The authors prepared an initial report covering their work for the 90th Annual Conference (see JOURNAL, Oct. 1970). Since then, they have had the opportunity to scrutinize the use of such treatment in several communities and have arrived at several additional conclusions.Since the first presentation of the paper, "Preventing Iron Deposition with Sodium Silicate," 1 work has con tinued on the use of silicates, and some thirteen Ontario communities now add silicate to their water supply for iron control on a regular basis, with six more municipalities about to follow suit. Observations on such usage date back over 2 yr. Further investigations into the nature of the pertinent water chemistry involved have also been possible, with some ob servations being made regarding man ganese sequestering and some initial tests directed toward removal of silicastabilized iron after complex forma tion.The initial policy adopted by the commission has been generally to limit recommendation of silicate addi tion to water supplies containing up to 1.3 mg/liter of iron. Although practical limitations on the amount of iron that can be handled by the sili cate procedure have yet to be en countered, such solubilization of sig nificant quantities of ferric ion in pot able water essentially represented a new phenomenon in water technology. The process, though viewed favorably, has been approached cautiously in or der to determine possible disadvan tages of the technique prior to any much broader application. The max imum silicate addition being used mu nicipally at present is 6.2 mg/liter SiO,, Two years of experience in the town of Markham have yielded very favorable results.The possibility that domestic hot-water tanks might still tend to accumulate iron by ther mal breakup of the silicate complex has not been indicated at Markham. Iron problems with hot-water tanks dropped abruptly from about three calls a day prior to the start of silicate addition and have continued to de crease to the present low of about one every six months. Even a year after commencement of the silica feed, im provements in the water quality in outlying areas of the distribution sys tem continued to be noticed as rem nant iron-staining properties dimin ished further.The latter observation seemed to be the result of a general slow clean ing of the distribution mains of iron deposits. A recent break in the town's main was serviced to find that even an old pipeline known to have been badly tuberculated had cleared up to become almost indistinguishable from quite recently replaced valve fit tings on the same line. A thin trans lucent coating was reported to be coat ing metal surfaces, suggesting that significant corrosion protection was also taking place.Briefly, the original paper described how the addition of a small amount of N sodium silicate to a water supply at the point of chlorination (that is, iron oxidation) would fully stabilize the water's iron content. Iron thus stabil ized avoids iron deposition in water distribution mains as well as the gen eral nuisanc...
Since not all water supplies respond to a standard iron removal process, it is often necessary to carry out pilot testing in order to determine a method that is effective, as well as economical.
The author of this letter to the editor details Canadian experience with the use of biological treatment for water purification. In a study designed to come up with parameters for new filtration facilities in Markam Township, Ontario, it was learned that filters without prechlorination had been removing an organic precursor to a strong chloroflavor problem. This study seemed to verify that biological growths absorb those substances that are most biologically accumulative. The new aeration‐plus‐pressure filter plant designed at 5 Igpm/sq ft successfully removed the chloroflavor. The author emphasizes the relative value of organic stabilization compared with the nitrification aspects of an earlier article by Rittman and Snoeyink entitled, “Achieving Biologically Stable Drinking Water” in the October 1984 Journal American Water Works Association. In another instance, a red water problem in the community of Brooklin, Ontario, was cleared up by reverting from prechlorination to postchlorination at the iron removal filter and by restoring the original prefilter air injection.
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