. Preventive medicine and hygiene. Fig. 125.—Cross Sectiox of IxTERiiiTTEXT Saxd Filter. are not overloaded. When raw sewage is applied directly to the bedsthe rates of application vary from 50,000 to 150,000 gallons per acredaily, the population served per acre being from 300 to 1,200. Withpreliminary treatment higher rates may be used, and the sewage of1,500 to 2,000 people applied per acre. The filters are usually dividedinto beds bv means of earth embankments which cover the distributingpipes. Often they are underdraiiiod with tiles laid 20 to 30 feet apart. Fig. 126.—Inclined Screen Opera
. Preventive medicine and hygiene. Fig. 125.—Cross Sectiox of IxTERiiiTTEXT Saxd Filter. are not overloaded. When raw sewage is applied directly to the bedsthe rates of application vary from 50,000 to 150,000 gallons per acredaily, the population served per acre being from 300 to 1,200. Withpreliminary treatment higher rates may be used, and the sewage of1,500 to 2,000 people applied per acre. The filters are usually dividedinto beds bv means of earth embankments which cover the distributingpipes. Often they are underdraiiiod with tiles laid 20 to 30 feet apart. Fig. 126.—Inclined Screen Operated by Water Wheel, BiRiiixGH-tii, England. in fine material, or 100 feet apart in coarse material, their depth belowthe surface varying from 3 to 8 feet. Crops are sometimes grown onthese beds, but agricultural operations are regarded as a secondary mat-ter. In winter the beds are plowed into ridges or the sludge is collectedinto piles so that ice may form and be supported upon them, leavingchannels beneath the ice by which the sewage can be distributed. Aftera few weeks or months the beds become clogged and it is ncessary to SEWAGE FILTEATIOX 969 JN^ rake the surface. At intervals the accumulated deposit on the sandhas to be scraped off. The efficiency of intermittent sand filtration is higher than that ofany other process. Well operated plants are capable of removing from95 to 98 per cent, of the suspended matter and bacteria, while the effluentis quite clear and non-putrescible. The method is limited, however, toregions where suitable and co
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Keywords: ., bookauthorwh, bookcentury1900, bookdecade1910, booksubjecthygiene
