Anaerobic degradation of a mixture of MtBE, EtBE, TBA, and benzene under different redox conditions.

The increasing use of biobased fuels and fuel additives can potentially change the typical fuel-related contamination in soil and groundwater. Anaerobic biotransformation of the biofuel additive ethyl tert-butyl ether (EtBE), as well as of methyl tert-butyl ether (MtBE), benzene, and tert-butyl alcohol (TBA, a possible oxygenate metabolite), was studied at an industrially contaminated site and in the laboratory. Analysis of groundwater samples indicated that in the field MtBE was degraded, yielding TBA as major product. In batch microcosms, MtBE was degraded under different conditions: unamended control, with medium without added electron acceptors, or with ferrihydrite or sulfate (with or without medium) as electron acceptor, respectively. Degradation of EtBE was not observed under any of these conditions tested. TBA was partially depleted in parallel with MtBE. Results of microcosm experiments with MtBE substrate analogues, i.e., syringate, vanillate, or ferulate, were in line with the hypothesis that the observed TBA degradation is a cometabolic process. Microcosms with ferulate, syringate, isopropanol, or diethyl ether showed EtBE depletion up to 86.5% of the initial concentration after 83 days. Benzene was degraded in the unamended controls, with medium without added electron acceptors and with ferrihydrite, sulfate, or chlorate as electron acceptor, respectively. In the presence of nitrate, benzene was only degraded after addition of an anaerobic benzene-degrading community. Nitrate and chlorate hindered MtBE, EtBE, and TBA degradation.

Stimulation of hexachlorocyclohexane (HCH) biodegradation in a full scale in situ bioscreen.

The feasibility of a bioscreen for the in situ biodegradation of HCH and its intermediates is demonstrated at a contaminated site in The Netherlands, via the discontinuous addition of methanol as electron donor. An infiltration system was installed and operated at the site over a length of 150 m and a depth of 8 m, to create an anaerobic infiltration zone in which HCH is converted. The construction of the infiltration system was combined with the redevelopment of the site. During passage through the bioscreen, the concentration of HCH in the groundwater decreased from 600 µg/L to the detection limit of the individual HCH isomers (0.01 µg/L) after one year of operation. The concentration of the intermediate biodegradation products benzene and chlorobenzene increased and achieved steady state values of respectively 800 and 2700 µg/L. Benzene and chlorobenzene were treated aerobically on site in an existing wastewater treatment plant. By changing the infiltration regime, it is conclusively shown that HCH removal is the result of the biological degradation and stimulated by the addition of methanol as electron donor. To our knowledge, this is the first successful field demonstration of the stimulated transformation of HCH to intermediates in a full scale anaerobic in situ bioscreen, combined with an aerobic on site treatment to harmless end products.