The Influence of pH on Removal of H2S and Natural Organic Matter by Anion Resin

8/12/2019 The Influence of pH on Removal of H2S and Natural Organic Matter by Anion Resin

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DesalinationandWater Treatment 21 (2010) 255-263y w w w. de sw ate r.co m September

A 1944-3994/1944-3986'' 2010 Desalination Publications.Allrights reservedU Hni-in5(104/Hwt7111n1545doi: 10.5004/dwt.2010.1545

The influenceofpH onr emova lofH^Sandna tura l o rganic mat te rby anion resinMilka M. Vidovic*, Jovan N. Jovicevic^ JelenaD .Krstic \ Ilija D . Tomi\ Sasa S. Rogan ' University ofBelgrade,TheInstitute of Chemistry, TechnologyandMetallurgy, Departm entfor EcologyandTechnoeconomics,12 Njegoseva, 11000Belgrade, SerbiaTel. +381113370225; F ax: +381113370225; e-mail: [email protected]''University ofPrishtina, Facultyof Sciences, Chemistry Department, 38220K.Mitrovica, SerbiaReceived5October 2009; accepted 18 February 2010

ABSTRACTA numberofexperiments with specific ground water from the Pannonian Plains(theRepublicof Serbia) were conductedinordertodefine a technological processfor drinking water treatment.The specificity of this raw waterisreflectedinincreasedpHvalueandincreased concentrationsof natural organic matter, ammonia, hydrogen-sulphideandsome toxic metals. Removalofnat-ural organic matterby the basic macroporous resinsinacid m edium (pH6.6-7.2) rangedup to92% ofthe input concentration,andof hydrogen-sulphideup to6O'Xi.Theremaining h ydrogen-sulphide, that wasnoteliminatedon themacrop orous resin, was completely removedbyadsorp-tionon the Filtersorb FMH.Thecorrelation betweentheconcentrationofnatural organic matterand the UV extinctionin raw andprocessed water, bothinthe acidand inthe alkaline med ia,wasestablished.Theadsorptionofnatural organic matteron macroporous resinsismo re efficientinthe alkaline medium thanin theacidone.Keywords: Hyd rogen-su lphide; Natural organic matter; Anion resin;UVextinction; Redox potential

1.Introduction Thehumic substancesaremadeup ofamorphousXTI 1 i.i. /u jr.1 -j j polydisperse colloids[1,21.Theirmacromolecularchar-Natural organic matter humicand fulvicacids, and . F , , ,, . N , r . ., u - l-i. J acteristicsare theresultofaggregates generatedbv

humics), hereinafter the humic substances,is anunde- , , , , , * " . , , ". 1 1 . J- i. J 1 i ri m I jj-^- hydrogen bonds, non-polar interactionsandpolyva-sirable ingredientindrinking water [1,21.Inaddition ,- . . . ^ , , ^ ^, . . . , ,. . . 1 1 lentcation interactions. These formsofnaturalorganicto Its influence upon the colour, taste and smell of the , . , . , , ,. . , . . . , 1 1 11 t- matter are complex mixtures of aromatic and aliphaticwater, the humic substances cause biologically quanti- , , , , . . . . . . , , , ,. . . u 1 1 , . > - > - j hydrocarbon chains to which amide, carboxyl, hydro-tative changes in a water supply system. During oxida- \ , . , , , . , , , ,.. J J- I- \u u- i. ,. xyl,ketonic andother functional groups arebondedtionanddisinfection processes they combinetocreate r ,T- . . , ^

J , r 1 u u uu J i.. U\-runctional groups with aromatic coresandhumiccompounds harmful tohuman healthandmaiorityof , . ? them areclassedascarcinogenicor aspromotersof ^^^stances with free p-electrons canparticipateincarcinogenic compounds [3-6]. ' ^ ^ * ' ' mcluding adsorption-desorption, oxidation-

reductionandformation ofcomplexes. Upon dissocia-tioninwater, the humic substances haveanegativecharge, duetothe presenceofcarboxylandother simi-


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M.M. Vidovic et al. / Desalination and Water Treatment 21 2010) 255-263 25 7

Fig. 1. The chart of the exp erimental pilot plan t.

