Horrible doesn't even begin to express it," Joe Johnson
says of the smell from the 21 hog barns that surround his home
in Faison, North Carolina. For Johnson and his wife,
Antoinette, the stench from the hog houses had turned their
home into a foul-smelling trap where even closed windows, air
conditioning, and incense couldn't drown the odor. Their
complaint, reported in the Raleigh News & Observer
in July 1998, echoes those of other people around the United
States who have reported symptoms ranging from nausea and
headaches to mood changes in association with exposure to
odors from animal waste.
The past decade has seen a transformation in U.S. livestock
operations. The livestock industry, and particularly pork
production, has consolidated into fewer, larger operations.
Many hog farms have become what some people call "hog
factories," with rising animal densities in barns and larger
anaerobic lagoons for waste. As a result, complaints about
odor emissions and groundwater safety have increased [see
EHP 106(5)A226-A227 (1998) and 103(12)1096-1100
(1995)].
The complaints and ensuing debate over how to address the
problem of animal waste odors have spurred legislation in
nearly a dozen states from Minnesota to North Carolina.
Regulations vary from state to state, but in late November
1998 the EPA moved closer toward federal involvement when it
made a deal with pork producers that would allow farmers to
avoid big penalties by participating in a national program of
odor and water-quality inspection. Although regulatory action
is one tack, hog and other animal farmers are also looking
into technologies being developed by both private industry and
universities to combat strong odors. Some of the most
promising strategies include the low-tech, such as barley
straw caps, and the more high-tech, such as waste biofilters.
The Science of Smells
The science of odor as a health concern is still new.
Merely identifying the hundreds of volatile organic compounds
(VOCs) that cause livestock odors poses a big challenge. Susan
Schiffman, a psychiatric researcher at Duke University Medical
School in Durham, North Carolina, says that offensive
livestock odors can potentially affect human health in several
ways. First, odorant compounds can irritate the eye, nose, and
throat, which can reduce respiratory volume. Second, the VOCs
that cause odors can stimulate sensory nerves to cause
neurochemical changes that might influence health, for
instance by compromising the immune system. Finally,
unpleasant odors can trigger memories or attitudes linked to
unpleasant odors, causing cognitive and emotional effects such
as stress.
Schiffman reported on how odors can affect mood and stress,
and thereby alter the immune system, in the Spring 1998 issue
of the Journal of Animal Science. "Because unpleasant
odors can produce impaired mood and stress," she wrote, "they
may influence health via biological mechanisms that include
immune changes or hippocampal damage."
Scientists who have investigated the health effects of the
odors note that physical symptoms can be exacerbated by social
divisions and perceptions. Kendall Thu, associate director of
the Iowa Center for Agricultural Safety and Health in Iowa
City, explains that "the physical properties of these
emissions and their potential physiological and psychological
effects are connected with the social conditions of rural
areas. People [in rural areas exposed to animal odors] feel
their sense of identity--their home, where they want their
children to grow up--has been violated." He adds, "The [World
Health Organization] definition of health includes social
health precisely because of this kind of situation."
Besides the effects of odor on neighbors, ammonia emissions
from open manure lagoons can return to surface water in
rainfall and foster harmful algal blooms. Researchers at North
Carolina State University (NCSU) in Raleigh found that the
ammonia content of rain in nearby Sampson County more than
doubled between 1985 and 1997. The researchers traced this
trend to growth in hog farm emissions.
The last straw. Covering animal waste
lagoons with barley straw significantly reduces odors for as
long as the waxy straw floats and no major cracks appear in
the surface.
Photo credit: Duratech
Methods of measuring odors vary from state to state. In the
1970s, North Dakota instituted standards for acceptable odor
levels in response to public concerns over hydrogen sulfide
(H2S) emissions from oil- and gas-producing wells.
The standards are based on the use of a scentometer, a device
that looks like a little black box that measures odor levels.
Although not as precise as mass spectroscopy, the scentometer
provides a basic gauge of odor level in the field, and is
inexpensive. Scentometer readings proceed stepwise in terms of
odor strength from 2 (a noticeable odor) through 7 (an odor
most people would find objectionable), 15 (most would declare
it a nuisance), and 31 (extremely nauseating). Francis
Schwindt, chief of the North Dakota Health Department's
environmental health section, believes that the odor levels
from livestock operations do not endanger public health. "The
main concern is from a nuisance standpoint," he says, but he
adds that odor problems can suggest problems with the VOCs
that cause them, particularly H2S, ammonia, and
methane-related compounds.
On the Trail of the Scent
Late in 1997, EnviroPork, a private hog facility in
Larimore, North Dakota, began operations with 5,000 sows
producing more than 100,000 piglets for sale each year. In
early 1998, passersby on U.S. Highway 2, a major four-lane
highway, complained of the facility's odor. The Health
Department took scentometer readings, found they exceeded
state standards, and directed EnviroPork to address odor
concerns by a deadline of 3 August 1998. The Health Department
recorded odor levels of 15 at the highway; in North Dakota any
reading greater than 2 is a violation.
