Sewer and Tank Flushing for Corrosion and Pollution Control

This paper presents an overview of causes of sewer deterioration together with a discussion of control methods that can prevent or arrest this deterioration. In particular, the paper covers inlineand 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 sewerline corrosion. 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 are reduced to hydrogen sulfide gas that can then be oxidized to sulfuric acid on pipes and structure walls by further biochemical transformation. Furthermore, these solids deposits or sediments are discharged to the urban streams during storm events which can cause degradation of receiving-water quality. Thus, dryweather sewer sedimentation not only creates hazardous conditions and sewer degradation but contributes significant pollutant loads to the urban receiving waters during wet-weather highflow periods. 1 Environmental Engineer and 2 Wet Weather Flow Research Program Leader, U.S. Environmental Protection Agency, National Risk Management Research Laboratory, Water Supply and Water Resources Division, Urban Watershed Management Branch, Edison, NJ 08837. 3 Montgomery Watson, 40 Broad Street, Suite 800, Boston, MA 02109. 4 Odor and Corrosion Technology Consultants, Inc., 11250 West Road, Building AL@ Houston, TX 77065.