Rapid initiation and stable maintenance of municipal wastewater nitritation during the continuous flow anaerobic/oxic process with an ultra-low sludge retention time

Rapid achievement of nitritation of mainstream municipal wastewater in a continuous-flow process is attractive since it favors the involvement of the anammox process and reduces the operational costs. In this study, a feasible and economical strategy is proposed to rapidly achieve the nitritation of municipal wastewater. By aggressively discharging excess sludge during the seasonal warming period (temperature increasing from 18 degrees C to 22 degrees C), nitritation was established in 15 days with a nitrite accumulation ratio of 85.09% in a continuous-flow anaerobic/oxic (An/O) reactor. Meanwhile, qPCR results revealed that amoA abundance increased from (1.78 +/- 0.10) x10(8) copies/(g VSS) to (1.05 +/- 0.11) x 10(10) copies/(g VSS) while the abundance of nitrite-oxidizing bacteria decreased from (1.1 +/- 0.02) x10(10) copies/(g VSS) to (5.01 +/- 0.02) x10(8) copies/(g VSS). The temperature gradually stabilized at 26 degrees C during the following operational period and stable nitritation was maintained with a nitrite accumulation ratio above 90%, which was mainly attributed to a short sludge retention time (SRT) of 4.3 days and a low dissolved oxygen of 0.86 +/- 0.5 mg/L. Falling temperature negatively impacted the stability of nitritation, but nitritation could be restarted by aggressively discharging excess sludge during another temperature increase period. Overall, this study provides a feasible strategy to start-up nitritation that has great potential applications for municipal wastewater treatment. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study proposes a feasible and economical strategy to rapidly achieve nitritation of municipal wastewater by aggressively discharging excess sludge during the seasonal warming period, which leads to the establishment and maintenance of stable nitritation. The results provide potential applications for municipal wastewater treatment.