AJChE2002,Vol.2,No.1,1-6 RotalingBiological Conlactor lor Biological Treatment 01PoultryProcessing Plant Wastewater Using Saccharomyces Cererlslae Dr. Ghasem D NaJafpour, Punlta Nook Naldu and Azllna Harun Kamaruddln Associate Professor, School, UniuersitiSains Malaysia,Engineering Campus 14300 Nibong Tebal,S.P.S. Pulau Pinang Tel:00604-5937788 ext. 5404, Fax: 00604 -5941013, [email protected]Biological treatment using attached growth on a rotating biological contactor (RBC) was implemented for wastewater from poultry industries, which contains a high level of organic compounds due to the slaughtering, rendering of bones and fats, and plucking processes. The wastewater mostly consists of proteins, blood, fat and feathers. Nutrients available in the wastewater may enhance the growth of microorganisms, thus, it allows biological treatment to be used effectively. On the other hand, there are problems associated with biological treatment processes such as nutrients promoting algae growth. The control variables for the attached growth in RBC were wastewater detention time, effective surface for attached growth, disc submerged level in the wastewater basin, shaft rotation for aeration, pH control and supplementary nutrients. The attached growth resulted to high COD refPoval. The best treatment was obtained after 24 hours with 29 % disc submergence level. The effective surface area for cell growth was 10.7 m2 using 60 discs mounted on a shaft. The microorganism used for the attached microbial growth was Saccharomyces cerevisiae. The shaft was rotating at 11 rpm. The treatment was improved with the addition of 1 v/v of 0.1 molar sodium hydroxide solution to the wastewater for controlling pH. A 91 % COD removal was obtained with RBC operating at optimum conditions, with a DO concentration of 3.98 mg/l. Key words: Rotating biological contactors, Aerobic treatment, Poultry processing wastewater, Saccharomyces cereuisiae, Attached growth. INTRODUCTION The surface of submerged discs in the wastewater is in the range of 25 to 40% (Scott and Smith, 1983). The selection of the bio-disc material is important because biofilm growth varies with differenttypes of materials (Apilanezet al. 1998). When the disc with the attached microbial growth slowly rotates, it carries a thin film of wastewater to the atmosphere whereby microorganisms on the disc will then use oxygen in the atmosphere Rotating biological contactor (RBC) is also popularly known as rotating bio-disc contactor. RBC contains a basin filledwith wastewater with closelyspaced discsmounted on a horizontalshaft above the wastewatertank. The discsare mounted perpendicularly to the flow of wastewater and a microbial growth is attached to one of the disc.
Dr. Ghasem D NaJafpour,Punlta Nook Naldu andAzllna Harun KamaruddlnAssociate Professor,School, UniuersitiSains Malaysia,Engineering Campus14300 Nibong Tebal,S.P.S. Pulau PinangTel:00604-5937788 ext. 5404, Fax:00604 -5941013, [email protected]
Biological treatment using attached growth on a rotating biological contactor(RBC) was implemented for wastewater from poultry industries, which containsa high level of organic compounds due to the slaughtering, rendering of bonesand fats, and plucking processes. The wastewater mostly consists of proteins,blood, fat and feathers. Nutrients available in the wastewater may enhance thegrowth of microorganisms, thus, it allows biological treatment to be usedeffectively. On the other hand, there are problems associated with biologicaltreatment processes such as nutrients promoting algae growth. The controlvariables for the attached growth in RBCwere wastewater detention time, effectivesurface for attached growth, disc submerged level in the wastewater basin, shaftrotation for aeration, pH control and supplementary nutrients. The attachedgrowth resulted to high COD refPoval. The best treatment was obtained after 24hours with 29 % disc submergence level. The effective surface area for cellgrowth was 10.7 m2 using 60 discs mounted on a shaft. The microorganismused for the attached microbial growth was Saccharomyces cerevisiae. The shaftwas rotating at 11 rpm. The treatment was improved with the addition of 1 v/vof 0.1 molar sodium hydroxide solution to the wastewater for controlling pH. A91 % COD removal was obtained with RBC operating at optimum conditions,with a DO concentration of 3.98 mg/l.
