ncasi 

NATIONAL COUNCIL FOR AIR AND STREAM IMPROVEMENT, INC. 

P.O. Box 13318, Research Triangle Park, NC 27709-3318 

Phone (919) 941-6400 Fax (919) 941-6401 Reid A. Miner 

 Vice President - 

 Sustainable Manufacturing 

 Phone (919) 941-6407 

 Fax (919) 941-6401 

 e-mail RMiner@ncasi.org 

Environmental research for the forest products industry 

May 21, 2008 

TO: Ms. Becky Nicholson, RTI International 

CC: Brad Upton, Ron Yeske, Al Lucier, Jay Unwin – NCASI 

 Rhea Hale, Jerry Schwartz – AF&PA 

FROM: Reid Miner 

SUBJECT: Calculations documenting the greenhouse gas emissions from the pulp and paper industry 

In your email of May 13, you asked a number of questions related to greenhouse gas emissions from pulp 

and paper mills. Herein, I attempt to address some of those questions. The material below is drawn largely 

from analyses done by others on our staff, especially Jay Unwin and Brad Upton. 

TOTAL INDUSTRY EMISSIONS

We have been assisting AF&PA in estimating CO2 emissions related to fossil-fuel consumption at 

AF&PA member companies as part of the industry’s commitment in the Climate VISION program. Rhea 

Hale will send you a copy of the latest VISION report which is now undergoing review. 

In a separate effort, we have been working with the U.S. Forest Service to develop a carbon and 

greenhouse gas profile of the U.S. forest products industry. Although that analysis is not complete, Brad 

Upton has finished his calculation of total industry emissions related to fossil fuel consumption (CO2, 

CH4 and N2O) and biomass fuel consumption (CH4 and N2O). The following text is copied from the draft 

report containing the full profile. 

“Almost all direct GHG emissions from forest products industry manufacturing facilities are the 

result of fossil fuel combustion. The industry satisfies much of its energy requirements by also 

burning large quantities of biomass fuels, but the CO2 released from biomass combustion is not 

included in GHG totals because it contains biogenic carbon.... Small amounts of nitrous oxide 

(N2O) and methane (CH4) are also released during combustion of biomass fuels and fossil fuels. 

[Note: These biomass-related emissions of CH4 and N2O are added to fossil fuel-derived 

greenhouse gas emissions below.] 

... Pulp and paper sector energy consumption during 1990 and 2004 were determined from data 

obtained from the American Forest and Paper Association (AF&PA). GHG emission factors 

from IPCC (1997) were used in conjunction with this data to calculate direct emissions from fuel 

combustion. The IPCC Tier 1 CH4 and N2O emission factors were used with the exception of 

CH4 and N2O from biomass fuel combustion, which were estimated using emission factors from 

the International Council of Forest and Paper Associations and NCASI (ICFPA/NCASI) 

[reference omitted]. Emission factors are shown in Table 2.1 [table omitted]. GHG emission 

estimates are expressed as CO2 equivalents (CO2 eq.) and include CO2, CH4, and N2O, including 
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CH4 and N2O from combustion of biomass fuels. Global warming potentials (GWPs) of 21 and 

310 were used for CH4 and N2O, respectively. 

... Available fuel consumption data for 2004... was obtained from [AF&PA] survey responses 

representing 84,660,000 metric tons of production. Total US pulp and paper sector production in 

2004 (including paper, paperboard, and market pulp production) was estimated to be 102,340,000 

metric tons based on data published by AF&PA (reference omitted). Therefore, in order to arrive 

at a representation of the total US pulp and paper industry the emission estimates based on 2004 

AF&PA energy data were multiplied by a factor of 1.21 (= 102,340,000 ÷ 84,660,000). 

Pulp and paper industry manufacturing direct emissions from fuel consumption were ... 57.7 

[million metric tons] CO2 eq. in 2004...“ 

We have not estimated biomass-derived CO2 emissions because they are not included in greenhouse gas 

emission totals in any of the protocols with which we are familiar. Furthermore, in our experience, 

estimates of biomass-derived CO2 emissions are never used. 

