integrated approach to reduce adsorbable organic halides

I

BLEACHING

Integrated Approach to Reduce AdsorbableOrganic Halides (AOX) in Pulp Manufacture

•.

Mittal S.K. and Maheshwari Subhash•

INTRODUCTION:

The pulp and paper industry due to its higherconsumption of resources including woody rawmaterial, water and energy, always remains underscrutiny by all the concerned who have ceo-efficientthinking. This environmental emphasis gradually furtherdeepended and shifted from comparatively short termeffects to effects by the persistent and bio accumulablecompounds formed in the manufacture of bleachedchemical pulp using chlorine compounds. Adsorbableorganic halides have gained more attention in thisregard in recent past.

Present paper discusses, the basis of AOXformation and its environmental impacts. The variousdevelopments taken in the direction to reduce formationof organically bound halides-including AOX aresummarized in this article. The issues related toreduction of organically bound halides in existing millsare presented in this paper. The efforts made atPHOENIX and in progress are also briefly described.

The various logical experiences and studiesclearly indicate that reduction of AOX depends onefficient operation of the mills and incorporation of anumber of modifications in the present mills, which inturn involved investments. In view of these facts it isconcluded that very positive and concerted efforts arerequired by the pulp and paper industry and regulatoryauthorities to address this issue, so that the requiredimprovements are achieved without jeopardizing theperformance, competitiveness and all economics of theindustry.

• The industrial activities and developments are theinseparable part of material civilization. By supplyingthe various products and services, the industrialactivities provided to humanity the most basic needs,which have become now the essential part of our life.These are also helping to meet the continuallyunfolding desires and aspirations of human being. Ingeneral the industries have contributed and continue tocontribute considerable economic benefits to the people

IPPTA CONVENTION IS~UE 2001

world over. But the activities of the many industriesalso proved to have potential for adverse impacts bothshort term and long term on the quality of life.

The pulp and paper industry world over has majorcontributions in the industrial structure of manycountries. The pulp, paper, paperboard and theproducts derived from them have become essentialneeds of the time. But the activities associated with thisindustry due to its higher consumptions of resourcesincluding woody raw material, water and energy alswaysremain under critical scrutiny by all the concerned whohave eco-efficient thinking.

The chlorinated organic compounds haveacquired bad reputation for the environmental concernsand first in series were DDT, then PCBs andsubsequently chlorinated in the environment fordecades and get accumulate inside the tissues of livingorganisms and where they interfere with the biochemical process. These worrisome observations andfacts attracted the attention of environmentalists andpublic. The bleached kraft pulp mills using chlorine andchlorine compounds have come under criticalobservations in this regard. The level of understandingof various toxic compounds in bleached kraft milleffluent has been increasing considerably in recentyears. Adsorbable Organic Halides (AOX) has becomeone main environmental indicator for the industry. Thepresent paper discusses the integrated approach for thepulp and paper industry for consideration to reduce theAOX concerns.

ADSORBABLE ORGANIC HALIDES (AOX)

Absorbable Organic Halides, mainly chlorides withreference to pulp bleaching, is not a single pure material.It is multitude of compounds of varying molecularweights and degrees of fat solubility with the latter

Phoenix Pulp & Paper Public Co., Ltd.183/2, MaHwan Road, P.B. No. 102Khon Kaen - 40, 000 Thailand

119

I.

BLEACHING

FIG. -1 CHARACTERISTICS OF AOX IN EFFLUENT

I AOX 100% 1I

I 1- 20% - 80%- -

Low MW Material High MW Material

I I Relatively Hydrophillic.

I I(Water soluble)

Mainly Non-aromatic.

r I r IDoes not Permeate Cell Walls.

