Effectiveness of using two-stage anaerobic digestion to recover bio-energy from high strength palm oil mill effluents with simultaneous treatment

Abstract This study aimed to investigate the biohydrogen and biomethane potential of palm oil mill effluent (POME) in a two-stage anaerobic digestion (AD) system under thermophilic (55 ± 3 °C) and mesophilic (30 ± 3 °C) conditions, respectively. Among the initial loadings of 0.5 g-COD, 1.0 g-COD, or 1.5 g-COD, the best production potentials of 106.13 mL-H2/g-COD and 334.56 m L-CH4/g-CODadded, corresponding to the total energy production of 13.61 kJ/g-CODadded, were obtained from POME with an initial 0.5 g-COD loading. The investigation also revealed that the energy yield (CH4+H2) achieved from two-stage AD was approximately 38.95 % higher than single-stage anaerobic digestion (single-stage AD), where only methane energy carrier was produced. Continuous hydrogen and methane production were subsequently performed in a series of continuous stirred tank reactor (CSTR) and anaerobic horizontal baffled channel (AHBC) reactor to treat POME without external supplement. The results revealed that the highest hydrogen yield of 86 m L-H2/g-CODadded was generated at 3-day HRT, while the highest methane production was obtained from HRT over 35 days with a yield of 250.33 m L-CH4/g-CODadded. Additionally, the overall COD removal in the continuous process was approximately 66.27 %. As a highly efficient organic matter removal and higher energy recovery, the continuous two-stage AD can be further developed to industrial-scale mixed hydrogen and methane production from POME.