Intensified nitrogen removal by endogenous denitrification in a full-scale municipal wastewater treatment plant

Flexible Carbon Source Regulation for Mitigating Greenhouse Gas Emissions in Full-Scale Wastewater Treatment

Achieving carbon neutrality in wastewater treatment plants (WWTPs) by 2060 requires effective strategies to mitigate greenhouse gas (GHG) emissions. This study explores the potential of flexible carbon source regulation to reduce GHG emissions while improving the nutrient removal efficiency under varying influent conditions. A plant-wide model was developed, calibrated with one year of hourly monitoring data, to quantify GHG emissions in a full-scale WWTP. We evaluated three carbon regulation strategies: anaerobic digestion (AD), short fermentation (SF), and adaptive carbon source regulation (ACSR). Results show that AD was most effective in high carbon-to-nitrogen (C/N) ratios, reducing GHG emissions by 29.2%. SF performed best at low C/N ratios, reducing N2O emissions by 56.3%. The ACSR strategy, which dynamically adjusts between AD and SF based on influent C/N, achieved a total GHG reduction of 18.2% compared with the base strategy (conventional activated sludge process with mechanical dewatering and landfill disposal of waste sludge). Seasonal variations significantly impacted emissions (p < 0.001), while C/N ratios, although not statistically significant in isolation, play a crucial role in influencing N2O emissions and sludge production, emphasizing the need for adaptive carbon allocation. This study underscores the viability of plant-wide, data-driven carbon source regulation as an integrated approach to achieving net-zero emissions in WWTPs, effectively addressing diverse GHG emission sources within the system.

Achieving advanced nitrogen removal from oxytetracycline wastewater by partial nitrification-endogenous denitrification: performance, metabolic pathways, microorganism community, and potential applications

Partial nitrification-endogenous denitrification (PNED) can achieve advanced nutrient removal from wastewater. Herein, an anaerobic/oxic/anoxic/oxic-sequencing batch reactor (AOAO-SBR) was used to treat real oxytetracycline (OTC) pharmaceutical wastewater via PNED. Partial nitrification with an average nitrite accumulation ratio of 91.5 % was achieved. When the influent total nitrogen was 105 ± 10 mg/L, the effluent of it was only 5.9 mg/L, and the removal efficiency was 94.8 %. In the typical cycle, multiple nitrogen removal pathways including endogenous denitrification, simultaneous nitrification-denitrification, and denitrification contributed to 68.0 %, 20.3 %, and 7.3 %. The effluent concentration of NH4+-N was 5 mg/L, and NO2--N and NO3--N were not detected. The biodegradation pathways of OTC were proposed, 47.1 % of OTC was degraded and eight possible degradation byproducts were detected with low toxicity in the extracellular and intracellular. Moreover, Extracellular polymeric substances increased from 35.3 (mg/gVSS) to 74.4 (mg/gVSS) during 120 days, which acts as a critical role in OTC degradation. High-throughput sequencing results showed that the relative abundance of ammonia-oxidizing bacteria was 2.4 %, and nitrite-oxidizing bacteria were washed out, which was conducive to partial nitrification. Candidatus_Competibacter (13.9 %) enhanced nitrogen removal by endogenous denitrification. Thauera (13.5 %), Ottowia (9.2 %), and OLB13 (1.2 %) are the main OTC-degrading bacteria. This study provides a valuable reference to treat OTC pharmaceutical wastewater effectively.

Efficient nitrogen and phosphorus removal performance and microbial community in a pilot-scale anaerobic/anoxic/oxic (AOA) system with long sludge retention time: Significant roles of endogenous carbon source

Stringent wastewater discharge standards require wastewater treatment plants (WWTPs) to focus on enhancing nitrogen (N) and phosphorus (P) removal efficiency. Increasing sludge concentration by regulation of sludge retention time (SRT) would enhance wastewater treatment loads. However, phosphorus-accumulating organisms (PAOs) would be outcompeted by glycogen-accumulating organisms (GAOs) under long SRT, leading to a collapse of P removal. In this work, pilot-scale anaerobic-oxic-anoxic (AOA) and anaerobic-anoxic-oxic (AAO) systems with long SRT (30 d) were parallelly established for actual urban wastewater treatment. The results indicated that sludge reflux ratio, temperature, and C/N ratio significantly impact N and P removal performance of AOA and AAO systems with long SRT, and removal efficiency of AOA system significantly exceeded that of AAO system. AOA system with long SRT achieved the optimal performance at sludge reflux ratio of 200%, temperature of 25 °C, and C/N ratio of 8, with COD, NH4+-N, TN, and PO43--P removal ratio of 92.80 ± 2.24%, 97.38 ± 0.89%, 88.97 ± 2.47%, and 94.33 ± 3.27%, respectively. In addition, compared to AAO system, AOA system could save 23.08% of the aeration volume. This work highlighted that AOA system with long SRT included multiple coupled nitrogen and phosphorus removal pathways, such as autotrophic/heterotrophic nitrification, anoxic/oxic denitrification, endogenous denitrification, and denitrifying phosphorus removal. Among these, the synergistic effect of endogenous denitrification and denitrifying phosphorus removal driven by internal carbon sources contributed to satisfactory nitrogen and phosphorus removal efficiency in AOA system with long SRT.