EOX- 1 % - 19% <10% Chlorine by Weight-Relatively Lipophilic Relatively Hydrophillic.(Fat Soluble) Includes CompoundsPotentially Toxic, Potentially Which Can BeBioaccumulable Hydrolyzed or Metabolized

(e.g. Trichloroacetic acid)

I 0.1% ILog Pow >3

Highly Lipophilic,Bioaccumulable

(e.g. Dioxin-44% Chlorine by Weight)

being measure of the tendency to accumulate in livingorganism. A typical physical as well as chemicalclassification of AOX presented in the effluent fromconventionally cooked and bleached pulp is given inFig-I.

It can be seen from the figure that as such 80% ormore organically bound chlorine corresponds to highmolecular weight (MW > 1000) chlorinated ligninmaterial. These fragments as reported are not amenableto compound - specific analysis because of theirrelating high molecular mass and heterogeneous nature.As these are relatively higher water soluble or so to sayhydrophilic in nature. It may be also mentioned thatthese compounds contain comparatively lower contentof chlorine approximately 10% by weight. In bleachingprocess due to oxidation of the aromatic structure oflignin gets destroyed and has very low possibility oftheir conversion to problematic poly chlorinatedaromatic compounds in nature.

The remaining 20% of organically bound chlorides

120

•

found in bleaching effluent correspond to relativelylower molecular weight (MW < 1000) material. Theinformation based on various research findings indicatethat this part of AOX contains those compounds whichthas potential environmental impacts due to their abilityto penetrate in cell membrane or their natural tendencyto bio accumulate in tissues of organism. Out of 20% fornineteen percent of these low molecular weight AOX arerelatively hydrophilic and can be hydrolyzed ormetabolized. The remaining 1% fraction, which isextractable only by non-polar solvents, is referred asExtractable Organic Halides (EOX) This fractioncontains compounds which are reported as potentiallytoxic and bio accumulable.

Keeping these facts in view and constant progressin research activities to get better information andunderstanding will help to judiciously conclude theenvironmental impact of these compounds. However, atpresent, the AOX has been considered asenvironmental parameter and hence requires greaterattention how to over come or reduce its generation and

IPPTA CONVENTION ISSUE 2001

or

Waves of Environmental Hot Topics

Environmental Issues Affecting the Industry

EMISSION STANSDARD

Intensity

••

Tree-free/Close Cycle.......__ :..:;;--:>'C--e-:Bio-diversity

1980 1990 Time1960 1970

discharge from bleached pull' and paper mills.

LIGNIN AND AOX- BASIC ISSUES

The main target for manufacture of bleachedchemical pulp from woody raw material is to remove ormodify lignin to maximum possible extent. Lignin, whichis a random, three-dimensional macromolecule of phenylpropane building blocks and due to its color and odorlignin, requires removal to get purer cellulose fibers. Thegeneration of AOX has been directly correlated to thelignin compounds, generally measured as Kappa No.,which enters to bleach plant.

The reduction of AOX generation and disposalcan be achieved by three main possible ways.

Reduction of lignin before pulp enters tobleach plant

Use of such chemicals which generateminimum AOX..•Destruction of AOX at end of the pipetreatment.

REDUCTION BEFORE BLEACH PLANT

The effective removal of lignin before bleach plantis considered as first and most appropriate approach toresolve the problem of AOX. The practice presentlyfollowed and efforts made and in use are summarized


below.

CONVENTIONAL COOKING

The convention kraft cooking is one mostcommonly used step to remove the lignin from rawmaterial and to make the content ready for bleaching.However, it has certain limitations to bring down lignini.e. pulp kappa number below certain level.vwithoutadversely affecting the process and quality of pulp.

OPERATING PARAMETERS

The operating parameters including cookingchemicals, temperature and time are very important forefficient removal of lignin these should be adjusted insuch a manner that maximum delignification is achievedwithout pulp degradation. The efforts should be madeto avoid lignin precipitation during the cooking or atstorage stages both for pulp and liquor. The ligninprecipitation results in higher bleaching chemicalconsumptions and higher AOX generation .

