Sludge Pretreatment by Combined Aerobic Ammonium Starvation and Oxygen Restriction to Simultaneously Suppress Nitrite-Oxidizing Bacteria and Heterotrophs for Rapid Start-Up of Partial Nitrification

Partial nitrification is crucial for achieving carbon- and energy-efficient nitrogen removal. This study introduces a sludge pretreatment strategy based on ammonium starvation and dissolved oxygen (DO) restriction for rapid start-up of partial nitrification. The 10 day pretreatment under the DO (1-2 mg/L) restriction and ammonium starvation condition was the most efficient, with nitrite-oxidizing bacteria (NOB) activity decreased by 46.5% and unrestorable, respectively. Though ammonium-oxidizing bacteria (AOB) activity decreased by 64.3% as well after the 10 day pretreatment, a 7 day reactivation allowed for a 101.1% restoration of AOB activity. Prolonging the pretreatment time to 20 days further exacerbated inhibition on AOB with the activity halved. Based on the increased organic release and the identification of tryptophan protein, the combination of ammonium starvation and DO restriction accelerated heterotrophic bacterial death and lysis, with the biomass concentration decreased by 59.8% and autotrophic proportion increased by 24.4% within 10 days. The pretreatment caused a 53.1% decrease in the abundance of only NOB Nitrospira and less than 13.5% decrease in total AOB abundance. Partial nitrification was successfully started within 13 days using the 10 day pretreated sludge. This study provides a valuable reference for promoting the application of partial nitrification in wastewater nitrogen removal.