemical oxidation on F-doped Ti120573-PbO2anode in filter press reactor
DMP was completely decomposed underelectrolyte Na2SO4 and low current densities(10mA) 120578TOC = 25
Chang et al [11]
Catalytic ozonation (OZ) in high-gravity rotatingpacked bed (HG) with catalyst (Pt-Al2O3) andultraviolet (UV) (mix of UV-C UV-B and UV-Awith 200ndash280 280ndash315 and 315ndash400 nm and withintensities of 373 159 and 399Wmminus2)
120578DMP at 50min near 100 for Pt-OZ andUV-Pt-OZ120578TOC at 1 h 45 (OZ) 56 (UV-OZ) 57(Pt-OZ) 68 (UV-Pt-OZ)
Chen et al [13]Photocatalytic degradation using magneticpoly(methyl methacrylate) (mPMMA) and UV254 nm
120578DMP at 4 h 55ndash100 via TiO2mPMMA (C1)68ndash100 via Pt-TiO2mPMMA (C2)120578TOC at 4 h 75ndash375 via C1 11ndash64 via C2
Chen et al [19] Photocatalytic ozonation using TiO2 Al2O3 andTiO2Al2O3 catalysts
120578DMP at 30min 2ndash22 without O3 90ndash100 withO3 120578TOC 16ndash93 32ndash97 at 1 4 h
Chen et al [12] Photocatalysis using magnetic Pt-TiO2mPMMA UV 185 nm contributes better removal efficiencythan UV 254 nm
This study Wet oxygen oxidation 120578DMP and 120578TOC are 93 and 36 at Nr = 500 rpm119879 = 483K 119875
119879= 241MPa and 119905 = 180min
12
345
678
910
pH
241 276310 345
18012060Time (min)
0i 0f
Figure 9 Time variation of pH value for decomposition of DMPvia WOP at various pressures I + and times 119875
119879= 241 276 310
and 345MPa 1198620= 100mg Lminus1 119881
119871= 400mL 119879 = 483K and Nr =
500 rpm Working gas after time = 0119891is O2 Mean and Standard
deviation (SD 119899 minus 1 method) at 119905 = 0119894 52 plusmn 02 and at 119905 = 0
119891 41 plusmn
02
It is noted that the 119875119879was the sum of partial pressures
of oxygen (119875O2) and water vapor (119875WV) The saturation 119875WV
varies with temperature and is about 23MPa at 483K [27]Setting 119875
119879at 241 and 345MPa gave 119875O2
of 011 and 115MParespectively for supplying the oxygen for mineralizationreaction Referring to the study of Lin and Ho [27] using
25MPa as the lowest setting at 473K this analysis thus didnot employ 119875
119879lower than 241MPa at 483K
34 Mechanism of Two-Stage Decomposition of DMP viaWOP In this test the reactions are involved in componentsof DMP oxygen intermediate products and ultimate endproducts of CO
2and H
2OThe intermediates are the decom-
posed short-chain hydrocarbon fragmentswhich are acidic asreflected by the low pH value Accordingly the mechanism oftwo-stage decomposition of DMP via WOP may be depictedin Figure 10 In the heating stage without oxygen DMP isessentially hydrothermally decomposed to acidic fragmentslowering the pH value with significant 120578DMP while forminglittle CO
2with low 120578TOC With the introduction of oxygen
in the second stage oxidation of DMP and its decomposedfragments takes place destructing them into short-chainacids such as aliphatic acids or more completely to CO
2
and H2O The produced CO
2 however was kept within the
closed-batch reaction system in this studyThe stoichiometry equation for the forward oxidation
reaction of DMP can expressed as follows
C10H10O4 + 105O2 997888rarr 10CO2 + 5H2O (1)
For complete mineralization of DMP each mole DMP con-sumes 105 moles of O
2while producing 10 moles of CO
2
The CO2partial pressure contributed from the complete
mineralization of DMP is about 0045MPa by consuming0047MPa O
2 This reaction reduces the total pressure
slightly In fact the oxygen is not a limited factor because
The Scientific World Journal 7
Hydrothermolysis
DMPN2
298ndash483K
O2 O2
483K 483K
Short-chainaliphatic acid CO2 + H2O
Wet oxidation
intermediatesDMP +
Figure 10 Two stages for the decomposition of DMP via WOP
the minimum pressure applied is 241MPa exceeding theneed However the mineralization of reaction (1) is hinderedby the accumulation of product CO
2in the closed-batch
reaction system It forces the backward reaction of reaction(1) according to Le Chatelierrsquos principle [31] The equilibriumbalance of the forward and backward reaction thus limits thecomplete mineralization of DMP A release of CO
2gas out
from the reaction system would certainly assist approachingthe complete mineralization of DMP
35 Comparison with Results of Others Comparison of theresults of this study with others is illustrated in Table 2 Thepresent WOP can reach 120578DMP of 93 as high as the advancedmethods (AMs) of electrochemical oxidation photocatalyticdegradation and photocatalytic ozonationThe 120578TOC ofWOPof 36 is lower than those of the aforementioned AMs atsome conditions however comparable at other conditionsIt is noted that the WOP simply uses oxygen with demandof the thermal energy while other AMs need to employchemical agents catalysts and ozone along with electric orUV energies Thus the WOP is comparatively simple toapplyThe discrepancy of incomplete mineralization ofWOPmay be consummated with the postbiological treatment ifnecessary [20] The predecomposition of DMP by WOPcertainly greatly enhances the followed biological processing