INTRODUCTION The surface of submerged discs in the wastewateris in the range of 25 to 40% (Scott and Smith,1983). The selection of the bio-disc material isimportant because biofilm growth varies withdifferenttypes of materials (Apilanezet al. 1998).When the disc with the attached microbial growthslowlyrotates, it carries a thin filmof wastewaterto the atmosphere whereby microorganisms onthe disc will then use oxygen in the atmosphere
Rotating biological contactor (RBC) is alsopopularly known as rotating bio-disc contactor.RBCcontains a basin filledwith wastewater withcloselyspaced discsmounted on a horizontalshaftabove the wastewatertank.The discsare mountedperpendicularly to the flow of wastewater and amicrobial growth is attached to one of the disc.
2 Najafpour, Naidu and Kamaruddin
to treat the nutrients in the wastewater (DavisandCornwell, 1991). The RBC used in this researchhas the capability to retain a large amount ofbiomass on the surface of the discs. Aside fromthat, the RBC has the ability to withstandhydraulic and organic surges (Canale, 1971).
One of the important parameters which hasto be considered in the scale of RBC is masstransfer coefficientfor oxygen. The experimentalvalue for oxygen transfer coefficient has beendetermined (Kimand Molof, 1982) and is in therange of 49 to 87 % theoretical value. The valueof dissolved oxygen in RBC process isproportionalto extended aeration surfaceand discrotational speed. The performance of RBC hasbeen demonstrated by other investigators, it wasfound to be highlyefficientin operatingat ambienttemperature (Wilsonand Meng, 1997).
Aproperlydesigned RBCisvety reliablebasedon the amount of biomass attached to the discs.The biomass permits the RBCto more effectivelywithstand hydraulic and organic surges. Thehydraulic characteristic of a bench scale modelis determined by liquid flow rate, the rotationalspeed of the discand the percentageof submergedsurface (Banerjee, 1998).
Wastewater sample for treatment wasobtained from Dindings Poultry Processing Plantin Sitiawan, Perak, Malaysia. The sample wastaken to the influent point of the wastewatertreatment system immediately after a rotaryscreeningwas done where largesolidchunks suchas feet, heads and feathers were removed. Theplant processeses up to 40, 000 birdsevetyday toproduce chicken meat, chicken ballsand nuggets.The plant discharges 1000 m3of wastewaterevetyday.
In this research, the optimum operationalparameters for the fabricated RBC were foundfor the treatment of the Dindings PoultryProcessing Plant's wastewater.
MATERIALS AND METHODS
The bench scale RBC,a rectangular tank, wasfabricated from an actylic plastic transparentsheet with a thickness of 10 mm, a length of 80cm, a width of 40 cm, and a depth of 30 cm. Atransparent material was used to build the tankin order to observe wastewater throughout theexperiment. The material was thick enough towithstand wastewater working volume pressure
on the tank walls.A galvanized hollow metal barwith a diameter of 1.93 cm was used as the shaft.A metal bar was used to support the weight of thediscs and the attached microbial growth as cellgrowth, was increased during each experimentalrun. The disc was made from aCtylicplastic platewhich is 1.5 mm thick and has a diameter of 35cm. Twosets of discswere fabricated with 40 and60 discs. For each set useful area available forattached growthwere 7 and 10.7 m2.Actylicsheetwas chosen because it is light weight and it doesnot react withmicrobialgrowth. In order to extendthe surfacearea of each discforefficienttreatment,actylicextended plates witha thicknessof 1.5 mm,a length of 12 cm and a width of 3 cm wereattached to the discs. This model is designed andfabricated for batch mode operation.
Saccharomyces cerevisiae, a strain of yeast,was used as the attached microbial growth onRBC.S. cerevisiae was selected because it growsfast, can be obtained in bulk, easily adaptableto a new habitat and, safe to handle (Campbelland Duffus, 1988). Prior to the start of anexperimental run, a 3 % agar solution was evenlysprayed on both sides of the discs. The seedculture of S. cerevisiae was grown separately ina medium which consisted of glucose, peptoneand yeast extracts in 3, 1 and 1 g/l respectivelyin a 250 mL flask. The 24-hour incubatedcultured medium was used as an inoculum for alarger volume and was introduced into thesystem. After a biofilm of microorganisms wasdeveloped on the thin layer of agar, an additional24-hour incubation secured the system forsufficient cell growth. Then the RBC was readyto start an experimental run. The RBC wasoperated for five days using 60 liters ofwastewater from Dindings Poultry ProcessingPlant and 1 liter of S. cerevisiae w~s used as astarter. Throughout the experimentS, five majorparameters have been observed, based on theStandard Methods for the Examination of Waterand Wastewater. These are: total solids, totalsuspended solids, total Kjeldahl nitrogen,chemicaloxygendemand (COD)and dissolvedoxygen (DO).ForCOD analysis, the closed refluxcalorimetric method was developed usingdichromate reagent. The COD calibration curvewas prepared using potassium hydrogenphthalate standard solution. Aspectrophotometer(Milton Roy Spectronic 200) at 600 nm wasused to measure the absorbance of samples
ASEAN Journal of CHEMICAL ENGINEERING ·Vol. 2 No. 1 September 2002
analyzed for COD. While for Total KjeldahlNitrogen (TKN),a semi-micro Kjeldahl methodwasused. Allother routine tests were carried outbased on instructions given in the StandardMethods for the Examination of Water andWastewater(Greenberg et aI., 1992).
