Researchers seek simple solution to selenium quandry

November 4, 1994

By Diane LaMacchia, [email protected]

A team of earth researchers are turning to tiny bacteria to tackle a big problem: reducing the dangerous levels of selenium in agricultural drainage water.

LBL earth scientist Nigel Quinn and Earth Sciences Division Director Sally Benson are collaborating with researchers from UC Berkeley on a three-year project to find out if certain types of algae and bacteria take up selenium well enough to form the basis of an efficient drainage treatment method.

To test this new microbial technology, a pilot water treatment plant will soon be built in the Panoche Water District in western San Joaquin Valley.

"This is a very promising system in that it's a very cheap technology, and likely to be affordable for farmers," Quinn says.

Funded by a grant from the US Bureau of Reclamation, the Panoche water-treatment project grew out of a one-year experiment the researchers conducted in the Grassland Water District. In that experiment, they studied agricultural drainage water flowing through a complex of privately and publicly-owned wetlands that serve as habitats for birds and other wildlife. Contaminated water flows through more than 100 miles of channels, passing several private duck hunting clubs and travelling through the middle of the State-run Los Banos Refuge before it discharges into the San Joaquin River.

Salt-laden agricultural water--salty from the leaching of naturally occurring alluvial deposits and the evaporation of irrigation water--routinely drains into the San Joaquin River from cotton and tomato fields and fruit and nut groves on what would otherwise be arid land. This drainage water also contains high levels of selenium and boron, naturally present in the shallow groundwater underlying the agricultural area.

The research was motivated by indications that 25-35 percent of the selenium entering the Grasslands Drainage Basin was not detected in Mud Slough and Salt Slough, the two major conveyances for selenium-contaminated water draining into the San Joaquin River from the basin. This caused concern that selenium might be accumulating in the Grasslands area. High concentrations of selenium can be devastating to aquatic wildlife, as deaths and deformities of waterfowl at Kesterson Reservoir showed in the late 1970s and mid 1980s.

In one phase of the experiment, the researchers performed flow-rate and salt-load tests on the drainage water. They observed that the greatest losses of selenium coincide with the fall season and human activity. In the fall, high volumes of fresh water are transported through the water district--where it can mix inadvertently with drainage water--before getting diverted to duck hunting clubs and refuges.

"Either the selenium is in a different form like algae and it's moving out of the system--so we're not measuring it--or the drainage water is mixing with fresh water and getting diverted into the duck clubs," Quinn says.

In the second phase of the project, UC Berkeley biochemist Terrance Leighton and plant biologist Robert Buchanan studied selenium concentrations in microorganisms they found in the bottom sediments, aquatic plants, and algae from the Agatha Canal in the south Grassland Water District. They cultivated individual strains and studied their growth and ability to remove selenium.

"They isolated some strains that appeared to be particularly good at taking up selenium," Quinn says.

In a process invented at the Algal Research Laboratory in Richmond by UCB environmental engineer William Oswald, the selenium that gets concentrated in bacterial cells can then be removed as sludge. This is the idea for the treatment plant, in which the scientists hope to create an environment that enhances the efficiency of the bacterial up-take.

"What we've done is made some observations in a natural system and now we're trying to apply some of what we've learned to an engineered treatment system," Quinn says.

If they are successful, the simple bacterial technology could have an enormous impact in helping to solve the drainage problems on the west side of the San Joaquin Valley.