introduction, summary, and findings

Chapter 1

Introduction, Summary,and Findings

CONTENTSPage

PURPOSE AND SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .THE U.S. PULP AND PAPER INDUSTRY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Pulp and Paper Making Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Environmental Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Pulp Bleaching Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Technologies for Reducing Dioxin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Chapter 1

Introduction, Summary, and Findings

PURPOSE AND SCOPE“Dioxin” is the term used in referring to the

family of 210 chlorinated chemicals known aschlorinated dibenzo-para-dioxins and chlorinateddibenzofurans. The most toxic member of thislarge family of compounds is 2,3,7,8 -tetrachloro-p-dibenzodioxin (2,3,7,8 -TCDD or TCDD); theclosely related compound 2,3,7,8 -tetrachloro-dibenzofuran (2,3,7,8 -TCDF or TCDF) is be-lieved to be about one-tenth as potent. Both ofthese chemicals can be formed during themanufacture of bleached wood pulp if chlorineis used as a bleaching agent. The amount ofTCDD and TCDF formed in the bleachingprocess is measured in parts per trillion (ppt).The relative toxicity of these chemicals ismeasured in ppt and expressed as “ToxicEquivalents” (TEQs) using TCDD as the stand-ard. TCDD is considered to be highly toxicbased on laboratory animal experiments and hasbeen linked to malignancies, birth defects, andphysical deterioration in animals, Evidence ofhuman health effects is less certain and remainsa contentious issue among scientists. The U.S.Environmental Protection Agency (EPA) classi-fies it as a “probable human carcinogen.”

The release of EPA’s National Dioxin Study in1987 focused attention on evidence that showeda pattern of dioxin concentrations in streambottom sediment and fish below pulp mill wasteoutfalls. Subsequent studies by the paper indus-tries and government agencies in North Americaand Europe have confirmed that detectableamounts of TCDD and TCDF are produced andreleased into the environment at many bleachedkraft pulp mills. Measurements of dioxin levelsin the three sources of pollution (pulp, effluent,and sludge) are being conducted at all U.S.chemical pulp mills using chlorine bleach underthe joint sponsorship of EPA and the Americanpaper industry. The results of these studies andothers underway in Canada and Europe will

- 3 -

contribute much more to the information basenow available, but final results are months away.

Bleached wood pulp is used in paper productssuch as writing and printing papers, rayon,tissues, towels, disposable diapers, food pack-aging, and a myriad of other products. Paper isused so widely in modern societies that everyperson comes in contact with bleached paperproducts almost daily. The knowledge thatTCDD and TCDF are produced and releasedduring the manufacture of chlorine-bleachedkraft pulp has prompted action by the Federalagencies charged with protecting health and theenvironment and has stimulated research by apaper industry faced with increasing publicconcern and, as a consequence, possible regula-tory action.

Environmental and consumer groups haveorganized an international action program toinform the public, prompt consumer action, andstimulate political and regulatory action in thepulp-producing countries of North America andEurope. The United Paperworkers InternationalUnion, the labor union that represents many ofthe paper mill employees in North America, andthe National Institute for Occupational Health(NIOSH) are monitoring the potential healthimpacts of exposure of workers to dioxin in pulpand paper mills.

This study reviews what is known about theproduction and fate of TCDD and TCDF andother associated chlorinated compounds duringthe course of pulp bleaching and brightening.The study is specifically aimed at assessing thestate of pulping and bleaching technologies thatshow promise for reducing the amount of thosechemicals resulting from the manufacture ofbleached kraft pulp, such as extended delignifi-cation, oxygen delignification, the use of bleach-ing chemicals that might substitute for some orall of the chlorine commonly used, modifi-cations of the timing, amount, and operating

4 • Technologies for Reducing Dioxin in the Manufacture of Bleached Wood Pulp

conditions of the chlorine bleach sequence, anda review of pulping and/or bleaching technolo-gies that are not yet commercially available, butmight be in the future.

Because this is a technical background report,neither an assessment of policy options relatedto the need for regulatory action, nor the formsuch regulations might take, are included. Further-more, this assessment assumes—based on pasttrends and industry projections—that a strongdemand for high-brightness bleached pulp andpaper products will continue in the future.Should the public boycott or avoid the use ofbleached paper products in the future because ofa perceived health risk, the paper industry wouldhave to adjust to the changing markets within itsown constraints.

