Comparative study of the synergistic effect of decanter cake (DC) and empty fruit bunch (EFB) as the co-substrates in the anaerobic co-digestion (ACD) of palm oil mill effluent (POME)

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Due to rapid depletion of non-renewable energy such as fossil fuel and increasing concerns for green environment, collection of biogas generated from palm oil mill effluent (POME) would be advantageous as source of energy. In this study, empty fruit bunch (EFB) and decanter cake (DC) were used as co-substrates separately with POME to enhance biogas production. Three parameters were evaluated for this experiment, including DC:POME ratio/EFB:POME ratio (in term of volatile solids (VS)), DC/EFB pre-treatment and mixing speed. It was observed that the anaerobic co-digestion (ACD) of DC and POME showed promising reduction in Chemical Oxygen Demand (COD) (>95%), total solids (>74%), VS (>90%), total suspended solids (>90%), volatile suspended solids (>92%) and volatile acid (>83%). The overall improved methane production results show that synergistic effects are observed for both co-substrates, i.e. DC and EFB. EFB was a better co-substrate than DC due to its higher methane yield improvement percentage as compared to mono-digestion of POME. The best ratio obtained for EFB:POME was 0.6:1 with improvement of 2.36 times more than mono-digestion of POME. It is also found that with increasing mixing speed, the methane production can be further improved. Preliminary cost analysis shows that EFB is a promising feedstock for ACD with POME, when considering in terms of technical (i.e. methane yield) and economic efficiencies (i.e. methane productivity and pre-treatment cost). Future works would be focused on the comprehensive optimization of the DC:EFB:POME co-digestion, particularly the improvement of the EFB pre-treatment method and settling characteristics of the digested sludge.