A prototype swirl degritter was tested by the Metropolitan Denver Sewage Disposal District No. 1. The unit was designed to duplicate the grit removal device needed to degrit the underflow from the proposed swirl concentrator as a combined sewer overflow regulator at Lancaster, Pennsylvania under EPA Grant No. S802219 (formerly 11023 GSC). Degritting is considered in Lancaster to protect pumps and prevent siltation in the interceptor. The 1.8 m (6 ft) diameter device was designed for a flow of 65.6 l/s (1.3 mgd). It was found that under the physical arrangements in Denver, testing with domestic sanitary wastewater, the swirl unit performed at slightly less efficiency than the conventional aerated grit unit which was operating at less than twice the normal flow-through rate. The characteristics of the grit removal from the swirl degritter were excellent and particles of 0.3 mm (.012 in.) were removed. Analyses of grit removal was accomplished with three Chasick sampling units. Blasting sand was added to provide extremely high concentrations of 0.2 mm (.008 in.) particles (lower definition of grit) to duplicate the concentrate from the swirl regulator. It was found that the unit could efficiently remove the small particles at the high concentrations. It was concluded that the degritter could be used for domestic wastewater, combined sewer overflows, or urban stormwater runoff treatment. The absence of moving parts in the basic unit and small relative volume 1:10 (compared to conventional grit chambers) may make the unit particularly desirable for many applications. A comparison of the present worth of the cost of construction, operation, and maintenance for a 20 year life indicates that the swirl degritter is from 26 to 38 percent less costly than a conventional aerated grit chamber.

"Grant no. S-803157." "September 1977." Includes bibliographical references (page 55).