Before I forget, in an earlier post on this thread I used the Teragram
unit. One Teragram equals 1,000 Gigagrams by the way. Also to be
cleared up...N2O has 300 times the global warming potential that carbon
dioxide does. In terms of waste activities (landfilling, wastewater
treatment, human sewage) N2O is associated with human sewage.|
The Intergovernmental Panel on Climate Change (IPCC) has estimated that slightly more than half of the current methane flux to the atmosphere is anthropogenic (human activity based or the result of natural processes that have been affected by human activity). Agriculture, fossil fuel use, and waste disposal are but a few anthropogenic sources.
Without getting into the level of detail Peter is suggesting here is how the EPA breaks down the relative contributions of greenhouse gas emission by gas to US GHG emissions in 2002.
HFC, PFCs, SF6 - 2.0%
N2O (Nitrous oxide) - 6.0%
CH4 (Methane) - 8.6%
CO2 (Carbon Dioxide) - 83.4%
Source - EPA, 2004. Inventory of US Greenhouse Gas Emissions and Sinks 1990 - 2002 (reports the latest information available)
Since 1990, methane emissions have steadily declined. Methane emissions result primarily from decomposition of wastes in landfills, natural gas systems (leaks/fugitive emissions), and enteric fermentation (primarily cattle belching) but also in progressively lesser amounts from coal mining, manure management, waste water treatment, petroleum systems, rice cultivation, stationary sources, mobile sources, abandoned coal mines, petrochemical production, iron and steel production, agricultural residue burning, and silicon carbide production!
Of the methane emission sources 32 percent of total CH4 emissions in 2002 came from landfills (after landfill gas recovery and combustion), the rest from the other sources in progressively lesser amounts. That's 32 percent of 8.6 percent. Since 1990, net methane emissions from U.S. landfills have decreased by 8 percent. Projections are that as more landfill gas (LFG) recovery and combustion projects come on-line along with improved recovery technology landfill methane collection will increase.
It should also be mentioned that reviewers who commented on the draft of the first edition of Solid Waste Management and Greenhouse Gases: A Life-Cycle Assessment of Emissions and Sinks (EPA, 2002) and sources in the literature have reported estimates from 60 to 95 percent for LFG collection system efficiency.
Interested parties might want to consider reading through the following references.
I know this thread has focused on methane and landfilling primarily but there's something else that deserves mention, maybe even a lot more than that.
I'm going to throw a real curve ball - Anaerobic landfills also store carbon! Yes! They do! Carbon is in practically everything we throw away! Think of the potential implications! Uh! Oh! At some point in the emission - sink equation it may just make sense to throw stuff away! Hmmm. Cut down older trees (don't sequester carbon nearly as rapidly as younger trees), make furniture, use it for a bit, then throw it away in an oxygen starved coffin of a landfill. Uh! Oh! Now, I'm sure to have stirred up a hornet's nest. Better start another thread, aye!
Peter Anderson wrote:
I don't think that this level of detail is what the list serve is thinking of plowing through when it comes to work in the morning, but, since, Stephen's question has been posted and led to other questions, here is the answer I gave him. To make life manageable for everyone, let me suggest that those who want to get into the details let me know and we can form a smaller off-list working group to plow through this, because in one thing Stephen is absolutely right, everyone should stand ready to substantiate their factual assertions when asked to do so. After we work through all this, we can report back to the listserve what our final conclusions are a brief summation. Peter ----- Original Message ----- From: Peter Anderson To: firstname.lastname@example.org Sent: Wednesday, February 09, 2005 4:05 PM Subject: Re: [greenyes] Relationship of Global Warming to Recycling Stephan- I'll be getting you something more detailed just as soon as I have a working draft for distribution. But, in the meantime, I read EPA's three percent value to be for landfills only, inasmuch as wastewater treatment is shown on another line of the table. But, if you have better information conclusively to the opposite effect, do pass that along. Yes, EPA's 3 percent number is built on 51% of landfills (weighted by waste volume) is at sites without gas collection. Going forward in an incremental sense, however, on a volume weighted basis, non-NSPS sites do not really seem to me to be a factor in the equation. In any event, the same multiplier that would be used to correct the 3 percent number for the true lifetime capture rate, would be applied against the same 193 Tg CO2 Eq, regardless of the fraction of landfills assumed to have gas collection on a weighted basis. Interesting that you also point to EPA's offset for energy recovery. First thing, as my report describes, is that this offset only becomes an item of significance IF one assumes high lifetime capture rates. In fact, while there is a 61% reduction in emissions when 75% lifetime capture rates are assumed, that net gain drops to 5% when a 20% figure is used, as I believe is far more representative of average real world conditions. The second thing that is not commonly understood is that the landfill operator manages the site very differently for energy recovery, than when the collected gases are just flared. To economically recover the latent energy value in landfill gas with the equipment currently available, the gas collection systems are typically operated in ways intended to maximize methane capture and generation, which has distinct differences from managing a waste field to