Pulp paper-pollution
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Pulp paper-pollution

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attention to making pulp paper industry more environment friendly is paid now.

attention to making pulp paper industry more environment friendly is paid now.

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Pulp paper-pollution Document Transcript

  • 1. Pulp & Paper industry & Pollution – A report from USA-1995  The manufacture of wood pulp is an important method for chemically converting wood into useful products. It is a highly important component of the global manufacturing industry in both economic and environmental terms.  Pulp and paper manufacture can have potentially serious impacts on environmental quality and hence the health of both human and wider ecosystems. In the United States alone, pulp and paper is recognized asone of the nations most highly polluting industries. The US--EPA’s 1994 Toxic Release Inventory (TRI) reported that suchfacilities generate the greatest quantities of polluting substances(measured in pounds per facility) of any industry sector. Each facility was reported as generating an average of 457,457pounds of reportable toxic substances every year. In addition, theseindustrial plants discharge an estimated 6.01 billion pounds ofother pollutants not covered by the TRI into national waterwaysand public sewerage systems. Great potential exists for both improving efficiency andmoving to sustainability in this industrial sector. Now, the state ofcurrent research and technology development in the field of 1
  • 2. ecologically responsible Kraft pulp manufacture, anddevelopments designed to mitigate and eliminate human andenvironmental health impacts are emphasized. Also explored indepth is the potential for operating closed loop pulp mills whichdischarge no wastewater into our rivers and oceans and minimizethe quantity and toxicity of air pollution and solid waste. While it is recognized that issues such as sustainable forestry,control of consumer demand and maximizing the use of recycledand alternative fibers are critical components in moving the entirepulp and paper industry onto a sustainable footing, these issues arenot addressed here. The concept of a closed loop mill aims to eliminate dischargesto the aquatic environment, recycle and reuse all possible solid andliquid process wastes, and reduce air emissions to the lowestpossible quantity and toxicity. A mill should be able to produce itsprimary product, with most of its by-products suitable for use assecondary products. To date, much of the by-product in existing mills attemptingto go closed loop is burned as a fuel for the mill. It is far from idealreuse for much of the waste-stream. Research must continue todevelop more sustainable reuse options for Kraft pulping solidwastes, as well as pulping methods that result in purified by- 2
  • 3. products that can serve as feedstock for other manufacturingprocesses. Since the discovery of highly toxic dioxin compounds in pulpmill effluent there has been a great deal of work on reducing thetoxicity of liquid discharges from pulp mills. There have beenefforts at both end-of-the-pipe control, and at eliminatingprecursors to known toxic compounds. Despite progress on these fronts, a variety of toxic impactspersist. Genetic to fish and toxicity to micro-organisms that help tobreak down waste are still present in secondarily treated effluentfrom mills employing only chlorine dioxide as a bleaching agent.The presence of resin acids and other unidentified constituentscontinue to have toxicity problems for all Kraft mills, regardless ofbleaching chemicals. Ecosystems near pulp mills which meet relatively toughexisting environmental regulations continue to experiencesignificantly reduced diversity in the plants and animals able tolive near them. These facts emphasize the need to pursue closedloop strategies. In this review, the literature on a wide variety of factors thatwill influence the overall impact of a pulp mill on its totalenvironment is discussed. An attempt is made to draw conclusionsabout which pathways the research and practical experience 3
  • 4. indicate are the best ways forward to a Kraft pulp industry with thelowest possible negative influence on its surroundings. Areas addressed include: effluent toxicity, air emissions,sludge and solid waste, raw material utilisation (i.e. energy usage,chemical consumption, wood yield and paper quality), bleachingmethods, capital, conversion and operating costs, and worker andcommunity health and safety. Current progress on closed loop mills is reviewed andevaluated with a particular look at non-bleach plant improvements,non-process element control to manage the build-up of recycledchemicals that can harm mill equipment and product quality,bleaching chemical choices and effects on mill equipment. Finally,looking to future improvements in the industry, emerging work onalternative pulping methods is discussed and a summary of nextsteps and gaps in existing research is presented. A different quality and quantity of information is availablefor each area reviewed. Effluent toxicity has been, and continues tobe, extensively researched. While the most advanced mills in theworld may have similar final effluent toxicity, those employingonly oxygen based bleaching chemicals continue to have thelowest toxicity on a full spectrum of toxicity parameters. Asimportant as this area of study is under existing circumstances, 4
  • 5. closed loop operations will eliminate all toxicity to aquaticenvironments by eliminating all discharge into them. The characteristics of air emissions have not been welldocumented, nor have there been adequate comparison studiesbetween various mill types. The current regulatory standards areinadequate. Existing data suggest that oxygen based closed loopoperations will have either no difference in air emission impacts,or an improved one.However, this conclusion warrants further testing, especially asemissions to air will continue as a major output of closed loopmills. The production of waste fibre sludge should end with aclosed loop pulp mill. Until that time, some sludge will continueto be produced as mills increase the degree of effluent recyclingthey are able to accommodate. An increasing push towards land-spreading of this material is being seen throughout manyjurisdictions with intensive pulp production. This method of sludgedisposal is an area of concern, as sludge constituents are not wellidentified, the sludge in any given mill is highly variable, and thefate of the sludge on land is not thoroughly researched. Welldesigned, independently monitored pilot projects of significantduration are necessary before this practise becomes widespread.The closed loop process will likely increase the amount of solid 5