GREENHOUSE GAS EMISSIONS BY EMISSION SOURCE

Our estimates of greenhouse gas emissions from combustion are based on corporate-wide reporting of 

fuel consumption preventing many of the disaggregated estimates you seek. We have, however, generated 

estimates for some of the non-combustion operations you listed and these are discussed below. 

On-site landfills

Summary: NCASI’s analysis indicates that these emissions could reasonably be excluded from EPA’s 

registry because they are small (on the order of 1% of the industry’s direct emissions) and estimated only 

with great uncertainty. Additional information is provided below. 

When the ICFPA/NCASI calculation tools for pulp and paper mills were first developed, the intent was to 

be as comprehensive as possible because (a) the tools would serve a range of purposes and (b) the 

experience at that point was inadequate to know whether certain emissions were so small that they could 

be ignored. At the time, there were no data on the methane emissions from mill landfills, so in the interest 

of being as comprehensive as possible, NCASI included calculation methods that were based largely on 

estimation methods for MSW landfills. Several years ago, NCASI began work to develop estimation 

methods better tailored to mill landfills. 

Wastewater treatment plant (WWTP) residuals (i.e. sludges) and ash comprise most of the material being 

placed in pulp and paper mill landfills (see Solid Waste Management Practices in the U.S. Paper Industry 

- 1995. NCASI Technical Bulletin No. 793, 1999). Because the ash is almost completely inert, any 

greenhouse gas emissions from mill landfills are likely attributable to WWTP residuals. Therefore, to 

better understand the contribution of mill landfills to methane emissions and carbon sequestration, 

NCASI conducted laboratory and field tests on several WWTP residuals. The work was only recently 

completed, but we can share some preliminary findings that help characterize the role of landfills. 

NCASI conducted laboratory studies using the methods of Dr. Morton Barlaz at North Carolina State 

University. These methods are the same as those used in USEPA studies to characterize landfill 

degradation of municipal solid waste, most of which have also been conducted by Dr. Barlaz. The 

laboratory studies indicate the ultimate methane yield of the WWTP residuals and, conversely, the 

fraction of the carbon in the WWTP residuals that is essentially non-degradable under anaerobic 

conditions. This non-degradable fraction of the organic carbon remains stored in landfills for very long 
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periods, sequestering the carbon. The laboratory studies yield data to calculate values for the parameter 

Lo, which is the “ultimate” cubic meters of methane generated per dry metric ton of waste. 

To calculate methane generation over time using EPA’s methods, you also need to know the first order 

rate parameter, k. NCASI constructed field test cells and operated them for over 5 years to generate data 

that could be used to estimate k. Below we summarize the findings of both the laboratory and field 

studies. 

The normal method to estimate methane emissions from landfills assumes that the generation process 

occurs according to first order kinetics. The rate of generation is defined by two parameters, a rate 

parameter, k (yr-1), and an ultimate yield parameter, Lo (m3/Mg). There are two primary ways to estimate 

these parameters from laboratory and field data. 

1. You can let the laboratory studies define Lo and then use this value with the field data to estimate 

k. 

2. You can rely entirely on the field data to determine Lo and k, using regression techniques to find 

the values for these parameters that best fit the field data and first order kinetics. 

NCASI found that the field data gave very different values for Lo than obtained from the laboratory tests. 

The reasons for this remain unclear although they may include (a) a lag period in the degradation process 

or (b) the inability of first order kinetics to describe the field data. Because of the large uncertainty in the

estimates for Lo obtained using method 2 above, NCASI decided to rely on method 1. The results are 

shown below. A much larger variation in k is seen than for Lo, but this may be because k is based, in part, 

on field data that showed much more variability than the laboratory data. To date, NCASI has been 

unable to explain the variability between the results for samples from different mills. 

Table 1. Methane generation parameters from laboratory and field data* 

Residual Description k, yr-1 Lo, m3/Mg

A Bleached Kraft, combined 0.0034 69.9

B Deinked, combined 0.020 73.0

C Deinked, primary 0.014 101

D Nonintegrated, primary 0.016 78.1

Average 0.013 80.5

* Lo was obtained from laboratory tests and then used in combination 

with the field data in a regression analysis to estimate k. 

