Sequential anaerobic/aerobic biodegradation of chlorinated hydrocarbons in activated carbon barriers

The aim of this study is to develop a long lasting, sequential anaerobic/aerobic biological activated carbon barrier. In the biobarrier, pollutant adsorption on granular activated carbon (GAC) and biodegradation occur simultaneously. Trichloroethene (TCE), chlorobenzene (CB), and benzene were used as model pollutants. In the first barrier, that was operated under anaerobic conditions with sucrose and ethanol as auxiliary substrates, TCE was completely converted to lower chlorinated metabolites, predominantly cis-dichloroethene (cis-DCE). The reductive dechlorination process was stable for about 300 d, although the concomitant sulphate-reducing and methanogenic processes varied considerably. In the second barrier, that was operated with addition of hydrogen peroxide and nitrate, dechlorination was limited by a lack of oxygen and restricted mainly to CB biodegradation. Additional aerobic batch tests revealed that the metabolites of anaerobic TCE dechlorination, i.e. cis-DCE and vinyl chloride, were oxidatively dechlorinated in the presence of suitable auxiliary substrates such as ethene, CB, benzene, or sucrose and ethanol. During periods of low biological activity, elimination of TCE and CB occurred by adsorption in the GAC barriers. The pre-sorbed pollutants were available for subsequent biodegradation resulting in a bioregeneration of the activated carbon barriers.