Evaluation of dechlorination mechanisms during anaerobic fermentation of bleached kraft mill effluent

Abstract

The impact of nucleophilic substitution of biologically mediated sulfide as a potential mechanism for dechlorination during anaerobic treatment of kraft mill bleach plant effluents was investigated. Batch anaerobic biodegradative studies employing a prepared solution of chlorinated organic matter with a low concentration of anions revealed that sulfate supplementation, with subsequent production of sulfide by anaerobic fermentation, did not significantly increase the extent of dechlorination. Competition with other degradative mechanisms, such as reductive dechlorination was concluded to be responsible for the reduced impact of sulfide on AOX removal in biological studies. Substantially more inorganic chloride was produced than could be accounted for by AOX reduction during the batch tests. Subsequent analyses revealed that the total chlorine concentration in the original effluent was greater than the sum of the AOX and chloride concentrations. It was concluded that the excess chloride produced in the batch tests resulted from the degradation of chlorinated organic matter which was not detected by the AOX technique.