Practical preventive medicine . the capacity of salt water for dissolved oxy-gen is about 20 per cent, less than fresh water. (c) The rate of the dispersion of the sewage in the must be quick. 5. Sewage Treatment.—When satisfactory disposal by dilu-tion cannot be secured, the treatment of the sewage is following results are sought: (a) A separation of the suspended matters (sludge) from theliquid sewage. io8 PRACTICAL PREVENTIVE MEDICINE {b) The destruction of the putrescible organic matter in theliquid sewage preparatory to its final mineralization by oxida-tion (no
Practical preventive medicine . the capacity of salt water for dissolved oxy-gen is about 20 per cent, less than fresh water. (c) The rate of the dispersion of the sewage in the must be quick. 5. Sewage Treatment.—When satisfactory disposal by dilu-tion cannot be secured, the treatment of the sewage is following results are sought: (a) A separation of the suspended matters (sludge) from theliquid sewage. io8 PRACTICAL PREVENTIVE MEDICINE {b) The destruction of the putrescible organic matter in theliquid sewage preparatory to its final mineralization by oxida-tion (non-putrescibility). (c) The transformation of the sludge into a stable and inertcondition, with or without the aid of oxidation. (d) The destruction or removal of bacteria from the methods are employed to secure the above results which are used either singlv or in various combinations. Greatcare and judgement must be employed in selecting the methodof treatment to be employed, since different methods of treat-. Fig. 12.—Fine mesh revolving screen at Birmingham, England. (Courtesyof J. D. Watson.) These screens constantly revolve so that a fresh surface isalways ready for use. (Am. Mus. Nat. Hist., Guide Leaflet, 33.) ment vary in the degree of their successfulness, depending uponthe character and composition of the sewage to be treated, aswell as the degree of attention paid to the care of the disposalplants. All sewage treatment plants require intelligent opera-tion, together with some degree of skill. Most dissatisfactionor failure can be traced to either neglect or ignorant treatment plants should be designed by competentsanitary engineers, after study and experimentation has re-vealed the method of treatment best suited to handle thelocal sewage. EXCRETA DISPOSAL 109 6. Preparatory Processes.—These are designed to effect aseparation of the suspended matter or sludge from the liquidsewage. (a) Screening.—Coarse or fine gratings or scr
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectprevent, bookyear1920
