Secondary Water Supply Research Articles

Optimizing Control of Secondary Water Supply Tanks for Demand Peak Staggering

Optimizing Control of Secondary Water Supply Tanks for Demand Peak Staggering

Tap water microbiome shifts in secondary water supply for high-rise buildings

In high-rise buildings, secondary water supply systems (SWSSs) are pivotal yet provide a conducive milieu for microbial proliferation due to intermittent flow, low disinfectant residual, and high specific pipe-surface area, raising concerns about tap water quality deterioration. Despite their ubiquity, a comprehensive understanding of bacterial community dynamics within SWSSs remains elusive. Here we show how intrinsic SWSS variables critically shape the tap water microbiome at distal ends. In an office setting, distinct from residential complexes, the diversity in piping materials instigates a noticeable bacterial community shift, exemplified by a transition from α-Proteobacteria to γ-Proteobacteria dominance, alongside an upsurge in bacterial diversity and microbial propagation potential. Extended water retention within SWSSs invariably escalates microbial regrowth propensities and modulates bacterial consortia, yet secondary disinfection emerges as a robust strategy for preserving water quality integrity. Additionally, the regularity of water usage modulates proximal flow dynamics, thereby influencing tap water's microbial landscape. Insights garnered from this investigation lay the groundwork for devising effective interventions aimed at safeguarding microbiological standards at the consumer's endpoint.

Achieving zero fouling in the ultrafiltration for secondary water supply systems in the absence of residual chlorine

Ultrafiltration (UF) technology is widely used in secondary water supply systems (SWSS) to provide high-quality drinking water. However, the challenge of severe membrane fouling, which leads to frequent cleaning requirements, makes UF maintenance intensive. In this study, we tried to validate the feasibility of achieving zero fouling without the need for cleaning in the UF for SWSS, i.e., the fouling resistance can be maintained for a very long time without any increase. We operated dead-end UF systems at different fluxes, both with and without residual chlorine, and monitored the formation of fouling layers during filtration. The results demonstrated the successful achievement of zero fouling under a flux of 10 L/(m2 h) in the absence of chlorine, evidenced by no increase in transmembrane pressure for three months. This zero-fouling phenomenon was attributed to the formation of a self-regulating biofouling layer. This biofouling layer could degrade the deposited foulants and featured a loose morphology, facilitated by microbial activities in the cake layer. Although residual chlorine reduced the fouling rate by half at a flux of 30 L/(m2 h), it hindered the achievement of zero fouling at the lower flux of 10 L/(m2 h), due to its inhibitory effect on microbial activity. Intermittent operation of UF was effective in achieving zero fouling at higher fluxes (e.g., 30 L/(m2 h)). This benefit was primarily ascribed to the biodegradation of accumulated foulants and the expansion of biofouling layer during the pause of the intermittent filtration, which prompted the formation of biofouling layers with loose structure and balanced composition. To the best of our knowledge, this study is the first attempt to achieve zero fouling in UF for SWSS, and the findings may offer valuable insights for the development of cleaning-free and low-maintenance membrane processes.

Deep Learning Model-Based Demand Forecasting for Secondary Water Supply in Residential Communities: A Case Study of Shanghai City, China

Deep Learning Model-Based Demand Forecasting for Secondary Water Supply in Residential Communities: A Case Study of Shanghai City, China

Drinking water quality & health risk assessment of secondary water supply systems in residential neighborhoods

Drinking water quality & health risk assessment of secondary water supply systems in residential neighborhoods

Unraveling bacterial and eukaryotic communities in secondary water supply systems: Dynamics, assembly, and health implications

Secondary water supply systems (SWSSs) are crucial water supply infrastructures for high-rise buildings in metropolitan cities. In recent years, they have garnered public attention due to increased microbial risks. However, our understanding of SWSS microbial ecology, particularly concerning the composition of eukaryotes and the underlying mechanisms driving microbial dynamics and assembly in SWSSs, remains elusive. Herein, we conducted a comprehensive investigation on both eukaryotes and bacteria along the water transportation pathway and across various microbial habitats (water, biofilm, and sediment) in SWSSs. Sequencing results revealed that eukaryotes within SWSSs predominantly consist of protists (average abundance: 31.23%) and metazoans (20.91%), while amoebae accounted for 4.71% of the total. During water transportation from the distribution mains to taps, both bacterial and eukaryotic communities exhibited significant community shifts, and higher degrees of variation were observed for eukaryotic community among different locations within SWSSs. The normalized stochasticity ratio (NST) analysis demonstrated that bacterial community assembly was governed by stochastic processes, while eukaryotic community assembly was primarily shaped by deterministic processes. Within SWSS tanks, bacterial communities significantly varied across water, biofilm, and sediment, whereas eukaryotic communities showed minor differences among these habitats. The co-occurrence networks analysis revealed that tank biofilm and sediment harbored more eukaryote-bacterium linkages than water, suggesting biofilm and sediment might be hotspots for inter-kingdom interactions. We also applied FEAST analysis to track the source of tap water microbiota, results of which showed that household-tap bacteria mainly originated from tank water. In contrast, tank biofilm was identified as the primary microbial source to eukaryotes in household tap water. Additionally, engineering factors such as tank materials significantly affected amoeba community, and the SWSS configuration was found to influence Legionella and Mycobacterium abundances in SWSSs. Overall, results of our study shed light on the microbial ecology in SWSS and provide insights into SWSS management and health risk control.

