22. Remediation of Chlorinated Hydrocarbon Solvents

A series oflaboratory scale studies were undertaken to study the rates ofbio­ logical (biotic) and non-biological (abiotic) dechlorination of chlorinated hydrocarbon solvents such as trichloroethylene (TCE). Microcosms were seeded with subsurface sediment samples drawn from a contaminated paint manufacturing facility in continental Europe, and incubated under a variety of anaerobic conditions to determine TCE removal rates by cometabolic oxidation, biological reductive dechlorination, and non-biological reductive dechlorination catalysed by supplementary additions of zero-valent Iron. Control microcosms conducted in parallel included incubations in the absence of sediments, and in the presence of sediments previously sterilised by autoclaving. TCE was added at an initial concentration of 6 mgll in all microcosms, together with methanol as a supplementary carbon source. The naturally-occurring abiotic dechlorination rate for TCE was determined to be 0.2 JLmole TCE degraded daily per litre of microcosm (0.2 JLmole/l/d). The biological reductive dechlorination rate was also 0.2 JLmole/l/d. The addition of zero-valent Iron (as coarse Iron filings) to a level of 12.5 gil increased the abiotic dechlorination rate to 0.6 JLmole/l/d in sterile microcosms. The dechlorination rate increased to 1.0 JLmole/l/d with the addition of 37.5 gil coarse Iron filings. Individual bacterial strains isolated from the sediments used in the microcosm studies have been found to have a high naturally-occurring resistance to heavy metals including copper, chromium, cobalt and lead. A number of experimental tools including biosensors, ion-specific electrodes, and growth response curves have been employed in an attempt to estimate the bioavailability of added metals to bacteria in both solid and liquid media.