Thông tin tài liệu
10
Treatment of Pulp and Paper Mill Wastes
Suresh Sumathi
Indian Institute of Technology, Bombay, India
Yung-Tse Hung
Cleveland State University, Cleveland, Ohio, U.S.A.
10.1 POLLUTION PROBLEMS OF PULP AND PAPER INDUSTRIES
Pulp and paper mills are a major source of industrial pollution worldwide. The pulping and
bleaching steps generate most of the liquid, solid, and gaseous wastes (Table 1) [1]. Pulping is a
process in which the raw material is treated mechanically or chemically to remove lignin in order
to facilitate cellulose and hemicellulose fiber separation and to improve the papermaking
properties of fibers. Bleaching is a multistage process to whiten and brighten the pulp through
removal of residual lignin. Pulping and bleaching operations are energy intensive and typically
consume huge volumes of fresh water and large quantities of chemicals such as sodium
hydroxide, sodium carbonate, sodium sulfide, bisulfites, elemental chlorine or chlorine dioxide,
calcium oxide, hydrochloric acid, and so on. A partial list of the various types of compounds
found in spent liquors generated from pulping and bleaching steps is shown in Table 2 [2 –4].
The effluents generated by the mills are associated with the following major problems:
. Dark brown coloration of the receiving water bodies result in reduced penetration of
light, thereby affecting benthic growth and habitat. The color responsible for causing
aesthetic problems is attributable to lignin and its degradation products.
. High content of organic matter, which contributes to the biological oxygen demand
(BOD) and depletion of dissolved oxygen in the receiving ecosystems.
. Presence of persistent, bio-accumulative, and toxic pollutants.
. Contribution to adsorbable organic halide (AOX) load in the receiving ecosystems.
. Measurable long-distance transport (.100 km) of organic halides (such as chloro-
guaiacols), thereby contaminating remote parts of seas and lakes [5].
. Cross-media pollutant transfer through volatilization of compounds and absorption of
chlorinated organics to wastewater particulates and sludge.
Significant solid wastes from pulp and paper mills include bark, reject fibers, wastewater
treatment plant sludge, scrubber sludge, lime mud, green liquor dregs, and boiler and furnace
ash. The bulk of the solid wastes is generated during wastewater treatment. Sludge disposal is a
serious environmental problem due to the partitioning of chlorinated organics from effluents to
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© 2006 by Taylor & Francis Group, LLC
solids. The major air emissions are fine and coarse particulates from recovery furnaces and
burners, sulfur oxides (SOx) from sulfite mills, reduced sulfur gases and associated odor
problems from Kraft pulping and chemical recovery operations, volatile organic compounds
(VOC) from wood chip digestion, spent liquor evaporation and bleaching, nitrogen oxides
(NOx), and SOx from combustion processes. Volatile organics include carbon disulfide,
methanol, methyl ethyl ketone, phenols, terpenes, acetone, alcohols, chloroform, chloro-
methane, and trichloroethane [1].
The extent of pollution and toxicity depends upon the raw material used, pulping method,
and pulp bleaching process adapted by the pulp and paper mills. For example, the pollution load
from hardwood is lower than softwood. On the other hand, the spent liquor generated from
pulping of nonwood fiber has a high silica content. Volumes of wastewater discharged may vary
from near zero to 400 m
3
per ton of pulp depending on the raw material used, manufacturing
process, and size of the mill [6]. Thus, the variability of effluent characteristics and volume from
one mill to another emphasizes the requirement for a variety of pollution prevention and
treatment technologies, tailored for a specific industry.
