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Influence of palm oil mill effluent as inoculum on anaerobic digestion of cattle manure for biogas production
Bioresource Technology xxx (2013) xxx–xxx
Contents lists available at SciVerse ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Influence of palm oil mill effluent as inoculum on anaerobic digestion of cattle manure for biogas production Mohammed Saidu a,⇑, Ali Yuzir a,⇑, Mohd Razman Salim a, Salmiati a, Shamila Azman a, Norhayati Abdullah b a b
Department of Environmental Engineering, Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Malaysia Department of Biosciences and Health Science, Faculty of Biosciences and Biomedical Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Malaysia
h i g h l i g h t s This study demonstrates methane production from cattle manure and POME as inoculum. POME addition improved both the start-up time and rate of biogas production. Biogas production was achieved at ambient temperature.
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Biogas Anaerobic digestion Cattle manure POME Bioreactor
a b s t r a c t Anaerobic digestion for palm oil mill effluent (POME) is widely known for its potential in biogass production. In this study, the potential of using cattle manure for biogas production in complete mix anaerobic bioreactor was investigated using POME at unregulated pH and temperature. Two identical bioreactors were used in this study; namely R1 and R2 fed with cattle manure without and with POME as inoculum, respectively. Both bioreactors were allowed for five days to run in batch mode followed by semi continuous operations at HRT of 20 days. R2 produced 41% methane content compared to 18% produced in R1. A better COD percentage reduction of 45% was found in R2 which was operated with POME as inoculum compared to R1 with 35%. These results indicated that POME as inoculum has an influence on the start-up time and the rate of biogas produced.This findings will help in waste reduction. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction The world’s energy demand has increased over time and over dependence on fossil fuel brought forward the need for alternative energy sources. As previously reported by Tock et al. (2010), extensive agricultural activities generate large quantity of waste which increases the concentration of carbon dioxide in the atmosphere and contributes to the accumulation of greenhouse gases (GHG). Biogas produces from agricultural wastes are regarded as readily available and hold a promising potential for future sustainable carbon-neutral fuel alternative source. The present cattle farming industries in Malaysia represent a constant pollution risk due to the production of large amount of cattle manure and slurries produced by the feedlot farming, thus, resulting in a magnitude of possible negative impact on the environment. Therefore, the supplementation of palm oil mill effluent (POME) in anaerobic digestion of cattle manure can be beneficial as POME provides the source of energy while simultaneously resolving the environmental issues that are associated with cattle manure. ⇑ Corresponding authors. Tel.: +60 162518700. E-mail addresses: [email protected] (M. Saidu), [email protected] (A. Yuzir).
Anaerobic digestion is the most widely studied technology for organic treatments for its efficiency in the waste reduction while producing renewable energy, reducing pathogen and organic waste. The associated by-product from the treatment processes may be used as fertilizers (El-Mashad and Zhang, 2010). Anaerobic digestion may be defined as the decomposition of organic material in the absence of oxygen while simultaneously producing useful biogas (Bruni et al., 2010; Macias-Corral et al., 2008; Zhong et al., 2012) consisting of mainly 60% methane (CH4), 35% carbon dioxide (CO2), and 5% ammonia (NH3) and other gases (Khanal et al., 2008). During anaerobic digestion process, there are four different stages of reaction: namely hydrolysis, acidogenesis, acetogenesis, and methanogenesis (Yuzir et al., 2012). Thus, anaerobic digestion may be operated at various temperature including psychrophilic temperature of below 25 °C (Alvarez and Lidén, 2009), mesophilic temperature of between 25 °C and 35 °C, thermophilic temperature of between 55 °C and 60 °C, and extremophiles temperature at above 65 °C as previously explained by Sánchez et al. (2001). In this study, the anaerobic bioreactor was operated at ambient temperature which ranged between 26 °C and 29 °C. According to Zeeman et al. (1985), cattle manure has a complex structure hence longer retention time is required during treatment