the temperature was measured by the pH meterINOLAB pH 730, WTW, Germany [31].In the statistical processing of data, methods ofcentral tendency arithmetic mean and standard devia-tion), regression and correlation analysis were used.The standard stastical package SPSS 8.0 was used.3.Results

The results are presented as average values of thedata obtained in the experiments performed.Fig. 2 presents the measured values of thehydrogen-sulphide concentrations at the inlet andthe outlet points of the column S Fig. 1) as a functionof the pH of the treated water. The percentage of thehydrogen-sulphide removed in column S, expressedas the outlet and inlet concentrations ratio, in relationto the change in the pH at point A Fig. 1) is show nin the Fig. 3.The percentage of the natural organic matterremoved as a function of the quantity of water treatedTable 2Characteristics of columns and FColumnFilling materialVolume chargeVolumecapacityManufacturer

Density

SLewatit MP6237 L48 LLanxess,Leverkusen,Germany1.03 g/mL

FFiltersorb

FM H30 L 8LCWG GmbH,Mannheim,Germany1.56 g/mL

6.7 7.1 7.3 7.6 7.9 8.2 8.5pH

Fig.2 . Average values of the hydrogen-sulphide concentra-tions at the inlet II) and the outlet poin ts III) of the natu ralorganic matter removal column, as a function of the con-trolled pH value.: Qnf;: C ff; Expo n. H2S inlet);: Expon.H2S outlet).

in the acid pH range of 6.6-7.0) and alkaline pH rang eof 7.0-8.5) m edia is presen ted in Fig. 4. The percentag eis defined as a ratio between the outlet and inlet con-centrations of natural organic matter and the quantityof water treated as a volume of treated water per resinvolume unit V^./V^, i.e., BV - bed volume).The relationship between the quantity of naturalorganic matter adsorbed on the resin and the volumeof treated water V^/V^), in fact the cum ulative qua n-tity of the adsorbed natu ral organic m atter on the resin,is graphically presented in Fig. 5.The cumulative quantity of the removed hydrogen-sulph ide in an acid m edium pH rang e of 6.6-7.2) inrelation to the treated water volume V^JV^) is pre-sented in Fig. 6.

^ 1.2O 0.9

g 0.3X 0.0y - 0 . 0 2 4 5 * *

R' - 0.8222

6 6.5 7 7.5 8 8.5 9pH

Fig. 3. Average values of the hydrogen-sulphide concentra-tions ratio at the outlet III) and the inlet poin ts II) of the col-umn for natu ral organic m atter removal, as a function of thecontrolled p H value. ) : Ceff/Ci,. H2S;: Expo n. {C^if/QfH2S).


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25 8 M.M. Vidovicetal. Desalination andWater Treatment2 2010) 255-263

C

oc

u.o0.50.40.30.20.10.0

y >0.491Sx +0.0797 y f.,

R'-0 . 9 7 9 2 x J^^ 0 '

V 1 ^ ^ * ' ^ ^' y 0.522X 0.079ea

0.0 0.4 0.8Vw/Vr

1.2 1.6

Fig.4. Average valuesof thenatural organic matter o utlet(III)and inlet (II) concentrations ratio as a function of thevolumeof the treated waterper resin volume unit (V/Vr)in acid and alkaline media. ( ) : acid cycles average; ( ) : acidcycle 1 ; (A): acid cycle 2; (): acid cycle 3; (O ): alkaline acidsaverage; (n ): alkaline cycle 1; (A): alkaline cycle 2; (O): alka-line cycle 3;: linear (alkaline processes average);: linear (acidprocesses average).

Fig. 7 presents the ratio of the water UV extinction(at 254 nm) measured in the samples obtained from theoutlet and the inlet points of the column S, as a functionof the ratio of natural organic matter concentrations atthe outlet and the inlet points of the column S, both forthe acid and for the alkaline media.

iscussionIn order to understand the chemistry of hydrogen-

sulphide removal, it was necessary to analyse the

0.4 0.6VwA/r

Fig. 6. Average valuesofcumulative quan tityofthe removedhydrogen-sulphide as afunctionofthe volumeof the treatedwa ter (Vw/V r)in acid medium.(): average H2S; (D):H2Scycle1; (A): H2S cycle 2; (x): H2S y le3 ;: pow er (average H2S).chemistry of the natural organic matter removal at theanion resin in the column S.