Hidden risks: Simulated leakage of domestic sewage to secondary water supply systems poses serious microbiological risks

There are continuous reports about the pollution of the secondary water supply systems (SWSSs), among which domestic sewage leakage is the most serious. In this study, a pilot experiment lasting 70 days was conducted to explore the changes in physicochemical water quality and the microbial profiles in SWSSs polluted by different doses of domestic sewage through qPCR and high-throughput sequencing methods. The results showed that when domestic sewage entered the simulated water storage tank, a large amount of organic matter brought by domestic sewage quickly consumed chlorine disinfectants. High pollution levels (pollution index ≥ 1/1000) were accompanied by significant increases in turbidity and ammonia nitrogen concentration (p < 0.05) and by abnormal changes in sensory properties. Although different microbial community structures were found only at high pollution levels, qPCR results showed that the abundance of the bacterial 16S rRNA gene and some pathogenic gene markers in the polluted tank increased with the pollution level, and the specific gene marker of pathogens could be detected even at imperceptible pollution levels. In particular, the high detection frequency and abundance of Escherichia coli and Enterococcus faecails in polluted tank water samples demonstrated that they can be used for early warning. Moreover, it seems that the microorganisms that came with the domestic sewage lost their cultivability soon after entering SWSSs but could recover their activities during stagnation. In addition, the biofilm biomass in the polluted tank with high pollution levels increased faster at the initial stage, while after a longer contact time, it tended to remain at the same level as the control tank. This study emphasized the high microbial risk introduced by sewage water leakage even at imperceptible levels and could provide scientific suggestions for early warning and prevention of pollution to SWSSs.

Study on Gamma selection in the optimal operation of secondary water supply system based on deep Q-learning network

Abstract When the requirements for water pressure and quantity of drinking water for residents and industrial buildings exceed the capacity of the urban water distribution system, a secondary water supply system (SWSS) is supplied to users by pipelines through storage, pressurization, and other facilities. In China, SWSS has been installed in 97% of residential buildings and the operation of SWSS is directly related to the water pressure and water quality of the users' tap water. In this paper, the operation optimization objectives for the SWSS with storage facilities were proposed, and deep Q-learning network (DQN) was applied to optimize the control of SWSS. In this study, the pressure, the water age in the roof water tank, and the power consumption of the pumps were selected as the optimization objectives. The equation for the qualitative selection of the key hyperparameter (Gamma) was proposed and verified by the experiments in a community of City S in East China. The results indicated that with the decrease in the volume of the water tank, the larger Gamma value was recommended, and the more future conditions were considered. It is hoped that the result can be used as a reference in SWSS operation optimization.

Electromagnetic noise analysis of servomotor used in secondary water supply equipment

The servo motor has the characteristics of high precision, high speed and stable operation, but it will produce large electromagnetic noise in the process of using, which will affect the user experience. Based on the ANSYS multi-physics finite element analysis platform, this paper studies the electrical noise characteristics of servo motors used in a secondary water supply equipment under different speed conditions. The time and space distribution characteristics of the radial electromagnetic force acting on the motor stator are obtained by electromagnetic field analysis and modal analysis respectively. The natural frequency of the motor structure modal mode can also be obtained from these analyses. The causes of large electromagnetic noise were analyzed from the aspects of radial electromagnetic force and structural mode, and the position distribution of large vibration on the motor is obtained by harmonic response analysis. On this basis, the sound pressure level distribution of servo electromagnetic noise at different frequencies is obtained through acoustic simulation, which has referential significance for noise prediction and shell noise reduction optimization of related servo motors.

