| Desalinated seawater instead of regular source water to provide drinking water was an important way to solve the shortage of drinking water,and also brought out a new challenge to the old drinking water distribution system.The water quality of low pH,low alkalinity and low hardness could make turbidity,color and iron concentrations exceeded,and led to red water problem.This paper mainly focused on the chemical stability of desalinated seawater in drinking water distribution system,the pipeline simulation reactors were built,the effects of regulation technology was studied,and a reasonabletarget was proposed.The relationship of water quality identification index and iron release,the effects of inorganic ions was studied,and the mechanisms of aggressive anions on corrosion scales were discussed.Comparison of five common pipe materials was a theoretical basis for laying new pipe so that desalinated seawater could be sent to Beijing.These were important technical and theoretical basis for sending desalinated seawater to Beijing.The main conclusions were listed as follows:There were positive effects of pH adjustment for stability of desalinated seawater,adjust pH to 7.8,the color,turbidity and total iron concentration decreased by 51.8%?60.8%and 32.7%,so the proposed pH was 7.8~8.5.The corrosion control effects of alkalinity adjustment was better than pH adjustment separately,when the alkalinity was above 130mg/L,the turbidity,color and total iron concentration decreased by 83.3%,78.8% and 73.4%,adjusting alkalinity above 130mg/L was recommended.Mixing the desalinated seawater with regular drinking water could improve water quality in many ways,when the ratio of desalinated seawater was 60%,the turbidity,color and total iron concentration decreased by 78.9%,83.9% and 89.5%,so mixing desalinated seawater with regular drinking water with the ratio of desalinated seawater was less than 60% could improve the effect of pipeline corrosion control.When the CCPP was above 0.9mg/L,it could be effectively to maintain the stability of desalinated seawater in the process of transmission and distribution.And when the water was corrosive(CCPP<-1.2mg/L,and LRI>0.85),the concentration of iron release and the chemical stability index was in good linear relationship.Chloride and sulfate could promote the corrosion,the higher the concentration,the stronger.With the low pH,low alkalinity and low hardness of desalinated seawater,there was a limit for corrosive anion of old pipelines,or the water quality would be dramatically worse.The limit for chloride was in the range of 42.6~213.0mg/L,and for sulfate was 57.6~192.0mg/L.Under the same equivalent concentration,the promoting corrosion effect of chloride was stronger than sulfate,the inhibiting corrosion effects of magnesium was stronger than calcium,combining magnesium and calcium was better than any separate ion,the closer the ratio was,the effect was better.In the terms of stability of water quality,cast iron pipes could be used to transport the desalinated seawater,the regulation of desalinated seawater quality was necessary.The ratio of desalinated seawater mixing with regular tap water was less than 40%,or adjusted the CCPP to above 0.89mg/L.The test water quality was not up to the drinking water standard,so the galvanized pipes and cement mortar lined pipeswithsmall diameter tube could not be used for transmission and distribution of desalinated seawater.Compared the PVC pipes with epoxy resin lined pipes,the TOC and the number of microbial of epoxy resin lined pipes were lower,the test water quality was better,so epoxy resin lined pipes was more suitable for transmission and distribution of desalinated seawater than PVC pipes. |
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