Enhanced Efficiency of Nitritating-Anammox Sequencing Batch Reactor Achieved at Low Decrease Rates of Oxidation–Reduction Potential

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The nitritation–anaerobic ammonium oxidation (anammox) process was studied for the first time using an oxidation–reduction potential (ORP) decrease rate control in the anammox sequencing batch reactor (SBR). SBR was inoculated and fed with high-strength N-rich real reject wastewater (containing an average of 740 mg NH4+-N/L) coming from a biogas plant. Start-up with total nitrogen removal rates (TNRRs) of 90 g N/[m3·day] (87 mg N/g VSS/day) was achieved shortly at 25°C within a 132-day operation period. However, during a further 470-day operation with ORP control using aeration “switch off” values in the aerobic and “switch on” values in the anoxic phase, much higher TNRRs of 220 g N/[m3·day] were achieved with maximum total nitrogen removal efficiency at 95%. The ORP decrease rate as a novel anammox treatment step shortening the control parameter was gradually decreased at values of 1.65, 0.9, and 0.4 mV/min ensuring a high TNRR and low accumulation of ammonium and nitrate. Batch testing showed the highest specific anammox activities of 4.4 (±1.8) mg N/g VSS/h at ORP decrease rates of 0.4 mV/min. Low optimum dissolved oxygen concentrations of up to 0.5 mg O2/L could reduce treatment costs in anammox full-scale systems in combination with ORP control. Among other microorganisms determined by pyrosequencing, anammox bacteria, Candidatus Brocadia fulgida and uncultured Planctomycetales bacterium clone P4 were determined and the latter bacterium's increase in quantities from 2.8 × 104 up to 1.6 × 106 copies/g TSS during ORP-controlled conditions were examined using a quantitative polymerase chain reaction.

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