Achieving partial denitrification using carbon sources in domestic wastewater with waste-activated sludge as inoculum.

Partial denitrification (PD, nitrate → nitrite) using carbon sources in domestic wastewater with waste-activated sludge as inoculum was firstly achieved in this study. Through controlling influent pH at about 9.0 and anoxic reaction time of 1 h in the start-up, the nitrite (NO2--N) production reached as high as 25.2 mg/L, with influent nitrate (NO3--N) of about 30 mg/L and chemical oxygen demand (COD) to NO3--N ratio of 5.9. Furthermore, PD performance remained stable without pH control during subsequent operations. Efficient NO2--N production was closely related to the consumed amount of readily biodegradable COD (Ss) fraction, with optimal Ss/NO3--N ratio of about 3.5. Thauera (19.1%), norank_f__Xanthomonadaceae (5.2%), and Thiobacillus (5.0%) were enriched during the 208-day operation, which may be responsible for high NO2--N production. These findings provided a novel strategy for promoting mainstream PD/Anammox application, without additional nitrite-accumulating denitrifying sludge and external carbon sources.