A literature survey had been conducted by the St. Anthony Falls Hydraulic laboratory to assess various methods for separation of sediment from storm water at construction sites. Two methods have shown some promise in this application, and a research program was initiated with the objective of evaluating the effectiveness of the methods in removing fine grained inorganic solids from water. Experimental facilities were set up to test full-scale units of an inclined tube settler and a Discostrainer in an environment approximating that in the field. These units were tested for removal efficiencies of inorganic solids with sizes less than 100 microns and influent concentrations of about 2000 mg/l. Measurements were made of the influent and effluent concentrations for various flow rates through the systems. Results indicated that the installation of an inclined tube settler also reduced the sensitivity of the overflow rate on the efficiency of sediment removal. Limited tests with alum added to the influent to increase flocculation indicated about 6 percent improvement in removal efficiency. The Discostrainer was found to be extremely sensitive to influent solids concentration. Thirty percent solids removal was the maximum attained for the tests conducted.

Prepared for U.S. Environmental Protection Agency, Office of Research and Development, Municipal Environmental Research Laboratory under Grant no. R 803579. Includes bibliographical references (page 33).