You are here:
FLUSHING FOR SEWER SEDIMENT, CORROSION, AND POLLUTION CONTROL
Citation:
Fan*, C Y. AND R Field*. FLUSHING FOR SEWER SEDIMENT, CORROSION, AND POLLUTION CONTROL. Presented at EPA and ASCE Urban Water Resources Res Council's United Engineering Foundation Conference on Linking Stormwater BMP Designs & Performance to Receiving Water Impacts Mitigation, Snowmass, CL, 8/19-24/2001.
Description:
This presentation overviews causes of sewer deterioration and heavy pollutant discharges caused by rain events together with a discussion of their control methods. In particular, it covers in-sewer- and combined sewer overflow- (CSO-) storage-tank-flushing systems for removal of sediments and minimizing hydrogen sulfide production resulting in the reduction of associated pollution and sewer line corrosion, respectively. During low-flow dry-weather periods, sanitary wastewater solids deposited in combined sewer systems can generate hydrogen sulfide and methane gases due to anaerobic conditions. Sulfates inherent in these solids are reduced to hydrogen sulfide gas that can then be oxidized to sulfuric acid on sewerage structure walls by further biochemical transformation. These solids deposits or sediments are discharged to urban streams by storm induced wet-weather flow that can cause degradation of receiving-water quality. Thus, dry-weather sewer sedimentation not only creates hazardous conditions and sewer degradation but contributes significant pollutant loads to the urban receiving waters during wet-weather, high-flow periods. Performance of two technologies, i.e., the tipping flusher and the flushing gate (FG) was evaluated by a detailed examination of 18 facilities in Germany, Canada, and the US. As a result, both the tipping flusher and FG technology appear to be cost-effective means for flushing soids and debris from CSO-storage tanks, while the FG is considered to be the most efficient method for flushing large diameter, flat sewers. In addition, reviews of several cost-effectiveness analyses are reported demonstrating the comparative benefits of flushing technology.