Techno-Economic Assessment of Cassava Starch Processing Effluent Treatment and Biogas Recovery in Ogun State

Cassava starch processing in Ogun State, South West Nigeria, generates large volumes of process water heavily loaded with cyanide, suspended solids, and organic matter that are routinely discharged into farmland and streams without treatment. This study assesses the technical and economic viability of a combined effluent treatment and biogas recovery system for a medium-scale cassava starch plant producing 10 tonnes of starch per day in Ifo Local Government Area. Effluent characterisation over three months revealed chemical oxygen demand values of 9,400 to 14,200 mg/L, cyanide concentrations of 48 to 76 mg/L, and total suspended solids of 2,600 to 4,100 mg/L. A treatment train incorporating alkaline cyanide oxidation, anaerobic digestion in a covered lagoon, aerobic polishing, and effluent reuse for crop irrigation was conceptually designed and sized for the plant effluent volume of 80 m3/day. Biogas production from anaerobic digestion was estimated at 480 m3/day, sufficient to generate 720 kWh/day of electricity when converted via an internal combustion generator. Capital cost of the proposed system was estimated at 85 million Naira, with an annual operating cost of 12 million Naira. Projected savings from electricity generation and reduced freshwater intake produced an estimated simple payback period of 4.8 years. The study recommends the proposed treatment system as the standard configuration for medium-scale cassava processing plants in Ogun State. Keywords: cassava effluent, biogas recovery, anaerobic digestion, techno-economic, Ogun State