0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2013.03.111
Please cite this article in press as: Saidu, M., et al. Influence of palm oil mill effluent as inoculum on anaerobic digestion of cattle manure for biogas production. Bioresour. Technol. (2013), http://dx.doi.org/10.1016/j.biortech.2013.03.111
2
M. Saidu et al. / Bioresource Technology xxx (2013) xxx–xxx
due to lignocellulose content and also high ammonia–nitrogen (NH3–H) concentration which could presumably affect the treatment process. The palm oil is the leading agro-based industry in Malaysia. However, the production of palm oil generates a large amount of wastes in the form of POME (Abdullah et al., 2011). POME in its untreated form is classified as a high strength agro-based wastewater with COD and BOD concentrations of 69,500 mg L 1 and 25,000 mg L 1, respectively (Abdullah et al., 2013). POME serves the benefit of being readily available sources of inoculum due to high biodegradable microorganisms’ content. Previous study by Yacob et al. (2006) has proven that by using POME as inoculums, the constraint in anaerobic digestion system such as longer start-up time has been successfully overcome with less than three months startup period showing better bioreactor performances and stability. The supplementation of POME in anaerobic digestion of cattle manure greatly helped in reducing the amount of waste produced by both agro-based industries. Therefore, the aim of this study is to assess the influence of POME on anaerobic digestion of cattle manure as one of the sources of biogas production at an ambient temperature. 2. Methods 2.1. Substrate preparations Fresh cattle manure was collected from Mujer Javanese Farm, Seri Bunian in Pontian, Malaysia with the following characteristics: chemical oxygen demand (COD) 35,200 mg L 1; total solid (TS) of 155 mg L 1; volatile solid (VS) of 34 mg L 1; NH3–N of 860 mg L 1 and pH 6.5. Prior to feeding, the cattle manure was mixed with distilled water at a ratio of 1:1 and filtered to remove unwanted particles and debris. Raw POME collected from Felda Besar Oil Mill; Kulai, Malaysia was used as inoculums having similar characteristics to that of Abdullah et al. (2013) as following: COD 69,500 mg L 1; TS 53,500 mg L 1; VS. 31 mg L 1; NH3–N 360 mg L 1 and pH 5.0. Samples were analyzed in triplicate. The collected POME and cattle manure were stored at temperature of 4 °C prior to feeding. 2.2. Experimental set-up Two identical complete mix anaerobic bioreactors made from stainless steel had a working volume of 10 L consisting of a top plate supporting a mixer, a mixer motor and equipped with several outlet sampling ports. Sludge was sampled from an outlet port located on the side of the bioreactor. Prior to daily feeds, an equivalent volume of 500 mL of digested sludge and fresh mixied sludge were sampled for analytical observations, respectively. Two completely mixed anaerobic bioreactors i.e. R1 and R2 were used throughout this study and were operated at uncontrolled pH and temperature with operating stirring speed of 300 rpm. Bioreactor R1 was fed with cattle manure as control reactor while bioreactor R2 was fed with cattle manure and seeded with 1L of POME. This was based on the biochemical methane potential (BMP) test that was carried out on different ratios of inoculum to feedstock (2:1; 1:2) to determine the conversion efficiency and ultimate methane yield of cattle manure feedstock. The quantity used was based on a similar study conducted by Kreuger et al. (2011). After seeding, both bioreactors were sealed and flushed with nitrogen gas to eliminate oxygen and protect the sensitive methanogenic bacteria. Both bioreactors were left to run in batch mode for five days and the HRT was maintained at 20 days. 2.3. Analytical methods Parameters such as biogas, total solid (TS), volatile solids (VS), chemical oxygen demand (COD) and ammonia–nitrogen (NH3–N)
were measured according to Standard Methods for the Examination of Water and Wastewater (APHA, 2005). The COD and NH3– N were analyzed by using HACH DR5000 spectrophotometer manual (HACH 2005). The biogas volume was determined by water displacement method and analyzed by using BW Gas Alert Micro Percentage analyzer to determine the methane content in percentage from the biogas produced. Both the temperature and pH were monitored by using HI 8424 Hanna instruments electrode/probe.
