Comparison of different substrates for the fast reductive dechlorination of trichloroethene under groundwater conditions

A mixture of four different anaerobic sludges was tested for the ability to transform varying concentrations (0.3–2.2 mg l−1) of trichloroethene (TCE) under groundwater conditions with methanol, ethanol, formate, lactate, acetate and H2/CO2 as reducing substrates. Seven fixed-bed reactors were operated from the start at 14°C over a period of 200 days. With lactate, TCE was completely transformed to cis-1,2-dichloroethene (cis-DCE) within 12 days. With formate, methanol, acetate, H2/CO2 and ethanol, more than 75% of the TCE was dechlorinated to cis-DCE within 24, 75, 144, 84 and 190 days, respectively. With mixtures of substrates, nearly complete transformation after 13 days and significant methane production could only be obtained with lactate + methanol, but not with formate + methanol. After the feed was changed to methanol only, transformation efficiency of TCE was still high and methane production increased in the reactor previously fed with lactate + methanol. In a column reactor fed with lactate for more than 100 days, TCE transformation could not be maintained at 100% efficiency and methane production was insignificant when only methanol was fed. The formation of other dichlorinated ethenes, ethanes or vinylchloride not observed in our experiments.