ABSTRACT
Small-scale rice industry produces about 7,000 l of effluent per day, having a Chemical Oxygen Demand (COD) ranging from 4,000 to 7,000 ppm. The effluent contains mainly long-chain carbohydrates, which is an ideal source for biogas production. In this research work, physical and chemical methods for treatment of rice mill waste were investigated and compared. Filtration, centrifugation and adsorption were used in the physical method, and chemical methods included lime and hydrogen peroxide treatments. Filtration and centrifugation did not reduce COD values because impurities were mainly in the form of dissolved solids. Adsorption using bottom ash obtained from the boiler located at a rice mill reduced the COD of effluent by c. 28%. Lime treatment ranging from 0.1 g to 2 g lime per 100 ml effluent reduced the COD by c. 23% to 43%, respectively. Hydrogen peroxide treatment gave the best results of all the treatments with c. 98% reduction in COD values. Sludge production was c. 60% lower in peroxide-treated effluent as compared to lime-treated effluent. The sludge obtained from lime and peroxide treatment methods was further added to a batch of anaerobic digester for biogas production. Lime-treated sludge reduced biogas production of a stable biogas-producing digester, due to an increase in pH from c. 7.2 to 11.5. Biogas production was enhanced markedly when hydrogen peroxide-treated sludge was added to an anaerobic digester, as compared to lime-treated sludge.
