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SEWER SEDIMENT CONTROL: AN OVERVIEW OF THE EPA WET WEATHER FLOW (WWF) RESEARCH PROGRAM
Citation:
Field*, R, C Y. Fan*, AND F H. Lai*. SEWER SEDIMENT CONTROL: AN OVERVIEW OF THE EPA WET WEATHER FLOW (WWF) RESEARCH PROGRAM. Presented at 2000 ASCE WRP&M Conference, Minneapolis, MN, July 30 - August 02, 2000.
Impact/Purpose:
To inform the public.
Description:
This paper presents an overview of EPA WWF Research Program projects related to causes of sewer solids deposition and control methods that can prevent accumulation of sewer sediments. In particular, discussion will focus on the relationship of wastewater characteristics to flow carrying velocity, abatement of solids deposition and resuspension in sewers, and sewerline-flushing systems for removal of sewer sediments. Dueing low-flow dry-weather periods, sanitary wastewater solids deposit in combined sewers, and the near-bed sediments contain a high concentration of pollutants (30,000-150,000 mg/L of BOD 5, 80,000-200,000 mg/L of COD, and 70-300 mg/L of NH3-N). These pollutants are discharged during storm events and cause degradation of receiving-water quality. In addition, these deposited solids contain organic matter that generates toxic and corrosive gases, e.g., hydrogen sulfide and methane due to anoxic conditions. Sulfates are reduced to hydrogen sulfide and then oxidized to sulfuric acid by biochemical transformation. Thus, dry-weather sediments not only contribute significant pollutant loads to urban receiving waters during wet-weather high-flow periods but also create hazardous conditions and sewer structure deterioration during dry weather. The paper will discuss feasible methods for controlling sewer sediments that include: (1) increasing sewer slopes, (2) pipe bottom shapes that maintain high velocity during low-flow periods, (3) upstream sediment trapping, and (4) sewer flushing.