Biotransformation rates of chloroform under anaerobic conditions—I. Methanogenesis

Abstract

Biotransformation of chloroform (CF) was studied in a methanogenic environment utilizing acetic acid as the primary substrate. CF removal efficiency of more than 99% was achieved in a chemostat, fed constant acetic acid concentration (2510 mg/l) and different CF concentrations, up to 16.74 μM. Biological methane potential tests were conducted in serum bottles using the culture from the chemostat with an average biomass concentration of 53 mg/l. The culture exhibited a maximum rate of CF transformation of 0.26 μM/h corresponding to an initial CF concentration of 1.25 μM. At initial CF concentrations higher than 2.76 μM, the rate of CF transformation became constant at 0.06 μM/h. CF present at any concentration inhibited the utilization of acetic acid, and at CF concentrations equal to or exceeding 2.7 μM, the culture was completely inhibited and no acetic acid was utilized by the culture even after the CF was completely degraded. The culture transformed CF without the addition of acetic acid, but the addition of acetic acid considerably increased the rate of biotransformation. However, increase in acetic acid concentration beyond 50 mg/l did not increase the rate. The culture exhibited higher rates of CF biotransformation when it was acclimated with higher influent concentration of CF in a chemostat. Reductive dehalogenation was one of the pathways for the transformation of CF leading to the formation of dichloromethane which was also transformed by the culture.