Status and Source Analysis of Aluminum Pollution in Xi'an Section of the Weihe River

A preliminary study on aluminum pollution in Xi'an section of the Weihe River was carried out during 2008-2009. The result indicated that aluminum salt concentration in the Weihe River ranged from 0.10 mg/L to 4.41 mg/L, all of which exceeded the water quality criteria of both the US and Canada and could do harm to human health. In normal period of 2008, although the flow rate of the Weihe River increased from 36.4 m³/s to 81.7 m³/s after flowing through Xi'an, the aluminum concentration still rose to 0.43 mg/L from the initial value of 0.29 mg/L; and a total of 66 tons of aluminum flowed into the Weihe River from Xi'an during March 2008, of which one-fifth came from the Zaohe River. In dry period of 2009, the aluminum concentration increased by almost 1.7 times, and would result in the acute toxicity effects to surrounding aquatic lives. According to this investigation, the major cause of the increase of aluminum concentration in rivers was the flocculants used in wastewater treatment process, a great part of which were from paper mills. Since August 2008, stricter discharge standards for the paper making industry have been put into practice in China, so chemical flocculation plays an increasingly important role in wastewater treatment. All plants investigated use aluminum salts as flocculants, and this is the main reason why the aluminum concentration rose in surface waters.