Ex-situ bioremediation of chlorobenzenes in soil

Chlorinated benzenes, including chlorobenzene (CB) and 1,2-dichlorobenzene (DCB) are widely used as chemical intermediates and solvents across industry. Soil contaminated with these compounds was treated in a pilot-scale trial in 6 m3 cells. Air was drawn through each cell and exhausted via an activated carbon (GAC) filter system. The trial objective was to stimulate native microflora with nutrients and varying levels of organic amendments (0%, 12% and 35%). Initial soil DCB concentrations varied from <1 to 6 mg/kg in the three cells with an average of 2 mg/kg. Approximately 90% of the DCB mass present in the soil was removed over a period of 2-3 weeks. Up to 100-fold increases in total heterotrophs (THP), CB+ and DCB+ degraders were observed. Residual concentrations of chlorinated benzenes were generally below detection limits (0.2 mg/kg). Adding organic matter did not enhance the removal of CB and DCB under the trial conditions, which were set up to minimize losses from volatilization. Biodegradation estimation calculations indicated that <5% of the chlorinated benzenes were removed by volatilization and 90% removed by biodegradation. Laboratory shake flask trials confirmed that the soils in the pilot-scale treatment contained a microbial consortium capable of mineralizing CB and DCB. This consortium was capable of mineralizing both CB and DCB with up to 50% of carbon added as chlorinated benzene substrate being recovered as CO2 and up to 44% of organic chlorine being released as chloride ion in mineralization tests, further confirming these chlorinated benzenes were biodegraded. The study confirms that vented ex-situ biotreatment processes for chlorinated benzenes can be achieved without excessive losses from volatilization and that naturally occurring microflora can be readily stimulated with aeration and nutrients.