Biological Dechlorination of Model Organochlorine Compounds in Bleached Kraft Mill Effluents

Abstract

Models of organochlorine compounds present in bleached kraft pulp mill effluent, with well-defined structure, can be used to provide information on the relationship between their chemical structure and their behavior toward biological dechlorination. The biological dechlorination of three monomeric model compounds, 4-methyl-5-chloromuconolactone monomethyl ester (MCME), 2-chloro-3-methylmuconolactone (CMML), and 3-chloro-4-methylcatechol (CMCA), and a dimeric model, 2-(4‘-methyl-2‘-muconylmethyl)-3-chloro-4-methylmuconic acid dilactone (CMDL), were studied. The first two monomers are products of simulated bleaching reactions (sequentially with ClO2 and NaOH) using a monomeric model compound of residual lignin, 4-methylguaiacol (MG), and are considered to be monomeric models of organochlorines in the ClO2 bleachery effluents. Similarly, the dimer model is a product of a dimeric lignin model reacting with ClO2 and NaOH and is considered to be a model of organochlorines of higher molecular weight. CMCA was chosen as a model compound for the phenolic portion in the effluent. It was found that MCME and CMDL do not undergo biological dechlorination. CMML did not dechlorinate in the absence of biomass for over 35 days, but it was dechlorinated by biomass from a pulp mill activated sludge system within 8 days. CMCA was found to be chemically unstable and rapidly dechlorinates when dissolved in water. The recalcitrance of MCME and CMDL to biological dechlorination is postulated to result from the fact that they both possess structural features that represent a dead-end intermediate of the ortho-cleavage pathway that is common to many aerobic bacteria.