USE OF ADDITIVES

The use of pulping additives can be alsoconsidered to get reduction in kappa number andsubsequently reducing the AOX generation, with otheradvantages like higher pulp yield, cooking chemicalreduction, lower odor etc depending on the presentoperating conditions and requirements of the mills andat the same time overall economics.

121

I·

Fig. -2 Active Chlorine - AOX generation

10~~8~

(JQ

~6-=c

"0 4

2

o 20 40 60

Active Chlorine, kg/T Pulp80

REMOVAL OF BARK

While using wood it is very important to removethe bark which constitutes average 12-18% on as suchbasis of wood depending on the wood type, age etc.

As such the lignin contant in bark is higher thendebarked wood and requires higher alkali duringcooking and at the same time gives very low pulp yieldand poor pulp quality. In spite of using higher alkali thisportion of wood gives high kappa number meaning morelignin entering to bleach plant from this fraction andultimately resulting in higher bleaching chemicalrequirement and AOX generation. It has beenexperienced by many mills that removal of bark improvesover all productivity of the mill. It may be mentionedthat bark can be utilized as fuel or can be converted tobio-fertilizer that is in great demand nowadays. Keepingthese facts in view, mills using woods with bark shouldconsider using debarked wood to reduce the AOXgeneration.

EXTENDED COOKING SYSTEM

The limitation in removal of lignin below certainlevel by conventional cooking process paved the wayfor modification of cooking process by increasing theselectivity of delignification and without adverselyaffecting the pulp quality and yield. This is achieved byusing higher hydroxide and hydrogen sulfide ionsconcentrations in bulk delignification phase and thereby decrease the amount of slowly reacting residuallignin. This also results in increase in rate ofde lignification in bulk phase, which helps to furtherreduce the cooking temperature. The decrease in

122

BLE~CHING

cooking .temperature minimizes carbohydratedegradation and pulp strength loss and improves pulpbleachability. The lowering of pulp kappa number andimproving bleachability of the pulp result in lowerbleach chemicals requirement and ultimately lower AOXgeneration. •OXYGEN DELIGNIFICATION

The use of oxygen as extension of delignificationhas become the integral part of new pulp mills. The mainadvantage of use of this stage is environmentalperformance .and to some extent operating costadvantage as it is in close cycle with brown stockwashing. However, it is capital intensive and requiresadditional capacity in recovery system. Due to thesereasons it becomes quite difficult to incorporate thesystem in existing mills until and unless the mill is goingahead with major expansion activity of recovery cyclesystem. However, this system can be incorporated ifrecovery system is operating under lower capacityutilization.

The most obvious benefit of incorporation ofoxygen delignification is to reduce of 35-40% bleachingchemicals requirement and which ultimately results inlowering of chlorinated organic compounds generationfrom in bleach plant. The exact advantage of AOXreduction is dependent on the type of chlorinecompounds are in use. If elemental chlorine is in use theadvantage is most significant. Apart from AOXreduction equivalent reduction of other pollution loadslike COD, BOD, color, dissolved solids both organic andinorganic is achieved. The use of single stage oxygenwas common till few years back, however now most ofnew mills are opting for two stages.

PULP BLEACHING

The extension of delignification or removal ofresidual lignin from unbleached pulp to make the pulpbrighter is the main function during pulp belaching. Thecommon bleaching chemicals used in bleach plant aregiven below.

Symbol Chemical Symbol Chemical

C Chlorine Z Ozone

D Chlorine dioxide E Sodium hydroxide

H Hypochlorite X Enzymes

0 Oxygen Q Chelating agent

P Hydrogen peroxide A Acid


Fig. -3 CI01 Substitution and AOX Formation

IIKappa NumberUnbleached 30.0 <>

7 23.5 fj.20.5 0

JII 111.1105

"~ 4

~ 3~2

00 20 40 110 80 100

Chlori1le Dioxide Sulmltrlti01l, "

Three chlorine compounds i.e. chlorine,hypochlorite and chlorine dioxide are commonly usedfor bleaching and these are also associated forgeneration of AOX. The use of chlorine came afterhypochlorite as preferred chemical because of its lowercost, improved selectively to remove lignin and also themetal ions from the pulp. The active chlorineequivalents for these chemicals are given below.

