anaerobic treatibility of agro indust

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Biodegradation 11: 401405, 2000. 2001 Kluwer Academic Publishers. Printed in the Netherlands.

401

Short communication

Anaerobic treatability and biogas production potential studies of different

agro-industrial wastewaters in Turkey

Gksel N. Demirer1, Metin Duran2, Tuba H. Ergder1, Engin Gven3, rgen Ugurlu4 & UlasTezel11Department of Environmental Engineering, Middle East Technical University, Ankara, Turkey; 2 Department of

Civil Engineering, Bucknell University, Pennsylvania, USA; 3Department of Civil and Environmental Engineering,

Marquette University, Wisconsin, USA; 4Department of Environmental Engineering, Istanbul University, Istanbul,

Turkey ( author for correspondence; e-mail: [email protected])

Accepted 8 August 2000

Key words: anaerobic treatment, cheese whey, olive-oil mills, poultry breeding

Abstract

The anaerobic treatability and methane generation potential of the wastewaters of the three important agro-industries in Turkey, namely, cheese-making, poultry breeding and the olive-oil mill industries were studied.Biochemical methane potential (BMP) experiments were conducted for different initial chemical oxygen demand(COD) concentrations. The results indicate that anaerobic treatment was possible for all the wastewaters studiedand the biogas produced had a high methane content.

Introduction

Agro-industries play a significant role and representa considerable share of the Turkish economy. For ex-ample, Turkey is the fifth largest country worldwideinvolved in the production of olive oil. Furthermore,poultry breeding has spread widely and 3 million tonsof wet manure was produced out of 50 million poultryin 1998.

Cheese whey is a protein- and lactose-richbyproduct of the cheese industry. It is highly biode-gradable with a very high organic content (up to 70g COD/L), and low alkalinity (50 meq/L) (Mawson1994). The high organic content of cheese whey

renders the application of conventional aerobic bio-logical treatment costly, mainly due to the high priceof oxygen supplementation. Anaerobic treatment re-quires no oxygen supplementation and generates asignificant amount of energy in the form of methanegas. However, Malaspina et al. (1996) stated that rawcheese whey is a quite difficult substrate to treat an-aerobically because of the lack of alkalinity, the high

chemical oxygen demand (COD) concentration andthe tendency to acidify very rapidly.

Poultry breeding wastes are characterized by high

total solids and organic content, NH4-N concentrationand pathogens. Because of insufficient or uncontrolledhandling and disposal, they present a danger to publichealth and the environment.

Olive-oil mills are small agro-industrial units loc-ated mainly around the Mediterranean, Aegean andMarmara seas and account for approximately 95%of the worldwide olive-oil production. They processolives for the extraction of olive oil either by meansof a discontinuous press (classical process), or asolid/liquid centrifuge (centrifugal process). Both pro-cesses produce two different forms of waste, namely,

olive mill residual solids (OMRS or prina) which con-tain oil that must be recovered by solvent extraction,and olive mill wastewater (OMWW or black water).The mean waste volumes from classical and centrifu-gal processes are 1.18 and 1.68 m3 per ton of olivesprocessed, respectively. The corresponding mean or-ganic loads in terms of COD are 79.2 and 121.7


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Table 1. Characterization of the wastewaters studied.

Parameter Cheese whey Poultry breeding Olive-oil mill

pH 3.92 4.63

COD 55,250 1344 mg/L 123,642 mg/L 138,250 7047 mg/L

Total phosphorus (TP) 124 mg/L 55.6 mg/L

Total Kjeldahl nitrogen (TKN) 145.6 mg/L 579 mg/L

Suspended solids (SS) 9380 453 mg/L 103,027 mg/L 42,833 mg/L

Volatile suspended solids (VSS) 8280 396 mg/L 67,720 mg/L 42,633 mg/L

These samples were analyzed in duplicate.

kg COD per ton of olives processed, respectively.The maximum biological oxygen demand (BOD) andCOD concentrations reach 100 and 200 g/L, respec-tively (Tsonis & Grigoropoulos 1993; Hamdi 1996;Ubay & zturk 1997).

Within the olive-growing countries of the Mediter-ranean area (Greece, Italy, Lebanon, Portugal, Spain,

Syria, Tunisia and Turkey), the olive-oil mill efflu-ent production is more than 30 million m3 per year(Beccari et al. 1996). It is known that olive-oil millwastes are a significant source of potential or existingenvironmental pollution in these countries (Bejarano& Madrid 1992; Borja et al. 1992; Angelidaki et al.1997). The treatment difficulties of olive-oil mill efflu-ents are mainly related with (a) high organic loading;(b) seasonal operation; (c) high territorial scattering;and (d) the presence of organic compounds which arehard to biodegrade such as long-chain fatty acids andphenolic compounds.

