This study compared the simulation results of the side-stream membrane-aerated biofilm reactor (MABR) in terms of total nitrogen (TN) removal and N2O production obtained by the conventional comammox-exclusive biological nitrogen removal (BNR) model and the novel BNR model with comammox-related model structures/parameters. Even though the conventional comammox-exclusive MABR obtained >85 % TN removal over a wide range of substrate conditions and achieved up to ∼92.0 % TN removal, it suffered from 0.90 %-4.80 % N2O production. Comparatively, despite the significantly lower N2O production (0.01 %-0.06 %), due to the undesired full nitrification of comammox bacteria, the novel comammox-inclusive MABR failed to provide adequate nitrite for anammox bacteria under exceeding substrate conditions and only obtained the maximum ∼88.0 % TN removal through comammox bacteria-based partial nitritation/anammox. Both MABRs should be operated at a moderate hydraulic retention time (e.g., 4.0 d) with a sufficient biofilm thickness (e.g., ≥300 μm) to attain efficient TN removal and reduced N2O production.
{"title":"Impact of comammox process on membrane-aerated biofilm reactor for autotrophic nitrogen removal","authors":"Jiaying Hou , Ying Zhu , Fangang Meng , Bing-Jie Ni , Xueming Chen","doi":"10.1016/j.wroa.2025.100318","DOIUrl":"10.1016/j.wroa.2025.100318","url":null,"abstract":"<div><div>This study compared the simulation results of the side-stream membrane-aerated biofilm reactor (MABR) in terms of total nitrogen (TN) removal and N<sub>2</sub>O production obtained by the conventional comammox-exclusive biological nitrogen removal (BNR) model and the novel BNR model with comammox-related model structures/parameters. Even though the conventional comammox-exclusive MABR obtained >85 % TN removal over a wide range of substrate conditions and achieved up to ∼92.0 % TN removal, it suffered from 0.90 %-4.80 % N<sub>2</sub>O production. Comparatively, despite the significantly lower N<sub>2</sub>O production (0.01 %-0.06 %), due to the undesired full nitrification of comammox bacteria, the novel comammox-inclusive MABR failed to provide adequate nitrite for anammox bacteria under exceeding substrate conditions and only obtained the maximum ∼88.0 % TN removal through comammox bacteria-based partial nitritation/anammox. Both MABRs should be operated at a moderate hydraulic retention time (e.g., 4.0 d) with a sufficient biofilm thickness (e.g., ≥300 μm) to attain efficient TN removal and reduced N<sub>2</sub>O production.</div></div>","PeriodicalId":52198,"journal":{"name":"Water Research X","volume":"28 ","pages":"Article 100318"},"PeriodicalIF":7.2,"publicationDate":"2025-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143436933","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-08DOI: 10.1016/j.wroa.2025.100315
Hong Tu, Bihong Tian, Zhichao Zhao, Renjiang Guo, Ya Wang, Shunhong Chen, Jian Wu
The structural modulation of pristine graphitic carbon nitride poses a considerable challenge in the rational design of catalysts for the efficient degradation of small organic pollutants under visible light. In this study, we combined first-principles calculations and the structure-function relationship to predict a high-performance catalyst. The results reveal that CN-8 demonstrates a remarkable degree of electron-hole separation. Notably, CN-8 shows exceptional degradation efficiency towards rhodamine B, tetracycline, bisphenol A, and fluralaner under visible light irradiation. Specifically, the degradation rate constants are 11, 4, 12, and 32 times higher, respectively, compared to bulk g-C3N4. Through density functional theory calculations and investigations of the structure-function relationship, it is confirmed that the superior catalytic activity of CN-8 lies in modifying the amino position, which alters the electron cloud distribution and promotes the efficient separation of photo-generated electron-hole pairs. This study provides valuable insights for the development of eco-friendly and efficient photocatalysts for environmental remediation.
