Effects of the carbon/nitrogen (C/N) ratio on a system coupling simultaneous nitrification and denitrification (SND) and denitrifying phosphorus removal (DPR)

Carbon Source in Tertiary Denitrification Regulates Dissolved Organic Nitrogen in Wastewater Effluent

With global eutrophication and increasingly stringent nitrogen discharge restrictions, dissolved organic nitrogen (DON) holds considerable potential to upgrade advanced wastewater denitrification because of its large contribution to low-nitrogen effluents and stronger stimulation effect for algae. Here, we show that DON from the postdenitrification systems dominates effluent eutrophication potential under different carbon sources. Methanol resulted in significantly lower DON concentrations (0.84 ± 0.03 mg/L) compared with the total nitrogen removal-preferred acetate (1.11 ± 0.02 mg/L) (p < 0.05, ANOVA). With our well-developed mathematical model (R2 = 0.867-0.958), produced DON instead of shared (persist in both influent and effluent) and/or removed DON was identified as the key component for effluent DON variation (Pearson r = 0.992, p < 0.01). The partial least-squares path modeling analysis showed that it is the microbial community (r = 0.947, p < 0.01) rather than the predicted metabolic functions (r = 0.040, p > 0.1) that affected produced DON. Carbon sources rebuild the microorganism-DON interaction by affecting the structure of microbial communities with different abilities to generate and recapture produced DON to finally regulate effluent DON. This study revalues the importance of carbon source selection and overturns the current rationality of pursuing only the total nitrogen removal efficiency by emphasizing DON.

Greywater treatment in SBR-SND reactor - optimization of hydraulic retention time, volumetric exchange ratio and sludge retention time

In this study, simultaneous nitrification and denitrification-sequencing batch reactor (SND-SBR) process was investigated to treat greywater. The effect of three process parameters, including hydraulic retention time (HRT), volumetric exchange ratio (VER) and sludge retention time (SRT), was optimised using a 23 full factorial design. The statistic model was developed for two response variables, i.e. chemical oxygen demand (COD) and ammonia (NH3-N) removal. The optimum conditions were 6.8 h HRT (anaerobic/aerobic/anoxic: 1.77 h/2.77 h/2.27 h), 0.7 VER and 7.94 d SRT, which resulted in 93.9% COD and 84.6% NH3-N removal efficiency. SRT was the most significant factor, followed by HRT and VER for COD and NH3-N removal. The interaction effect of VER and SRT was significant in COD removal. On the other hand, the interaction effects of HRT-VER and HRT-SRT were significant in NH3-N removal. The removal efficiencies of 89.6 ± 1.1% and 83.7 ± 2.3% were observed for TKN and TN, respectively, in the optimised SND-SBR system. NH3-N removal was obtained via nitrate pathway in the SND-SBR system. The PO43--P removal of 74.2 ± 3.4% was obtained via aerobic phosphorus uptake and post anoxic denitrification at the optimal condition. To enhance PO43--P removal, adsorption (using corn cob adsorbent) was integrated with SBR by adding the optimum adsorbent dose (0.5 g/L). The PO43--P removal efficiency in the SBR-adsorption system was found to be 80 ± 1.5%. The biodegradation of emerging contaminants (ECs) was also carried out in the SND-SBR system, and the results showed removal rate of 58.9 ± 2.3% benzophenone-3 (BP) and 80.1 ± 2.2% anionic surfactant (AS).

Modification of a plant-scale semi-centralized wastewater treatment system to enhance nitrogen and phosphorus removal from black water

Owing to the low ratio of chemical oxygen demand to total nitrogen (SCOD/TN), effective removal of nutrient pollutants from black water is difficult. In this study, to enhance nitrogen and phosphorus removal from such wastewater, a series of operational modification strategies was investigated and applied to a plant-scale semi-centralized system used for black water treatment. The results showed that 21 mg Fe³⁺/L was the optimal dosage for the chemical-enhanced pretreatment process, achieving average removal efficiencies of 51.1 and 74.1% for organics and phosphorus, respectively, with a slight enhancement in nitrogen removal by 2.3%. However, nitrogen and phosphorus removal could be further enhanced to 88 and 96%, by the addition of carbon sources in the post-anoxic zone of the reversed anaerobic-anoxic-aerobic process. Contrastingly, neither the addition of carbon sources in the pre-anoxic zone nor the prolongation of the time for pre-denitrification could significantly improve the nitrogen and phosphorus removal efficiencies. Furthermore, reducing the aeration intensity promoted simultaneous nitrification and denitrification in aerobic reactors, thereby making it a potential energy-saving method for system operation.