Ii Hypochlorite

Chlorine - 1.0 kg Active chlorine/kg Cl]

- 0.95 kg A~tive chlorine/kg Naoc'!

iii Chlorine dioxide - 2.63 kg Active chlorine/kg C!O]

The use of hypochlorite has come under questionmainly due to formation of chloroform during removal oflignin and adverse affect on pulp properties. Hence, itsuse is avoided in any modern bleach plant and graduallybeing removed from existing bleach plants. The

'.. ~ 75c:i§

50I•••t-:'

..; 25•••

0

Fig. -4 Effect of CI01 substitution and Chlorinemultiple on Dioxin Formation

,"

"0.06 0.10 0.15 0.20

a1MuIIIpk

I I

0,25 0.30

100 80 80 40 211" of C/o, Substltullq1l

o


chemicals/stages in bleach plant, which requires specialattention for reduction of AOX, are briefly consideredbelow.

USE OF CHLORINE

The chlorination stage traditionally has been thefirst and main stage for major removal of lignin andpurification of the pulp during bleaching. Thechlorination followed by alkali extraction selectivelyremoves about 75-80% lignin from the unbleached pulp.However, use of chlorine has come under strict scrutinydue to formation of organically bound halides. AOXformation has been shown to be directly proportional tothe amount of active chlorine consumed in bleaching(Fig. 2).

USE OF CHLORINE DIOXIDE

Chlorine dioxide has emerged as one of the mostimportant chemicals used for pulp bleaching due to itsselectivity towards removal of lignin and as very goodparticle bleaching chemical. At the same time chlorinedioxide is most common and widely recognized solutionboth for reduction of AOX and dioxin emission problem.The substitution of chlorine by chlorine dioxide and itsimpact on AOXlDioxin are presented in Fig-2 & 4. It maybe noted that unlikely to chlorine it has to bemanufactured at the plant site used.

It may be noted that there is also direct relationbetween chlorine multiple i.e. the ratio of percent activechlorine. and pulp kappa number on Dioxin formation(Fig.-4).

OXIDATIVE EXTRACTION

The use of oxygen reinforced caustic extraction,as designated as Eo stage, has rapidly spreadthroughout the bleached kraft pulp mills. The actualprocess changes required for this stage are installationof reactor before extraction and addition of 5 kg oxygenwith little extra alkali. The cost of additional chemicalsnormally justified in all cases by reduction of bleachingchemicals in early stage or subsequent stages. the useof peroxide in this stage along with oxygen has alsogradually becoming popular. However; the economicsof use of peroxide depends on individual millsoperations and performance.

The increase in the oxidative potential byreinforcement of oxygen and/or peroxide in extractionstage is an effective way to also break the chemicalbonds between halogen and carbon of AOX molecules.

123

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124

BLEACHING

This ultimately results in reduction of AOX. The overalloxidative extraction stage is most operation and costfriendly stage in bleach plant to reduce the organicallybound halides.

USE OF ENZYME..

The use of enzymes - Xylanases has extensivelybeing researched at laboratory stage to reduce thelignin in the pulp entering to bleach plant andconsequently reduce bleaching chemicals. Many plantscale trials are also performed and some of them met thetargets set. In general it can be confirmed that use ofenzyme offers reduction in bleaching chemicals andconsequently AOX reduction. The efforts arecontinuing to isolate more selective xylanses enzyme,which will be operation friendly, cost effective andcause minimum adverse affect on pulp quality and yield.

