Enrichment of high-rate PCE dechlorination and comparative study of lactate, methanol, and hydrogen as electron donors to sustain activity

Abstract

The influence of three electron donors on the ability to sustain rapid tetrachloroethene (PCE) dechlorination in mixed cultures was investigated. Experiments were performed in recycle columns containing either a high-rate PCE dechlorinating culture developed from granular sludge or a (1:1) mixture of this culture with an enrichment culture derived from soil cores taken from a chlorinated ethene contaminated site. Columns were fed PCE (aqueous concentration of 5 mg/L) and either lactate, methanol, or H2 as their electron donor. Comparisons between electron donors were formulated using the observed rates of PCE disappearance and the extent of dechlorination achieved in each column. Over a period exceeding 1 year, the observed PCE half-life in each column was found to decrease from approximately 13 h to slightly less than 2 h, regardless of electron donor fed. Although initial mass balance studies demonstrated that the extent of dechlorination varied between inoculum and electron donor, overtime, the recycle columns behaved similarly, and PCE was recovered as approximately 80% vinyl chloride and 20% ethene in all systems. Rates and extents of PCE dechlorination were improved over time in systems containing high H2 partial pressures (0.8 atm) in the presence of an active methanogenic community.