Performance of partial denitrification (PD)-ANAMMOX process in simultaneously treating nitrate and low C/N domestic wastewater at low temperature

The simultaneous treatment of nitrate (NO3−-N ∼ 50 mg L−1) and domestic wastewater (ammonia (NH4+-N) ∼ 60.6 mg L−1, COD ∼ 166.3 mg L−1) via a novel partial denitrification (PD)-ANaerobic AMMonium OXidation (ANAMMOX) process was investigated at low temperature (12.9 ∼ 15.1 °C). Results showed that desirable performance was achieved with average NO3−-N, NH4+-N and COD removal efficiencies of 89.5%, 97.6% and 78.7%, respectively. However, deteriorated sludge settleability in PD reactor was observed during operation, which bulked with serious sludge wash-out, leading to excess NO3−-N remaining in PD effluent. Fortunately, a satisfactory nitrogen removal was still achieved due to the occurrence of partial denitrification in ANAMMOX reactor. This was demonstrated by high-throughput sequencing, which revealed that the high nitrite (NO2−-N) production denitrifying bacteria of Thauera was detected (6.1%). ANAMMOX (above 70%) maintained the dominant pathway for nitrogen removal, and Candidatus Jettenia was identified as the major ANAMMOX species accounted for 2.7%.