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ClO2 - Strong Performer, Bright Future
By Douglas C. Pryke, AET Executive Director
Guest Editorial in Paper Age *
April 1994

Amid growing public and scientific debate about bleaching technologies, consensus is emerging around three important developments. First, chlorine dioxide is an environmentally superior bleaching process. Second, chlorine dioxide is not an obstacle to closing a mill's process water loop. Third, market growth is being driven by ECF (Elemental Chlorine-Free) pulp, not TCF (Totally Chlorine Free). This consensus suggests that chlorine dioxide is not an interim technology, nor is it a transitional phase in the quest for the minimum effluent mill. In the end, chlorine dioxide may offer the key to achieving our industry's vision of the minimum impact mill.

The clear and urgent need to eliminate persistent and bio-accumulative toxic substances in mill waste water has pushed the conversion to chlorine dioxide bleaching. But many feel this conversion is simply not enough. This has raised discussion of the minimum effluent mill, which isolates the mill's process water circulation from the environment. In theory, if there is no mill process waste water, there is no impact from the bleaching process on the receiving ecosystem.

Two divergent approaches now shape the public debate: ECF and TCF. Recent U.S. legislative and regulatory moves have sharpened the focus on these two pollution prevention technologies. These initiatives include the U.S. EPA's cluster rule for pulp and paper mill water and air emissions. Congressman Richardson's Zero Chlorine Discharge Act, and the Clean Water Act Reauthorization, which may include President Clinton's recommendation for a national strategy to substitute, reduce or prohibit the use of chlorine and chlorinated compounds.

TCF proponents argue that chlorine dioxide-based technology is obsolete. Their case rests on three principal arguments: first, that chlorine dioxide is nothing but chlorine in disguise, i.e., still a source of harmful chlorinated organics; second, that eliminating process waste water from a mill using chlorine dioxide, even if possible, will be far more difficult than for a TCF process; and third, failure to jump on the TCF bandwagon is eroding the competitive position of the North American pulp and paper industry. None of these arguments is convincing nor can they withstand careful analysis.

Chlorine Dioxide: A Unique Performer

Last summer, the Alliance for Environmental Technology commissioned a panel of five prominent scientists to prepare an expert opinion on the use of chlorine dioxide. The scientists examined the compound's chemistry and assessed the potential biological impact of waste water from pulp and paper mills using only chlorine dioxide in the first stage of bleaching.

Their October 1993 report, "An Assessment of the Ecological Risks Associated with the Use of Chlorine Dioxide in the Bleaching of Pulp," reached two major conclusions. First, chlorine dioxide is fundamentally different from chlorine; and second, due to chlorine dioxide's chemical properties, the resulting compounds in mill waste water have a very different environmental character.

As Dr. Robert Huggett, a report co-author and member of the EPA's Science Advisory Board's Ecological Processes and Effects Committee, stated at the February 10, 1994, EPA hearing on its proposed cluster rule, "the environmental risks of chlorinated compounds from bleaching with chlorine dioxide are insignificant. Chlorine dioxide solves the problem of dioxin and other persistent and bio-accumulative toxic substances in mill waste water."

Field evidence backs up this opinion. An extensive two-year study of a pulp mill in Northern Alberta, Canada demonstrates that not only are dioxin and the poly-chlorinated phenols reduced to levels below analytical detectability, but that the body burdens of in the exposed fish are approaching those in fish in streams without such mills. Also, there was no evidence of deleterious effects on fish species composition, distribution or relative abundance and reproductive rates.

This is strong indication that bleaching with chlorine dioxide is having no adverse effects on the fish and aquatic ecosystem.

These findings are not unique. Other mills using chlorine dioxide bleaching, both in Canada and the U.S., are reporting ecosystem recovery, as witnessed by the lifting of fishing bans and consumption advisories on the rivers where the mills are located.

Closing the Loop

The second argument - that closing an ECF mill will be difficult, if not impossible hangs on the assumptions that chloride will be introduced into the mill's recovery system, and that it will be corrosive. This position ignores at least four minimum process effluent ECF designs under development around the world, several of which do not introduce chloride to the chemical recovery cycle. Those that do, can be designed to manage the chloride concentrations. As we know, sodium chloride, which is a natural constituent of wood, is accommodated in today's very "tight" mills. The chloride ion can be recovered, removed, and may be remade into chlorine dioxide.

Chloride is only one among many challenges facing minimum effluent mill development. How to deal with the required water reduction, the calcium concentration profiles and deposition, the sodium-sulfur balances, along with the build-up of other non-process elements such as potassium, manganese, copper. zinc, etc., remains an open question.

