You are here:
COLLECTION SYSTEM SOLIDS CONTROL: OVERVIEW OF AN EPA WET-WEATHER FLOW RESEARCH PROGRAM
Citation:
Fan*, C, R Field*, F Lai*, AND D Sullivan*. COLLECTION SYSTEM SOLIDS CONTROL: OVERVIEW OF AN EPA WET-WEATHER FLOW RESEARCH PROGRAM. Presented at WEF 2001 Collection Systems Odyssey: integrating O&M and Wet-Weather Solutions, Bellevue, WA, 7/8-11/2001.
Description:
This paper presents an historical overview of the sewer-solids control projects conducted by the Wet-Weather Flow Research Program of the US EPA. Research includes studies of the causes of sewer-solids deposition and development/evaluation of control methods that can prevent sewer-sediment accumulation. Discussions focus on the relationship of wastewater characteristics to flow-carrying velocity, abatement of solids deposition and solids resuspension in sewers, and sewerline-fluishing systems for removal of settled solids. During low-flow dry-weather periods, sanitary wastewater solids deposit in combined sewers. During a storm-flow event, near-bed sediment containing a high concentration of pollutants (150,000 mg/L of BOD5, 200,000 mg/L of COD, and 300 mg/L of NR3-N) is resuspended and discharged directly into receiving waters. In addition, these deposited solids contain organic matter that due to anoxic conditions generate toxic and corrosive gases, e.g., hydrogen sulfide and methane. Sulfates are reduced to hydrogen sulfide and then oxidized to sulfuric acid by biochemical transformation. Thus, control of sewer sediment not only protects urban receiving-water quality but also prevents hazardous conditions in sewers and protects sewer structural integrity. Methods for abating sewer sedimentation are presented including steeper sewer slopeage and pipe bottom shapes that maintain high velocity during low-flow conditions, improving upstream sediment trapping, and periodic sewer flushing.