Insights into impact of tire additives on activated sludge systems: Treatment performance, extracellular polymeric substances, and microbial community.

Seasonal temperature variations significantly impact biological wastewater treatment performance, particularly affecting extracellular polymeric substance (EPS) composition and sludge settling characteristics in activated sludge systems. This study investigated the temperature-induced EPS response mechanisms and their effects on nitrogen removal efficiency in a full-scale modified Bardenpho wastewater treatment plant, combined with laboratory-scale evaluation of EPS-optimizing microbial agents for performance enhancement. Nine-month seasonal monitoring revealed that when the wastewater temperature dropped below 15 °C, the total nitrogen (TN) removal efficiency decreased from 86.5% to 80.6%, with a trend of significantly increasing polysaccharides (PS) in dissolved organic matter (DOM) and loosely-bound EPS (LB-EPS) and markedly decreasing tightly-bound EPS (TB-EPS). During the low-temperature periods, when the sludge volume index (SVI) exceeded 150 mL/g, deteriorated settling performance could primarily be attributed to the reduced TB-EPS content and increased LB-EPS accumulation. Microbial community analysis showed that EPS secretion-promoting genera of Trichococcus, Terrimonas, and Defluviimonas increased during the temperature recovery phase rather than initial temperature decline phase. Laboratory-scale experiments demonstrated that EPS-optimizing microbial agents dominated by Mesorhizobium (54.2%) effectively reduced protein (PN) and PS contents in LB-EPS by 70.2% and 54.5%, respectively, while maintaining stable nutrient removal efficiency. These findings provide mechanistic insights into temperature–EPS interactions and offer practical technology for improving winter operation of biological wastewater treatment systems.

Tuning pH to motivate chain reaction of iron release with extracellular polymeric substances formation for long lasting Fe0-driven autotrophic denitrification.

Nitrogen removal enhancement using lactic acid fermentation products from food waste as external carbon sources: Performance and microbial communities

Zero valent iron supported biological denitrification for farmland drainage treatments with low organic carbon: Performance and potential mechanisms

Perfluorooctanoic acid (PFOA), an emerging organic contaminant frequently detected in wastewater, inhibits biological nitrogen removal processes, posing challenges to sustainable wastewater treatment. Mitigating the adverse effects of PFOA while enhancing total nitrogen (TN) removal efficiency remains a critical concern. In this study, three sequencing batch biofilm reactors (SBBRs) were operated under low-oxygen conditions with a C/N ratio of 4.0 to investigate enhanced nitrogen removal under PFOA stress using biochar. Compared to the 78.1% TN removal efficiency in the control reactor (SBBR-0) with an initial TN concentration of 50 mg/L, the addition of PFOA decreased TN removal by 2.3% in SBBR-1, while the combined addition of PFOA and biochar increased it by 3.2% in SBBR-2. Biochar, acting through its electron-donating surface functional groups, mitigated PFOA-induced reactive oxygen species accumulation and increased adenosine triphosphate production. These effects promoted the generation of quorum sensing (QS) signaling molecules, facilitating microbial communication and cooperation. Consequently, the relative abundance of key nitrogen-removing bacteria, such as Thauera (from 7.90% to 9.92%) and Nitrosomonas (from 1.42% to 5.75%), increased, leading to enhanced nitrogen removal efficiency. A metagenomic analysis revealed that biochar significantly reduced the production of antibiotic resistance genes without promoting their dissemination. These findings provide new insights into mitigating the negative effects of PFOA and improving TN removal through QS promotion, offering a potential approach for enhancing the sustainability of wastewater treatment systems.

Membrane bioreactor using a submerged hollow fiber membrane was applied in laboratory scale conditions to treat household wastewater including toilet-flushing water. The bioreactor was aerated intermittently to alternate anoxic/oxic conditions while membrane filtration occurred during the aeration period to take advantage of the air bubbles for fouling control. After being operated for about 150 days, the initial flux and suction pressure were maintained almost constant at 0.01m hr−1 and 4-6 kPa, respectively, indicating fouling control by air bubbling was very effective. With 10-15 hour hydraulic retention time (HRT), and a very long solid retention time (SRT), 97% of Total chemical oxygen demand (TCOD) and 100% suspended solids (SS) could be removed. On average, removal efficiencies for total nitrogen (TN) and total phosphorus (TP) were 83% and 55% respectively. Ammonia and coliform bacteria were completely removed. Due to the long SRT and sufficient oxygen supply, fast and complete nitrification was accomplished regardless of operational mode, and denitrification was the rate-limiting step. Results from track study revealed that the initial specific denitrification rate (SDNR) varied between 0.6 and 1.8 mg g−1VSS hr−1. Endogenous SDNR was found to be 0.35-0.51 mg g−1VSS hr−1. Nitrogen removal was controlled mainly by the value of BOD/TN of the influent. However, the role of endogenous denitrification was relatively significant under the high mixed liquor volatile suspended solid (MLVSS) condition, making the system more robust to the fluctuation of external carbon supply. The anoxic/oxic cycle of 60/90 minutes with an hydraulic retentin time (HRT) of 10 hrs appears to be an appropriate choice for the process.