Markets for unbleached hygienic paper prod-ucts, disposable diapers, coffee filters, and milkcartons, for example, have developed in Swedenwhere “environment-graded” or “environment-positive” lines of unbleached paper products areretailed along with bleached grades. Recently,the Canadian pulp and paper industry has agreedto reduce the amount of dioxin in paper stockused for milk containers after Health andWelfare Canada, a government agency, discov-ered trace amounts of dioxin leaching into milkfrom plastic-coated paper cartons. The pulp andpaper industry claims that paper products requir-ing high strength and long-term durabilitygenerally must be made with a highly bleachedpulp, and industry analysts believe that this willlikely continue to be a major proportion of thepulp produced.

Market pulp is a commodity traded widely inworld markets. The possibility exists that somecountries in the future may impose limits on theamount of residual chlorine compounds ordioxin in pulp and paper products that can beimported. If similar collective action were to betaken by a large number of trading partners, such

as the European Economic Community or acoalition of Pacific Rim countries, a significantportion of North America’s export market couldbe affected. If such trade restrictions werebroadly adopted, it could, for practical purposes,impose de facto international performance stan-dards on those firms wanting to compete ininternational markets.

OTA convened a workshop in November1988 to discuss the latest information regardingthree aspects of dioxin and bleached wood pulpmanufacture:

1.

2.

3.

What is known about the distribution andeffects of TCDD and TCDF resulting fromenvironmental releases by pulp mills?What is known about the amount ofresidual TCDD and TCDF in paper prod-ucts, and what is the level of risk toconsumers and mill workers?What is the current understanding of theprecursors that react with chlorine to formTCDD and TCDF, and what is knownabout the means to reduce their formation?

As a result of the workshop, we were impressedby how fast knowledge about TCDD and TCDFin bleached wood pulp is accumulating. Thisreport is on] y a “snapshot” of the technology andknowledge about the formation of dioxin andpossible means to reduce it as of December1988.

THE U.S. PULP AND PAPERINDUSTRY

The United States leads the world in percapita paper consumption. In 1986 U.S. con-sumers used over 660 pounds of paper productsper person.1 This new record of paper consump-tion continues the steady increase in the domes-tic use of paper that saw per capita consumptionrise about 16 percent between 1976 and 1986.Paper, which is indirectly correlated with gen-

l~erlcm Papr In.ql[u[e, ]9/?7 statistics of Paper, Paperboard& Wood Pulp (New York, NY: Associated Press International, 198’7), p. 2.

Chapter 1—Introduction, Summary, and Findings ● 5

eral economic activity, is currently being con-sumed at the rate of about 21,000 tons per billiondollars of the real gross national product (GNP)generated. For a variety of reasons, including thereduction of solid waste, efforts to recycle scrappaper are expanding, particularly in urban areas.

Nearly 73 million tons of paper, board, andconstruction board were produced in the UnitedStates in 1986.2 Although 4.8 million tons ofpaper products were exported by U.S. produc-ers, almost 12 million tons were imported fordomestic consumption. Most of the importsoriginated in Canada and were newsprint. Morethan 70 percent of U.S. exports and 80 percentof imports in 1987 were bleached or semi-bleached pulps.3

Pulp products valued at $3.9 billion wereshipped from U.S. pulpmills in 1987. The paperand allied products industry (SIC 26) employedover 674,000 persons in 1986, with aboutone-third of those directly involved in theproduction of paper and pulp (SIC 261, 262,266).4 In general, pulp mills have tended toconcentrate in the South and Northwest nearmajor sources of wood, while allied industriesand conversion facilities are more broadlydistributed near primary markets.

Future prospects for the pulp and paperindustry are bright. In the Pacific Rim countrieswhere industrial expansion is expected to in-crease dramatically, forest-deficient countrieslike Japan, Korea, and Taiwan are consideredlarge potential markets. The United States andCanada, with their vast forest resources, theirestablished industries, and technological capac-ity, are well positioned to take advantage of newexport markets. However, international competi-tion for new markets is sharpening, with over-seas suppliers in Brazil, Portugal, Spain, Mo-

rocco, and South Africa expanding their capac-ity.

