Environmental impact of pulp and paper mills

Abstract

The paper aims to present the environmental impact of pulp and paper manufacturing and the most important production and control practices to minimizing this impact. The environmental consequences of manufacturing pulp and paper from pulping and bleaching processes are discussed in qualitative and quantitative terms. In these processes, sulfur compounds and nitrogen oxides are emitted to the air, and chlorinated and organic compounds and nutrients are discharged to the wastewaters. Large quantities of solid wastes and sludges are also generated.

Full text

Environmental Engineering and Management Journal
January 2012, Vol.11, No. 1, 81-85
http://omicron.ch.tuiasi.ro/EEMJ/
“Gheorghe Asachi” Technical University of Iasi, Romania
ENVIRONMENTAL IMPACT OF PULP AND PAPER MILLS
Dan Gavrilescu
1
, Adrian Catalin Puitel
1
, Gheorghe Dutuc
2
, Grigore Craciun
2
1
“Gheorghe Asachi” Technical University of Iasi, Faculty of Chemical Engineering and Environmental Protection,
Department of Pulp, Paper and Fibers, 73 D. Mangeron Street, 700050 Iasi, Romania,
2
SOMES Pulp and Paper Mill, 63 Bistritei Str., Dej, Romania
Abstract
The paper aims to present the environmental impact of pulp and paper manufacturing and the most important production and
control practices to minimizing this impact. The environmental consequences of manufacturing pulp and paper from pulping and
bleaching processes are discussed in qualitative and quantitative terms. In these processes, sulfur compounds and nitrogen oxides
are emitted to the air, and chlorinated and organic compounds and nutrients are discharged to the wastewaters. Large quantities of
solid wastes and sludges are also generated.
Key words: air emissions, environment, liquid discharges, paper, pulp, solid wastes
Received: September, 2011; Revised final: January 2012; Accepted: January, 2012

Author to whom all correspondence should be addressed: e-mail: gda@ch.tuiasi.ro
1. Introduction
Pulp and paper are manufactured from raw
materials containing virgin cellulosic fibers on wood
basis and recovered paper (Bobu and Gavrilescu,
2010). Another important source of cellulosic fibers
originates from nonwood raw materials such cereal
straw, reeds, esparto grass, jute, flax, and sisal
(Gavrilescu et al., 2009; González-García et al., 2010;
Puitel et al., 2011; Rodríguez et al., 2010).
The main steps in pulp and paper manufacture
are: raw material preparation, (wood debarking and
chipping), wood pulping; pulp bleaching; paper
manufacturing. Pulp mills and paper mills may exist
separately or as integrated operations. Pulp
manufacturing starts with raw material preparation,
which includes wood debarking, logs chipping and
chips screening. In the chemical pulping process the
fibers are liberated from the wood matrix as the lignin
is removed by dissolving in the cooking liquor at a
high temperature.
In the kraft pulp process the active cooking
chemicals are sodium hydroxide (NaOH) and sodium
sulphide (Na
2
S).
As a result of the large amount of sodium
hydroxide used, the pH value at the start of a cook is
between 13 and 14 (Sixta et al., 2006). After cooking,
pulp is washed and screened, and then is bleached
(Fig. 1) (Puitel et al., 2010). The objective of pulp
bleaching is to remove residual lignin remaining after
cooking in order to enhance pulp brightness. Oxygen,
hydrogen peroxide, ozone, peracetic acid, sodium
hypochlorite, chlorine dioxide, chlorine, and other
chemicals are used to transform lignin into a soluble
form. An alkali, such as sodium hydroxide is
necessary in the bleaching process to extract the
alkali-soluble form of lignin. In modern pulp mills,
oxygen is normally used in the first stage of
bleaching. The trend is to avoid the use of any kind of
chlorine chemicals and employ “Total Chlorine-Free”
(TCF) bleaching (Bouiri and Amrani, 2010;
Gavrilescu, 2010; Iosip et al., 2010; McKague and
Carlberg, 1996; Takagi and Nakagawa, 2009).
The use of elemental chlorine for bleaching is
not recommended. Only “Elemental Chlorine Free”
(ECF) processes are acceptable, and from an
environmental perspective, TCF bleaching is
preferred (Craciun et al., 2010; Gavrilescu, 2010).

