Improving continuous anaerobic digestion of cassava pulp by potassium hydroxide pretreatment

Cassava pulp (CP), a by-product from a large cassava industry in Thailand, is a potential feedstock for anaerobic digestion. However, its complex structure from fibers is hardly digested, causing low hydrolysis rate, accumulation of solids, and digester failure at high organic loadings. Chemical pretreatment has been used to overcome hydrolysis limitation. Among various alkalis, potassium hydroxide (KOH) has benefit on improvement of methane yield and digestate quality as biofertilizer. This study aimed to investigate the effect of KOH pretreatment during continuous anaerobic digestion for methane production from CP. Pretreatment with KOH at the concentration of 0.5-3.0% (w/v) increased 29-54% for COD solubilization. Pretreatment with 0.5% KOH reduced hemicellulose and lignin content for 58 and 24%, respectively. Biomethane potential (BMP) assay of pretreated CP with 0.5% KOH produced methane yield of 321 ml CH4/gVS, accounting for 25% improvement than that of untreated CP. The effect of pretreatment on biogas production by mesophilic continuous anaerobic digestion was investigated. Methane yield of pretreated CP was at 337 ± 20 ml/gVS, which is not significantly different from that of untreated CP. However, pretreatment reduced the accumulation of total suspended solids in the digester by 55%, which benefits the stability of the digestion at higher organic loading rates.