Venting from Farms
There are various efforts ongoing to collect and
process cow manure and process it via digesters to produce bio-gas (https://www.epa.gov/agstar/anaerobic-digestion-right-your-farm. While admirable, this does not address the
fact that bovine each emit 200-1000 liters of gas every day from burps and
flatulence. This may not be a lot per
cow, but assuming an average of 500 liters per cow per day, it adds up to almost
7.5 trillion cubic feet of gas (3.6 trillion cubic feet of methane) per year
from 1.4 billion cows world-wide.
While the concept of collecting cow flatulence may
seem excessive, particularly as seen in Figure 6
below, nations that depend on cattle-related industries are hard-pressed to
find solutions because methane is many times worse (estimated at between 30-70
times depending on source) for the environment then CO2.
The image below is from a study conducted by the government
of Argentina to collect cow flatulence via back-packs. While intriguing, this concept may be impractical
on an individual cow basis in the industrialized world where labor costs are
Figure 6 - Cow Flatulence Back-Pack
The idea of collecting the bovine off-gas though is
intriguing and may deserve consideration, particularly if the cattle are tightly
An example of a consolidated area is the dairy farm
shown in Figure 7a & 7b,
where cattle feed, drink and are milked under sheds. While the average dairy farm has a few
hundred of cattle, the largest dairy farm has over 30,000 head. Assuming a farm with at least 5,000 head, and
if “all” the gas excreted from each cow is collected, then the sheds could
collect up to 250,000 liters or 8828 cubic feet per day or 3.2 million cubic
feet per year. This is important because
unlike flared gas, where the gas is converted to CO2, the natural
gas excreted by the bovine is many times worse.
Considering that there are over 9.5 million dairy cows
in the USA alone
A particularly interesting trend, observed by the USDA
from 1996 to 2006, was that the number of overall farms fell and the number of
head per farm rose over that period.
Thus, a commercially viable solution, either
stand-alone or in conjunction with gas processing from the manure digesters,
could result in significant environmental benefit.
The authors admit, that this particular opportunity is
potentially the most difficult to address, but there is on-going research and
development at various universities which could lend itself to a commercially
viable solution; thus, it should not be discounted.