SITE-SPECIFIC VARIABILITY IN BTEX BIODEGRADATION UNDER DENITRIFYING CONDITIONS

Laboratory microcosm experiments were conducted to evaluate the feasib ility of benzene, toluene, ethylbenzene, m-xylene, and o-xylene (BTEX) biodegradation under denitrifying conditions. Nine different sources of inocula, including contaminated and uncontaminated soil cores from four different sites and activated sludge, were used to establish micr ocosms. BTEX was not degraded under denitrifying conditions in microco sms inoculated with aquifer material from Rocky Point and Traverse Cit y. However, rapid depletion of glucose under denitrifying conditions w as observed in microcosms containing Rocky Point aquifer material. TEX degradation was observed in microcosms containing Rocky Point aquifer material. TEX degradation was observed in microcosms containing aquif er material from Fort Bragg and Sleeping Bear Dunes and sewage sludge. Benzene was recalcitrant in all microcosms tested. The degradation of o-xylene ceased after toluene, ethylbenzene, and m-xylene were deplet ed in the Fort Bragg and sludge microcosms, but o-xylene continued to degrade in microcosms with contaminated Sleeping Bear Dunes soil. The most probable number (MPN) of denitrifiers in these nine different ino cula were measured using a microtiter technique. There was no correlat ion between the MPN of denitrifiers and the TEX degradation rate under denitrifying conditions. Experimental results indicate that the degra dation sequence and TEX degradation rate under denitrifying conditions may differ among sites. Results also indicate that denitrification al one may not be a suitable bioremediation technology for gasoline-conta minated aquifers because of the inability of denitrifiers to degrade b enzene.