Degradation of pentachlorophenol (PCP) by Arthrobacter strain ATCC 33790 in biofilm culture

Degradation of pentachlorophenol (PCP) by Arthrobacter strain ATCC 33790 naturally immobilized on glass beads in a column was studied. PCP was removed from mineral salts medium 4–5 d after inoculation of the column with PCP-acclimated cells grown in batch culture. Adherence to the glass occurred with production of extracellular polymer. The laboratory reactor operated without aseptic precaution for over 300 d employing a feed containing 12–366 mg/l PCP as the predominant carbon source. Transient studies were done with both ammonia and nitrate in the feed. With ammonia in the feed the system lost its ability to respond effectively to step increases in PCP feed concentration from 12–170 mg/l within 4 months. After 6 months, even at very low flow rate, the column was unable to efficiently remove PCP after 2 abrupt increases in hydraulic load. The presence of 120 mg/l nitrite in the effluent indicated that nitrification caused deterioration in column performance. Replacement of the ammonia in the feed with nitrate reestablished PCP removal efficiency. Effluent concentrations were typically less than 1 mg/l with 20 mg/l in the feed. In transient studies the amplitude of response to 5 step increases in feed concentration of 20–150 mg/l decreased in time from 91.5 to 11 mg/l. The column responded well to a step increase from 20 to 366 mg/l but was stunned following a subsequent step change from 20 to 1000 mg/l.