Thecellopticaldensity was measured by lightabsorbance at 520 nm using aspectrophotometer. The dissolved oxygenconcentration in wastewater was measured inmg/Iby a DO meter. The DO meter was WTWDOCell OX325 electro DO probe, Germany.
RESULTS AND DISCUSSION
Rotating biological contactors used in allexperimental runs were loaded with inducedbiofilm of S. cereuisiae on the agar-coatedsurface of contacting discs. The fast growingmicroorganisms enhanced the treatment andreduced the hydraulic retention time. The RBCwithinduced biofilmof S. cereuisiae was quicklystabilizedthen used for wastewater treatment.The advantage of bench scale RBC was toconductseriesof experimental parameters whichwereinfluencingon the biological treatment. Theinfluent wastewater samples taken from thepoultry processing plant were characterized.Several batches of wastewater samples weretaken at different times of operation and hadbeen analyzed. The characteristic of poultryprocessing wastewater has been summarizedwiththe analysis of several samples. An averageCODconcentration of 2200, total solids (TS) of500-1500, total suspended solids (TSS) of 650,TKNof 15-25, and DO of 0.3 mg/l were obtainedbased on experimental data resulting from theanalysis.
The fabricatedbench scale RBCwas used forthe treatment of .poultry processing wastewater.Attachedgrowth of microbial filmof S. cereuisiaewas developed on the surface of discs for anincubationperiod of 24 hours. A fixed volume of60 liters wastewater was used. Mounted discshaftswitha sufficientload of biomass on 40 and60 discs were rotated for 13 and 11 rpm,respectively.One v/v % of 0.1 Msodium hydroxidesolutionwasused for the pretreatment stage. Eightsets of experimental runs were selected torepresentmajor parameters affected on RBC.
The wastewater for runs 36, 38, 42 and 47weretreated for 96 hours. The experimental runs
of 50, 54, 57 and 60 were carried out in shorterperiod of 24 hours. All experimental runs has aneffective surface area of 7 m2except runs 57 and60, where the surface area for the extra load ofbiomass was increased by 53 %. Initially,the discssubmergence levelwas 35 % and the rotation was13 rpm. Modification for improved shafts withextra discsresulted to the submergence levelbeingreduced to 29 % and the rotation to 11 rpm.
The treatment of wastewater was monitoredbased on COD reduction and cell optical density.Since the process is aerobic, the DOconcentration was detected in the entiretreatment process. The constant DO level, whichwas in a reasonable range, represents the systembeing sufficiently aerated and the growth of thebiofilm on the discs proved that the attachedgrowth occurred while the biofilm was exposedto the air. If the DO level was very low, thisshowed that the system had a deficiency foraeration. In contrast, at high levels of DO, thebiomass growth was enhanced because theactivity of microorganisms exponentiallydeveloped. Figure 1 shows the last data pointsfor DO concentrations were 6, 5, 6.7 and 7 mg/I for runs 36, 38, 42 and 47, respectively. TheDO level for 29 and 35 % was compared, as thediscs submergence level was 6 % lowered, theDO concentration was higher since the discssurface exposed to air was also higher. Themaximum microbial activities based on celloptical density was experimentally determinedin wastewater treatment at 24 hours, therefore,the next set of experiments were carried out forshorter periods of treatment. More than 70 % ofthe cell optical density dropped after 48 hours oftreatment due to nutrient depletion and/or thedevelopment of inhibitors in the wastewater.Biomass activities and cell growth rate aredirectly related to the DO level in the wastewater.