{"title":"Research on the influence of g-C3N4 microstructure changes on the efficiency of visible light photocatalytic degradation","authors":"Hong Tu, Bihong Tian, Zhichao Zhao, Renjiang Guo, Ya Wang, Shunhong Chen, Jian Wu","doi":"10.1016/j.wroa.2025.100315","DOIUrl":"10.1016/j.wroa.2025.100315","url":null,"abstract":"<div><div>The structural modulation of pristine graphitic carbon nitride poses a considerable challenge in the rational design of catalysts for the efficient degradation of small organic pollutants under visible light. In this study, we combined first-principles calculations and the structure-function relationship to predict a high-performance catalyst. The results reveal that CN-8 demonstrates a remarkable degree of electron-hole separation. Notably, CN-8 shows exceptional degradation efficiency towards rhodamine B, tetracycline, bisphenol A, and fluralaner under visible light irradiation. Specifically, the degradation rate constants are 11, 4, 12, and 32 times higher, respectively, compared to bulk g-C<sub>3</sub>N<sub>4</sub>. Through density functional theory calculations and investigations of the structure-function relationship, it is confirmed that the superior catalytic activity of CN-8 lies in modifying the amino position, which alters the electron cloud distribution and promotes the efficient separation of photo-generated electron-hole pairs. This study provides valuable insights for the development of eco-friendly and efficient photocatalysts for environmental remediation.</div></div>","PeriodicalId":52198,"journal":{"name":"Water Research X","volume":"28 ","pages":"Article 100315"},"PeriodicalIF":7.2,"publicationDate":"2025-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143377460","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-07DOI: 10.1016/j.wroa.2025.100314
Yongxia Huang , Min Deng , Shuni Zhou , Yunpeng Xue , Senbati Yeerken , Yuren Wang , Lu Li , Kang Song
Submerged plant (SP) restoration is a crucial strategy for restoring aquatic ecosystem. However, the effect of SP on nitrous oxide (N2O) emissions remains controversial, and the impact of SP-attached biofilms on N2O emissions is often overlooked. In this study, SP and non-submerged plant (NSP) systems were set up and operated continuously for 189 days, revealing that SP reduced N2O flux by 42.4 %. By comparing the N2O net emission rates from water, sediment, and biofilms, we identified biofilms as the primary medium responsible for the reduction in N2O emissions in both SP and NSP systems. Further analysis of N2O metabolic rates from nitrification, denitrification, and abiotic processes under light and dark conditions confirmed that counter-diffusion of dissolved oxygen and nutrients in SP biofilms plays a key role in reducing denitrification-driven N2O emissions. Additionally, SP-attached biofilms increased nosZII-type denitrifiers (e.g., Bacillus) and reduced N2O production potential ((nirS+nirK)/(nosZI+nosZII)). Notably, the establishment of a SP restoration project in a typical eutrophic freshwater lake demonstrated that SP could reduce N2O fluxes by 61.5 %. This study provides significant insights for strategies aimed at mitigating N2O emissions.
{"title":"Microbial mechanisms underlying the reduction of N2O emissions from submerged plant covered system","authors":"Yongxia Huang , Min Deng , Shuni Zhou , Yunpeng Xue , Senbati Yeerken , Yuren Wang , Lu Li , Kang Song","doi":"10.1016/j.wroa.2025.100314","DOIUrl":"10.1016/j.wroa.2025.100314","url":null,"abstract":"<div><div>Submerged plant (SP) restoration is a crucial strategy for restoring aquatic ecosystem. However, the effect of SP on nitrous oxide (N<sub>2</sub>O) emissions remains controversial, and the impact of SP-attached biofilms on N<sub>2</sub>O emissions is often overlooked. In this study, SP and non-submerged plant (NSP) systems were set up and operated continuously for 189 days, revealing that SP reduced N<sub>2</sub>O flux by 42.4 %. By comparing the N<sub>2</sub>O net emission rates from water, sediment, and biofilms, we identified biofilms as the primary medium responsible for the reduction in N<sub>2</sub>O emissions in both SP and NSP systems. Further analysis of N<sub>2</sub>O metabolic rates from nitrification, denitrification, and abiotic processes under light and dark conditions confirmed that counter-diffusion of dissolved oxygen and nutrients in SP biofilms plays a key role in reducing denitrification-driven N<sub>2</sub>O emissions. Additionally, SP-attached biofilms increased <em>nosZII</em>-type denitrifiers (e.g., <em>Bacillus</em>) and reduced N<sub>2</sub>O production potential ((<em>nirS</em>+<em>nirK</em>)/(<em>nosZI</em>+<em>nosZII</em>)). Notably, the establishment of a SP restoration project in a typical eutrophic freshwater lake demonstrated that SP could reduce N<sub>2</sub>O fluxes by 61.5 %. This study provides significant insights for strategies aimed at mitigating N<sub>2</sub>O emissions.</div></div>","PeriodicalId":52198,"journal":{"name":"Water Research X","volume":"28 ","pages":"Article 100314"},"PeriodicalIF":7.2,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143349792","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-05DOI: 10.1016/j.wroa.2025.100313
Zhenyu Huang , Yiming Wang , Xin Dong
Reducing combined sewer overflows and flooding is crucial for the efficient operation of urban drainage systems. Traditional real-time control (RTC) methods often fall short in efficiency and performance, which prompts the exploration of innovative approaches. Deep reinforcement learning (DRL) has recently emerged as a promising technique to enhance RTC performance. This study evaluates the effectiveness of RTC using a multi-agent-based DRL approach. We developed a comprehensive evaluation framework incorporating multiple quantitative indicators, including control objectives, decision time, robustness, and adaptability. To validate our framework, we conducted a case study on an urban drainage system in Suzhou, China, analyzing 31 historical rainfall events. Our findings reveal that DRL can reduce flooding and overflow risks by 15.1 % to 43.5 % on average compared to conventional RTC methods. Additionally, DRL demonstrates superior efficiency, robustness, and adaptability. This study not only highlights the potential of DRL in urban drainage management but also provides insights into its broader application in enhancing the resilience of urban infrastructure systems.
