The impact of thermal pretreatment on various solid-liquid ratios of palm oil mill effluent (POME) for enhanced thermophilic anaerobic digestion performance

An advancement to the treatment process of palm oil mill effluent (POME) was proposed whereby a pretreatment technology and a dewatering device are introduced into the existing treatment process. Thermal pretreatment is a robust technique with the ability to enhance the rate and increase the biogas production of anaerobic digestion. The dewatering device will confer a means of control on the digester’s load, allowing the removal of microbes and impurities as well as assist in the residual oil removal. The proposed advancement to the treatment process allows the removal of cooling ponds making the treatment process more sustainable in terms of the substantial reduction in the amount of greenhouse gas emission, improved residual oil removal efficiency in the waste stream, and better treated effluent quality. However, to be able to implement this innovative treatment method effectively, it is fundamental to know how thermal pretreatment undertook on the solid content of POME impacts on the anaerobic digestion process performance. To conduct the study mentioned above, POME was pretreated at 120 °C and was allowed to settle to separate the settled suspension and the clear liquor phases (hereafter denoted “solid” as S and “liquid” as L). Batch thermophilic anaerobic digestion was conducted on various solid: liquid ratios (i.e., the 20S:80L, 40S:60L, 50S:50L, 75S:25L, and 100S). It was found that the optimal ratios were 20S:80L and 40S:60L, which generated approximately 9-fold and 6-fold higher methane yield, respectively, in contrast to their untreated counterparts. Thermally pretreated 40S:60L solid loading exhibited a higher removal efficiency in terms of chemical oxygen demand (COD), biological oxygen demand (BOD), total suspended solids (TSS), and oil & grease (O&G), a higher methane yield of 328 mL CH₄/g CODᵣₑₘₒᵥₑd and biogas production of 1886 ± 21 mL from a working volume of 100 mL compared to all the other pretreated and untreated ratios.