Table 1 Types of Pollutants Generated During Chemical (Kraft) Pulping and Bleaching Steps
Pollution generating step
Pollution
output phase Nature of pollution
Wood debarking and
chipping, chip washing
Solid Bark, wood processing residues
Water SS, BOD, color, resin acids
Chemical (Kraft) pulping,
black liquor evaporation, and
chemical recovery steps
Air Total reduced sulfur (hydrogen
sulfide, methyl mercaptan,
dimethyl sulfide, dimethyl
disulfide), VOC
Wood chip digestion, spent pulping liquor
evaporator condensates
Water High BOD, color, may contain
reduced sulfur compounds,
resin acids
Pulp screening, thickening, and cleaning
operations
Water Large volume of waters with SS,
BOD, color
Smelt dissolution, clarification to generate
green liquor
Solid Green liquor dregs
Recausticizing of green liquor, clarification
to generate white liquor
Solid Lime slaker grits
Chlorine bleaching of pulp Water BOD, color, chlorinated
organics, resin acids
Air VOC
Wastewater treatment Solid Primary and secondary sludge,
chemical sludge
Air VOC
Scrubbing for flue gases Solid Scrubber sludge
Recovery furnaces and boilers Air Fine and coarse particulates,
nitrogen oxides, SO
2
Solid Ash
SS, suspended solids; VOC, volatile organics; BOD, biochemical oxygen demand.
Source: Ref. 1.
454 Sumathi and Hung
© 2006 by Taylor & Francis Group, LLC
Table 2 Low-Molecular-Weight Organic Compounds Found in the Spent Liquors from Pulping and Bleaching Processes
Class of compounds
Acidic
Wood extractives
Lignin/carbohydrate
derived Phenolic Neutral Miscellaneous
Category: Fatty acid
Formic acid (S)
Acetic acid (S)
Palmitic acid (S)
Heptadecanoic acid (S)
Stearic acid (S)
Arachidic acid (S)
Tricosanoic acid (S)
Lignoceric (S)
Oleic (US)
Linolenic acid (US)
Behenic acid (S)
Category: Resin acid
Abietic acid
Dehydroabietic acid
Mono and dichloro
dehydrabietic acids
Hydroxylated-
dehydroabietic acid
Levopimaric acid
Pimaric acid
Sandracopimaric acid
Category: Hydroxy
Glyceric acid
Category: Dibasic
Oxalic acid
Malonic acid
Succinic acid
Malic acid
Category: Phenolic
acid
Monohydroxy benzoic
acid
Dihydroxy benzoic
acid
Guaiacolic acid
Syringic acid
Category: Phenolic
Monochlorophenols
Dichlorophenols
Trichlorophenols
Tetrachlorophenol
Pentachlorophenol
Category: Guaiacolic
Dichloroguaiacols
Trichloroguaiacols
Tetrachloroguaiacol
Category: Catecholic
Dichlorocatechols
Trichlorocatechols
Category: Syringic
Trichlorosyringol
Chlorosyringaldehyde
Hemicelluloses
Methanol
Chlorinated acetones
Chloroform
Dichloromethane
Trichloroethene
Chloropropenal
Chlorofuranone
1,1-dichloro-
methylsulfone
Aldehydes
Ketones
Chlorinated sulfur
Reduced sulfur
compounds
Category: Dioxins
2,3,7,8-tetrachloro-
dibenzodioxin (2,3,7,8-TCDD)
2,3,7,8-tetrachloro-dibenzofuran
(2,3,7,8-TCDF)
Wood derivatives
Monoterpenes
Sesquiterpenes
Diterpenes: Pimarol
Abienol
Juvabiones
Juvabiol
Juvabione
Lignin derivatives
Eugenol
Isoeugenol
Stilbene
Tannins (monomeric, condensed
and hydrolysable)
Flavonoids
S, saturated; US, unsaturated
Source: Refs 2–4.
Treatment of Pulp and Paper Mill Wastes 455
© 2006 by Taylor & Francis Group, LLC
The focus of this chapter is to trace the origin and nature of the major pollution (especially
water) problems within the pulp and paper industries and to present an overview of the pollution
mitigation strategies and technologies that are currently in practice or being developed
(emerging technologies).
10.2 NATURE AND COMPOSITION OF RAW MATERIALS USED
BY PULP AND PAPER INDUSTRIES
The pulp and paper industries use three types of raw materials, namely, hard wood, soft wood,
and nonwood fiber sources (straw, bagasse, bamboo, kenaf, and so on). Hard woods (oaks,
maples, and birches) are derived from deciduous trees. Soft woods (spruces, firs, hemlocks,
pines, cedar) are obtained from evergreen coniferous trees.
