Spent liquors from pulp bleaching Present knowledge of the chemical composition of these wastes is discussed, with emphasis on toxic compounds
Knut P.Kringstad Krister Lindstrom Swedish Forest Products Research Laboratory
toxic compounds. Some alternative bleaching procedures, perhaps with less severe environmental effects, will be considered briefly.
Box5604,S-l1486,Stockholm, The composition of wood Sweden Wood is by far the most important
Many halogenated organic compounds are toxic and may show considerable resistance to biological and chemical degradation. Thus, the growing concern about the release of these materials into the environment is well understood. The industry thai manufactures bleached chemical pulp consumes considerable quantities of chlorine and discharges large quantities of chlorinated organic matter into rivers, lakes, and oceans. Improved knowledge of its chemical composition and biological effects would facilitate a meaningful assessment of any risks involved in releasing such material into receiving waters. This discussion will focus on the composition and sources of pulp bleaching wastes, with special emphasis on kraft pulp bleaching and on
raw material for the production of chemical pulp. Its main component groups are cellulose, hemicelluloses, lignin, and extractives ( 1 ) . Cellulose (Figure I ) is a linear polysaccharide consisting of P-D-glUcopyranose units, which are linked by (1-4)-glucosidic bonds. Wood cellulose in its native state is composed of at least 10 000 anhydro glucose units. Cellulose molecules are bundled together in wood to form microfibrils. These in turn build up fibrils and, finally, cellulose fibers. About 40% of most wood is cellulose that has a molecular weight in excess of 10 000. Wood hemicelluloses are composed of different carbohydrate units. Unlike cellulose, hemicelluloses are branched to various extents; their relative molecular masses, with a degree of polymerization on the order of 200, are
much lower. Also, the content and types of hemicellulose in softwoods differ considerably from those in hardwoods. In the former, galactoglucomannans (1 5-20%). arabinoglucuronoxylan (5-10%) and arabinogalactan (2-3%) are the most common. In the latter, glucuronoxylan (20-30%) and glucomannan (1-570) are the most important hemicelluloses. Lignin is essentially an aromatic polymer. It is formed in wood by an enzyme-initiated dehydrogenative polymerization of a mixture of three different 4-hydroxyarylpropenyl alcohols (Figure 2). The proportions of these alcohols vary with different wood species. Thus, softwood lignin is largely a polymerization product of coniferyl alcohol (Figure 2, 11). The lower portion of Figure 2 shows a summary of prominent structures in such lignin, as suggested by Adler (2). The relative molecular mass of native lignin is considered infinite. The scheme shown in Figure 2 contains only 16 monomeric units and does not set forth all of the known
FIGURE 1
The I?--
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structure of cellulose
Environ. Sci. Technol.. Vol. 18. No. 8. 1984
0013-936X/84/0916-0236A$01.50/0
@
1984 American Chemical Society
FIGURE2
Lignin precursors.
..
. . .and prominent st~ucturesin softwood lignin
CkOH
structural details. It does show, however, that softwood lignin is a branched molecule in which the phenylpropane-based units are linked by different types of bonds. These include ether bonds of alkyl-aryl, alkyl-alkyl, and aryl-aryl configurations. Various types of carbon-carbon bonds are also
found. The aromatic content, expressed as monomeric phenol, is approximately 51%. Figure 2 alsoshows characteristic functional groups such as primary and secondary hydroxyl, etherified, free phenolic hydroxyl, and carbonyl groups of various types. In wood, lignin is probably chemi-
cally linked to hemicelluloses. In hardwoods, lignin is formed by copolymerization of coniferyl (Figure 2, 11) and sinapyl (Figure 2,111) alcohols. The ratio between the two may vary from 4:l to 1:2. Figure 3 shows the cross section of softwood fibers photographed by UV Envirm. Sci. Technol., Vol. 18, No. 8, 1984
237A
radiation at a wavelength of 240 nm. Absorption takes place only in the lignin part of the fiber material (3). The densitometer curve taken across the two fiber walls and the middle lamella between them shows that lignin is present in the fiber walls, as well as in the middle lamella. Lignin performs such functions as imparting rigidity to the fiber walls, and acting as a bonding agent between the fibers. The term “extractives” is normally used for those components of wood that can be extracted by organic solvents such as ethanol, acetone, or dichloromethane. They include a variety of compounds that may be subdivided into aliphatic extractives, consisting nearly of fats and waxes; terpenoid compounds-present only in softwoods-to which class a number of mono-, sesqui-, and diterpenes, as well as various resin acids belong; and finally, phenolic extractives, which include hydrolyzable tannins, flavonoids, lignans, stilbenes, and tropolines ( 4 ) . Examples of extractives are shown in Figure 4. The total content of extractives in wood varies greatly (1.5-5%), depending on the species, place of growth, and the age of the tree. Even