This does not mean that these and other obstacles cannot be overcome. It does suggest, however, that what seems clear and simple as a designer's simulation is far more complex in the real world of an operating pulp and paper mill.

The Market's Future

The third argument is that the North American reluctance to embrace TCF will spell competitive failure. This is a curious argument given the facts. Today TCF accounts for only five percent of the world's bleached chemical pulp production. In the United States, there is only one TCF pulp mill in operation.

The greatest share of TCF's market pulp is produced primarily in Sweden and Finland for export to the Germanic-speaking countries of Europe. It is far from clear whether TCF will expand appreciably beyond its current market.

AET market research confirms that it is ECF, not TCF, that accounts for the pulp market's strongest growth. In North America, approximately 41 million tons of bleached chemical pulp are produced annually. ECF production in Canada has grown from 0.7 million tons in 1990 to an estimated 5.5 million tons in 1994, an 800 percent increase representing 50 percent of total Canadian bleached chemical pulp. In the U.S., growth in ECF production will rise to about 7 million tons by the end of 1994, or almost 25 percent of total American bleached chemical pulp.

By the end of 1994, ECF will have penetrated 30 percent of the North American market. In contrast, North American TCF production at the end of the year will be no more than 300,000 tons, or less than one percent of the market.

While there is some demand for TCF products in the U.S., it is hard to see how this market will amount to more than a specialized niche, since U.S. consumers are clearly demanding ECF pulp.

Moreover, TCF is vulnerable since TCF pulp strength, at best, can only approach that of ECF pulp. This being the case, there will always be an upper limit to the market size for such pulp, since large volume converters and paper makers will require higher strength ECF pulp to remain cost effective.

The ultimate success of either technology will depend on many variables, some of which can only be guessed at. Invariably, the highest quality product with the lowest environmental impact, and manufactured at the lowest cost will emerge victorious. So should TCF prove comparable to ECF on environmental grounds, TCF's market success will depend on product quality and cost -- two very traditional parameters.

The reasons why the North American pulp and paper industry is making the transition to the ECF process are straightforward. The industry, because of its capital-intensive nature, can only afford to invest incrementally in proven, practical technological advancements for which there is a well-defined market. ECF fits the bill, especially since chlorine dioxide is a well known bleaching technology, whose cost and environmental benefits, in comparison with TCF, are well established.

New Concerns

But is bleaching with or without chlorine dioxide an environmentally important issue at all? Have we, in the rush to be "environmentally correct," overlooked compounds discharged in process effluents from the unbleached part of the mill?

Environment Canada has raised new concerns. In an ongoing effort begun two years ago, their research has uncovered a number of physiological effects in fish and other aquatic organisms living downstream from some pulp and paper mills. These effects include liver enlargement and activation of detoxification enzymes, reproductive effects such as sexual hormone suppression and delayed sexual maturation, bio-accumulation of dioxins/furans, and genotoxicity and metabolic changes such as larger and fatter fish.

Except for the body burdens of dioxin which, as other research indicates, is decreasing with the conversion to chlorine dioxide bleaching, all the other effects are seen in fish downstream from both bleached and non-bleached pulp mills. In other words, yet unidentified non-chlorinated compounds, having nothing to do with bleaching, are prime suspects.

TCF proponents counter that a minimum effluent TCF mill will make these concerns irrelevant. That is true; but it is also true for a minimum effluent ECF mill. Today there are no operating full-scale mills, neither TCF nor ECF, recovering or eliminating all process effluents. So until one is built and operating, all mills, with or without ECF or TCF bleaching processes, may have to contend with and address these physiological effects on fish in the receiving ecosystem.

Chlorine dioxide bleaching is well-known and the environmental effects of the compounds produced are well understood. The same is not yet true for TCF bleaching. Very little is known about its environmental impact, since the waste water produced has just been subjected to long-term eco-toxicological testing. Until the results are in and have been accepted, the assertion that TCF is "more environmentally correct" than ECF is premature.

Chlorine dioxide may just be the cornerstone for the future minimum impact mill in North America. The continent's consumer demand is pushing conversion to this bleaching process, an attractive technology option with clear environmental benefits.

Its prospects are very bright indeed.



Mr. Pryke is the Executive Director of the Alliance for Environmental Technology. He has been instrumental in the practical implementation of high substitution chlorine dioxide bleaching at many kraft pulp mills throughout North America. Mr. Pryke was the startup engineer for the world's first closed-cycle bleached kraft pulp mill. He received a B.A.Sc. in Chemical Engineering from the University of British Columbia.

* Used with permission from Paper Age Magazine.