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.

Effects of secondary water curing on the long-term strength and durability of concrete after steam-autoclave curing

To study the effects of secondary water( SW) curing of 20 ℃ for 7 d on concrete long-term strength and durability after steam-autoclave curing, concrete specimens were fabricated and subjected to standard,steam-autoclave or steamautoclave + SW curing. The compressive strength,accelerated carbonation depth, and Coulomb electric charges of the specimens were tested at the ages of 28,90,180,and 360 d.Furthermore,mercury intrusion porosimetry experiments on the specimens were conducted at the age of 180 d. Results indicate that compared with standard curing,steam-autoclave curing can enhance the early-age strength of concrete; however, it is detrimental to the development of later-age strength, and reduces chloride and carbonation resistance. Due to the replenishment of water into concrete,SW curing can refine the micro-pore size and decrease the ratio of harmful and more harmful pores in concrete. As a result,SW curing is effective in improving the long-term strength and durability of steamautoclaved concrete,and makes it approach that under standard curing. The improvement amplitudes of SW curing on the concrete compressive strength, chloride and carbonation resistance at 360 d can reach 20. 3%,48. 6%,and 80. 9%,respectively.

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.

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.

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.

Secondary cooling technology for high-efficiency continuous billet-casting

The mathematical model of high-efficiency continuous billet casting was developed, incorporating the effective spraying water coefficient and the effective specific spraying water flowrate of secondary cooling. To realize uniform cooling in secondary cooling zones, the spraying cooling structure and the arrangement of nozzles were redesigned and optimized, and an additional spraying cooling zone was used. A new secondary cooling model of spraying water was built. It was found that the required spraying water flowrate of a cooling zone was related with the casting speed, the casting temperature, the compositions of liquid steel and the cooling water temperature of secondary cooling. The operation of the reformed caster proved that the spraying cooling structure and the new secondary cooling model were suitable, and the casting speed was greatly enhanced. The highest casting speed was （3.8 to 4.0） m/min for billet with a section of 150× 150 mm^2. The quality And the outout of the billet were imoroved, andthe economical benefit was heightened.

Molecular characterization of effluent organic matter in secondary effluent and reclaimed water:Comparison to natural organic matter in source water

Municipal wastewater reclamation is becoming of increasing importance in the world to solve the problem of water scarcity. A better understanding of the molecular composition of effluent organic matter（Ef OM） in the treated effluents of municipal wastewater treatment plants（WWTPs） is crucial for ensuring the safety of water reuse. In this study, the molecular composition of Ef OM in the secondary effluent of a WWTP in Beijing and the reclaimed water further treated with a coagulation–sedimentation–ozonation process were characterized using a non-target Fourier transform ion cyclotron resonance mass spectrometry（FT-ICR MS） method and compared to that of natural organic matter（NOM） in the local source water from a reservoir. It was found that the molecular composition of Ef OM in the secondary effluent and reclaimed water was dominated by CHOS formulas, while NOM in the source water was dominated by CHO formulas. The CHO formulas of the three samples had similar origins. Anthropogenic surfactants were responsible for the CHOS formulas in Ef OM of the secondary effluent and were not well removed by the coagulation-sedimentation-ozonation treatment process adopted.

Numerical simulation on solidification behavior and structure of 38CrMoAl large round bloom using CAFE model

A coupled cellular automaton-finite element model was developed to simulate the solidification behavior and structure of 38CrMoAl large round bloom,in which mold electromagnetic stirring+final electromagnetic stirring was taken into consideration,under different superheat,casting speeds,and secondary cooling water flow.Industrial trials for infrared temperature measurement and macro etch experiments of the post-test round bloom samples were used to verify the simulated solidification structure and temperature field.The simulation results show that superheat and secondary cooling water flow have little influence on the surface temperature,center temperature,and center solid fraction while casting speed has a more obvious influence on solidification behavior.With the increase in the casting speed of 0.02 m min^(-1),the solidification position is prolonged by about 1.64 m.With the increasing specific water ratio by 0.02 L kg^(-1) each,the surface temperature of the secondary cooling zones decreases by about 18℃,and the solidification position shortens by about 0.11 m.As the superheat increases from 10 to 40℃,the ratio of the equiaxed crystal zone decreases from 35.98% to 23.98%.The casting speed and secondary cooling water flow increase the equiaxed crystal ratios of the large round bloom,but neither is significant,both being about 2%.

Chemical characteristics and source apportionment of PM_(2.5) between heavily polluted days and other days in Zhengzhou, China

PM（2.5） samples were collected in Zhengzhou during 3 years of observation, and chemical characteristics and source contribution were analyzed. Approximately 96% of the daily PM（2.5） concentrations and annual average values exceeded the Chinese National Ambient Air Quality Daily and Annual Standards, indicating serious PM（2.5） pollution. The average concentration of water-soluble inorganic ions was 2.4 times higher in heavily polluted days（daily PM32.5 concentrations ＆gt; 250 μg/mand visibility ＆lt; 3 km） than that in other days, with sulfate, nitrate, and ammonium as major ions. According to the ratio of NO-3/SO2-4,stationary sources are still the dominant source of PM（2.5） and vehicle emission could not be ignored. The ratio of secondary organic carbon to organic carbon indicated that photochemical reactivity in heavily polluted days was more intense than in other days.Crustal elements were the most abundant elements, accounting for more than 60% of 23 elements. Chemical Mass Balance results indicated that the contributions of major sources（i.e., nitrate, sulfate, biomass, carbon and refractory material, coal combustion, soil dust,vehicle, and industry） of PM（2.5） were 13%, 16%, 12%, 2%, 14%, 8%, 7%, and 8% in heavily polluted days and 20%, 18%, 9%, 2%, 27%, 14%, 15%, and 9% in other days, respectively.Extensive combustion activities were the main sources of polycyclic aromatic hydrocarbons during the episode（Jan 1-9, 2015） and the total benzo[a]pyrene equivalency concentrations in heavily polluted days present significant health threat. Because of the effect of regional transport, the pollution level of PM（2.5） in the study area was aggravated.