Abstract |
Microstraining (Trade Name), using a Microstrainer screen of a nominal aperture of 23 microns, removed up to 98% of the suspended solids from a combined sewer overflow. The sewer, in a residential area of Philadelphia, has an average dwf of 1,000 gph. The maximum combined sewer flow during rainstorms in one year of operation was 304,000 gph (11.3 cfs). Volatile suspended solids removals with the above screen have averaged 68% and 71% during different test periods. Results indicated that there was a slightly better kill of coliform group bacteria with chlorine than with ozone in the Microstrainer effluents when both were used at an initial nominal concentration of 5 ppm, with 5 to 12 minutes detention time. However, chlorine was applied at slightly higher levels and with better control than ozone. Preliminary estimates of the costs of treatment via Microstraining, using tentatively-established throughput rates, show that the capital costs per acre of drainage would be approximately $10,200 for Microstraining alone, $11,200 for Microstraining plus chlorination, and $19,800 for Microstraining plus ozonation. Of eight other currently-proposed schemes, whose costs were estimate, only surface impoundment (where aesthetically acceptable and where low cost land is available) appears competitive. (Author) |