4 Conclusions
This study treated the toxic endocrine disrupter substance(EDC) of DMP via wet oxidation using oxygen (WOP)without other oxidant additives being beneficial to thesubsequent biological process if necessary while avoiding thetreatment of unwanted oxidant residuesTheWOP effectivelydecomposed the DMP indicating its feasible application forthe treatment of other EDCs
Among the three factors investigated namely rotationspeed Nr reaction temperature 119879 and operation pressure 119875
119879
the effects of 119879 are most significant The proper conditionsfound are at 483K 241MPa and 500 rpm The 120578DMP and120578TOC of 93 and 36 respectively can be achieved at180minThe produced CO
2kept in the closed-batch reaction
system seems to resist the further mineralization reactionfrom intermediates The application of sequential releaseof CO
2while addition of O
2to improve the 120578TOC is thus
suggested
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors are grateful for the financial supports of thisresearch provided by theMinistry of Science and Technology(formerly the National Science Council) of Taiwan
References
[1] M J Bauer R Herrmann A Martin and H Zellmann ldquoChe-modynamics transport behaviour and treatment of phthalicacid esters in municipal landfill leachatesrdquo Water Science andTechnology vol 38 no 2 pp 185ndash192 1998
[2] M Zhang S Liu H Zhuang and Y Hu ldquoDetermination ofdimethyl phthalate in environment water samples by a highlysensitive indirect competitive ELISArdquoApplied Biochemistry andBiotechnology vol 166 no 2 pp 436ndash445 2012
[3] J P Sumpter ldquoEndocrine disrupters in the aquatic environmentan overviewrdquo Acta Hydrochimica et Hydrobiologica vol 33 no1 pp 9ndash16 2005
[4] C A Staples D R Peterson T F Parkerton and W J AdamsldquoThe environmental fate of phthalate esters a literature reviewrdquoChemosphere vol 35 no 4 pp 667ndash749 1997
[5] W Den H C Liu S F Chan K T Kin and C Huang ldquoAdsorp-tion of phthalate esters with multiwalled carbon nanotubesand its applicationrdquo Journal of Environmental Engineering andManagement vol 16 no 4 pp 275ndash282 2006
[6] A J Kumar andCNamasivayam ldquoUptake of endocrine disrup-tor bisphenol-A onto sulphuric acid activated carbon developedfrom biomass equilibrium and kinetic studiesrdquo SustainableEnvironment Research vol 24 no 1 pp 73ndash80 2014
[7] M F N Secondes V Naddeo F J Ballesteros and V BelgiornoldquoAdsorption of emerging contaminants enhanced by ultrasoundirradiationrdquo Sustainable Environment Research vol 24 no 5 pp349ndash355 2014
[8] DW Liang T Zhang H H P Fang and J He ldquoPhthalates bio-degradation in the environmentrdquo Applied Microbiology andBiotechnology vol 80 no 2 pp 183ndash198 2008
[9] D LWu B L Hu P Zheng andQMahmood ldquoAnoxic biodeg-radation of dimethyl phthalate (DMP) by activated sludge cul-tures under nitrate-reducing conditionsrdquo Journal of Environ-mental Sciences vol 19 no 10 pp 1252ndash1256 2007
[10] D L Wu Q Mahmood L L Wu and P Zheng ldquoActivatedsludge-mediated biodegradation of dimethyl phthalate underfermentative conditionsrdquo Journal of Environmental Sciences vol20 no 8 pp 922ndash926 2008
[11] C-C Chang C-Y Chiu C-Y Chang et al ldquoCombined pho-tolysis and catalytic ozonation of dimethyl phthalate in a high-gravity rotating packed bedrdquo Journal of Hazardous Materialsvol 161 no 1 pp 287ndash293 2009
8 The Scientific World Journal
[12] Y-H Chen L-L Chen and N-C Shang ldquoPhotocatalytic deg-radation of dimethyl phthalate in an aqueous solution with Pt-doped TiO
2-coated magnetic PMMAmicrospheresrdquo Journal of
Hazardous Materials vol 172 no 1 pp 20ndash29 2009[13] Y-H Chen N-C Shang L-L Chen et al ldquoPhotodecomposi-
tion of dimethyl phthalate in an aqueous solution withUV radi-ation using novel catalystsrdquo Desalination and Water Treatmentvol 52 no 16ndash18 pp 3377ndash3383 2014
[14] Y Jing L Li Q Zhang P Lu P Liu and X Lu ldquoPhotocatalyticozonation of dimethyl phthalate with TiO
[15] W Jiang J A Joens D D Dionysiou and K E OrsquoShea ldquoOpti-mization of photocatalytic performance of TiO
2coated glass
