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Procedia Engineering 50 ( 2012 ) 904 – 912

1877-7058 © 2012 Elsevier B.V...Selection and peer-review under responsibility of Bin Nusantara Universitydoi: 10.1016/j.proeng.2012.10.098

International Conference on Advances Science and Contemporary Engineering 2012 (ICASCE 2012)

Palm Oil Mill Effluent as an Additive with Cattle Manure in Biogas Production

I.M.Nasir,T. I. Mohd Ghazi*, R. Omar, A.Idris

Department of chemical and Environmental Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Malaysia

Abstract

Biogas production from cattle manure (CM) is of growing importance as it offers considerable environmentalbenefits. The supplementation of palm oil mill effluent (POME) in anaerobic digestion of CM can be beneficial as itprovide a source of energy, while simultaneously resolving ecological and water pollution. Biogas production wasinvestigated in a 10 L bioreactor operated in batch and semi-continuous mode at 53oC. An enhanced biogas yield of0.346 m3 kg-1 VS added was observed from the CM with POME digestion, while the biogas production is not higherwhen CM was digested alone. Also, the VS and COD reduction for CM with POME digestion were 69 and 65%higher than raw CM digestion. The results showed that valid contribution has been done by the use of POME.

© 2012 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Bina Nusantara University

Keywords:Biogas; Cattle manure; Anaerobic digestion; Palm oil mill effluent

1. Introduction

With fossil fuel supplies depleting and oil prices rising, the search is on for a carbon-neutral fuel as analternative source that is sustainable and efficient. Biogas produced from agriculture, industrial andmunicipal waste waters, food industries and municipal garbage, not only fits this criteria, it is also readilyavailable and holds promise for the future. Therefore, biogas could be regarded as an alternative andaffordable green fuel that deserves study.

Biogas constitutes mainly methane and carbon dioxide and may contain traces of gases. Biogas powerhas a higher potential in the Asian countries due to the availability of palm oil residue,______

*T.I. Mohd Ghazi, Tel.: +603-89464427; Fax: +603-86567120

Available online at www.sciencedirect.com

© 2012 Elsevier B.V...Selection and peer-review under responsibility of Bin Nusantara University

905 I.M.Nasir et al. / Procedia Engineering 50 ( 2012 ) 904 – 912

E-mail address: [email protected]; [email protected]

industrial wastewater and livestock manure. The rise of intensive livestock production with focus moreon cattle farming is causing major environmental damage around the world. In Malaysia for example,the large amount of cattle manure and slurries produced today by the feedlot farming represent aconstant pollution risk with a potential negative impact on the environment, if not properly managed[1].The prospects of biogas power generation are possibly to be high in India, China, Malaysia, Thailand,Indonesia and the Philippines because of their favorable renewable energy policies and targets [2]. InSouth East Asia, particularly in Malaysia, Indonesia and Thailand, effluent from palm oil mills referredto as Palm oil mill effluent (POME) can be converted into biogas. This in addition can be used togenerate electric power through gas turbines or gas-fired engines. In Malaysia, there are around 410palm oil mills producing around 58 million tons of POME [3], and it is estimated that the existingpotential for electricity generation from POME is above 300 MW. Raw POME contains a considerableamount of oil and fatty acids which all contribute to its high oxygen demand. Hence, it has to be treatedin a series of open oxidation ponds, for the organic matter to be biodegraded to a much lower oxygendemand before being discharged [4]. POME has the ability to support bacterial growth with the wastebiodegradation because of its high nutrient content [5]. Anaerobic digestion for biogas production has become a worldwide focus of research, because it is anattractive waste treatment practice where both pollution control and energy recovery can be attained[6].Anaerobic digestion is a naturally occurring process, bywhich anaerobic micro-organisms convertbiodegradableorganic matter into biogas in the absence of oxygen [7].In addition, a nutrient-richdigestate is also produced which offer either fertilizer or soil conditioner properties [8]. Therefore, it isexpected that the nutrients within the POME to produce a viable additive for biogas production fromcattle manure. The purpose of this work is to demonstrate the feasibility of producing enhanced biogasusing POME as an additive for the treatment of cattle manure.

