Biodegradable products are not major contributors to methane emissions from landfills, as claimed in the Environmental Science & Technology (ES&T) article.
A North Carolina State University study, published online in the May 27 issue of Environmental Science & Technology (ES&T), leaves the impression that “biobased biodegradable products” potentially generate large amounts of methane when they are landfilled. The Biodegradable Products Institute believes that the headlines and conclusions of this work are inappropriate.
There are two fallacies in the article’s arguments.
First, the author, James Levis, leads the reader to believe that since a biobased material will quickly biodegrade under aerobic conditions, such as composting, that it will also do so under the anaerobic conditions found in landfills. This is not the case.
Composting is designed to promote rapid aerobic biodegradation by optimizing the moisture, temperature and feedstocks in the compost piles. Landfills are largely anaerobic and the microbial population in them differs significantly from that of a compost pile. We know that within a few months, products made from polylactic acid (PLA) will biodegrade rapidly and completely under composting conditions.
However, research shows that this is not the case for PLA under anaerobic conditions. The chart below shows that very little biodegradation of PLA takes place under standardized testing.
Testing for other “compostable” resins shows much the same result-limited biodegradation under anaerobic conditions.
Second, biodegradable products make up a miniscule portion of the solid waste stream. Today, the projected annual market sales for all ‘compostable’ resins in North America are approximately 100,000 tons. By comparison, the EPA’s Solid Waste Characterization for 2009 shows US generated:
- 25.9 million tons of Paper and Board
- 33.4 million tons of Food Waste
- 13.3 million tons of Yard Trimmings.
Source: Table 3 Chap. 2: http://www.epa.gov/epawaste/nonhaz/municipal/pubs/msw2009rpt.pdf
One can see that the volume of “compostable” resins is dwarfed by the millions of tons rapidly biodegrading paper, food and yard debris that the US continues to landfill every year.
Oddly, the ES&T article does not mention Dr. Barlaz’s prior work, Estimation of Waste Component-Specific Landfill Decay Rates Using Laboratory-Scale Decomposition Data, published in 2010.
In this study, Dr. Barlaz explored the kinetics of biodegradation of different feedstocks. One of the conclusions of his research: eliminating all food and yard waste can reduce the total landfill methane production by 30-35%.
The BPI believes that the May 2011 ES&T article should have focused on the key contributors to greenhouse gases and should been titled “Food Scraps and Paper: The Root Cause of Methane from Landfills.”
The BPI believes that the May article should have focused on the key contributors to greenhouse gases and should been titled “Food Scraps and Paper: The Root Cause of Methane from Landfills”.
A More Logical Conclusion
Rather than maintaining the current status quo of solid waste handling, the BPI believes the real issue is to prevent putrescible materials from being landfilled in the first place. Communities should work to recycle food scraps and wet unrecyclable papers in managed compost facilities, where they will be converted aerobically into useful soil amendments, or send to anaerobic digesters, where the methane can be captured much more safely than in a landfill.
Maybe we can learn something from our neighbor’s to the north. Today 25% of Canada’s population has access to residential collection of food scraps. After only a few years of operation, today these organics recycling programs are diverting approximately 12-15% of Canadian food waste.
Finally, the BPI shares Dr. Barlaz’s concern for the growing number of “biodegradable” claims, for products that are typically landfilled. Many of these claims are spurred by additive suppliers that would like consumers to think that it is OK to throw products in the trash, as they will somehow magically disappear. The National Advertising Division of the Better Business Bureau (NAD) and the Federal Trade Commission (FTC) have repeated determined that these types of claims are misleading.
Moreover, the BPI has conducted three anaerobic biodegradation tests on plastic products with “biodegradable additives”. At the end of 60 days, little or no biodegradation was evident. Further, the tests indicated that no biodegradation could be anticipated in the future. These tests are published on the BPI Website.
The BPI applauds those responsible marketers who are making efforts to convert packaging products and products so that they can be effectively diverted from landfills through composting and recycling, rather than following the Siren’s call of “biodegradable.”
Steven A. Mojo
BPI Executive Director
July 5, 2011