Prediction and optimization of partial denitrification and anammox performance by machine learning and key bioindicators identification.

Effect of elemental sulfur on anaerobic ammonia oxidation: Performance and mechanism

Enhanced nitrogen and carbon removal performance of simultaneous ANAMMOX and denitrification (SAD) process with trehalose addition treating saline wastewater was investigated in a sequencing batch reactor (SBR). The optimal nitrogen removal was achieved at 0.25 mmol·L-1 trehalose, during which NH4+-N, NO2--N, NO3--N, and COD could be completely removed. Compared to no addition of trehalose, ammonium removal efficiency (ARE), nitrite removal efficiency (NRE) and total nitrogen removal efficiency (TNRE) increased by 50%, 43% and 46%. Ammonium removal rate (ARR) and nitrite removal rate (NRR) increased by 81.25% and 75%, respectively. With increasing concentration of trehalose to 0.5 mmol·L-1, ARE was only 58.82% and the effluent concentration of NH4+-N was 33.25 mg·L-1. Compared to the Haldane model and the Aiba model, the Luong model was the most suitable to simulate the nitrogen removal performance of SAD with trehalose addition treating saline wastewater. The NRRmax, KS, Sm, and n fitted from Luong model were 0.954 kg·(m3·d)-1, 0 mg·L-1, 184.785 mg·L-1, and 0.718, respectively. Compared to the modified Logistic model and the modified Boltzman model, the modified Gompertz model was the most suitable to describe the degradation of a substrate in a single cycle.

A biological nitrogen removal model was established by AQUASIM software to model the autotrophic nitrogen removal performance of membrane aerated biofilm (MAB). The effects of biofilm thickness, hydraulic retention time (HRT) and influent ammonia concentration on microbial community and total nitrogen (TN) removal efficiency were investigated. The results show that the large biofilm thickness of counter-diffusion MAB contributed to the small proportion of AOB and low TN removal efficiency. It is worth noting that the TN removal efficiency reached 84% when the membrane thickness was 500 μm. Regarding with the HRT and influent ammonia nitrogen concentration, the low influent ammonia nitrogen concentration and HRT resulted in the high TN removal efficiency. The influent ammonia nitrogen concentration of 450 mg/L and HRT of 5.5 days contributed to the highest TN removal efficiency of 87%.

A novel post-denitrification system fed by carbon source from primary sludge (PS) was used for enhancing biological nitrogen removal (BNR) of low C/N wastewater. This system included one anoxic/oxic (AO) reactor and a special reactor for simultaneous sludge fermentation and denitrification (Sifeden). Ammonia was nitrified to nitrate in AO and then the nitrate was reduced to dinitrogen in Sifeden , into which PS was added intermittently. Results showed that this system had high performance on nitrogen removal. Total nitrogen (TN) removal efficiency was higher than 85% and the effluent TN≤10mg/L in the condition of influent C/N≤2. In Sifeden, volatile fatty acid (VFA) produced from PS fermentation provided electron donor for nitrate reduction, and PS was preliminarily stabilized simultaneously. Oxidation-Reduction Potential (ORP) had a significant correlation with the denitrification performance. TN removal efficiency could be further improved if adopting proper PS addition strategy according to the ORP profiles.

This study uses three different operating phases for a sequencing batch reactor (SBR) combined with an anaerobic baffled reactor (ABR) to determine the effect of deep nitrogen and carbon removal by the "partial nitrification-anaerobic ammonium oxidation combined denitrification" (termed PN-SAD) reaction. The effluent of the SBR (NO2--N/NH4+-N ratio range of 1-1.32) was accessed directly to the single compartment ABR anammox system in phase Ⅰ. The results showed that although the anammox reaction was stable, the combined process total nitrogen (TN) removal efficiency was<80%, and the TN concentration of effluent was~20 mg·L-1. In order to increase the denitrification function in the ABR, denitrifying sludge was added to the third compartment of the ABR in phase Ⅱ. We found that the TN removal efficiency of the coupling reaction was still low. An organic carbon source should be supplied in the latter stage of anammox if deep nitrogen removal is required. Therefore, in phase Ⅲ, the effluent of the SBR (NO2--N/NH4+-N ratio of ~5) was mixed with the partial raw water (mixed water NO2--N/NH4+-N ratio of ~1.4; C/N ratio of 2.5). The mixed water was connected to the single compartment of the ABR. The PN-SAD system not only achieved a good matrix ratio at the anammox stage, but also provided a good carbon source for denitrification. The chemical oxygen demand (COD) concentration of the effluent in the whole process was 50 mg·L-1, the TN concentration of the effluent was<6 mg·L-1, and the TN removal efficiency was 95%. We conclude that the stable operation of the combined PN-SAD reaction provides the basis for deep nitrogen and carbon removal using the combined SBR-ABR process.

Sulfide promotes nitrogen removal in anammox low-strength ammonium wastewater treatment system

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−.

Biomass retention and microbial segregation to offset the impacts of seasonal temperatures for a pilot-scale integrated fixed-film activated sludge partial nitritation-anammox (IFAS-PN/A) treating anaerobically pretreated municipal wastewater

Integrating network and in-silico simulation insights into the ecological interactions shaped by carbon sources in partial denitrification and anammox system.

Effect of zinc on anammox activity and performance of simultaneous partial nitrification, anammox and denitrification (SNAD) process

Highly efficient and synchronous nitrogen removal from ammonia-rich wastewater and domestic wastewater via a novel anammox coupled with double-nitrite-shunt process at low temperature

Advantages of partial denitrification-anaerobic ammonium oxidation system under sulfamethoxazole stress: Adaptive mechanisms and synergistic metabolism.

Membrane distillation as post-treatment for anaerobic fluidized bed membrane bioreactor for organic and nitrogen removal

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.