SUMMARY

The Pulp and Paper Making Process

The manufacture of pulp and paper involvesthe separation and purification of cellulosicwood fibers from which paper is formed. Abouthalf of the wood raw material is cellulosic fiber,and half is lignin, hemicellulose, and otherextractive compounds that cement and strength-en the fibers. The pulping process involveseither the use of chemicals, heat, and pressure ina digester to dissolve the lignin and free thefibers from one another or, in the case ofmechanical pulp and chemical-mechanical pulp,the abrasion of wood in a grinder or refiner tophysically tear the fibers apart.

Zlbid.3u,s, ~pmenl of Commerce, IWM U,S IIIAStria/ Outlook (Washington, DC; Intcmational Trade tiinw~iont 19~8)t PO 6-3

~~crlcm pWr ]n~l[utc, ~p, ~1[,, nolc ], p, 54, Nom: “S[C”r~fers[0“S~d~d lndustri~ Co&,” a classification of U.S. industries UWd by tkU.S. Depactmenl of Commerce.

6 • Technologies for Reducing Dioxin in the Manufacture of Bleached Wood PUlp

New pulping technologies are emerging, buttheir acceptance will depend on efficiency, pulpquality, cost effectiveness, or other factors thatmake them competitive with conventional tech-nology. To the extent that new pulping systemsmight reduce the amount of residual lignincarried over to the bleaching process, theamount of chemical bleaching required to attainthe desired brightness might be reduced andsubsequently the amount of chlorine used as ableaching agent trimmed.

Environmental Considerations

Effluents from bleached pulp mills contain avariety of substances, some of which are knownor suspected of being toxic, genotoxic, muta-genic, or teratogenic. Chlorinated organics,including TCDD and TCDF, that appear to beproduced in the chlorine bleaching and de-lignification processes, are of particular con-cern. The composition of bleaching effluent isextremely complex and varies widely from millto mill. The chlorinated components of thewaste stream consist of a variety of compounds,including simple phenols, high and low molecu-lar weight polymers, and neutral and acidicmaterials from the breakdown of the phenolicrings in lignin. An average North American pulpmill produces between 35 and 50 tons ofchlorinated substances daily. Greenpeace Inter-

national, the Environmental Defense Fund, andother environmental organizations advocate imme-diately minimizing and eventually eliminatingthe use of chlorine in order to avoid additionalreleases of these compounds into the environmentthrough effluent, sludge, or via paper products.

About 10 percent of the total solids in thewaste streams of bleaching plants contain chlo-rinated derivatives, but this varies among millsdepending on the degree of filtration. SomeEuropean countries, Sweden and the FederalRepublic of Germany in particular, have im-posed restrictions on the amount of total organi-cally bound chlorine (TOC1) that they will allowtheir pulp and paper industry to dischargesSweden has cut the amount of allowable TOC1discharge more than half, from the 5 to 6kilograms per metric ton (kg/t) of pulp normallyproduced with conventional chlorine bleaching,to 2 kg/t. Oxygen delignification and chlorinedioxide substitution have been the technology ofchoice to meet Sweden’s environmental re-quirements. The National Swedish Environ-mental Protection Board hopes to reduce TOC1to 0.1 kg/t by 2010 and to 1.5 kg/t by 1992. Withfurther reductions in allowable discharges, theSwedish industry may need to adopt closed-cycle processes to eliminate chlorinated dis-charges entirely.

SBetween 25CI ~d XXI ch~micals have been identified in pulp mill effluents. Many of them arc chlorinated organic compounds. SCe Lccna R. Suntio.Wan Ying Shiu, and Donald Mackay, “A Review of (he Nautre and Properties of Chemicals Present in Pulp Mill Effluents,” Chemo@ere, vol. 17, No.7, 1988, pp. 1249-1290. TCDD and TCDF make up a very small fraction of the total organochlonne emissions.

