Characterizing Pipe Wall Demand: Implications for Water Quality Modeling

It has become generally accepted that water quality can deteriorate in a distribution system through reactions in the bulk phase and at the pipe wall. These reactions may be physical, chemical, or microbiological in nature. Perhaps one of the most serious aspects of water-quality deterioration in a network is the loss of disinfectant residual that can weaken the barrier against microbial contamination. Recent studies have suggested that one factor contributing to the loss of disinfectant residuals is internal corrosion of the pipe wall material. Recent studies have suggested that in older unlined metal pipes, the loss of chlorine residual may increase with increasing flow rates. To systematically assess the effect of free chlorine loss in corroded metal pipes, subject to changes in velocity, the authors conducted a study under controlled conditions in a specially constructed pipe loop located at the U.S Environmental Protection Agencyʹs (U.S. EPAʹs) Test and Evaluation (T&E) Facility in Cincinnati, Ohio. Results from the pipe-loop study supported the concept that the rate of free chlorine residual loss increased with velocity.