Gavrilescu et al./Environmental Engineering and Management Journal 11 (2012), 1, 81-85
82
Fig. 1. Overview of the processes of a pulp mill
Paper is made from pulp by deposition of
cellulosic fibers from a water suspension onto a
moving forming fabric that also removes water from
the pulp. The water remaining in the wet web is
removed by pressing and then by drying. Chemical
additives are added to impart specific properties to
paper, and pigments may be added for color (Ek et al.,
2009). Fig. 2 shows the papermaking process scheme.
In an integrated pulp and paper mill, there are
various sources of pollution, as is presented in Table
1 (Hynninen, 1998). Table 1 shows that in each step
of pulp and paper manufacture various pollutants are
generated in air emissions, as liquid effluents and as
solid wastes.
2. Pollutants quantities and characteristics
The environmental impact generated by the
manufacture of pulp and paper results mainly from
the wood pulping and pulp bleaching. In pulping
processes, sulfur compounds and nitrogen oxides are
emitted to the air, and during pulp bleaching
chlorinated and organic compounds and nutrients are
discharged to the wastewaters. The environmental
impact of paper manufacture is lower, wastewater
discharge being the most important source of
pollution.
2.1. Air emissions
Chemical pulping is the main source for air
emissions in the pulp and paper industry, mainly due
the fact that chemical pulping is operating at higher
temperatures.
Table 1. Pollution sources in producing pulp and paper
(adapted from Hynninen, 1998)
Main imput Process step Pollutants
Raw material
(wood)
Wood
preparation
Solid wastes
Wastewater
Chemicals
Energy
Pulp
manufacture
Air emissions
Used water
Process water
Pulp washing
and screening
Dissolved material
Residual chemicals
Wastewater
Chemicals
Energy Pulp
bleaching
Air emissions
Dissolved material
Residual chemicals
Wastewater
Energy Pulp drying Air emissions
Energy
Water
Chemicals
Paper
manufacture
Solid wastes
Dissolved material
Residual chemicals
Wastewater
Within chemical pulping, the origins for air
emissions can be found from the chips storage,
cooking, pulp washing, bleaching, bleaching
chemicals preparation, chemicals recovery,
evaporation plant, bark furnace, recovery and
auxiliary boilers, white liquor preparation, the lime
kiln, storage tanks and in case of market pulp, pulp
drying process. Table 2 shows the process stages and
the generated emissions.

Environmental impact of pulp and paper mills
83
Fig. 2. Papermaking process
Major source of air emissions in a pulp mill is
recovery boiler (Table 3). These emissions are mainly
represented by sulfur dioxide but there are also
particulate emissions, nitrogen oxides and
malodorous compounds. NOx emissions depend on
nitrogen content in the black liquor (dry solids
content) and support fuel rate used in recovery boiler.
Table 2. Air emissions in a kraft pulp mill
(Biermann, 1996)
Process Emissions
Energy generation
Recovery boiler
Lime kiln
Burning malodorous
gases
Pulp bleaching
Others
Particulates, SO
2
, NOx
Particulates, SO
2
, TRS
Particulates, TRS
SO
2
, TRS
ClO
2
, VOC (methanol,
chloroform)
VOC
Steam and electricity generating units using
coal or fuel oil emit fly ash, sulfur oxides, and
nitrogen oxides (Table 3). Coal burning in a power
boiler can emit fly ash at the rate of 100 kg/t of pulp
(Meij, 2000).
2.2. Liquid effluents
Pulp and paper manufacture represents a large
consumer of process water. Wastewater is discharged
at a rate of 20–100 cubic meters per metric ton of
product (Gavrilescu et al., 2008). Wastewater is high
in biochemical oxygen demand (BOD), total
suspended solids, chemical oxygen demand (COD),
nitrogen and phosphorus (Table 4). In addition,
chlorinated organic compounds are generated, which
include dioxins, furans, and other absorbable organic
halides (AOX), that represent 0–4 kg/t of pulp.
In producing chemical pulp, effluent rate
represents 20-50 m
3
/t of pulp, which contains up to 15
kg/t suspended solids. Wastewater from chemical
pulping contains 5–20 kg of BOD/t of pulp and 20-40
kg of COD/t. The main source of nutrients, nitrogen,
and phosphorus compounds is raw material used in
pulp manufacture.
Table 3. Average emissions to the atmosphere from kraft
pulp mill (Genco and Heiningen, 2001)
Source of
emission
Total
gaseous S
kg/t
NOx
kg/t
Particulates
kg/t
Recovery
boiler
Lime kiln
Bark boiler
Digesters
0.01-2.0
0.07-0.7
0.02-0.06
0.01-2
0.8-1.8
0.02-0.6
0.03-0.2
-
0.2-1.8
0.02-0.9
0.03-0.3
-
Total
emissions
from
pulp mill
0.04-4.1 0.85-2.60 0.25-3.1
Paper manufacture generates 15-40 m
3
of
wastewater per tone of paper depending on the paper
grade. Wastewaters resulting from pulp and paper
manufacture must be processed in a wastewater
treatment plant.
2.3. Solid waste
Pulp manufacture generates large quantities of
solid wastes. Solid waste includes wood waste
(mainly bark), sodium salts from recovery boiler, pulp
screening rejects and dregs and gritt from causticizing
plant. In addition, ashes are generated during burning
of wood wastes and sludges. An overall view of the
solid waste rates in a pulp mill is presented in Table 5
(Gavrilescu, 2004).
Wood waste represents the most important
residue of a pulp mill, and they are represented by
bark, sawdust and other wood fragments. Wood
wastes are incinerated in a boiler to produce energy
for the mill. Pulp screening rejects (knots) are mixed
with wood residue and are burned in the same boiler.
Dregs and gritt generated in the causticizing plant
(15-40 kg/t of pulp) are landfilled (Gavrilescu, 2005).

