PARTICLE DESTABILIZATION FOR TERTIARY-TREATMENT OF MUNICIPAL WASTE-WATER BY FILTRATION

Optimization of the chemical pretreatment process prior to tertiary fi ltration of municipal secondary effluent was studied. Jar tests involv ing coagulation with alum, flocculation, settling and filtration were conducted on secondary effluent samples and these established the occu rrence of two distinct coagulation mechanisms: the mechanism of charge neutralization, and the mechanism of sweep coagulation at different a lum dosages and pH conditions. An optimum design region on the alum co agulation diagram also was established where the removals of various w astewater parameters were the highest. This region was bound by alum d osages of 55 to 60 mg/l and pH values of 6 to 6.5. In the above domain , the BOD5, TOC, turbidity, total-P, and the orthophosphate levels of the secondary effluent were reduced by 73%, 57%, 98%, and 99% respecti vely after tertiary filtration. Particle size analysis of the settled and altered effluent also was conducted in both the charge neutralizat ion and the sweep coagulation zones. A wide difference was observed in particle sizes between the effluents after settling and after filtrat ion in the charge neutralization zone. In comparison, the difference i n panicle size between the settled and the filtered effluents was smal ler in the sweep coagulation zone.