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Arsenic (As) is common in US raw watersources, particularly in groundwater ofthe midwestern and western states.Most water utilities meet the currentAs maximum contaminant level (MCL) of 50ug/L, but if the MCL is lowered to 10 ug/L,cost-effective As removal will be critical to anincreased number of water utilities.Groundwaters that have high As concentrationssometimes also contain moderate tohigh concentrations of ferrous iron (Fe).When conventional water treatment methodsare used to remove the soluble Fe by oxidizingit to hydrous ferric oxide, As is alsoremoved. Thus, this paper discusses optimizingAs removal at water treatment plants thatremove Fe.Common dissolved substances, includingbicarbonate, silica (Si), and phosphate(PO43-) interfere with As removal by ironoxide. This study was undertaken because theeffects of bicarbonate and Si on As removalwere not well known. However, these substancesare present in all source waters andmay affect As removal at many water treatmentplants. Holm shows how a widely usedchemical-equilibrium computer model can beeasily modified to predict such interferences.The article also describes experiments thatwere designed to simulate the effects of bicarbonate,Si, and PO43- on concurrent Fe andAs removal. According to the author, if asource water contains As and Fe, it may bepossible to improve As removal by loweringthe pH. He also points out that the computermodel may be useful in designing processessuch as Fe removal or ferric chloride coagulationto remove As. Includes 50 references, table, figures.

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Edition: Vol. 94 - No. 4 Published: 04/01/2002 Number of Pages: 8 File Size: 1 file , 440 KB