At equilibrium a relationship exists between theconcentration of the species in solution, C, and the concentration of the same species in the adsorbedstate X/M (i.e., the amount of species adsorbed per unitmass of adsorbent) [35-38]. The adsorption equili-brium relates X/M to C. The equilibrium is a functionof the temperature. The adsorption equilibrium rela-tionship obtained at a given temperature is typicallyreferred to asadsorption isotherm,i.e.:(X/M) =/(Ce), (1 )where X is the mass of the adsrbate; M is the mass ofthe adsorbent (X/M isequilibrium concentration of

y10.517xR =0.9771

0.5 1.0VwA/r

1.5

Fig.5.Average valuesof cumulative quantitiesof adsorbednatural organic matteras a function of thevolumeofwatertreated (V/Vr)inacidandalkaline m edia.():acid cyclesaverage;(): acid cycle1; (A): acid cycle 2; () : acid cycle3; (O): alkaline acids average; (Q): alkaline cycle 1; (A): alka-line cycle2; (O): alkaline cycle 3;: linear (alkaline processesaverage);: linear (acid processes average).

nf

5 10.4

3

0.2

0.1

y R 0.9204X>0.9795y0.9688X 0.9621

0.0 0.2 0.4 0.6

Fig. 7. Dependen ceofthe average values UV w ater ex tinctionratioatthe outlet (III) and the inlet po ints (II)ofthe column Son the natural organic m atter concentration ratioforthe alka-line process; see same water in the acid and the alkalinemedia. (): acid process;(A):linear (acid process);: linear(alkaline process).


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M.M . Vidovic et al. / Desalination and Water Treatment 22 (2020) 255-263 259adsorbable species in solid adsorbent); Cp is anadsrbate equilibrium concentration in the solution.Since no assumption of reversible adsorption and des-orption of the adsrbate molecules can be made andadsorption of mixtures of compounds on the resin isvery probable, in our case the removal of the adsrbatefrom the solution can be described by Freundlich'sadsorption isotherm:(X/M)=:r ' / , 2wherekand n are specific adsorption coefficients (/c isrelated to the capacity of the adsorbent, and 1/n is afunction of the strength of adsorption).To determine the relationship between the concentra-tion of an adsrbate in solution (C) and the amount ofadsrbate adsorbed per unit mass of adsorbent (X/M)one can proceed with the solution being sampled andanalyzed for the adsrbate.A mass balance for the adsrbate in the system is:V(Co-C)=M[(X/M)- (X/M)o] 3from which a relationship betw een a value of and thecorresponding eq uilibrium value ofX/Mcan be estab-lished. Co = Cinf = initial adsrbate concentration insolution (mg/L); X/M)Q - (X/M)inf initial amo un t ofadsrbate per unit mass of adsorbent (mg/g resin);M = mass of resin (g) and V = volume of the waterin contact with the adsorbent-the resin (L).In ourcase,virgin resin w as used to determine equi-librium relationship: (X/M)o = 0, and at the beginningof the experiment, i.e. for the time t =0:

4Note that V/M is the ratio between the volum e of thewater treated in contact with the resin and the massof the resin, i.e., the value of the bed volume (B) andat any time f:Q = Cin f - (M/V)[ (X/M) , ] . 5This equation represents anoper ting line (from a massbalance) for the system. If the time elapsed is longenough for equilibrium to be established then thisequation becomes:

(6)In our case the long enough time is the time elapsedfrom the beginning of the contact of the raw water(starting concentration of the adsrbate Ci^) with theresin, and the time when the concentration of the

adsrbate in the treated water reaches maximumallowed value,Qa [39,40].Using Eq. (1) and Eq. (6) one can write- Ceff)V/M = X/M = kC \/neff 7where V/M is V^/V^ = bed volume.The adsorp tion is affected by the pH of the solution[22], therefore the experiments were conducted in bothalkaline and acid m edia. The values presen ted in Fig. 4show that the specific adsorption is approximatelyequal in both alkaline and acid media (see the inter-cepts). However, the slopes of the linear approxima-tions differ. The slope is higher in the acid medium.This points to a higher quality adsorption representedin a larger quantity of adsorbed natural organic matterper unit of resin volume. This simultaneously means

