Urban Water Systems Research Articles

Experimental investigations and three-dimensional computational fluid dynamics modeling of sediment transport in tanks influenced by cavities

Sediment transport is a very complex process in urban water systems, and sediment movement mechanisms are poorly understood. However, it is necessary to comprehend sediment transport to optimize stormwater and sewer tank designs for better performance in trapping particulate pollutants. This work focuses on the numerical simulation and experimental investigation of tank sediment transport. In the numerical simulation, a discrete phase model is applied to calculate particle trajectories, and the particle tracking calculation is coupled with the steady-state flow calculation. A user-defined function is developed in the Fluent computational fluid dynamics (CFD) code to implement the settling condition and improve the particle motion predictions. In the experimental work, a back-scattered ultrasonic method is used to measure the velocity field, and the accumulation of particles at the bottom is reproduced by transforming the raw experimental data. The sediment deposition is also recorded photographically, and the trap efficiency is calculated. The CFD and experimental results are compared to estimate the accuracy of the modified settling boundary condition, showing an improvement in the trap efficiency and deposition zone predictions. High water level in the tank corresponds to higher sediment trap efficiency, and sediment deposition type is strongly affected by the water level. Tank length and the presence of cavity alter the sediment deposition zone, and the presence of cavity increases the trap efficiency of tank.

Greenhouse Gas Emissions of an Urban Water System in Korea: A case study of Paju city

Objectives : This study assessed the greenhouse gas emissions (GHG) in the urban water system from a life cycle perspective in the city of Paju. It serves as a case study to provide a quantitative basis for the net-zero water management.Methods : The scope of the study included the centralized local water supply and inter-basin water import system (water abstraction facilities, water treatment plants, pump stations, and water pipelines), wastewater system (wastewater pipelines, pump stations, and wastewater treatment plants, public industrial wastewater treatment plants, on-site wastewater treatment facilities), and circular water use (rainwater harvesting, greywater reuse, and wastewater recycling). This study considered scope 1 emissions, specifically CH<sub>4</sub> and N<sub>2</sub>O emissions generated from wastewater treatment plants, scope 2 emissions from the electricity use during the operation of water infrastructure, and scope 3 emissions associated with the production of water and wastewater pipelines and chemicals. Scope 1 emissions were quantified using both the national guidelines and the 2019 IPCC guideline, and the estimates based on the two methods were compared. Scope 2 and scope 3 emissions were evaluated using life cycle assessment. To quantify GHG emissions for the year 2018, data were collected or estimated from various sources, including public statistics, field interviews, and the literature.Results and Discussion : In 2018, the total GHG emissions from Paju’s water system were 197.4 thousand tons of CO<sub>2</sub> eq. Among these emissions, the scope 2 emissions accounted for the largest share, comprising 66.3% of the total. Notably, circular water use, which included wastewater recycling for high-quality industrial uses, accounted for 41.0% of the scope 2 emissions. Scope 1 emissions accounted for 25.5% and scope 3 emissions accounted for 8.2% of the total emissions. However, in the case of scope 1 emissions, the estimates varied significantly by 2.9 to 6.5 times, depending on the calculation methods and emission factors provided by two different guidelines.Conclusion : To achieve carbon neutrality in the water sector of the city of Paju, two approaches are required: enhancing energy efficiency to reduce scope 2 emissions and implementing measures to reduce scope 1 emissions. However, to obtain accurate and reliable estimates of the GHG emissions, it is crucial to develop applicable scope 1 emission factors based on field data. Furthermore, to gain a comprehensive understanding of GHG emissions in the water sector, further studies are necessary to analyze embodied GHG emissions in water infrastructure and GHG emissions associated with the end use of water.