2. Materials and Methods

2.1Substrate

Fresh cattle manure (CM) was collected from the National Feedlot Corporation (NFC) Gemas, NegeriSembilan, Malaysia. The feedlot constantly confined approximately 5,000 head of beef cattle for about 3months to be fattened up before being slaughtered. The confined cattle produce wet manure and arenormally deposited on the ground. The CM used for the current study was scraped directly from thedeposit. Samples were packed in polythene bags and stored at 4oC until use. The palm oilmill effluent (POME) used as an additive was obtained from the POME open oxidation pond of the Seri-Ulu Langkat Palm Oil Mill, Dengkil, Selangor, Malaysia. The Mill produces about 200,000 tons ofPOME annually. POME in the oxidation pond is a potential source to harbour bacteria which coulddegrade the constituents of palm oil. The POME inoculum was kept in a tightly closed plastic containerand stored at 4oC until use.

2.2Experimental procedure

10 L capacity jacketed fermenter (Biostat B, Sartorius, Germany) made from a glass vessel with astainless steel cover was used as digester. The content of the digester were continuously mixedthroughout the period of digestion by means of an industrial motor (Fig.1). The reactor is equipped withpH, sampling port and a temperature controller.

In commencement of the experiment, fresh CM (500 g) with fresh POME (1.5 L) was initially digestedin batch and semi-continuous mode. In the next treatment, fresh CM (500g) was used and digestion wasallowed to progress with the native micro flora. The CM was made into slurry with distilled water to a


total solid content of 9%. Process temperature was maintained at thermophillic (53oC) by circulatingwater from a thermostatically controlled heater through a water jacket surrounding the bioreactor. The pH was controlled automatically by adding 1 N HCl and 1 N NaOH as appropriate and stirring wasmaintained at a speed of about 150 rpm. The reactor was sealed and Nitrogen gas was used to purge while filled with substrate and POME in order to ensure anaerobic environment in the headspace. In the batchtest, the substrate at each operation was loaded into the bioreactor and digestion was carried out for 10days. Whereas, in the semi-continuous operation, digested slurry (defined by the hydraulic retention timevalue) was withdrawn daily, and replaced with an equal volume of the fresh cattle waste.

Fig.1. Schematic diagram of the experimental set-up; 1. Control unit. 2. Acid pump. 3. Base pump. 4. Antifoam pump. 5. pH probe. 6. Temperature controller. 7. Electric motor. 8. Sampling port.9. Condenser. 10. Off to gas bag.

2.3 Analytical Method

Samples were withdrawn daily from the reactor and analysed for Total solids (TS), volatile solids (VS),biochemical oxygen demand (BOD) and chemical oxygen demand (COD) using the Standard Methods[9]. Ammonia nitrogen (NH3-N) content was determined using the spectrophotometer (HACH, DR/2500). The methane content of the biogas was analysed using a gas chromatograph (HP 6890N) equipped with athermal conductivity detector (TCD) and a HP Molesieve column (30m length x 0.5mm ID x 40µm filmthickness). The splitless inlet, oven and TCD detector temperatures were set at 60oC, 70oC and 200°C,respectively. Argon served as the carrier gas while nitrogen was used as the makeup gas. Additionally, the biogas produced from the reactor was monitored and measured daily by water displacement method.

3. 3.Results and Discussion

Table 1 shows the component characteristics of the substrates fed to the reactor. POME used in theexperiments contained higher amount of solids which comes possibly from the insoluble organic matterwashed out during the palm oil production process. Moreover, since the COD/BOD ratio of POME in thecurrent study was about 1.61, there is a good possibility that the organic matter is biodegradable whichwas almost similar to the value previously reported by Choorit and Wisarnwan [10]. The CM solidcontent relatively high therefore dilution is required as most existing anaerobic reactors operate at a TSranging of 8 and 12%. Meanwhile, initial concentration of COD and NH3-N of the cattle manure showeda higher value.