3. Results and discussion 3.1. Biogas production and methane content Fig. 1 shows the daily biogas production in both R1 and R2 during the study period. It was observed that biogas production in R1 had a lag period of 6 days which may be due to low hydrolytic activity as cattle manure contains high lignocellulosic material when compared to biogas production in R2 which started at day 1. This indicates that cattle manure does not have enough essential microbes for early biodegradation and enriched inoculum which contributes to its early biogas production. As previously reported by (Sunarso et al., 2010), the rate of cattle manure biodegradation becomes lower at high lignin content. The biogas produced in R1 continued to increase up to day-23 at 0.41 Ld 1 and significantly declined to 0.3 L 1 over a 3-days period. Bioreactor R1 demonstrated significant decrease in biogas production rate as it was operated without inoculums due to depletion of bacterial growth activity. In contrast, when POME was added as inoculum in R2, a steady increase in daily biogas production was observed after day-2 of experiments. The methanogens were shown to have taken less time to produce biogas in bioreactor operated with POME as inoculums as compared to R1, which was operated without inoculums. The higher biogas produced and less lag period observed in R2 could also presumably be attributed to the inoculum used which served as buffer during bioreactor start-up which also subsequently affect the rate of biogas produced. This is in agreement with the previously reported literature by Budiyana et al. (2010) which stated that bioreactor operated with inoculum produced more biogas compared to bioreactor operated without inoculums. Fig. 1 also depicts the trend in methane production for both R1 and R2. Without inoculum (i.e. POME in R1), the methane production was observed after day-6 of experiments. The percentage of methane produced was found to be lower than 40% and continuously fluctuated throughout the experimental period until day-23
Fig. 1. Daily biogas production and methane percentage content of the complete mix anaerobic digester (s) R1daily biogas of cattle manure; (h) R1 CH4 percentage content of cattle manure; (d) R2 daily biogas of cattle manure with POME; (j) R2 CH4 percentage content of cattle manure with POME.
Please cite this article in press as: Saidu, M., et al. Influence of palm oil mill effluent as inoculum on anaerobic digestion of cattle manure for biogas production. Bioresour. Technol. (2013), http://dx.doi.org/10.1016/j.biortech.2013.03.111
M. Saidu et al. / Bioresource Technology xxx (2013) xxx–xxx
3
of 41% and less lag time were achieved which reflects the efficiency in bioreactor operation. Better COD removal reduction was observed in bioreactor operated with POME as inoculums. These results demonstrated that POME as inoculum has an influence on bioreactor start-up time and biogas production. Therefore, POME may be considered as an inoculum in anaerobic digestion, which will contribute to the proper management of cattle manure and POME and simultaneously reduce the effect it has on the environment. Acknowledgements
Fig. 2. COD concentration and COD percentage reduction of the complete mix anaerobic bioreactor (s) R1 with cattle manure; (h) R1 COD percentage reduction; (d) R2 with cattle manure + POME; (j) R2 COD percentage reduction.
when methane content stabilized at 30%. In addition, without inoculum, the percentage of methane gradually decreased to 18% at the end of the experiments. However, relatively higher methane content was observed in R2 which was operated with POME as inoculum. It was observed that 46% of methane was peak on day-15 upon experimental start-up. Since there was only a small decline in methane content, approximately 41% of methane was observed when the experimental period ended on day-30. Higher methane content in R2 indicated a substantial rate of biogas produced which reflects the efficiency in bioreactor operation, particularly R2. This is in agreement with previous research demonstrating rate of biodegradation and methane yield with addition of inoculum (ForsterCarneiro et al., 2008). The percentage of methane production in R2 also indicated significant improvement in the fermentation rate as compared to R1. 