. Preventive medicine and hygiene. d 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^ r
. Preventive medicine and hygiene. d 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 convenient areas of sandy soil Fig. 127.—Cross Section of Contact Bed. CoxTACT Beds.—Contact beds are water-tight compartments filledwith porous material, such as broken stone or coke, and operated asfollows: The bed is slowly filled with sewage, which has previouslypassed through a septic tank, and allowed to remain full for a briefperiod, after which it is emptied and allowed to remain empty for alonger period. A cycle commonly employed is to allow one hour forfilling, two hours for contact, one hour for emptying, and four hoursfor rest. During the period of contact the suspended matter tends tosettle upon and adhere to the exposed surfaces of the broken stone or
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Keywords: ., bookauthorwh, bookcentury1900, bookdecade1910, booksubjecthygiene