Integrated process of Tetrasphaera-dominated in-situ waste activated sludge fermentation, biological phosphorus removal and endogenous denitrification in single reactor for treatment of wastewater with limited carbon sources

An integrated process of sludge in-situ fermentation, biological phosphorus removal and endogenous denitrification (ISFPR-ED) was developed to treat low ratio of chemical oxygen demand to nitrogen (COD/N) wastewater and waste activated sludge (WAS) in a single reactor. Nutrient removal and WAS reduction were achieved due to Tetrasphaera-dominated sludge fermentation provided organic carbon in extending the anaerobic duration. The WAS reduction efficiency, effluent orthophosphate (PO43--P) and total inorganic nitrogen reached 28.1 %, less than 0.4 and 7.2 mg/L, respectively. While organic carbon was reduced by 67 %. Tetrasphaera, conventional polyphosphate accumulating organisms (PAOs) stored glycogen, amino acids, and PHA for nutrient removal. Excess energy from fermentation enhanced anaerobic PO43--P uptake by Tetrasphaera. Tetrasphaera was the dominant PO43--P removal and fermentation bacteria, working synergistically with conventional PAOs and fermenting microorganisms. This integrated process improves nutrient removal efficiency and reduces operating costs for carbon addition and WAS disposal in wastewater treatment.

First application of the novel anaerobic/aerobic/anoxic (AOA) process for advanced nutrient removal in a wastewater treatment plant

The stringent effluent quality standards in wastewater treatment plants (WWTPs) can effectively mitigate environmental issues such as eutrophication by reducing the discharge of nutrients into water environments. However, the current wastewater treatment process often struggles to achieve advanced nutrient removal while also saving energy and reducing carbon consumption. The first full-scale anaerobic/aerobic/anoxic (AOA) system was established with a wastewater treatment scale of 40,000 m3/d. Over one year of operation, the average TN and TP concentration in the effluent of 7.53 ± 0.81 and 0.37 ± 0.05 mg/L was achieved in low TN/COD (C/N) ratio (average 5) wastewater treatment. The post-anoxic zones fully utilized the internal carbon source stored in pre-anaerobic zones, removing 41.29 % of TN and 36.25 % of TP. Intracellular glycogen (Gly) and proteins in extracellular polymeric substances (EPS) served as potential drivers for post-anoxic denitrification and phosphorus uptake. The sludge fermentation process was enhanced by the long anoxic hydraulic retention time (HRT) of the AOA system. The relative abundance of fermentative bacteria was 31.66 - 55.83 %, and their fermentation metabolites can provide additional substrates and energy for nutrient removal. The development and utilization of internal carbon sources in the AOA system benefited from reducing excess sludge production, energy conservation, and advanced nutrient removal under carbon-limited. The successful full-scale validation of the AOA process provided a potentially transformative technology with wide applicability to WWTPs.

Ultra-high nitrogen removal from real municipal wastewater using selective enhancement of glycogen accumulating organisms (GAOs) in a partial nitrification-anammox (PNA) system

Integrating endogenous denitrification (ED) into partial nitrification-anammox (PNA) systems by adequately utilizing organics in municipal wastewater is a promising approach to improve nitrogen removal efficiency (NRE). In this study, a novel strategy to inhibit phosphorus-accumulating organisms (PAOs) by inducing phosphorus release and exclusion was adopted intermittently, optimizing organics allocation between PAOs and glycogen-accumulating organisms (GAOs). Enhanced ED-synergized anammox was established to treat real municipal wastewater, achieving an NRE of 97.5±2.2% and effluent total inorganic nitrogen (TIN) of less than 2.0 mg/L. With low poly-phosphorus (poly-P) levels (poly-P/VSS below 0.01 (w/w)), glycogen accumulating metabolism (GAM) acquired organics exceeded that of phosphorus accumulating metabolism (PAM) and dominated endogenous metabolism. Ca. Competibacter (GAO) dominated the community following phosphorus-rich supernatant exclusion, with abundance increasing from 3.4% to 5.7%, accompanied by enhanced ED capacity (0.2 to 1.4 mg N/g VSS /h). The enriched subgroups (GB4, GB5) of Ca. Competibcater established a consistent nitrate cycle with anammox bacteria (AnAOB) through endogenous partial denitrification (EPD) at a ∆NO₂^--N/∆NH₄⁺-N of 0.91±0.11, guaranteeing the maintenance of AnAOB abundance and performance. These results provide new insights into the flexibility of PNA for the energy-efficient treatment of low-strength ammonium wastewater.

Balance nitrogen and phosphorus efficient removal under carbon limitation in pilot-scale demonstration of a novel anaerobic/aerobic/anoxic process

Nutrient removal in carbon limited wastewater with high efficiency and energy saving remains a bottleneck for wastewater treatment plants (WWTPs). This study established a pilot-scale anaerobic/aerobic/anoxic (AOA) system with processing capacity of 100 m³/d for the first time. During almost 300 days of stable operation, enhanced nitrogen and phosphorus removal at a C/N of 5 was achieved, and the concentrations of total nitrogen (TN) and total phosphorus (TP) in effluent were 3.60 ± 1.55 and 0.24 ± 0.13 mg/L. Tetrasphaera and Candidatus Competibacter were the dominant phosphorus accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs) in the AOA system. Moreover, the low phosphorus release ensured sufficient intracellular carbon storage by endogenous denitrification, which was the critical factor for nitrogen and phosphorus removal in carbon limited wastewater. The denitrification phosphorus removal (DPR) ability further removed phosphorus and prevented secondary phosphorus release to maintain a low phosphorus concentration in effluent. Finally, rapid start-up, high nutrient removal efficiency and low energy consumption make the proposed AOA process suitable for application in newly constructed and renovated WWTPs.