Effects of pipe materials, orthophosphate, and flow conditions on chloramine decay and NDMA formation in modified pipe loops

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Courtesy of IWA Publishing

This study examined the effects of pipe materials (iron, copper, lead and PVC) and orthophosphate on chloramine decay and N-nitrosodimethylamine (NDMA) formation under stagnant, laminar and turbulent conditions using modified pipe loops. As expected, chloramine decay rates generally increased with increasing flow velocity. In the presence of orthophosphate, chloramine degradation in the iron loop increased regardless of flow conditions, whereas chloramine decay rates decreased for the copper and lead loops, especially under turbulent conditions. NDMA formation in the copper loop was consistently higher than it was in the PVC control loop under laminar conditions, supporting the theory of a possible catalytic effect of copper on NDMA formation (as reported elsewhere). Iron catalysis of NDMA formation became more prominent in the presence of orthophosphate, but copper catalysis became less significant after the addition of orthophosphate. Only in the copper loop, the released metal concentrations were decreased under laminar conditions compared with turbulent flow, and they were also reduced effectively due to the addition of orthophosphate, suggesting that the catalytic effect was not primarily due to dissolved copper but likely included copper-based solids (corrosion products).

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