ENHANCING BIOTRANSFORMATION OF CASSAVA PULP TO BIOMETHANE WITH LIQUID HOT WATER AND MICROBIAL PRETREATMENTS

Cassava pulp (CP), a major agro-industrial byproduct of cassava starch processing in Thailand, contains high residual organic matter, making it a potential feedstock for anaerobic digestion. However, much of its starch is trapped within the lignocellulosic cell wall, which limits biodegradability. This study investigated two pretreatment strategies to improve CP conversion: (a) liquid hot water (LHW) under optimized conditions, and (b) microbial hydrolysis and fermentation of starchy lignocellulose using Clostridium manihotivorum CT4T (CT4T), both aimed to disrupt the cell wall structure of CP and solubilized hemicellulose and starch into saccharides as well as enhancing volatile fatty acids (VFAs) production for biomethane generation. Under the selected optimum LHW condition (186.67 ºC and 6.97 min), glucose was released at 444 mg/gTS-CP, along with detectable amount of galactose, xylose, L-arabinose and mannose. Inhibitory compounds, including furfural and hydroxymethylfurfural, were presented only at low concentrations (0.031 and 0.032 g/L, respectively). Biochemical methane potential tests of LHW-pretreated CP showed a biomethane yield of 328±2.59 mL/g VS and substrate degradation efficiency of 75.0±2.28%, representing a 35% improvement over untreated CP and reducing the anaerobic digestion time from 22 d to 10 d. These results demonstrated that LHW was an efficient, chemical-free pretreatment for enhancing CP biodegradability. In the biological pretreatment, CP hydrolysis and fermentation by CT4T found only low sugar accumulation (0.21–0.24 mg/mL) but generated substantial yields of acetic acid (0.24–0.28 g/g VS) and butyric acid (0.29–0.32 g/g VS). Subsequent methanogenesis, initiated with a syntrophic-methanogenic consortium and fed with the VFAs-rich leachate, biomethane yielded of 325±3.94 mL/g VS, with a substrate degradation efficiency of 66.8±1.79%; a 30% improvement compared to untreated CP. Both LHW and CT4T effectively disrupted the CP cell wall, releasing starch that was readily utilized and completely degraded. These pretreatment strategies significantly enhanced CP conversion to biomethane in a shorter time than non-pretreated CP. Overall, LHW and CT4T provide environmentally friendly and promising approaches for accelerating and improving biomethane production in the cassava starch industry.