Reactors R2 and R3 were investigated for biodegradation of 1,1,2-Trichloroethane and 1,1,2,2-Tetrachloroethane respectively, during acclimation phase. Reactor R1 was maintained as control. The stepwise increment in concentration of 1,1,2-TCA from 5 mg/L to 40 mg/L in R2 caused no inhibition to reactor performance. The percentage of 1,1,2-TCA and COD removal was 99.9% and 98.6%, respectively. Severe inhibition to methanogenesis occurred at 30 mg/L of 1,1,2,2-TeCA, showing decrease in percentage COD removal to 45.5%, reduction in biogas production by 45?60% and increase in effluent VFA concentration to 172 mg/L. The sludge in R3 was acclimated upto 20 mg/L of 1,1,2,2-TeCA.The percentage of 1,1,2,2-TeCA and COD removal was 99.1% and 98.2%, respectively.

Keywords: acclimation, biodegradation, UASB reactors, upflow anaerobic sludge blanket, 1,1,2-TCA, 1,1,2-Trichloroethane, 1,1,2,2-TeCA, 1,1,2,2-Tetrachloroethane, wastewater treatment