Emerging micropollutants in aquatic ecosystems and nanotechnology-based removal alternatives: A review

There is a significant concern about the accessibility of uncontaminated and safe drinking water, a fundamental necessity for human beings. This concern is attributed to the toxic micropollutants from several emission sources, including industrial toxins, agricultural runoff, wastewater discharges, sewer overflows, landfills, algal blooms and microbiota. Emerging micropollutants (EMs) encompass a broad spectrum of compounds, including pharmaceutically active chemicals, personal care products, pesticides, industrial chemicals, steroid hormones, toxic nanomaterials, microplastics, heavy metals, and microorganisms. The pervasive and enduring nature of EMs has resulted in a detrimental impact on global urban water systems. Of late, these contaminants are receiving more attention due to their inherent potential to generate environmental toxicity and adverse health effects on humans and aquatic life. Although little progress has been made in discovering removal methodologies for EMs, a basic categorization procedure is required to identify and restrict the EMs to tackle the problem of these emerging contaminants. The present review paper provides a crude classification of EMs and their associated negative impact on aquatic life. Furthermore, it delves into various nanotechnology-based approaches as effective solutions to address the challenge of removing EMs from water, thereby ensuring potable drinking water. To conclude, this review paper addresses the challenges associated with the commercialization of nanomaterial, such as toxicity, high cost, inadequate government policies, and incompatibility with the present water purification system and recommends crucial directions for further research that should be pursued.

A novel free nitrous acid (FNA)-generation pathway via ferric salts hydrolysis to mitigate sulfide and methane production in sewer: Insights into the performance and microbial mechanisms

Ferric chloride (FeCl3) served as a solid acid has attracted attention recently. However, the feasibility of FeCl3 combined with nitrite for free nitrous acid (FNA) generation in controlling sulfide and methane as well as the triggering mechanisms in the complex syntrophic consortium (i.e., sewer biofilm) remain largely unknown. This work disclosed FeCl3 as an alternative acid source could obtain comparable sulfide and methane mitigations at a low FNA dose (i.e., 0.26 mg N/L), compared to that of HCl acid source. Whereas, a faster recovery rate of sulfide production was observed using FeCl3 under a higher FNA dose (i.e., 0.81 mg N/L) despite the methane control still being comparable. The toxicological mechanisms revealed FNA reacted with proteins amide Ⅰ in extracellular polymeric substances and destroyed protein hydrogen bond. Enzymatic and genic analysis unveiled the overall suppression of hydrolysis, acidogenesis, acetogenesis, sulfidogenesis and methanogenesis steps due to the inactivation of viable cells by reactive nitrogen species. Economic and environmental assessments demonstrated that the ferric-based FNA strategy reduced chemical costs and N2O emission (ca. 26.5% decrease) compared to the traditional HCl-based FNA method. This work broadens the application of iron salt-based technology in urban water system, together with understanding the biological mechanisms of FNA-based technology.

Impacts of the steel industry on sediment pollution by heavy metals in urban water system

The impact of the steel industry on sediment heavy metal (HM) pollution in urban aquatic environments was investigated in a major iron ore-producing area (Ma'anshan) in China. The concentrations of Cd, Cr, Cu, Ni, Pb, and Zn were 9.68 ± 3.56, 170.31 ± 82.40, 90.62 ± 19.54, 30.61 ± 6.72, 125.43 ± 63.60, and 1276.59 ± 701.90 mg/kg in the steel industry intruded upon sediments and 4.63 ± 1.41, 87.60 ± 10.96, 52.67 ± 19.99, 37.49 ± 6.17, 35.84 ± 11.41, and 189.02 ± 95.57 mg/kg in the control area, respectively. Comparing with the local soil background (0.08 mg/kg for Cd, 62.6 mg/kg for Cr, 19.3 mg/kg for Cu, 28.1 mg/kg for Ni, 26.0 mg/kg for Pb, and 58.0 mg/kg for Zn), significantly higher levels of Cd, Cr, Cu, Pb, and Zn were detected in the steel industry affected sediments. The enrichment factor and principal component analysis indicated that the heavy metals (HMs), except for Ni, were primarily derived from anthropogenic inputs, particularly from steel industrial activities. Multiple risk assessment models suggested that the sediments affected by industrial activities showed significant toxic effects for Cd, Cr, Pb, and Zn, with Cd being the main contributor to sediment toxicity. However, the alkaline nature of the sediments (pH = 7.85 ± 0.57) and the high proportion of residual fraction Cd (61.09% ± 26.64%) may help to reduce the toxic risks in the sediments. Effective measures to eliminate tinuous thethe continous input of Cd and Zn via surface runoff are crucial.