Chapter I--Introduction, Summary, and Findings ● 7

In 1988 the Board also considered the overallproblem of dioxin in the Swedish environmentand concluded that standards established forreducing TOC1 would suffice to reduce thedioxin levels from bleached pulp as well.Chlorinated organic effluents from pulp andpaper manufacture have created environmentalproblems in coastal waters and estuaries of theBaltic Sea, particularly in the enclosed Gulf ofBothnia. Unlike U.S. pulp mills that use second-ary biological sewage treatment technologies totreat waste effluents, mills in Sweden, some inFinland, and many in Canada do not usecomparable treatment methods before discharginginto the environment. Biological treatment canremove large amounts of chlorinated contami-nants (particularly those that adhere tightly tosediments such as TCDD and TCDF) from milleffluents when operated properly. Biologicaltreatment transfers the contaminants from thewater and concentrates it in the sludge. Thesludge must then be disposed of in a safe andacceptable manner. Biological treatment sys-tems require constant attention to ensure thatthey are working efficiently.

The Federal Republic of Germany will begintightening restrictions on the discharge of chlori-nated organics in 1989. Maximum alloweddischarges of organochlorines will be 1.0 kg/t ofbleached pulp under the new regulations. Untilrecent] y, West German regulations for pulp mill

discharges have not been overly strict. Feeslevied on discharged amounts of oxygen de-mand, solids, and measures of toxicity to fishhave allowed the German industry to “buy” theright to pollute.

Chlorinated organic residues from pulp bleach-ing have caused less concern in North Americawhere little research into adverse impacts onfisheries and aquatic biota has been conducted.There is ample experimental evidence, however,that pulp mill effluents, unless adequatelytreated, can be toxic to fish and some chlorinatedcompounds may ultimately find their waythrough the food web. Dioxin has been shown tobe extremely toxic to fish at very low concentra-tions under controlled laboratory experimentsand has been linked to periodic reductions inreproductive rates of some bird species. U.S.mills, unlike their European counterparts, haveinstalled extensive biological treatment systemsto reduce the biological and chemical oxygendemand (BOD and COD) of their waste efflu-ents before discharging them into streams. U.S.environmental requirements for the issuance ofa discharge permit for conventional pollutants,such as BOD, COD, and suspended solids, andtoxicity tests on mill effluents make biologicalwaste treatment a preferred technology for U.S.mills.

The detection of dioxin in some fish samplesreported in EPA’s National Dioxin Study has

8 ● Technologies for Reducing Dioxin in the Manufacture of Bleached Wood Pulp

raised concern about the possible effects onhuman health. Less than 20 percent of therandomly selected sites sampled by EPA in thestudy showed detectable quantities (more thanone part per trillion [ppt]) in whole fish samples.Other samples collected at over 300 regionalsites selected by EPA for high probability ofdioxin contamination showed that nearly one-third of the rivers, lakes, coastal waters, andestuaries contained fish with detectable amountsof dioxin that ranged up to 85 ppt—significantlyhigher than the 25 ppt determined to be unsafeby the Food and Drug Administration (con-tained in edible fillets, not in whole fish)-butit is not certain that pulp mill waste was thesource of all contamination. Only 4 of 57estuarine and coastal sites sampled in theNational Dioxin Study had detectable levels ofdioxin in fin fish or shellfish. Based on labora-tory tests, fish have been shown to accumulatedioxin in their bodies at rates approximately20,000 to 85,000 times the concentrations towhich they are exposed in water. Fishing hasbeen prohibited in several rivers because ofdioxin levels, and advisories have been issuedby Wisconsin, Maine, and Louisiana warning ofthe possible risks of eating contaminated fish.

A screening analysis of pulp waste at fivebleached kraft pulp mills, which was conductedjointly by EPA and the U.S. paper industry, andother research in Europe and Canada clearlylinks the formation of TCDD and TCDF to thechlorine bleaching process. TCDD was detectedin seven of nine bleached pulps sampled, somewith levels as high as 51 ppt. TCDF, which isless toxic than TCDD, was found in eight of ninepulps sampled, with levels ranging up to 330ppt.

