EFFECTS OF NITRATE AND ACETATE AVAILABILITY ON CHLOROFORM PRODUCTION DURING CARBON-TETRACHLORIDE DESTRUCTION

Fed batch experiments were performed to test the effects of electron d onor and electron acceptor availability on the production of chlorofor m (CF) during carbon tetrachloride (CT) destruction by a denitrifying bacterial consortium. In one series of tests, acetate (electron donor) was present in excess while nitrate and nitrite (electron acceptor) w ere limiting. In the other series of tests, acetate was the limiting n utrient, and nitrate and nitrite were in excess. Under nitrate limitin g conditions, 50% (+/-17%) of the CT transformed by the microorganisms was converted to CF. However, under acetate limiting conditions, only 4% (+/-4%) of the CT that was degraded appeared as CF. Previous resea rch had suggested that denitrifying bacteria can degrade CT via two co mpeting pathways. One of these pathways produces CF as the predominant end product. The second pathway produces CO2 as the primary end produ ct, The results shown here suggest that the first pathway is dominant when nitrate and nitrite are depleted while the second pathway, which produces little CF, dominates when nitrate or nitrite are available. ( C) 1996 John Wiley & Sons, Inc.