Challenges and countermeasures of urban water systems against climate change: a perspective from China

Urban water systems are facing various challenges against climate change, impacting cities’ security and their sustainable development. Specifically, there are three major challenges: submersion risk of coastal cities as glaciers melt and sea level rises, more and severe urban flooding caused by extreme weather like intensified storm surge and heavy precipitation, and regional water resource patterns challenged by alteration of spatial distribution of precipitation. Regarding this, two strategies including proactive adaptation and positive mitigation were proposed in this article to realize the reconstruction and optimization of urban water systems, to enhance their resilience, and eventually increase their adaptability and coping ability to climate change. The proactive adaptation strategy consists of 1) construction of sponge cities to accommodate the increased regular rainfall and to balance the alterations of spatial redistribution of precipitation; 2) reconstruction of excess stormwater discharge and detention system to increase capability for extreme precipitation events based on flood risk assessment under future climate change; 3) deployment of forward-looking, ecological, and integrated measures to improve coastal protection capability against inundation risks caused by climate change and sea level rise. The positive mitigation strategy is to employ the systematic concept in planning and design and to adopt advanced applicable energy-saving technologies, processes, and management practices, aiming at reduction in flux of urban water systems, reinforcement in energy conservation and carbon reduction in both water supply systems and wastewater treatment systems, and thus a reduction of greenhouse gas emission from urban water systems.

Microplastic transport dynamics in surcharging and overflowing manholes

The transport of microplastics within urban water systems remains poorly understood, with little prior research on their behaviour within manhole configurations. This study represents the first to measure and model the transport dynamics of microplastics within circular and square manholes under different hydraulic scenarios. The transport and fate of polyethylene (PE) was quantified and compared to solutes (Rhodamine WT dye) using energy losses, residence time distributions (RTDs), and mixing models within surcharging and overflowing manholes. The bulk mass of solute and PE concentrations followed similar flow paths across all conditions except for 17.3 ± 7.9 % of PE mass that was immobilized in a dead zone above the inlet pipe for manholes with a surcharge to pipe diameter ratio ≥2. Consequently, these microplastics only exit after a significant change in hydraulic regime occurs, causing microplastics to be at risk of being contaminated over a prolonged duration. No significant mixing differences for PE and solutes were found between manhole geometries. The deconvolution method outperformed the ADZ model with goodness of fit (Rt2) values of 0.99 (0.60) and 1.00 (0.89) for PE and solute mixing, respectively. This establishes the deconvolution method as the most accurate and appropriate model to accurately predict microplastic mixing in manholes and urban drainage systems.

Institutions, Voids, and Dependencies: Tracing the Designs and Robustness of Urban Water Systems

Institutions, Voids, and Dependencies: Tracing the Designs and Robustness of Urban Water Systems

Prioritizing selection criteria of distributed circular water systems: A fuzzy based multi-criteria decision-making approach

Extreme weather events, population growth, and industrial activities all contribute to the worldwide water crisis. The traditional linear water management model is one of the causes of global water shortage, following a take-make-use-dispose pattern that is both environmentally and economically unsustainable. The circular economy has been proposed to mitigate water shortages, encouraging a paradigm shift in urban water systems. A circular water system seeks to close the water loop by reducing consumption, recovering natural resources, and minimizing waste. Compared with a centralized water system, a distributed water system is more flexible and resilient as it allows neighborhoods to prepare for unexpected stressor events. However, there have been no thorough investigations of essential factors that primarily impact the decision-making process of implementing distributed water systems. Thus, this study aims to uncover significant selection criteria that impact the assessment of feasible options to assist in the planning phase. The researchers proposed a systematic framework to develop criteria and their relative weights for selecting the most appropriate distributed water system to be deployed in a neighborhood. The authors identified four criteria and seventeen sub-criteria through a comprehensive literature review. Then, the Fuzzy Delphi Method (FDM) was performed to collect experts’ opinions to remove insignificant sub-criteria. Subsequently, a Fuzzy Analytical Hierarchy Process (FAHP) was conducted to obtain relative weights of the eleven remaining sub-criteria via pairwise comparison. In conclusion, this study contributes to the body of knowledge by proposing selection criteria to facilitate the assessment of implementing distributed water systems. In addition, the proposed framework is applicable to other urban systems, such as food and energy.

