Perchlorate - how do we get rid of it?

By David F. Walling

What is Perchlorate?

Perchlorate is the electrochemical oxidation product of chlorate. Perchlorate is a very strong oxidant (and highly explosive in its solid state} (e.g., ammonium Perchlorate [NH4CI04] is used as a solid rocket fuel), it is extremely stable when dissolved in water at concentrations as high as 1,000 mg/L.

Perchlorate is used in solid rocket fuel, fireworks, and various pyrotechnics. Unfortunately, trace levels of Perchlorate contaminated several groundwaters in California. California Department of Health Services (CalDHS) has adopted a provisional action level of 18 micrograms per liter for Perchlorate in drinking water. Wells in California that contain Perchlorate above this level should be removed from service. This has resulted in the closure of several groundwater wells in the state. Only recently have some water companies conducted tests that will detect perchlorate Due to the use of perchlorate in military applications and an alleged concern for secrecy, the federal government kept it off of the list of contaminants that water authorities should test for. Large volumes of perchlorate have been disposed of since the 1950's. Perchlorate has been detected in at least 14 states, every one of those states has a confirmed perchlorate manufacturer or user. In 2001 the EPA will begin requiring monitoring for Perchlorate in the nation's drinking water. Reminisant of the debates over a safe Arsenic level the EPA is considering a safe drinking water standard. The reference dose being considered for the EPA standard is 32 parts per billion.

A part per billion is equivalent to about one grain of sand in three residential swimming pools. That would be less stringent than California's guideline of 18 parts per billion, a so-called action level that requires notifying health officials but not necessarily shutting down a tainted water supply. Perchlorate has been detected in 69 out of 232 wells monitored. Of those wells, 24 had Perchlorate levels above the state provisional action level. Perchlorate has been detected in the Colorado River the highest reading for perchlorate in Lake Mead water after treatment was 24 parts per billion, or 9 parts more than the previous high on June 17, 1999. The highest concentration of raw water from the lake before treatment has been about the same, 16 parts per billion, and the average for treated water since monitoring began in 1997 has been about 9 parts.

Health Effects of Perchlorate

Perchlorate, in very high doses, has been used in medicine in the treatment of Graves' disease and therefore, there is an abundance of health effects information. When ingested, Perchlorate inhibits the ability of the thyroid gland to perform its normal function. Studies are under way to determine how much perchlorate humans can consume without adversely affecting thyroid gland functions that control growth and metabolism.

Treatment Alternatives

Currently, there are four treatment alternatives for removing Perchlorate from groundwater that are being actively considered. These include 1) anaerobic biodegradation, 2) Reverse-Osmosis (RO), 3) removal with GAC, and 4) Ion Exchange (IX)

Anaerobic Biodegradation

In this process, microorganisms are used to biologically reduce Perchlorate to other reduced forms such as chlorate or chloride. The process could be considered as a surface treatment process in that water would be pumped to the surface and treated using a suspended growth or attached growth process.

Reverse Osmosis

RO membrane filtration has long been used to remove ions from water supplies. It is commonly used for the treatment of groundwaters with high TDS levels. It also serves as the primary treatment for making seawater safe to drink.

Removal with GAC

GAC is commonly used for the removal of organic contaminants from drinking water supplies. GAC has also been considered for the removal of highly oxidized chemicals such as chlorine, bromate, and chlorite. However, in the case of these compounds, studies have shown that the removal mechanism is not via. Conventional’ adsorption, but rather through a chemical reduction reaction occurring on the surface of the carbon. It seems likely this is also true for Perchlorate

This reaction is similar to that for the removal of chlorine from water with GAC. The City of Riverside, California indicate that perrhlorate that is removed with GAC.

Ion-Exchange

The main problem with the use of IX for Perchlorate removal is the production of a high TDS brine stream during the regeneration process. Approximately 1 0 lbs. of salt (about 10 gallons of a 10% solution for example) is required for each cubic foot of resin regenerated. In addition there is rinse water that must be disposed of.

For more information, please contact R/O CONN at (602) 432-5402,  or fax (602) 942-1451. Or you can E-mail us at roinfo@roconn.com.

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