June 28, 2010 – The
approach the U.S. Environmental Protection Agency (EPA) uses to estimate
greenhouse gas emissions from agricultural anaerobic lagoons that treat manure
contains errors and may underestimate methane emissions by up to 65 percent,
according to scientists from the University of Missouri.
June 28, 2010 – The
approach the U.S. Environmental Protection Agency (EPA) uses to estimate
greenhouse gas emissions from agricultural anaerobic lagoons that treat manure
contains errors and may underestimate methane emissions by up to 65 percent,
according to scientists from the University of Missouri.
Anaerobic lagoons treat
manure on some animal feeding operations prior to application to crops as a
fertilizer. Methane, one byproduct of the treatment process, has 21 times the
warming potential of carbon dioxide.
A 2007 U.S. Supreme Court
ruling mandated the EPA consider greenhouse gases a pollutant. This led the EPA
in 2009 to approve greenhouse gas reporting requirements for any facility that
annually releases 25,000 metric tons or more of carbon dioxide equivalents to
the atmosphere. The objective of these reporting requirements is to quantify
emissions as a first step towards developing strategies to reduce greenhouse
gas losses.
Direct measurements of
methane emissions from anaerobic lagoons are technically difficult and very
expensive, so the EPA adopted a calculation method to estimate methane
emissions from anaerobic digesters. They relied on the method used by the
International Panel on Climate Change (IPCC) in their 2006 worldwide estimate
of greenhouse inventories.
An interdisciplinary team
of scientists from the University of Missouri evaluated the EPA and IPCC
approach to estimate greenhouse emissions from anaerobic lagoons. They reported
the results of their analysis in the May-June 2010 issue of Journal of
Environmental Quality, published by the American Society of Agronomy, Crop
Science Society of America, and Soil Science Society of America.
The team documented errors
in the approach, which the EPA and IPCC adapted from a method used to estimate
methane production from anaerobic digesters. A literature review of the
performance of uncovered anaerobic lagoons indicated that there are important
difference between anaerobic lagoons and anaerobic digesters that were not
accounted for in the EPA and IPCC approach. They found that uncovered anaerobic
lagoons were more efficient at converting waste to methane than predicted using
literature based on digesters. The team also found mistakes in the equations the
EPA and IPCC used.
“Our calculated estimates
of methane emissions from anaerobic lagoons indicated that the EPA approach
could substantially underestimate methane emissions from these facilities,
perhaps by as much as 65 percent,” said John Lory, a member of the team that
reviewed the EPA rule.
The report also suggested
that other operations currently excluded under the rules may in fact produce
emissions beyond the threshold. Manure storage facilities are the only on-farm
source required to report under the current rules. The most likely manure
storage facilities to meet the current reporting requirements are anaerobic
lagoons. The EPA projected that operations with more than 3,200 dairy cows or
34,100 pigs would likely meet the reporting requirement.
Lory emphasized there have
been few direct measurements of methane emissions from anaerobic lagoons and
the few measurements that exist indicate that both the University of Missouri
calculated estimate and the EPA calculated estimate of methane loss from these
facilities may be high.
Though the research team
outlined a different approach to measuring methane emissions, they also pointed
out that understanding of anaerobic lagoons is still evolving.
“More research is needed
before we can provide accurate estimates of methane losses from anaerobic
lagoons,” added Lory.
View the abstract at
http://jeq.scijournals.org/cgi/content/abstract/39/3/776.