Performance Assessment Method for Small- and Medium-Sized Urban Water Systems: Development and Implementation

ABSTRACT Performance assessment of Small and Medium-Sized Water Systems (SMWSs) is important for operational, tactical, and strategic decision-making. In this study, a performance assessment method has been developed and applied to five drinking water, three wastewater, and two stormwater utilities using 39, 30 and 27 Key Performance Indicators (KPIs) in a semi-arid region. The KPIs were aggregated to determine a performance index using a Technique for Order of Preference by Similarity to Ideal Solution method. K-nearest neighbors and penalty methods were used to estimate missing KPIs data. The results indicated that only two drinking water utilities and one wastewater utility had been rated as ‘high’ performance. None of the utilities in stormwater performance was rated as ‘high’. The developed method can assist decision-makers in evaluating SMWSs performance holistically, build operational management strategies, and identify necessary interventions in overcoming water systems challenges across each urban water system component.

Conceptual model of one water community: A path to move forward

Water is a finite resource. Increasing population, rapid urbanization, and climate change incidents are continuously adding pressure on freshwater supplies. Overcoming these issues require change in current urban water management (UWM) strategy. In this study, a conceptual model of One Water Community has been developed that aims to reduce potable water use (RPWU) using One Water Approach (OWA). Based on OWA's six guiding principles, five interventions (i.e., control factors) and sixteen parameters have been identified. Each parameter is simulated twice by running 10,000 iterations to calculate a percentage reduction of potable water use at 90th, 50th, and 10th percentiles. A Taguchi-based optimization method has been used to determine the optimum combination of parameters from each of the five control factors [water saving appliances (WSA), reclaimed water use (RWU), resource recovery (RR), low impact development (LID), and good governance (GG)]. L16 orthogonal array experimental design plan was considered in conducting the trials. ANOVA analysis showed that RWU, RR, and WSA were the most influential factors on RPWU performance at 90th, 50th, and 10th percentiles. Validation tests validated the model by predicting the S/N ratio at the optimum condition. The findings indicated that water sense labeled urinals, reclaimed water for agriculture purposes, emissions reductions from treatment plants, bioswales, and increased public awareness were the most optimum parameters in achieving the highest potable water reduction potential at the 90th percentile. The developed model will open new avenues in UWM, which will assist decision-makers in building sustainable, reliable, and resilient urban water systems.

Comprehensive essentiality analysis of the Mycobacterium kansasii genome by saturation transposon mutagenesis and deep sequencing.

Mycobacterium kansasii (Mk) is an opportunistic pathogen that is frequently isolated from urban water systems, posing a health risk to susceptible individuals. Despite its ability to cause tuberculosis-like pulmonary disease, very few studies have probed the genetics of this opportunistic pathogen. Here, we report a comprehensive essentiality analysis of the Mk genome. Deep sequencing of a high-density library of Mk Himar1 transposon mutants revealed that 86.8% of the chromosomal thymine-adenine (TA) dinucleotide target sites were permissive to insertion, leaving 13.2% TA sites unoccupied. Our analysis identified 394 of the 5,350 annotated open reading frames (ORFs) as essential. The majority of these essential ORFs (84.8%) share essential mutual orthologs with Mycobacterium tuberculosis (Mtb). A comparative genomics analysis identified 139 Mk essential ORFs that share essential orthologs in four other species of mycobacteria. Thirteen Mk essential ORFs share orthologs in all four species that were identified as being not essential, while only two Mk essential ORFs are absent in all species compared. We used the essentiality data and a comparative genomics analysis reported here to highlight differences in essentiality between candidate Mtb drug targets and the corresponding Mk orthologs. Our findings suggest that the Mk genome encodes redundant or additional pathways that may confound validation of potential Mtb drugs and drug target candidates against the opportunistic pathogen. Additionally, we identified 57 intergenic regions containing four or more consecutive unoccupied TA sites. A disproportionally large number of these regions were located upstream of pe/ppe genes. Finally, we present an essentiality and orthology analysis of the Mk pRAW-like plasmid, pMK1248. IMPORTANCE Mk is one of the most common nontuberculous mycobacterial pathogens associated with tuberculosis-like pulmonary disease. Drug resistance emergence is a threat to the control of Mk infections, which already requires long-term, multidrug courses. A comprehensive understanding of Mk biology is critical to facilitate the development of new and more efficacious therapeutics against Mk. We combined transposon-based mutagenesis with analysis of insertion site identification data to uncover genes and other genomic regions required for Mk growth. We also compared the gene essentiality data set of Mk to those available for several other mycobacteria. This analysis highlighted key similarities and differences in the biology of Mk compared to these other species. Altogether, the genome-wide essentiality information generated and the results of the cross-species comparative genomics analysis represent valuable resources to assist the process of identifying and prioritizing potential Mk drug target candidates and to guide future studies on Mk biology.