minimize fugitive emissions. For that reason, energy recovery can work at cross-purposes with gas collection. To optimize gas collection, the system should be operated for maximum extraction at all times, short of overpumping and drawing air from the surface that might cause a fire. For gas is continuously being generated and, if released uncontrolled, the emissions threaten health and the global environment. That is not always what happens when energy recovery is added to the equation. The two can work at cross-purposes because, the new need to maximize only high Btu gas imposes competing demands. Electric generation requires a ratio of methane to carbon dioxide of close to 50%. When negative pressures are exerted to extract methane out of the waste load, significant volumes of condensed moisture - necessary for further methane production - is drawn out of the refuse at the same time. If the collection systems continue pulling gas, without adequate moisture remaining behind, the proportion of methane in the landfill gas will fall below the level needed for the generators that produce electricity, and the surrounding field will be tapped out as a power source. To prevent that, gas managers throttle back on those wells where low methane ratios are recorded in order to give that surrounding field time to recharge. But, when gas collection is postponed to give time for methane levels to restore the necessary high Btu levels for power engines or turbines to work, more of the landfill gases escape uncontrolled to the atmosphere. The fact that the uncollected emissions are low Btu gas does nothing to minimize the health impacts from the hazardous compounds on neighbors and only a little to lessen the proportion of methane per cubic foot of landfill gas adding to climate change. Another reason that landfill owners that manage the site for maximum energy recover may dampen the negative pressures is to be doubly sure that they are not drawing any air. For the presence of oxygen at far lower levels than cause explosions can poison methanogenesis. Protecting anaerobic conditions from air infiltration by reducing suction is another reason that managers for energy recovery will have tend to experience more difficulty in pulling gas from the far side of the zones of influence. Unfortunately, data on landfill gas is so fragmented at the national and state level that it is impossible to document the magnitude of the difference in gas efficiency in comparable landfills with gas collection that have energy recovery from those that do not. But, until we get real data, I would have to guess that the resulting losses in collection efficiency that arise in the real world when managing a site for energy generation far exceed the very small net offset of 5% when more realistic lifetime gas collection rates are used. Do, though, give me a week or two to get this report ready to review. Peter ----- Original Message ----- From: Stephan Pollard To: RecycleWorlds Cc: GreenYes Sent: Wednesday, February 09, 2005 2:34 PM Subject: Re: [greenyes] Relationship of Global Warming to Recycling Peter, RELATIONSHIP OF GLOBAL WARMING TO RECYCLING Included in that litany is the inability to prevent the contemporaneous release of most of the gases generated in landfills, 46%-50% of which is methane, a greenhouse gas more than 21 times as virulent as CO2. Although hard data does not exist, based upon what is known, almost certainly less than 25%, and probably less than 20% of the lifetime emissions are actually captured. The vast majority of methane emitted from in landfills, which does not exist in the garbage we discard, but instead is generated in significant quantities only in the anaerobic (or oxygen starved) conditions of large lined landfills, adds substantially to mankind's climate-changing gases, very likely in the U.S. greater than 10% of the total. To put things a bit more into perspective. Assuming the science employed was "good" according to the The Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 - 2002 published by the US EPA in April of 2004 waste activities as a portion of all US GHG emissions represented 3.4% (237.2 Terragrams of Carbon Dioxide Equivalent) in 2002. The term "waste" includes landfills, wastewater treatment, and human sewage. That 3.4% includes methane and nitrogen oxide and relatively insignificant amounts of other GHG. Nitrogen oxide (a hugely more "virulent" GHG than methane) is associated with human sewage while methane is associated with landfills and wastewater treatment. The EPA estimates that LFG recovery systems have an efficiency of 75%. It also estimates that 49% of all landfill methane was generated at landfills with recovery systems, and the remaining 51% was generated at landfills without LFG recovery. Additionally, of the 49% of all methane generated at landfills with LFG recovery, 49% (or 24% percent of all methane) was generated at landfills that use LFG to generate electricity, and 51% (or 25% of all methane) at landfills that flare LFG (flaring removes the virulency). See EPA 2002. EPA530-R-02-006 - Solid Waste Management and Greenhouse Gases: A Life-Cycle Assessment of Emissions and Sinks. All in all the contribution of landfilling US style to US GHG emissions would seem to be arguably insignificant relative to the amount of carbon dioxide being pumped skyward from power plants, automobiles, volcanic eruptions, forest fires, etc. even more so when you consider the portion of methane currently being collected in landfill gas operations. Respectively Yours, Stephan Peter ____________________________ Peter Anderson RECYCLEWORLDS CONSULTING 4513 Vernon Blvd. Suite 15 Madison, WI 53705 (608) 231-1100 / Fax 233-0011 email@example.com
-- Stephan Pollard Environmental Dynamics Doctoral Program University of Arkansas Rm 113 Ozark Hall Fayetteville, AR 72701 Tel: (479) 575-6603 http://www.cast.uark.edu/~sp