Determination of the Influence of Polyurethane Lining on Potable Water Quality
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The corrosion of the drinking water distribution system is a serious problem in the United States. The annual cost to repair damages related to corrosion for public utilities in the United States are estimated at $22 billion. Polyurethane can be used as an in situ pipe liner which reduces the overall cost to rehabilitate water mains. Polyurethane is gaining popularity as a drinking water pipe liner. Not much is known about the effects of polyurethane to reline potable pipes. Polyurethane has only recently begun to be approved by the U.S. Environmental Protection Agency for use in drinking water piping, although it has been used in the United Kingdom since 1999. The American National Standards Institute/National Sanitation Foundation 61 Drinking Water System Components â Health Effects (ANSI/NSF 61) for pipe and pipe liners was used to investigate changes in water quality in contact with polyurethane lining material. In addition, the exposure time was extended to 30 days and odor analysis was performed. Polyurethane coupons were placed in headspace free borosilicate glass vessels with a surface area to volume ratio of 0.39. The water was pH 8 and comprised of salts: MgSO4, NaHCO3, CaSO4, CaC12, Na2SiO3 and KNO3 in a ratio typical of standard drinking water. Three types of disinfectant were used: no disinfectant, chlorine and monochloramine. The water was removed, sampled and replaced on days 1, 2, 4, 9, 11, 14, 15, 19, 21 and 30. The sample water was tested for pH, temperature, total organic carbon concentration (TOC), disinfectant residual, ammonia concentration as N-NH3, hardness as combined Ca and Mg concentrations, alkalinity and temperature on days when the sample water was changed. Total solids (TS), odor, trihalomethanes (THMs), haloacetic acids (HAAs), and semivolatile organic carbons (SVOCs) were tested on days 1, 4, 9, and 14. The polyurethane lining had major impacts on pH, odor and haloacetic acids throughout the 30 day experiment. A 2-3 pH unit decrease to pH 6 was constant for all conditions tested. Odor panelists described the odor for both chlorinated and monochloraminated waters as â chlorinousâ and either pleasant as â sweet chemicalâ or putrid as â locker roomâ . Haloacetic acids were formed and increased in concentration (by approximately 30 Î¼g/L, which is half the US EPA regulated value of 60 Î¼g/L). Trihalomethane formation was not seen. Total organic carbon leached from the polyurethane liners reached 0.65 mg/L above background on day 1 but by day 15 was only >0.1 mg/L above background. Chlorine and monochloramine were consumed by the polyurethane and increased exposure time leads to decreased disinfectant residual. It is important for water utilities to know how a lining material will affect the water quality. It has been shown that other polymeric lining materials have impacted the disinfection by-products as well as producing odor. Water treatment facilities are responsible for the water quality throughout the infrastructure and with Environmental Protection Agency regulations becoming stricter they cannot afford to not know the impact of polymeric lining materials in their system.
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