Optimization of enzymatic pretreatment and biogas production for palm oil mill effluent (POME)

Liew, Yuh Xiu (2019) Optimization of enzymatic pretreatment and biogas production for palm oil mill effluent (POME). PhD thesis, University of Nottingham.

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The rapid growth in oil palm industry has caused huge amount of waste biomass being produced. One of the highly polluting wastewater generated is known as Palm Oil Mill Effluent (POME). POME has strong wastewater characteristics due to the high content of biodegradable organic matter. Currently, the most widely adopted treatment method is anaerobic digestion. However, the current anaerobic method used requires longer retention times, low overall degradation efficiency and could hardly meet the progressively stringent Environmental Quality Act (EQA) 1974 requirements. Therefore, this research aims to improve the anaerobic digestion by implementing enzymatic pre-treatment prior to the anaerobic digestion. With a clear understanding of the effect of enzymes on hydrolysis, the enzymatic pre-treatment can be optimized and thereby improving the overall digestibility of POME. This will in turn enhance the anaerobic digestion and increase the yield of biogas.

From the wastewater characteristic study on POME conducted, it was observed that, POME has a higher concentration of COD (82100 mg/L), BOD (38670 mg/L) O&G (24720 mg/L), suspended solids (29050 mg/L) and lignin (1912 mg/L) that could cause operational problems to various high-rate anaerobic digesters. These constituents can be degraded by various microorganisms or enzymes during the hydrolysis stage. Through thorough literature review, lipase and ligninolytic enzymes (LMEs) which consist of laccase, manganese peroxide (MnP) and lignin peroxide (LiP) were identified to be used for the study of enzymatic pre-treatment of POME.

Optimization study was conducted on enzyme production to obtain maximum enzyme activity. For lipase production from Burkholderia cepacia (B. cepacia) through submerged fermentation (smF), the optimum operating conditions for the fermentation to obtain maximum production of lipase (11.18 U/mL) was at pH 9.0, 300 rpm and incubation time of 72 h with mixed fermentation medium before autoclave. While for the LMEs production using 5 different strains from Ganoderma boninense (G. boninense), the strain G21B was chosen to be used in this study as it produces highest amount of laccase and MnP at shorter incubation time (15 days). At optimum operating conditions of 220 rpm, pH 5.4, and 37 °C, 44.52±0.36 U/L of laccase, 0.046±0.01 U/L of MnP and 32.6±0.51 U/L of LiP were produced.

The optimum operating condition for the pre-treatment of POME using lipase was obtained to be an enzyme dosage of 1.3 %v/v, pre-treatment time of 12 h, agitation of 120 rpm, temperature of 37°C and pH of the medium of 4.5. At the optimum conditions, 29% COD reduction, 63% BOD reduction, 50% OG reduction, 87% FFA production, 52% VFA production, 26% lignin reduction, 2.5% cellulose production, 42% TRS production and 41% TSS reduction were obtained. While for the optimization of pre-treatment using LMEs resulted in 78% COD reduction, 43% BOD reduction, 22% OG reduction, 12% FFA production, 31% VFA production, 98.5% lignin reduction, 44% cellulose production, 57% TRS production and 72% TSS reduction at the optimum operating condition of enzyme dosage of 1.3 %v/v, pre-treatment time of 14 h, agitation of 200 rpm, temperature of 45°C and with a pH medium of 5.7.

The combination of both enzymes during the pre-treatment has shown synergistic effect. At the optimum operating condition of lipase to LMEs ratio of 0.5, agitation of 230 rpm, initial pH of 5.7, temperature of 45 °C and pre-treatment time of 13 h yielded 46% COD reduction, 46% BOD reduction, 81% OG reduction, 65% FFA production, 49% VFA production, 51% lignin reduction, 56% cellulose production, 62% TRS production and 73% TSS reduction. The pre-treated POME was then subjected to anaerobic digestion.

The anaerobic digestion using lipase, LMEs, enzyme cocktail pre-treated POME showed a positive improvement in COD (3.61%, 4.07%, and 6.47% respectively) and BOD reduction (5.06%, 7.27% and 7.50% respectively). Not only that, the biogas production (1.77%, 5.60%, and 17.11% respectively) and methane yield (11.54%, 19.23%, 30.77% respectively) have also shown a positive improvement. Hence, this ascertains the applicability of enzymatic pre-treatment in POME treatment or even in other high-strength wastewaters treatment.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Chan, Yi Jing
Manickam, Sivakumar
Chong, Mei Fong
Keywords: enzymatic pretreatment, palm oil, biomass energy, renewable energy source, anaerobic digestion, wastewate
Subjects: T Technology > TD Environmental technology. Sanitary engineering
Faculties/Schools: UNMC Malaysia Campus > Faculty of Engineering > Department of Chemical and Environmental Engineering
Item ID: 55881
Depositing User: LIEW, Yuh
Date Deposited: 03 Apr 2019 07:53
Last Modified: 07 May 2020 13:01
URI: http://eprints.nottingham.ac.uk/id/eprint/55881

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