10.2.1 Composition of Wood and Nonwood Fibers
Soft and hard woods contain cellulose (40–45%), hemicellulose (20–30%), lignin (20–30%),
and extractives (2–5%) [7]. Cellulose is a linear polymer composed of
b
-D-glucose units linked
by 1–4 glucosidic bonds. Hemicelluloses are branched and varying types of this polymer are
found in soft and hard woods and nonwood species. In soft woods, galactoglucomannans
(15–20% by weight), arabinoglucurono-xylan, (5–10% by weight), and arabinogalactan (2–3%
by weight) are the common hemicelluloses, while in hard woods, glucuronoxylan (20–30% by
weight) and glucomannan (1–5% by weight) are found [2,3]. Lignin is a complex heterogeneous
phenylpropanoid biopolymer containing a diverse array of stable carbon–carbon bonds with
aryl/alkyl ether linkages and may be cross-linked to hemicelluloses [8]. Lignins are amorphous,
stereo irregular, water-insoluble, nonhydrolyzable, and highly resistant to degradation by most
organisms and must be so in order to impart resistance to plants against many physical and
environmental stresses. This recalcitrant biopolymer is formed in plant cell walls by the enzyme-
catalyzed coupling of p-hydroxycinnamyl alcohols, namely, p-coumaryl, coniferyl, and sinapyl
alcohols that make up significant proportion of the biomass in terrestrial higher plants. In
hardwoods, lignin is composed of coniferyl and sinapyl alcohols and in softwoods is largely a
polymer of coniferyl alcohol. The solvent extractable compounds of wood termed as
“extractives” include aliphatics such as fats, waxes, and phenolics that include tannins,
flavonoids, stilbenes, and terpenoids. Extractives comprise 1–5% of wood depending upon the
species and age of the tree. Terpenoids that include resin acids are found only in soft wood and
are derived from the “pitch” component of wood. Compared to wood, the structures of nonwood
species are not well studied. Grasses usually contain higher amounts of hemicelluloses, proteins,
silica, and waxes [9]. On the other hand, grasses contain lower lignin content compared to wood
and the bonding of lignin to cellulose is weaker and therefore easier to access.
10.3 PULPING PROCESSES
The steps involved in pulping are debarking, wood chipping, chip washing, chip crushing/
digestion, pulp screening, thickening, and washing (Fig. 1). The two major pulping processes
that are in operation worldwide are mechanical and chemical processes. Mechanical pulping
methods use mechanical pressure, disc refiners, heating, and mild chemical treatment to yield
pulps. Chemical pulping involves cooking of wood chips in pulping liquors containing
chemicals under high temperature and pressure. Other pulping operations combine thermal,
mechanical, and/or chemical methods. Characteristic features of various pulping processes are
summarized in Table 3 and are further described shortly in the following subsections [3,10–12].
456 Sumathi and Hung
© 2006 by Taylor & Francis Group, LLC
Figure 1 Steps involved in the pulping and pulp bleaching processes (from Ref. 2).
