Estimation of chloramine decay in drinking water distribution systems
Journal of Water Process Engineering(2022)
Abstract
When compared to free chlorine, chloramines represent an established secondary disinfectant that may be utilized to reduce disinfection by-product formation and improve residual stability. Maintaining an acceptable residual in distribution systems however may be challenging due to potential high maintenance costs associated with uni-directional flushing and swabbing. This study was designed to identify the primary sources of chloramine demand for a distribution system receiving surface and groundwater. Decay in the bulk water was quantified using a bottle point method. Bench-scale pipe section reactors (PSRs) were utilized to evaluate decay associated with cast‑iron and polyvinyl chloride (PVC) pipe sections that had been harvested from a distribution system, as well as to allow comparisons with new pipe material. Bulk water decay was compared to that observed in PSRs at flow rates of 0.03 m/s and 0.09 m/s, representative of distribution system conditions. Pipe material type and associated surface conditions were identified as the most critical factors influencing decay. Observed first-order decay rates for harvested cast‑iron pipe with an established microbial community and metal/silicate scale were significantly higher than those for PVC. In contrast, first-order decay rates for harvested PVC were comparable to new pipe, with water velocity exerting a negligible impact. Overall, these results reinforce the importance of determining the primary sources of chloramine decay in distribution systems.
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Key words
CI,Cl2(final),Cl2(initial),DI,kb,kf,kobs,kw,NR,PSR
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