In the present study, the effect of external mass transfer on the rate of butachlor biodegradation was studied using calcium alginate immobilized microbial consortium SMC1 in a re-circulated up-flow packed bed bioreactor in a batch scale. By assuming the biodegradation kinetics to be first order, the effect of various operational parameters such as feed flow rate, substrate concentration, and the external mass transfer on the bio-removal of butachlor from the aqueous medium has been explored. Using external film diffusion models and Colburn analogy, the mass transfer correlations at several feed rates were worked out. The correlational analysis obtained in the form of J D = 1.341 N − 0:3 Re was found to predict the experimental data precisely.