{"title":"Dimensions of superiority: How deep reinforcement learning excels in urban drainage system real-time control","authors":"Zhenyu Huang , Yiming Wang , Xin Dong","doi":"10.1016/j.wroa.2025.100313","DOIUrl":"10.1016/j.wroa.2025.100313","url":null,"abstract":"<div><div>Reducing combined sewer overflows and flooding is crucial for the efficient operation of urban drainage systems. Traditional real-time control (RTC) methods often fall short in efficiency and performance, which prompts the exploration of innovative approaches. Deep reinforcement learning (DRL) has recently emerged as a promising technique to enhance RTC performance. This study evaluates the effectiveness of RTC using a multi-agent-based DRL approach. We developed a comprehensive evaluation framework incorporating multiple quantitative indicators, including control objectives, decision time, robustness, and adaptability. To validate our framework, we conducted a case study on an urban drainage system in Suzhou, China, analyzing 31 historical rainfall events. Our findings reveal that DRL can reduce flooding and overflow risks by 15.1 % to 43.5 % on average compared to conventional RTC methods. Additionally, DRL demonstrates superior efficiency, robustness, and adaptability. This study not only highlights the potential of DRL in urban drainage management but also provides insights into its broader application in enhancing the resilience of urban infrastructure systems.</div></div>","PeriodicalId":52198,"journal":{"name":"Water Research X","volume":"28 ","pages":"Article 100313"},"PeriodicalIF":7.2,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143349793","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-04DOI: 10.1016/j.wroa.2025.100312
Yi Liu , Jiachen Dong , Xiaohui Cheng , Xiaotong Cen , Yan Dang , Kangning Xu , Min Zheng
Feammox is a novel microbial process that enables simultaneous nitrogen and phosphorus removal in wastewater treatment. This study investigated the role of organic matter in Feammox-driven nutrient removal during long-term bioreactor operation by gradually increasing the influent chemical oxygen demand (COD) concentration from 0 to 50, and then to 100 mg/L. The results revealed that the ammonium removal efficiency was reduced from 60.5 % to 20.7 % with COD concentration increasing from 0 to 100 mg/L. In contrast, organic matter enhanced nitrate removal through heterotrophic denitrification, which outcompeted nitrate-dependent Fe(II) oxidation. Phosphorus removal was increased up to approximately 90 % via Fe(II)-mediated precipitation, forming vivianite crystals, evidenced by X-ray diffraction analysis. Continuous addition of Fe(III) alleviated the inhibitory effect of organic matter on ammonia oxidation by serving as an alternative electron acceptor, reducing competition. Therefore, optimizing organic matter levels and ensuring sufficient Fe(III) availability are crucial for achieving efficient nutrient removal in Feammox systems, particularly for treating wastewater with a low carbon/nitrogen ratio.