within the same stem, the content of extractives may vary considerably. Principles of pulping Most chemical pulping is carried out either according to the kraft (sulfate) process or the sulfite process ( 5 ) . The purposes of pulping are to remove lignin in order to facilitate fiber separation and to improve the papermaking properties of the fibers. The kraft process (Figure 5 ) is presently the most important by far. It entails treating wood chips at 160180 OC with a liquor that contains sodium hydroxide and sodium sulfide, which promote cleavage of the various ether bonds in the lignin. The lignin degradation products so formed dissolve in the alkaline pulping liquor. Depending on pulping conditions, as much as 90-95% of the lignin is removed from wood at this stage. In addition, portions of the wood polysaccharides, especially those of the hemicelluloses, are dissolved during the pulping operation. That is because cellulose and hemicelluloses are sensitive to alkali through their aldehydic end groups, and will thus degrade by a mechanism known as the peeling reaction ( 5 ) . As a result, isosaccharinic acid and a number of other organic acids are formed and dissolved in the pulping liquor. The peeling reaction is ended by the so-called stopping reaction, in which the end group rearranges 2301
Environ. Sci. Techml.. VoI. 18, No. 8. 1984
FIGURE 3
Cross section of black spruce earlywood fibeW
FIGURE 4
Examples of wood extracthres..
monoterpenes.
..
.
FIGURE 5
Kraft pulp mill, including a conventional bleach plant
I
-
Chipper
........ _..-. _. .................. ....... ...............
Chip pile
nl I n
I
II I I
n_____
-8lack' liquor Ileolchil
Bleached
'P
I
-
I Alkali stage
to an alkali-stable m-saccharinic end group. Wood extractives are also dissolved or dispersed in the kraft pulping liquor. If softwood is the raw material, the extractives are to a large degree recovered as important by-products, such as sulfate turpentine and tall oil. Turpentine contains a mixture of the lower terpenes, whereas a raw tall oil consists mainly of fatty and resin acids. The content of residual extractives in unbleached kraft pulp is low. In a kraft process for bleached pulp, somewhat more than 55% of the total weight of the wood is dissolved in the pulping liquor. After separation from the pulp, the spent liquor is evaporated to a high concentration and then burned to recover energy and inorganic chemicals. By comparison, the sulfite process solubilizes lignin through sulfonation at elevated temperatures. The pulping liquor contains sulfur dioxide and an alkaline oxide such as that of sodium, magnesium, or calcium. Principlesof bleaching Neither the kraft nor the sulfite process removes all lignin. About
1
Chlorine dioxae lower D,staw
1
1
Hypochhte
K i g e
t,stage
I
CI, lowe
............... .........
c,
.1':i,
I
\BLE 1
ield loss in kgltonne of pulp in the bleaching of various ulp types swrce ol YleM losf
SOnWO*d
Lignin Polysaccharides Extractives Total
50 19 1 70
sunn* NIP
N d I pllD
5-10'70 of the original lignin remains in the pulp, since it cannot be removed by extended pulping without seriously degrading the polysaccharide fraction. Removal of the residual lignin, which is responsible for the dark color of kraft pulps, calls for a multistage bleaching process ( 5 ) . For softwood kraft pulps (Figure 5 ) , bleaching is normally accomplished by successive treatments with chlorine (Cl), alkali (El), chlorine dioxide (D,),alkali (Ez) and Often, a hypochlorine dioxide (Dz). chlorite stage (H) may be inserted between the E, and D,stages. The largest quantity of material is
Birch
?O 22
Paper
35 12
3
8
45
55
RWW
12 70 8 90
dissolved from the pulp during the C and El stages. The C stage consists of a treatment of a slurry of the pulp with elemental chlorine. Normally, the slurry's consistency is 3% the charge of chlorine (depending upon the content of the residual lignin) is about 60-70 kg/tonne (metric ton) of pulp; the temperature is 15-30 ' C , and the final pH is 1.5-2.0. The subsequent El stage is an extraction of the chlorinated pulp with alkali. Here, the consistency is usually somewhat more than 10%; the charge of alkali is about 35-40 kg/tonne of pulp; the temperature is 55-70 "C;and Envlron. Sci. Technol.. VoI. 18. No. 8. 1984
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FIGURE 6
Reactions between residual llgnin in pulp and chlorine
cally bound chlorine, the relative molecular mass distribution, and the solubility properties of the organic material are important. Available figures on the content of organically bound chlorine vary to some degree ( 9 , 12-16), but in the bleaching of a softwood kraft pulp would normally correspond to about
Estimating organic chlorine discharges World production of bleached chemical pulp is presently on the order of 50 million tonnesly. The discharge of organically bound chlorine could be estimated at 250 000 tonnesly, if one assumes that all the pulp produced is bleached by conventional means and that the total quantity of organically bound chlorine formed (including final bleaching) is 5 kgltonne pulp. The actual discharge is probably somewhat lower, since variations in factors such as pulp types, bleaching sequences, --A --'?mal treatments are not taken iount.
