|July 1, 2004:
Livestock operations often struggle with the
best way to effectively dispose of their animals' waste.
Straight application of manure to the land can give off
dangerously high emissions of ammonia, odor and greenhouse
gases, and lead to groundwater contamination. While composting
can be a viable alternative to direct application and
is especially effective in returning valuable nutrients
back the to soil, it too has left livestock farmers wondering
what to do about escaped atmospheric gases.
Composting by forced aeration--a common composting
practice that requires regular turning--causes high
emissions of ammonia during the initial stages of composting.
Biofilter or acid scrubbers can be used to prevent the
ammonia gas from entering the environment, but this
is not easily accomplished on-farm. Intensive, forced-aeration
composting can also be expensive and impractical for
some livestock operations.
Another method of composting, called passively-aerated
composting, has proved to be a better option for livestock
farmers. Unlike intensive composting, passively composted
beds do not need to be turned; instead they rely on
the temperature of the compost bed to facilitate the
composting process. The passive process releases comparatively
low levels of ammonia gas. The difficulties of the passively
aerated system stem lie in ensuring the compost reaches
the correct temperate. Too high, and it could lead to
anaerobic regions and emissions of methane and odors.
Too low, and the temperature is insufficient to kill
Temperature in a passively aerated system cannot be
directly controlled. In the past, there was a lot of
guess work and crossed fingers in hoping the pile would
reach but not exceed optimum temperature. Now, new research
suggests that temperature can be controlled through
the initial porosity and structure of the compost bed.
The Dutch researchers who conducted the study show
that pile texture and cover are crucial to efficient
composting and reducing ammonia and methane losses.
If a compost pile density of 1100 kilograms per cubic
meter was used, conditions quickly become starved for
oxygen, resulting in high methane losses. If a pile
density of 560 kg/cu m was used, no heating occurred
and pathogens and weed seeds were not killed. Optimum
heating and minimized losses were found at 700 kg/cu
m pile density.
Lead researcher Adrie Veeken and his co-workers also
found that covering the compost pile with a layer of
straw trapped ammonia and prevented its loss to the
environment. Use of natural filters composed of materials
such as straw and clay provide a means to trap otherwise
harmful emissions for beneficial use as soil amendments.
While loss of nitrogen during composting is inevitable,
from an environmental standpoint the emission of nitrogen
as a gas is preferable to emissions of nitrous oxide
(a greenhouse gas emitted by storage and direct application
of raw manure.)
Composting may never be able to solve the problems
created by modern concentrated animal feeding operations
(CAFOs), and further research still needs to be done
to evaluate the contribution of passively aerated composting
to global warming. However, this research does provide
exciting new possibilities for responsible, environmentally-conscious
livestock operations and manure management.
Veeken et al., 2002, Passively aerated composting of
straw-rich pig manure, Compost Science and Utilization
Dr. Paul Hepperly manages the research and training
programs for the Rodale Institute. Paul has over 45
years farm and 25 years experience in conducting and
managing agricultural research. Prior to accepting his
current position he worked with ginger farmers in India
and Hawaii to resolve major disease losses.