Nitrogen Removal via Nitrite from Municipal Wastewater at Low Temperatures using Real-Time Control to Optimize Nitrifying Communities

TLDR

Nitrogen removal via nitrite has been studied, but few investigations focus on low‑temperature conditions. The study aimed to enhance nitrogen removal from municipal wastewater by testing a 54 m³ sequencing batch reactor at both normal and low temperatures. The reactor’s performance was monitored by fluorescence in situ hybridization to track changes in nitrifying microbial communities. High nitrogen removal (<3 mg N/L) was achieved, with stable nitrite‑based removal over 180 days and >95 % nitrite accumulation, driven by a shift to ammonia‑oxidizing bacteria dominance and loss of nitrite oxidizers.

Abstract

Although many studies regarding nitrogen removal via nitrite have been carried out, very limited research has been undertaken on nitrogen removal via nitrite at low temperatures. In this study, to improve the nitrogen removal efficiency from municipal wastewater, a pilot-plant of sequencing batch reactor with a working volume of 54 m3 was used to investigate nitrogen removal via nitrite from municipal wastewater at normal and low water temperature. The obtained results showed that high nitrogen removal efficiency with effluent total nitrogen below 3 mg/L could be achieved. Using real-time control with temperature ranging from 11.9 to 26.5 °C under normal dissolved oxygen condition (≥2.5 mg/L), nitrogen removal via nitrite was successfully and stably achieved for a long period (180 days) with average nitrite accumulation rate above 95%. Fluorescence in situ hybridization was carried out to investigate the quantitative changes of nitrifying microbial community in the activated sludge. Fluorescence in situ hybridization results approved that the nitrifying microbial communities were optimized; ammonia oxidizing bacteria became the dominant nitrifying bacteria and nitrite oxidizing bacteria had been washed out of the activated sludge.