the final pH is about 11. The C and El stages constitute the prebleaching part, and the successive stages make up the final bleaching_part . of the bleachingprocess. During the conventional bleaching of a softw'bod kraft pulp, perhaps 70 k i of material for each tonne of pulp will dissolve from the pulp into the bleaching liquors (Table 1). About 50 kg of this material originates from the residual lignin; about 19 kg comes from the polysaccharide fraction; and approximately 1 kg is from the extractives portion of the pulp (6).Most of this material-75%-is dissolved during the C and El stages. When chlorine isdissolved in water, the following equilibria form: CIz
+ H 2 0 a H+ + CI- + HOCl HOCl =, H+ + OCI-
(1)
(2) At 25 T, the equilibrium constants are KI= 3.0 X and Kz = 2.9 X 10-8. Chlorine may react in two different ways with organic material. In one case, it reacts as a molecular species, and in the other, it acts after decomposition into a radical. The latter mechanism is believed to be important in reactions with carbohydrates. However, during pulp chlorination, chlorine reacts primarily with residual 2401
Enviran. Scl. Technol.. VoI. 18. No. 8. 1984
lignin. In these reactions, it acts in its molecular form. As summarized in Figure 6, oxidation and substitution by chlorine and the addition of hydrogen chloride are important reactions in this stage ( 7 ) . These reactions lead to a substantial depolymerization of the lignin, as well as to the introduction of chlorine and various acidic groups into its structure. As a result, part of the residual lignin will dissolve in the chlorination liquor. The reactions in the alkali extraction stage El are less understood. Apart from ionizing the acidic groups formed during the C stage, which facilitates the solution of the chlorinated lignin, treatment with alkali will cause a substantial loss of the organically bound chlorine introduced during chlorination (8-11). A marked decrease in the content of carbonyl groups also has been observed (8). Spent liquor composition In view of this great variety of reactions, one readily perceives the extreme complexity of the organic chemical composition of spent chlorination and alkali extraction liquors. From an environmental standpoint, it is of interest to ascertain the nature and content of as many of the compounds present as possible. Moreover, data regarding the content of organi-
1
4 kg/tonne of pulp for the two types of
spent liquor. Organically bound chlorine is present in a wide range of organic material found in spent liquors. This may be seen by dividing the organic material into fractions of different relative molecular mass and then determining the organically bound chlorine in each of these fractions ( 1 2-1 5 ) . Figure 7 shows results from the most recent investigations in which such determinations were made. It appears that in spent chlorination liquor, about 70% of the organically bound chlorine is present as high-relative-molecular-mass material (M, > 1000);whereas in alkali extraction liquor, about 95% of the organically bound chlorine belongs to this class. It should be emphasized that thesevalues have been obtained through ultrafiltration of the spent liquor, using one special type of membrane filter (40).
