Biological treatment of wastewater from the cassava meal industry

Biological treatments of cassava meal processing wastewaters were investigated by aerobic and combined anaerobic/aerobic reactors. As a pretreatment, flocculation and sedimentation with aluminum salts and natural polyelectrolytes were employed, in order to change the effluent concentration of organics from 14,000 to 2000 mg/L in the bench scale reactor, with a hydraulic retention time of 37 min and an influent rate of 0.56 L/cm. Biological degradation by an activated sludge process was carried out using a reactor volume of 20 L. The observed organic matter removal rates were 89 to 93%, the cyanide removal was 95 to 99%, and the food to microorganisms ratio was found to be in the range of 0.166 to 0.242/day, with a hydraulic residence time of 1.4 to 4.2 days. As a posttreatment, flocculation and coagulation were employed, resulting in an effluent of good quality, as shown by turbidity measurements and negative tests for fecal and total coliforms.