Factors Affecting Nitrite Buildup in Submerged Filter System

Abstract

The accumulation of the nitrification intermediate, nitrite, is undesirable because of its toxicity to fish. The elevated nitrite concentration in wastewater‐treatment processes significantly increases the amount of chlorine required for disinfection. Consequently, environmental and operational factors of hydraulic and ammonium loading rates as well as pH and alkalinity were evaluated for their effects on the accumulation of nitrite in a fixed‐film submerged filter system. Elevated nitrite levels were observed at higher hydraulic (5 L/d·cm²) and ammonium loading rates (0.7 kg N/d·m²), $\mathrm{pH}=8.8$ and low alkalinity/ammonium ratio $(6\mathrm{mg}{\mathrm{CaCO}}_3/\mathrm{mg}{\mathrm{NH}}_4^{+}‐N)$. Addition of 2.5–5 mg N/L hydroxylamine, an intermediate in the ammonium oxidation to nitrite, also significantly enhanced the accumulation of nitrite concentration. The inhibitory effect of hydroxylamine on Nitrobacter was irreversible.