{"title":"Dual role of organic matter in Feammox-driven nitrogen and phosphate removal","authors":"Yi Liu , Jiachen Dong , Xiaohui Cheng , Xiaotong Cen , Yan Dang , Kangning Xu , Min Zheng","doi":"10.1016/j.wroa.2025.100312","DOIUrl":"10.1016/j.wroa.2025.100312","url":null,"abstract":"<div><div>Feammox is a novel microbial process that enables simultaneous nitrogen and phosphorus removal in wastewater treatment. This study investigated the role of organic matter in Feammox-driven nutrient removal during long-term bioreactor operation by gradually increasing the influent chemical oxygen demand (COD) concentration from 0 to 50, and then to 100 mg/L. The results revealed that the ammonium removal efficiency was reduced from 60.5 % to 20.7 % with COD concentration increasing from 0 to 100 mg/L. In contrast, organic matter enhanced nitrate removal through heterotrophic denitrification, which outcompeted nitrate-dependent Fe(II) oxidation. Phosphorus removal was increased up to approximately 90 % via Fe(II)-mediated precipitation, forming vivianite crystals, evidenced by X-ray diffraction analysis. Continuous addition of Fe(III) alleviated the inhibitory effect of organic matter on ammonia oxidation by serving as an alternative electron acceptor, reducing competition. Therefore, optimizing organic matter levels and ensuring sufficient Fe(III) availability are crucial for achieving efficient nutrient removal in Feammox systems, particularly for treating wastewater with a low carbon/nitrogen ratio.</div></div>","PeriodicalId":52198,"journal":{"name":"Water Research X","volume":"27 ","pages":"Article 100312"},"PeriodicalIF":7.2,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143328163","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-03DOI: 10.1016/j.wroa.2025.100311
Xiang Li , Yingxin Jin , Yanying He , Yufen Wang , Tingting Zhu , Yingxin Zhao , Bing-Jie Ni , Yiwen Liu
Partial Nitritation/Anammox (PN/A) can achieve green, economical, and efficient biological nitrogen removal; however, the PN process contributes significantly to nitrous oxide (N2O, the third most important greenhouse gas) emissions. Balancing the stability of PN systems while reducing N2O emissions, particularly under varying salinity conditions, is a key challenge in applying PN/A for high-salinity and high-ammonia wastewater treatment. This study explored the long-term effects of salinity on PN performance and N2O emissions in PN systems treating high-ammonia wastewater. The results showed that the specific ammonia oxidation rates of the control and two salinity-acclimated PN reactors were 78.84, 75.03, and 42.60 mg N/(g VSS·h), indicating that low salinity (2.5 g NaCl/L) had minimal effect, while high salinity (10 g NaCl/L) significantly inhibited ammonia-oxidating bacteria and associated nitritation processes. Moreover, N2O emission factors increased from 0.08 ± 0.04% to 0.24 ± 0.03% as salinity rose from 0 to 10 g NaCl/L. Further analysis revealed that salinity stimulated N2O production in both aerobic and anoxic stages. Particularly, the N2O production increased by 2.84–11.14 times in the aerated stage and by 0.61–2.04 times in the nonaerated stage (i.e. anoxic and settling stages). Isotopic pathway analysis indicated that salinity enhanced N2O production primarily by stimulating the nitrite reduction pathway. Additionally, the mechanism investigation examined the combined effects of salinity-induced changes in sludge properties and microbial community on N2O emissions. These findings provide valuable insights for applying PN systems to treat high-strength wastewater and understanding the mechanisms of N2O emissions.
{"title":"Mechanisms of N2O production in salinity-adapted partial nitritation systems for high-ammonia wastewater treatment","authors":"Xiang Li , Yingxin Jin , Yanying He , Yufen Wang , Tingting Zhu , Yingxin Zhao , Bing-Jie Ni , Yiwen Liu","doi":"10.1016/j.wroa.2025.100311","DOIUrl":"10.1016/j.wroa.2025.100311","url":null,"abstract":"<div><div>Partial Nitritation/Anammox (PN/A) can achieve green, economical, and efficient biological nitrogen removal; however, the PN process contributes significantly to nitrous oxide (N<sub>2</sub>O, the third most important greenhouse gas) emissions. Balancing the stability of PN systems while reducing N<sub>2</sub>O emissions, particularly under varying salinity conditions, is a key challenge in applying PN/A for high-salinity and high-ammonia wastewater treatment. This study explored the long-term effects of salinity on PN performance and N<sub>2</sub>O emissions in PN systems treating high-ammonia wastewater. The results showed that the specific ammonia oxidation rates of the control and two salinity-acclimated PN reactors