Biotransformation rates of chloroform under anaerobic conditions—II. Sulfate reduction

Biotransformation of chloroform (CF) was studied in a sulfate-reducing culture utilizing acetic acid as the primary substrate. In a chemostat, CF and its biotransformation product, dichloromethane (DCM) were transformed and CF removal efficiency of more than 96% was achieved, with influent CF concentrations up to 16.74 μM. Serum bottle reactor tests were conducted using the culture from the chemostat with an average VSS concentration of 259 mg/l. These tests showed that the culture exhibited a maximum rate of CF transformation of 16.3 μM/h corresponding to an initial CF concentration of 22.6 μM. The culture degraded CF primarily by reductive dehalogenation leading to the formation of DCM which degraded at a very slow rate compared to CF. No inhibition of acetic acid utilization was observed in the culture for CF concentrations as high as 29.3 μM. Compared to no acetic acid addition, acetic acid at 50 mg/l considerably increased the rate of CF transformation but further increase in acetic acid concentration to 200 mg/l did not affect the rate of CF biotransformation. Additional acclimation of the culture for 1 yr did not affect the rate of transformation of CF. The results indicate that the sulfate-reducing culture has much higher rates of CF transformation than a methanogenic culture, also grown on acetic acid at the same concentration.