Abstract |
The feasibility, both economic and technical, of using ultrasonic filtration as an aid to removing suspended impurities was investigated. Inputs to the test apparatus included drinking water, simulated sewage, primary and secondary sewage effluents, algae pond effluent, coarsely screened, raw sewage diluted 2:1, 5:1, and 10:1 with simulated storm drainage, and deliberately concentrated raw sewage. Dirt, sand, and leaves were added in some test runs with no apparent effect on performance. 20 and 50 micron filter elements, operated at approximately 10 gpm/sq ft2 with head losses from 1 to 4 psi, reduced the BOD and suspended solids of raw sewage diluted in varying degrees with water by an average of 40 and 70% respectively. System performance was intermediate between that of primary and secondary treatment. Other benefits included: Application of ultrasonic energy increased the total quantity of effluent filtered between backwash cycles; from 4 to 18 times that treated with similar equipment without ultrasonics applied; and Application of ultrasonic energy restored the filter elements to 'like-new' condition without necessitating frequent filter replacement. Cost figures for an ultrasonic filtration system capable of handling 1.4 mgd, exhibiting performance midway between primary and secondary treatment, and occupying only several hundred square feet, ranged between 2.8 and 3.5 cents/ 1000 gallons. By comparison, combined primary-secondary treatment cost figures were reported as 10 cents/1000 gallons excluding the cost of the considerable amount of land involved. (WRSIC abstract) |