Gavrilescu et al./Environmental Engineering and Management Journal 11 (2012), 1, 81-85
84
Table 4. Effluent loads from the manufacture of pulp and paper (European Commission, 2001)
Product
Effluent
m
3
/t
Suspended
solids
kg/t
BOD
kg/t
COD
kg/t
N
g/t
P
g/t
Pulp manufacture
Unbleached 20-40 12-15 5-10 20-30 200-400 80
Bleached 30-50 10-15 14-18 25-40 400-600 100
Paper manufacture
Packaging 15-30 5-10 2-4 4-8 100-200 15
Newsprint 10-25 5-10 1-3 2-4 10-20 5
Sanitary 20-40 5-10 1-3 3-6 50-80 8
Table 5. Waste generation in a sulfate pulp mill
Solid wastes Yield, kg/t pulp
A. Wood wastes:
1. Sawdust
coming from the slasher deck
2. Bark
falling from the debarking drum
3. Pins and fines
from chip screening
4. Wood waste
from woodyard
Total A:
B. Knots from pulp deknotting
C. Sodium salts from recovery boiler
D. Dregs and grit from causticizing:
1. Dregs
2. Grit
Total D:
Total A, B, C, D:
10-30
100-300
50-100
0-20
160 – 450
25-70
5-15
5-10
10-30
15-40
220-615
The second residue as importance of the pulp
and paper mill is the sludge generated during
wastewater treatment. The volume of sludge varies
greatly according to the paper grade being
manufactured.
Pulp production generates 20-25 kg/t sludge
and paper manufacture produces another 5-10 kg/t. If
the paper is produced from recovered paper, sludge
quantity rise up to roughly 150 kg/t of paper. After
dewatering, sludge is burned (Gavrilescu, 2008).
3. Pollution prevention and control
The most significant environmental issues are
the discharge of chlorine-based organic compounds
from bleaching and of other toxic organics. The
unchlorinated material is essentially black liquor that
has escaped the mill recovery process.Some mills are
approaching 100% recovery.
Industry developments demonstrate that total
chlorine-free bleaching is feasible for many pulp and
paper products but cannot produce certain grades of
paper. The adoption of these modern process
developments, wherever feasible, is encouraged.
Pollution prevention programs should focus on
reducing wastewater discharges and on minimizing
air emissions. Process recommendations may include
the following (Gavrilescu et al., 2008; EIPPCB, 2001;
World Bank, 1996):
a. Use energy-efficient pulping processes wherever
feasible. Acceptability of less bright products should
be promoted.
b. Minimize the generation of effluents through
process modifications and recycle wastewaters,
aiming for total recycling.
c. Reduce effluent volume and treatment
requirements by using dry instead of wet debarking;
recover pulping chemicals by black liquor
evaporation and burning of black liquor in a recovery
furnace; recover cooking chemicals by recausticizing
of green liquor; use high-efficiency pulp washing and
bleaching equipments.
d. Reduce bleaching requirements by process design
and operation. Use the following measures to reduce
emissions of chlorinated compounds to the
environment: before bleaching, reduce the lignin
content in the pulp by extended cooking and by
oxygen delignification; optimize pulp washing prior
to bleaching; use TCF or ECF bleaching systems; use
oxygen, ozone, hydrogen peroxide, peracetic acid, or
enzymes as substitutes for chlorine-based bleaching
chemicals; recover and incinerate maximum material
removed from pulp mill.
e. Minimize sulfur emissions to the atmosphere by
using a modern low-odor black liquor recovery boiler.
f. Minimize unplanned discharges of wastewater
and black liquor, caused by equipment failures,
human error, and faulty maintenance procedures, by
training operators, establishing good operating

Environmental impact of pulp and paper mills
85
practices; provide sumps and other facilities to
recover liquor spills from the process.
4. Conclusions
1. The environmental impact of pulp and paper
manufacture results mainly from wood pulping and
pulp bleaching processes. The pollutants are
represented by sulfur compounds and nitrogen oxides
that are emitted to the air, and by bleaching
chlorinated and organic compounds and nutrients that
are discharged to the wastewaters.
2. Pulp and paper manufacture need a large volume
of process water. Wastewaters are discharged at a rate
of 20–100 cubic meters per ton of product, and these
are high in biochemical oxygen demand (BOD), total
suspended solids, chemical oxygen demand (COD),
nitrogen and phosphorus.
3. Wood wastes and sludge represent the most
important residues of a pulp and paper mill. These
wastes are used to obtain energy by their burning in a
suitable boiler.
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