Development of an anoxic nitrification-denitrification process in a granulated nanoscale oxyhydroxides of Fe packed bed reactor for the simultaneous removal of NH4+-N and COD

Abstract

A simultaneous anoxic nitrification-denitrification process was developed for the removal of NH4+-N and COD from synthetic wastewater with COD/NH4+-N ratio of 0.5 representing a fertilizer effluent, using Granulated Nanoscale Oxyhydroxides of Fe (GNOF) as electron acceptor. Seed biomass, procured from the aeration tank of a common effluent treatment plant treating combined tannery effluent, was used to develop the process in an anoxic GNOF packed bed reactor and the NH4+-N and COD removal efficiency was tested. The operation was carried out for 260 days in three different phases at Hydraulic Retention Time (HRT) of 1 d by varying the influent COD and NH4+-N concentrations, while COD/NH4+-N ratio was maintained as 0.5. Removal of 64.12 ± 3.05 % of NH4+-N, 62.01 ± 3.41 % of TN, and 40.80 ± 17.08 % of COD was achieved at NH4+-N loading rate of 100 ± 6 mg/L/d. After closing the operation of continuous reactor, batch studies were conducted to understand the kinetics of NH4+-N removal, effect of GNOF, biomass, and influent NH4+-N concentrations on NH4+-N removal using the biomass and GNOF obtained from the reactor. The results showed a second order kinetics with rate constant of 0.0023 L mg−1 h−1. Optimum NH4+-N removal was obtained at 214 g (GNOF)/L and increases in direct proportion to the concentration of biomass. The developed nano-biotechnological process shows the potential for economical treatment of fertilizer effluent having up to 250 mg/L NH4+-N with less COD in the absence of external addition of air and chemicals in contrast to conventional nitrification-denitrification process.