To calculate industry methane emissions over time, the average values for Lo and k were used, together 

with data on the historical rates of placement of mill WWTP residuals in landfills back to 1970. The 

calculation method was the same as used by EPA and IPCC. A global warming potential of 21 was used 

to convert methane to CO2 equivalents. Methane releases in 2005 are estimated to have been 

approximately 1.2 million metric tons CO2 equivalents. These emissions are offset, to a significant 

degree, by carbon storage in these same landfills, discussed below. 

To understand the net impact of mill landfills, one needs to examine the potential significance of landfill 

sequestration as an offset to methane emissions from mill landfills. The carbon not degraded in the 

landfill, and remaining in long-term storage, can be estimated directly from Lo by assuming that (a) the 

gas generated from decomposing biomass is a 50/50 mix of methane and carbon dioxide and (b) material 

not degraded to gas remains stored in the landfill. Using this approach, one finds that on a long-term basis 
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approximately 2/3 of the carbon remains sequestered in the landfill representing a net removal of carbon 

from the atmosphere. Considering global warming potentials, this is adequate to offset approximately 

one-half of the long-term methane emissions from these same landfills. 

Consequently, while the estimates shown above for methane emissions from mill landfills are small (1.2 

million metric tons CO2 equivalents in 2005), the net emissions associated with mills landfills are smaller 

still. With the true net impact of mill landfills being closer to 0.6 million tons CO2 equivalents per year, 

these emissions are barely 1% of emissions related to burning fossil fuels at all U.S. pulp and paper mills, 

estimated by NCASI to be 57.7 million metric tons CO2 equivalents in 2004. 

Therefore, it appears reasonable not to include mill landfill emissions in a mandatory greenhouse gas 

reporting program. Not only are the emissions very small, their estimation is subject to large uncertainty 

associated with (a) uncertainty in the proper form of the equation describing the decay process, and (b) 

the unexplained variability among WWTP residuals, especially evident in the field testing. 

On-site wastewater treatment

Summary: NCASI’s recent measurements of methane emissions from mill wastewater treatment plants 

indicate that these emissions can reasonably be excluded from reporting in EPA’s registry because they 

are small (less than 1% of the industry’s direct emission) and are estimated only with great uncertainty. 

Information explaining these observations follows. 

As noted above, when the ICFPA/NCASI calculation tools for pulp and paper mills were first developed, 

the intent was to be as comprehensive as possible. At the time, the only recommendations from IPCC for 

estimating emissions from wastewater treatment were for methane emissions from systems that were 

designed to accomplish removal of organic matter under anaerobic conditions. The IPCC methods for 

such systems, therefore, were included in the ICFPA/NCASI tools, although it was known that there 

were, and still are, very few such systems in the industry, especially in the U.S. 

 

In its annual inventory, however, EPA had been estimating methane emissions from a range of types of 

treatment plants in the pulp and paper industry. These estimates were not based on data generated at mill 

treatment plants so NCASI undertook a sampling program (in conjunction with a program to measure 

releases of sulfur compounds) to generate data that would improve the ability to estimate these emissions. 

The data have been gathered and the report will be published soon. The data reveal several important 

findings. 

NCASI studies have confirmed that mechanical clarifiers and aerobic biological treatment systems with 

high-intensity mixing, such as activated sludge treatment systems, do not generate significant amounts of 

methane. Anaerobic treatment systems are known to generate methane, but there are very few biological 

treatment systems in the U.S. forest products industry that are designed to provide treatment via the 

anaerobic decomposition of organic matter. There are, however, a number of operations that can have 

zones within them that become anaerobic; namely, aerated stabilization basins (ASBs), primary settling 

basins, and post-aeration basins. These emissions are estimated below. 