  • 6. waste being generated in the dregs, grit, and ash of pulp mills asthese waste streams become the only remaining options for thepurge of chemicals and elements that can upset the process ordamage equipment. While the quantity of dregs, grit, and ash in aclosed loop mill will increase over current mill designs, total solidwaste will be significantly reduced. Recovery of process chemicalsfrom these purge points should be maximized. Remaining wasteswill likely be committed to secure landfills. Therefore, more workon the composition and reprocessing of these waste streams isneeded. The review of total energy consumption is a criticalelement of evaluating an ecologically responsible pulp mill. A major factor in this calculation is the energy balance inherentin the various bleaching chemicals. Almost without exception, theliterature indicates that oxygen based bleaching sequences have asuperior efficiency over chlorine dioxide based sequences in thisarea. Even when combined with potential increased energyconsumption in some oxygen based configurations, these milldesigns are the most energy efficient available.Wood yield and paper quality are two areas that have beenfrequently used by the North American pulp industry, in particular,to suggest that oxygen based bleaching sequences are neitherecologically, nor economically preferable. Many of thesecomparisons cite reductions in wood yield based on how the wood 6
  • 7. fibre is turned into pulp. This type of comparison is spurious andhas no bearing on yield variations due to the type of bleaching usedin a mill. Setting aside the yield effects of pulping processes, assertionsmade about yield loss due to oxygen based bleaching have beenbased on measurements of carbohydrate content in effluent and theresulting Chemical Oxygen Demand (COD), a standard regulatorymeasurement. These have suggested that there is between 0-1%increase in wood consumption for oxygen based production. Theseestimates, based on secondary measurements, have not beensubstantiated on a practical basis. The widely reported fall in yieldof 6% at the Wisaforest TCF mill in Finland is thought to be due tothe fact that the mill switches between ECF and TCF pulpproduction and as a result is not optimised for TCF productionmethods. Södra Cell has not seen a change in wood consumptionsince full conversion to TCF bleaching, in common with reportsfrom the Louisiana Pacific mill in Samoa California afterconversion to TCF. While there is undoubtedly a need to evaluatethe yield aspect in greater detail, on the basis of the availableevidence, yield loss does not appear to be a significant factordetracting from the overall benefits of using oxygen based bleachprocesses. 7
  • 8. Similarly, claims made about inferior pulp quality from oxygenbased sequences, while touching on an area of real concern for asmall portion of the market pulp produced worldwide, seem tohave been exaggerated, presented as representative of the fullspectrum of bleach kraft pulp, and continually based on outdatedinformation. As a general observation it appears that oxygen basedkraft pulps show no appreciable shortcomings in quality relative tochlorine dioxide bleached products and that the unhelpful debatewhich has surrounded the product quality issue is of rapidlydiminishing relevance both to pulp users and wider consumermarkets. The costs of converting an existing mill to closed loopoperations are one area where there is extensive and oftencontradictory information in the public realm. Finding estimatesthat consider all relevant aspects of mill conversion and haveaccess to enough detailed, mill specific information is nearlyimpossible. In general, it appears that costs for converting anexisting mill to a closed loop mill are similar regardless the type ofbleaching chemicals used. The authors acknowledge that the actual cost of anyconversion will be highly influenced by the state of the mill inquestion and we encourage the industry to open the evaluation 8
  • 9. process to public scrutiny. New, or “greenfield”, mills appear to bemost financially efficient when designed to optimise oxygen basedbleaching and a closed-loop design. As mentioned earlier, thehealth and welfare of the workers and surrounding communitieshas not been a regular feature of the debate over how to achieve anecologically responsible pulp industry. This is most unfortunatebecause workers, especially, have often had to suffer increasedworkplace concentrations of hazardous chemicals as lawspreventing those substances from entering the environment havebeen tightened. While no bleaching chemical is benign, theconclusion based on extensive available literature is that theoxygen based bleaching chemicals present the least immediate andlong term hazards for workers and the general public. Additionally,the upgrades inherent in designing a closed loop mill shouldinclude other improvements, such as light gas strippers and, non-condensable gas collection systems which will remove hazardousand foul smelling pollution from the air and increase workplacesafety.Finally, we look at the current state of efforts to build and run anactual industrial scale closed loop mill. Efforts continue with bothchlorine dioxide- and oxygen-based systems.Progress has been made on both fronts, with non-process elementcontrol (i.e., managing the build-up of chemicals which are 9
  • 10. recycled through the system), being the greatest barrier to finaleffluent circuit closure. For oxygen based sequences, the control ofmetals in the process liquor is the greatest challenge, while systemsemploying chlorine dioxide must have as primary concernequipment damage from the recirculation of highly corrosivechlorides. A final solution has not been achieved for either approach.However, mills attempting to run chlorine dioxide based recyclinghave not been able to run at a high degree of effluent closure forextended periods. Oxygen based sequences have reached thelowest effluent levels and been able to run for longer periodsbetween system purges. The conclusion, given the best research in all of these areas,is that oxygen based, closed loop kraft pulp mills are the best routeforward to a successful and ecologically responsible kraft pulpindustry. 10