INTER-STAGE WASHING

The inter stage washing both at the brown stockand bleach plant has significant effect on reduction ofAOX. The efficient inter stage brown stock washingwith the use of minimum dilution water and results inminimum carry over of both inorganic and organic load

, and at the same time lower volume to bleach liquorrecovery cycle. The increase organic load results inincrease bleaching chemical demand and internadditional pollution load on effluent, in terms of COD,BOD dissolved solids, color and organically boundchlorides, the inter stage washing in bleach plant stagesalso has similar effect as of brown stock washing. It isrecommended to use suitable and efficient equipment,optimum processing parameters and efficient recyclingof backwater.

TOTAL CHLORINE FREE BLEACHING

The total chlorine free (TCF) bleaching took goodposition in Scandinavian countries to accommodate thecustomers' requirement and regulatory demand toeliminate organically bound chlorides discharge.However, many research findings and mill experiencesshowed that no signification environmental benefitscould be achieved comparatively while using the TCFbleaching sequence. This is mainly due to most of themills are unable to close fully their bleach plants. EDT AIDTPA or similar chelating agents, used in TCFbleaching sequence where ozone and peroxide are themain bleaching chemicals, are carried to effluent. Thesechemicals have comparatively lower rate ofbiodegradability and ultimately adverse environmentalacceptance.

•


••

EJ

Fig. -5 Lignin Balance - Conventional Process

RM-Wood.1 ~ IUnbId. P\Ip 18~ 1 Bid. P\Ip1~ 1 c-.g IF;;;;13~.K=---· I 0.5"

END-OF-PIPE TREATMENT

...

As mentioned above effluent from bleaching pulpmills contains wide variety of high and molecular weightorganically bound chlorides. The removal of chlorinatedorganics from bleach plant effluent both by aerobic andanaerobic treatments is reported. It has been alsoexperienced that activated sludge system for effluenttreatment has been found more effective to remove morethan 50% AOX from the effluent. It has been alsoreported that sequential anaerobic/aerobic treatmenthas been found more effective to remove the chlorinatedorganic compounds. It may be mentioned thatimplementation and adoption of effluent treatmenttechnology will depend on individual mills requirement.

The removal of AOX can also be accomplished bychemical treatment methods i.e. using Ozone. Peroxideor advance Oxidation Process. lime/alum treatment etc.The implementation of end- of-pipe treatment requiresvery careful assessment with respect to both capitalinvestment and operating cost.

LIGNIN BALANCE IN PULp·· MAKINGPROCESS

As mentioned above the lignin entry in bleach

plant is the main criteria of use of bleaching chemicalsand ultimately the formation of organically boundhalides. Hence lignin removal both at cooking stage andbleach plant is very important. The following fourapproaches for bleached pulp manufacture, except TCFbleaching, are mainly in practice world over withmarginal variations and which involves for generationof organically bound chlorides. The typical ligninbalance in fiber lines of these four approaches ispresented below :-

CONVENTIONAL COOKING & BLEACHING

The conventional kraft cooking for bleachedchemical pulp is quite common where we get pulp kappanumber around 25. The pulp passes through the bleachplant of 3-4 stages with use of combination of differentbleaching chemicals. The lignin balance of such plant ispresented in Fig-5. The discharge of lignin as shown inthe figure indicates the expected generation of AOXfrom the bleach plant.

CONVENTIONAL COOKINGOXYGEN DELIGNIFICATION

WITH

The introduction of oxygen delignification asextension of delignification for conventional cookinghas shown appreciable advantage to reduce ligninentering to bleach plant and use of bleaching chemicals.A reduction of 35-40% pollution load including AOX,COD, BOD. Color, dissolved solids are obtained. Thefigure-6 shows that only about 9.5% of total lignin inwood goes to effluent from the bleach plant.

EXTENDED COOKING SYSTEM WITHOXYGEN DELIGNIFICATION

The most commonly acceptable system at presentis use of extended cooking system to further reduce the

Fig. -6 Lignin BalanceConventional Cooking with ODL

RM-Wood Conventional Unbid. Pulp' Oxy.Delig.

