Chemical Treatment Plans for the South District Filtration Plant

Abstract

NOTED in the paper by Paul Hansen (immediately preceding) the physical equipment of the South District Filtration Plant Chemical Building will be both adequate and flexible, allowing for the adaptation of treatment procedure to that best suited to the condition of the raw water. General plans for treatment procedure have been made on the basis of results obtained from the operation of an experimental plant, but final methods must of course await the dictates of experience. As now planned, the coagulant will be aluminum sulfate or one of the iron compounds, depending on market prices of the materials. Efficiency of the products for treating the Lake Michigan water at Chicago allows some price differential. This is known and can be taken into consideration. During times when microscopic organisms are abundant, the intention is to use lime to produce a precipitate of calcium carbonate, which, when coagulated, will settle rapidly. During periods in the winter when the coagulation is weak, acid-treated sodium silicate is to be used to strengthen the coagulation. Activated carbon will be used for taste and odor removal, chlorine for sterilization, ammonia for the maintenance of residual chlorine in the distribution system, and sodium hexametaphosphate or carbon dioxide will be used when lime is added to the water. Table 1 gives the estimated chemical dosages. Clarification of the lake water at Chicago by processes commonly used in rapid sand filtration plants is simple. The chief filtration difficulty is the rapid clogging of filters and the passage of coagulated matter through the filters. The lake water at the south side intake has an average turbidity slightly less than 10, a peak turbidity near 200, and a minimum turbidity of 1 ppm. The pH of the lake water before treatment remains