were 78.84, 75.03, and 42.60 mg N/(g VSS·h), indicating that low salinity (2.5 g NaCl/L) had minimal effect, while high salinity (10 g NaCl/L) significantly inhibited ammonia-oxidating bacteria and associated nitritation processes. Moreover, N<sub>2</sub>O emission factors increased from 0.08 ± 0.04% to 0.24 ± 0.03% as salinity rose from 0 to 10 g NaCl/L. Further analysis revealed that salinity stimulated N<sub>2</sub>O production in both aerobic and anoxic stages. Particularly, the N<sub>2</sub>O production increased by 2.84–11.14 times in the aerated stage and by 0.61–2.04 times in the nonaerated stage (i.e. anoxic and settling stages). Isotopic pathway analysis indicated that salinity enhanced N<sub>2</sub>O production primarily by stimulating the nitrite reduction pathway. Additionally, the mechanism investigation examined the combined effects of salinity-induced changes in sludge properties and microbial community on N<sub>2</sub>O emissions. These findings provide valuable insights for applying PN systems to treat high-strength wastewater and understanding the mechanisms of N<sub>2</sub>O emissions.</div></div>","PeriodicalId":52198,"journal":{"name":"Water Research X","volume":"27 ","pages":"Article 100311"},"PeriodicalIF":7.2,"publicationDate":"2025-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143328162","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-25DOI: 10.1016/j.wroa.2025.100307
Yuqi Yang , Xin Yuan , Longfei Yu , Mui-Choo Jong , Otwil Pius , Nan Zou , Zhiqiang Zuo , Jingyi Yang , Jiane Zuo
Sewer networks are essential components of urban infrastructure, yet their contribution to greenhouse gas (GHG) emissions remains poorly understood. In this study, we deployed a new approach of in situ measurements to assess methane (CH4) and nitrous oxide (N2O) emissions across an urban sewer network, which spans 4769.43 m and receives about 750 m3 of domestic sewage per day. By monitoring at 248 and 151 sites for concentrations and fluxes respectively, we confirmed local GHG hotspots. Overall, the sewer network's total GHG emissions were estimated to be 763.3 g CO2eq/h, with CH4 accounting for 99.4 % of the emissions. The mean emission factor was estimated to be 1.05 kg CO2eq/(m·yr). N2O concentrations above the atmospheric background were detected in almost every manhole. Septic tanks (n = 19) were identified as the predominant sources, accounting for 92.5 % of emissions, while sewer pipes (n = 132) contributed the remaining 7.5 %. Emissions exhibited significant spatiotemporal variability, with daily fluctuations in CH4 and N2O ranging from 17- to 138-fold and 3- to 5-fold, respectively. Additionally, strong correlations were observed between CH4 emissions and sewage temperature (R = 0.70, p = 0.017), as well as manhole depth (R = 0.67, p = 0.016). For N2O, its emission strength was mostly related to the sewage temperature (R = 0.67, p = 0.024). These findings indicate that sewage temperature and sewer ventilation are critical factors influencing non-CO2 GHG emissions. This study represents the first direct measurement of GHG emissions from an urban community sewer network in China, providing vital field evidence for regional GHG estimations and further management practices for GHG mitigation.
{"title":"Assessment of methane and nitrous oxide emissions from urban community sewer networks: Field quantification and insights into environmental factors","authors":"Yuqi Yang , Xin Yuan , Longfei Yu , Mui-Choo Jong , Otwil Pius , Nan Zou , Zhiqiang Zuo , Jingyi Yang , Jiane Zuo","doi":"10.1016/j.wroa.2025.100307","DOIUrl":"10.1016/j.wroa.2025.100307","url":null,"abstract":"<div><div>Sewer networks are essential components of urban infrastructure, yet their contribution to greenhouse gas (GHG) emissions remains poorly understood. In this study, we deployed a new approach of <em>in situ</em> measurements to assess methane (CH<sub>4</sub>) and nitrous oxide (N<sub>2</sub>O) emissions across an urban sewer network, which spans 4769.43 m and receives about 750 m<sup>3</sup> of domestic sewage per day. By monitoring at 248 and 151 sites for concentrations and fluxes respectively, we confirmed local GHG hotspots. Overall, the sewer network's total GHG emissions were estimated to be 763.3 g CO<sub>2</sub>eq/h, with CH<sub>4</sub> accounting for 99.4 % of the emissions. The mean emission factor was estimated to be 1.05 kg CO<sub>2</sub>eq/(m·yr). N<sub>2</sub>O concentrations above the atmospheric background were detected in almost every manhole. Septic tanks (<em>n</em> = 19) were identified as the predominant sources, accounting for 92.5 % of emissions, while sewer pipes (<em>n</em> = 132) contributed the remaining 7.5 %. Emissions exhibited