Sewer and Tank Flushing for Corrosion and Pollution Control (EPA/600/J-01/120) 2001
This paper presents an overview of the causes of sewer deterioration and a discussion of control methods that can prevent or arrest this deterioration. In particular, the paper covers inline and combined sewer overflow (CSO) storage tank flushing systems for removing sediments and minimizing hydrogen sulfide production, resulting in the reduction of associated pollution and sewer line 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 additional biochemical transformation. Furthermore, these solids, deposits, or sediments are discharged to urban streams during storm events, which can cause degradation of receiving water. Thus, dry-weather sewer sedimentation not only creates hazardous conditions and sewer degradation, but contributes significant pollutant loads to urban receiving water during wet-weather, high-flow periods.
Performance of two technologies (the tipping flusher and the flushing gate) was evaluated by a detailed examination of 18 facilities in Germany, Canada, and the United States. Both the tipping flusher and flushing gate technology appear to be cost-effective means for flushing solids and debris from CSO storage tanks, while the flushing gate is considered to be the more efficient method for flushing large-diameter, flat sewers. The paper also includes capsulated reviews of several cost-effectiveness analyses that demonstrate the comparative benefits of flushing technology.
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