Measurement and Effect of Trace Element Contaminants in Alum

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.

Coagulant Recovery from Water Treatment Residuals: A Review of Applicable Technologies

“…Despite this, some studies have suggested that recycled coagulant does have a detrimental impact on treated water quality with respect to color in treated water when dosed at 3.9 mg/L Al (Eyring et al, 2002) Unselectively recovered alum worst-case potential conc. in treated water when dosed at 26 mg/L Al (Bishop et al, 1987) Selectively recovered alum diluted when dosed at 3.9 mg/L recovered Al ( Recovered with 20% extra dose of fresh alum * Recovered (81% of total) 0 3.2 (11.5) 3.2 (11.5) Fresh 3.9 0.7 1.5 Total 3.9 3.9 (11.5) 4.7 (11.5) * A hypothetical extra dose of coagulant to compensate for removal of organic contaminants carried over in recovered coagulant.…”

“…in treated water when dosed at 26 mg/L Al (Bishop et al, 1987) Selectively recovered alum diluted when dosed at 3.9 mg/L recovered Al ( Recovered with 20% extra dose of fresh alum * Recovered (81% of total) 0 3.2 (11.5) 3.2 (11.5) Fresh 3.9 0.7 1.5 Total 3.9 3.9 (11.5) 4.7 (11.5) * A hypothetical extra dose of coagulant to compensate for removal of organic contaminants carried over in recovered coagulant. Doses and recovery yield adapted from Eyring et al (2002); and Prakash and Sengupta (2004). (Lindsey and Tongkasame, 1975), although reported increases in trihalomethane formation potential (TTHMFP) have been small (Bishop et al, 1987).…”

Hexavalent chromium review, part 2: Chemistry, occurrence, and treatment

“…Cr may also be a trace contaminant in treatment chemicals. For example, Eyring et al (2002) measured Cr in alum coagulants, potentially yielding 0.24 µg/L Cr in water at commonly applied alum doses. More recently, a water treatment plant in Missouri found that Cr(VI) increased from 0.1 µg/L in the raw water to 0.6 µg/L at the end of the treatment plant (MDNR, 2010), with the suspected source being the plant's alum and/or lime.…”

Trace Contaminants in Water Treatment Chemicals: Sources and Fate

“…One important advantage of using this technique is that low dilution factors (1:4) are suitable. A second major advantage of ICP–OES versus other methods is that multiple metals (up to 28 in this study) can be analyzed in a single run (compare 12 metals analyzed using five separate analytical methods, as outlined in Eyring et al, 2002). Before aspiration into the ICP–OES apparatus, the treatment‐chemical samples were diluted with distilled water and acidified with reagent‐grade hydrochloric acid.…”

“…The most recent data available in the literature on the trace metal composition of alum products were reported by Eyring et al (2002). These alum products were not identified, but they are characteristic of low‐iron alum.…”