microspheres using response surface methodology and theapplication for degradation of dimethyl phthalaterdquo Journal ofPhotochemistry and Photobiology A Chemistry vol 262 pp 7ndash13 2013
[16] Y Wang Y Liu T Liu et al ldquoDimethyl phthalate degradationat novel and efficient electro-Fenton cathoderdquo Applied CatalysisB Environmental vol 156-157 pp 1ndash7 2014
[17] F L Souza J M Aquino K Irikura D W Miwa M ARodrigo and A J Motheo ldquoElectrochemical degradation of thedimethyl phthalate ester on a fluoride-doped Ti120573-PbO
2
anoderdquo Chemosphere vol 109 pp 187ndash194 2014[18] F Charest and E Chornet ldquoWet oxidation of active carbonrdquo
Canadian Journal of Chemical Engineering vol 54 no 6 pp190ndash196 1976
[19] Y-H Chen D-C Hsieh and N-C Shang ldquoEfficient miner-alization of dimethyl phthalate by catalytic ozonation usingTiO2Al2O3catalystrdquo Journal of Hazardous Materials vol 192
no 3 pp 1017ndash1025 2011[20] M J Dietrich T L Randall and P J Canney ldquoWet air oxidation
of hazardous organics in wastewaterrdquo Environmental Progressvol 4 no 3 pp 171ndash177 1985
[21] S Imamura H Kinunaka andN Kawabata ldquoThewet oxidationof organic compounds catalyzed by Co-Bi complex oxiderdquoBulletin of the Chemical Society of Japan vol 55 no 11 pp 3679ndash3680 1982
[22] M M Ito K Akita and H Inoue ldquoWet oxidation of oxygen-and nitrogen-containing organic compounds catalyzed bycobalt(III) oxiderdquo IndustrialsampEngineeringChemistry Researchvol 28 no 7 pp 894ndash899 1989
[23] J Levec M Herskowitz and J M Smith ldquoActive catalyst foroxidation of acetic-acid solutionsrdquo AIChE Journal vol 22 no5 pp 919ndash920 1976
[24] L X Li P S Chen andE FGloyna ldquoGeneralized kinetic-modelfor wet oxidation of organic-compoundsrdquo AIChE Journal vol37 no 11 pp 1687ndash1697 1991
[25] W H Li J L Huang H Wang A J Qi and J Xie ldquoTreatmentof acrylic acid waste water by catalytic wet oxidationrdquo Journalof Jilin Institute of Chemical Technology vol 24 no 3 pp 3ndash62007
[26] S H Lin and Y F Wu ldquoCatalytic wet air oxidation of phenolicwastewatersrdquo Environmental Technology vol 17 no 2 pp 175ndash181 1996
[27] S H Lin and S J Ho ldquoTreatment of high-strength industrialwastewater by wet air oxidationmdasha case studyrdquoWaste Manage-ment vol 17 no 1 pp 71ndash78 1997
[28] H Lin Sheng and S J Ho ldquoKinetics of wet air oxidation ofhigh-strength industrial wastewaterrdquo Journal of EnvironmentalEngineering vol 123 no 9 pp 852ndash858 1997
[29] V S Mishra V V Mahajani and J B Joshi ldquoWet air oxidationrdquoIndustrial and Engineering Chemistry Research vol 34 no 1 pp2ndash48 1995
[30] A Sadana and J R Katzer ldquoCatalytic oxidation of phenol inaqueous solution over copper oxiderdquo Industrial and EngineeringChemistry vol 13 no 2 pp 127ndash134 1974
[31] P W Atkins ldquoPrinciples of chemical equilibriumrdquo in The Ele-ments of Physical Chemistry chapter 7 Oxford University PressOxford UK 3rd edition 1993
Table 2 Comparison with some results of others for the decomposition of DMP via various methods
Study Method Result
Bauer et al [1] Anaerobic process in field municipal landfillleachates
DMP was completely hydrolysis to phthalic acidbut no cleavage for aromatic ring at different pHvalues
Wang et al [16]Electro-Fenton methods by electrodes traditionalgraphite cathode (G) carbon nanotube sponge(CNTS) and graphite gas diffusion electrode(GDE)
120578TOC G 15 GDE 35 CNTS 75
Souza et al [17] Electrochemical oxidation on F-doped Ti120573-PbO2anode in filter press reactor
DMP was completely decomposed underelectrolyte Na2SO4 and low current densities(10mA) 120578TOC = 25
Chang et al [11]
Catalytic ozonation (OZ) in high-gravity rotatingpacked bed (HG) with catalyst (Pt-Al2O3) andultraviolet (UV) (mix of UV-C UV-B and UV-Awith 200ndash280 280ndash315 and 315ndash400 nm and withintensities of 373 159 and 399Wmminus2)
120578DMP at 50min near 100 for Pt-OZ andUV-Pt-OZ120578TOC at 1 h 45 (OZ) 56 (UV-OZ) 57(Pt-OZ) 68 (UV-Pt-OZ)
Chen et al [13]Photocatalytic degradation using magneticpoly(methyl methacrylate) (mPMMA) and UV254 nm
120578DMP at 4 h 55ndash100 via TiO2mPMMA (C1)68ndash100 via Pt-TiO2mPMMA (C2)120578TOC at 4 h 75ndash375 via C1 11ndash64 via C2
Chen et al [19] Photocatalytic ozonation using TiO2 Al2O3 andTiO2Al2O3 catalysts
120578DMP at 30min 2ndash22 without O3 90ndash100 withO3 120578TOC 16ndash93 32ndash97 at 1 4 h
Chen et al [12] Photocatalysis using magnetic Pt-TiO2mPMMA UV 185 nm contributes better removal efficiencythan UV 254 nm
This study Wet oxygen oxidation 120578DMP and 120578TOC are 93 and 36 at Nr = 500 rpm119879 = 483K 119875
119879= 241MPa and 119905 = 180min
12
345
678
910
pH
