California Dept. of Health Services (CDHS) gave conditional acceptance In early March to a new biological perchlorate removal process for drinking water. The fixed-bed biological treatment by Fountain Valley, Calif.-based Carollo Engineers "give engineers another type of technology that can be used as an alternative to the anion exchange process," says Dr. Richard Sakaji, P.E., CDHS senior sanitary water
treatment engineer.
The benefit, according to Dr. Jess Brown, project manager, biological treatment for the six-month pilot study at Castaic Lake Water Agency in Santa Clarita, Calif., is that it "eliminates the disposal problem." The prevailing anion exchange method captures the perchlorate using a salt solution that must be disposed of in an evaporation pond or some other method. "This can introduce metals and solid hazardous waste and is expensive," Brown explains.
In the six-month test case, fixed-bed biological treatment removed perchlorates that had been introduced to the water at various levels to less than 1 ppb by running it over a media of biological agents that convert the chemical to harmless chloride and oxygen. A similar process has been used to treat nitrogen and a fluidized bed reactor is being used in Rancho Cordova where a superfund site is cleaning up groundwater.
The cost for maintenance and operation in the preliminary design was estimated at 12 cents per thousand gallons with the total water production costs of 70 cents per gallon, including capital expenses. Other destructive methods include chemical and electrochemical reduction. Physical removal processes, including membrane filtration, electrodialysis and anion exchange all require subsequent disposal of the perchlorate waste.
"The process has been used in Europe for decades," says Brown, "but there is a perception problem here with introducing biological agents to drinking water."
CDHS conditions include the requirement that any full scale plant maintain a minimum flow at all times. "Rather than feeding them breakfast, lunch and dinner, it is important these microbes are always eating to keep them conditioned." Also, because temperatures, conditions and water quality are different in each case, any proposed full-scale plant would have to get it's own approval.
Phil Brandhuber, Ph.D. a scientist at consulting engineer HDR's Denver office, was not surprised that California was one of the first to approve the process. "California is in the forefront of development because of contamination in the Colorado River, which is a major source of drinking water." Additionally, California was home to a number of military bases that left the substance in the
groundwater.
Why worry about perchlorate? Dr. Richard B. Johnston, Jr., associate dean for research development at the University of Colorado School of Medicine explains in a report titled, Health Implications of Perchlorate Ingestion.
The perchlorate tetrahedron of four oxygen atoms surrounding a central chlorine atom is an oxidant used in solid rocket fuels. It was detected at concentrations of at least 4 parts per billion in public drinking water supplies of more than 11 million people. "It can interfere with the uptake of iodide in the thyroid and could reduce hormone production," Johnston warns.
While that still leaves about 95 percent of the water in the nation safe, Johnston is on a National Sciences Academy committee that recommended the EPA adopt a reference dose that would be safe at .0007 ml perchlorate per kg of body weight per day total.
