REDUCTIVE DEHALOGENATION OF CHLORINATED HYDROCARBONS DURING ANAEROBIC STABILIZATION OF MUNICIPAL WASTES

During sequential anaerobic digestion of municipal wastes, distinct biogeochemical phases exist which show different capabilities to transform halogenated hydrocarbons. Chlorophenols, tetrachloroethylene, and chloroanilines codisposed together with organic-rich waste substrates are reductively dehalogenated during methanogenic conditions. Lindane is degraded during acidogenesis as well as during methanogenesis. However, degradation in methanogenic leachates is faster by a factor of 10. The poor transformation potential during acidogenesis compared to subsequent transient methanogenic and stabile methanogenic phases cannot be explained by inadequate acclimation of prevailing microorganisms to the codisposed organochlorines. Thus, observed transformation capabilities are a pertinent feature of methanogenic leachates, probably due to prevailing low redox potential and/or presence of suitable microbial activities (not necessarily methanogenis). Dehalogenation of 2,3,4,6-tetrachlorophenol as a model compound is hampered in methanogenic leachate by addition of a surplus of sulfate and is completely suppressed by addition of molybdate which selectively inhibits sulfate reducing microorganisms. Competition for common electron donators (e. g. H-2) is discussed as an explanation of these results. The results point to sulfate reducing microorganisms being involved in reductive dehalogenation of chlorophenols.