3.2. Chemical oxygen demand (COD) concentrations The bioreactor COD and COD percentage reductions for both R1 and R2 are given in Fig. 2. Due to depletion in substrate availability, the director COD in R1 was gradually declined from 31,000 mg L 1 to 20,000 mg L 1 over a period of 23 days upon start-up before stabilizing at a constant COD concentration of 20,000 mg L 1 until the end of the experimental period. Despite constant COD concentrations in R1, the COD percentage reduction was 35%. Bioreactor R1 demonstrates lower COD concentrations as expected as it was operated without POME supplementation as inoculum. In contrast, due to higher COD concentrations in POME, R2 demonstrated higher bioreactor COD of above 60,000 mg L 1. Moreover, the COD percentage reduction peaks at 45% before declined to 38% at the end of the experimental period. The fluctuation in bioreactor R2 indicates the unstable nature of the microorganism due to ambient temperature adopted, but it still have high COD removal efficiencies at the low temperature and may be associated to an increase in VFA during the reaction (McHugh et al., 2006). The COD average percentage reduction efficiency in R2 was more than 40% but less than the one achieved by Castrillón et al. (2002) in a similar study of cattle manure. 4. Conclusion The viability of using POME as inoculum in an anaerobic digestion of cattle manure was observed when higher methane content
The authors wish to thank Universiti Teknologi Malaysia and Ministry of Higher Education Malaysia (Grant No Q.J130000. 02H66) for financial support of this project. References Abdullah, N., Ujang, Z., Yahya, A., 2011. Aerobic granular sludge formation for high strength agro-based wastewater treatment. Bioresour. Technol. 102, 6778– 6781. Abdullah, N., Yuzir, A., Curtis, T.P., Yahya, A., Ujang, Z., 2013. Characterization of aerobic granular sludge treating high strength agro-based wastewater at different volumetric loadings. Bioresour. Technol. 127, 181–187. Alvarez, R., Lidén, G., 2009. Low temperature anaerobic digestion of mixtures of llama, cow and sheep manure for improved methane production. Biomass Bioenergy 33, 527–533. APHA, 2005. Standard Method for the Examination of Water and Waste Wastewater. American Public Health Association, Washington D.C. Bruni, E., Jensen, A.P., Angelidaki, I., 2010. Comparative study of mechanical, hydrothermal, chemical and enzymatic treatments of digested biofibers to improve biogas production. Bioresour. Technol. 101, 8713–8717. Budiyana, W., Johari, I.N., Sunarso, S., 2010. Increasing biogas production rate from cattle manure using rumen fluid as inoculums. Int. J. Basic Appl. Sci. 10, 68–75. Castrillón, L., Vázquez, I., Marañón, E., Sastre, H., 2002. Anaerobic thermophilic treatment of cattle manure in UASB reactors. Waste Manage. Res. 20, 350–356. El-Mashad, H.M., Zhang, R., 2010. Biogas production from co-digestion of dairy manure and food waste. Bioresour. Technol. 101, 4021–4028. Forster-Carneiro, T., Pérez, M., Romero, L.I., 2008. Influence of total solid and inoculum contents on performance of anaerobic reactors treating food waste. Bioresour. Technol. 99, 6994–7002. Khanal, S.K., 2008. Overview of anaerobic biotechnology. In: Khanal, S.K. (Ed.), Anaerobic biotectnology for bioenergy production: principle and application. John Wiley & Sons, New york, USA. Kreuger, E., Nges, I.A., Björnsson, L., 2011. Ensiling of crops for biogas production: effects on methane yield and total solids determination. Biotechnol. Biofuels 4, 1–8. Macias-Corral, M., Samani, Z., Hanson, A., Smith, G., Funk, P., Yu, H., Longworth, J., 2008. Anaerobic digestion of municipal solid waste and agricultural waste and the effect of co-digestion with dairy cow manure. Bioresour. Technol. 99, 8288– 8293. McHugh, S., Collins, G., O’Flaherty, V., 2006. Long-term, high-rate anaerobic biological treatment of whey wastewaters at psychrophilic temperatures. Bioresour. Technol. 97, 1669–1678. Sánchez, E., Borja, R., Weiland, P., Travieso, L., Martı´n, A., 2001. Effect of substrate concentration and temperature on the anaerobic digestion of piggery waste in a tropical climate. Process Biochem. 37 (5), 483–489. Sunarso, J., Widiasa, S., Budiyono, I.N., 2010. The Effect of feed to inoculums ratio on biogas production rate from cattle manure using rumen fluid as inoculums. Int. J. Sci. Eng. 1, 41–45. Tock, J.Y., Lai, C.L., Lee, K.T., Tan, K.T., Bhatia, S., 2010. Banana biomass as potential renewable energy resource. A Malaysian case study. Renew. Sust. Energy Rev. 14, 798–805. Yacob, S., Shirai, Y., Hassan, M.A., Wakisaka, M., Subash, S., 2006. Start-up operation of semi-commercial closed anaerobic digester for palm oil mill effluent treatment. Process Biochem. 41, 962–964. Yuzir, A., Chelliapan, S., Sallis, P.J., 2012. Impact of the herbicide (RS)-MCPP on an anaerobic membrane bioreactor performance under different COD/nitrate ratios. Bioresour. Technol. 109, 31–37. Zeeman, G., Wiegant, W.M., Koster-Treffers, M.E., Lettinga, G., 1985. The influence of the total-ammonia concentration on the thermophilic digestion of cow manure. Agr. Wastes 14, 19–35. Zhong, W., Zhang, Z., Luo, Y., Qiao, W., Xiao, M., Zhang, M., 2012. Biogas productivity by co-digesting taihu blue algae with corn straw as an external carbon source. Bioresour. Technol. 114, 281–286.
