In-situ bioremediation of benzene, toluene, ethylbenzene and the xylenes (BTEX) was carried out in an O2-poor (approx. 1 mg O2/l) fuel-contaminated aquifer. Extracted groundwater, enriched with ammonium polyphosphate (nutrients) and KNO3 (electron acceptor), was piped to an infiltration gallery over the contaminated site. Before, during and after infiltration, BTEX, nitrate and different populations of culturable bacteria were measured. BTEX declined by 78% in water from the monitoring well which was most contaminated initially and by nearly 99% in water from one of the extraction wells. These declines persisted after cessation of nutrient and nitrate addition. During the second half of the nutrient and nitrate addition period (weeks 107 to 160.5), nitrate appeared 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, respectively. At one of the extraction wells, down-gradient of the monitoring well, nitrate appeared in significant concentrations after week 124; this appearance coincided with a marked decline (> 90%) in BTEX concentration and 21- and 10-fold increases, respectively, in BTX- and phenanthrene-degrading bacteria. Low concentrations of BTEX and nitrate in down-gradient, off-site wells showed that water washing did not mobilize BTEX from the aquifer. The data indicate that the BTEX in this nitrate-enriched aquifer was biodegraded in-situ under denitrifying conditions.

A series of experiments was conducted to examine the effects of chemical pretreatment on biodegradation of 14C-labeled PCB congeners in aqueous systems. Fenton's reagent was used to generate hydroxyl radicals (OH) which were successful in partially oxidizing/transforming otherwise recalcitrant molecules of tetrachlorinated PCB, but had little or no impact on the biodegradation of a monochlorinated congener. Application of Fenton's reagent (1% H2O2, 1 mM FeSO4) followed by inoculation with pure cultures Pseudomonas sp, strain LB 400 and Alcaligenes eutrophus, strain H850 resulted in the removal of approximately 38% of 2-chlorobiphenyl and 51% of 2,2',4,4'-tetrachlorobiphenyl in the form of 14CO2. Comparison of the rate and extent of biodegradation of 2,2',4,4'-tetrachlorobiphenyl after the application of Fenton's reagent with the dynamic and final level of radioactivity in the aqueous phase of experimental system suggests two possible means of microbial utilization of tetrachlorinated PCB congener altered by chemical oxidation: (a) consumption of the partially oxidized chemical dissolved in the aqueous phase, and (b) direct microbial attack on the transformed compound, which may still be adhered to the solid surface.

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A series of experiments was conducted on the integrated chemical–biological treatment of 14C‐labelled polychlorinated biphenyl congeners in soil/sediment‐containing systems. The hydroxyl radicals, generated by Fenton's reagent (1% (v/v) H2O2, 1 mmol dm−3 FeSO4), followed by inoculation with Pseudomonas sp., strain LB400, and Alcaligenes eutrophus, strain H850, increased the overall extent of 2‐chlorobiphenyl mineralisation in slurries of contaminated manufactured gas plant soil and sediment by 2·9 and 7·4 times, respectively, compared with biodegradation alone. In uncontaminated topsoil slurries the effect of chemical pretreatment was not observed. In the systems amended with 2,2′,4,4′‐tetrachlorobiophenyl, the application of Fenton's reagent increased the overall extent of mineralisation by 2·4 times, compared with the biological treatment alone, but had no effect in the slurries of contaminated soil and sediment. The increased level of radioactivity in the liquid phase of experimental systems suggests that intermediates produced in the process of chemical oxidation are less hydrophobic than parent polychlorinated biphenyls and therefore more available for further biodegradation.

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