CHEMICAL AND MICROBIAL EVALUATION OF IN-SITU BIOREMEDIATION OF HYDROCARBONS IN ANOXIC GROUNDWATER ENRICHED WITH NUTRIENTS AND NITRATE

In-situ bioremediation of benzene, toluene, ethylbenzene and the xylen es (BTEX) was carried out in an O-2-poor (approx. 1 mg O-2/l) fuel-con taminated aquifer. Extracted groundwater, enriched with ammonium polyp hosphate (nutrients) and KNO3 (electron acceptor), was piped to an inf iltration gallery over the contaminated site. Before, during and after infiltration, BTEX, nitrate and different populations of culturable b acteria were measured. BTEX declined by 78% in water from the monitori ng well which was most contaminated initially and by nearly 99% in wat er from one of the extraction wells. These declines persisted after ce ssation of nutrient and nitrate addition. During the second half of th e nutrient and nitrate addition period (weeks 107 to 160.5), nitrate a ppeared in the monitoring well, denitrifying bacteria increased about 50-fold and bacteria degrading benzene, toluene and xylenes (BTX) and phenanthrene (enumerated aerobically) increased 16- and 121-fold, resp ectively. At one of the extraction wells, down-gradient of the monitor ing well, nitrate appeared in significant concentrations after week 12 4; this appearance coincided with a marked decline (>90%) in BTEX conc entration and 21- and 10-fold increases, respectively, in BTX- and phe nanthrene-degrading bacteria. Low concentrations of BTEX and nitrate i n down-gradient, off-site wells showed that water washing did not mobi lize BTEX from the aquifer. The data indicate that the BTEX in this ni trate-enriched aquifer was biodegraded in-situ under denitrifying cond itions.