Please cite this article in press as: Saidu, M., et al. Influence of palm oil mill effluent as inoculum on anaerobic digestion of cattle manure for biogas production. Bioresour. Technol. (2013), http://dx.doi.org/10.1016/j.biortech.2013.03.111
Contents lists available at SciVerse ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Influence of palm oil mill effluent as inoculum on anaerobic digestion of cattle manure for biogas production Mohammed Saidu a,⇑, Ali Yuzir a,⇑, Mohd Razman Salim a, Salmiati a, Shamila Azman a, Norhayati Abdullah b a b
Department of Environmental Engineering, Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Malaysia Department of Biosciences and Health Science, Faculty of Biosciences and Biomedical Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Malaysia
h i g h l i g h t s This study demonstrates methane production from cattle manure and POME as inoculum. POME addition improved both the start-up time and rate of biogas production. Biogas production was achieved at ambient temperature.
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Biogas Anaerobic digestion Cattle manure POME Bioreactor
a b s t r a c t Anaerobic digestion for palm oil mill effluent (POME) is widely known for its potential in biogass production. In this study, the potential of using cattle manure for biogas production in complete mix anaerobic bioreactor was investigated using POME at unregulated pH and temperature. Two identical bioreactors were used in this study; namely R1 and R2 fed with cattle manure without and with POME as inoculum, respectively. Both bioreactors were allowed for five days to run in batch mode followed by semi continuous operations at HRT of 20 days. R2 produced 41% methane content compared to 18% produced in R1. A better COD percentage reduction of 45% was found in R2 which was operated with POME as inoculum compared to R1 with 35%. These results indicated that POME as inoculum has an influence on the start-up time and the rate of biogas produced.This findings will help in waste reduction. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction The world’s energy demand has increased over time and over dependence on fossil fuel brought forward the need for alternative energy sources. As previously reported by Tock et al. (2010), extensive agricultural activities generate large quantity of waste which increases the concentration of carbon dioxide in the atmosphere and contributes to the accumulation of greenhouse gases (GHG). Biogas produces from agricultural wastes are regarded as readily available and hold a promising potential for future sustainable carbon-neutral fuel alternative source. The present cattle farming industries in Malaysia represent a constant pollution risk due to the production of large amount of cattle manure and slurries produced by the feedlot farming, thus, resulting in a magnitude of possible negative impact on the environment. Therefore, the supplementation of palm oil mill effluent (POME) in anaerobic digestion of cattle manure can be beneficial as POME provides the source of energy while simultaneously resolving the environmental issues that are associated with cattle manure. ⇑ Corresponding authors. Tel.: +60 162518700. E-mail addresses: [email protected] (M. Saidu), [email protected] (A. Yuzir).
Anaerobic digestion is the most widely studied technology for organic treatments for its efficiency in the waste reduction while producing renewable energy, reducing pathogen and organic waste. The associated by-product from the treatment processes may be used as fertilizers (El-Mashad and Zhang, 2010). Anaerobic digestion may be defined as the decomposition of organic material in the absence of oxygen while simultaneously producing useful biogas (Bruni et al., 2010; Macias-Corral et al., 2008; Zhong et al., 2012) consisting of mainly 60% methane (CH4), 35% carbon dioxide (CO2), and 5% ammonia (NH3) and other gases (Khanal et al., 2008). During anaerobic digestion process, there are four different stages of reaction: namely hydrolysis, acidogenesis, acetogenesis, and methanogenesis (Yuzir et al., 2012). Thus, anaerobic digestion may be operated at various temperature including psychrophilic temperature of below 25 °C (Alvarez and Lidén, 2009), mesophilic temperature of between 25 °C and 35 °C, thermophilic temperature of between 55 °C and 60 °C, and extremophiles temperature at above 65 °C as previously explained by Sánchez et al. (2001). In this study, the anaerobic bioreactor was operated at ambient temperature which ranged between 26 °C and 29 °C. According to Zeeman et al. (1985), cattle manure has a complex structure hence longer retention time is required during treatment
