Study of Bio-Waste Anaerobic Digestion and its Membrane Purification Technologies in Oversea: I. Malaysian Biogas Scale-up Case

Abstract

The palm oil mill industry in Malaysian generates 100 million ton of palm oil mill effluent (POME) and EFB (empty fruit bunch) as byproducts annually. This study identified the location, capacity and technology of biogas refinery plants for the production of biogas from the byproducts of the Malaysian palm oil mill plant. This study investigated the production of biogas via the anaerobic co-digestion of EFB under mesophilic anaerobic condition. The results revealed that subjecting EFB to an alkaline pretreatment method enabled a high-concentration methane yield. The raw biogas obtained from the anaerobic co-digestion of POME and EFB at 1.013 bar contained 61% CH₄, 33.5% CO₂ and 180 ppm H₂S and was produced at rate of 51 - 68㎥/h. The utilization of biomethane as a bio-CNG gas has been unexplored: hence, this study investigated the purification of POME biogas into bio-CNG gas. The pretreatment of raw biogas using chelate-iron (EDTA-iron solution) process, which is the most promising technique for the removal of 99% H₂S, was employed in this study. A pilot-scale separation plant with a capacity of 20㎥/hr that utilize cellulosic spiral wound membrane (MTR, USA) for upgrading biogas to CNG fuel quality was constructed and operated at the biogas plant. The result contained 99.1% CH₄, 1.8% CO₂, 0.004% H₂O and 0.9 ppm H₂S. These results indicate that the energy contents of biogas can be significantly enhanced by upgrading it to CNG fuel.