Bioaugmentation for low C/N ratio wastewater treatment by combining endogenous partial denitrification (EPD) and denitrifying phosphorous removal (DPR) in the continuous A2/O - MBBR system

Abstract

Endogenous partial denitrification (EPD) and denitrifying phosphorous removal (DPR) were combined in a novel A2/O - MBBR (Anaerobic Anoxic Oxic - Moving Bed Biofilm Reactor) system for low carbon/nitrogen (C/N) ratio wastewater treatment. The DPR performance was compared and the nutrient metabolism was elucidated based on the optimization of hydraulic retention time (HRT, 4–12 h) and nitrate recycling (R, 200%–600%). In the continuous-flow, the nitrate (NO3−) denitrification accompanied by nitrite (NO2−, via EPD) accumulation with the nitrate-to-nitrite transformation ratio (NTR) of 35.87%–43.31% in the anoxic zones. At HRT of 12 h with R of 500%, batch test initially revealed the DPR mechanism using both NO3− and NO2− as electron acceptor, where denitrifying phosphorus accumulation organisms (DPAOs) and denitrifying glycogen accumulation organisms (DGAOs) were the main contributors for EPD with incomplete denitrification (NO3− → NO2−). Furthermore, stoichiometry-based functional bacteria analysis displayed that higher bioactivity of DPAOs (NO2−→N2, 57.30%; NO3−→N2, 35.85%) over DGAOs (NO3−→N2, 6.85%) facilitated the anoxic NO3− reduction. Microbial community analysis suggested that Cluster I of Defluviicoccus-GAO group (∼4%) was responsible for stable NO2− accumulation performance via EPD, while increased Accumulibacter-PAO group (by ∼15%) contributed to the advanced nutrient removal. Based on the achievement of NO2− accumulation, the application feasibility of integrated EPD - DPR - Anammox for deep-level nutrient removal was discussed.