I was recently introduced to Prof. R. S. Silver’s 1979 history of desalination, slyly titled For want of a nail (Desalination Volume 31, Issues 1–3, October 1979, Pages 39-44). Silver summarizes his career in desalination research, noting that it is often the small things in desalination that end up mattering the most.
This cautionary tale weighed on my mind when I recently toured the Advanced Water Treatment Plant (AWTP) located in Cambria, California. Prior to the development of the plant, Cambria had relied on groundwater from a nearby creek. The Central Californian local community knew it was time for a water-supply related change after years of low rainfall and over-reliance on a single water supply.
Cambria’s AWTP—a secondary water supply based on reuse of treated wastewater—was thus built in 2015 during the height of California’s most recent multi-year drought.
The picturesque town’s treated wastewater is first diverted to a percolation basin where it seeps into the subsurface. It then interacts with freshwater percolating from the mountains to the East and seawater seeping inland from the West. The mixed groundwater is then pumped out of the basin, filtered, and desalinated with a 2-stage Reverse Osmosis (RO) system. This RO system recovers 92% of the fresh water, which is then reintroduced into the town’s groundwater well-field further upslope. The MF-RO-UV-H2O2 unit processes of the packaged desalination facility are elegantly housed in a set of cargo containers, cleverly laid out so that the entire system resembles a set of large tan Legos.
Unfortunately, R. S. Silver’s admonition became particularly apparent once the system was up and running. The small amount of brine generated from the facility was disposed of by pumping it into an evaporation basin nearby. The evaporation basin itself was rigorously engineered to prevent leaks but… the cool foggy weather common for the central coast resulted in very low evaporation rates. And, when a winter storm caused runoff to overtop the basin, the entire water project was put on indefinite hold.
The entire “kingdom” of brackish desalination has been waiting for a brine disposal nail.
On a related note, NAWI has begun to review Concept Papers submitted in response to our recent call for proposals for piloting novel small-scale desalination systems (read the Pilot Program FAQ for more information). I am very hopeful that the desalination community will come forward with breakthrough approaches to further treating and reducing (or even eliminating?) the liquid brine waste stream that has bedeviled brackish desalination for so long.
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