Disparities in disruptions to public drinking water services in Texas communities during Winter Storm Uri 2021

Winter Storm Uri of February 2021 left millions of United States residents without access to reliable, clean domestic water during the COVID19 pandemic. In the state of Texas, over 17 million people served by public drinking water systems were placed under boil water advisories for periods ranging from one day to more than one month. We performed a geospatial analysis that combined public boil water advisory data for Texas with demographic information from the 2010 United States Census to understand the affected public water systems and the populations they served. We also issued a cross-sectional survey to account for people’s lived experiences. Geospatial analysis shows that the duration of boil water advisories depended partly on the size of the public water system. Large, urban public water systems issued advisories of intermediate length (5–7 days) and served racially diverse communities of moderate income. Small, mostly rural public water systems issued some of the longest advisories (20 days or more). Many of these systems served disproportionately White communities of lower income, but some served predominantly non-White, Hispanic, and Latino communities. In survey data, “first-generation” participants (whose parents were not college-educated) were more likely to be placed under boil water advisories, pointing to disparate impacts by socioeconomic group. The survey also revealed large communication gaps between public water utilities and individuals: more than half of all respondents were unsure or confused about whether they were issued a boil water advisory. Our study reinforces the need to improve resilience in public water services for large, diverse, urban communitiesandsmall, rural communities in the United States and to provide a clear and efficient channel for emergency communications between public water service utilities and the communities they serve.

Statistical quality control based on control charts and process efficiency index by the application of fuzzy approach (case study: Ha'il, Saudi Arabia).

Fuzzy methods using linguistic expressions and fuzzy numbers can provide a more accurate examination of manufacturing systems where data is not clear. Researchers expanded fuzzy control charts (CCs) using fuzzy linguistic statements and investigated the current process efficiency index to evaluate the performance, precision, and accuracy of the production process in a fuzzy state. Compared to nonfuzzy data mode, fuzzy linguistic statements provided decision makers with more options and a more accurate assessment of the quality of products. The fuzzy index of the actual process efficiency analyzed the process by considering mean, target value, and variance of the process simultaneously. Inspection of household water meters in Ha'il, Saudi Arabia showed the actual process index values were less than 1, indicating unfavorable production conditions. Fuzzy methods enhance the accuracy and effectiveness of statistical quality control in real-world systems where precise information may not be readily available. In addition, to provide a new perspective on the comparison of urban water and sewage systems, the results obtained from fuzzy-CC were compared with various machine learning methods such as artificial neural network and M5 model tree, in order to identify and understand their respective advantages and limitations.

Construction and application of urban water system connectivity evaluation index system based on PSR-AHP-Fuzzy evaluation method coupling