DO concentration was increased with theaddition of 1 v/v % of 0.1 molar sodium hydroxidesolution. This phenomenon was due to chemicalactivities and the shift of pH from 6 to 8.5 whichimproved the solubility of oxygen and decreasedmicrobial growth activities. The ethanol producerS. cereuisiae has maximum activities at aroundpH of 4.5-5.0. Since microbial growth wassuppressed, the DO level has increased. The celldensity of S. cereuisiae was drastically decreasedafter 48 hours of incubation and fast growingmicroorganisms reached their death phase.
September 2002 Vol.2 No.1. ASEANJournalof CHEMICALENGINEERING
4 Najafpour,NaiduandKamaruddin
-+-Run.'Mhoun.,~8Ubm8f9M, 13rpm,700m2
Run38. M houl'8.3M't~. 13fl"", 7.0m2.N80H
-a-RWl42.18 houf8,2ft, ~ged. 13rpm.7.0m2
_Run 47 .Mhowa. ~8Vbm8tpd.13rpm. 7.0m2,N80H
1.5 2 2.5 3 3.5 4 4.5Time (day)
Figure 1: The DO level In the treated wastewater forruns 36, 38, 42 and 47
Figure 2 shows the DO levelsin the treatedwastewater for 24 hours, 2.8, 3.0, 5.0 and 4.0mg/l for runs 50, 54, 57 and 60, respectively. Acomparison of DO levelsfor runs 50 and 60 showsthat DO level increased by about 50 % as thedisc surface exposed to the air increased.Prolonging wastewater treatment duration for fourdays may not improve treatment since S.cerevisiae and other microbial popu1ationsdrastically decreased after 48 hours of treatment.The duration of treatment caused ammonia
Figure 2: The DO levels In the treated wastewater forruns 50, 54, 57 and 60
build-up in the treatment system. In addition, thelong period of treatment may also caused allmicroorganisms in the treated wastewater to gothrough endogenous phase since nutrient wasdepleted. Figure 3 shows the general trend ofammonia build up in most experimental runs asmicrobial activities declined. The minimum TKNconcentration was at 24 hours of treatment. Theresults obtained from six experimental runs thatused batches of wastewater sample,
comparatively showed the same trend. The DOshowed a constant increment ranging from 5 to 6mg 0/1. On the other hand, the TKN showedreductions ranging from 50 to 65 % by 24 hoursdue to nitrificationwhereby ammonia-nitrogen isconverted to nitrites and nitrates.
Figure 3: TKN concentrations In the treatedwastewater for runs 36, 38, 42 and 47
251
Figure 4 shows the reduction of TS, TSS andCOD. TS and COD had showed steady removalrate of 65 to 80 % and 70 to 90 %, respectively.Meanwhile,TSS exhibited a sinusoidal trend. TheTSS recorded a removal rate of about 80 % for atotal retention timeof 96 hours. The TSS reductionwithin 24 hours, which ranged from 60 to 77 %,occurred due to suspended organic matters usedby microbes for metabolism. A sudden increasein TSS from 24 hours to 72 hours was probablyinitiated by the high death rate of S. cerevisiaeand other microorganisms. When nutrients weretotallydepleted after 72 hours, the amount of TSSdecreased again.
Basically, the trend shown in Figures 3 and 4were due to the slow rotation of the shaft, the lowsubmergence level of the disc in the wastewaterwhere a large part of the disc is exposed to theatmosphere, and the large surface area fortreatment. These factors contributed to a highaeration rate in the system. Thus, the COD levelwas effectively reduced while DO was kept at asatisfactory level.
The low rotation of 11-13 rpm and low shearforces did not cause any turbulence to break solidfloes. Therefore, TS and TSS were effectivelyreduced. Aerobic conditions and the existence ofnitrificationbacteria and Nitrobacter inthe systemcaused the nitrificationprocess. These species of
ASEAN Journal of CHEMICAL ENGINEERING . Vol. 2 No. 1 September 2002
8
7
I 6
ls
Ii 4
o 3
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00 0.5
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Figure 4: EjJlciency of treatment observed throughTS, TSS and COD
microbes, also kpown as Nitrifiers, convertsammonia nitrogen to nitrites and nitrates, whichreduces TKNlevel.A sudden increase inTKNlevelwas probably due to depletion ofNitrifiers.Certainmodes of toxicity for Nitrifiers also occurredcausing the TKNto drop. This isdue to the suddenhigh concentration level of nitrites. A highconcentration of nitrites and ammonia may causetoxicity for Nitrifiers. Nitrite concentration haveincreased due to the doubling of DOconcentration after 24 hours and onwards.
