WASTE MANAGEMENT OPTIONS TO REDUCE
GREENHOUSE GAS EMISSIONS FROM PAPER
J. G. Pickin1 and S. T. S. Yuen2
1. Environment Protection Authority, 477 Collins Street, Melbourne 3000
2. Department of Civil and Environmental Engineering, University of Melbourne,
Parkville, Victoria 3052
ABSTRACT
This study employed a spreadsheet model to simulate the greenhouse gas emissions (GGEs) from the paper
production and consumption system. The GGEs generated by paper in Australia during 1994/95 were
equivalent to about 13.5Mt of CO2, corresponding to almost 2.5% of Australia’s emission total. More than
half of this amount consisted of CH4 emissions from landfilled waste paper. Waste management options
effective in reducing GGE emissions from the paper life-cycle include incineration with energy recovery
(most effective), paper recycling, landfill gas recovery and composting. These findings can be extended to
other wood-based and organic wastes.
KEYWORDS
Greenhouse effect, methane, carbon dioxide, paper, waste management, recycling, landfill, bioreactor.
1.
INTRODUCTION
The enhanced greenhouse effect is likely to boost the earth’s average temperature by 1.5 to 4.5C during the
next century, leading to changed regional climates, increased global rainfall and a rise in sea levels of up to
50cm. Australia’s greenhouse gas emissions (GGEs) are mostly due to fossil fuel use and land clearing but
about 3% can be directly attributed to decay of organic material in landfills (NGGIC 1996a). Despite
increasing recycling, paper makes up a significant proportion of Australian municipal waste, comprising
some 10% of the total and 30% of the organic fraction (RRRC 1995; Yuen et al. 1996; WMC 1995).
This paper describes a life-cycle study of the greenhouse impact of paper (Pickin 1996) and assesses the
effects of various waste management options. A spreadsheet model simulated the GGEs from the paper
production and consumption system using a wide range of data on inputs and outputs, physical and chemical
processes and material mass flows. Two analyses were undertaken:
1. total GGEs associated with the paper life-cycle in Australia during 1994/95; and
2. ‘cradle-to-grave’ GGEs from one tonne of paper under a range of scenarios.
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2.
THE ANALYSIS FRAMEWORK
GGEs from the paper system are of two distinct origins:
 fossil fuel use during harvesting, manufacturing, transport etc; and
 uptake and emission of carbon-bearing gases during growth and decay of organic material used in paper
production (the organic material cycle).
The major GGE of fossil fuel use is carbon dioxide (CO2) emitted mostly as a by-product of the energy
harvesting process. Best available point data were used with no estimation of uncertainty.
Assessing the GGEs from the organic material cycle required construction of a carbon balance for the paper
life-cycle in which decay emissions were weighed against CO2 uptake by the plants used in the production
system. Data are scant, and some broad assumptions were necessary (Pickin 1996) including:
 Soil carbon was in equilibrium throughout the production system.
 Five percent of consumed paper entered net storage.
 Energy recovered from landfill gas and incineration of waste paper was exported from the system,
offsetting some GGEs from the use of conventional fuels.
 (Relevant to Analysis 1 only.) Logging for domestic pulp production occurred at the sustainable yield but
hardwood plantations were unlogged so their growth represented a net uptake of carbon. The export
woodchip industry was excluded.
The assumptions and rationale relating to waste processes are described below. The issue of concern is the
fate of the carbon in paper.
Decay in municipal landfills follows a predictable sequence in which aerobic processes producing CO2 are
succeeded by anaerobic processes producing a high proportion of methane (CH4), a potent greenhouse gas.
The rate of progression is highly variable and is critically dependent on the amount of moisture. Most
organic carbon leaving a landfill does so as CO2 or CH4, a minor proportion leaches out in solution and the
rest becomes incorporated in humic materials and microorganism cells in the landfill (Belevi and Baccini
1989; van den Broek and Sinanian 1990).
Three questions are pertinent:
(a) What is the average decay rate for paper in landfills? (This is relevant only in Analysis 1 - the scenarios
of Analysis 2 assume production at a constant rate and a system in equilibrium.)
(b) What is the average proportion of organic carbon in paper that is gasified during decay?
(c) What are the average proportions of CO2 and of CH4 formed from the gasified carbon?
