Evaluating the bio-methane potential by anaerobic tri-digestion of palm oil mill effluent, sewage sludge and food waste in Malaysia

The ever-increasing organic waste in Malaysia is one of the major factors of the increase in Green House Gases (GHGs) emissions. Some of the organic wastes, however, can be utilized to produce biogas by anaerobic digestion (AD), which is a promising option for both energy and material recovery from organic wastes with high moisture content. This study was formulated to investigate the feasibility of tri-digestion of three of the major organic wastes which are generated in huge quantities in Malaysia such as Sewage Sludge (SS), Palm Oil Mill Effluent (POME), and Food Waste (FW). Tri-digestion on mixture of these organic wastes was examined to establish a stable and balanced microbial community, which may be lacking in mono-digestion of a single organic waste, to improve biogas production. Batch anaerobic digestion experiment of selected samples was conducted for 33 days under mesophilic condition. The Anaerobic tri-digestion was evaluated and compared with anaerobic mono-digestion for the same samples at different mixing ratios. The experiments were designed in two groups A and B, at food to micro-organisms (F/M) ratios of 1 and 5, respectively. From the results obtained, tri-digestion of the wastes at 80:10:10 (FW:POME:SS) proportion yielded the highest biogas production of 245.04 mL CH4/g-COD at F/M ratio of 1, which was greater than the methane production in mono-digestion of food waste at the same F/M ratio. In addition, tri-digestion showed better methane yield for all the samples at F/M= 1 compared to mono-digestion for an individual substrate. The results were significantly different at F/M=5 for POME and FW as the production of methane during the first half of the test period was not stable, compared to SS which showed consistency and stability at both F/M ratios. From the results obtained, it is evident that tri-digestion of FW, POME and SS is an attractive option to be explored for improving biogas production by AD in Malaysia due to the abundance of these three organic wastes and the mesophilic conditions naturally available.