100%Cooking • Stage

13.9%

86.1%Black Liquor Spent Liquor 3.9%to Recovery

90%

Oxy. Delig. Pul2

10.0%

Bleaching Bid. PulpPlant •

0.5%

Effluent 9.5%

,1.

IPPTA CONVENTION ISSUE 2001 125

BLEACHING

Oxy. Delig. Pule Bleaching,. Plant

6.1%

Effluent 5.6%

~

ETP

Fi~. -7 Lignin Balance EDL with ODL

RM-Wooct Extd. Unbid. PulR Oxy. DeligCooking • Stage

100% 9.4%

90.6°",Black liquor Spent Liquor 3.3%to Recovery ~....•

,Ir 93.9 %

Fig. -8 Lignin Balance Light-ECFBleaching

Bid. Pulp•0.5%

Bid. Pulp

0.4%Two Stage Olty. Oeijg.Pulf1 Pre Bid. PulpO D I· Pre Bleaching ~:..:..:~~

xy. e Ig. 5.3% 1.7%RM-Wood Extd. Unbid.Pulp

100% Cooking 9.4%

Black Liquor toRecovery

BleachPlant

1.3%Efftuent

16

14

~"" 12::II

!E:10~

.5 8I:::-I:::.~ 6

...;j

~ 4

2

0

Spent Liquor 4.1%90.6% spent Liquor 3.6%

98.3%

Fig. -9 Process Approach -Lignin Balance

CC CC+ODL EDL+ODL

Process Approach

L-ECF

•.

described above or rather close the system thisapproach is adopted. In this approach after extendeddelignification, which commonly uses two-stage oxygendelignification. The pulp obtained is passed throughchelating stage to remove the metal ion and ozone inused in first stage of bleaching which is followed byoxidative extraction stage mayor may not be useperoxide. The Eo stage becomes the part of brown stockwashing and recovery operation. This systemsignificantly reduces AOX formation and discharges toeffluent. The lignin balance is shown in Fig-S,

lignin and subsequently carry out oxygendelignification. In this system pulp of at 10-11 kappanumber enters in bleach plant and about 5.6% ligningoes to the effluent from bleach plant (Fig. 7). The AOXcompound will be formed in bleaching and go with theeffluent. It is quite common that for the system chlorinein normally not considered as bleaching chemical andbleaching sequence is normal as elemental chlorine free.

LIGHT- ELEMENTAL CHLORINE FREEBLEACHING

In order to further improve the system as A summary of lignin balance of above approaches

126 IPPTA CONVENTION ISSUE 2001

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128 IPPTA CONVENTION ISSUE 2001

TABLE-2 TYPICAL INVESTMENT COSTS

Basis: 100,000 TPA Pulp Mill

S. No.

••

1.

2

3.

4.5.6:.7.

3 Disposal of bark.12 Higher recovery capacity10 Higher recovery capacity

2161

10

System Cost (M.USD) Remarks

Debarking DrumExtended DelignificationOxygen DelignificationWash PressCI02 generation plantOxygen Reactor for Eo stageActivated Sludge Process-ETP

is presented in Table-I and Fig.-9 for comparison. Atypical investment costs for installation of some ofthese systems individually are presented in Table-2.

PHOENIX EXPERIENCE

Phoenix Pulp and Paper Public Co., Ltd., Thailand,is a 200,000 TPA market pulp mill from Bamboo, Kenafand Eucalyptus. Its line 1 started in 1982 and secondline started in 1994. The present system in both the fiberline are briefly described below:

Process Details

Phoenix I (Fig. - 10)

Raw material handling part debarking, chippingand screening.

Convention kraft process with continuousKamyr digester.

Knotters, brown stock washer and screening.

Medium CR.ii~istency oxygen delignification(introduced in 1994).

Bleaching sequence C/O Eo D D.

Bleaching stage cleanliness and screening.

Phoenix II (Fig.-ll)

Sheeting M/C.

Wood handling, debarking chipping andscreening.

