Desalination plant’s nitrate removal has hidden benefits

A water district in California has found a novel way to remove multiple contaminants from groundwater currently feeding a desalination plant without creating waste that requires costly treatment and disposal.

The treatment could replace processes such as ion-exchange, reverse-osmosis and electrodialysis-reversal.

Western Municipal Water District (WMWD) is moving ahead with plans to expand the Arlington Desalter to 7,500 acre-feet (9.2 million m³) of drinking water per year and has awarded an $815,000 contract to Carollo Engineers to design what is anticipated to be the USA’s only operating full-scale biologically active denitrification facility for drinking water.

Project design of the US$ 7.98 million plant will begin immediately. This will consist of a series of large biofilters, polishing filters and backwash equalization tanks as well as supply pumps and a new groundwater well. Once complete, the expansion will provide 2,300 acre-feet (2.8 million m³) per year of biodenitrification treatment capacity.

“With reduced imported water supplies from the Colorado River and the State Water Project, this action moves us one step closer to reaching our goal of increased water independence,” said WMWD board president Thomas P Evans.

WMWD completed extensive facility testing of the fixed-bed biological treatment (FXB) process in late 2008. The district and Carollo have received provisional approval from the California Department of Public Health to use FXB to remove nitrate from drinking water.

A key benefit discovered during testing is the ability to remove multiple contaminants from the water supply. In addition to removing nitrate, the FXB process destroys perchlorate and volatile organic compounds (VOC).

While existing nitrate treatment processes such as ion-exchange, reverse-osmosis and electrodialysis-reversal remove nitrate effectively, each creates a nitrate-laden concentrate waste requiring treatment and disposal. The FXB process converts nitrate to harmless byproducts such as nitrogen gas, thereby also eliminating the need for nitrate-waste handling, making this technology sustainable.

Other benefits include competitive operating cost and highly efficient water recovery.