Figure 5 shows COD reduction for runs 36,38, 42 and 47 with a fixed disc surface of 7 m2.The final COD values were less than 400 mg/I.The rate of COD removal for runs 36, 38, 42 and47 were 78, 72,88 and 94 %, respectively. Thehigher rate of COD removal for runs 42 and 47compared to runs 36 and 38 were due to betteraeration as 6 % more of the surface area of thediscs were exposed to the air. However, theaddition of chemical did not have any positiveeffect on COD removal. Based on data availablethe reduction of COD was 70% within 24 hours.
Figure 5: COD concentration reductions inwastewater for runs 36,38,42 and 47
The effect of additional .surface area of discand more surface exposure to air is shown inFigure 6. By comparing runs 50 and 54, theadditional 6 % surface exposure to air showedthat COD reduction in the 24-hour wastewatertreatment improved from 60 to 75 %. The use ofa higher disc surface area of 10.7 m2,which is 53% higher, improved the rate of COD removal from60 to 90 % and 75 to 92 % in experimental runs57 and 60, respectively. The DO level in thewastewater for experimental run 60 was about 4mg/l and the TKNremoval rate was 75 % after 24hours of treatment. Addition of S. cerevisiae asattached growths on the RBC system enhancedthe treatment process and shorten the durationof the treatment since fast growing bacteria wasincorporated. A 24-hour treatment showed highachievement.
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Figure 6: COD concentration reductions inwastewater for Run 50, 54, 57 and 60
CONCLUSION
This research concludes that the bench scalefabricated RBC model using an attached film ofS. cerevisiae is best during a retention time of 24hours, since TKNvalue was at its lowest level atthis point. But in order to improve TS, TSS andCOD removal rate, shaft rotation speed must befurther reduced. In addition, discs surface areafor the treatment must be extended or more discsmust be added. Runs must also be based onoptimum surface loading. In the latter stage of thisresearch, the RBC bench model was modifiedbased on the primary results gathered to optimizethe operational parameters for effective aerationand the design parameters for efficientwastewatertreatment. Application of S. cerevisiae as a filmof fast-growing biomass on disc surface reduced
September 2002 Vol. 2 No, 1 ·ASEAN Journal of CHEMICAL ENGINEERING
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6 Najafpour,NaiduandKamaruddin
treatment period of the poultry processingwastewater to about one day.
ACKNOWLEDGEMENT
The authors would like to acknowledge theResearch and Development Committee of theUniversitiSains Malaysiafor funding the researchbased on IRPAgrant No. 0735115. We also liketo thank the Dindings Poultry Processing Plant inSitiawan, Perak State, Malaysia for theircooperation.
REFERECENCES
Scott, J. S. and Smith, ~ G., (1983).Dictionaryof Wasteand WaterTreatment,Butterworth, London. Scott and Smith,262.
Apilanez, I., Gutierrez, A., and Diaz, M.,(1998). Effect of Surface Materials onInitial BioflimDevelopment, BioresourceTechnology~.66 (3), 225-230.
Davis, M. L. and Cornwell, D. A., (1991).Introduction to EnvironmentalEngineering 2ndEd., McGraw-Hill,NewYork,368 - 370.
Canale, R. P., (1971). Biotechnology andBioengineering Symposium No.2:Biological Waste Treatment, John Wiley& Sons, New York, 131 - 140.
Kim, B. J. and Molof, A. H., (1982). The Scaleup and Limitation of Physical OxygenTransferin RotatingBiologicalContactors,WaterScienceand Technology:14, 569-579.
Wilson, F. and Meng, L. W., (1997). RotatingBiological Contactors for WastewaterTreatment in an Equatorial Climate, WaterScience and Technology: 35 (80), 177-184.
Campbell, I. and Duffus, J. H., (1988). Yeast:A PracticalApproach. IRL Press, Oxford,Washington D.C., 1 - 5.
Greenberg, A. E., Clescerf, L. S. and Eaton,A. D., (1992). Standard Methods for theExamination of Waterand Wastewater18thEd. APHA,AWWAand WEF,WashingtonD.C., 5.1 - 5.15.
ASEAN Journal of CHEMICALENGINEERING ·Vol. 2 No. 1 September 2002
