WASTE TREATMENT IN THE URBAN SOCIETY.

DOMESTIC AND INDUSTRIAL WASTES ARE TREATED FOR TWO DISTINCT PURPOSES: (1) separation of water from the putrescible organic material, dissolved and particulates; (2) disinfection of the water to prevent the transmission of water-borne pathogens.Currently, in North America, disinfection is accomplished by the addition of a powerful oxidizing chemical such as chlorine or a related compound.Separation of solids from liquid is achieved by flocculation followed by sedimentation. Flocculation may be biologically or chemically induced, the former being more economical where practical. Methods of bioflocculation described include the following processes: (1) activated sludge, (2) contact stabilization, (3) tapered aeration, (4) step aeration, (5) total oxidation, and (6) trickling filter.Non-mechanical processes of sewage treatment are economically and technically sound in many rural and semi-rural applications. The oxidation pond ((lagoon) is not mechanical, but this consideration must not lead rural municipalities to a program of neglect. All plants treating human wastes should provide a disinfection process at the effluent.