High-molecular-mass materials The structures of high-relativemolecular-mass materials are poorly defined at present. Determination of the elemental composition has given C9H904C1, C10H1407Cl and CgHloOsCI ( 1 7-19) as representative formulas for high-relative-molecular-mass compounds in spent chlorination liquor. For corresponding ma-
FIGURE 7
Distribution of organically bound
terial present in alkali extraction liquor, formulas such as C 1 4 H I ~ 0 & I and C I ~ H I ~ Owere ~ C Iobtained. These results show that both types of material have high chlorine-to-carbon ratios. Studies of these materials were carried out by means of oxidative degradation involving a combination of permanganate, periodate, and hydrogen peroxide. Results suggest that the content of aromatic nuclei is surprisingly low for both types (17, 20, 21). The same conclusions may be drawn from UV studies ( 1 2 , 13), which indicate that a major part of the material consists of cross-linked, probably unsaturated aliphatic compounds. Moreover, the oxidative degradation experiments also show that such aromatic nuclei as are present in the material are demethylated to a considerable degree as compared with those of the original lignin, and that the nuclei carry 0-3 chloro substituents in the material from both types of liquor. High-relative-molecular-mass materials in spent chlorination and alkali extraction liquors are probably biologically inactive, because they cannot penetrate cell membranes of living organisms. However, such materials are still of environmental importance, because they carry chromophoric structures that cause bleaching plant Environ. Sci. Technai., Val. 18. NO.8. 1984
241
FIGURE 8
Phenolic compounds most frequently identified in spent liquors
Chbinated
ChlMlnated
Spent liquom fmm soffwood krafl pulps
-
Y mbldtng d M and MrEh krafl pylp Smms Refemwe 87
effluents to impart light-absorbing qualities to receiving waters. In addition, it is an open question whether and to what degree these materials are broken down biologically and chemically to form low-relative-molecularmass compounds possibly having detrimental biological effects. Studies aiming at answering the latter question deserve high priority in future research. Low-molecular-mass materials About 30% of the organically bound chlorine in spent chlorination liquor and approximately 5% in alkali extraction liquor (Figure 7) is of low relative molecular mass (M, < 1000). Considerable effort has been made in recent years to determine the nature and content of individual components. This effort has been facilitated by rapid new developments in the fields of analytical and physical organic chemistry. Table 2 represents an attempt to list some of the individual compounds that have so far been identified in spent chlorination and alkali extraction liquors. The nomenclature used does not fully conform to that of the International Union of Pure and Applied Chemistry (IUPAC); many trivial names, common in the field of wood chemistry, are used. Materials are listed in three main groups: acidic, phenolic, and neutral compounds. Available information on quantities of the various compounds also is included. Since several factors may have influenced the data presented, great care should be exercised in using these values. Such factors include wood species, the degree of delignification and washing of unbleached pulp, the 242A
Environ. Sci. Technol.. VOI. 18, NO. 8, 1984
FIGURE 9
Chlorinated phenolic corn unds in spent chlorination liquora,
go
Total content of chlorinated phenolic compounds @tlm unbleached 150
I
1
loo] 50
bleaching conditions, and the analytical procedures used. Several of the compounds have been detected only qualitatively, but that does not necessarily mean that such compounds are. present in trace quantities. Acidic compounds. This group may be subdivided into five categories of acids: fatty, hydroxy, dibasic, aromatic, and resin acids. The higher fatty acids and resin acids originate from extractives; however, some of these acids were identified in a total mill
effluent and may therefore not originate from the bleach plant. Formic and acetic acids are quantitatively the most important fatty acids. Among the hydroxy acids identified, glyceric acid predominates. Except for 3-bydroxypropanoic and glyceric acids, the hydroxy acids are very likely oxidation products of carbohydrates. The dibasic acids-oxalic, malonic, succinic, and malic acids-are present in considerable quantities in both types of spent liquor. The lower dibasic acids
