Abstract
A lime softening flotation process is described for the purification of secondary treated sewage effluent to potable quality. Excess lime treatment is used as a coagulant in the flotator, and micro bubble aeration is achieved by centrifugal pump action. Flotation is followed by recarbonation and contact stabilization on ferric hydroxide, before sand filtration. ABS is removed by foam fractionation and ammoniacal nitrogen by “breakpoint” chlorination. Active carbon filtration is applied as a polishing stage to remove residual ABS and chloronous tastes and odours. The use of excess lime has the advantages of a sterilizing action, low cost and complete removal of phosphates. An ultimate reduction of total dissolved solids is also achieved. The importance of Mg(OH) 2 and Fe(OH) 3 for entrainment of suspended CaCO 3 in the flotator and stabilizer is emphasized. The aeration technique used appears to have economic advantages in comparison with conventional dissolved air flotation. Tentative cost figures for a 1 million gal/day demonstration plant are derived.
Published Version
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