0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2013.03.111
Please cite this article in press as: Saidu, M., et al. Influence of palm oil mill effluent as inoculum on anaerobic digestion of cattle manure for biogas production. Bioresour. Technol. (2013), http://dx.doi.org/10.1016/j.biortech.2013.03.111
2
M. Saidu et al. / Bioresource Technology xxx (2013) xxx–xxx
due to lignocellulose content and also high ammonia–nitrogen (NH3–H) concentration which could presumably affect the treatment process. The palm oil is the leading agro-based industry in Malaysia. However, the production of palm oil generates a large amount of wastes in the form of POME (Abdullah et al., 2011). POME in its untreated form is classified as a high strength agro-based wastewater with COD and BOD concentrations of 69,500 mg L 1 and 25,000 mg L 1, respectively (Abdullah et al., 2013). POME serves the benefit of being readily available sources of inoculum due to high biodegradable microorganisms’ content. Previous study by Yacob et al. (2006) has proven that by using POME as inoculums, the constraint in anaerobic digestion system such as longer start-up time has been successfully overcome with less than three months startup period showing better bioreactor performances and stability. The supplementation of POME in anaerobic digestion of cattle manure greatly helped in reducing the amount of waste produced by both agro-based industries. Therefore, the aim of this study is to assess the influence of POME on anaerobic digestion of cattle manure as one of the sources of biogas production at an ambient temperature. 2. Methods 2.1. Substrate preparations Fresh cattle manure was collected from Mujer Javanese Farm, Seri Bunian in Pontian, Malaysia with the following characteristics: chemical oxygen demand (COD) 35,200 mg L 1; total solid (TS) of 155 mg L 1; volatile solid (VS) of 34 mg L 1; NH3–N of 860 mg L 1 and pH 6.5. Prior to feeding, the cattle manure was mixed with distilled water at a ratio of 1:1 and filtered to remove unwanted particles and debris. Raw POME collected from Felda Besar Oil Mill; Kulai, Malaysia was used as inoculums having similar characteristics to that of Abdullah et al. (2013) as following: COD 69,500 mg L 1; TS 53,500 mg L 1; VS. 31 mg L 1; NH3–N 360 mg L 1 and pH 5.0. Samples were analyzed in triplicate. The collected POME and cattle manure were stored at temperature of 4 °C prior to feeding. 2.2. Experimental set-up Two identical complete mix anaerobic bioreactors made from stainless steel had a working volume of 10 L consisting of a top plate supporting a mixer, a mixer motor and equipped with several outlet sampling ports. Sludge was sampled from an outlet port located on the side of the bioreactor. Prior to daily feeds, an equivalent volume of 500 mL of digested sludge and fresh mixied sludge were sampled for analytical observations, respectively. Two completely mixed anaerobic bioreactors i.e. R1 and R2 were used throughout this study and were operated at uncontrolled pH and temperature with operating stirring speed of 300 rpm. Bioreactor R1 was fed with cattle manure as control reactor while bioreactor R2 was fed with cattle manure and seeded with 1L of POME. This was based on the biochemical methane potential (BMP) test that was carried out on different ratios of inoculum to feedstock (2:1; 1:2) to determine the conversion efficiency and ultimate methane yield of cattle manure feedstock. The quantity used was based on a similar study conducted by Kreuger et al. (2011). After seeding, both bioreactors were sealed and flushed with nitrogen gas to eliminate oxygen and protect the sensitive methanogenic bacteria. Both bioreactors were left to run in batch mode for five days and the HRT was maintained at 20 days. 2.3. Analytical methods Parameters such as biogas, total solid (TS), volatile solids (VS), chemical oxygen demand (COD) and ammonia–nitrogen (NH3–N)
were measured according to Standard Methods for the Examination of Water and Wastewater (APHA, 2005). The COD and NH3– N were analyzed by using HACH DR5000 spectrophotometer manual (HACH 2005). The biogas volume was determined by water displacement method and analyzed by using BW Gas Alert Micro Percentage analyzer to determine the methane content in percentage from the biogas produced. Both the temperature and pH were monitored by using HI 8424 Hanna instruments electrode/probe.