Extended delignification - SuperBatch Cooking.

Medium consistency oxygen bleaching.


Element chlorine free bleaching sequence Do EoD.D2'

Bleaching stage centricleaning and screening.

Sheeting Machine.

WASTE WATER MANAGEMENT

The effluent from both lines is treated in ActivatedSludge based effluent treatment plant. The treatedeffluent which meets all regulatory norms i.e. BOD,COD, TDS, SS, etc. All the treated effluent is used forirrigation of eucalyptus plantation.

A periodic check of Dioxin in treated effluent isdone and the values are coming as not detectable level.Presently this is no regulation for AOX. However, theAOX values tested for treated effluent of mill are below0.3 kg/tonne pulp. Further efforts are in progress toimprove overall environmental performance withrespect to utilization of resources and reduction ofemissions.

ENVIRONMENTAL REGULATION

It is always advocated by most of the regulatingauthorities to adopt best available economicallyachievable technology with respect to addressenvironmental concerns. US Environmental ProtectionAgency (EPA) is considered world over as a referenceorganization to adopt regulatory norms. EPA clusterrules phase-I to control both effluent discharge and airemission from pulp, paper and paperboard. millpublished in 1998. This was the first time EPA issuedintegrated, multi-media regulations. AOX limits forbleached kraft mills in the regulation are given as0.95 kg/Tonne pulp for discharge maximum and 0.62 kg!Tonne pulp as monthly average. It may be mentionedthat minimum three years compliance time frame has

129

l.

been given. The rule also provide individual mills withincentives to adopt Advanced Pollution ControlTechnologies that will lead to further reduction in toxicpollutants discharge beyond the water discharge limitsset in the rule.

Many of the countries have also fixed with theirnorms for AOX discharge. It may be mentioned thatafter taking basic guide lines from the experience andinformation from advance countries and at the same timereal environmental impacts, the regulatory authorities ofthe country has to undertake extensive study incooperation with industry to evolve a logical andachievable guide lines and norms to address AOXissue. The environmental indicator setting up exercisefor the country has to be taken up very seriously. Theregulatory authorities should continue to offerincentives to adopt the advanced technologies toreduce the pollutants discharge.

CONCL USIONS

Amid growing public, environmental and scientificconcerns the generation and discharge of organicallybound chlorides from a recognized as an importantenvironmental indicator in many countries formonitoring the performance of bleached pulp mills usingthe chlorine compounds. Based on the varioustechnological developments and as presented in thepaper it can be concluded that mills have to identitymost techno-economically viable configuration ofprocess from cooking area, through bleached plant toeffluent treatment and disposal. It may be mentionedthat the regulations are to be based on overall structureof the indusrty and its environmental impacts. However,necessary considerations should be also given withregard to technological and environmental

130

BLEACHING

advancements in progress on global basis.

REFERENCE

1. Stringer, AM, Industrial Environmental Control -Pulp & Paper Industry, TAPPI Press, USA. 1993.

2. Reeve, DW, etal, Pulp Bleaching & PracticesTappi Press, 1996.

..

3. Patrick K.L., Bleaching Technology Chemical &Mechanical Pulp, Miller Freeman Publication,1991.

4. Berry Rechard; World Pulp & Paper, Internationalreview 1992, Sterling Publication, UK.

5. Miner Reid, etal, Tappi VoL 82 No.4 Page 135-1999.

6. Vice K, Pulp & Paper Canada, Pulp & PaperCanada W 99, No. 12 T 456 (1998).

7. Hsich, s.r., etal, Tappi Vol 74 No. 11, P 117-1998.

8. Pryke, DC, etal, Pulp & Paper Canal, Vol. 96, 11 P76-1995.

9. Chopped. D., etal, Tappi Vol 84, No.2, P-26-2001.

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11. Matsukura. M, Tappi, Vol 77, No.1, P176-1964.

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integrated approach to reduce adsorbable organic halides

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