Issues with distribution of desalinated seawaters: Are corrosion indicators sufficient?: Fid-Bau Portal

Issues with distribution of desalinated seawaters: Are corrosion indicators sufficient?

Cheng, Robert C. / Andrews-Tate, Cynthia E. / Tseng, Tai J. / Wattier, Kevin L.

In anticipation of future water supply limitations, the Long Beach Water Department (LBWD) is currently performing extensive research into desalinating seawater as a future potable water supply source. Corrosion potential is a central issue with regards to distributing new water sources, particularly with a source that is as unique as desalinated seawater. LBWD will ultimately perform a year-long pipe-loop study with 4in diameter, 20-ft long pipe sections with different likely blends of desalinated waters. To better define the scope of testing, blends from 100-percent distribution system water (DSW) 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, including LSI (Langelier saturation index), CCCPP (calcium carbonate precipitation potential), RSI (Ryznar stability index), WSI (Wollastonite saturation index), and CSMR (chloride-to-sulfate mass ratio) were calculated and compared to better guide the pipe-loop testing phase. Good correlations between the indices were obtained from the test results, and it appears 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 the use of lining in distribution system pipes (e.g. epoxy seal coating) may improve corrosion resistance. The initial lead and zinc release tests were conducted with brass coupons for six weeks, showed that higher permeate blends resulted in higher zinc and lead release, and may require additional adjustment to mitigate the effects.