ZHAO Bei,ZHANG Hai-xiang,LI Li,et al.Risk Assessment for Water Quality of Distribution Network in Areas Using Self-supply Wells after Water Source Replacement[J].China Water & Wastewater,2021,37(13):32-39.
自备井置换区域管网水质风险评估
- Title:
- Risk Assessment for Water Quality of Distribution Network in Areas Using Self-supply Wells after Water Source Replacement
- 摘要:
- “南水北调”工程全面通水后，受水区城市供水保证率提高。为保护地下水资源，北方某市正在逐步推进自备井区域水源置换工作。该市不同区域自备井水源置换后，碱度、硬度、硝酸盐、氯化物和硫酸盐含量均明显降低，用户水质得到改善，但部分小区在水源置换初期存在浊度和总铁含量升高现象。经管垢取样分析，老旧管道内管垢层厚且疏松，基本以针铁矿为主，稳定性较差，水源置换后管垢中的铁易释放。采用水质差异度指数计算方法，并结合管道现状、新水源消毒剂浓度和用水量调整情况，所确定的“黄水”发生风险级别与实际监测结果基本一致。自备井模拟水源置换试验结果表明，对于管龄>20年的铸铁管，停滞时间为4 h时出水浊度和总铁的增加量需3个月才可趋于稳定并达标，管垢内的主要成分在508 d试验期间基本与初始相同，稳定性无提高，当水质变化时有再次发生“黄水”的风险。
- Abstract:
- After the South-to-North Water Diversion Project completely finished, the water supply guarantee rate of intake cities had been improved. In order to protect groundwater resource, the city in northern China was promoting the water source replacement in areas using self-supply wells. For obvious decrease of the alkalinity, hardness, nitrate, chloride and sulfate, the water quality of consumers in different areas using self-supply wells had all been significantly improved after water source replacement, while the turbidity and total iron of tap water increased in some communities during the initial stage. By analyzing of pipe scales, the corrosion layers in old pipes were thick, loose, and mainly goethite with poor stability, which were tending to release iron after water source replacement. The prediction risk level of “red water”, determined by the water quality diversity index, as well as combining the pipe condition, the disinfectant concentration of new water source and the water consumption, was conformed to the actual monitoring results. According to simulated water source displacement test, it took 3 months for the increased turbidity and total iron in the tap water in cast iron pipes with age greater than 20 years to stabilize and meet the standard when the stagnation time was 4 h. The main component of pipe scales was basically as same as the initial ones during 508 days of operation, which meant high risk of “red water” recurring when water quality changed.
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