Improving performance and efficiency of partial anammox by coupling partial nitrification and partial denitrification (PN/A-PD/A) to treat municipal sewage in a step-feed reactor

[Display omitted] •PN/A-PD/A was efficiently realized in typical UCT process to treat municipal sewage.•TIN in influent and effluent were 51.3 and 11.0 mg/L even with COD/TIN ratio of 2.9.•Anammox activity improved from 6.52 to 9.68 mg NH4+-N/gMLSS/d with abundance raised.•Anammox contributed 47% for NRE with two coupled ways for continuous supply of NO2–. Improving contribution and nitrogen removal efficiency (NRE) of partial anammox in municipal wastewater is a researching hotspot. This study developed an innovative PN/A-PD/A process with fixed biocarriers in anaerobic/anoxic chambers for actual sewage treatment in a typical step-feed reactor over 390 days. Two coupled pathways providing continuous NO2– (partial nitrification in oxic chambers and partial denitrification in anaerobic/anoxic chambers) for anammox were introduced to the process, achieving 47% nitrogen loss by anammox in stable phase. The influent and effluent total inorganic nitrogen (TIN) were 51.3 and 11.0 mg/L, respectively, even with chemical oxygen demand (COD)/TIN ratio of 2.9. Anammox activity improved from 6.52 to 9.68 mg NH4+-N/gMLSS/d and abundance on the biocarriers raised to 3.16 × 1010 gene copies/g dry sludge. Overall, this study confirmed partial anammox, spatially coupled with partial nitrification and partial denitrification via oxic/anoxic distribution with step feed mode, as an alternative for application of mainstream anammox.