Combined effects of volume ratio and nitrate recycling ratio on nutrient removal, sludge characteristic and microbial evolution for DPR optimization.

The optimization of volume ratio (VAn/VA/VO) and nitrate recycling ratio (R) in a two-sludge denitrifying phosphorus removal (DPR) process of Anaerobic Anoxic Oxic-Moving Bed Biofilm Reactor (A2/O-MBBR) was investigated. The results showed that prolonged anaerobic retention time (HRTAn: 1.25→3.75 hr) exerted favorable effect on chemical oxygen demand (COD) removal (57.26%→73.54%), poly-ß-hydroxyalkanoates (PHA) synthesis (105.70→138.12 mgCOD/L) and PO43- release (22.3→38.9 mg/L). However, anoxic retention time (HRTA) and R exhibited positive correlation with PHA utilization (43.87%-81.34%) and denitrifying phosphorus removal (DPR) potential (ΔNO3-/ΔPO43-: 0.57-1.34 mg/mg), leading to dramatical TN removal variations from 68.86% to 81.28%. Under the VAn/VA/VO ratio of 2:6:0, sludge loss deteriorated nutrient removals but the sludge bioactivity quickly recovered when the oxic zone was recovered. The sludge characteristic and microstructure gradually transformed under the dissolved oxygen (DO) control (1.0-1.5→1.5-2.0 mg/L), in terms of sludge volume index (SVI: 194→57 mL/gVSS), median-particle-size (D50: 99.6→300.5 µm), extracellular polymeric substances (EPS) (105.62→226.18 mg/g VSS) and proteins/polysaccharides (PN/PS) ratio (1.52→3.46). Fluorescence in situ hybridization (FISH) results showed that phosphorus accumulation organisms (PAOs) (mainly Cluster I of Accumulibacter, contribution ratio: 91.79%-94.10%) dominated the superior DPR performance, while glycogen accumulating organisms (GAOs) (mainly Competibacter, contribution ratio: 82.61%-86.89%) was responsible for deteriorative TN and PO43- removals. The optimal HRTA and R assembled around 5-6.5 hr and 300%-400% based on the PHA utilization and DRP performance, and the oxic zones also contributed to PO43- removal although it showed low dependence on DO concentration and oxic retention time (HRTO).

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 ± 2℃). 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 â†’ 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.

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 (AAO - MBBR), nitritation was practicable through the combined regulation of high temperature (T: 30-32 °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% â†’ 2.35%) gradually outcompeted Nitrobacter (1.19% â†’ 0.31%) under higher temperature. During the transition from nitration to nitritation, the DPR potential (characterized by ΔPO43-/ΔNOx-) increased by 11.90% while the energy requirement of poly-ß-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.

Nutrient metabolism, mass balance, and microbial structure community in a novel denitrifying phosphorus removal system based on the utilizing rules of acetate and propionate.

The effect of acetate (HAc) and propionate (HPr) on denitrifying phosphorus removal (DPR) was evaluated in a novel two-sludge A2/O - MBBR (anaerobic/anoxic/oxic - moving bed biofilm reactor) system. Results showed that it was the carbon source transformation and utilization especially the composition of poly-ß-hydroxyalkanoates (PHA) (mainly poly-ß-hydroxybutyrate (PHB) and poly-bhydroxyvalerate (PHV)) decided DPR performance, where the co-exist of HAc and HPr promoted the optimal nitrogen (85.77%) and phosphorus (91.37%) removals. It facilitated the balance of PHB and PHV and removing 1 mg NO3- (PO43-) consumed 3.04-4.25 (6.84-9.82) mgPHA, where approximately 40-45% carbon source was saved. Mass balance revealed the main metabolic pathways of carbon (MAn,C (consumed amount in anaerobic stage) and MA-O,C (consumed amount in anoxic and oxic stages): 66.38-76.19%), nitrogen (MDPR,N (consumed amount in DPR): 57.01-65.75%), and phosphorus (MWS,P (discharged amount in waste sludge): 81.05-85.82%). Furthermore, the relative abundance and microbial distribution were assessed to elucidate DPR mechanism (e.g. Accumulibacter, Acinetobacter, Dechloromonas, Competibacter, and Defluviicoccus) in the A2/O reactor and nitrification performance (e.g. Nitrosomonas, Nitrosomonadaceae and Nitrospira) in the MBBR. Carbon source was demonstrated as the key point to stimulate the biodiversity and bioactivity related to DPR potential, and the operational strategy of carbon source addition was proposed based on the utilizing rules of HAc and HPr.

Elucidating sludge characteristic, substrate transformation and microbial evolution in a two-sludge denitrifying phosphorus removal system under the impact of HRT.

Granule formation has been recognized as a promising biotechnology in denitrifying phosphorus removal (DPR) systems by facilitating phosphorus accumulation organisms (PAOs) especially denitrifying PAOs (DPAOs), and hydraulic selection made this a more difficult task in continuous operation. This study aimed at exploring the microscopic mechanism and putting forward an effective strategy for DPR granulation under the impact of hydraulic retention time (HRT) (12 h, 10 h, 8 h) in a novel Anaerobic Anoxic Oxic - Moving Bed Biofilm Reactor (A2/O - MBBR) system. With the reduction of intracellular carbon storage (CODintra) efficiency (88.58%-78.53%), nitrogen (N) (85.45%-79.11%) and phosphorus (P) (96.55%-92.47%) removals both dropped, but it exhibited a growth of anoxic phosphorus uptake rate (PURA) (3.79-5.68 mg P/(gMLVSS·h)). The batch tests associating with substrate transformation of poly-ß-hydroxyalkanoates (PHA), glycogen (Gly) agreed well with the corresponding stoichiometry of phosphorus release rate (PRR) (4.83-7.53 mg P/(gMLVSS·h)), PURA (3.55-5.43 mg P/(gMLVSS·h)), oxic phosphorus uptake rate (PURO) (6.08-6.21 mg P/(gMLVSS·h)), and DPAOs/PAOs ratios (57.17%-89.31%), indicating a shift of microbial community. DPR granules gradually stabilized with low sludge volume index (SVI5/SVI30 ratio = 1.1-1.2), dense and compact structure, higher P content (11.63%), more extracted extracellular polymeric substances (EPS) (111.40-160.31 mg/gMLVSS) as proteins/polysaccharides (PN/PS) ratios (1.70-3.47) increased, leading to better sludge settleability and cell hydrophobicity. Fluorescence in situ hybridization (FISH) results showed that PAOs (mainly Cluster I: 20.20%) were the dominant bacteria in the A2/O reactor although a small amount of Defluviicoccus (3.18-3.48%) was responsible for nitrite accumulation, while ammonium-oxidizing bacteria (AOB) (mainly Nitrosomonas: 10.75%) and nitrite-oxidizing bacteria (NOB) (mainly Nitrospira: 15.06%) were enriched in the MBBR.