that the resin will become saturated faster in the acidmed ium. Therefore, the volume of the processed w aterwill be smaller compared to the alkaline medium, asindicated by a steeper slope of the straight line in Fig. 4.There is also a possibility that alongside the naturalorganic matter slow adsorption process an ionexchange pro cess is carried o ut, the latter being a fasterone.The straight line, representing the organic matteradsorption in alkaline medium (Fig. 4), shows a lowerslope. This means a smaller quantity of organic matteradsorbed from the same quantity of water in alkalinethan in acid medium, and therefore a larger quantityof processed water in this med ium.The saturation level of the resin is defined by theconcentration of 8 mg L ' KMnO4 in effluent water.This value is also the maximum allowable concentra-tion (IVIAC) in drinking water. Using this criterion, itwas found that 669 dm ' of water per resin dm'' wereprocessed in the acid medium and as much as 934dm were processed in the alkaline one before the resinsaturation level was reached. The average values lineshave revealed that at the very beginning of the workcycle of the column S the organic matter concen trationreduction was 92%, declining to an average of 60%towards the end of the working period (Fig. 4). Thecumulative effect of natural organic matter removalup to the resin saturation level presented by averagevalues in Fig. 5 shows that the adsorption is moreintensive in the acid m ediu m. This was reflected in theslope of the average values line. In the acid m edium theresin adsorbed 7.64 g L ^ natural organic matter, whichamounts to 11.4 mg g ' of the resin. In the alkalinemedium this mass was 11.24 g L ', which equals16.77 mg g^' of the resin. The technical data providedby the manufacturer (Lanxess, Germany) state that theresin can adsorb 12 mg of organic matter (expressed in


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M.M. Vidovic et al. /Desalination and W ater Treatment 22 2010) 255-263 2610.6

0 50.6

0 0 0 2 0.4 0.6 0.8VwA/r

1.0 1.2

Fig. 9. Average values of the UV extinction ratio and the ratioof the natural organic matter concentrations at the outlet (III)and the inlet points (II) of fhe column S, as a function of thevolume of the water treated V^/V^) in the alkaline medium.(A):Q,f,/Cf.KMnO4; ( ):Ce/Qnf.UV;: Expon. Ceff./Qnf.KMnOj);: E xpon. C,.ff/Cif. UV).that it is hydrogen-sulphide. This is supported by Figs.9 and 10, which present the comparison of the ratio(percentage) of natural organic matter removal and theratio of the UV extinction values for the effluent andinfluent water ratios in the alkaline and the acid med ia,both as a function of the quantity of water treated (BV).Fig. 10 shows that the value of the UV extinctionratio in the acid medium is considerably lower com-pared to the ratio of natural organic matter removedfor the same BV. In the alkaline medium (Fig. 9), thedifference between the value of the UV extinction ratioand that of the percentage of the natural organic matterremoved for the same BV is considerably smaller thanthat shown in Fig. 10.

^ 0 . 67 0.50.3C

0 0

f 'y 0.1324' * 0.9782

0.6

0.4 0.0

0 0 0 2 0 4 0 6VwA/r

0 8

Fig. 10. Average values of the UV extinction ratio and theratio of the natural o rganic matter concentrations at the ou tlet(III) and the inlet p oints (II) of the colum nS,as a function ofthe volume of the w ater treated Vyj/V, in the acid medium.(O):Ceff./Cinf.KMnO4; ( ): C^JC^. UV;: Expo n.KMnO4);: Expo n.{C,,tt./Cn,. UV).

The analysis of the results obtained by measuringthe redox potential has shown that the redox potentialof raw water ranged from -160 to -31 mV vs. N.H.E.,that of the water leaving the column S ranged from -74 to 60 mV vs. N.H.E., wh ereas after the column withFiltersorb FMH it ranged from 56 to 272 mV vs. N.H.E.In the alkaline medium, the redox potential after thecolumn S ranged from -74 to 19 mV vs. N.H.E.,whereas in the acid medium it ranged from 13 to60 mV vs. N.H.E. The measurements of the redoxpotential after the colum n F show ed the value s from100 to 272 mV vs. N.H.E. for the acid medium, andfrom 56 to 166 mV vs. N.H.E. for the alkaline me dium .This suggests that hydrogen-sulphide is removed inthe acid medium and that the water from the reductionstate passes into the oxidation one.

