Microbial adaptation to hydrogen peroxide and biodegradation of aromatic hydrocarbons.

This research investigated microbial responses to bioremediation with hydrogen peroxide (H2O2) as a supplemental oxygen source. Columns containing aquifer material from Traverse City, MI, USA, were continuously supplied with benzene, toluene, ethylbenzene, o-xylene and m-xylene (BTEX) and H2O2 in increasing concentration. The microbial responses studied were changes in microbial numbers, community structure, degradative ability, and activity of catalase and superoxide dismutase (SOD). Both adaptation to H2O2 and stress-related consequences were observed. Adaptation to H2O2 was demonstrated by increased catalase and SOD activity during the course of the experiment. The microbial community in the untreated aquifer material used in the columns consisted primarily of Corynebacterium sp and Pseudomonas fluorescens. Following amendment with 500 mg L-1 H2O2, the column inlet was dominated by P. fluorescens with few Corynebacterium sp present; Xanthomonas maltophilia dominated the middle and outlet sections. Dimethyl phenols detected in the effluent of two of the biologically active columns were probably metabolic products. The ratio of oxygen to BTEX mass consumed was approximately 0.3 before H2O2 addition, 0.7 following 10 mg L-1 H2O2 supplementation, and 2.6 over the course of the experiment. Abiotic decomposition H2O2 was observed in a sterile column and impeded flow at a feed concentration of 500 mg L-1 H2O2. Increasing the BTEX concentration supplied to the biologically active columns eliminated flow disruptions by satisfying the carbon and energy demand of the oxygen evolved by increasing catalase activity.