Distribution of Desalinated Seawaters: Are Corrosion Indicators Sufficient?

Abstract

In anticipation of future water supply limitations, the Long Beach (Calif.) Water Department (LBWD) is conducting extensive research into desalinating seawater as a future potable water supply source. Corrosion potential is a central issue with regard to distributing any new water sources, particularly desalinated seawater. LBWD will ultimately perform a year-long pipe-loop study with 4-in. diameter, 20-ft long pipe sections with different blends of desalinated waters. To better define the scope of testing, blends from 100 percent distribution system water to 75 percent desalinated seawater (permeate) in 25 percent increments were evaluated through desktop calculations (corrosion indices) and bench-scale tests, including pipe-section (AWWA Standard C104) and marble testing. Various corrosion indices were calculated and compared to help guide the pipe-loop testing phase. Good correlations between the indices were obtained from the test results, and it appeared that modest adjustments (e.g., pH control) would allow blends up to 50 percent permeate to be used in the distribution system, but higher permeate blends would require more treatment. It was observed that use of lining (e.g., epoxy seal coating) in distribution system pipes could improve corrosion resistance. Initial lead and zinc release tests conducted with brass coupons for six weeks showed that higher permeate blends resulted in higher zinc and lead release, possibly requiring additional adjustment to mitigate the effects.