ASB Emissions: NCASI measurements suggest that, although there is great unexplained variability 

between the few systems for which emissions have been measured, on average about 1 percent of 

removed BOD is converted to methane by ASBs. Several sources of information were used to identify 

125 U.S. mills operating ASBs in the U.S. and the final effluent BOD loads from these ASBs. The sum of 

annual final effluent BOD for all mills with ASBs was used to derive an estimate on incoming BOD loads 

by assuming a treatment efficiency of 90% across the ASBs. Using these data, the annual mass of 

methane emitted from ASBs was calculated to be 6,563 metric tons, or approximately 0.14 million metric 

tons CO2 equivalents. 
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Settling Pond Emissions: In lieu of mechanical clarifiers, some mills use earthen primary settling ponds to 

remove suspended solids from the wastewater prior to entering an ASB or activated sludge treatment 

system. Temporary storage of solids in these ponds can result in anaerobic conditions and the subsequent 

release of methane. NCASI measured the methane generation rate at one primary settling pond. These 

data were used to generate an industry-wide estimate using statistics presented in EPA’s 1993 Technical 

Development Document wherein it was noted that approximately 10 % of U.S. pulp and paper production 

is associated with treatment of wastewaters in such ponds. Using the same production data as described 

above, the annual mass of methane emitted from settling ponds was calculated to be 5,094 metric tons, or 

approximately 0.11 million metric tons CO2 equivalents. 

Post-Aeration Basins: Many mills that operate ASBs use a post-ASB (quiescent) basin to allow 

suspended solids to settle out. In situations where mills do not have a separate quiescent basin, they often 

use a non-aerated tail-end portion of the ASB to settle solids. In either arrangement, the mixing energy is 

low enough that some of the solids settle to the bottom of these basins. The storage of solids in these 

ponds can result in anaerobic conditions and the subsequent release of methane. Methane emission 

measurements from post-aeration basins are limited to one study by NCASI conducted at a southern Kraft 

mill that utilizes a quiescent basin to settle solids prior to final discharge. Using annual methane emission 

rates for this quiescent basin and the annual production for the mill, the methane emitted on a per metric 

ton basis was calculated. This emission rate was multiplied by the sum of the production for all mills 

operating ASBs. The resulting sum of methane produced by solids in quiescent basins was 9,538 metric 

tons methane in 2004, equal to approximately 0.2 million metric tons CO2 equivalents per year. 

Total on-site wastewater management-related emissions: Based on the estimates above, it appears that the 

combined emissions of methane from industry wastewater management systems were approximately 0.45 

million metric tons CO2 equivalents 2004, which is less than 1% of the emissions associated with burning 

fossil fuels at pulp and paper mills, according to NCASI estimates. 

It is important to emphasize that the factors used by NCASI to estimate methane releases from the 

industry’s wastewater treatment plants are not appropriate for use at individual mills. In some cases, for 

instance, NCASI scaled up from a single treatment plant to the entire industry based only on production. 

Clearly, there are many mill-specific factors that this does not consider. We know, for instance that 

methane emissions should be related in some way to organic load from the mill, the degree of aeration, 

the basin area, the amount of settled solids in a basin, how frequently solids are removed and perhaps 

other factors. All of these would be expected to affect the methane emissions from a pulp and paper mill 

wastewater treatment plant but currently there is inadequate knowledge of the mechanisms for methane 

generation and release to include these factors in predictive equations or emission factors. Consequently, 

there is a significant risk of unintended consequences if a reporting program is based on emission factors 

normalized to only one of these factors. For instance, if an emission factor is based on raw waste load, a 

mill that reduced methane emissions by improving mixing intensity would not be able to show this and 

would actually be required to report increased methane emissions if raw waste load increased. 

Accordingly, because the emissions from wastewater treatment plants are so small and because the 

uncertainty associated with estimating these emissions at individual mills is so large, it is reasonable omit 

them from a mandatory GHG reporting program. 

On-site mobile sources and machinery

Because the estimates we make are usually based on corporate-wide fuel use data, these emissions, to the 

extent they are direct emissions for the company, are usually included in the emissions totals that we 

calculate. Of course, in some cases, these emissions are not direct emissions for the reporting company. 

We have been told by several companies that have examined these emissions that they represent around 
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one percent (give or take) of a pulp and paper mill’s direct emissions, but this will of course vary 

depending on how large the mill’s direct emissions are. 

Make up chemicals

Summary: Information from a variety of sources provide a basis for excluding from reporting 

requirements the CO2 emissions associated with purchased make-up carbonates at Kraft mills because 

these emissions are very small (certainly less than 0.7% of the industry’s direct emissions) and are offset, 

to at least some degree, by the sequestration of carbonates in Kraft recovery system wastes in landfills. 

