Evaluation of Upflow Filters for Stormwater Treatment at Critical Source Areas

Abstract

The U.S. Environmental Protection Agency (EPA) has identified stormwater runoff as a leading cause of water quality impairment nationwide. In order to prevent water-quality degradation due to urbanization, stormwater runoff from certain locations should be treated prior to discharge to prevent harm either to the surface waters or to the groundwater. One potentially cost-effective approach is the treatment of runoff from these "critical source areas" (locations where pollutant contributions appear to be higher) before it mixes with cleaner runoff from 'non-problem' areas. Past research has shown that filtration can be effective in reducing pollutant levels in stormwater runoff prior to its discharge.In this research, an upflow filtration system was designed and developed, and the effectiveness of upflow filtration was demonstrated. Four different filtration media, namely, lightweight sand (pool sand meant for swimming pool filters), fine (sandblast) grade sand, peat moss and compost were examined in bench-scale upflow filters for solids removal. The purpose of the overall research project was threefold: first, to investigate the applicability of upflow filtration for stormwater treatment; second, to investigate the removal capacity of the various filter media when used in upflow mode; and, third, to evaluate the applicability of an upflow pilot-scale filter using an influent of pre-settled stormwater runoff. The objectives of the bench-scale research were to determine (1) for each medium, the optimum flow rate (no rising or separation of either the media from the gravel layer or within the media itself) where suspended solids removal was "best"; (2) the suspended solids loading on the media that reduced the flow rate to certain end points; (3) the breakthrough point (i.e., where the effluent concentration equaled the influent concentration) for each media. Influent and effluent samples were collected throughout the run and analyzed for turbidity, total solids and particle size distribution.Pilot-scale testing was conducted to replicate the design employed in the laboratory and investigate potential scale-up issues. The test water was from a stormwater detention pond in Hoover, AL. The media selected for the pilot-scale testing were the same four media used in the laboratory. The results of the upflow pilot-scale tests are compared with prior downflow tests using the same media and test water.