WASTE MANAGEMENT OPTIONS TO REDUCE GREENHOUSE GAS EMISSIONS FROM

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06096 DEPARTMENT OF ENVIRONMENTAL PROTECTION CHAPTER 900 BIOMEDICAL WASTE

PAPER AND THE GREENHOUSE EFFECT

WASTE MANAGEMENT OPTIONS TO REDUCE GREENHOUSE GAS EMISSIONS FROM PAPER

J. G. Pickin¹ and S. T. S. Yuen²

Environment Protection Authority, 477 Collins Street, Melbourne 3000
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.

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:

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.)
What is the average proportion of organic carbon in paper that is gasified during decay?
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 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	Assumed Decay Time of Paper
Bingemer and Crutzen (1987)	5-20 years
Barson and Gifford (1989: 438)	Exponential decay function with a half-life of one year
Grierson et al. (1991: 24)	1 to 5 years
NGGIC (1994)	1 year
Diaz (pers. comm.)	30 years maximum (chemically pulped paper)

3. 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).

WASTE MANAGEMENT OPTIONS TO REDUCE GREENHOUSE GAS EMISSIONS FROM

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

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:

paper recycling;
waste paper incineration with energy recovery; and
various adjuncts to paper recycling.

In all cases logging was assumed to occur at the sustainable yield.

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.

WASTE MANAGEMENT OPTIONS TO REDUCE GREENHOUSE GAS EMISSIONS FROM

Figure 2: Total life-cycle GGEs at different recycling rates.

WASTE MANAGEMENT OPTIONS TO REDUCE GREENHOUSE GAS EMISSIONS FROM

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.

WASTE MANAGEMENT OPTIONS TO REDUCE GREENHOUSE GAS EMISSIONS FROM

Figure 4: Total life-cycle GGEs at different rates of waste paper incineration with energy recovery.

WASTE MANAGEMENT OPTIONS TO REDUCE GREENHOUSE GAS EMISSIONS FROM

Figure 5: Life-cycle GGEs at different rates of waste paper incineration with energy recovery,

by emission category.

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 Australian-consumed 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.

WASTE MANAGEMENT OPTIONS TO REDUCE GREENHOUSE GAS EMISSIONS FROM

Figure 6: Total life-cycle GGEs for various adjuncts to 50% recycling.

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.

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.

WASTE MANAGEMENT OPTIONS TO REDUCE GREENHOUSE GAS EMISSIONS FROM

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.

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

Waste management option	Potential for reducing GGEs	Time frame over which benefit occurs*	Management organisation(s)
Increase recycling	High	Short-term	Gov’t, pulp & paper industry
Incinerate waste paper with energy recovery	Very high	Short & long-term	Gov’t, energy industry
Recover more landfill gas	High	Short & long-term	Gov’t, energy industry
Compost waste paper	High	Short-term	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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