Laboratory Evaluation of Methods to Separate Fine Grained Sediment from Stormvvater

Abstract

A literature survey had been conducted by the St. Anthony Falls Hydraulic Laboratory to assess various methods for separation of sediment from stormwater 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~ 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 improved the efficiency of a sedimentation.ta'2k by about 20 percent at the highest overflow rate tested of about 200 lpm/m (Sgpm/ft) for an average removal efficiency of about 60 percent. the inclined tube settler also reduced the sensivity of the overflow rate on the efficiency of sediment removal. Limited tests with alum added to the influent to increase flocculation indicated about a 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. Higher removal percentages may possibly be obtained by reducing the flow rate or influent concentration. This report Was submitted in fulfillment of Grant No. R803579 by the St. Anthony Falls Hydraulic Laboratory of the University of Minnesota under the sponsorship of the U.S. Environmental Protection Agency. This report covers a period from October 1, 1976 to July 1, 1978, and work was completed as of December 15, 1978.