Nitrite accumulation and microbial behavior by seeding denitrifying phosphorus removal sludge for partial denitrification (PD): The effect of COD/NO3- ratio

Effect of influent COD/NO3- ratios (2.0-5.0) on partial denitrification (PD, NO3- to NO2-) was investigated by seeding denitrifying phosphorus removal (DPR) sludge at ambient temperature (16 +/- 2celcius). At COD/NO3- ratio of 2.5, the optimal NO2- effluent and nitrate-to-nitrite transformation ratio (NTR) reached up to 27.18 mg/L and 82.18%, respectively, and nitrate removal efficiency (NRE) (59.34 -> 97.98%) showed positive relationship with increasing COD/NO3- ratios. The variations were further illustrated by denitrification kinetics, where faster COD degradation (1.55 g COD/(gVSS.d)), more NO3- consumption (0.55 gN/(gVSS.d)) and higher NO2- production (0.52 gN/(gVSS.d)) were observed although the NO2- peaks happened at anoxic 30 min. Microbial analysis showed lower community diversity and more concentrated composition with dominated genera Thauera (14.10%), Terrimonas (9.40%), Saprospiraceae (13.50%) and Flavobacterium (28.23%) at COD/NO3- ratio of 2.5. Based on the achievement of PD, the application feasibility of integrated PD-DPR-Anammox in a two-sludge DPR system for deep-level nutrient removal was discussed.

Automated summary

The study investigated the effect of influent COD/NO3- ratios on partial denitrification, showing that higher ratios led to improved denitrification efficiency and nitrate removal. Microbial analysis indicated lower diversity and more concentrated microbial communities at a specific COD/NO3- ratio.