Evaluation and optimization of secondary water supply system renovation

Due to pollution in second water supply system (SWSS),nine renovation alternative plans were proposed and com-prehensive evaluations of different plan based on Analytical Hierarchy Process (AHP) were presented in this paper. Comparisons of advantages and disadvantages among the plans of SWSS renovations provided solid foundation for selecting the most appro-priate plan for engineering projects. In addition,a mathematical model of the optimal combination of renovation plans has been set up and software Lingo was used to solve the model. As a case study,the paper analyzed 15 buildings in Tianjin City. After simulation of the SWSS renovation system,an optimal scheme was obtained,the result of which indicates that 10 out of those 15 buildings need be renovated in priority. The renovation plans selected for each building are the ones ranked higher in the com-prehensive analysis. The analysis revealed that the optimal scheme,compared with two other randomly calculated ones,increased the percentage of service population by 19.6% and 13.6% respectively,which significantly improved social and economical benefits.

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

Secondary water supply systems(SWSSs)are important components of the water supply infrastructure that ensure residents’drinking water safety.SWSSs are characterized by long detention time,warm temperature,and unreasonable management,which may trigger the deterioration of water quality and increase risks.In this study,drinking water quality index(DWQI)and health risk assessment(HRA)were selected and modified to quantitatively assess the water quality and health risks of SWSSs in residential neighborhoods.In total,121 seasonal water samples were selected.It was observed that the water quality was excellent with the DWQI of 0.14±0.04,excluding one sample,which was extremely poor owing to its excessive total bacterial count.The HRA results revealed that the health risks were low:negligible non-carcinogenic risk for any population;negligible and acceptable carcinogenic risk for children aged 6–17 and adults.However,samples revealed higher carcinogenic risk(7.63×10−5±3.29×10−6)for children aged 0–5,and arsenic was the major substance.Summer samples had poor water quality and higher health risks,which called for attention.To further investigate the water quality and health risks of SWSSs,monthly sampling was conducted during summer.All 24 water samples were qualified in Chinese standard(GB 5749-2022)and characterized as excellent quality.Their HRA results were consistent with the seasonal samples’and the health risks were mainly concentrated in May.Overall,our study provides a suitable framework for water quality security,advice for managers,and references for administrators in other cities.

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(NO, TN, and SO;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.

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 a-Proteobacteria to g-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.