Diane LaMacchia, [email protected]
BERKELEY, CA -- At a pilot water treatment plant soon to be built in the Panoche Water District in the western San Joaquin Valley, scientists will test the ability of bacteria to reduce dangerous selenium levels in agricultural drainage water.
Scientists from the Lawrence Berkeley Laboratory and the University of California, Berkeley, are collaborating 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.
"This is a very promising system in that it's a very cheap technology, likely to be affordable for farmers," says LBL earth scientist Nigel Quinn.
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.
Funded by a grant from the US Bureau of Reclamation, the Panoche water treatment project grew out of a one-year experiment in the Grassland Water District. In that experiment, scientists 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.
The experiment was prompted by indications that 25 to 35 percent of the selenium entering the Grasslands Drainage Basin was not detected in Mud and Salt sloughs, the major conveyances for selenium-contaminated water leaving the drainage basin and going into the San Joaquin River. This caused concern that selenium might be accumulating in the Grasslands area. Deaths and deformities of waterfowl at Kesterson Reservoir in the late 1970s to mid-1980s have shown that concentrations of selenium can be extremely harmful to aquatic wildlife. Since then, scientists have searched for solutions to the problems associated with agricultural drainage water.
Two monitoring sites approximately four miles apart were set up along the Agatha Canal in the south Grassland Water District. Scientists monitored electrical conductivity and flow rate to determine net gain or loss of water and selenium load from one site to the other.
Initial data from the monitoring stations showed only small differences in selenium concentrations from one site to another. Other observations made during the year suggest that human activity within the Grassland Basin may be a major cause for the loss of selenium from drainage water in transit through the area. It turns out that the greatest losses coincided with the fall season when high volumes of fresh water transported through the water district have the opportunity to mix with the drainage water before it's diverted to duck hunting clubs and refuges.
"We can't account for the selenium, because either it's 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.
A second part of the experiment consisted of intensive studies of selenium concentrations in bottom sediments, aquatic plants, and algae.
UC Berkeley biochemist Terrance Leighton and plant biologist Robert Buchanan conducted a series of experiments on microorganisms from the bottom sediments of the Agatha Canal. They cultivated individual strains and studied their growth and their ability to remove selenium from fixed concentrations.
"They isolated some that appeared to be particularly good at taking up selenium," says Quinn.
In a process invented at the Algae Research Laboratory in Richmond by UC Berkeley environmental engineer William Oswald, the selenium that gets concentrated in bacterial cells can then be removed as sludge. That 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," says Quinn.
If they are successful, this simple bacterial technology could have an enormous impact in helping to solve the drainage problems on the west side of the San Joaquin Valley.
LBL is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California.