also may be derived from residual lignin and carbohydrates. Table 2 indicates that thecontent of aromatic acids is probably low. These acids are unquestionably formed from residual lignin by oxidation of the a-carbon in the phenylpropane unit (Figure 2. bottom). Like the phenolic compounds, three kinds of aromatic acids are formed: those with one hydroxyl group (phenolic), those with two hydroxyl groups (catecholic), and those with one hydroxyl and one methoxyl group (guaiacolic). Resin acids have been identified only in caustic extraction liquor. I t is noteworthy that the number of rhhinared acids identified in both liquors is very low. This is surprising, because the content of organically bound chlorine in the acid fraction (M, < 1000) has been found to constitute about 70% of such chlorine present in the ether-soluble fraction (71). Phenolic compounds. Figure 8 presents 3 summary of the chemical structures of those phenolic compounds that have been identified most frequently in the two types ofspent liquor. Chlorinated catechols occur primarily in spent chlorination liquor. whereas most chlorinated guaiacols and vanillins are found in spent alkali extraction liquor (29,67). All of these compounds are formed from residual lignin. Figure 9 illustrates the dependence of phenolic content on the charge of chlorine and the end-pH used in the chlorination stage (53). Also, the relative amounts of individual phenolic compounds will be influenced to a considerable degree by variations in these parameters. For example, underchlorination as well as overchlorination will lead to lower contents of triand tetrachlorocatechols in the spent chlorination liquor. I n the case of underchlorination. this is attributable to insufficient quantities of chlorine; in the case of overchlorination. to oxida live ring cleavage reactions. The formation of trihydroxybenzenes in the bleaching of sulfite pulp has not ye! been explained and requires more ex. tensive study. Neutral compounds. Quantitatively. methanol and various hemicelluloses are by far the dominant neutral compounds. The chief source of methanol is the methoxyl groups abundant i n lignin (Figure 2). Compared with quantities of methanol and hemicellulose. the total amount of chlorinated compounds in the neutral fraction is very small. The neutral compounds consist of a
wide spectrum of chemicals, ranging from a number of chlorinated saturated and unsaturated hydrocarbons, aldehydes, ketones, and esters to various chlorinated benzene derivatives and chlorinated sulfur-containing materials. Quantitatively, thc various chlorinated acetones, chloroform, dichloromethane, and 1 ,I-dichloromethylsulfone predominate in the two types of spent liquors. The total quantity of chloroform and dichloromethane formed in a conventional bleach plant will be much higher than that indicated in Table 2 if the bleaching sequence involves a hypochlorite stage (Figure IO). Therefore. reports in the literature of total chloroform production of up to 0.3 kg/tonne of pulp are understandable ( 4 2 . 44. 5 2 ) . Table 2 also shows that bromodichloromethane and dibromochloromethane are present (37, 38). possibly as a result of bromide in raw water. The quantities of these brominated compounds are, however, extremely small. I t is difficult to decide from which wood component the various chlorinated neutral compounds originate. Many of these compounds may well be degradation products of residual lignin. But some also may be formed from impurities in the pulp. One striking example is the occurrence of
chlorinated dimethyl sulfones, of which I ,I-dichloromethyl sulfone (DDS) predominates (36, 40, 50). DDS was found at -50 g/tonne pulp in a total mill effluent (72). and is most likely formed from dimethyl thioether (dimethyl sulfide) during cooking. Oxidation and chlorination of the thioether yield DDS as the main chlorination product, which seems to be extremely persistent (36). A rough estimate has been madeof the total content of organically bound chlorine in compounds identified so far in spent chlorination liquor. Indications are that this chlorine will account for about 10% of the total content of organically bound chlorine present in low-relative-molecular-mass (M, < 1000) materials in this liquor. The equivalent figure for alkali extraction liquor is about 35%. These estimates suggest that a considerable number of individual low-relative-molecularmass compounds remain to be identified in both types of liquor. Compounds with toxic effects Acute toxicity. Spent chlorination and alkali extraction liquors from the bleaching of softwood kraft pulp are mildly toxic to fish and other aquatic organisms ( 5 4 . 5 5 ) .The toxicity of the alkali extraction liquor is ascribable mainly to the presence of 3.4.5-tri-
FIGURE 10
Formation of chloroform in the different stages of a conventional bleaching sequences
C
E,
H
D,
E2
D,
Total
Enviran. Sci. Technol.. VoI. 18. NO. 8. 1984
245A
