Reductive dechlorination of chlorophenols in methanogenic cultures

Anaerobic biodegradation of a group of 12 chlorophenols (2-CP; 3-CP; 4-CP; 2,3-DCP; 2,6-DCP; 3,4-DCP; 3,5-DCP; 2,3,6-TCP; 2,4,5-DCP; 2,3,4,6-TeCP; 2,3,5,6-TeCP; and PCP) was examined in an unacclimated digester sludge culture and in a phenol-enriched, 2-CP and 3-CP acclimated methanogenic culture. The phenol-enriched culture degraded all chlorophenols except 4-CP, whereas the digester sludge culture did not degrade PCP or 2,3,4,6-TeCP. Dechlorination products were observed in the phenol-enriched culture but not in the fresh sludge. Based on the observed dechlorination products, degradation pathways for chlorophenols in the phenol-enriched culture were proposed. The phenol-enriched culture degraded chlorophenols at much higher rates than the digester sludge by dechlorinating at the ortho and meta positions. In both cultures, the rate of degradation depended on the number as well as the ring position of chlorine substituents. Higher rates were generally observed with ortho dechlorination and for compounds with lower numbers of chlorine substituents. The average rate of degradation did not vary significantly between mono- and dichlorophenols or between triand tetrachlorophenols. Analysis with the Haldane expression revealed that the phenol-enriched culture was less susceptible to inhibition caused by chlorophenols and that it possessed a higher affinity for substrate than the digester sludge culture.