Distribution System Water Quality Following BlendingSurface, Ground, and Saline Sources

摘要

The University of Central Florida is conducting a $3,000,000 Tailored Collaboration Project todetermine the effects of blended water quality on distribution system water quality. Finishedwaters from seven different processes are blended in varying ratios before distribution toeighteen pilot distribution systems (PDS) in a facility that includes 8500 ft 2 of roofing and 4500ft 2 of cement pad. The facility is operated continuously. Processes include conventional groundwater, softening, enhanced surface water, integrated membrane system and reverse osmosistreatment. The PDS were made from galvanized, cast iron, lined cement and PVC pipe takenfrom actual distribution systems. Findings are: (1) Alkalinities less than background (200 mg/LCaCO3) have resulted in release of apparent color to 50 CPU. Apparent color release is duealmost totally to particulate iron, and appears independent of pH, LSI, calcium and all otherparameters associated with CaCO3 associated indexes except for alkalinity, Color release is alsopositively correlated with chloride and sulfate concentrations. (2) Color release has continuedthrough six months of equilibration and 15 months of field testing from CI pipes receiving lessthan background alkalinity, (3) Total and free chlorine dissipation was accurately predicted bymodeling residual as a function of pipe material, UV-254, temperature and time. Field data andmodel projections have shown: (a) The dissipation rate of Total or free chlorine is approximatelyan order of magnitude greater in galvanized and CI pipe than in lined cement and PVC pipe, (b)Maintenance of required residuals in galvanized and CI pipe is practically impossible insummertime conditions, ? pipe material is the most significant factor affecting residualmaintenance for expected water quality conditions in distribution systems, (4) Ferric hydroxideand Cupric hydroxide appear to be the controlling solid films based on surface and equilibriumanalyses, (5) Biological stability did not change as a result of film disruption as indicated byapparent color release. Field investigations will continue until June 2003.