Many studies have been
conducted to determine malodors from manures and composts. The majority of
these have been based on subjective measurement of perceived odors or have been
measured in association with non-quantifiable matrices such as open streams of
air. A major limitation of such studies is that it is very difficult to
correlate concentrations of specific malodorous compounds with bioprocesses that
form or destroy the offensive chemicals. The studies reported in this
seminar were designed to monitor and quantify a select group of known malodorous
chemicals in dairy manures and during composting.
To analyze odor components,
fresh, aged and composted dairy manures were placed in closed vessels that
permitted accurate monitoring of influents, effluents, and temperature. The
compounds quantified, volatile fatty acids (6), phenolics (2), indolics (2) and
ammonia, were measured over sixteen days. The experimental variables for
these studies were: fresh vs 12-day aged manure; days of composting; freestall
barn of manure origin (lactating cows vs growing heifers); and intermittent vs
continuous aeration. Aging of all manures greatly increased the
concentrations of all the chemicals studied, however, increases in the various
compounds were not proportional. Formation of the chemicals was very rapid
and appeared to reach steady state by 6 to 8 days. Aerobic composting
rapidly destroyed the odorous chemicals with the onset of composting. Most
of these chemicals were absent from the composting mass by 7 days and only
traces of acetate and iso-butyrate were present by day 16. Analysis of the
exhaust stream revealed that only small quantities (<0.25%) of the chemicals
were released to the atmosphere and those only occurred with excessive
(continuous) aeration.
Emissions of ammonia were not
influenced by aging of the manures. However, the source of manure and
extent of compost aeration had significant effects. Manures from the
lactating cows that were fed rations containing 18.7% protein emitted
significantly more ammonia than from growing heifers that were fed 13% protein
rations. Similarly, the continuous aeration (29 kg/day) emitted twice as
much ammonia as the intermittent aeration (6 kg/day).
These studies demonstrated that
preventing anaerobic storage of manures, even for short intervals, is important
in any odor control strategy. Composting can quickly utilize odor causing
chemicals, however, it is desirable to strive for minimal aeration.
Excessive aeration drives malodors and ammonia to the atmosphere. These
studies provided additional quantitative evidence that feeding excessive
quantities of nitrogen (protein) will result in increased ammonia emissions to
the atmosphere. Considering that livestock production is responsible for
up to 75% of the atmospheric ammonia, animal husbandry and manure management
practices that reduce these emissions are prudent.
Discussion:
Maria Sol Morales (OSU) asked
about the consistency of dry matter concentration.
Willett responded that variations reflect differences in seasonal
temperature and precipitation. Also,
because urine is present in the manure, as pH increases during composting, the
formation of ammonia increases.
Harold Keener (OSU) questioned
the impact on the environment if no ammonia were emitted to the atmosphere.
Would it affect the sustainability of the plant ecosystem?
Willett noted that based on EPA data concerning amounts emitted, it
should not be a problem.
Maurice Watson noted that there
is some evidence that too little contact with animals has increased the
incidence of asthma in the U.S. Willett
cited a University of Pittsburgh report that suggests that decreases in sulfur
emissions by power plants has resulted in an increased concentration of nitrates
in the atmosphere and that nitrates are more irritating to lung tissue than
sulfates.
David Munn (ATI) asked if any
data are available documenting the potential impacts of CAFOs (confined animal
feeding operations) on health. Willett
noted that the data on chronic exposure (long term, low concentration) are poor
as there have been no controlled studies. However,
acute exposures (short term, high concentration) are documented and can be very
serious.
Keener suggested that during
the summer when ventilation rates for livestock building are high, ammonia
concentrations in the building are low. In
general 10 ppm is the level which begins to affect animals and it may get to as
high as 20 ppm during winter months.
Floyd Schanbacher (OSU) asked
for clarification of differences in ammonia levels in manure from lactating cows
as compared to heifers. Also, what has the greatest impact on ammonia production
- protein, urine or amino acids? Willett confirmed that emissions vary during composting
for different manures and that urine has the greatest effect.
Schanbacher noted that urease activity (catalyst for ammonia production)
is increased when feces are in contact with urine.
John Lengacher (ATI) asked how
the loss of ammonia affects the use of manure as a fertilizer.
Willett replied that any loss of nitrogen in the form of ammonia,
decreases the nitrogen in the manure. There
are three ways to minimize ammonia formation:
1) separation of urine and feces; 2) management of nutrition and manure
storage and handling; and 3) treatment.
Schanbacher asked if pH levels
as high as 9 reflect the release of urea to free ammonia.
Watson asked if acid had been added to decrease pH.
Willett responded that no acid had been added because data on and
understanding of the basic behavior between different inputs was needed first.
The ammonia emissions correlate with other studies that use olfactometry
measurements.
Paul Dillon (ATI) asked how
compost applied to land can affect different soils as well as reclaimed land
from mining. It was noted that
Northern Ohio soils tend to be fertile and sandy whereas Southern Ohio soils are
rocky and used more for grazing. Watson
commented that the nutrient content and pH of the final product is important and
that compost typically has a pH of 8-8.5 Southeastern
Ohio soils tend to be acidic so compost could improve the soil, but in the west
it could increase pH too much. Nitrogen and phosphorus content of the compost should also be
considered.
Notes
by Mary Wicks
The
OCAMM (Ohio Composting and Manure Management) Program is funded by OARDC/OSU.