Agro-industrial wastes could be a serious envir-onmental concern if they are not properly handled.Therefore, the agro-industrial wastes should be treatedwith the most economical and efficient technologiesbefore their disposal into the surrounding environ-ments. Anaerobic systems offer such an option for thesafe treatment of agro-industrial wastewaters, mainlydue to their special advantages such as lower en-ergy requirement, less waste biomass generation, auseful and economically valuable end-product (meth-ane/biogas), suitability for seasonal operations andthe elevated organic loading rates achievable. Thus,anaerobic treatment is an attractive option for agro-industrial wastes that are seasonally produced, havea high organic content and the potential toxicity prob-lems.

In this study, the anaerobic treatability and meth-ane generation potential of the wastewater streams ofthe three important agro-industries in Turkey, namely,cheese-making, poultry breeding and the olive-oil mill

industries were studied. Biochemical methane poten-tial (BMP) experiments were conducted and the cor-responding methane gas productions were determined.This study constitutes only a part of a broader work onanaerobic industrial wastewater treatment conductedby our research team.

Materials and methods

The characterization of the cheese-making, poultrybreeding and olive-oil mill industry wastewaters usedin the experiments were carried out and are tabulatedin Table 1.

The COD values were measured using a Hachspectrophotometer (Model: P/N 45600-02) and vialsfor COD 01500 ppm. The pH measurements weretaken with a pH meter (Model 2906, Jenway Ltd.),and a pH probe (G-05992-55, Cole Parmer Instrument

Co.). The SS and VSS concentrations were measuredby following standard methods (2540 E) (StandardMethods 1995). The TP and TKN concentrations werealso determined by standard methods (4500-P-E and4500-NorgB, respectively) (Standard Methods 1995).

In order to determine the anaerobic biodegradab-ility and biogas production of the wastewaters stud-ied, the BMP experiments (Owen et al. 1979) wereperformed in 125-mL serum bottles capped with nat-ural rubber sleeve stoppers. The liquid volume of theserum bottles was 50 mL and they were maintainedat 35 2 C in a temperature-controlled room. The

serum bottles were seeded with mixed anaerobic cul-tures obtained from the anaerobic sludge digesters ofthe Ankara wastewater treatment plant with a solidsretention time (SRT) of 14 days. The culture was thor-oughly mixed and filtered through a screen with a poresize of 1 mm before use.

The composition of the basal medium (BM)used in the experiments was as follows (concen-


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Figure 1. The results of the BMP experiments for cheese whey.

trations of the constituents are given in paren-theses as mg/L): NH4Cl (1200), MgSO47H2O (400),KCl (400), Na2S9H2O (300), CaCl22H2O (50),(NH4)2HPO4 (80), FeCl24H2O (40), CoCl26H2O(10), KI (10), MnCl24H2O (0.5), CuCl22H2O (0.5),ZnCl2 (0.5), AlCl36H2O (0.5), NaMoO42H2O (0.5),H3BO3 (0.5), NiCl26H2O (0.5), NaWO42H2O (0.5),Na2SeO3 (0.5), cysteine (10), NaHCO3 (6000). Thisbasal medium contained all the necessary micro- andmacro-nutrients required for an optimum anaerobicmicrobial growth (Demirer and Speece 1998).

The cheese-making, poultry breeding and olive-oil mill wastewater samples were added to the serumbottles yielding initial COD concentrations of 5525,11050 and 22100 mg/L; 1262, 3785, 6708, 12617 and17633 mg/L; and 2765, 8295, 13825 and 27650 mg/L,respectively (Figures 13). Then the serum bottles

were purged with 25% CO2 and 75% N2 gas mix-ture for 34 minutes to maintain the proper pH andanaerobic conditions. The gas produced in each serumbottle was measured daily using a gas displacementdevice. The percentage of CH4 in biogas was deter-mined as follows. A known volume of the headspacegas (V1) produced in a serum bottle from Experiment1 was extracted by a syringe and injected into anotherserum bottle which contained only a 20-g/L KOHsolution. This serum bottle was then shaken manuallyfor 34 minutes so that all the CO2 and H2S was ab-sorbed in the concentrated KOH solution. The volume

of the remaining gas (V2) which was 99.9% CH4 in theserum bottle was determined by means of a syringe.The ratio of V2/V1 provided the percentage of CH4 inthe headspace gas.

The control serum bottles were also run in allexperiments to determine the background gas produc-tion. Before the experiments, the serum bottles wereoperated until the variation in daily gas production

Figure 2. The results of the BMP experiments for the poultrybreeding wastewater.

Figure 3. The results of the BMP experiments for the olive-oil millwastewater.

was less than 15% for at least 7 consecutive days. Theserum bottles for one out of four COD concentrationswere run as duplicates.