241 276310 345
18012060Time (min)
0i 0f
Figure 9 Time variation of pH value for decomposition of DMPvia WOP at various pressures I + and times 119875
119879= 241 276 310
and 345MPa 1198620= 100mg Lminus1 119881
119871= 400mL 119879 = 483K and Nr =
500 rpm Working gas after time = 0119891is O2 Mean and Standard
deviation (SD 119899 minus 1 method) at 119905 = 0119894 52 plusmn 02 and at 119905 = 0
119891 41 plusmn
02
It is noted that the 119875119879was the sum of partial pressures
of oxygen (119875O2) and water vapor (119875WV) The saturation 119875WV
varies with temperature and is about 23MPa at 483K [27]Setting 119875
119879at 241 and 345MPa gave 119875O2
of 011 and 115MParespectively for supplying the oxygen for mineralizationreaction Referring to the study of Lin and Ho [27] using
25MPa as the lowest setting at 473K this analysis thus didnot employ 119875
119879lower than 241MPa at 483K
34 Mechanism of Two-Stage Decomposition of DMP viaWOP In this test the reactions are involved in componentsof DMP oxygen intermediate products and ultimate endproducts of CO
2and H
2OThe intermediates are the decom-
posed short-chain hydrocarbon fragmentswhich are acidic asreflected by the low pH value Accordingly the mechanism oftwo-stage decomposition of DMP via WOP may be depictedin Figure 10 In the heating stage without oxygen DMP isessentially hydrothermally decomposed to acidic fragmentslowering the pH value with significant 120578DMP while forminglittle CO
2with low 120578TOC With the introduction of oxygen
in the second stage oxidation of DMP and its decomposedfragments takes place destructing them into short-chainacids such as aliphatic acids or more completely to CO
2
and H2O The produced CO
2 however was kept within the
closed-batch reaction system in this studyThe stoichiometry equation for the forward oxidation
reaction of DMP can expressed as follows
C10H10O4 + 105O2 997888rarr 10CO2 + 5H2O (1)
For complete mineralization of DMP each mole DMP con-sumes 105 moles of O
2while producing 10 moles of CO
2
The CO2partial pressure contributed from the complete
mineralization of DMP is about 0045MPa by consuming0047MPa O
2 This reaction reduces the total pressure
slightly In fact the oxygen is not a limited factor because
The Scientific World Journal 7
Hydrothermolysis
DMPN2
298ndash483K
O2 O2
483K 483K
Short-chainaliphatic acid CO2 + H2O
Wet oxidation
intermediatesDMP +
Figure 10 Two stages for the decomposition of DMP via WOP
the minimum pressure applied is 241MPa exceeding theneed However the mineralization of reaction (1) is hinderedby the accumulation of product CO
2in the closed-batch
reaction system It forces the backward reaction of reaction(1) according to Le Chatelierrsquos principle [31] The equilibriumbalance of the forward and backward reaction thus limits thecomplete mineralization of DMP A release of CO
2gas out
from the reaction system would certainly assist approachingthe complete mineralization of DMP
35 Comparison with Results of Others Comparison of theresults of this study with others is illustrated in Table 2 Thepresent WOP can reach 120578DMP of 93 as high as the advancedmethods (AMs) of electrochemical oxidation photocatalyticdegradation and photocatalytic ozonationThe 120578TOC ofWOPof 36 is lower than those of the aforementioned AMs atsome conditions however comparable at other conditionsIt is noted that the WOP simply uses oxygen with demandof the thermal energy while other AMs need to employchemical agents catalysts and ozone along with electric orUV energies Thus the WOP is comparatively simple toapplyThe discrepancy of incomplete mineralization ofWOPmay be consummated with the postbiological treatment ifnecessary [20] The predecomposition of DMP by WOPcertainly greatly enhances the followed biological processing
4 Conclusions
This study treated the toxic endocrine disrupter substance(EDC) of DMP via wet oxidation using oxygen (WOP)without other oxidant additives being beneficial to thesubsequent biological process if necessary while avoiding thetreatment of unwanted oxidant residuesTheWOP effectivelydecomposed the DMP indicating its feasible application forthe treatment of other EDCs
Among the three factors investigated namely rotationspeed Nr reaction temperature 119879 and operation pressure 119875
119879
the effects of 119879 are most significant The proper conditionsfound are at 483K 241MPa and 500 rpm The 120578DMP and120578TOC of 93 and 36 respectively can be achieved at180minThe produced CO
2kept in the closed-batch reaction
system seems to resist the further mineralization reactionfrom intermediates The application of sequential releaseof CO
