Aerobic biodegradation of benzene was studied using activated sludge immobilized in calcium alginate (immobilization by entrapment), and also attached to a silica based catalyst.support (immobilization by attachment). Hydrogen peroxide was used as a source of dissolved oxygen to eliminate physical removal of benzene due to aeration. Abiotic losses of benzene were accounted for.

A recirculation reactor, run in both batch and continuous feed mode, was used to determine the kinetic parameters. The system response was examined by tollowing changes in benzene concentration, flow rate, and biomass loading. The system was modeled mathematically and the kinetic parameters were determined.

Biological removal of a mixture of benzene, toluene and o, m and p-xylene (BTX) was also studied.

In a typical batch experiment starting with 100 ppm benzene, the substrate utilization rate (k_M), when expressed per unit weight of dry catalyst, had a value of 0.4453 ppm/h/g dry beads for the alginate system, and 0.067 ppm/h/g dry beads for the celite catalyst carrier.

Activated sludge was characterized for biodegradation of benzene. Isolations were done for unacclimated, acclimated and end run samples. About 67% of the isolates could be assigned to a genus. These were Bacillus, Microbacterium, Plesiomonas, Kurthia, Klebsiella, Lactobacillusj and Pseudomonas.

From among the fifteen isolates found in the end run group,- an isolate identified as Pseudomonas was established as a primary degrader of benzene.