Dioxin was detected in wastewater at four ofthe five mills, but concentrations varied greatlyamong the mills sampled. The highest levels ofTCDD and TCDF were associated with wastefrom the caustic extraction stage, which isdesigned to remove the dissolved materials afterthe chlorine treatment. EPA and the paper

industry are currently surveying 104 additionalmills to better determine the scope and extent ofdioxin and furan formation. Detailed analyses ofTCDD levels and bleaching processes at 25 pulpmill bleach lines will be conducted in the courseof the study.

The detection of TCDD and TCDF inbleached pulp samples raised concern aboutwhether residual dioxin was being carried for-ward into finished paper products. The NationalCouncil of the Paper Industry for Air and StreamImprovement, Inc. (NCASI), the industry’senvironmental research arm, commissioned anassessment of the potential risks to humanhealth from skin exposure to a variety of paperproducts, including disposable diapers, facialtissue, toilet tissue, sanitary napkins, coffeefilters, and paper towels. The assessment con-cluded that TCDD equivalents in all productstested presented a lifetime cancer risk of lessthan one in a million.

Environmentalists note that NCASI’s assess-ment only considered the risks for 2,3,7,8-TCDD and 2,3,7,8-TCDF without examining


the risks from the several hundred other chlori-nated byproducts that are also found in paperproducts, and that NCASI failed to consider thecumulative risk of using a wide range of paperproducts daily. Environmentalists also faultNCASI for not using appropriate testing proce-dures for evaluating the possible enhancedmobility of dioxin when in the presence oflipids, solvents, and fats, such as encounteredwhen using paper towels for cooking or whenusing creams and baby oils with disposablediapers.

OTA learned at its dioxin workshop that thereis considerable disagreement about the validityof the testing protocols for determining the rateof migration of dioxin from paper products andinto the human body. For instance, there arewidely differing opinions about how to estimatethe effect of urine leaching from disposablediapers into the skin of babies, and how tosimulate the environment of a tampon in determin-ing the movement of dioxin into a woman’sbody. Without standard protocols, disagreementsover the meaning of dioxin risk data leaves OTAwith no means to evaluate the industry’s find-ings and conclusions. Evaluation of these testingtechniques is beyond the scope of this as-sessment.

Agreement is also lacking on how to expresslevels of risk. Does one accept a one in a millionrisk of cancer as did the U.S. paper industry inits study of risks from dermal exposure todioxins, or should the acceptable risk be one ina thousand? There are no Federal regulatorystandards. Arbitrary levels of risk are used forconvenience, and experts differ over the mostappropriate levels to use.

Semantics also contribute to the confusion:Should dioxin exposure levels be expressed as“virtually safe dose,” which implies that there“is a level of exposure at which the cancer riskis zero,” or should the term “risk specific dose”be used since it does not imply that there is anydose above zero that is “safe”?

Couple the uncertainties over testing proto-cols with disagreement over levels of acceptablerisk, and add to it the lack of consensus about thepotency of dioxin to humans, and a confusedpicture is presented to those attempting to gaugethe danger of dioxin from pulp manufacture andpaper use.

OTA is aware of no published studies thathave attempted to define worker exposures todioxin in paper mills using environmental measure-ments or biological exposure measurements,such as serum or fat TCDD/TCDF concentrations.The National Institute of Occupational Safetyand Health (NIOSH), the Federal agencycharged with occupational and health research,is currently developing personal exposure moni-toring methods to address pulp and paperworkers’ exposure to dioxin.

EPA is currently coordinating an InteragencyTask Force on Dioxin in Paper aimed at gaugingthe cumulative risk of all of the media that couldcontribute to human exposure. Other coop-erating agencies include the Food and DrugAdministration and the Consumer Product Safe-ty Commission (CPSC). The interagency effortwas characterized by an EPA official at theNovember 1988 OTA dioxin workshop as aneffort to “determine whether there is a risk—nota ‘gold plated’ risk assessment,” and a “snapshotin time” as to the risk aimed at determiningwhether regulation is needed. The interagencystudy will build on both the EPA/Industry104-mill study and estimates of migration ratesof dioxin from paper products. It will include anassessment, based on product-use scenarios, oftechnologies that could reduce dioxin exposure.