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Table 3 Comparison of Various Pulping Processes
Name of the pulping process
Process features Mechanical CTMP NSSC Kraft Sulfite
Pulping
mechanism
Grinding stone,
double disc refiners,
steaming, followed
by refining in TMP
process
Chemical treatment
using NaOH or
NaHSO
3
þ
steaming followed
by mechanical
refining
Continuous digestion in
Na
2
SO
3
þ Na
2
CO
3
liquor using steam
followed by
mechanical refining
Cooking at 340–3508F,
100–135 psi for
2– 5 hours in
NaOH, Na
2
S, and
Na
2
CO3; efficient
recovery of chemicals
Sulfonation at 255 – 3508F,
90–110 psi for
6–12 hours in H
2
SO
3
and Ca, Na, NH
4
,
Mg(HSO
3
)
2
Cellulosic
raw material
Hard woods like
poplar and soft woods
like balsam, fir,
hemlock
Hard and
soft woods
Hard woods like aspen,
oak, alder, birch, and
soft wood sawdust
and chips
Any type of hard and
soft wood, nonwood
fiber sources
Any hard wood and
nonresinous soft woods
Pulp
properties
Low-strength
soft pulp, low
brightness
Moderate
strength
Good stiffness and
moldability
High-strength brown
pulps, difficult to
bleach
Dull white-light brown
pulp, easily bleached,
lower strength than
Kraft pulp
Typical
yields of pulp
92–96% 88–95% 70–80% 65–70% for brown
pulps, 47–50% for
bleachable pulps,
43– 45% after
bleaching
48–51% for bleachable
pulp, 46–48% after
bleaching
Paper
products
Newspaper, magazines,
inexpensive writing
papers, molded
products
Newspaper, magazines,
inexpensive writing
papers, molded products
Corrugating medium Bags, wrappings,
gumming paper,
white papers from
bleached Kraft pulp,
cartons, containers,
corrugated board
Fine paper, sanitary
tissue, wraps, glassine
strength reinforcement
in newsprint
TMP, thermomechanical pump; CTMP, chemi-thermomechanical pump; NSSC, neutral sulfite semichemical pulp.
Source: Refs. 3, 10, and 12.
458 Sumathi and Hung
© 2006 by Taylor & Francis Group, LLC
Nonconventional pulping methods such as solvent pulping, acid pulping, and biopulping are
discussed in subsection 10.9.1.
10.3.1 Mechanical Pulps
Stone-Ground Wood Pulp
Wood logs are pushed under the revolving grindstone and crushed by mechanical pressure to
yield low-grade pulps. Lignin is not removed during this process and therefore imparts a dark
color to the pulp and paper product.
Refiner Mechanical Pulp
Wood chips are passed through a narrow gap of a double-disc steel refiner consisting of
stationary and rotating plates having serrated surfaces. This process results in the mechanical
separation of fibers that are subsequently frayed for bonding. The strength of the refiner pulp is
better than that of ground-wood pulps.
Thermomechanical Pulp (TMP)
Wood chips are preheated in steam before passage through disc refiners. Heating is meant for
softening the lignin portion of wood and to promote fiber separation. This pulp is stronger than
that produced by the ground-wood process.
10.3.2 Semichemical Pulp
Wood chips are processed in mild chemical liquor and subjected to mechanical refining
using disc refiners. Semichemical pulping liquors have variable composition ranging from
sodium hydroxide alone, alkaline sulfite (sodium sulfite þ sodium carbonate), mixtures of
sodium hydroxide and sodium carbonate, to Kraft green or white liquors [3]. Sodium sulfite/
sodium carbonate liquor is most commonly used and the pulp product obtained thereafter is
referred to as neutral sulfite semichemical (NSSC) pulp.
10.3.3 Chemithermo Mechanical Pulp (CTMP)
This process involves a mild chemical treatment of wood chips in sodium hydroxide or sodium
bisulfite before or during steaming. Chemically treated chips are passed through mechanical disc
refiners.
10.3.4 Chemical Pulps
Chemical pulping of wood is commonly carried out according to the Kraft (sulfate) or sulfite
processes [13]. These methods are described in the following subsections.
Kraft Pulping
Kraft pulping involves the cooking of wood chips at 340– 3508F and 100–135 psi in liquor that
contains sodium hydroxide, sodium sulfide, and sodium carbonate. This process promotes
cleavage of the various ether bonds in lignin and the degradative products so formed dissolve in
alkaline pulping liquor. The Kraft process normally incorporates several steps to recover
chemicals from the spent black liquor [3].