The connectivity of urban water systems can enhance the connectivity of regional rivers, lakes, and water systems, which can improve the regional water environment and water ecology to a certain extent, and enhance the water disaster prevention capability. To scientifically evaluate the effect of water system connectivity in the comprehensive urban water system management project. In this study, a regional waterlogging model based on the coupling of ArcGis and SWMM is established. At the same time, the evaluation index system of water system connectivity effect of regional town water system comprehensive management project was constructed regarding PSR (“Pressure-Status-Response”) theory with structural connectivity, hydraulic connectivity and ecological and environmental improvement as the criteria, and the fuzzy evaluation method was used for analysis and evaluation. The results show that the improvement in the water environment is obvious after the water system is connected. The total length and area of rivers in the study area increased by 68.98% and 57.51%, respectively. River network density increased from 0.66 km/km2 to 0.69 km/km2, an increase of 4.55%; the regional water surface rate increased from 2.22% to 3.51%, an increase of 58.11%; the river frequency increased from 0.15/km2 to 0.29/km2, an increase of 93.33%. The water exchange capacity increased by 37.5% and the flow rate increased by 30%. All water systems have a better degree of connectivity and a better structure of river network water system. The decay rate of point source pollution increased by 40.61%, the water quality of rivers reached V standard, and the area covered by green areas increased to 32.29%. The evaluation grade of hydraulic characteristics and ecological environment indexes was “excellent”. The total evaluation set D=[0.5417,0.0791,0.2125,0] for the effect of water system connection in the study area. According to the principle of maximum affiliation, the improvement effect of the water system connection project in the study area is “excellent”.

Water security and health risk assessment of an urban household-level drinking water and sanitation system, Punjab, India.

The water scarcity and deteriorating water quality are major issues of concern to the agrarian state of Punjab, India. The focus of the study is to assess the status of drinking water and sanitation systems of Punjab using an exhaustive dataset of 1575 drinking water samples from 433 sampling locations in 63 urban local bodies of Punjab. Water security index(WSI) indicate that out of 63 urban local bodies, 13 are categorized into good class, 31 fall under fair class, and 19 fall under poor class. The access indicator under sanitation dimension shows that Bathinda region has maximum sewerage network coverage relative to other regions, whereas ca. 50% of the ULBs in Amritsar region do not have sewerage facility. It is clearly depicted that the variation in WSI is mainly attributable to sanitation dimension (10-22.5) as variation in water supply dimension (29-35) is relatively less. Hence,emphasis on indicators and variables of sanitation dimension is required for the improvement of overall WSI. The assessment of qualitative aspects of drinking water and health risk depicts that the drinking water quality of southwest part of the state (i.e. Malwa region) is under good quality class contrary to its poor groundwater quality. Kapurthala district shows high health risk due to the presence of trace metals despite being classified into good class within water security index. The drinking water quality is better and health risks are minimal in regions where drinking water is supplied via treated surface water sources (e.g. Bathinda region). Furthermore, the results of health risk assessment correlate with M[Formula: see text]-WaterQualityIndex outcome owing to presence of trace metals in groundwater above permissible limits. These results will help in identification of shortcomings in water supply and sanitation infrastructure and its management in urban areas.

Amsterdam urban water system as entry point of river plastic pollution

Accumulation of plastic litter in aquatic environments negatively impacts ecosystems and human livelihood. Urban areas are assumed to be the main source of plastic pollution in these environments because of high anthropogenic activity. Yet, the drivers of plastic emissions, abundance, and retention within these systems and subsequent transport to river systems are poorly understood. In this study, we demonstrate that urban water systems function as major contributors to river plastic pollution, and explore the potential driving factors contributing to the transport dynamics. Monthly visual counting of floating litter at six outlets of the Amsterdam water system results in an estimated 2.7 million items entering the closely connected IJ river annually, ranking it among the most polluting systems measured in the Netherlands and Europe. Subsequent analyses of environmental drivers (including rainfall, sunlight, wind speed, and tidal regimes) and litter flux showed very weak and insignificant correlations (r = -0.19–0.16), implying additional investigation of potential drivers is required. High-frequency observations at various locations within the urban water system and advanced monitoring using novel technologies could be explored to harmonize and automate monitoring. Once litter type and abundance are well-defined with a clear origin, communication of the results with local communities and stakeholders could help co-develop solutions and stimulate behavioral change geared to reduce plastic pollution in urban environments.

