The composite tannery waste water has been treated by anaerobic digestion using varying organic loads. The chromium present has been removed by precipitation method using lime as the agent. The treated water was analysed for pH, influent BOD (So), effluent BOD (Se), mixed liquor volatile suspended solids (MLVSS) before sludge wasting, initial MLVSS and the net growth rate of microorganisms. Results indicated that the BOD and COD removal efficiency decreases with decrease in mean cell residence time c and decrease with increase in F/M ratios. A maximum BOD reduction of 96.9% was obtained at the BOD loading rate of 0.80 kg BOD/m3/day and throughout different loading rates and modified Monod’s equation was used to determine the biokinetic coefficients. A mathematical model was developed to predict the BOD removal efficiency and the model signifies the prediction with a deviation of ±3.6.