This study investigates the nitrogen removal pathways and microbial community dynamics in a novel system coupling simultaneous nitrification and denitrification (SND) with sulfur autotrophic denitrification (SAD) for the treatment of mariculture tailwater. High-throughput sequencing and predictive functional analysis were employed to examine microbial compositions and their functional roles across varying carbon-to-nitrogen (C/N) ratios. The results revealed that SND occurred in the aerobic stage, with Nitrosomonas and Nitrospira facilitating nitrification, while Denitromonas and Paracoccus drove denitrification. In the anaerobic stage, SAD was the primary nitrogen removal process, with sulfur metabolism supported by Thiobacillus and Desulfobacteria. Increasing C/N ratios enriched denitrifying bacteria, enhancing nitrogen removal performance, but reduced nitrifying activity. Functional gene analysis demonstrated the upregulation of denitrification genes (napAB, nirS, norBC, nosZ) with higher carbon inputs, while sulfur metabolism genes (sqr, soxB, dsrAB) confirmed the critical role of sulfur cycling in SAD. The integration of SND and SAD pathways, supported by carbon addition, achieved efficient nitrogen removal, while promoting sulfur bioavailability. Under C/N ratios of 1.2, the nitrate nitrogen (NO3−-N) removal efficiencies reached 93.48%, respectively, while the total nitrogen (TN) removal efficiencies were 95.06%. Ammonia nitrogen (NH4+-N) removal efficiency consistently exceeded 95%, stabilizing at 99.00% in the steady-state operation. This research provides a comprehensive understanding of the microbial and functional mechanisms underlying SND–SAD systems, offering an innovative solution for sustainable mariculture tailwater management.

Microbial fuel cells (MFCs) can use nitrate as a cathodic electron acceptor for electrochemical denitrification, yet there is little knowledge about how to apply them into current wastewater treatment process to achieve efficient nitrogen removal. In this study, two dual-chamber MFCs were integrated with an aerobic membrane bioreactor to construct a novel membrane bioelectrochemical reactor (MBER) for simultaneous nitrification and denitrification under specific aeration. The effects of chemical oxygen demand (COD) loading rate, COD/N ratio, hydraulic retention time (HRT), and external resistance on the system performance were investigated. High effluent quality was obtained in the MBER in terms of COD and ammonium. During the operation, denitrification simultaneously occurred with nitrification at the bio-cathode of the MBER, achieving a maximal nitrogen removal efficiency of 84.3%. A maximum power density of 1.8W/m3 and a current density of 8.5A/m3 were achieved with a coulombic efficiency of 12.1%. Furthermore, compared to the control system, the MBER exhibited lower membrane fouling tendency due to mixed liquor volatile suspended solids (MLVSSs) and extracellular polymeric substance (EPS) reductions, EPSp/EPSc ratio decrease, and particle size increase of the sludge. These results suggest that the MBER holds potential for efficient nitrogen removal, electricity production, and membrane fouling mitigation.

ABSTRACTA coupled system of membrane bioreactor-nitritation (MBR-nitritation) and up-flow anaerobic sludge blanket-anaerobic ammonium oxidation (UASB-ANAMMOX) was employed to treat mature landfill leachate containing high ammonia nitrogen and low C/N. MBR-nitritation was successfully realized for undiluted mature landfill leachate with initial concentrations of 900–1500 mg/L and 2000–4000 mg/L chemical oxygen demand. The effluent concentration and the accumulation efficiency were 889 mg/L and 97% at 125 d, respectively. Half-nitritation was quickly realized by adjustment of hydraulic retention time and dissolved oxygen (DO), and a low DO control strategy could allow long-term stable operation. The UASB-ANAMMOX system showed high effective nitrogen removal at a low concentration of mature landfill leachate. The nitrogen removal efficiency was inhibited at excessive influent substrate concentration and the nitrogen removal efficiency of the system decreased as the concentration of mature landfill leachate increased. The MBR-nitritation and UASB-ANAMMOX processes were coupled for mature landfill leachate treatment and together resulted in high effective nitrogen removal. The effluent average total nitrogen concentration and removal efficiency values were 176 mg/L and 83%, respectively. However, the average nitrogen removal load decreased from 2.16 to 0.77 g/(L d) at higher concentrations of mature landfill leachate.

