Mohd Yusof, Mohd Amran
(2025)
Performance optimization of industrial scale in-ground lagoon anaerobic digester for palm oil mill effluent (POME) treatment.
PhD thesis, University of Nottingham.
Abstract
Despite advancements in treating Palm Oil Mill Effluent (POME) using anaerobic methods, challenges persist in optimising biogas production and effluent treatment due to unpredictable characteristics influenced by palm oil extraction efficiency and mill processes. Recent changes in Malaysia's Feed-In Tariff (FiT) program, particularly the introduction of an e-bidding system have led to reduced average FiT rates, impacting biogas plant developers with high capital expenditure. Additionally, long-term operational challenges in biogas plants require an understanding of POME characteristics and factors influencing anaerobic digestion performance throughout the Renewable Power Purchase Agreement (REPPA) period of 21 years. Therefore, the main objective of this study is to maximise methane yield of the biogas plant through optimisation analysis and assess its feasibility via techno-economic analysis.
Initially, this study evaluates different operating systems based on two years of experimental data in four Palm Oil Mills (POMs) and in-ground lagoon anaerobic digesters (AD) to identify the most critical operating parameters. This step is crucial as it contributes valuable insights to optimize biogas plant operations and enhance their overall efficiency. As most biogas plants in Malaysia are built for power generation, the focus of this study is on evaluating four industrial-size biogas plants (BGPs) participating in Malaysia's FiT Program. The analysis shows that POM A was the only mill equipped with a three-phase decanter, which reduced the total solid (TS) concentration in POME and recorded the lowest TS content (25,580 mg/L) compared to POM B, C, and D. However, the chemical oxygen demand (COD) of POM A was still high due to the continuous addition of effluent from the empty fruit bunch (EFB) press station. POM B and D had the highest COD (more than 80,000 mg/L) due to low water consumption, absence of decanter, and direct discharge of sterilizer condensate to the sludge pit. ANOVA analysis concluded that different equipment and processes in POM produced different qualities of POME characteristics.
Two years of biogas plants (BGPs) operation and process data show that all BGPs are still functioning well with satisfactory methane yield (0.135 - 0.364 Nm3 CH4/kgCODremoved) and COD removal efficiencies (67% - 85%). Sensitivity analysis concluded that moderate OLR (<1.6), moderate T (<44°C), and moderate RR (<2.3) are required to achieve optimum COD removal and biogas production for each biogas plant.
While temperature is identified as a crucial parameter through the performance evaluation analysis, the existing pretreatment facilities were not able to control, stabilize, and provide a consistent temperature of POME entering the AD. To address this, a twin packed crossflow induced draft cooling tower (CT) was installed at BGP A to control the inlet POME temperature below 40°C. This strategy was coupled with anaerobic co-digestion (ACoD) of POME with decanter cake (DC), which is a waste product in the palm oil mill, to enhance methane yield. The integration of both the cooling tower and ACoD technology successfully improved the methane yield by more than 40%.
Performance evaluation, prediction and optimisation of the cooling tower and ACoD system was conducted using Artificial Neural Network (ANN) and response surface methodology (RSM) based on six months of operation data. After the implementation of the cooling tower, the average outlet temperature of POME in 2022 was 39.29°C±0.91, within the target range for the operating temperature of mesophilic bacteria. The methane (CH4) content averaged 65.71%±0.97, with an average biogas production rate of 12,683 m3/day and a methane yield of 0.3135 Nm3/kgCODremoved. In the ACoD process, the highest methane yield (0.379 Nm3 CH4/ kgCODremoved) was found to be at an OLR of 2.5 kg COD/m3.day and a Treated Effluent/DC ratio of 10. Economic analysis shows that both cooling tower and ACoD technologies has the potential to generate revenue of RM879,000/year with a payback period of less than one year, indicating its effectiveness in improving the economics aspect of the biogas plants, which can be replicated in existing and new biogas plants in the near future.
The findings from this research benefit all FiT Biogas Plant Developers in Malaysia. Future works could focus on evaluating different pretreatment methods for the DC in the ACoD system to further improve methane yield and stable biogas production throughout the 21-year REPPA period. Furthermore, investigating the potential utilization of byproducts from ACoD, such as the residual sludge, for value-added applications would be beneficial. This comprehensive approach could continuously improve the sustainability and profitability of anaerobic digestion processes in the palm oil industry.
| Item Type: |
Thesis (University of Nottingham only)
(PhD)
|
| Supervisors: |
Chan, Yi Jing |
| Keywords: |
palm oil mill effluent (POME); biogas production; anaerobic digestion (AD); Malaysia feed-in tariff (FiT) program; e-bidding system |
| Subjects: |
T Technology > TD Environmental technology. Sanitary engineering |
| Faculties/Schools: |
University of Nottingham, Malaysia > Faculty of Science and Engineering — Engineering > Department of Chemical and Environmental Engineering |
| Item ID: |
80045 |
| Depositing User: |
Mohd Yusof, Mohd
|
| Date Deposited: |
08 Feb 2025 04:40 |
| Last Modified: |
08 Feb 2025 04:40 |
| URI: |
https://eprints.nottingham.ac.uk/id/eprint/80045 |
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