chloroguaiacol, tetrachloro-guaiacol, and mono- and dichlorcdehydroabietic acid ( 2 6 ) . Of these, tetrachloroguaiacol is the most toxic. The toxic effects of spent chlorination liquor are normally lower than those of spent alkali extraction liquor. However, because of the much larger volumes of chlorination liquor produced, the total toxicity released with this liquor is considerably larger ( 5 6 ) . Identification of the compounds responsible for the toxicity of spent chlorination liquor has not progressed as far as the identification of alkali extraction liquor toxicants. It is likely, however, that chlorinated catechols contribute significantly to toxicity (50, 53,57,58). In such compounds, toxicity will increase with the increasing number of chlorine substitutents (31, 57). Various chlorinated phenolic compounds have been identified in liver fat from fish caught in thevicinity of a pulp bleaching plant (77). Cenotoxic compounds. In recent years, it was found that spent chlorination liquor from the bleaching of softwood kraft pulp (and most other pulp types) is mutagenic (59,60). This was determined (Figure I I ) by testing the spent liquor by the Ames test ( 6 1 ) . as well as by other laboratory techniques used for testing for genetic effects (62-64). Table 3 lists several mutagenic compounds that have been identified. Of these, 1,3-dichloroacetone ( 3 9 ) . 3-chloro-4-dichloromethyl-5hydroxy-2(5H)-furanone (Reference 41; Figure 12) and 2-chloropropenal ( 3 8 , 3 9 ) are strong mutagens in their pure state. Chloroacetones ( 6 4 ) , chlorinated derivatives of the chlorofuranone mentioned above, and 2chloropropenal are regarded as major contributors to the mutagenicity of spent chlorination liquor. However, additional mutagens may be identified. Spent chlorination and alkali extraction liquors also contain compounds that have been classified as carcinogens on the basis of standard methods of animal testing. Among these are chloroform and carbon tetrachloride. Some other compounds, such as various chlorinated benzenes and phenols, epoxystearic acid and dichloromethdne, have been classified as suspected carcinogens. With current knowledge, it is not possible to perform a complete assessment of the risks involved in releasing such compounds into rivers and lakes ( 6 5 ) .One reason is found in the lack of animal carcinogenicity data. Nevertheless. this risk was estimated 24841
Environ. Scl. Technol.. VoI. 18. NO.8. 1984
FlOURE
11
Number of revertants/plate*.b,c Number of revertantdplate
Control
C
E,
H D, Bleaching stages
to be extremely low to nonexistent after a recent evaluation of the three major inland receiving waters in Sweden ( 6 6 ) . This conclusion was reached through figures showing that when spent bleach liquors were released into those receiving waters, chloroform, chlorinated phenols, and some of the identified mutagenic compounds were diluted to low levels. These levels were actually far below those of identical compounds formed during the disinfection of drinking water by chlorination. At present, available information on the fate of genetically active compounds in receiving waters is very limited. Future research should emphasize studies aimed at increasing this knowledge substantially. Other liquors
Prebleaching kraft pulp with oxygen, partial replacement of chlorine with chlorine dioxide during the first stage of bleaching and biological treatment are well-known techniques used to reduce the toxicity, mutagtmicity, color, and organic load of bleach plant effluents. However, current knowledge about the way these techniques influence the organic chemical composition of bleach plant effluents is limited. In recent investigations, it has been shown that the elemental compositions of high-relative-molecular-mass material in spent chlorination and alkali
E2
D2
extraction liquors from the bleaching of oxygen-prebleached softwood kraft pulp correspond to CloH1007CIand C I R H I ~ O ~respectively ~CI, (17). These compositions are quite similar to those of materials found in equivalent liquors from pulp that was not prebleached with oxygen. With respect to individually identified compounds. the limited number of investigations conducted so far suggest that oxygen pre-bleaching does not significantly alter the spectrum of chemicals formed. However. when properly conducted, oxygen prcbleaching will generate smaller quantities of all of these compounds. Moreover, bleaching operations using oxygen do not normally call for a hypochlorite stage. Therefore. only very small quantities of chloroform are found in such liquors ( 2 3 ) . When softwood kraft pulp is bleached with a partial replacement of chlorine by chlorine dioxide. the quantity ofchlorinated phenols formed increases with the increasing degreeof replacement (31). I t reaches a maximum at 50% of chlorine dioxide, above which the quantity of chlorinated phenols declines. In a recent study in which chlorine was completely replaced with chlorine dioxide, the only phenolic compound found in the spent liquor was 6-chlorovanillin (67). The total replacement of chlorine with chlorine dioxide also significantly influences thc elemental
TABLE 3