2while addition of O
2to improve the 120578TOC is thus
suggested
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors are grateful for the financial supports of thisresearch provided by theMinistry of Science and Technology(formerly the National Science Council) of Taiwan
References
[1] M J Bauer R Herrmann A Martin and H Zellmann ldquoChe-modynamics transport behaviour and treatment of phthalicacid esters in municipal landfill leachatesrdquo Water Science andTechnology vol 38 no 2 pp 185ndash192 1998
[2] M Zhang S Liu H Zhuang and Y Hu ldquoDetermination ofdimethyl phthalate in environment water samples by a highlysensitive indirect competitive ELISArdquoApplied Biochemistry andBiotechnology vol 166 no 2 pp 436ndash445 2012
[3] J P Sumpter ldquoEndocrine disrupters in the aquatic environmentan overviewrdquo Acta Hydrochimica et Hydrobiologica vol 33 no1 pp 9ndash16 2005
[4] C A Staples D R Peterson T F Parkerton and W J AdamsldquoThe environmental fate of phthalate esters a literature reviewrdquoChemosphere vol 35 no 4 pp 667ndash749 1997
[5] W Den H C Liu S F Chan K T Kin and C Huang ldquoAdsorp-tion of phthalate esters with multiwalled carbon nanotubesand its applicationrdquo Journal of Environmental Engineering andManagement vol 16 no 4 pp 275ndash282 2006
[6] A J Kumar andCNamasivayam ldquoUptake of endocrine disrup-tor bisphenol-A onto sulphuric acid activated carbon developedfrom biomass equilibrium and kinetic studiesrdquo SustainableEnvironment Research vol 24 no 1 pp 73ndash80 2014
[7] M F N Secondes V Naddeo F J Ballesteros and V BelgiornoldquoAdsorption of emerging contaminants enhanced by ultrasoundirradiationrdquo Sustainable Environment Research vol 24 no 5 pp349ndash355 2014
[8] DW Liang T Zhang H H P Fang and J He ldquoPhthalates bio-degradation in the environmentrdquo Applied Microbiology andBiotechnology vol 80 no 2 pp 183ndash198 2008
[9] D LWu B L Hu P Zheng andQMahmood ldquoAnoxic biodeg-radation of dimethyl phthalate (DMP) by activated sludge cul-tures under nitrate-reducing conditionsrdquo Journal of Environ-mental Sciences vol 19 no 10 pp 1252ndash1256 2007
[10] D L Wu Q Mahmood L L Wu and P Zheng ldquoActivatedsludge-mediated biodegradation of dimethyl phthalate underfermentative conditionsrdquo Journal of Environmental Sciences vol20 no 8 pp 922ndash926 2008
[11] C-C Chang C-Y Chiu C-Y Chang et al ldquoCombined pho-tolysis and catalytic ozonation of dimethyl phthalate in a high-gravity rotating packed bedrdquo Journal of Hazardous Materialsvol 161 no 1 pp 287ndash293 2009
8 The Scientific World Journal
[12] Y-H Chen L-L Chen and N-C Shang ldquoPhotocatalytic deg-radation of dimethyl phthalate in an aqueous solution with Pt-doped TiO
2-coated magnetic PMMAmicrospheresrdquo Journal of
Hazardous Materials vol 172 no 1 pp 20ndash29 2009[13] Y-H Chen N-C Shang L-L Chen et al ldquoPhotodecomposi-
tion of dimethyl phthalate in an aqueous solution withUV radi-ation using novel catalystsrdquo Desalination and Water Treatmentvol 52 no 16ndash18 pp 3377ndash3383 2014
[14] Y Jing L Li Q Zhang P Lu P Liu and X Lu ldquoPhotocatalyticozonation of dimethyl phthalate with TiO
[15] W Jiang J A Joens D D Dionysiou and K E OrsquoShea ldquoOpti-mization of photocatalytic performance of TiO
2coated glass
microspheres using response surface methodology and theapplication for degradation of dimethyl phthalaterdquo Journal ofPhotochemistry and Photobiology A Chemistry vol 262 pp 7ndash13 2013
[16] Y Wang Y Liu T Liu et al ldquoDimethyl phthalate degradationat novel and efficient electro-Fenton cathoderdquo Applied CatalysisB Environmental vol 156-157 pp 1ndash7 2014
[17] F L Souza J M Aquino K Irikura D W Miwa M ARodrigo and A J Motheo ldquoElectrochemical degradation of thedimethyl phthalate ester on a fluoride-doped Ti120573-PbO
2
anoderdquo Chemosphere vol 109 pp 187ndash194 2014[18] F Charest and E Chornet ldquoWet oxidation of active carbonrdquo
Canadian Journal of Chemical Engineering vol 54 no 6 pp190ndash196 1976
[19] Y-H Chen D-C Hsieh and N-C Shang ldquoEfficient miner-alization of dimethyl phthalate by catalytic ozonation usingTiO2Al2O3catalystrdquo Journal of Hazardous Materials vol 192
no 3 pp 1017ndash1025 2011[20] M J Dietrich T L Randall and P J Canney ldquoWet air oxidation
of hazardous organics in wastewaterrdquo Environmental Progressvol 4 no 3 pp 171ndash177 1985
[21] S Imamura H Kinunaka andN Kawabata ldquoThewet oxidationof organic compounds catalyzed by Co-Bi complex oxiderdquoBulletin of the Chemical Society of Japan vol 55 no 11 pp 3679ndash3680 1982
