2-Chlorophenol consumption by cometabolism in nitrifying SBR reactors

Cometabolic consumption of 2-chlorophenol (2-CP) by a nitrifying sludge was evaluated in two SBR reactors fed with 60 mg 2-CP-C/L and different initial ammonium concentrations (100, 200, 300, 400, and 500 mg NH4+-N/L). Irrespectively to the increase in ammonium concentration and throughout the operational cycles, the sludge achieved a complete nitrification in 14 days, accounting for ammonium consumption efficiencies close to 99% and nitrate production yields between 0.93 and 0.99. The sludge was able to completely consume 2-CP within 7 days. The increase in ammonium concentration provoked an increment in the specific rates of both ammonium (qNH4+-N) and 2-CP (q2-CP-C) consumption up to 5.2 and 3.1 times, respectively. The cometabolic effect of the increase in ammonium concentration on 2-CP consumption was supported by a direct and significant relationship between the qNH4+-N and q2-CP-C (r = 0.83). Moreover, batch assays conducted with ammonium, 2-CP, allylthiourea as specific inhibitor of the ammonium monooxygenase (AMO) enzyme, and the sludge inoculated into the reactors, resulted in a decrease of 34% in q2-CP-C, evidencing the participation of the AMO in the consumption of 2-CP. When the same assays were carried out with the sludge obtained from the SBR reactors after 13 operating cycles, a higher participation of the AMO in 2-CP consumption was noticed with a decrease of 53% in q2-CP-C. According to these results, the use of nitrifying sludge and high ammonium concentrations in SBR systems can be a suitable alternative for increasing the cometabolic consumption of recalcitrant compounds like 2-CP.