significant spatiotemporal variability, with daily fluctuations in CH<sub>4</sub> and N<sub>2</sub>O ranging from 17- to 138-fold and 3- to 5-fold, respectively. Additionally, strong correlations were observed between CH<sub>4</sub> emissions and sewage temperature (<em>R</em> = 0.70, <em>p</em> = 0.017), as well as manhole depth (<em>R</em> = 0.67, <em>p</em> = 0.016). For N<sub>2</sub>O, its emission strength was mostly related to the sewage temperature (<em>R</em> = 0.67, <em>p</em> = 0.024). These findings indicate that sewage temperature and sewer ventilation are critical factors influencing non-CO<sub>2</sub> GHG emissions. This study represents the first direct measurement of GHG emissions from an urban community sewer network in China, providing vital field evidence for regional GHG estimations and further management practices for GHG mitigation.</div></div>","PeriodicalId":52198,"journal":{"name":"Water Research X","volume":"28 ","pages":"Article 100307"},"PeriodicalIF":7.2,"publicationDate":"2025-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143394365","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-22DOI: 10.1016/j.wroa.2025.100305
Ying Zhu , Jiaying Hou , Fangang Meng , Meiying Xu , Limin Lin , Linyan Yang , Xueming Chen
This study attempted to compare the enrichment of complete ammonium oxidation (comammox) bacteria, which are affiliated with Nitrospira and not able to generate nitrous oxide (N2O, a potent greenhouse gas) through biological pathways, in two commonly-utilized configurations of floccular sludge reactors, i.e., sequencing batch reactor (SBR) and continuous stirred tank reactor (CSTR), under the ammonium condition of mainstream wastewater (i.e., 40.0 g-N/m3). The results in terms of nitrification performance and microbial analyses during 216-d operation showed that compared with SBR offering a fluctuating but generally higher in-situ ammonium concentration (i.e., 1.0–6.0 g-N/m3) which was favorable for the growth of ammonium-oxidizing bacteria (AOB, belonging to Nitrosomonas in this study), CSTR managed to lower the in-situ ammonium level to < 2.0 g-N/m3, thus creating a competitive advantage for comammox bacteria with a highly oligotrophic lifestyle. Such an argument was further supported by dedicated batch tests which revealed that Nitrospira-dominant sludge had a lower maximum ammonium oxidation rate and lower apparent ammonium and oxygen affinity constants than Nitrosomonas-dominant sludge (i.e., 33.5 ± 2.1 mg-N/h/g-MLVSS vs. 139.9 ± 26.7 mg-N/h/g-MLVSS, 1.1 ± 0.1 g-N/m3 vs. 17.6 ± 4.6 g-N/m3, and 0.017 ± 0.002 g-O2/m3 vs. 0.037 ± 0.013 g-O2/m3, respectively), proving the nature of comammox bacteria as a K-strategist. Overall, this study not only provided useful insights into the effective enrichment of comammox bacteria in floccular sludge but also further revealed the interactions between comammox bacteria and AOB, thereby contributing to the future development of comammox-inclusive biological nitrogen removal technologies for sustainable wastewater treatment.
{"title":"Comparative enrichment of complete ammonium oxidation bacteria in floccular sludge reactors: Sequencing batch reactor vs. continuous stirred tank reactor","authors":"Ying Zhu , Jiaying Hou , Fangang Meng , Meiying Xu , Limin Lin , Linyan Yang , Xueming Chen","doi":"10.1016/j.wroa.2025.100305","DOIUrl":"10.1016/j.wroa.2025.100305","url":null,"abstract":"<div><div>This study attempted to compare the enrichment of complete ammonium oxidation (comammox) bacteria, which are affiliated with <em>Nitrospira</em> and not able to generate nitrous oxide (N<sub>2</sub>O, a potent greenhouse gas) through biological pathways, in two commonly-utilized configurations of floccular sludge reactors, i.e., sequencing batch reactor (SBR) and continuous stirred tank reactor (CSTR), under the ammonium condition of mainstream wastewater (i.e., 40.0 g-N/m<sup>3</sup>). The results in terms of nitrification performance and microbial analyses during 216-d operation showed that compared with SBR offering a fluctuating but generally higher <em>in-situ</em> ammonium concentration (i.e., 1.0–6.0 g-N/m<sup>3</sup>) which was favorable for the growth of ammonium-oxidizing bacteria (AOB, belonging to <em>Nitrosomonas</em> in this study), CSTR managed to lower the <em>in-situ</em> ammonium level to < 2.0 g-N/m<sup>3</sup>, thus creating a competitive advantage for comammox bacteria with a highly oligotrophic lifestyle. Such an argument was further supported by dedicated batch tests which revealed that <em>Nitrospira</em>-dominant sludge had a lower maximum ammonium oxidation rate and lower apparent ammonium and oxygen affinity constants than <em>Nitrosomonas</em>-dominant sludge (i.e., 33.5 ± 2.1 mg-N/h/g-MLVSS vs. 139.9 ± 26.7 mg-N/h/g-MLVSS, 1.1 ± 0.1 g-N/m<sup>3</sup> vs. 17.6 ± 4.6 g-N/m<sup>3</sup>, and 0.017 ± 0.002 g-O<sub>2</sub>/m<sup>3</sup> vs. 0.037 ± 0.013 g-O<sub>2</sub>/m<sup>3</sup>, respectively), proving the nature of comammox bacteria as a K-strategist. Overall, this study not only provided useful insights into the effective enrichment of comammox bacteria in floccular sludge but also further revealed the interactions between comammox bacteria and AOB, thereby contributing to the future development of comammox-inclusive biological nitrogen removal technologies for sustainable wastewater treatment.