Degradation of 2-chlorophenol via a hydrogenotrophic biofilm under different reductive conditions

This research studies the 2-chlorophenol (2-CP) degradation by the hydrogenotrophic biofilm cultivated in three silicone-tube membrane bioreactors under the conditions of denitrification (DN), sulfate-reduction (DS) and dechlorination (DC). Experimental results showed that after acclimation for more than four months with 2-CP, the respective 2-CP removal efficiency was 95% in DN, 94% in DS and 95% in DC reactors, under the condition of influent 2-CP 25 mg/l with hydraulic retention time (HRT) of 15 h. The metabolic pathway of 2-CP was different in different reactors. The 2-CP was thought to be utilized as carbon and energy source in DN and DS reactors, while the dechlorination occurred in the DC reactor in lack of nitrate and sulfate. The pH dramatically affected the 2-CP degradation in all reactors. Experimental results showed that the optimal pH range was around 6+/-0.2 in DN, 7+/-0.2 in DS, and 5.8-7.2 in DC reactors. Both nitrate and sulfate inhibited the 2-CP dechlorination, but the inhibition levels were different. Nitrate completely inhibited the dechlorination at once, while sulfate took a longer time to reach complete inhibition, only after the bacteria were adapted to the sulfate-reducing condition. Both inhibitions were accomplished by taking the place of 2-CP as electron acceptors. H2 served as an electron donor for dechlorination of 2-CP. The dechlorination was apparently stopped when lacking H2 and another pathway was responsible for the 2-CP degradation.