Distribution Characteristics and Health Risk Assessment of Emerging Contaminants from Raw Water to Drinking Water in Shanghai

By monitoring the distribution of emerging contaminants in drinking water from the source to the tap, the concentration of algal toxins, endocrine disruptors, and antibiotics in each water supply link were determined, and the health risks of emerging contaminants to the human body were evaluated. The results showed that algal toxins in the waterworks inflow were mainly MC-RR and MC-LR, whereas the only endocrine disruptors in the waterworks inflow were bisphenol-s and estrone. The algal toxins, endocrine disruptors, and antibiotics were removed effectively after the water treatment process in the waterworks. During the monitoring period, florfenicol (FF) was mainly detected, except in January 2020 when a large number of sulfa antibiotics were detected. The removal effect of FF was obviously correlated with the form of chlorine. Compared with that of combined chlorine disinfection, free chlorine disinfection had a better effect on the removal of FF. The health risk numbers of algal toxins, endocrine disruptors, and antibiotics were far less than 1, especially in the secondary water supply. The results showed that the three emerging contaminants in drinking water did not pose a direct threat to human health.

To close or open the tank input water valve: Secondary water-supply systems with double tanks will induce a higher microbial risk

Secondary water supply systems (SWSSs) are widely used to supply water to high-rise households in urban residential buildings. A special mode of double tanks with one used while another was spared was noted in SWSSs, which would facilitate microbial growth due to longer water stagnation in the spare tank. There are limited studies on the microbial risk of water samples in such SWSSs. In this study, the input water valves of the operational SWSSs consisting of double tanks were artificially closed and opened on time. Propidium monoazide-qPCR and high-throughput sequencing were performed to systematically investigate the microbial risks in water samples. After closing the tank input water valve, it may take several weeks to replace the bulk water in the spare tank. The residual chlorine concentration in the spare tank decreased by up to 85 % within 2–3 days compared with that in the input water. The microbial communities in the spare and used tank water samples clustered separately. High bacterial 16S rRNA gene abundance and pathogens-like sequences were detected in the spare tanks. Most antibiotic-resistant genes (11/15) in the spare tanks showed an increase in their relative abundance. Moreover, when both tanks within one SWSS were in use, the water quality of the used tank water samples deteriorated to varying degrees. Overall, running SWSSs with double tanks will reduce the replacement rate of water in one storage tank, and consumers who use taps served by the presented SWSSs may have a higher microbial risk.

Nitrifier Assemblages and Dynamics in Secondary Water Supply Systems: Predominance of Comammox Nitrospira in Tank Biofilm and Sediment

Nitrifiers in chloraminated drinking water distribution systems can trigger severe nitrification, resulting in subsequent water quality deteriorations. However, the occurrence and dynamics of nitrifiers in secondary water supply systems (SWSSs), an important water supply component beyond the distribution mains, remain largely unexplored. This study investigated the density, distribution, and diversities of nitrifiers in different microbial habitats (water, biofilm, and sediment) in SWSSs with different characteristics. Quantitative polymerase chain reaction analysis indicated higher gene copy numbers of ammonia-oxidizing archaea, ammonia-oxidizing bacteria, comammox clade A, and strict nitrite-oxidizing bacteria in SWSSs relative to the distribution mains (1.3–2.1 log10GC/mL increase, P < 0.05). Comammox were preferentially enriched in biofilm and sediments of SWSS tanks, highlighting biofilm and sediment as important ecological niches for comammox. Illumina sequencing of 16S rRNA genes revealed the presence of diverse nitrifiers (e.g., Nitrospira, Nitrosomonas, Nitrotoga, and Nitrobacter) in SWSSs, with distinct bacterial nitrifier communities noted in SWSS water compared to the distribution main water (analysis of similarity (ANOSIM), P < 0.05). Different bacterial nitrifier communities were noted between water and sediments in SWSS tanks, indicating niche segregations of nitrifiers (ANOSIM, P < 0.05). The results highlight SWSS as an important reservoir of nitrifiers and provide insights into nitrification monitoring and control strategies in SWSSs.

CFD simulation of spatiotemporal distribution of residual chlorine in secondary water supply tanks

The mixing, transportation, and reaction of chlorine in a secondary water supply system were investigated by a computation fluid dynamics model coupling with reaction kinetics.

A Large Acute Gastroenteritis Outbreak Associated with Both Campylobacter coli and Human Sapovirus - Beijing Municipality, China, 2021.