OTA found that, as with many other Federalactivities, the analytical and regulatory authorityfor dealing with dioxin in paper is fragmentedamong several agencies, none of which haveclear responsibility for dealing with the problemin its entirety. While EPA has jurisdiction overwater pollution and dioxin in pulp (dealt with intwo separate offices), FDA has responsibility


for regulating dioxins in coffee filters andsanitary napkins, and CPSC has responsibilityfor dioxin in disposable diapers, paper towels,facial tissues, and toilet tissues.

The lack of published independent Federalresearch on the risks associated with dioxin inpaper products and the absence of governmentinformation on paper worker’s environmentalexposure to dioxin required OTA to rely almostwholly on industry-sponsored research. Thepaucity of government information on workers’risk and exposure to dioxin in paper productsmay change in the future as a result of theInteragency Task Force on Dioxin in Papermentioned above, but in the meantime we haveonly industry information available to evaluatethe potential risks from dioxin in paper.

Pulp Bleaching Technology

About 10 percent of the lignin found origi-nally in wood is carried over from the chemicaldigestion process to the bleaching stages in kraftmills. This residual lignin must be substantiallyreduced if pure cellulose products or brightpaper are to be produced. The less ligninretained in the pulp as it leaves the digester, theless bleaching needed. There are limits, how-ever, as to how much digestion wood fibers canendure without sacrificing pulp strength andpaper durability or significantly reducing pulpyield.

Bleaching is a continuation of the delignifica-tion process and is used to brighten and purifythe wood pulp. The purer the cellulose andbrighter the paper, the less lignin retained, andthe longer the paper will last without yellowingand becoming brittle. Chlorine gas has becomethe preferred bleaching agent because of itsrelatively low cost and high effectiveness.However, a number of other bleaching chemi-cals are also used, including hypochlorite,chlorine dioxide, oxygen, and hydrogen perox-ide. Ozone has also been tried under experi-mental conditions, but is not yet commerciallyavailable. Each has its advantages and disadvan-tages, and several are usually used in sequenceto achieve the final result. Between bleachingstages caustic chemicals are often used toremove the dissolved lignin and wash the fibersbefore they are subjected to additional bleach-ing. It is apparently during this extraction thatmuch of the dioxin created by chlorine bleach-ing finds its way into the waste stream.

It has been shown that by reducing the use ofchlorine gas in the bleaching process, theamount of chlorinated organic residues andcontaminates can be reduced. Oxygen delignifica-tion shows some promise for reducing theamount of lignin carried with the pulp to thebleach process, thus reducing the amount ofchlorine gas needed to bleach the pulp to thedesired brightness. Current commercial oxygendelignification technology can reduce the use ofchlorine gas by 40 to 50 percent. Further


reductions in the use of chlorine by more intenseoxygen delignification is limited by severelosses in pulp yield and strength properties.Pretreatment of the pulp with nitrogen dioxidebefore oxygen treatment shows promise forincreased delignification before bleaching.

The cost advantage that chlorine gas once hadover many other bleaching agents does not applyto oxygen. If the U.S. pulp and paper industry isrequired to reduce the amount of chlorinatedorganics and dioxin produced in bleaching pulp,oxygen may become a partial substitute forchlorine because of its low operating cost.Capital cost for oxygen treatment is very high,however, and installation of oxygen delignifica-tion in existing mills can reduce productioncapacity as much as 4 or 5 percent. Any eval-uation of the comparative costs of oxygentechnology with other delignification systemsshould consider both capital costs, life-cyclecosts based on operating costs and depreciation,and gains and losses in productivity and quality.Such analyses were not made by OTA in thisstudy.

Technologies for Reducing Dioxin

There are several ways to reduce the amountof pollution contributed by bleach plants. Theseinclude:

●

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●

●

●

●

●

further delignification of pulp before bleach-ing;improved washing of the unbleached pulp(brownstock);substitute nonchlorinated bleach agents;substitute chlorine dioxide for some or allchlorine gas;apply multiple additions of chlorine in splitcharges instead of using a single, massivecharge (low chlorine multiple);improve chemical mixing with the pulp;adjust the acidity of the unbleached stockbefore adding chlorine;

use “cleaner” oil-base defoamers that donot contain dioxin precursors;remove dioxin precursors prior to treat-ment of the pulp with chlorine; andimprove secondary waste treatment andwaste-disposal practices.

