Enhancing microbial trichloroethylene dechlorination by controllingpH with encapsulated phosphate buffer

Trichloroethylene (TCE) is a solvent that widely contaminates groundwater. Neutral pH has been shown to optimize TCE reductive dehalogenase activity in cell extracts and cell suspensions. Anaerobic bacteria from TCE-contaminated subsurface sediment might also show maximum dechlorinating activity when the pH is neutralized in the sediment.; Encapsulated phosphate buffers were investigated as a method for controlling pH in situ where neutral pH might improve dechlorination of TCE. These capsules (1 mm average diameter), which are coated with a pH-sensitive polymer (Eudragit™ S100), release KH₂PO₄ into sediment pore water when pH levels rise above 7.0. These capsules were tested in sediment microcosms and sand and sediment flow-through columns. The sediment was obtained from a contaminated groundwater aquifer at the Department of Energy's Savannah River Site (SRS).; The initial test of capsule release occurred in denitrifying sediment microcosms. pH levels above 8.0 were measured in microcosms to which no capsules had been added while the pH in bottles containing capsules remained within 0.2 pH units of 7.0. Two more tests to characterize the capsules were performed in sand columns specially designed to house the capsules. Near complete conversion of 80 mg N/L of nitrate and 152 mg/L of ethanol per day resulted in a mean pH increase from 6.2 to 8.2 in the column without capsules. The column containing the capsules maintained the target pH of 7.0 ± 0.2 for four weeks. The encapsulated phosphate buffer was effective at neutralizing a 1.5-unit pH change in saturated sediment microcosms and sand columns. This study demonstrates the potential for this technology to mediate pH changes in situ.; The pH in microcosms containing sediment from SRS was adjusted to different set points in order to determine whether 7.0 is the optimum pH level for reductive dechlorination of TCE in sediment. Statistically, maximum vinyl chloride production occurred at a pH of 4 (p < 0.0001). The results implied that a pH of 7 would not necessarily optimize TCE dechlorination in sediment. Though pH appeared to have affect TCE dechlorination, the low production of metabolites indicated that in situ pH control would not be efficacious for promoting reductive dechlorination at SRS.