Campylobacter is a significant foodborne pathogen that leads to global outbreaks of acute gastroenteritis (AGE) usually affecting less than 30 individuals. Human sapovirus (HuSaV) is an enteric virus responsible for sporadic cases and outbreaks of AGE worldwide. In a study conducted in Beijing, HuSaV detection ranked second after norovirus. We present a discussion of the first large-scale outbreak of AGE caused by both Campylobacter coli (C. coli) and HuSaV. The outbreak involved a total of 996 patients and exhibited two distinct peaks over a period of 17 days. Through case-control studies, we identified exposure to raw water from a secondary water supply system as a significant risk factor. Among 83 patients, 49 samples tested positive for C. coli, 39 samples tested positive for HuSaV, and 27 samples tested positive for both pathogens using real-time polymerase chain reaction detection. Furthermore, whole-genome sequencing of 17 C. coli isolates obtained from 17 patients revealed that all isolates belonged to a highly clonal strain of C. coli. Outbreaks of AGE resulting from multiple pathogen infections warrant increased attention. This report emphasizes the significance of ensuring the safety of drinking water, particularly in secondary supply systems.

UV pretreatment reduced biofouling of ultrafiltration and controlled opportunistic pathogens in secondary water supply systems

Secondary water supply systems (SWSSs) with low residual chlorine may pose a risk to consumers due to the regrowth of some pathogenic microbes. This study investigated how UV pretreatment would affect biofouling of UF membrane when it was used to remove opportunistic pathogens (OPs) in SWSSs. Our results indicated that UV pretreatment inactivated OPs effectively through OH. and O2.−, when residual chlorine was present in water from SWSSs. After UV-UF treatment, Legionella spp., Legionella pneumophila, Mycobacterium spp., and Acanthameoba spp. were undetected in the water. After UV pretreatment, the extracellular polymeric substances (EPS) production and associated β-sheet in the protein of EPS were reduced due to the inhibition of related functional genes. Foulant analysis indicated that biofilms formed on the UF membrane after UV pretreatment had visible crevices and small pores, a lower bacterial volumetric fraction and lower roughness than the untreated UF membrane. This structure improved the UF flux and reduced the biofouling. The transmembrane pressure (TMP) of UF membrane gradually decreased from 74 KPa to 60 KPa after 70 days running. Therefore, UV pretreatment could be used to reduce the potential microbial risk of water from SWSSs, and mitigate biofouling of UF membranes.

Influencing factors of Legionella reproduction in secondary water supply operation and management

Objective: To analyze the pollution status and influencing factors of Legionella pneumophila in a secondary water supply facility in a city. Methods: From June to August 2020, a survey on the level of Legionella pneumophila in secondary water supply unit was carried out in a city in northern China, and 304 sets of secondary water supply facilities were included in the study. A total of 760 water samples were collected from the inlet and outlet water of the secondary water supply facilities and some water samples in the water tank were collected for the detection of Legionella pneumophila, standard plate-count bacteria and related physical and chemical indicators. Through questionnaire survey, the basic information of secondary water supply facilities and daily management of water quality were collected. Multivariate logistic regression model was used to analyze the influencing factors of Legionella pneumophila contamination. Results: Among 304 sets of secondary water supply facilities, most of them were located in residential buildings [57.24% (174/304)]. High and low water tank water supply, low water tank variable frequency conversion water supply and non-negative pressure water supply accounted for 26.6% (81/304), 36.8% (112/304) and 36.5% (111/304), respectively. About 25.7% of facilities (78/304) were positive for Legionella pneumophila. Among them, the positive rates of Legionella pneumophila in high and low water tank water supply, low water tank variable frequency conversion water supply and non-negative pressure water supply facilities were 38.3% (31/81), 29.5% (33/112) and 12.6% (14/111), respectively. The results of multivariate logistic regression model analysis showed that the disinfectant residue could reduce the risk of Legionella pneumophila contamination in water samples, and the OR (95%CI) value was 0.083 (0.022-0.317). The increase of the standard plate-count bacteria and conductivity might increase the risk of Legionella pneumophila contamination in water samples. The OR (95%CI) values were 3.160 (1.667-5.99) and 1.004 (1.001-1.006), respectively. Compared with the non-negative pressure water supply, the risk of Legionella pneumophila contamination of secondary water supply facilities was increased by water supply from high and low water tanks and variable frequency conversion water supply from low water tanks, with OR (95%CI) values of 4.296 (2.096-8.803) and 2.894 (1.449-5.782), respectively. Conclusion: The positive rate of Legionella pneumophila in secondary water supply in the study city is high. Disinfectant residue, conductivity and method of water supply are associated with the positive rate of Legionella pneumophila.

