COMETABOLIC AND INHIBITORY INTERACTIONS DURING ANAEROBIC BIODEGRADATION OF ALKYLBENZENE MIXTURES

摘要

Mixed and pure culture experiments were conducted with aquifer bacteria to elucidate the effect of substrate interactions on the biodegradation of alkylbenzenes and polycyclic aromatic hydrocarbons (PAHs) under strict anaerobic denitrifying conditions. In the first experiment, a column consisting of aquifer sands collected from the site of a former manufactured gas plant (MGP) was fed a synthetic groundwater mixture containing benzene, toluene, ethylbenzene, and xylene (BTEX), naphthalene, and (1- and 2-) methylnaphthalene. Complete removal of toluene, m-xylene, and partial removal of o-xylene was evident after several months of operation. Degradation of o- and p-xylene occurred only in the presence of toluene, indicating cometabolism with toluene as the primary substrate. Benzene, ethylbenzene, and the PAHs resisted biodegradation in this 2-year study, providing further evidence of the difficulty in achieving biodegradation of these compounds under anaerobic conditions. A separate experiment evaluated the simultaneous biodegradation of toluene and m-xylene by denitrifying Azoarcus sp. strain T. In batch reactors receiving equimolar concentrations of m-xylene and toluene, strain T consistently degraded m-xylene first. Increasing the ratio of m-xylene to toluene caused an increase in the lag time for toluene degradation, suggesting that m-xylene competitively inhibits biodegradation of toluene by strain T. These experiments demonstrate that both synergistic and antagonistic interactions are possible during biodegradation of BTEX mixtures in the absence of oxygen. In addition, these data suggest that substrate interactions can significantly affect the biodegradation kinetics for individual alkylbenzenes in anaerobic groundwater.