Characteristic hydrogen concentrations for various redox processes in batch study

The dissolved hydrogen concentrations under various redox processes were in vestigated based on batch experiments. Chloroethenes including tetrachloroe thene (PCE), cis-dichloroethene (cis-DCE) and vinylchloride (VC) were respe ctively used as culture substrates. For each chloroethene, a series of bott les were prepared with the additions of different electron acceptors or don ors such as nitrate, manganese oxide, ferrous iron, sulfate, carbondioxide and volatile fatty acids. Hydrogen concentrations as well as redox species were measured over time to ensure the achievements of characteristic hydrog en levels in various enrichment batches. The results showed that redox proc esses with nitrate, manganese oxide and ferric iron as the electron accepto rs exhibited hydrogen threshold values close to PCE/TCE dechlorination, whe reas cis-DCE and VC dechlorinations exhibited hydrogen threshold values in the range of sulfate reduction and methanogenesis, respectively. Characteri stic hydrogen concentrations for various redox processes were as follows (n M): denitrification, 0.1-0.4; manganese reduction, 0.1-2.0; iron reduction, 0.1-0.4; sulfate reduction, 1.5-4.5; methanogenesis, 2.5-24; PCE/TCE dechl orination, 0.6-0.9; cis-DCE dechlorination, 0.1-2.5; and VC dechlorination, 2-24.