Wastewater

Volatile suspended solids

Engineering

Sewage treatment

Ecology

Bacteria

Biology

Anammox

Denitrification

Activated sludge

Nitrogen

Heterotroph

Genetics

Environmental engineering

Organic chemistry

Anoxic waters

Environmental chemistry

Biomass (ecology)

Effluent

Environmental science

Denitrifying bacteria

Chemistry

Pulp and paper industry

Water Research

This study proposes a novel strategy of stably enriching anammox in mainstream, based on the competitive difference to NO2− between anoxic biofilms and suspended sludge. A modified anaerobic-anoxic-oxic (A2/O) process run for 500 days with actual municipal wastewater. Microbial analysis revealed that anoxic-carrier biofilms had a significantly higher abundance of anammox (qPCR: 0.74% – 4.34%) than suspended sludge (P< 0.001). Batch tests showed that anammox within anoxic-carrier biofilms contributed to significant nitrogen removal, coupled with partial-denitrification (NO3− → NO2−). The anammox genus, Ca. Brocadia, was highly enriched when suspended sludge was accidentally lost. Further batch tests found that reducing suspended biomass helped anammox enrichment in anoxic-carrier biofilms, because the suspended sludge had strong NO2− competition (NO2− → N2) with anammox (increased nirK). Metagenomic sequencing revealed that Ca. Brocadia dominates in the anoxic-carrier biofilms, and is the most important narG contributor to NO3− → NO2−, which could have promoted the competition of NO2− with heterotrophic bacteria. For this A2/O process, the low effluent total nitrogen (8.9 mg ± 1.0 mg N/L) was attributed to partial-denitrification coupling with anammox, demonstrating that this process is applicable to the general influent N-concentration range (30 mg – 50 mg NH4+-N/L) of municipal wastewater treatment plants (WWTPs). Based on the special competitive preference of anammox for NO2−, this study provides a promising and practical alternative for enriching anammox bacteria in municipal WWTPs.

Highly enriched anammox within anoxic biofilms by reducing suspended sludge biomass in a real-sewage A2/O process