Simultaneous nitrification, denitrification and phosphorus removal: What have we done so far and how do we need to do in the future?

Nitrogen and phosphorus contamination in wastewater is a serious environmental concern and poses a global threat to sustainable development. In this paper, a comprehensive review of the studies on simultaneous nitrogen and phosphorus removal (SNPR) during 1986-2022 (538 publications) was conducted using bibliometrics, which showed that simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) is the most promising process. To better understand SNDPR, the dissolved oxygen, carbon to nitrogen ratio, carbon source type, sludge retention time, Cu²⁺ and Fe³⁺, pH, salinity, electron acceptor type of denitrifying phosphorus-accumulating organisms (DPAOs), temperature, and other influencing factors were analyzed. Currently, SNDPR has been successfully implemented in activated sludge systems, aerobic granular sludge systems, biofilm systems, and constructed wetlands; sequential batch mode of operation is a common means to achieve this process. SNDPR exhibits a significant potential for phosphorus recovery. Future research needs to focus on: (1) balancing the competitiveness between denitrifying glycogen-accumulating organisms (DGAOs) and DPAOs, and countermeasures to deal with the effects of adverse conditions on SNDPR performance; (2) achieving SNDPR in continuous flow operation; and (3) maximizing the recovery of P during SNDPR to achieve resource sustainability. Overall, this study provides systematic and valuable information for deeper insights into SNDPR, which can help in further research.

Performance and mechanism of modified biological nutrient removal process in treating low carbon-to-nitrogen ratio wastewater

For solving the challenge of difficult nutrient removal, high running cost and CO₂ emission at low carbon-to-nitrogen (C:N) ratio, Bi-Bio-Selector for nitrogen and phosphorus removal (BBSNP) process was developed. Under parallel operation conditions, full-scale BBSNP was less influence by low C:N ratio (3.5-2) than Anaerobic-anoxic-aerobic (AAO) and achieved better nitrogen removal performance. The mechanism of performance advantage in BBSNP was analyzed by mass balance and high throughout sequencing. It demonstrated BBSNP developed unique microbial community at C:N ratio of 2. Higher abundance of Saccharibacteria, Ferruginibacter, Ottowia, Dokdonella, Candidatus_Nitrotoga and Nitrospira in BBSNP was responsible for better chemical oxygen demand (COD) utilization efficiency, denitrification, denitrifying phosphorus removal and nitrification. Meanwhile, under low C:N ratio, BBSNP could save 10% organic carbon and 15% oxygen requirement, reduce 53% running cost and 21% CO₂ emission, which had practical value in relieving energy crisis and carbon emission of wastewater treatment plants (WWTPs).

Optimization of the Anaerobic-Anoxic-Oxic Process by Integrating ASM2d with Pareto Analysis of Variance and Response Surface Methodology

Wastewater treatment plants (WWTPs) are high-energy-consuming units. Reasonable operation strategies can enable WWTPs to meet discharge standards while reducing the operating cost. In this study, the activated sludge model 2d (ASM2d), Pareto analysis of variance (ANOVA), and response surface methodology (RSM) were jointly used to simulate and optimize the operation of a lab-scale anaerobic-anoxic-oxic (AAO) reactor. The optimization objective was to determine the optimal design and operational parameters (DOPs) that could enhance both pollutant removal and energy saving. The DOPs that had significant influence on the optimization objective, such as sludge retention time (SRT), dissolved oxygen (DO), and the ratio of biodegradable chemical oxygen demand to total nitrogen (BCOD/TN), were identified by Pareto ANOVA. The optimal DOPs with SRT of 15 days, DO concentration of 0.5 mg/L, and BCOD/TN of 5.21 were determined by RSM. Under the optimal conditions, the removal efficiencies of NH4+-N, total nitrogen (TN), and total phosphorus (TP) were 96.2%, 76.8%, and 92.8%, respectively, and the annual operating cost was $26.4. Furthermore, this combination of DOPs was validated using a pilot-scale AAO system. The TN and TP removal efficiencies were improved by 11.0% and 5.0%, respectively, and the annual operating cost could be reduced by 15.0%. Overall, this study confirmed that the method integrating ASM2d with Pareto ANOVA and RSM was effective in optimizing wastewater treatment processes.