COSOLVENT MOBILIZATION AND ENHANCED BIOREMEDIATION OF RESIDUAL PHASE SOLVENT HYDROCARBONS

摘要

An area previously occupied by an underground storage tankfarm near Dusseldorf, Germany, was subjected to intensive in situ bioremediation over a three-year period using saturated zone biosparging, unsaturated zone bioventing and six complete pore volume exchanges of laterally-infiltrated aerated water. Approximately 9 tons of solvent hydrocarbons were biodegraded leading to a reduction of benzene, toluene, ethylbenzene, xylene (BTEX) and tri-methylbenzene (TMB) levels in groundwater to consent levels in most monitoring wells. However, the central area of the previously heavily contaminated tankfarm consistently returned BTEX and TMB levels in groundwater suggestive of the presence of residual or free-phase non-aqueous phase liquid (NAPL) hydrocarbons. The area of residual contamination was subjected to multiple rounds of cosolvent flooding using isopropanol to mobilise any accessible BTEX and TMB into a mobile isopropanol/water liquid phase for subsequent recovery by groundwater surface dual-phase “slurping” or for biodegradation in situ. The isopropanol injections stimulated the mobilization of additional BTEX and TMB into the surrounding groundwater, with the extent of mobilization progressively decreasing with subsequent injections. The BTEX & TMB mobilised by the isopropanol-based cosolvent approach were initially subjected to further mobilization bioremediation using standard biosparging methods, which promote mobilization aquifer mixing, and then by the infiltration of aqueous solutions of nitrate as an electron acceptor to further enhance the mobilization biodegradation.