IN-SITU BTEX BIOTRANSFORMATION UNDER ENHANCED NITRATE-REDUCING AND SULFATE-REDUCING CONDITIONS

In situ anaerobic biotransformation of BTEX (benzene, toluene, ethylbe nzene, o-xylene, and m-xylene) was investigated under enhanced nitrate - and sulfate-reducing conditions. Controlled amounts of BTEX compound s added to slugs of treated groundwater were released into a gasoline- contaminated aquifer at Seat Beach, CA. In a series of studies, the sl ugs, 470-1700 L in volume, were released into the aquifer through a mu lti-port injection/extraction well and were subsequently withdrawn ove r a 2-3-month period. To evaluate unamended in situ conditions, the in jectate was treated with granular activated carbon (GAC) and augmented with bromide as a tracer. To evaluate nitrate- and sulfate-reducing c onditions,the injectate was also deionized and augmented with 200-300 mu g/L BTEX, nitrate or sulfate, and background electrolytes. Under un amended conditions, transformation appeared to be limited to the slow removal of toluene and m,p-xylene (i.e., sum of m+p-xylene). Under nit rate-reducing conditions, toluene, ethylbenzene, and m-xylene were tra nsformed without a lag phase in less than 10 days, and o-xylene was tr ansformed in 72 days. Under sulfate-reducing conditions, toluene, m-xy lene and o-xylene were completely transformed in less than 50 days, an d ethylbenzene was removed in 60 days. Benzene appeared to be removed under sulfate-reducing conditions, but the trend was pronounced only a t some levels. A two-dimensional model is presented for the evaluation of reactive solute behavior in such slug tests. For compounds that ar e transformed without a fag phase, zero-order kinetics appears to be m ore applicable than first-order kinetics.