Nitrite production mechanism and microbial evolution characteristic influenced by pH during partial denitrification (PD) process

Abstract

Partial denitrification (PD) has been proved technically feasible and economically favorable to produce nitrite (NO2--N) for anammox. To obtain stable NO2--N accumulation, the effects of pH (6.0, 7.5, 9.0, 10.0) on nutrient removal mechanism and microbial community evolution were investigated. Higher pH benefited PD performance with the optimal NO2--N and nitrate-to-nitrite transformation ratio (NTR) reaching to 43.50 mg/L, 81.64% at pH= 9.0 although slight NO2--N inhibition occurred caused by biomass loss and proton deficiency at pH= 10.0. Batch testes showed the same change trends of NTR (pH=9.0 >pH=7.5 >pH=6.0 >pH=10.0), where pH and oxidation reduction potential (ORP) also proved the “NO2--N knee” as pH varied around 7.5–9.0. The denitrification kinetic proved the closely relationship among carbon consumption rate (CCR), poly-β-hydroxyalkanoates transformation rate (PTR), NO2--N accumulation rate (N2AR), NO2--N reduction rate (N2RR) and nitrate (NO3--N) reduction rate (N3RR) although COD release, nitrogen loss and floc disintegration were observed under different pH conditions. Meanwhile, more aggregated microbial compositions formed (562–605 OTUs) at the optimal pH range of 7.5–9.0, where Terrimonas, norank_f_A4b, Defluviicoccus, Hyphomicrobium, norank_f_Blastocatellaceae, and OLB13 were the main contributors for NO2--N maintenance, with the proportions accounting for 35.29–39.60%.