The cyanide component of cassava mill effluent (CME) is highly toxic to man and its environment. This research was aimed at biodegrading cyanide from cassava mill effluent with various concentrations of cyanide, variable pH
values, inoculum size and phenol. The heterotrophic bacterial and fungal counts were 6.32 x 108±0.01cfu/ml and 2.87 x 108±0.11cfu/ml, respectively. The microorganisms isolated and characterized were: Staphylococcus aureus, Bacillus sp., Escherichia coli, Lactobacillus sp., Micrococcus sp., Klebsiella sp., Pseudomonas, sp. Salmonella sp., Corynebacterium sp., Aspergillus niger, Penicillium sp., Fusarium sp. and Saccharomyces sp. The physicochemical parameters: pH (4.81), electrical conductivity (4860uS/cm), cyanide (17.13 mg/l), chemical oxygen demand (2041.20
mg/l), biological oxygen demand (1490.08mg/l), total dissolved solids (2478.60 mg/l), Chromium (19.44 mg/l), Manganese (136.08mg/l), Iron (340.20 mg/l) and Nickel (121.50 mg/l) were above the Federal Environmental Protection Agency standard for effluent discharge. Pseudomonas, Bacillus and Aspergillus species which had the highest turbidity values with enrichment medium supplemented with 1% cyanide were used for the batch biodegradation studies. Pseudomonas sp. had the best degradative ability of all isolates used even in the presence of phenol, an inhibitory substance. However, of all the varied substrate concentration used, 30ppm with other conditions remaining constant gave the highest degradative ability of 32.73% at a residence time of 8 days. Also, the highest biodegradation rate of 74.5% and 71.03% were achieved at pH, 6 and inoculum size of 6ml respectively at a
residence time of 8days for 30ppm while other parameters were kept constant. The findings revealed that Pseudomonas sp., Bacillus sp. and Aspergillus sp. could be utilized for remediating cassava mill effluent contaminated environment containing cyanide.