Treatment of Pulp and Paper Mill Wastes 459
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Sulfite Pulping
The sulfite process solubilizes lignin through sulfonation at 255–3508F under 90 –110 psi. The
pulping liquors are composed of mixture of sulfurous acid (H
2
SO
3
) and bisulfites (HSO
3
22
)of
ammonium, sodium, magnesium, or calcium, and lignin is separated from the cellulose as
lignosulfonates [3]. Bisulfite pulping is performed in the pH range of 3–5 while acid sulfite
pulping is carried out with free sulfurous acid at pH 1–2. Sulfite pulping mills frequently adapt
methods for the recovery of SO
2
, magnesium, sodium, or ammonium base liquors [3].
10.4 COMPOSITION OF SPENT PULPING LIQUORS
10.4.1 Kraft Pulping Liquors (Black Liquors)
During Kraft pulping, about 90 –95% of the reactive biopolymer, namely lignin, becomes
solubilized to form a mixture of lignin oligomers that contribute to the dark brown color and
pollution load of pulping liquors. Lignin oligomers that are released into the spent liquors
undergo cleavage to low-molecular-weight phenylpropanoic acids, methoxylated and/or
hydroxylated aromatic acids. In addition, cellulose and hemicelluloses that are sensitive to alkali
also dissolve during the pulping processes [13]. Black liquors generated from the Kraft pulping
process are known to have an adverse impact on biological treatment facilities and aquatic life.
Emissions of total reduced sulfur (TRS) and hazardous air pollutants (HAP) are also generated.
Black liquors typically consist of the following four categories of compounds derived from
dissolution of wood [3]:
. ligninolytic compounds that are polyaromatic in nature;
. saccharic acids derived from the degradation of carbohydrates;
Table 4 Components of Kraft Black Liquor and Characteristics of Kraft
Evaporator Condensate
Kraft black liquor characteristics
Component Weight %, dry solids basis
Lignin 30–45
Hemicellulose and sugars 1
Hydroxy acids 25–35
Extractives 3–5
Acetic acid 2–5
Formic acid 3–5
Methanol 1
Sulfur 3–5
Sodium 17–20
Kraft liquor evaporator condensate characteristics
COD 1000–33,600 mg/L
Major organic component Methanol, 60–90% of COD
Anaerobic degradability 80–90% of COD
Compounds that inhibit
anaerobic metabolism
Reduced sulfur, resin acids, fatty acids,
volatile terpenes
COD, chemical oxygen demand.
Source: Refs 3 and 6.
460 Sumathi and Hung
© 2006 by Taylor & Francis Group, LLC
. solvent extractives that include fatty acids and resin acids;
. low-molecular-weight organic acids.
Table 4 shows the typical ranges of black liquor constituents and characteristics of Kraft
evaporator condensates. The composition of liquors may vary significantly, depending upon the
type of raw material used. Inorganic constituents in black liquor are sodium hydroxide, sodium
sulfate, sodium thiosulfate, sodium sulfide, sodium carbonate, and sodium chloride [11].
10.4.2 Sulfite Pulping Liquors (Red Liquors)
Table 5 summarizes the composition of ammonia, sodium, magnesium, and calcium base sulfite
pulping liquors. In general, spent ammonia base liquors have higher BOD
5
, COD, and dissolved
organics and exhibit more toxicity as compared to sodium, calcium, or magnesium base liquors.
Higher toxicity is attributed to ammoniacal compounds in the spent liquors. The sulfite-spent
liquors contain COD values typically ranging from 120–220 g/L and 50 –60% of these are
lignosulfonates [6]. The sulfite-spent liquor evaporator condensates have COD values in the
range of 7500 –50,000 mg/L. The major organic components in the condensates are acetic acid
(30–60% of COD) and methanol (10– 25% of COD). Anaerobic biodegradability of the
condensates is typically 50–90% of COD and sulfur compounds are the major inhibitors of
methanogenic activity [6].
