Potential impact of enhanced coagulation on corrosion by-product release in a distribution system

As an effective disinfection by-product control strategy, enhanced coagulation has been being widely used for surface water treatment. In this paper, the influences of adopting enhanced coagulation on possible water quality changes in distribution system were evaluated through a long-term field investigation using pilot water treatment and distribution systems. The finished waters were produced by different post-treatments following enhanced coagulation: ozonation combined with biologically activated carbon filtration and membrane nanofiltration. The pilot distribution systems were constructed using old pipes of four different materials including PVC, lined and unlined iron pipes as well as galvanized steel pipes. Copper loops were also set up for monitoring lead and copper corrosion compliances. A yearlong investigation revealed that reduced alkalinity and increased salinity resulted from enhanced coagulation could cause severe iron release and heavy discolored water, but such water quality changes did not increase copper corrosivity. The copper corrosion by-product release was primarily affected by alkalinity and also sensitive to pH variations. Membrane desalination together with alkalinity adjustment mitigated the iron release significantly. Iron release could be accelerated by high temperature.