(a) Paper displays “a high degree of biodegradability in a microbially active environment” and significant
deterioration can occur in a matter of weeks (RTI 1990: 1-3). The major constituents, cellulose and
hemicellulose, are readily broken down when conditions are suitable (Barlaz et al. 1989). Deterioration is
generally slower in paper that is derived from mechanical pulp (RTI 1990: i; IIED 1995: C100), which
contains a high proportion of lignin - a “natural plastic” which is “slowly metabolised by microorganisms in
air” but is “biologically inert in the absence of molecular oxygen” (Zeikus 1980: 105). The ‘typical’ decay
time of paper in landfills estimated in various studies is shown in Table 1.
For Analysis 1, waste paper degradation was assumed to follow a simplified exponential decay curve with a
half-life of five years. Although some paper may survive more than 20 years, particularly if it is lignin-rich,
the proportion was assumed to be negligible.
(b) The proportion of biodegradable carbon gasified during decay is temperature dependant. Based on
observed mass balances and gas production rates in landfills and laboratory experiments, and an estimated
Second International Conference on Environmental Management (ICEM2)
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average temperature in the anaerobic zone of landfills of 35°C, the amount of carbon assumed to be gasified
was 77% (Bingemer and Crutzen 1987, NGGIC 1996b: 11).
(c) In relation to the last question it was assumed that paper decays similarly to other organic material,
producing CH4 to CO2 in the proportion 1:1 (NGGIC 1996b: 10).
TABLE 1
ESTIMATED TYPICAL DECAY TIMES FOR LANDFILLED PAPER
Source
Bingemer and Crutzen (1987)
Barson and Gifford (1989: 438)
Grierson et al. (1991: 24)
NGGIC (1994)
Diaz (pers. comm.)
3.
Assumed Decay Time of Paper
5-20 years
Exponential decay function with a half-life of one year
1 to 5 years
1 year
30 years maximum (chemically pulped paper)
ANALYSIS 1 RESULTS: AUSTRALIAN GREENHOUSE GAS EMISSIONS FROM PAPER,
1994/95
The GGEs generated by paper in Australia during 1994/95 were calculated at about 13.5Mt of CO2
equivalent - almost 2.5% of Australia’s GGEs in that year. CH4 represented 59% of the total net emissions
and the rest was almost all CO2.
The GGEs were divided into eight emission categories as shown in Figure 1. GGEs from fossil carbon were
dominated by the manufacturing phase, with pulping, recycling and paper making summing to 42% of the
total. The combined effect of processing, commerce, material acquisition and transport was a further 20%.
The largest category was CH4 emissions from landfilled paper which gave rise to over 50% of the net
emissions. This is about 6% of the CH4 emitted in Australia during 1994/95 (NGGIC 1996a: 17).
Fossil fuel use in material
acquisition & transport
Fossil carbon use in pulping &
recycling
Fossil fuel use in paper making
Fossil fuel use in processing &
commerce
Methane from landfilled waste
paper
Methane & nitrous oxide from
other degradation processes
Offset by energy recovery from
waste paper
Net carbon dioxide balance in
the organic material cycle
-3
-2
-1
0
1
2
3
4
5
6
7
Greenhouse gas emissions (Mt CO2 equivalent)
Figure 1: GGEs from the paper life-cycle, Australia 1994/95, by emission category.
4.
ANALYSIS 2 RESULTS: EMISSIONS FROM A TONNE OF PAPER IN A RANGE OF
SCENARIOS
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This analysis modelled GGEs from the life-cycle of a tonne of paper under a range of conditions in order to
compare the effects of different waste management options (Pickin 1996). Three options were simulated:
(a) paper recycling;
(b) waste paper incineration with energy recovery; and
(c) various adjuncts to paper recycling.
In all cases logging was assumed to occur at the sustainable yield.
Greenhouse emissions
per t paper
(t CO2 equivalent)
Figure 2 demonstrates the effect of option (a). GGEs fall from 7.0t of CO2 equivalent with no recycling to
4.6t with 60% recycling. Figure 3 gives GGEs in the 8 emission categories used above. This shows that
higher recycling rates cause changes in five of the categories but by far the most significant effect is a large
decrease in CH4 emissions from landfills due to a lower input of paper.
