Carboxymethylcellulose microspheres cross-linked via aluminum ions were used as a support material for immobilization of Methylosinus isolated from soil contaminated with aldicarb. The degradation capacity of immobilized bacteria, different parameters such as substrate concentration (50-800 ppm), flow rate (10-60 ml h(-1)), and continuous contact with reaction medium (flow rate, 20 mi h(-1) and concentration, 100 ppm) that affect aldicarb degradation were investigated in a packed-bed reactor. Increases in the flow rate decreased the conversion of aldicarb into its metabolites. On the other hand, increasing the substrate concentration up to 400 ppm led to an increase in the amount of aldicarb converted (max 16%). Beyond this, the proportion of aldicarb that converted was decreased, reaching approximately 7% at 800 ppm. The apparent kinetic parameters, K-m' and V-max, were determined to be as 310.11 ppm and 2.29 X 10(-2) ppm s(-1), respectively. Operation of the bioreactor in the recycled mode was much more efficient, degrading 50% of the aldicarb in 24 h and 100% in four days. (C) 1999 Elsevier Science Inc.