Sewage disposal . three-quarters of a mile from the press house. The removal of the suspended organic matter by the aboveprocess, measured by albuminoid nitrogen, has in the past aver-aged about 85 to 90 per cent, which is roughly 50 per cent of thetotal organic matter in the sewage; but in 1916 the purificationamounted only to 71 per cent of the suspended, or 38 per cent ofthe total nitrogen, on account of a great excess of iron sulphate inthe sewage and a shortage of lime. The cost of chemical treat-ment in 1916 was $ per million gallons and the cost of sludgepressing $ per million g
Sewage disposal . three-quarters of a mile from the press house. The removal of the suspended organic matter by the aboveprocess, measured by albuminoid nitrogen, has in the past aver-aged about 85 to 90 per cent, which is roughly 50 per cent of thetotal organic matter in the sewage; but in 1916 the purificationamounted only to 71 per cent of the suspended, or 38 per cent ofthe total nitrogen, on account of a great excess of iron sulphate inthe sewage and a shortage of lime. The cost of chemical treat-ment in 1916 was $ per million gallons and the cost of sludgepressing $ per million gallons. The sewage to be purified by intermittent filtration, 5 mil-lion gallons per day, after passing through the grit chamber is 128 TREATMENT BY CHEMICAL PRECIPITATION caused to flow through a sedimentation tank having a capacityof about one-half hours flow. Here the grosser suspended mat-ters are removed and disposed of by pumping onto adjacentfields. The ordinary dose of sewage applied to the filters is from. Fig. 38. Sludge Presses at Worcester Chemical Precipitation Plant. 300,000 to 400,000 gallons per bed, and the average rate peracre amounts to about 75,000 gallons daily. The accumula-tion on the surface of the beds is raked up late in the fall intosmall piles about 4 feet apart, which are left during the winterto assist in holding up the ice from the surface. In the springthe beds are given a thorough cleaning, and the surface accu-mulation, unavoidably mixed with some sand, is carted away andused for filling in the swamps and lowlands. The cloggingmatter so removed amounts to about 250 cubic j^ards per acreor 10 cubic yards per million gallons of sewage filtered. Thecost of cleaning averages 35 cents per cubic yard. The ferrous sulphate present in great quantities in Worcestersewage is largely oxidized during the process of filtration, and ACID PRECIPITATION OF SEWAGE 129 much of it settles out as hydrated ferric oxide in the gravelaround the open joints of the und
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Keywords: ., bookcentury1900, bookdecade1910, bookpublisherlondo, bookyear1919
