Spatial variations of aluminum species in drinking water supplies in Xi'an studied applying geographic information system

Abstract

This article aimed to investigate the variation of aluminum species and the effects of coagulant type and water quality on aluminum speciation in drinking water. Statistical analysis showed that the concentration of total aluminum (Al T) of drinking water in Xi'an ranged from 0.051 to 0.417 mg/L and the concentration of Al T in about 24.7% studied samples was higher than the currently recommended value (0.2 mg/L). The areas fed by surface water plants had a larger portion (39.4%) of samples over the recommended value. In drinking water treated by alum coagulant, the average concentration of monomeric aluminum (Al a) was higher than that in water treated by poly aluminum chlorine (PACl) and poly aluminum ferric chloride (PAFC). The average concentrations of polynuclear aluminum (Al b) and colloidal/suspended aluminum (Al c) in the drinking water treated by alum were lower than those in water treated by PACl and PAFC. There was a notable decrease in Al T along with the delivery pipeline away from the plants, with an average decline of about 36 μg/(L·km). Besides coagulant type, water quality also could affect aluminum speciation. In drinking water without orthophosphate, the concentrations of Al a and Al T were positively correlated with pH; while, in drinking water with orthophosphate, the concentrations of Al a and Al T were negatively correlated with pH. The addition of orthophosphate salts in the drinking water treatment process would be an effective method for aluminum control in pH range 6.5–8.2.