A review of chlorate- and perchlorate-respiring microorganisms

Chlorate (ClO₃^-) and perchlorate (ClO₄^-) have been manufactured in large quantities, and therefore it is not surprising that they have been found at high concentrations (>50 mg/L and >1000 mg/L, respectively) in surface waters and groundwaters around the world. These compounds are chemically stable in water, and they are difficult to remove using typical physical-chemical water treatment technologies. Fortunately, chlorate and perchlorate can be removed by biodegradation to low levels in water. Both compounds are highly oxidized and can serve as electron acceptors for several strains of microorganisms under anoxic conditions. Although it has been known for more than 40 years that chlorate can be reduced by mixed cultures, several bacteria have been isolated recently that are able to respire using either chlorate or perchlorate. The purpose of this paper is to review the characteristics of these mixed cultures and isolates in order to assess their future potential for biological water and wastewater treatment processes.