Reflections on maintenance in traditional and rudimentary urban water systems: the city of Uíge case

The players of maintenance of systems of worldwide institutions of service or production, put the maintenance, as a top factor in the continuous operation, who ignore can lose customers, because the variable can double the costs of recovery of projects and/or infrastructures. The maintenance of water systems is a useful factor in the operation, for the socio-economic progress of countries and balances local well-being. Describe the maintenance plan applied in the urban water supply system of the city of Uíge, from 2012 to 2016. Methodical quali-quantitative of theoretical level, is a case study. The bibliographic survey was carried out, on-site visits in the field, reports, interviews, bibliographic review that allowed diagnosing the problems about the maintenance plan in traditional and rudimentary urban water systems according to the criteria of the Ministry of Energy and Water of Angola and what international standards establish in a system of this nature. To contribute to improve the forms of poorly practiced maintenance and adapt them to internationally accepted standards, to the academic world I believe to be an innovative study for processes of traditional urban rudimentary systems from the catchment to the water treatment plant

Occurrence and transport of N-nitrosamines in the urban water systems of the Pearl River Delta, southern China

The discharge of substantial amounts of N-nitrosamines-contained wastewater into receiving rivers can significantly deteriorate water quality, as these carcinogenic compounds can be easily transported into groundwater and drinking water systems. This study investigated the distribution of eight species of N-nitrosamines in river water, groundwater, and tap water located in the center of the Pearl River Delta (PRD), China. The results showed that three major N-nitrosamines, including N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), and N-nitrosodibutylamine (NDBA), with concentrations of up to 64 ng/L, were observed in river water, groundwater, and tap water, whereas the other compounds occurred sporadically. In river water and groundwater, high concentrations of NDMA, NDEA, N-nitrosomorpholine (NMOR), and NDBA were found in industrial and residential lands as compared to agricultural lands owing to the influence of various human activities. The primary sources of N-nitrosamines in river water were industrial and domestic wastewater, and the infiltration of river water was responsible for the high levels of N-nitrosamines in groundwater. Among the target N-nitrosamines, NDEA and NMOR with long biodegradation half-lives (>4 days) and low LogKow values (<1) displayed the highest potential for groundwater. N-nitrosamines in groundwater and tap water pose significant potential cancer risks to residents, especially children, and juveniles, with lifetime cancer risks of over 10−4, necessitating advanced water treatments for drinking water and critical controls on primary industrial discharge in urban areas.

Stagnant water environmental management in urban river networks: An integrated risk analysis involving hydraulic potential dissipation

Rapid urbanization has led to water stagnation by temporal and spatial imbalances of the hydrodynamics in urban river networks, which further entails environmental risks to drinking and recreational water supplies. The establishment of a succinct hydraulic potential dissipation (HPD) index to indicate the spatiotemporal stagnant water environmental risks quickly and intuitively is of vital significance to urban river networks with complicated water regimes and diversified water diversion measures. On this basis, an integrated stagnant water environmental risk analysis model (ISWERA) was established by coupling the process-based model and stochastic process to comprehensively and accurately assess risks, which has been calibrated and validated against the real data of 11 monitoring stations from May 3 to May 11 in 2017 and November 28 to December 10 in 2020, respectively. To represent the rationality of stagnant water environmental risks assessment using HPD, ISWERA was used to evaluate the temporal- and spatial-varying stagnant water environmental risk intensity and probability of 270 water diversion schemes formed by the combination of water diversion duration, flow, route, and potential in the Changzhou urban river network along the Yangtze River. For time-varying results, it revealed that cumulative risk intensity was reduced by nearly 15%, and risk probability was significantly reduced by nearly 50% with the increase of diversion duration to 5 days in general. For spatial-varying results, most of the rivers reached the low-risk grade under the optimized diversion duration, flow, route, and potential. While the rivers adjacent to densely populated areas still presented a moderate-risk state. The positive correlation was significant between HPD and stagnant water environmental risk intensity and probability results, with R2 = 0.86 and 0.74 respectively. When the HPD of upstream channels are below 63.4%, 74.1%, and 57.7% and the downstream HPD of S1 to T1, S2 to T2, S2 to T3, and S3 to T4 are below 40.6%, 32.9%, 22.4%, and 19.1%, respectively, the stagnant water environmental risk is lower. Arguably, this study could provide a scientific reference and foundation for water environmental management of similar urban stagnant water systems.