Volatile fatty acids as electron donors for the reductive dechlorination of chloroethenes

Uses of a mixture of six volatile fatty acids (VFAs) including acetic, propionic, butyric, isobutyric, valeric and isovaleric acids as electron donors for the reductive dechlorination of chloroethenes have been investigated by both microcosm and column studies. The fates of tetrachloroethene (PCE), cis-dichloroethene (cis-DCE) and vinyl chloride (VC) in the presence of VFAs and in the absence of VFAs were respectively documented. The results showed that VFAs stimulated complete reductive dechlorination of chloroethenes, either as direct substrates for the dechlorinating bacteria or via H2 formed during VFAs-degradation. There were sequential utilizations of different VFAs by fermenting bacteria. In the microcosm, propionic acid was the first to be used, followed by acetic, butyric, isobutyric, valeric, and isovaleric acids, and their mean first-order degradation rates obtained were 0.128, 0.048, 0.016, 0.027, 0.025 and 0.003 day(-1), respectively. In the column, propionic acid was the first to be used, followed by butyric and valeric acids, and their calculated first-order degradation rates were 0.833, 0.403 and 0.260 day(-1), respectively.