Pitting corrosion of 304 stainless steel in secondary water supply system

The effect of NaClO solution on pitting behavior of 304 stainless steel was investigated by electrochemical tests and composition analysis. The results show that the open circuit potential (OCP) shifts to the positive direction with the increase of [ClO−], indicating that the passivation film formed on the sample surface is faster, but, has no effect on pitting potential (Eb) in the first stage (< 24 h). After 24 h immersion, the pitting occurs because Cl− is detected in the wake of the decomposition of ClO− for its thermodynamics instability. In the later stage, the [Cl−] increases with the increase of [ClO−], correspondingly resulting in lower pitting resistance. X-ray photoelectron spectroscopy (XPS) reveals that the Cr/Fe atomic ratio in the passivation film decreases with the increase of [ClO−], because Cr(III) is oxidized to Cr(VI) and dissolves in the solution, which further weakens the pitting resistance of 304 stainless steel. The electrochemical impedance spectroscopy (EIS), combined with the Mott-Schottky analysis (MSA) was employed to verify the properties of the passivation film related to pitting.

Modeling of Water Distribution System Based on Ten-Minute Accuracy Remote Smart Demand Meters

In the process of water distribution system modeling, nodal demands have been deemed to be the most significant input parameters causing uncertainties. Conventionally, users of the same type are assigned the same demand pattern, which does not reflect the variability in demand patterns. In Hefei City, a lot of remote smart demand meters were installed in recent years, providing real-time water consumption data for different water user sites. In this study, the water consumption data based on 10 min accuracy were collected and used in the established EPANET model of the study area. A 48 h simulation, including workdays and weekends, was carried out, and each node’s base demand and demand pattern were accurately calculated according to the remote data. The results show that the accuracy of the model has met the modeling criteria (less than 2 m for all pressure monitoring points), and there is no need to calibrate the nodal demand. The established offline hydraulic model can better reflect the water consumption characteristics of each type of user and has revealed the significant influence of secondary water supply systems.

Numerical Simulation of Water Tank Circulation and Water Age Under Different Working Conditions

AbstractWith increasing real estate and apartment vacancy rates, the utilization rate of the water in water tanks is decreasing; this leads to an increase in the water age and deteriorates the water quality in water tanks. The general hydrostatic numerical model cannot simulate the flow field and water age of a water tank correctly because the horizontal scale of the water tank is equivalent to the vertical scale, and the vertical hydrostatic approximation assumption is no longer applicable. In this paper, the water age module is added to a three‐dimensional numerical model based on estuarine and coastal oceans, and a nonhydrostatic numerical model is developed to simulate and analyze the three‐dimensional flow field and the temporal and spatial variations in the water age of the water tank under different working conditions. The total water consumption and the effective volume of the water tank are the main factors affecting the water age, followed by the water level change range. The water age can be reduced to a lesser extent by setting the position of the inlet and outlet at a diagonal angle and adopting a larger inflow velocity. The distributions of the circulation and water age are mainly determined by the inlet in the influent process. There is no obvious dead water zone in the tank due to the strong disturbance, advection and diffusion in the secondary water supply process. The water age distribution in the water tank is mainly affected by advection, while diffusion plays a secondary role.

A survey on heavy metal concentrations in residential neighborhoods: The influence of secondary water supply systems

Water quality deterioration often occurs in secondary water supply systems (SWSSs), and increased heavy metal concentrations can be a serious problem. In this survey, twelve residential neighborhoods were selected to investigate the influence of SWSSs on the seasonal changes in heavy metal concentrations from input water to tank and tap water. The concentrations of nine evaluated heavy metals in all groups of water samples were found to be far below the specified standard levels in China. The concentrations of Fe, Mn, and Zn increased significantly from the input water samples to the tank and tap water samples in spring and summer (p < 0.05), especially for the water samples that had been stagnant for a long time. Negative correlations were found between most of the heavy metals and residual chlorine (Fe, Cu, Zn, and As, r = -0.186 to -0.519, p < 0.05). In particular, a high negative correlation was observed between Fe and residual chlorine (r = -0.489 to -0.519, p < 0.01) in spring and summer. Fe and Mn displayed positive correlations with turbidity (r = 0.672 and 0.328, respectively; p < 0.05). In addition, Cr and As were found to be positively associated with some nutrients (NO3−, TN, and SO42−; r = 0.420-0.786, p < 0.01). The material of the storage tanks had little influence on the difference in heavy metal concentrations. Overall, this survey illustrated that SWSSs may pose a chronic threat to water quality and could provide useful information for practitioners.