Pilot-scale ultrastable nitritation in municipal wastewater based on the loading rate switch strategy

This is the authors' abstract. We don't add key points for this paper.

In the present work, quick start-up ultrastable nitritation was successfully demonstrated in a pilot-scale sequencing batch reactor (SBR; V = 6.5 m3) treating real municipal wastewater (5.9°C–29.8°C). The SBR was operated under a high influent loading rate by aggressively discharging surplus sludge and controlling a short aeration time, resulting in a significant decrease of both ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) abundances. Subsequently, the influent loading rate sharply dropped from 312 mg COD/(g VSS∙d) to 55 mg COD/(g VSS∙d) with the extension of aeration time. According to qPCR and batch test results, the AOB abundance increased 106-fold and 136% of its initial bioactivity level was recovered. The NOB abundance was maintained at a low level, resulting in incomplete nitrification and nitrite accumulation. Nitritation with an ultra-high nitrite accumulation ratio (NAR) of 97% started in seven days. Moreover, despite the decrease of temperature from 17.5°C to 5.9°C, a high NAR (98.1 ± 1.1%) was maintained for over 450 days. The NOB abundance was below the detection level, and a high AOB (Nitrosomonas; 0.95%) level was effectively maintained. Importantly, the average levels of ammonium and nitrite effluents were maintained at 8.3 mg N/L and 13.8 mg N/L, respectively, favoring the application of an anammox process. Therefore, the proposed nitritation start-up strategy provides a practical alternative for extending anammox into sewage treatments.