Mathematical optimisation for sustainable bio-methane (Bio-CH4) production from palm oil mill effluent (POME)

Palm oil mill effluent (POME) is recognised as one of the effluents which may cause environmental pollution when it is not properly treated. Conventional open pond systems are inefficient in treating POME as they generate and release biogas into the atmosphere, causing greenhouse effects. Number of anaerobic digestion systems were introduced in the market to recover the generated biogas for energy and electricity production. To synthesise an optimal integrated network for the conversion of POME into bio-methane, bio-CH4, a systematic screening approach is needed. This work aims to develop a systematic optimisation model for synthesis of a sustainable production system of bio-CH4 from POME based on economic and environmental performances. As the above-mentioned considerations are conflicting with each other, a multiple-objective optimisation approach (fuzzy optimisation approach) is adopted in the optimisation model to trade-off the objectives. Based on the optimised results for a typical 60 t/h of FFB palm oil mill in Malaysia, Integrated Anaerobic-Aerobic Bioreactor (IAAB) at 45 °C and cryogenic separator are selected to produce 90 wt% of bio-CH4 from POME. The total GHG emission from the synthesized integrated network is estimated as 2.31 million tons of CO2 per year with total economic performance of USD 7.24 million per year. •Systematic approach to select an optimal pathway for the conversion of POME into bio-CH4.•Multi-objective optimisation to trade-off economic and environmental performances.•A typical case study in Malaysia is solved to illustrate the proposed approach.•Scenario analysis is performed for different optimisation objectives.