Abstract
| - Previous studies indicated that dechlorinators can utilizeH2 at lower concentrations than can methanogens.Thissuggests a strategy for selective enhancement ofdechlorinationmanaging H2 delivery so as to impartacompetitive advantage to dechlorinators. FourH2donorsbutyric and propionic acids, which can only befermented when the H2 partial pressure is lower than10-3.5or 10-4.4 atm, respectively, and ethanol andlactic acid,which are readily fermented at H2 partial pressures2−3orders of magnitude higherwere administered toanaerobicmixed cultures. Comparison of the resultingenrichmentcultures during time-intensive, short-term tests showedsignificant differences in patterns of donor degradation,H2 production and use, and distribution of reductionequivalentsbetween dechlorination and competing methanogenesis.Amendment with butyric and propionic acids resulted inlessmethanogenesis than did amendment with ethanol orlactic acid, which generated much higher H2 levels.Ethanoldid not support complete dechlorination during short-term tests, but it was a viable donor over long-termtestingbecause a portion was converted to a pool of slowlydegraded propionic acid and because during long-termtests,cultures were routinely co-amended with pre-fermentedyeast extract, a source of slowly fermented volatile fattyacids.Understanding the fate of electron donors and theirfermentation products is an important component inunderstanding dechlorinating communities.
|