Optimization of Biological Nitrogen Removal over Nitrite in the Presence of Lipid Matter by Regulation of Operational Modes

Abstract

Optimization of total nitrogen (TN) removal via the nitrite path was studied at a sequential batch reactor (SBR) from anaerobic reject water (ARW) with a content of slowly degrading organic matter of lipid structure. The study was conducted as a pilot-scale side-line treatment in a large-scale municipal and industrial wastewater treatment plant (WWTP). Operational mode was modified based on feeding pattern, sequence order, phase duration, and number to maximize TN removal and minimize lipid-related interferences. Ammonium loading rate (ALR) proceeded at 0.2–0.7 kg N/m3 · day and the optimum range was determined for maximum TN removal. An insufficient HCO3−/N ratio was further lowered by volatile fatty acids (VFA) production via beta-oxidation of long-chain fatty acids (LCFA) during nitritation. The organic content of ARW and VFA showed a low degradability by denitrifying bacteria and limited TN removal. Modifications in the operational mode increased ammonium and nitrite removal and reduced toxic-free VFA and nitrous acid (FNA) with increased anoxic and aerobic denitritation. Ammonium nitrogen at 180–478 mg N/L was reduced to approximately 20 mg N/L in all effluents and TN removal was achieved at 84–86%. Temperature sensitivity was higher for denitritation than nitritation.