Periodic aerated treatment and in-situ bioremediation strategies for polyhalogenated compounds

Polyhalogenated compounds are known to resist aerobic degradation but are subject to anaerobic reductive dehalogenation. The anaerobic biotransformation often result in the accumulation of toxic and carcinogenic compounds. An example is the production of trichloroethylene (TCE), cis-1,2-dichloroethylene (cDCE), trans-1,2-dichloroethylene (tDCE), 1,1-dichloroethylene (1,1-DCE) and vinyl chloride (VC), from anaerobic dechlorination of tetrachloroethylene (PCE). However, the anaerobic dehalogenation products are known to be susceptible to aerobic methanotrophic oxidative mineralization. Therefore, the treatment of polyhalogenated compounds and field remediation of sites contaminated by these compounds involve anaerobic biotransformation followed by aerobic mineralization. As opposed to two stage treatment and remediation which involve anaerobic environment followed by an aerobic environment in two separate systems or environments, recent focus on the detoxification of polyhalogenated compounds involve the development of engineering systems which can accomplish anaerobic biotransformation and aerobic oxidative mineralization in a single reaction environment. Periodic aerated anaerobic batch systems, including systems for ex-situ and in-situ biodetoxification of polyhalogenated compounds are being developed at San Jose State University under the direction of Dr Udeme J. Ndon. These systems and results of preliminary studies are presented in this report. Results of the preliminary experiments showed minimum accumulation of PCE biotransformation products in comparison to strict anaerobic conditions. Results also show that PCE degradation may have occurred during the transition between anaerobiosis and aerobiosis.