Occurrence and removal of dissolved metals in surface drinking water sources from Yangtze River Delta Region, East China

Multiple factors such as temperature, human activity, climate and hydrochemistry conditions affect water quality of drinking water sources. This research mainly focused on monitoring the dissolved trace metal concentrations from water samples in several important drinking water sources including the Huangpu River, Qingcaosha Reservoir and several reservoirs for West Tai Lake from spring to summer in 2013. The changes of trace metal concentrations and removal efficiencies in four typical water treatment plants (WTPs) in China corresponding to these water sources were also investigated. Results indicated that Qingcaosha Reservoir, Hengshan Reservoir and Youche Reservoir were less influenced by anthropogenic activities, therefore the change of dissolved metal concentrations was not significant except for local geochemical elements such as Sr and Ba. The other two water sources that flow through large industrial areas were greatly affected with elevated trace metal concentrations such as Fe, Mn, Zn, Ni, P, which can be attributed to anthropogenic and socio-economic impacts. High Fe and Mn concentrations were observed at low pH while high electric conductivity gained relevance with high geochemical metal concentrations. The occurrence of high dissolved Ni, Cu, Co and Zn was associated with high ammonia concentration and low pH, which might result from the formation of metal ammine complexes. In addition to the raw water information, dissolved metal concentrations after the treatment by individual WTP processes indicated that biological activated carbon and sand filtration achieved significant removal of Mn and Fe, while coagulation/flocculation efficiently reduced the concentrations of As, Pb and Zn. However, oxidation processes might form highly toxic Cr(VI) and increase the dissolved Cr concentrations which posed a potential threat to human safety. These preliminary results showed the necessity of control technology for dissolved trace metals in micro-polluted water sources for providing safe water.