Performance and mechanisms of nitrogen removal from low-carbon source wastewater in an iron-carbon coupled biofilm airlift internal circulation sequencing batch reactor

Low carbon and phosphorus concentrations were controlled to investigate their influences on nitrogen removal in activated sludge reactors. Results demonstrated that when the initial COD/NH 4 +-N (C/N) ratio was adjusted to 4/1, NH 4 +-N removal efficiency achieved the maximum value of 93.0%. With the rising of C/N ratio, total nitrogen (TN) removal efficiencies increased gradually while NH 4 +-N removal efficiencies had slight downward trend. When the C/N ratio was 10/1, TN removal efficiency in the system reached the maximum value of 64.2% comparing to those at C/N ratios of 8/1, 6/1 and 4/1. However, TN removal efficiencies decreased with the reduction of total phosphorus concentration in the influent at constant C/N ratio. When the C/P ratio varied from 100/1 to 100/0.6, TN removal efficiencies declined a little. When the C/P ratio decreased to 100/0.4, TN removal efficiencies reduced dramatically. In general, low carbon level had little impact on NH 4 +-N removal efficiency, just adverse to total nitrogen removal efficiency which was low at C/N ratio of 4/1. Low phosphorus concentration had a significant negative effect on NH 4 +-N and total nitrogen removal efficiency. Low phosphorus concentration had significant negative effect on NH 4 +-N and total nitrogen removal efficiency which even resulted in sludge bulking.

Low organic carbon‐to‐nitrogen ratio and existing sulfate (SO42−) in industrial wastewater limited nitrogen removal. Coupling SO42− reduction with sulfide autotrophic denitrification provides a novel strategy. Herein, bioelectrochemical sulfate reduction was coupled with heterotrophic sulfate reduction to drive sulfide autotrophic denitrification. In this coupled system, total nitrogen (TN) removal efficiency was increased from ~25% to ~85% by inputting −45 mA electricity. With the help of supplying electrons to denitrification through SO42− reduction, coulomb efficiency was improved to 61.5%. Also, bioelectrochemical sulfate reduction could improve sulfur recovery and thus increase TN removal efficiency. Furthermore, through tuning turnover numbers of SO42−, high TN removal efficiency can be obtained at various concentrations of SO42−. Moreover, main functional bacteria in this system were identified. Finally, ~75% TN removal efficiency was achieved with real wastewater in this system. Overall, this work offered a new approach for efficient nitrogen removal from industrial wastewater containing SO42−.

Enhanced nitrogen removal and mitigation of nitrous oxide emission potential in a lab-scale rain garden with internal water storage

The role of beneficial microorganisms in an anoxic-oxic (AO) process for treatment of ammonium-rich landfill leachates: Nitrogen removal and excess sludge reduction

Although the role of extracellular polymeric substances (EPSs) as a viscous high-molecular polymer in biological wastewater treatment has been recognized, in-depth knowledge of how EPSs affect nitrogen removal remains limited in biofilm-based reactors. Herein, we explored EPS characteristics associated with nitrogen removal from high-ammonia (NH4+-N: 300 mg/L) and low carbon-to-nitrogen ratio (C/N: 2–3) wastewater in a sequencing batch packed-bed biofilm reactor (SBPBBR) under four different operating scenarios for a total of 112 cycles. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier-transform infrared (FTIR) analysis revealed that the distinct physicochemical properties, interface microstructure, and chemical composition of the bio-carrier were conducive to biofilm formation and microbial immobilization and enrichment. Under the optimal conditions (C/N: 3, dissolved oxygen: 1.3 mg/L, and cycle time: 12 h), 88.9% ammonia removal efficiency (ARE) and 81.9% nitrogen removal efficiency (NRE) could be achieved in the SBPBBR. Based on visual and SEM observations of the bio-carriers, biofilm development, biomass concentration, and microbial morphology were closely linked with nitrogen removal performance. Moreover, FTIR and three-dimensional excitation–emission matrix (3D-EEM) spectroscopy demonstrated that tightly bound EPSs (TB-EPSs) play a more important role in maintaining the stability of the biofilm. Significant shifts in the number, intensity, and position of fluorescence peaks of EPSs determined different nitrogen removal. More importantly, the high presence of tryptophan proteins and humic acids might promote advanced nitrogen removal. These findings uncover intrinsic correlations between EPSs and nitrogen removal for better controlling and optimizing biofilm reactors.