Simultaneous treatment of raw palm oil mill effluent and biodegradation of palm fiber in a high-rate CSTR

•A modified CSTR was used to treat raw palm oil mill effluent without pretreatment.•Neither physical nor chemical pretreatment of the raw POME was performed.•The deflector installed at the CSTR’s upper section promoted retention of fibers.•Simultaneous degradations of palm fibers and soluble parts in POME were achieved.•Methane production rate was 4.14 l/l d at a highest OLR 19.0 g COD/l d.

A high-rate continuous stirred tank reactor (CSTR) was used to produce biogas from raw palm oil mill effluent (POME) at 55 °C at a highest organic loading rate (OLR) of 19 g COD/l d. Physical and chemical pretreatments were not performed on the raw POME. In order to promote retention of suspended solids, the CSTR was installed with a deflector at its upper section. The average methane yield was 0.27 l/g COD, and the biogas production rate per reactor volume was 6.23 l/l d, and the tCOD removal efficiency was 82%. The hydrolysis rate of cellulose, hemicelluloses and lignin was 6.7, 3.0 and 1.9 g/d, respectively. The results of denaturing gradient gel electrophoresis (DGGE) suggested that the dominant hydrolytic bacteria responsible for the biodegradation of the palm fiber and residual oil were Clostridium sp., while the dominant methanogens were Methanothermobacter sp.

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