[22] M M Ito K Akita and H Inoue ldquoWet oxidation of oxygen-and nitrogen-containing organic compounds catalyzed bycobalt(III) oxiderdquo IndustrialsampEngineeringChemistry Researchvol 28 no 7 pp 894ndash899 1989
[23] J Levec M Herskowitz and J M Smith ldquoActive catalyst foroxidation of acetic-acid solutionsrdquo AIChE Journal vol 22 no5 pp 919ndash920 1976
[24] L X Li P S Chen andE FGloyna ldquoGeneralized kinetic-modelfor wet oxidation of organic-compoundsrdquo AIChE Journal vol37 no 11 pp 1687ndash1697 1991
[25] W H Li J L Huang H Wang A J Qi and J Xie ldquoTreatmentof acrylic acid waste water by catalytic wet oxidationrdquo Journalof Jilin Institute of Chemical Technology vol 24 no 3 pp 3ndash62007
[26] S H Lin and Y F Wu ldquoCatalytic wet air oxidation of phenolicwastewatersrdquo Environmental Technology vol 17 no 2 pp 175ndash181 1996
[27] S H Lin and S J Ho ldquoTreatment of high-strength industrialwastewater by wet air oxidationmdasha case studyrdquoWaste Manage-ment vol 17 no 1 pp 71ndash78 1997
[28] H Lin Sheng and S J Ho ldquoKinetics of wet air oxidation ofhigh-strength industrial wastewaterrdquo Journal of EnvironmentalEngineering vol 123 no 9 pp 852ndash858 1997
[29] V S Mishra V V Mahajani and J B Joshi ldquoWet air oxidationrdquoIndustrial and Engineering Chemistry Research vol 34 no 1 pp2ndash48 1995
[30] A Sadana and J R Katzer ldquoCatalytic oxidation of phenol inaqueous solution over copper oxiderdquo Industrial and EngineeringChemistry vol 13 no 2 pp 127ndash134 1974
[31] P W Atkins ldquoPrinciples of chemical equilibriumrdquo in The Ele-ments of Physical Chemistry chapter 7 Oxford University PressOxford UK 3rd edition 1993
Figure 10 Two stages for the decomposition of DMP via WOP
the minimum pressure applied is 241MPa exceeding theneed However the mineralization of reaction (1) is hinderedby the accumulation of product CO
2in the closed-batch
reaction system It forces the backward reaction of reaction(1) according to Le Chatelierrsquos principle [31] The equilibriumbalance of the forward and backward reaction thus limits thecomplete mineralization of DMP A release of CO
2gas out
from the reaction system would certainly assist approachingthe complete mineralization of DMP
35 Comparison with Results of Others Comparison of theresults of this study with others is illustrated in Table 2 Thepresent WOP can reach 120578DMP of 93 as high as the advancedmethods (AMs) of electrochemical oxidation photocatalyticdegradation and photocatalytic ozonationThe 120578TOC ofWOPof 36 is lower than those of the aforementioned AMs atsome conditions however comparable at other conditionsIt is noted that the WOP simply uses oxygen with demandof the thermal energy while other AMs need to employchemical agents catalysts and ozone along with electric orUV energies Thus the WOP is comparatively simple toapplyThe discrepancy of incomplete mineralization ofWOPmay be consummated with the postbiological treatment ifnecessary [20] The predecomposition of DMP by WOPcertainly greatly enhances the followed biological processing
4 Conclusions
This study treated the toxic endocrine disrupter substance(EDC) of DMP via wet oxidation using oxygen (WOP)without other oxidant additives being beneficial to thesubsequent biological process if necessary while avoiding thetreatment of unwanted oxidant residuesTheWOP effectivelydecomposed the DMP indicating its feasible application forthe treatment of other EDCs
Among the three factors investigated namely rotationspeed Nr reaction temperature 119879 and operation pressure 119875
119879
the effects of 119879 are most significant The proper conditionsfound are at 483K 241MPa and 500 rpm The 120578DMP and120578TOC of 93 and 36 respectively can be achieved at180minThe produced CO
2kept in the closed-batch reaction
system seems to resist the further mineralization reactionfrom intermediates The application of sequential releaseof CO
2while addition of O
2to improve the 120578TOC is thus
suggested
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
The authors are grateful for the financial supports of thisresearch provided by theMinistry of Science and Technology(formerly the National Science Council) of Taiwan
References
[1] M J Bauer R Herrmann A Martin and H Zellmann ldquoChe-modynamics transport behaviour and treatment of phthalicacid esters in municipal landfill leachatesrdquo Water Science andTechnology vol 38 no 2 pp 185ndash192 1998
[2] M Zhang S Liu H Zhuang and Y Hu ldquoDetermination ofdimethyl phthalate in environment water samples by a highlysensitive indirect competitive ELISArdquoApplied Biochemistry andBiotechnology vol 166 no 2 pp 436ndash445 2012
