No abstract

Analytical methods were developed to accurately determine the levels of the most prevalent trace metal contaminants in a variety of alum feedstocks used in the coagulation process of drinking water treatment. A combination of chelation ion chromatography, chelation extraction–atomic absorption spectrometry, and hydride generation atomic fluorescence allowed for the selective isolation of trace metals from the alum matrix with a high degree of precision and sensitivity. Trace levels of arsenic, cadmium, chromium, copper, manganese, nickel, lead, and zinc were found in the range of 20–330 μg/g aluminum (Al); iron, recognized as a co‐contaminant in the raw material, was present at 20 mg/g Al. By extrapolating these measured levels to an upper yet realistic applied dosage of alum in drinking water treatment, the authors could predict the contaminants' concentrations (under a worst‐case scenario) in both the finished water and alum sludge. For finished water even if it was assumed that none of the trace metals was removed during coagulation, the contaminants' concentrations did not exceed drinking water standards, and their contribution reached only a small fraction of the permitted maximum contaminant level. In a scenario in which the trace metals were assumed to be removed during the coagulation process, levels that would accumulate in the alum sludge would not be significant enough to heavily influence decisions to apply alum sludge to land for agricultural uses.