Explanatory material follows. 

When companies first began estimating mill emissions of CO2, questions arose about how to handle the 

emissions from Kraft mill lime kilns. These kilns are very different from cement kilns or other types of 

lime kilns in that essentially all of the CaCO3 fed to Kraft mill lime kilns contains carbon that originated 

in the tree and is therefore biogenic. This biogenic carbon is not included in greenhouse gas totals 

(although the CO2 released from burning fossil fuels in Kraft mill lime kilns is included). To be 

comprehensive, the ICFPA/NCASI calculation tools included methods to estimate the CO2 emissions 

formed via the disassociation of that small fraction of the CaCO3 that contains carbon not of biogenic 

origin. This small amount of CaCO3 is added to the process at some mills to make up for small amounts of 

chemical that are lost on a routine basis. The potential significance of these make-up carbonates was 

examined in a paper by Miner and Upton (Methods for estimating greenhouse gas emissions from lime 

kilns at Kraft pulp mills. Energy, Volume 27 No. 8, Sept. 2002). In that paper the following assessment 

was described. 

“At some Kraft mills, a small portion of the CaCO3, fed to the kiln contains carbon of fossil and 

mineral origin. These small amounts originate in purchased calcium carbonate and sodium 

carbonate that some mills use to make up normal losses of sodium and calcium from the recovery 

system. In most cases, the carbon in these purchased carbonates is fossil (or mineral) in origin. 

For several reasons, however, it is clear that these amounts are so small that they can be ignored 

in developing estimates of overall industry greenhouse gas emissions. First of all, at many mills, 

sodium and calcium are added to the recovery system in forms that do not contain carbon, such as 

sodium sulfate, sodium hydroxide, and calcium oxide [reference omitted]. Furthermore, even in 

those cases where sodium- and/or calcium carbonate are used, the amounts of make-up chemical 

are small. Calcium make-up, required to compensate for losses in the recovery cycle, normally 

amounts to only 2 to 5% of the kiln throughput [references omitted]. As far as sodium carbonate 

is concerned, the United States Geological Survey (USGS) estimates that, in 1999, the pulp and 

paper industry used 121,000 metric tons of sodium carbonate for all purposes [reference 

omitted].” 

The paper goes on to indicate that “US Kraft mills released about 9.6 million metric tons of calcium 

carbonate-derived CO, in 1995.” If 3.5% of this was derived from make-up chemicals (the mid-point of 

the range noted above) it would amount to 340,000 metric tons CO2 potentially associated with the use of 

make-up calcium carbonate. If the 121,000 metric tons of sodium carbonate, noted above, are converted 

to CO2, it amounts to 50,000 tons CO2 per year. Together, therefore, emissions related to make-up 

calcium carbonate and sodium carbonate are less than 390,000 tons CO2 per year, or less than 0.7% of the 

industry’s direct emissions. One can be confident that the emissions are less than this, mostly because 

many mills compensate for calcium and sodium losses by using make-up chemicals that do not contain 

carbon (e.g. CaO and NaOH). In addition, since the writing of the paper discussed above, it has been 

realized that some of the calcium carbonate and sodium carbonate that is lost on a routine basis from the 

Kraft recovery system is contained in solids that are sent to landfills where the carbon is, for all intents 

and purposes, permanently sequestered, representing an offset to the small amounts of CO2 released from 
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make-up chemicals. It is evident, therefore, that the emissions associated with make-up carbonates are 

very small and it is reasonable to exclude them from EPA’s reporting requirements. 

Flue gas desulphurization (FGD) systems

Methods for estimating emissions from FGD systems were added to the ICFPA/NCASI calculation tools 

to address the potential that such systems are used in the pulp and paper industry. This is not, however, a 

process that is unique to the pulp and paper industry. Indeed, we have never given this aspect of the tools 

much attention because there are very few such systems used in the U.S. pulp and paper industry. 

EMISSIONS DISTRIBUTION CURVES

This is a question we have forwarded to AF&PA and I expect that you (or EPA) will be hearing from 

them. 

We hope you find this information helpful.