Study On The Structural Impact Of Boiling On Pipe Network Particles And Its Water Quality Ris

Discoloration events in drinking water distribution systems（DWDSs）caused by iron particles have occurred worldwide,boiling has been applied in drinking water treatment household globally,but the effects of boiling on iron particles are not clear.This article investigated the effects of boiling on water quality under different crystal forms of iron particles,temperature gradients,and initial chlorine concentrations,revealing the potential health risks during the boiling process in the presence of particulate matter in the pipeline network.The main conclusions are listed as follows:（1）For effect of boiling on different kinds of iron particles（including loose deposits from DWDS and their main components Fe OOH,Fe₂O₃ and Fe₃O₄）,when At 10 mg/L,the turbidity values before/after boiling of Fe₂O₃,Fe₃O₄ and Fe OOH were 134.00/121.00 NTU,25.07/21.22NTU and 120.40/114.20 NTU respectively.All the particles had a lower degree of crystallinity after boiling.After boiling,the number of particles in loose deposits increased and the particle size decreased,while iron oxides were on the contrary.Among the three iron oxides,the existence Fe₃O₄ and Fe₂O₃ had different effects on disinfection by-product（DBPs）formation.The activity of microorganisms was the highest under particle concentration 0.1 mg/L than other concentrations for all the particles,but the total microbiological risks were still very low after boiling.Thus,the boiling treatment would increase the chemical risks due to particle structure change and DBPs formation.（2）By studying the mechanism of changes in the structure of particles under different temperature gradients,we found that during the boiling process of tap water containing particles,the turbidity did not change significantly before 60°C,but suddenly increased after 90°C.Under the condition of particle concentration of 100 mg/L,the initial concentration was 194NTU,and after boiling（100°C）,it reached about 220 NTU;After boiling,the particle size decreases,the number of particles increases,and the agglomeration decreases.Boiling increased the content of dissolved organic matter in water,and the presence of particulate matter led to an increase in DOM.In addition,the specific surface area and roughness of the particles increased after boiling,increasing from 106.8 to 123.4 cm²/g.The toxicity of pipeline particulate matter to human gastric epithelial cells is high,and there is a good negative linear relationship between turbidity and cell survival rate.The particulate matter led to an increase in intracellular reactive oxygen species.In addition,the presence of particles promoted the generation of disinfection by-products with more aromatic structures and higher toxicity.（3）By exploring the impact of boiling on the water quality of actual"yellow water"under different residual chlorine concentrations,we found that residual chlorine cannot be completely eliminated after boiling when the residual chlorine level was high.When the residual chlorine value was 2 mg/L or above,boiling can eliminate residual chlorine from clear tap water by about0.9-1.0 mg/L,and remove residual chlorine from"yellow water"by about 1-1.5 mg/L;When residual chlorine was 5 mg/L,only 16.9%of residual chlorine was removed from clear water,while"yellow water"is 28.0%.Old cast iron pipes will release natural organic matter（NOM）into the water,and NOM will generate disinfection by-products under the action of residual chlorine,thus accelerating the decay of residual chlorine.Boiling"yellow water"significantly increased NOM content,and after keeping the water sample boiling for 60 minutes,the NOM content increased by about 50%.Residual chlorine will accelerate the release of iron particles from the pipe wall into the water,and compared to 3 mg/L residual chlorine,the release of iron within 12 h of 5 mg/L residual chlorine increased by 29%.After boiling,the amount of trihalomethane in clear water decreased by 67.42%,while the amount of haloacetic acid increased by 29.81%;For"yellow water",after boiling,trihalomethane decreased by 48.00%and haloacetic acid increased by 40.27%.Thus,the presence of particulate matter can improve the effectiveness of boiling in eliminating residual chlorine,but increases the risk of DBPs.Therefore,though boiling is an effective means to eliminate microbial risks in water quality,in the presence of particles,new chemical risks may arise during the boiling process due to structural changes in particles and the transformation of harmful DBPs.