4-Nitrophenol Biodegradation in a Sequencing Batch Reactor Operating with Aerobic−Anoxic Cycles

The study regards 4-nitrophenol removal performed in a lab-scale sequential batch reactor with an integrated aerobic−anoxic cycle. The purpose of the study was to examine the kinetics of 4-nitrophenol biological oxidation and denitrification in order to test the feasibility of the proposed technological solution for xenobiotic removal. The results obtained show that high removal efficiency of 4-nitrophenol is easily achieved when the compound is fed into the reactor as the sole carbon source. Residual concentrations of 4-nitrophenol and nitrous/nitric nitrogen in the effluent lower than 1 mg L-1 were observed in the range of applied feed concentration (200−320 mg L-1). Low concentrations of dissolved oxygen (≤2 mg L-1) in the feed and aerobic phases lead to appreciable simultaneous denitrification. As regards the denitrification process, while no carbon-limiting effects were observed at COD/N ratios ≥ 3, a significant decrease in the rate of denitrification is detected for COD/N ratios ≤ 2. The denitrification rate obtained in tests with no external carbon addition proved very low and unsuitable for practical application. A model of the denitrification process taking into account both the limiting effect of nitrogen and carbonaceous substrate has been proposed and applied for experimental data correlation.