Dissolved air flotation (DAF) is used in place of conventional gravity settling as a means to separate low density floc particles from water. The following objectives were: (1) to compare DAF to conventional water treatment of coagulation-flocculation followed by gravity settling (CGS) for removals of particles, color, dissolved organic carbon (DOC), trihalomethane (THM) precursors, and total organic halide (TOX) precursors; (2) to examine the effects of raw water quality, water temperature, chemical variables, flocculation period prior to DAF, and DAF design and operating variables on DAF performance; and (3) to evaluate alum and polyaluminum chloride (PAC1) as pretreatment coagulants for DAF. The results of the DAF experiments using synthetic and natural waters showed that good DAF treatment requires good coagulation. The experimental results also showed that flotation without a prior flocculation period is effective. For waters containing humic substances, there was no significant difference in the removal of UV, true color, DOC, and dissolved organic halide precursors (THM and TOX) between DAF and conventional treatment.

Study carried out by University of Massachusetts Dept. of Civil Engineering for Risk Reduction Engineering Laboratory, U.S. Environmental Protection Agency. "EPA/600/2-89/032." "PB89-214407." Includes bibliographical references (pages 160-163).