Ames-test-positive compounds identified in spent chlorination liquor a s1.m 01 sslmwlfa COlqarnd
Dichloromethane Bromcdichloromethane Dibromochloromethane Trichloroethene Telrachloroelhene Telrachloropropene Pentachlotopropene 1,3-DichIormcetone 1.13-Trichloroacetone 1.1.3.3-Tetrachlor0ace1one Pentachloroacelone Hexachloroacetone Chloroacelaldehyde 26hlwopropenal 36hloro-4dichloromethyl5-hydroxy-2(5Htfuranone
lyphlmurlum
TA TA TA TA TA TA TA
100 100 100 100 100 98 100 T... A 1515 TA 100 TA 1535 TA 100 TA 1535 TA 100 TA 100 TA 100 TA 100 TA 100 TA 1535 TA 100 TA 1535 TA 100
0.5
12 -
0.7
0.4 0.2
-
1.5
-
a From bleaching 01 sottwocd krafl pulp Sources: References 38.39.41.64. 78. 80
FIGURE 12
Compounds contributing to the mutagenicity of spent chlorination liquors."c
treatment conditions and can be quite low (36.67,69,70,79).Thus, chlorinated phenols and guaiacols are easily detectable in biologically treated bleached kraft total mill effluents (85) and also often in receiving waters (84). Similar observations have been made with regard to various Chlorinated resin acids (85). A new aspect of the biological treatment of spent-bleach-liquorcontaining effluent arises from recent laboratory studies. It was found that bacteria may transform high-relative-molecular-mass materials, as well as monomeric chlorinated phenols, to chlorinated veratroles of various types in surprisingly high yields (88).Some chlorinated veratroles are highly lipophilic and could, i f formed in aerated lagoons or receiving waters. be expected to hioaccumulate in the tissues of higher organisms such as fish (88). Investigations aimed at identifying chlorinated veratroles in effluents, receiving waters, and aquatic organisms are now under way. I t would seem, then. that there is less knowledge concerning the organic chemical composition of spent liquors from alternativc bleaching sequences than there is about spent liquors from conventional bleaching processes. Research to improve such knowledge should be a matter of high priority. Acknowledgments
This article updates a paper presented at a Tcchnical Association of the Pulp and Papcr Industry Research and Development Conference held a t Asheville. S . C . . in August 19x2, Before publication. this paper was reviewed for suitability as an ES& Tcritical review by Joseph Delfino. University of Florida. Cainesville, Fla. 3261 I ; Larry Keith. Radian Carp.. Austin. Tex. 78766: and Raymond Young. University of Wisconsin, Madison, Wis. 53706. composition of the high-relative-molecular-mass material. For example, C J ~ H ~ ~ Oand K IC I I ~ H ~ , ? O were found in spent chlorine dioxide and alkali extraction liquors; this corresponds to a very marked decrease in the content of orgenically bound chlorine ( 1 7 ) . Alsu,. only vcry small amounts of chloroform (-I g/tonne of pulp) are formed i n such liquors. Biological treatment reduces the total organic carbon load of bleached kraft total mill effluents (82). However. there is much less information available concerning the presence of chlorinated organic compounds in biologically treated effluents than there is concerning such compounds in individual spent bleach liquors.
Still. i t is known that biological treatment reduces the content of or~ ganically ~CI bound chlorine to some degree ( 1 6 ) .This might beascribable in part to a reduction in the content of chlorinated neutral organic compounds. For instance, aerated lagoons are highly efficient in removing chloroform (42. 85-87). Furthermore. a recent investigation showed that di-. tri-. and tetrachlorodimethyl sulfones were the only detectable chlorinated neutral organic compounds (in addition to chloroform) in nine biologically treated bleached kraft total mill cffluents (87). Chlorinated phenols arc also biodegradable ( 5 7 . 6 8 ) .However. the rate of removal depends very much on Environ. Sci. Technol.. VoI. le. NO.8. 1984
247A
been doing research on the chlorinated organic matter in pulp mill bleach plant effluents, and has reported on these and other research activities in a number of publications. Supplementary material available. In addition to those formulas shown in Table 2, a list of 192 organic compounds found in spent chlorination and alkali extraction liquors is available. These are subdivided into acids, phenolics, and neutral compounds, and are keyed to reference numbers. The supplementary material from this paper is available in photocopy or microfiche (105 X 148 mm, 24X reduction, negatives) from Business Operations, Books and Journals Division, American Chemical Society, 1155 16th St., N.W., Washington, D.C. 20036. Full bibliographic citation (journal, title of article, author) and prepayment by check or money order for $19.50 for photocopy ($2 1 foreign), or $6 for microfiche ($7 foreign) are required. Prices are subject t o change without notice.
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