</div></div>","PeriodicalId":52198,"journal":{"name":"Water Research X","volume":"27 ","pages":"Article 100305"},"PeriodicalIF":7.2,"publicationDate":"2025-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143180426","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-22DOI: 10.1016/j.wroa.2025.100306
Yingrui Liu , Feng Chen , Yanying He , Yufen Wang , Tingting Zhu , Yindong Tong , Yingxin Zhao , Bing-Jie Ni , Yiwen Liu
Solid carbon-driven biofilm system can provide sufficient carbon source for denitrification, while its counter-diffusional structure could inevitably induce the delayed carbon-nitrogen contact and electron transport, further affecting carbon footprints mainly contributed by nitrous oxide (N2O) at wastewater treatment plants (WWTPs). However, the detailed understanding of N2O dynamics during solid-phase denitrification (SPD) has not been disclosed. In this work, a fixed bed bioreactor driven by polycaprolactone (PCL) was constructed and operated over 180 days, achieving 97 %-99 % of total nitrogen (TN) removal efficiency. Biochemical results indicated that under the condition that each nitrogen oxide (NOx) concentration was maintained at 30 mg-N/L, the electron competition between upstream and downstream electron pools was still observed during PCL-driven denitrification even providing sufficient carbon source. For example, under the coexistent nitrate (NO3-)+ nitrite (NO2-)+N2O condition, few electrons (i.e., 12.6 %) distributed to N2O reductase (Nos), significantly decreasing the N2O reduction rate (i.e., 1.42 mg/g VSS/h). Under the condition that TN concentration was maintained at 30 mg-N/L, the TN removal rate in the scheme containing NO3-+NO2-+N2O was observed to be 1.75–2.3 times higher than that of the scheme with sole NOx of 30 mg-N/L. This suggested that when treating wastewater containing multiple NOx, the PCL-driven biofilm denitrification system can not only relatively improve the total nitrogen removal efficiency, but also relatively alleviate N2O emissions. The higher abundance of Bacteroidota and Comamonadaceae ensured the stable carbon source release and nitrogen conversion states.
{"title":"Evaluation of nitrous oxide reduction in solid carbon source-driven counter-diffusional biofilm denitrification system","authors":"Yingrui Liu , Feng Chen , Yanying He , Yufen Wang , Tingting Zhu , Yindong Tong , Yingxin Zhao , Bing-Jie Ni , Yiwen Liu","doi":"10.1016/j.wroa.2025.100306","DOIUrl":"10.1016/j.wroa.2025.100306","url":null,"abstract":"<div><div>Solid carbon-driven biofilm system can provide sufficient carbon source for denitrification, while its counter-diffusional structure could inevitably induce the delayed carbon-nitrogen contact and electron transport, further affecting carbon footprints mainly contributed by nitrous oxide (N<sub>2</sub>O) at wastewater treatment plants (WWTPs). However, the detailed understanding of N<sub>2</sub>O dynamics during solid-phase denitrification (SPD) has not been disclosed. In this work, a fixed bed bioreactor driven by polycaprolactone (PCL) was constructed and operated over 180 days, achieving 97 %-99 % of total nitrogen (TN) removal efficiency. Biochemical results indicated that under the condition that each nitrogen oxide (NO<em><sub>x</sub></em>) concentration was maintained at 30 mg-N/L, the electron competition between upstream and downstream electron pools was still observed during PCL-driven denitrification even providing sufficient carbon source. For example, under the coexistent nitrate (NO<sub>3</sub><sup>-</sup>)+ nitrite (NO<sub>2</sub><sup>-</sup>)+N<sub>2</sub>O condition, few electrons (i.e., 12.6 %) distributed to N<sub>2</sub>O reductase (<em>Nos</em>), significantly decreasing the N<sub>2</sub>O reduction rate (i.e., 1.42 mg/g VSS/h). Under the condition that TN concentration was maintained at 30 mg-N/L, the TN removal rate in the scheme containing NO<sub>3</sub><sup>-</sup>+NO<sub>2</sub><sup>-</sup>+N<sub>2</sub>O was observed to be 1.75–2.3 times higher than that of the scheme with sole NO<em><sub>x</sub></em> of 30 mg-N/L. This suggested that when treating wastewater containing multiple NO<em><sub>x</sub></em>, the PCL-driven biofilm denitrification system can not only relatively improve the total nitrogen removal efficiency, but also relatively alleviate N<sub>2</sub>O emissions. The higher abundance of <em>Bacteroidota</em> and <em>Comamonadaceae</em> ensured the stable carbon source release and nitrogen conversion states.