3. Results and discussion 3.1. Biogas production and methane content Fig. 1 shows the daily biogas production in both R1 and R2 during the study period. It was observed that biogas production in R1 had a lag period of 6 days which may be due to low hydrolytic activity as cattle manure contains high lignocellulosic material when compared to biogas production in R2 which started at day 1. This indicates that cattle manure does not have enough essential microbes for early biodegradation and enriched inoculum which contributes to its early biogas production. As previously reported by (Sunarso et al., 2010), the rate of cattle manure biodegradation becomes lower at high lignin content. The biogas produced in R1 continued to increase up to day-23 at 0.41 Ld 1 and significantly declined to 0.3 L 1 over a 3-days period. Bioreactor R1 demonstrated significant decrease in biogas production rate as it was operated without inoculums due to depletion of bacterial growth activity. In contrast, when POME was added as inoculum in R2, a steady increase in daily biogas production was observed after day-2 of experiments. The methanogens were shown to have taken less time to produce biogas in bioreactor operated with POME as inoculums as compared to R1, which was operated without inoculums. The higher biogas produced and less lag period observed in R2 could also presumably be attributed to the inoculum used which served as buffer during bioreactor start-up which also subsequently affect the rate of biogas produced. This is in agreement with the previously reported literature by Budiyana et al. (2010) which stated that bioreactor operated with inoculum produced more biogas compared to bioreactor operated without inoculums. Fig. 1 also depicts the trend in methane production for both R1 and R2. Without inoculum (i.e. POME in R1), the methane production was observed after day-6 of experiments. The percentage of methane produced was found to be lower than 40% and continuously fluctuated throughout the experimental period until day-23
Fig. 1. Daily biogas production and methane percentage content of the complete mix anaerobic digester (s) R1daily biogas of cattle manure; (h) R1 CH4 percentage content of cattle manure; (d) R2 daily biogas of cattle manure with POME; (j) R2 CH4 percentage content of cattle manure with POME.
Please cite this article in press as: Saidu, M., et al. Influence of palm oil mill effluent as inoculum on anaerobic digestion of cattle manure for biogas production. Bioresour. Technol. (2013), http://dx.doi.org/10.1016/j.biortech.2013.03.111
M. Saidu et al. / Bioresource Technology xxx (2013) xxx–xxx
3
of 41% and less lag time were achieved which reflects the efficiency in bioreactor operation. Better COD removal reduction was observed in bioreactor operated with POME as inoculums. These results demonstrated that POME as inoculum has an influence on bioreactor start-up time and biogas production. Therefore, POME may be considered as an inoculum in anaerobic digestion, which will contribute to the proper management of cattle manure and POME and simultaneously reduce the effect it has on the environment. Acknowledgements
Fig. 2. COD concentration and COD percentage reduction of the complete mix anaerobic bioreactor (s) R1 with cattle manure; (h) R1 COD percentage reduction; (d) R2 with cattle manure + POME; (j) R2 COD percentage reduction.
when methane content stabilized at 30%. In addition, without inoculum, the percentage of methane gradually decreased to 18% at the end of the experiments. However, relatively higher methane content was observed in R2 which was operated with POME as inoculum. It was observed that 46% of methane was peak on day-15 upon experimental start-up. Since there was only a small decline in methane content, approximately 41% of methane was observed when the experimental period ended on day-30. Higher methane content in R2 indicated a substantial rate of biogas produced which reflects the efficiency in bioreactor operation, particularly R2. This is in agreement with previous research demonstrating rate of biodegradation and methane yield with addition of inoculum (ForsterCarneiro et al., 2008). The percentage of methane production in R2 also indicated significant improvement in the fermentation rate as compared to R1. 3.2. Chemical oxygen demand (COD) concentrations The bioreactor COD and COD percentage reductions for both R1 and R2 are given in Fig. 2. Due to depletion in substrate availability, the director COD in R1 was gradually declined from 31,000 mg L 1 to 20,000 mg L 1 over a period of 23 days upon start-up before stabilizing at a constant COD concentration of 20,000 mg L 1 until the end of the experimental period. Despite constant COD concentrations in R1, the COD percentage reduction was 35%. Bioreactor R1 demonstrates lower COD concentrations as expected as it was operated without POME supplementation as inoculum. In contrast, due to higher COD concentrations in POME, R2 demonstrated higher bioreactor COD of above 60,000 mg L 1. Moreover, the COD percentage reduction peaks at 45% before declined to 38% at the end of the experimental period. The fluctuation in bioreactor R2 indicates the unstable nature of the microorganism due to ambient temperature adopted, but it still have high COD removal efficiencies at the low temperature and may be associated to an increase in VFA during the reaction (McHugh et al., 2006). The COD average percentage reduction efficiency in R2 was more than 40% but less than the one achieved by Castrillón et al. (2002) in a similar study of cattle manure. 4. Conclusion The viability of using POME as inoculum in an anaerobic digestion of cattle manure was observed when higher methane content
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Please cite this article in press as: Saidu, M., et al. Influence of palm oil mill effluent as inoculum on anaerobic digestion of cattle manure for biogas production. Bioresour. Technol. (2013), http://dx.doi.org/10.1016/j.biortech.2013.03.111