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The Case for Cl02: Pollution Prevention Chemistry at its best
by Charles E. Swann
Papermaker *
January 1994


Even as the industry continues its seemingly un-ending quest to find an acceptable and readily usable alternative to chlorine bleaching, the most obvious answer may be right at its fingertips -- chlorine ioxide.

A recent study undertaken by an independent panel of scientists has concluded as much, stating that a high degree of chlorine dioxide (Cl02) substitution in bleaching is an effective solution to the problem of dioxin and other persistent bio-accumulative toxic substances in mill waste water.

"The environmental risks from chlorinated organics are insignificant at mills bleaching with chlorine dioxide, using secondary treatment and with receiving-water dilutions typically found in North America," said Keith Solomon, the panel's chairman. He said that the five-person panel was unanimous.

The study in question was commissioned by the Alliance for Environmental Technology (AET), an alliance of 15 Canadian and American pulp, paper and chemical manufacturers. Its results were presented to the International Joint Commission (IJC), the Canadian-American bilateral organization established to monitor the Great Lakes Water Quality Agreement, at its meeting in Windsor, Ont., Oct 22-24. The IJC is considering a recommendation to phase out the use of chlorine and chlorine-containing compounds as industrial feed stocks, as on step in the virtual elimination of chlorinated organics from Great Lakes waters.

Against the background of the IJC's deliberations, the AET asked a five-person panel of scientists and academicians to prepare an opinion on the effects of chlorine dioxide on the nature, quantity, environmental exposures and environmental impact of chlorinated organic compounds produced in papermaking. The panel was asked to examine the likely ecological and environmental results of increasing the proportion of chlorine dioxide to 70% to 100% in the first stage of bleaching, with biological treatment of wastewater to follow.

Members of the panel were Keith Solomon, Center for Toxicology, University of Guelph, Ont.; Harold Bergman, Department of Zoology and Physiology, University of Wyoming; Robert Hugget Virginia Institute of Marine Sciences, College of William and Mary; Donald Mackay, Institute for Environmental Studies, University of Toronto (and member of the IJC's Virtual Elimination Task Force); and Bruce McKague, CanSyn Chemical Corp., Toronto. The panel's analysis included building a conceptual model, reviewing nearly 300 papers on the subject and undertaking a comprehensive risk assessment. The study was the first of its kind to follow the U.S. EPA's "Framework for Ecological Risk Assessment," published in 1992.

The panel's review focused on the effects of pulp mill effluents in the aquatic ecosystem, including possible effects on wildlife via bio-accumulation through the food chain. It excluded air emissions, sludge, and other environmental concerns outside the mill.

The panel examined various environmental processes, including biological and nonbiological transformations, partitioning from water to particles, sedimentation, resuspension, diffusion, advective flows, and dilution uptake, release and metabolism in organisms and food chains.

Based on the evidence from laboratory and field studies and the application of predictive models, the reviewers concluded that chlorine dioxide bleaching at levels of 70% to 100% provides the following benefits:

  • An 80% reduction in the quantity and a 90% reduction in the degree of chlorination of the chlorinated organics detected in mill waste water.
  • A drop in the persistence of these compounds and their potential for bioaccumulation and food-chain transfer.
  • A reduction in the potential for negative ecological effects, and
  • A substantial reduction or virtual elimination of the formation of dioxin.
In presenting the findings of the panel, panelist McKague said, "It's fundamental chemistry that explains the environmental benefits of chlorine dioxide. Chlorine dioxide, except for sharing the same word in its name, is a very different chemical from chlorine gas."

The panel's report noted the fundamental chemical difference between chlorine dioxide and chlorine and the way they react with organic compounds, such as lignin. In the chlorine bleaching process, a significant portion of the chlorine combines directly with lignin, which has aromatic components. Aromatic compounds have atoms arranged in rings and chlorine atoms may become attached to the rings. Dioxins are part of the group of chlorinated aromatics.

Chlorine dioxide's behavior, on the other hand, is completely different. Instead of combining with the aromatic rings, it breaks them apart. Thus, the generation of chlorinated organics falls sharply as the substitution of chlorine dioxide increases.

"A well-operated mill using chlorine dioxide could possibly achieve the IJC's goal calling for the virtual elimination of these substances," said panelist MacKay.

For more information on the full 75-page report, entitled "A Review and Assessment of the Ecological Risks Associated with the Use of Chlorine Dioxide for the Bleaching of Pulp," call Doug Pryke, Alliance for Environmental Technology, 519/855-4979.


AET is an association of 15 Canadian and U.S. chemical manufacturers and forest products companies. Members are:

Alabama River Pulp, Champion International, Eka Nobel, Federal Paper Board Co., Georgia-Pacific Corp., Huron Tech Corp., James River Corp., Kerr-McGee Chemical Corp. and Potlatch Corp in the United States, and Albchem Industries Ltd., Celgar Pulp Co., Domtar Inc., Fraser Inc., Saskatoon Chemicals Ltd. and ERCO Wordlwide in Canada.

AET's published mission is "to promote practical, proven advances in the environmental performance of modern papermaking, and to help achieve sound Canadian and American federal, state and provincial policies."

The association maintains and office at RR#1 Erin, Ontario N0B 1T0, telephone 519/855-4979.


* Used with permission from Papermaker Magazine.