Pretreatment before bleaching can reducethe amount of chlorine or other bleachingchemical used. Technologies for prebleachdelignification include: 1) extended de-lignification, 2) oxygen delignification, 3)pretreatment with nitrogen dioxide beforeoxygen delingification (PRENOX allowsmore lingin to be removed without dam-aging fibers), 4) pretreatment with otherchemicals such as chlorine dioxide, and 5)extraction with sodium hydroxide supple-mented with oxygen and hydrogen perox-ide. Only extended delignification andoxygen delignification are currently usedcommercially.

Other technologies used to conserve waterand reduce energy consumption may also helpreduce the amount of chlorinated products in thewaste stream:

recycle process water from the chlorinationstage (although this may actually com-pound the dioxin problem),use countercurrent washing systems afterchlorination, andreduce water use by using higher ratios offiber pulp to water (higher consistency).

Elimination of chlorine in the bleach se-quence combined with internal recycling ofprocess water aimed at developing a “pollution-free” pulping system seems to offer a goodstrategy over the long term, but has not yet beenadopted for commercial use.


It is believed that if the use of chlorine gas isreduced or eliminated in the bleaching process,the amount of TCDD and TCDF formed will belowered or eliminated along with other chlori-nated organics. However, the relationship is notlinear, and other factors, such as mixing effi-ciency, have significant effects on the relation-ship. Oxygen is one of the most promisingbleaching chemicals for displacing some of thechlorine used in the bleaching cycle. In no casethus far has oxygen been able to completelyeliminate the need for chlorine.

Chlorine dioxide, a more efficient oxidantthan chlorine, can be substituted for substantialamounts of chlorine gas. The use of chlorinedioxide in conjunction with chlorine gas isincreasing at U.S. mills. It has been demon-strated that substitution of chlorine dioxide forsome optimum portion of chlorine gas cansignificant] y reduce the formation of TCDD andTCDF. However, the effects of chlorine dioxidesubstitution on the formation of other chlori-nated compounds are not known.

Recent research has also shown that theamount of dioxin can be reduced by lowering theacidity (raising the pH) of the pulp beforechlorination, by applying the chlorine charge inthree parts instead of one shot, and by usingchlorine dioxide after an initial charge ofchlorine gas. A very recent discovery by scien-tists at the Pulp and Paper Institute of Canadahas identified oil-based defoamers as one possi-ble source of the precursors that form dioxinwhen chlorinated. As a consequence, the U.S.industry and chemical suppliers are currentlyseeking cleaner oil-based defoamers.

Defoamers are added to the unbleached pulpin small amounts to improve washing. If adefoamer is made from used oil contaminatedwith unchlorinated dioxins (DBD) and furans(DBF), these precursors convert to their chlori-nated forms as TCDD and TCDF when exposedto chlorine gas. The United States regulates theuse of contaminated recycled oil, so furtherinvestigation is needed to determine whetherdefoamers are a problem for U.S. mills usingdomestically produced products. Recent in-vestigations by American scientists using test-ing protocols more sensitive than those used inCanada have raised doubts as to whether anyoil-based defoamers—whether made from ei-

Chapter 1—Introduction, Summary and Findings ● 13

ther virgin, hydro-treated oil, or used oil—arefree of contaminating precursors.

Water-based defoamers are also available,and tests show them to be free of DBD and DBFprecursors. Unfortunately, while water-baseddefoamers can be used at other washing stagesin the mill, they are not effective for washingbrownstock. The use of “cleaner” defoamers isanother option for reducing some of the dioxinproduced in the bleaching process, but moreresearch and development may be needed todevelop suitable products.

