Deep-level nutrient removal and denitrifying phosphorus removal (DPR) potential assessment in a continuous two-sludge system treating low-strength wastewater: The transition from nitration to nitritation

In a continuous two-sludge denitrifying phosphorus removal (DPR) process of anaerobic anoxic oxic - moving bed biofilm reactor (MO - MBBR), nitritation was practicable through the combined regulation of high temperature (T: 30-32 degrees C), short hydraulic retention time (HRT: 8 h) and low dissolved oxygen (DO: 1.0-1.5 mg/L).The system lasted for 90 days with stable nitrite accumulation ratio (NAR > 60%), and the total inorganic nitrogen (TIN) removal was 7% higher than complete nitrification. Ammonia oxidizing bacteria ((AOB) 6.18-9.41%) responsible for nitritation showed a clear relationship with NAR, but Nitrospira (2.11% -> 2.35%) gradually outcompeted Nitrobacter (1.19% -> 0.31%) under higher temperature. During the transition from nitration to nitritation, the DPR potential (characterized by Delta PO43-/Delta NOx-) increased by 11.90% while the energy requirement of poly-beta-hydroxyalkanoates (PHA) and glycogen (Gly) decreased by 12.58% and 14.50%, respectively, contributing to higher TIN (84.83%) and TP (97.45%) removals. DPR batch tests using different electron acceptors (NO3- .vs. NO3- + NO2-) revealed that removing 1 mg PO43- only consumed 7.12 +/- 0.25 mg PHA via NO3- + NO2- (.vs. 8.50 +/- 0.12 mg PHA via NO3-) and 16% carbon source was saved although the DPR capability was suppressed as NO2- concentration exceeded 15 mg/L. Based on the achievement of nitritation, the feasibility of integrated DPR - Anammox in the AAO - MBBR system for deep-level nutrient removal was discussed. (C) 2020 Elsevier B.V. All rights reserved.