南方某市锰致规模性“黄水”发生规律及应对

Occurrence of and Response to Large-scale Manganese-caused“Yellow Water”Events in a Southern City

南方某市2019年以来给水管网“黄水”问题投诉占到用户关于水质问题投诉的约50%。总结多个水厂供水区域“黄水”发生规律发现,集中发生在2019年7月和8月的规模性“黄水”主要致色成分为锰,其与出厂水锰浓度升高至0.02 mg/L以上直接相关,“黄水”样品中的锰超过0.1 mg/L标准限值,反映出管网中发生了锰的沉积再释放问题;色度与锰浓度呈显著正相关。主要致色成分为铁锰的非规模性“黄水”的主要原因是管网腐蚀以及锰的沉积再释放。因水源而引发“黄水”的水厂在将水库水切换回Mn(Ⅱ)浓度较低的江水后,集中性“黄水”投诉很快消失。对于另一因原水锰浓度升高而导致“黄水”投诉的水厂,在水库水锰浓度升高后加大投氯量、投加氢氧化钠等控锰效果并不理想;随后同时投加5 mg/L粉末活性炭(PAC)和1 mg/L氯,通过构建催化氧化能将出厂水锰浓度迅速控制在0.01 mg/L以下,成功抑制管网“黄水”。提升水库取水高度后进厂水锰浓度也相应下降。综上,监测原水Mn(Ⅱ)浓度,采取高效除锰措施将出厂水锰浓度控制在0.02 mg/L以下,以及对管网进行维护更新是控制“黄水”的关键。

Complaints about yellow water in drinking water distribution system(DWDS)in a southern city since 2019 accounted for 50% of user complaints about water quality problems.By analyzing the pattern of yellow water occurrence in the water supply area of several water treatment plants(WTPs),it was found that the main color-causing component of the large-scale yellow water events that occurred in July and August 2019 was manganese,which was directly related to the increase of manganese concentration in the finished water to more than 0.02 mg/L.Yellow water with Mn concentration exceeding the standard limit of 0.1 mg/L reflected the problem of Mn deposition and re-release in DWDS.The Mn concentration was significantly and positively correlated with the chromaticity of yellow water samples.The small-scale yellow water events with iron and manganese being the main color-causing components was mainly caused by corrosion of DWDS and the deposition and re-release of Mn.WTPs with yellow water events had no concentrated yellow water complaints after switching the reservoir water back to river water with lower Mn(Ⅱ)concentrations.For another WTP that had been using reservoir water,after the Mn concentration of reservoir water increased,the efficiency of Mn control was not effectively reduced by increasing the dose of chlorine and sodium hydroxide.Then 5 mg/L powdered activated carbon and 1 mg/L chlorine were added simultaneously,and the Mn in the finished water was rapidly controlled below 0.01 mg/L by catalytic oxidation mechanisms,which successfully suppressed the yellow water occurrence in DWDS.The concentration of Mn in the influent also decreased after the depth of the reservoir water uptake location was reduced.In conclusion,monitoring Mn(Ⅱ)concentration in source water,taking efficient Mn removal measures,maintaining the Mn concentration in the finished water below 0.02 mg/L and renewing DWDS are critical for controlling yellow water events.