8
No recycling
30% recycling
60% recycling
6
4
2
0
Figure 2: Total life-cycle GGEs at different recycling rates.
No recycling
30% recycling
60% recycling
Fossil fuel use in material
acquisition & transport
Fossil carbon use in pulping &
recycling
Fossil fuel use in paper making
Fossil fuel use in processing &
commerce
CH4 from landfilled waste paper
CH4 & N2O from other degradation
processes
Offset by energy recovery from
waste paper
Net CO2 balance in the organic
material cycle
-1
0
1
2
3
Greenhouse gas emissions per tonne of paper
(t CO2 equivalent)
4
5
Figure 3: Life-cycle GGEs at different recycling rates, by emission category.
In option (b) the same waste paper recovery rates as above are modelled, but this time the waste is
incinerated to produce electricity. The fall in GGEs with recovery, shown in Figure 4, is sharper than with
recycling, indicating that this approach is more effective for GGE abatement. The major difference is a large
gain from using the recovered energy to offset GGEs from fossil fuel usage, as shown in Figure 5.
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Greenhouse emissions
per t paper
(t CO2 equivalent)
8
No incineration with energy
recovery
30% incineration with
energy recovery
60% incineration with
energy recovery
6
4
2
0
Figure 4: Total life-cycle GGEs at different rates of waste paper incineration with energy recovery.
No incineration with energy recovery
30% incineration with energy recovery
60% incineration with energy recovery
Fossil fuel use in material
acquisition & transport
Fossil carbon use in pulping &
recycling
Fossil fuel use in paper making
Fossil fuel use in processing &
commerce
CH4 from landfilled waste paper
CH4 & N2O from other degradation
processes
Offset by energy recovery from
waste paper
Net CO2 balance in the organic
material cycle
-4
-3
-2
-1
0
1
2
Greenhouse gas emissions per tonne of paper
(t CO2 equivalent)
3
4
5
Figure 5: Life-cycle GGEs at different rates of waste paper incineration with energy recovery,
by emission category.
Greenhouse emissions
per t paper
(t CO2 equivalent)
Option (c) explores post-consumer management further, comparing the effect of three waste treatments as
adjuncts to a 50% recycling rate. From left to right, Figure 6 shows the effect of:
 50% recycling and no additional waste treatment (this approximates the GGEs from a typical Australianconsumed tonne of paper under current conditions, estimated at 5.0t of CO2 equivalent);
 50% recycling and recovery of 30% of CH4 emitted from landfilled paper for generating electricity;
 50% recycling and 25% composting of waste paper; and
 50% recycling and 25% incineration with energy recovered for electricity production.
Again, incineration produces the biggest reductions due to its efficient energy recovery, but landfill gas
recovery and composting are also beneficial.
No other waste treatment
5
4
30% landfill gas recovery
3
25% composting
2
1
25% incineration with energy
recovery
0
Figure 6: Total life-cycle GGEs for various adjuncts to 50% recycling.
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5.
THE SIGNIFICANCE OF PLANNING HORIZON IN GGE ASSESSMENT
Comparison of the warming effect of different greenhouse gases employs the unit ‘Global Warming
Potential’ (GWP), defined as the degree of warming caused by unit mass of gas relative to CO2 from the start
of the assessment period to some selected planning horizon. A time frame must be specified because each
gas has a different atmospheric residency period.
CH4 has a strong greenhouse warming effect but a relatively short atmospheric residency time, and
consequently its GWP falls sharply from 56 over 20 years to only 6.5 over 500 years (IPCC 1996). Most
GGE assessments (including this work) use an intermediate 100 year planning horizon over which CH4 has a
GWP of 21.
Greenhouse emissions
per t paper
(t CO2 equivalent)
Figure 7 illustrates the effect of altering the planning horizon in assessing the GGEs from a typical tonne of
paper under current conditions. The 5.0t of GGEs in a 100 year planning horizon, shown in the first column,
becomes 8.9t over 20 years and 3.3t over 500 years. This does not imply that the actual warming effect
decreases with assessment time, but rather that the mass of CO2 required to produce a warming effect
equivalent to that of the gases actually emitted declines with time, following the GWP of CH4. The
consequence of this variability is that CH4 from landfills dominates GGEs over the short-term and fossil
carbon use in manufacturing processes dominates over the long-term.