Table 5 Composition of Ammonia, Sodium, Magnesium, and Calcium Base Sulfite Pulping Liquors
Parameter
Ammonia
base mill
a
Sodium
base mill
b
Magnesium
base mill
c
Calcium
base mill
d
Pulp liquor volume
(m
3
/ODT)
9.46 7.10 6.08 9.28
pH range 1.5–3.3 2.1– 4.8 $3.4 5.3
BOD (kg/ODT) 413 235 222 357
COD (kg/ODT) 1728 938 975 1533
Dissolved organics
(kg/ODT)
1223 595 782 1043
Dissolved inorganics
(kg/ODT)
12.5 226 126 250
Lignin as determined
by UV absorption
(kg/ODT)
892 410 501 800
Total sugars
(kg/ODT)
288 137 129 264
Reduced sugars (kg/
ODT)
212 74 106 238
Toxicity emission
factor
e
(TEF)
3663 714 – 422
a
Average data based on 4 mills;
b
Average data based on 12 mills;
c
Average data based on 2 mills;
d
Composition of one
mill;
e
Toxicity emission factors are based on static 96 hour bioassays and factored to the volume of liquor production.
ODT ¼ Oven dried ton of pulp.
Source: Refs. 3 and 10.
Treatment of Pulp and Paper Mill Wastes 461
© 2006 by Taylor & Francis Group, LLC
10.4.3 Thermomechanical Pulp (TMP), CTMP, and
Semichemical Pulping Liquors
Thermomechanical pulp (TMP) and CTMP pulping liquors exhibit COD values in the ranges of
1000–5600 mg/ L and 2500– 13,000 mg/L, respectively [6]. Lignin derivatives can constitute
anywhere from 15 to 50% of the soluble COD values in these spent liquors. The composition of
spent NSSC pulping liquors and evaporator condensates are shown in Table 6. In general,
anaerobic biodegradability of semichemical pulping and CTMP effluents are low as well as
inhibitory to methanogenic metabolism [6].
10.4.4 Spent Liquors from Agro-Residue Based Mills
Agro-residue mills typically employ a soda or alkaline sulfite pulping process [14]. Typical
compositions of the spent liquors generated from the small-scale, agro-residue utilizing pulp and
paper mills are shown in Table 7. It is evident from the table that 45– 50% of the total solids is
represented by lignin. Most of the lignin present in the black liquor is the high-molecular-weight
fraction, a key factor contributing to low BOD/COD ratio.
10.5 TOXICITY OF PULPING LIQUORS
A number of studies have evaluated the toxicity of pulping liquors, in particular the black liquors
generated from Kraft mills. Table 8 shows a partial representation of toxicity data compiled by
the NCASI (National Council of the Paper Industry for Air and Stream Improvement) and
McKee and Wolf for Kraft mill pulping wastewaters [15,16]. The table indicates that hydrogen
sulfide, methyl mercaptan, crude sulfate soap, and salts of fatty and resin acids are particularly
Table 6 Composition of Spent NSSC Pulping Liquor
Spent NSSC pulping liquor characteristics
Parameter Average value
Total solids (%) 12
Volatile solids (% of total solids) 48
COD (mg/L) 40,000
BOD
5
(mg/L) 25,000
Wood sugars (mg/L) 7000
Lignin (mg/L) 45,000
Acetate (mg/L) 18,000
pH range 6.5–8.5
Anaerobic degradability NR
Compounds that have the potential to
inhibit anaerobic process
Tannins, sulfur
compounds
NSSC pulping liquor condensate characteristics
COD 7000 mg/L
Major organic component Acetic acid, 70% of COD
Anaerobic degradability NR
Inhibitors of anaerobic degradation process Sulfur compounds
NR, not reported; COD, chemical oxygen demand; BOD, biochemical oxygen demand.
Source: Refs. 3 and 6.
