A Technical and Economic Analysis of Heat and Power Generation from Biomethanation of Palm Oil Mill Effluent

Abstract

Palm oil mill effluent (POME) has been identified as one of the major sources of aquaticpollution in Malaysia. due to its high strength and economic importance. With more than 330 palmoil mills in operation, Malaysia produces some 10.6 million tonnes of crude palm oil annually,accounting for 52% of the total world production, and concomitantly generates some 27 x 106 m3POME. To meet with the regulatory requirement, more than 85% of the mills use solely lagoonsystems in wastewater treatment, typically anaerobic first stage followed by facultative treatment.Research data associated with this study revealed that methane yield ranging from 0.47 to 0.92m3kg-1-BODadded was attainable in the biomethanation of POME for reaction temperature of between35 to 55?C. Considering the associated socio-environmental impact, an analysis of the researchdata indicates that about 375 x 106 m3, or 225 Gg of CH4 is evolved from open ponding systems usedin POME treatment, accounting for 10% of the CH4 inventory in Malaysia. In terms of greenhousegas effect, this source amounts to 5,170 Gg in CO2 equivalent, or 3.6% of the estimated total emissionsin Malaysia. As methane can be harnessed for the generation of either thermal or electric energy, aneconomic assessment based on a life-cycle cost-benefit model as elucidated in this study shows thatan annual return on investment of 31 to 58%, or payback period of 2.5 to 1.5 years, is possible inresource recovery systems utilising methane for heat generation and land application of digestereffluent. The corresponding figures for electricity generation systems are 1.8 to 6.4% and 9.6 to 6.7years. In the latter case, the palm oil industry as a whole would be in a position to potentiallycontribute 2,250 x 106 kWh annually, equivalent to about 4% of the national electricity demand.This compares favourably with the Malaysian Government policy to achieve 5% of the total electricitygeneration by 2005 from renewable bioenergy sources. In terms of thermal energy generation, thepotential would be equivalent to 715 x 106 litres, worth some USD 120 million according to theprevailing price. Bioenergy recovery from the treatment of POME therefore not only contributestowards the sustainable growth of the palm oil industry, but also assists Malaysia in achieving itssustainable development objectives in connection with the United Nations Framework Conventionon Climate Change.