Municipal wastewater treatment with limited carbon sources: The significance and advantages of transformation from partial denitrification to partial nitrification coupling with anammox

Anaerobic ammonium oxidation (anammox) combined with partial nitrification (PN) is expected to achieve energy self-sufficiency in wastewater treatment, while its advantages have not been fully revealed. An anaerobic/aerobic/anoxic (AOA) system was established to treat low chemical oxygen demand (COD)-total inorganic nitrogen (TIN) (C/N) ratio (3.08) municipal wastewater. Anammox bacteria were enriched from 7 × 106 to 3 × 108 copies/gSS during partial denitrification coupling with anammox (PDA) phase. With the PN achievement, the anammox hotspot zone transformed from the anoxic zone through PDA (37%) to the aerobic zone by partial nitrification coupled with anammox (PNA) (12%). As the nitrite accumulation rate increased to 97%, the TIN removal efficiency and rate increased to 95% and 0.12 kgN/(m3·d). Although anammox performance weakened after this transformation, the carbon sources saved by PN drove more nitrogen removal. PNA was beneficial for advanced and efficient nitrogen removal in carbon-limited wastewater treatment and was less dependent on higher anammox contribution.