An engineering investigation and evaluation of vortex devices as bubble makers for use in the removal of suspended solids from wastewaters was conducted. Specific objectives included the development and test of bubble makers capable of generating bubbles having mean diameters of about 100 microns with vortex devices having minimum liquid passageways of 1/4 inch or greater. Bubbles having a mean diameter of 80 to 85 microns, with virtually no bubbles greater than 130 microns, were successfully produced. This mean size and size range are substantially the same as bubbles produced by pressurized water processes at similar operating pressures. Bubbles were produced both by aspirating atmospheric air directly into the vortex unit, and by aspirating atmospheric air at the suction side of the pump, dissolving it, and precipitating it or effervescing it at the vortex unit. Sufficient data now exist, however, to design vortex systems for direct functional tests in conventional air flotation systems.

Pilot plant studies were conducted to develop and demonstrate the capabilities of the deep bed, dual media, high rate filtrate treatment process for storm caused combined sewer overflows. The treatment system is comprised of a drum screen with a 40 mesh screening element (420 microns opening) followed by a deep bed, dual media, high rate filter of five feet of No. 3 anthracite (effective size 4 mm) over three feet of No. 612 Sand (effective size 2 mm). The results show suspended solids removals of 93 percent, with polyelectrolyte addition, at a filtration rate of 24 gpm/sq ft at an average influent suspended solids of 411 mg/l. Reductions in biochemical oxygen demand averaged 65 percent. Capital costs and operating costs for a high rate filtration plant are given. Principal advantages of the proposed system are: high treatment efficiencies, automated operation, and limited space requirements as compared with alternate flotation or sedimentation systems.

The report documents a study to develop a treatment system for combined sewer overflows. The processes of chemical oxidation, screening, dissolved-air flotation, and disinfection were evaluated in the laboratory. A 5 MGD demonstration system was designed, installed and evaluated. Suspended solids and volatile suspended solids removal in the range of 65-80% were consistently obtained at influent concentrations of 150 to 600 mg/l. BOD and COD removals were slightly lower at 55 to 65% for influent concentrations of 50 to 500 mg/l. Addition of chemical flocculents (ferric chloride and a cationic polyelectrolyte) was necessary to obtain these removals. Without the use of chemical flocculents, removal of BOD, COD, suspended solids, and volatile suspended solids were all in the range of 40-50%. The screening flotation system provided sufficient detention time (difference 15 minutes) for adequate disinfection with hypochlorite salts. Cost estimates are presented.