Purification of Sewage.
The purification of sewage before it is discharged into streams has been practiced so long in England that it is but rarely that a case arises when the engineers find it difficult to obtain a fairly good effluent from the filtration fields or the chemical works where the purification is carried on. One of the English cities where the purification has long been regarded as particularly difficult is Nuneaton, which has a population of about 11,000, on the line of the sewers. Attempts made to treat the sewage failed uniformly until within a year. During the summer time numerous letters were received from the owners of property on the banks of the stream below the place where the sewage was discharged complaining of the condition of the river. It was described as a constant stream of a milky white odor, like thick, horribly smelling whitewash. Two-thirds of the sewerage only comes from houses, the remaining third consisting of the liquid wastes from fellmongers, wool scourers and hat factories. It was finally discovered that these liquid wastes were discharged into the sewers at irregular intervals and without any treatment to reduce their offensiveness. The liquids from the wool scourers reacted on those from the fellmongers and produced the white matter of which complaint was made. The manufacturers finally agreed to neutralize these wastes with sulphuric acid before discharging them into the sewers, and to allow them to flow in a continuous stream into the sewer instead of discharging them at intervals as formerly. The new works in which the sewage is now treated satisfactorily cover about six acres, and are partly chemical and partly on the filtration system. Generally from thirty-five to forty-five grains of chemicals are added to each gallon of sewage, but on the few holidays when the manufacturing establishments are not running from six to twelve grains are sufficient, which shows the degree of pollution caused by the wastes from such sources. From the tanks in which the chemicals are added the sewage runs to the filter beds, of which there are eight, each covering about 900 square feet. Four of the filters are kept in use while the remainder are being cleaned. Both the chemicals and the filter beds are prepared in accordance with patented formulas, and the combined process is known to engineers as the “polorite and ferrozone ” method of treatment. The municipal engineer in charge of the works ascribes their success to the following conditions : The treatment by the manufacturers of their waste liquids at their own works, the use of proper chemicals to effect thorough clarification, the use of polorite filters to remove the putrefactive materials in solution which the chemicals would not affect, and the provisions made for treating the sewage twice if necessary.