[3] J P Sumpter ldquoEndocrine disrupters in the aquatic environmentan overviewrdquo Acta Hydrochimica et Hydrobiologica vol 33 no1 pp 9ndash16 2005
[4] C A Staples D R Peterson T F Parkerton and W J AdamsldquoThe environmental fate of phthalate esters a literature reviewrdquoChemosphere vol 35 no 4 pp 667ndash749 1997
[5] W Den H C Liu S F Chan K T Kin and C Huang ldquoAdsorp-tion of phthalate esters with multiwalled carbon nanotubesand its applicationrdquo Journal of Environmental Engineering andManagement vol 16 no 4 pp 275ndash282 2006
[6] A J Kumar andCNamasivayam ldquoUptake of endocrine disrup-tor bisphenol-A onto sulphuric acid activated carbon developedfrom biomass equilibrium and kinetic studiesrdquo SustainableEnvironment Research vol 24 no 1 pp 73ndash80 2014
[7] M F N Secondes V Naddeo F J Ballesteros and V BelgiornoldquoAdsorption of emerging contaminants enhanced by ultrasoundirradiationrdquo Sustainable Environment Research vol 24 no 5 pp349ndash355 2014
[8] DW Liang T Zhang H H P Fang and J He ldquoPhthalates bio-degradation in the environmentrdquo Applied Microbiology andBiotechnology vol 80 no 2 pp 183ndash198 2008
[9] D LWu B L Hu P Zheng andQMahmood ldquoAnoxic biodeg-radation of dimethyl phthalate (DMP) by activated sludge cul-tures under nitrate-reducing conditionsrdquo Journal of Environ-mental Sciences vol 19 no 10 pp 1252ndash1256 2007
[10] D L Wu Q Mahmood L L Wu and P Zheng ldquoActivatedsludge-mediated biodegradation of dimethyl phthalate underfermentative conditionsrdquo Journal of Environmental Sciences vol20 no 8 pp 922ndash926 2008
[11] C-C Chang C-Y Chiu C-Y Chang et al ldquoCombined pho-tolysis and catalytic ozonation of dimethyl phthalate in a high-gravity rotating packed bedrdquo Journal of Hazardous Materialsvol 161 no 1 pp 287ndash293 2009
8 The Scientific World Journal
[12] Y-H Chen L-L Chen and N-C Shang ldquoPhotocatalytic deg-radation of dimethyl phthalate in an aqueous solution with Pt-doped TiO
2-coated magnetic PMMAmicrospheresrdquo Journal of
Hazardous Materials vol 172 no 1 pp 20ndash29 2009[13] Y-H Chen N-C Shang L-L Chen et al ldquoPhotodecomposi-
tion of dimethyl phthalate in an aqueous solution withUV radi-ation using novel catalystsrdquo Desalination and Water Treatmentvol 52 no 16ndash18 pp 3377ndash3383 2014
[14] Y Jing L Li Q Zhang P Lu P Liu and X Lu ldquoPhotocatalyticozonation of dimethyl phthalate with TiO
[15] W Jiang J A Joens D D Dionysiou and K E OrsquoShea ldquoOpti-mization of photocatalytic performance of TiO
2coated glass
microspheres using response surface methodology and theapplication for degradation of dimethyl phthalaterdquo Journal ofPhotochemistry and Photobiology A Chemistry vol 262 pp 7ndash13 2013
[16] Y Wang Y Liu T Liu et al ldquoDimethyl phthalate degradationat novel and efficient electro-Fenton cathoderdquo Applied CatalysisB Environmental vol 156-157 pp 1ndash7 2014
[17] F L Souza J M Aquino K Irikura D W Miwa M ARodrigo and A J Motheo ldquoElectrochemical degradation of thedimethyl phthalate ester on a fluoride-doped Ti120573-PbO
2
anoderdquo Chemosphere vol 109 pp 187ndash194 2014[18] F Charest and E Chornet ldquoWet oxidation of active carbonrdquo
Canadian Journal of Chemical Engineering vol 54 no 6 pp190ndash196 1976
[19] Y-H Chen D-C Hsieh and N-C Shang ldquoEfficient miner-alization of dimethyl phthalate by catalytic ozonation usingTiO2Al2O3catalystrdquo Journal of Hazardous Materials vol 192
no 3 pp 1017ndash1025 2011[20] M J Dietrich T L Randall and P J Canney ldquoWet air oxidation
of hazardous organics in wastewaterrdquo Environmental Progressvol 4 no 3 pp 171ndash177 1985
[21] S Imamura H Kinunaka andN Kawabata ldquoThewet oxidationof organic compounds catalyzed by Co-Bi complex oxiderdquoBulletin of the Chemical Society of Japan vol 55 no 11 pp 3679ndash3680 1982
[22] M M Ito K Akita and H Inoue ldquoWet oxidation of oxygen-and nitrogen-containing organic compounds catalyzed bycobalt(III) oxiderdquo IndustrialsampEngineeringChemistry Researchvol 28 no 7 pp 894ndash899 1989
[23] J Levec M Herskowitz and J M Smith ldquoActive catalyst foroxidation of acetic-acid solutionsrdquo AIChE Journal vol 22 no5 pp 919ndash920 1976
[24] L X Li P S Chen andE FGloyna ldquoGeneralized kinetic-modelfor wet oxidation of organic-compoundsrdquo AIChE Journal vol37 no 11 pp 1687ndash1697 1991
[25] W H Li J L Huang H Wang A J Qi and J Xie ldquoTreatmentof acrylic acid waste water by catalytic wet oxidationrdquo Journalof Jilin Institute of Chemical Technology vol 24 no 3 pp 3ndash62007
