Effect of phenol and acetate addition on 2-chlorophenol consumption by a denitrifying sludge

Chlorophenols are widely distributed in the environment. Various strategies have been used to improve their biological elimination under anaerobic conditions; however, such information is still scarce. The aim of this study was to evaluate in batch assays the consumption of 2-chlorophenol (2-CP) by a denitrifying sludge and the influence of acetate or phenol as co-substrates in the 2-CP consumption. It was observed that phenol (69 and 92 mg phenol-C L-1) and acetate (60 and 108 mg acetate-C L-1) enhanced 2-CP consumption by the denitrifying sludge, increasing both the efficiency (up to 100%) and specific rate of 2-CP consumption. When phenol was added at 92 mgC L-1, the specific consumption rate of 2-CP increased 2.6 times with respect to the control lacking co-substrates, whereas with acetate (108 mgC L-1) the increase was 9.0 times. Acetate appeared to be a better co-substrate for 2-CP consumption, obtaining a specific consumption rate of 2.48 +/- 0.14 mg 2-CP-C g(-1) VSS d(-1) at 108 mg acetate-C L-1. The mass balance analysis indicated that the denitrifying sludge was able to simultaneously mineralize 2-CP, phenol or acetate (E2-CP, E-Phenol, and E-Acetate close to 100% [E = consumption efficiency], YHCO3- of 0.90 +/- 0.10 [Y = yield]) and reduce nitrate to nitrogen gas (ENO3- of 100% and Y-N2 of 0.96 +/- 0.02). It was shown that the addition of co-substrates as phenol or acetate could be a good alternative for improving the elimination of chlorophenols from wastewaters by denitrifying sludges.