Biomass retention and microbial segregation to offset the impacts of seasonal temperatures for a pilot-scale integrated fixed-film activated sludge partial nitritation-anammox (IFAS-PN/A) treating anaerobically pretreated municipal wastewater

Partial nitritation-anammox (PN/A) is a promising deammonification process to develop energy-neutral waste-water treatment plants. However, the mainstream application of PN/A still faces the challenges of low nitrogen concentration and low temperatures, and has not been studied under a realistic condition of large-scale reactor (kiloliter level), real municipal wastewater (MWW) and seasonal temperatures. In this research, a pilot-scale one -stage PN/A, with integrated fixed-film activated sludge (IFAS) configuration, was operated to treat the real MWW pretreated by anaerobic membrane bioreactor. The removal efficiency of total nitrogen (TN) was 79.4%, 75.7% and 65.9% at 25, 20 and 15 degrees C, corresponding to the effluent TN of 7.3, 9.7 and 12.0 mg/L, respectively. The suppression of ammonium-oxidizing bacteria (AOB) and anammox bacteria (AnAOB) occurred at lower temperatures, and the significant decrease in AOB treatment capacity was the reason for the poorer nitrogen removal at 15 degrees C. Biomass retention and microbial segregation were successfully achieved. Specifically, Candi-datus_Brocadia and Candidatus_Kuenenia were main AnAOB genera and mainly enriched on carriers, Nitro-somonas and uncultured f_Chitinophagaceae were main AOB genera and mainly distributed in suspended sludge and retained by sedimentation tank. Moreover, nitrite-oxidizing bacteria (NOB) were sufficiently suppressed by intermittent aeration and low dissolved oxygen, the presence of heterotrophic bacteria upgraded the PN/A to a simultaneous partial nitritation, anammox, denitrification, and COD oxidation (SNADCO) system, which improved the overall removal of TN and COD. The results of this investigation clearly evidence the strong feasibility of PN/A as a mainstream nitrogen removal process in temperate climates.

Automated summary

Partial nitritation-anammox (PN/A) is a promising energy-neutral wastewater treatment process. However, the mainstream application of PN/A still faces challenges of low nitrogen concentration and low temperatures. In this study, a pilot-scale one-stage PN/A with an integrated fixed-film activated sludge (IFAS) configuration was successfully operated to treat real municipal wastewater. The results demonstrate the strong feasibility of PN/A as a mainstream nitrogen removal process in temperate climates.