Following the treatment in the column S, theremaining hydrog en-su lphid e in the water (40 in theacid me dium and about 100 in the alkaline me dium )is successfully removed in the column F. Furthermore,it was established that the water redox potential valuesat the outlet of the column F were positive vs. N.H.E. inthe case wh en the colum n S functioned in the acid aswell as in the alkaline media. This allows for thehypothesis that dissolved hydrogen-sulphide contri-butes to the negative values of the raw water redoxpotential. In the acid medium the column has a consid-erably longer working cycle due to the quantity of thehydrogen-sulphide removed in the previous segment(the column S with macro poro us resin).5.Conclusions

The research into the removal of natural organicmatter from specific ground waters on alkaline macro-porous resin shows that the quantities of naturalorganic matter removal differ in relation to the pH ofthe water, which is reflected in the volume of the pur-ified water. The alkaline medium allows for a largerquantity of water to be purified.The removal of hydrogen-sulphide was planned tobe performed in the column F placed after the scaven-ger filter S. However, the experimental results haveshown that the hydrogen-sulphide can also beremoved on the macroporous resin scavenger filter S,and that its removal depends on the conditions underwhich the natural organic matter is removed. There-fore, the column F was used only for an additionalremoval of the hydrogen-sulphide.The experiments conducted have shown thathydrogen-sulphide was efficienfly removed in an acidmedium (pH range of 6.6-7.2) of the natural organicmatter removal column (S).The research has shownthat fhe removal of hydrogen-sulphide on


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M.M. Vidovic et al. / Desalination and W ater Treatment 21 (2010) 255-263

macroporous resin is directly preconditioned by thepH of water. In the acid medium, and up to the pH7.2, the hydrogen-sulphide is being removed inten-sively, whereas in the alkaline me dium the hyd rogen-sulphide is not removed on macroporous resin, whichis the information of importance when designing thetechnology of water purification.

The hydrogen-sulphide that is not removed in thenatural organic matter removal column S is success-fully removed on the Filtersorb FMH up to the valueslower than the detection limit, in both the acid andalkaline media.The correlation between the UV extinction at254 nm and the concentration of natural organic matterin the water is a valid indicator for tracking the satura-tion of the alkaline macroporous resin for naturalorganic matter removal in the water treatment plants.The determination of the resin saturation level on thebasis of the potassium-permanganate consumption ineffluent water is a slower and a more de ma nding ana-lysis, and measuring of UV extinction can be per-formed on line in the water preparation processes.cknowledgements

The authors would like to acknowledge the fundingof the Ministry of Science and Environmental Protec-tion of the Serbian Government (project number:146021B).eferences[1] M. Schnitzer and S.U. Khan, Extraction, Fractionation, and Pur-ification of Humic Substances, In: Humic Substances in theEnvironment, Marcel Dekker, New York 1972, pp. 9-23.[2] S. Hesse, G. Kleiser and F.H. Frimmel, Characterization ofrefractory organic substances (ROS) in Water Treatment, WaterSei.Technol., 40 (1999) 1-7.[3] P.C. Singer, Humic substances as precursors for potentiallyharmful disinfection by-products. Water Sei. Technol., 40(1999) 25-30 .[4] G. Guo and X. Chen, Halogenating reaction activity of aromaticorganic compounds during disinfection of drinking water, J.Hazard. Mater., 163 (2009) 1207-1212.[5] H. Gallard and Urs von Gunten, Chlorination of natural organic

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[37] D. A. Fungaro, M. Bruno and L. C. Grosche, Adsorption andkinetic studies of mthylne blue on zeolite synthesized from flyash. Desalination Water Treat., 2 (2009) 231-239. http://www.norit-americas.com/pdf/lsotherm_Test_rev2.pdf.[38] R. C. Bansal and M. Goyal, Activated Carbon Adsorption fromSolutions, In: Activated Carbon Adsorption, CRC Press 2005,pp . 145-196. http://cpe.njit.edu/dlnotes/CHH6 85/Clsll-l.pdf.[39] A.E. Lewis, O. Laha\ and R.E. Loewonthal, Chemical considera-tions of sulphur recovery from acid mine drainage . Proceedingsof the Water Institute of Si)uth Africa Biennial Conference, SunCity 2000, pp. 1-11.


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The Influence of pH on Removal of H2S and Natural Organic Matter by Anion Resin

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