[26] S H Lin and Y F Wu ldquoCatalytic wet air oxidation of phenolicwastewatersrdquo Environmental Technology vol 17 no 2 pp 175ndash181 1996
[27] S H Lin and S J Ho ldquoTreatment of high-strength industrialwastewater by wet air oxidationmdasha case studyrdquoWaste Manage-ment vol 17 no 1 pp 71ndash78 1997
[28] H Lin Sheng and S J Ho ldquoKinetics of wet air oxidation ofhigh-strength industrial wastewaterrdquo Journal of EnvironmentalEngineering vol 123 no 9 pp 852ndash858 1997
[29] V S Mishra V V Mahajani and J B Joshi ldquoWet air oxidationrdquoIndustrial and Engineering Chemistry Research vol 34 no 1 pp2ndash48 1995
[30] A Sadana and J R Katzer ldquoCatalytic oxidation of phenol inaqueous solution over copper oxiderdquo Industrial and EngineeringChemistry vol 13 no 2 pp 127ndash134 1974
[31] P W Atkins ldquoPrinciples of chemical equilibriumrdquo in The Ele-ments of Physical Chemistry chapter 7 Oxford University PressOxford UK 3rd edition 1993
[12] Y-H Chen L-L Chen and N-C Shang ldquoPhotocatalytic deg-radation of dimethyl phthalate in an aqueous solution with Pt-doped TiO
2-coated magnetic PMMAmicrospheresrdquo Journal of
Hazardous Materials vol 172 no 1 pp 20ndash29 2009[13] Y-H Chen N-C Shang L-L Chen et al ldquoPhotodecomposi-
tion of dimethyl phthalate in an aqueous solution withUV radi-ation using novel catalystsrdquo Desalination and Water Treatmentvol 52 no 16ndash18 pp 3377ndash3383 2014
[14] Y Jing L Li Q Zhang P Lu P Liu and X Lu ldquoPhotocatalyticozonation of dimethyl phthalate with TiO
[15] W Jiang J A Joens D D Dionysiou and K E OrsquoShea ldquoOpti-mization of photocatalytic performance of TiO
2coated glass
microspheres using response surface methodology and theapplication for degradation of dimethyl phthalaterdquo Journal ofPhotochemistry and Photobiology A Chemistry vol 262 pp 7ndash13 2013
[16] Y Wang Y Liu T Liu et al ldquoDimethyl phthalate degradationat novel and efficient electro-Fenton cathoderdquo Applied CatalysisB Environmental vol 156-157 pp 1ndash7 2014
[17] F L Souza J M Aquino K Irikura D W Miwa M ARodrigo and A J Motheo ldquoElectrochemical degradation of thedimethyl phthalate ester on a fluoride-doped Ti120573-PbO
2
anoderdquo Chemosphere vol 109 pp 187ndash194 2014[18] F Charest and E Chornet ldquoWet oxidation of active carbonrdquo
Canadian Journal of Chemical Engineering vol 54 no 6 pp190ndash196 1976
[19] Y-H Chen D-C Hsieh and N-C Shang ldquoEfficient miner-alization of dimethyl phthalate by catalytic ozonation usingTiO2Al2O3catalystrdquo Journal of Hazardous Materials vol 192
no 3 pp 1017ndash1025 2011[20] M J Dietrich T L Randall and P J Canney ldquoWet air oxidation
of hazardous organics in wastewaterrdquo Environmental Progressvol 4 no 3 pp 171ndash177 1985
[21] S Imamura H Kinunaka andN Kawabata ldquoThewet oxidationof organic compounds catalyzed by Co-Bi complex oxiderdquoBulletin of the Chemical Society of Japan vol 55 no 11 pp 3679ndash3680 1982
[22] M M Ito K Akita and H Inoue ldquoWet oxidation of oxygen-and nitrogen-containing organic compounds catalyzed bycobalt(III) oxiderdquo IndustrialsampEngineeringChemistry Researchvol 28 no 7 pp 894ndash899 1989
[23] J Levec M Herskowitz and J M Smith ldquoActive catalyst foroxidation of acetic-acid solutionsrdquo AIChE Journal vol 22 no5 pp 919ndash920 1976
[24] L X Li P S Chen andE FGloyna ldquoGeneralized kinetic-modelfor wet oxidation of organic-compoundsrdquo AIChE Journal vol37 no 11 pp 1687ndash1697 1991
[25] W H Li J L Huang H Wang A J Qi and J Xie ldquoTreatmentof acrylic acid waste water by catalytic wet oxidationrdquo Journalof Jilin Institute of Chemical Technology vol 24 no 3 pp 3ndash62007
[26] S H Lin and Y F Wu ldquoCatalytic wet air oxidation of phenolicwastewatersrdquo Environmental Technology vol 17 no 2 pp 175ndash181 1996
[27] S H Lin and S J Ho ldquoTreatment of high-strength industrialwastewater by wet air oxidationmdasha case studyrdquoWaste Manage-ment vol 17 no 1 pp 71ndash78 1997
[28] H Lin Sheng and S J Ho ldquoKinetics of wet air oxidation ofhigh-strength industrial wastewaterrdquo Journal of EnvironmentalEngineering vol 123 no 9 pp 852ndash858 1997
[29] V S Mishra V V Mahajani and J B Joshi ldquoWet air oxidationrdquoIndustrial and Engineering Chemistry Research vol 34 no 1 pp2ndash48 1995
[30] A Sadana and J R Katzer ldquoCatalytic oxidation of phenol inaqueous solution over copper oxiderdquo Industrial and EngineeringChemistry vol 13 no 2 pp 127ndash134 1974
[31] P W Atkins ldquoPrinciples of chemical equilibriumrdquo in The Ele-ments of Physical Chemistry chapter 7 Oxford University PressOxford UK 3rd edition 1993