</div></div>","PeriodicalId":52198,"journal":{"name":"Water Research X","volume":"27 ","pages":"Article 100306"},"PeriodicalIF":7.2,"publicationDate":"2025-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143180427","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-13DOI: 10.1016/j.wroa.2025.100303
Chen-Yuan Zhou , Kun Dai , Yi-Peng Lin , Xing-Chen Huang , Yan-Lin Hu , Xuan-Xin Chen , Xiao-Fei Yang , Qi-Yuan Sun , Yong Zhang , Mark C.M. van Loosdrecht , Raymond Jianxiong Zeng , Fang Zhang
The hydrolysis of structural extracellular polymeric substances (St-EPS) is considered a major limiting step in the anaerobic fermentation of waste activated sludge (WAS). However, the degradation of heteropolysaccharides, characterized by complex monomers of uronic acids and neutral saccharides in St-EPS, has rarely been reported. In this study, microbial-produced xanthan-like heteropolysaccharides, characterized by a blue filamentary film, were identified. The xanthan-producing bacteria comprised ∼7.2% of total genera present in WAS. An xanthan-degrading consortium (XDC) was enriched in an anaerobic batch reactor. This consortium could degrade Xanthan for over 90% and disrupt the gel structure of xanthan while promoting methane production from WAS by 29%. The xanthan degradation network consisting of extracellular enzymes and bacteria was elucidated by combining high-throughput sequencing, metagenomic, and metaproteomic analyses. Five enzymes were identified as responsible for hydrolyzing xanthan to monomers, including xanthan lyase, β-d-glucosidase, β-d-glucanase, α-d-mannosidase, and unsaturated glucuronyl hydrolase. Seven genera, including Paenibacillus (0.2%) and Clostridium (3.1%), were identified as key bacteria excreting one to five of the aforementioned enzymes. This study thus provides insights into the complex conversions in anaerobic digestion of WAS and gives a foundation for future optimization of this process.
{"title":"Elucidating the complex hydrolysis and conversion network of xanthan-like extracellular heteropolysaccharides in waste activated sludge fermentation","authors":"Chen-Yuan Zhou , Kun Dai , Yi-Peng Lin , Xing-Chen Huang , Yan-Lin Hu , Xuan-Xin Chen , Xiao-Fei Yang , Qi-Yuan Sun , Yong Zhang , Mark C.M. van Loosdrecht , Raymond Jianxiong Zeng , Fang Zhang","doi":"10.1016/j.wroa.2025.100303","DOIUrl":"10.1016/j.wroa.2025.100303","url":null,"abstract":"<div><div>The hydrolysis of structural extracellular polymeric substances (St-EPS) is considered a major limiting step in the anaerobic fermentation of waste activated sludge (WAS). However, the degradation of heteropolysaccharides, characterized by complex monomers of uronic acids and neutral saccharides in St-EPS, has rarely been reported. In this study, microbial-produced xanthan-like heteropolysaccharides, characterized by a blue filamentary film, were identified. The xanthan-producing bacteria comprised ∼7.2% of total genera present in WAS. An xanthan-degrading consortium (XDC) was enriched in an anaerobic batch reactor. This consortium could degrade Xanthan for over 90% and disrupt the gel structure of xanthan while promoting methane production from WAS by 29%. The xanthan degradation network consisting of extracellular enzymes and bacteria was elucidated by combining high-throughput sequencing, metagenomic, and metaproteomic analyses. Five enzymes were identified as responsible for hydrolyzing xanthan to monomers, including xanthan lyase, β-<span>d</span>-glucosidase, β-<span>d</span>-glucanase, α-<span>d</span>-mannosidase, and unsaturated glucuronyl hydrolase. Seven genera, including <em>Paenibacillus</em> (0.2%) and <em>Clostridium</em> (3.1%), were identified as key bacteria excreting one to five of the aforementioned enzymes. This study thus provides insights into the complex conversions in anaerobic digestion of WAS and gives a foundation for future optimization of this process.</div></div>","PeriodicalId":52198,"journal":{"name":"Water Research X","volume":"27 ","pages":"Article 100303"},"PeriodicalIF":7.2,"publicationDate":"2025-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11783115/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143081971","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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