Oxygen delignification technology was discov-ered in 1952, and the first commercial unit wasinstalled in the 1960s. Since then, oxygentechnology has advanced steadily until it is nowconsidered a mature and proven process. In1988, world installed capacity using oxygendelignification is expected to exceed 10 millionmetric tons per year. Several manufacturers ofpulp and paper equipment market oxygen delig-nification systems. Over 50 oxygen units havebeen installed worldwide. About half the oxy-gen capacity is in Scandinavia and Europe,one-fifth is in Japan, and one-fifth is in NorthAmerica. About 92 percent of the oxygenbleaching capacity is installed in kraft mills, buta number of sulfite mills—mostly in the FederalRepublic of Germany—have also installed oxy-gen delignification units.

Oxygen can also be used in combination withextended digestion (modified cooking). By modify-ing the chemical addition and allowing it to cooklonger, the amount of residual lignin in the pulpcan be reduced prior to bleaching. Furtherpre-bleaching with oxygen can produce pulpwith even lower amounts of lignin. With pre-bleached pulps of low lignin content, it may betechnically possible to eliminate the use ofchlorine gas in the bleaching process if chlorinedioxide is used as a substitute.

No reliable data exist that directly link thereduction of TCDD and TCDF wholly tooxygen delignification, and in some cases oxy-

Modem mills are designed to match thecapacity of the chemical recovery plant with theplanned production capacity of the mill. Theaddition of an oxygen delignification stageincreases the volume of effluent that must behandled by the chemical recovery plant. In newmills recovery plants can be designed to handlethe additional load, but retrofitting an existingmill with an oxygen delignification system canresult in overloading the chemical recoverycapacity. If a larger size recovery furnace orevaporators are required, the additional capitalexpense may make oxygen delignification a lessattractive alternative for economic reasons. It isestimated that adding an oxygen stage to a millwhose chemical recovery plant is operating atfull capacity will reduce the productivity of thatmill 4 to 5 percent.

Given a range of equally effective technolo-gies to reduce the use of chlorine gas, capital and


operating costs may determine the most cost-effective strategy for reducing the amount ofchlorinated organic chemicals produced by pulpmills. Although operating costs may be lower ifoxygen delignification is used to replace someof the chlorine gas now used in the bleach cycle,the capital cost of oxygen systems is large. Bothcapital costs and operating costs must be consid-ered in a balanced assessment. Furthermore,cost factors will differ from mill-to-mill, mak-ing generalizations difficult. OTA did not at-tempt to assess these costs. On the other hand,by using “cleaner” defoamers, coupled withsubstitution of chlorine dioxide for chlorine, itmay be possible to achieve much lower levels ofTCDD and TCDF in pulp. Whether or not thiswould also lower the level of other chlorinatedcompounds is uncertain.

Further reductions in environmental releasesfrom pulp mill waste outfalls may result fromimproving the control of suspended solids in thesecondary waste treatment plant. TCDD andTCDF are relatively insoluble in water, but theyadhere tightly to fine colloidal material andsuspended solids. A well-designed, properlyoperated secondary treatment plant is capable ofremoving up to 90 percent of the TCDD and

TCDF released. Dioxins are retained intreatment plant sludge. The sludge is normallydisposed of in landfills, where limited studiesshow that it remains isolated and immobile.Some sludge is retained in sludge lagoons or isincinerated, but a portion is used for soilconditioners. The remaining 10 percent of thedioxin that remains in suspension can find itsway in to the water coarse and remain assediment in streambeds. The use of clarifiers,chemicals, and settling basins to improve theefficiency of waste treatment, coupled withchlorine dioxide substitution and/or perhapsother delignification technology might prove tobe the optimum solution for some existing pulpmills.

More questions remain than do answers as towhat risk dioxin from pulp and paper manufac-ture presents to humans and the environment:will additional regulations be needed to reducethe risk of human exposure from dioxin andother chlorinated compounds produced in pulpmills? and which technologies or mix of tech-nologies are best suited for reducing the produc-tion of dioxin in the pulp bleaching process? Thepulp and paper industry has a number oftechnical options available to meet the problem.Other technologies, such as extended delig-nification and the substitution of other oxidantsin the bleach process for chlorine gas, may be aseffective as oxygen delignification in reducingthe use of chlorine. All of these questionsrequire more detailed study before they can beanswered with acceptable certainty. Final deci-sions to meet regulatory requirements will haveto be made on a case-by-case, mill-by-mill basis.

introduction, summary, and findings

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