Table 1: Feed Component Characteristics

Substrate Type of Analysis InitialConcentration

CM TS (%wet) 18.5

TS(mg/L) 189.8±2.7

VS (%wet) 68

COD (mg/L) 126.7±10.5

NH3-N (mg/L) 24,858±664.4

Moisture (%) 76

pH 7.25±0.2

POME TSS (mg/L) 16,760

TVS (mg/L) 31,300

COD (mg/L) 51,560

BOD (mg/L) 32,200

NH3-N (mg/L) 51

pH 4.2

Fig. 2 shows the cumulative biogas production in CM with POME and CM during the digestion period.It was observed that biogas production from the CM with POME was continuous and declined after thesixth day in the batch operation, but biogas production was rapid during the semi-continuous operation;however biogas production was produced rapidly during the semi-continuous operation. It was observedto be higher during the first half than the second half of the semi-continuous digestion period maintainedat an OLR of 1.7 kg VS m-3 day-1 equivalent to 20 days HRT. The methane content of the biogas variedbetween 52 and 55%. In the CM batch digestion, biogas production started from day 2 and reached itspeak after four days. Whereas, during the semi-continuous operation, biogas production increasedgradually and seizes on day 20 with nearly 20% methane content. In general, biogas yield of 0.346 m3 kg-

1VS added was achieved in the CM with POME digestion; this is nearly 3 fold the yield observed for CMdigestion (0.1 m3 kg-1 VS added). Dubrovskis et al. [11] digested cattle manure with mink manureinoculum and obtained a yield of 0.303 m3 biogas kg-1 VS added. Whereas, Satyanarayan and Murkute[12] have obtained biogas from cattle manure with mustard oil cake in a yield between 0.239 to 0.329 m3

kg-1 VS added. These values is in good accordance with that obtained in the performed operation thatgave a biogas yield range of 0.346 m3 kg-1 VS added. Similar studies involving CM with POME inoculum at mixing ratio of 5:1 conducted by Omar et al. [13] and Muhammad [1] observed biogas yield of 0.159m3 kg-1 VS added and 0.226 m3 kg-1 VS added, respectively. Hence, this demonstrates that the observedincrease in biogas potential of the cattle manure is probably caused by the microbial degradation oforganic matter left in the POME and manure. As reported by Mohd [14], POME contains anaerobicbacteria that are able to improve the degradation of waste in an anaerobic environment.


Fig.2. Cumulative biogas production during anaerobic digestion

Fig.3 shows the NH3-N of the CM with POME and CM digestion during the period of anaerobicdigestion. During the batch process, NH3-N concentration of the CM with POME digestion increased to780 mg/L in the day 3 and decreased thereafter, whereas the NH3-N content of the CM digestiondecreased gradually up to the day 6, then increased thereafter. After daily loading, NH3-N concentrationwas observed to decrease in the CM digestion until day 15, and then shot up to about 800 mg/L towardsthe end of the experiment. However, the CM with POME digestion tended to stabilize all through theperiod of the experiment. Hansen et al. [15] noted an inhibition for the adapted anaerobic digestion ofmanures at the range between 700 mg/L to 1100 mg/L. Therefore, it is interesting to note that there wasno sign of inhibition due to NH3-N in the CM with POME digestion and a higher biogas and methane was achieved. Meanwhile, the CM digestion observed accumulation of NH3-N during the semi-continuousoperation which is near moderate inhibition on micro-organisms resulting to lower biogas yield.


Fig.3. Ammonia-nitrogen concentration during the anaerobic digestion

Fig.4 and Fig.5 shows the COD and VS profile during the CM with POME and CM digestionrespectively. As it can be seen, VS content was observed to decrease at higher rate after 3 days of thedigestion. This could probably due to the acclimatization of the microbial population and the favourablepH and temperature employed in this experiment [11], but increased slightly after day 7. This is possiblydue to sampling difficulties. More so, a higher VS removal was achieved during the semi-continuousoperation with a tendency for further VS removal. The COD concentration was observed to decreasecontinuously during the batch digestion (Fig.4). This is due to the result of substrate conversion fromparticulate matter to soluble compound which suggested that the hydrolysis of the cattle waste hasoccurred. It was reported by Gungor-Demirci and Demirer [16] that high biogas production rate duringthe anaerobic digestion of broiler and cattle manure observed at the beginning of the experiment was theresult of consumption of easily degradable COD. Relatively, COD concentration was observed tosomewhat fluctuate during the semi-continuous operation where the concentration ranged between 77.4 to 47.5 g/L. This is clear evidence that the bioreactor microbial population was continuously adapting to thechange in environmental condition due to daily organic loading [1]. On the other hand, the CM batchdigestion shows a similar trend with the CM with POME digestion. In the semi-continuous operation,decrease in COD concentration was quite low with little fluctuations from 59.4 to 45.1 g/L.