Results and discussion

Cheese whey wastewater

The gas production values of the serum bottles usedin the cheese whey wastewater BMP experiments for68 days are shown in Figure 1. For the influent CODconcentration of 5525 mg/L, the cultures exerted morethan 90% (157 mL) of the total gas production (176mL) in the first 16 days without any indication ofinhibition. Similarly, cultures for the influent CODconcentration of 11,050 mg/L exerted more than 90%

of (292 mL) total gas production (325 mL) in 24 days.For the highest influent COD concentration of 22,100mg/L, the cultures produced 598 mL of gas. The aver-age anaerobic methane generation for the cheese wheystudied was found to be 23.4 L CH4/L cheese whey.The result of a series of determinations indicated thatthe CH4 content of the biogas produced from cheesewhey was 77 5%.


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Table 2. The experimental results for all the wastewaters studied.

Wastewater COD concentration Methane content of the Methane generation

range studied (mg/L) biogas produced (%) (L methane/L wastewater)

Cheese whey 552522,100 77 5 23.4

Poultry breeding 126217,633 78 3 33.5

Olive-oil mill 276527,650 77 6 57.5

Poultry breeding wastewater

The gas production values of the serum bottles usedin the poultry breeding wastewater BMP experimentsfor 70 days are shown in Figure 2. The acclimationtime required for the anaerobic cultures to reach themaximum gas production rates were observed as 12,15, 16, 20 and 20 days for the COD concentrationsof 1262, 3785, 6708, 12,617 and 17,633 mg/L, re-spectively. The increase in acclimation times neededwith the increase in initial COD concentrations wasexpected since none of the cultures used in this studywere acclimated to the substrate. Poultry breedingwastewater samples produced 84.1, 266.7, 453.9, 914,and 1274 mL of total gas for the COD concentra-tions of 1262, 3785, 6708, 12617, and 17633 mg/L,respectively. These values indicated that the averageanaerobic methane generation for the poultry breedingwastewater studied is 33.5 L CH4 /L poultry breedingwastewater. The result of a series of determinationsindicated that the CH4 content of the biogas produced

from poultry breeding wastewater was 78 3%.

Olive-oil mill wastewater

Daily gas production in serum bottles was monitoredfor 44 days and the results are given in Figure 3. Thetotal gas production in serum bottles having COD con-centrations of 2765, 8295, 13,825 and 27,650 mg/Lwas observed as 94, 240, 408, and 758 mL, respect-ively. Before reaching maximum daily gas productionlevels, the cultures needed acclimation periods of 13,

16, 21 and 23 days for initial COD concentrations of2765, 8295, 13,825 and 27,650 mg/L, respectively.Depending on the methane gas produced in each re-actor, it was found that 1 l of olive-oil mill wastewaterproduced 57.5 1.5 l of methane gas. The result of aseries of determinations indicated that the CH4 contentof the biogas produced from olive-oil mill wastewaterwas 77 6%.

Conclusions

The following conclusions can be drawn based on theexperimental results (Table 2) presented in this paper: Anaerobic bioconversion of cheese whey, poultry

breeding and olive-oil mill wastewaters yieldedbiogas with a high methane content of 775,783and 77 6%, respectively.

The anaerobic methane generation from the

bioconversion of cheese whey, poultry breedingand olive-oil mill wastewaters studied was foundto be 23.4, 33.5, and 57.5 L CH4 /L wastewater.Therefore, it can be stated that anaerobic treatment

presents a viable alternative for the treatment of agro-industrial wastewaters in Turkey yielding significantenergy recovery in the form of methane gas.

Acknowledgment

This study was funded by the State Planning Organiz-ation of the Republic of Turkey.

References

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Beccari M, Bonemazzi F, Majone M & Riccardi C (1996) Interac-tions between acidogenesis and methanogenesis in the anaerobictreatment of olive mill effluents. Water Res. 30: 183189

Bejarano M & Madrid L (1992) Solubilization of heavy metalsfrom a river sediment by a residue from olive oil industry. Env.Technol. 13: 979985

Borja R, Martin A, Maestro R, Alba J & Fiestas JA (1992) Enhance-ment of the anaerobic digestion of olive mill wastewater by theremoval of phenolic inhibitors. Process Biochem. 27: 231237

Demirer GN & Speece RE (1998) Anaerobic biotransformation offour 3-carbon compounds (acrolein, acrylic acid, allyl alcoholand n-propanol) in UASB reactors. Water Res. 32: 747759

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Malaspina F, Cellamare CM, Stante L & Tilche A (1996) Anaer-obic treatment of cheese whey with a downflow-upflow hybridreactor. Biores. Technol. 55: 131139


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Mawson AJ (1994) Bioconversion for whey utilization and wasteabatement. Biores. Technol. 47: 195203

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Tsonis SP & Grigoropoulos SG (1993) Anaerobic treatability ofolive mill wastewater. Wat. Sci. Technol. 28: 3544

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