10
8
6
4
100 years
20 years
500 years
2
0
Figure 7: Total life-cycle GGEs assessed over different time scales.
6.
DISCUSSION
Limitations in the data mean the results are indicative rather than precise. The most critical uncertainty
relates to the fate of organics in landfills. The input data were derived from rather scant landfill literature
which is disputed by some. The archaeologists Rathje and Murphy (1992), for example, deny that rapid
biodegradation in landfills is the norm, and pulp and paper industry researchers Gilbreath (1991) and Stott
(1991) conclude that paper in many landfills will emit little or no greenhouse gas.
These findings allude to the ‘dry tomb’ management approach which aims to seal landfills from water
ingress to minimise biodegradation. This approach is increasingly regarded as flawed since containment is
bound to eventually fail, permitting biodegradation to begin (Ham et al. 1993; Lee and Jones-Lee 1993;
Muntoni et al. 1995). However, the dry tomb approach will delay biodegradation and the emission of
greenhouse gases. In contrast, the ‘bioreactor’ landfill design - which aims to speed up decay processes to
achieve rapid stabilisation (Yuen et al. 1994) - will accelerate GGE production and concentrate the
greenhouse impact nearer to the present.
The results of the analyses demonstrate the significance of landfills as sources of GGEs from paper and the
importance of post-consumer waste management in controlling these emissions. The pulp and paper
industry’s main GGE abatement efforts have focused on production processes (Jones 1995) but
improvements in recycling rates in recent years have probably provided greater benefits, mainly through
directing waste paper away from landfills.
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Table 2 lists some of the waste management options for reducing GGEs from paper together with an
assessment of their potential effectiveness, the time frame over which they deliver benefits (dependent on
whether they affect CH4 or CO2 emissions) and the relevant management organisations.
The most promising option is incineration of waste paper for energy recovery in place of fossil fuels. Both
CO2 and CH4 emissions are reduced, providing both long and short-term benefits. Incineration of municipal
waste with energy recovery is practiced widely overseas but has not been adopted in Australia, partly because
of community fear that incinerator emissions may pose a health risk (Winder 1993).
TABLE 2
WASTE MANAGEMENT OPTIONS FOR GREENHOUSE GAS EMISSION ABATEMENT IN THE PAPER LIFE-CYCLE
1.
2.
3.
4.
Waste management option
Increase recycling
Incinerate waste paper with energy
recovery
Recover more landfill gas
Compost waste paper
Potential for
reducing GGEs
High
Very high
Time frame over
which benefit occurs*
Short-term
Short & long-term
Management
organisation(s)
Gov’t, pulp & paper industry
Gov’t, energy industry
High
High
Short & long-term
Short-term
Gov’t, energy industry
Gov’t, particularly local
* Short-term = years or decades; long-term = centuries
Recycling is also beneficial, providing mostly short-term gains from displacement of CH4 emissions. It is
particularly important as the only current large scale alternative to landfilling.
Landfill gas energy recovery is now occurring at a number of Australian landfills but the recovery rate is still
very small in relation to the quantity of gas emitted. Th process is probably cheaper and less politically
controversial than incineration but has less potential greenhouse benefit.
Where recycling is uneconomic, composting is perhaps the cheapest post-consumer management alternative
to landfills. Its greenhouse benefit derives from limiting CH4 production and retaining carbon as organic
matter.
7.
CONCLUSION
This study provides guidance to the pulp and paper industry and to government in relation to greenhouse gas
abatement strategies. The principle of Extended Producer Responsibility would advocate a pulp and paper
industry role in appropriate management of waste paper.
The findings can be extended to other wood-based products and the organic wastes which collectively form
over half Australia’s municipal waste stream (Bullock 1994: 4; RRRC 1995: 9). A strong general argument
can be made in favour of composting, landfill gas recovery and, especially, incineration with energy recovery
based on the reduced GGEs afforded.
ACKNOWLEDGMENTS
Many people contributed towards the preparation of this work. We are particularly indebted to Professors
Michael Webber and David Evans of the University of Melbourne and Dr. Huntley Higgins from CSIRO
Division of Forestry and Forest Products.
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