462 Sumathi and Hung
© 2006 by Taylor & Francis Group, LLC
[...]... treatment systems for the pulp and paper mill discharges are activated sludge plants, aerated lagoons, and anaerobic reactors Sequential aerobicanaerobic systems (and vice versa) are a recent trend for handling complex wastewaters of pulp and paper mills that contain a multitude of pollutants The application of various types of biological reactor systems for treating pulp and paper mill effluents are discussed... Taylor & Francis Group, LLC Treatment of Pulp and Paper Mill Wastes 473 The major disadvantages of coagulation and precipitation are the generation of chemical sludge and the need for subsequent treatment of the sludge to eliminate the adsorbed toxic pollutants prior to disposal Advanced Oxidation Processes Destruction of chromophoric and nonchromophoric pollutants in pulp and paper effluents may be achieved... LLC Treatment of Pulp and Paper Mill Wastes Figure 3 Up-gradation of an existing activated sludge plant in Poland by installation of FlooBed reactors (from Ref 75) 477 © 2006 by Taylor & Francis Group, LLC 478 478 Figure 4 Up-gradation of a Danish pulp and paper mill activated sludge plant through installation of an anoxic selector (from Ref 76) Sumathi and Hung © 2006 by Taylor & Francis Group, LLC Treatment. .. method of pulp bleaching is being increasingly preferred by a number of pulp and paper industries, especially in the West, because it is a cost-effective and environmentally sound technology [32] The distinct advantages of enzyme-mediated pulp bleaching are: minimal energy input; specificity in reactivity, unlike that of chemicals; © 2006 by Taylor & Francis Group, LLC Treatment of Pulp and Paper Mill Wastes. .. detoxification and an increase in the biodegradability of bleach effluents by ozonation at low dosages [0.5 – 1 kg/ADMT (air-dried metric ton)] of pulp The researchers observed significant elimination of the residual COD by catalyzed ozone treatment of hardwood and softwood pulp and paper mill final discharges Such a treatment method may allow for reutilization of treated process waters and reduce consumption of. .. variety of substrates and therefore have significant potential for applications to pulp and paper effluent treatment [48,49] The applicability of the laccase mediator system for lignolytic bleaching of pulps derived from hard wood, soft wood, and bagasse has been reviewed and compared by Call and Mucke [47] The major advantage of enzymatic bleaching is that the process may be employed by the mills over and. .. final discharges The possibility of obtaining solid free effluents is a very attractive feature of this process Ultrafiltration was used by Jonsson et al [54] for the treatment of bleach plant effluents Figure 2 Flow sheet showing the unit processes employed by pulp and paper mills for effluent treatment © 2006 by Taylor & Francis Group, LLC Treatment of Pulp and Paper Mill Wastes 471 Sierka et al [55] described... principle Control of nutrients, aeration, low loading rates, introduction of equalization, and buffer basins seemed to be the key process control parameters for successful treatment BOD7 and COD removal averaged 94 and 82%, respectively, at paper mills while at pulp mills, the values were 82 and 60%, respectively All paper mill activated sludge plants required dosing of nitrogen and phosphorus Narbaitz... improving the texture of paper through the specific degradative action of these enzymes on pitch-derived extractives such as fatty acids and waxes The innovative approach of using microorganisms or microbial enzymes to reduce the consumption of chemicals in the pulp and paper industry is known as biopulping Biopulping has generated much interest among the pulp and paper industries because of the following... minimal clogging and reduces the risk of toxic effects of the incoming wastewater HRT values ranging from 0.2 to 2 days and VLR above 20 kg COD/m3 day are common [77] Figure 8 Diagrammatic representation of anaerobic filter process (from Ref 77) © 2006 by Taylor & Francis Group, LLC Treatment of Pulp and Paper Mill Wastes 485 Figure 9 Diagrammatic representation of fluidized and expanded bed reactor . PROBLEMS OF PULP AND PAPER INDUSTRIES Pulp and paper mills are a major source of industrial pollution worldwide. The pulping and bleaching steps generate most of the liquid, solid, and gaseous wastes. volume of liquor production. ODT ¼ Oven dried ton of pulp. Source: Refs. 3 and 10. Treatment of Pulp and Paper Mill Wastes 461 © 2006 by Taylor & Francis Group, LLC 10.4.3 Thermomechanical Pulp. years, Treatment of Pulp and Paper Mill Wastes 465 © 2006 by Taylor & Francis Group, LLC the pulp and paper industry has taken great strides forward in recognizing and solving many of the
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