Fig.4. COD concentration during the anaerobic digestion

Fig.5. VS concentration during the anaerobic digestion


Data on the VS, TS, COD reductions and gas yield in the anaerobic digestion of CM with POME andCM are presented in Table 2. During the period of digestion, the reduction of TS, VS and COD in the CM digestion can be significantly improved by 1 to 2 times using CM with POME. The practical significanceof our observation is clear because they provide an explanation to why addition of POME should improve biogas production at thermophillic temperatures in bioreactor.

Table 2: Changes in the substrate contents during anaerobic digestion and biogas production

Digestion Composition NH3-N (mg/L) Initial Final

COD reduction (%)

TS reduction (%)

VS reduction (%)

Gas Yield(m3 kg-1 VS)

CM + POME 600 380 33 56 58.6 0.346

CM 580 780 20 36 34.7 0.1

4. Conclusion

The supplementation of POME in anaerobic digestion of cattle manure can be advantageously used forbiogas generation. Results shows that the making of these two materials in different proportions enhanced the biogas production, by using more of the complex substrates than when used alone. The anaerobicdigestion of CM with POME gave biogas production of 0.346 m3 kg-1 VS added with an average contentof 55% in methane. A clear effect of POME in the cattle manure treatment for biogas production wasobserved, as the biogas yield was improved by almost 66% in comparison to the digestion of only cattlemanure. More so, the digestion performance in terms of average removal of TS, VS, COD and NH3-N atCM digestion can be significantly improved by 1 to 2 times by CM with POME digestion. The outcomeof these results implied that POME should be seriously considered as an additive for the production ofbiogas via anaerobic digestion. This could pave a way for the efficient management of POME andindirect eradication of its environmental problems.

Acknowledgements

The authors would like to thank Universiti Putra Malaysia for the financial assistance and facilities, andNational Feedlot Corporation for the feedstock supply.

References

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[9] APHA. Standard Methods for the Examination of Water and Wastewater. American Public Health Association 1998;Washington, DC. [10] Choorit W, Wisarnwan P. Effect of temperature on the anaerobic digestion of palm oil mill effluent. Electronic J Biotechnol2007; 10:376-385.[11] Dubrovskis V, Plume I, Straume I. Investigation of biogas production from mink and cow manure. In Proceedings of the 8thInternational Scientific Conference, Engineering for rural development, Jelgava, Latvia, May 24-25, 2009.[12] Satyanarayan S, Murkute P. Biogas production enhancement by Brassica compestries amendment in cattle dung digesters.Biomass Bioener 2008; 32: 210-215.[13] Omar R, Harun RM, Mohd Ghazi TI, Wan Azlina WAKG, Idris A, Yunus R. Anaerobic treatment of cattle manure for biogasproduction. In Proceedings of the Annual meeting of American Institute of Chemical Engineers Philadelphia, USA, Nov. 16-21,2008.[14] Mohd RZ. Biogas production and determination of methanogens from digester-treated palm oil mill effluent. Master Thesis2007; Department of Biological Sciences, Universiti Putra Malaysia.[15] Hansen KH, Angelidaki I, Ahring BK. Anaerobic digestion of swine manure: inhibition by ammonia. Water Res 1998; 32:5-12.[16] Gungor-Demirci G, Demirer GN. Effect of initial COD concentration, nutrient addition, temperature and microbial acclimationon anaerobic treatability of broiler and cattle manure. Biores Technol 2004; 93: 109-117.

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