Bob Bergquist, EnviroPork's owner, says his facility tried
several odor-reducing strategies, including feed additives to
improve the pigs' digestive efficiency and enzymes to break
down compounds in its waste lagoon. When these didn't solve
the problem, the Health Department suggested EnviroPork
contact the Energy and Environmental Research Center (EERC) at
the University of North Dakota in Grand Forks.
 |
The nose knows. An
apparatus called a scentometer enables researchers to
measure the strength of animal waste odors.
Photo
credit: Texas Agricultural Extension
Service |
The EERC reviewed EnviroPork's operation and suggested two
main innovations: cover the waste lagoon with barley straw,
and filter the exhaust air from the barns. The EERC had
previously tested a straw cover on a wastewater lagoon at a
sugar processing facility and found that barley straw
substantially reduces odors at a relatively low cost and with
minimal maintenance. According to EERC research engineer Tom
Moe, the center learned of the covers from the Prairie
Agricultural Machinery Institute (PAMI) in Portage la Prairie,
Manitoba. The cover reduces odor as long as the straw floats
and no major breaks appear on the lagoon surface. Barley
straw, applied to the lagoon using a specialized cannon that
broadcasts up to 150 feet, provides the best unsupported cover
because of its waxy coating and the stalks' tubular nature.
The EERC has evaluated other options, says Moe, but because
EnviroPork was under the gun to implement a solution quickly,
they recommended the barley straw, a relatively quick
solution. "Put it on properly and you can basically forget
about it," says Moe. If applied early in the spring, the
covering may require only a few touch-up treatments over the
summer. For EnviroPork, Moe estimates that the lagoon cover,
including material, labor, and equipment rental, cost just
over $11,500 to install.
Barnstorming Solutions
Experts generally agree that waste lagoons pose a greater
odor hazard than livestock barns. "Well over half of [the
odor] comes from the lagoon," says John Pickrell, an
environmental toxicologist at Kansas State University in
Manhattan. However, barns produce excessive dust emissions, an
even greater health threat than odor, and thus may present a
clearer opportunity for reducing health hazards. In recent
years, researchers have revised their view of the symptoms
experienced by some barn workers. The cough, chest tightness,
and wheezing that were previously seen as an allergic reaction
are now viewed as an inflammatory reaction to dust that could
cause chronic lung disease, Pickrell says. "Some of these are
pulmonary symptoms," Pickrell says; "some are pretty common
with stress."
To reduce odor as well as trap particulate matter that may
pose an inhalation hazard, the EERC developed a filter for the
ventilation fans in the barns, says Dan Stepan, EERC research
manager. Most agricultural biofilter designs use a horizontal
orientation with the biomass bed spread out in pallets on the
ground. This wouldn't work at EnviroPork because the filter
would extend into the right-of-way of the nearby highway. So
the EERC created its own design, using barley straw as a
medium. They constructed filter walls measuring 80 feet long
by 8 feet high by 2 feet thick near the exhaust of each set of
ventilation fans, using a treated wood frame and chicken wire.
Although research is still needed to gauge the filter's
long-term effectiveness, tests showed that the biofilter walls
removed dust particles, redirected airflow upward for better
dispersion, and significantly lowered scentometer readings
from above 15 down to 2 or below in almost all cases.
 |
Gimme a break. Windbreak
walls divert air and odors away from neighbors and trap
particulate matter from hog barns.
Photo credit:
North Carolina State Animal and Poultry Waste Management
Center |
Bergquist confirms
that both technologies appear to be working. Both
H
2S levels and scentometer readings have declined
since the straw cap went on the lagoon, with scentometer
readings near the lagoon plunging from 31 to "negligible."
Readings outside the hog barn filter walls showed
H
2S concentrations of 2 parts per billion (ppb),
down from almost 50 ppb inside the barn. "We're still doing
follow-up tests with the EERC staff to find out why things
work," says Bergquist. "I don't think there's one big magic
wand," he adds. "It's a combination of management practices
and technology that make it a success."
Schwindt says the Health Department is satisfied with these
improvements, although additional biofilters may be needed for
other ventilation fans on the farm. Ventilation fan filters
and lagoon covers are now recommended by the American Society
of Agricultural Engineers in its standard for controlling
manure odors (last revised in November 1997).
In Minnesota, potential violations of the state's
H2S emission standards led state health officials
to respond to odor complaints. "Where there's odor, there may
or may not be H2S, but when there's H2S,
there will be odor," says Robert Criswell, a staff engineer
with the state's Pollution Control Agency in St. Paul.
Minnesota has a two-step standard: 30 ppb in half an hour may
not be exceeded twice in a five-day period, and a yearly
standard of 50 ppb may not be exceeded twice in a year.
Measurements are taken at the property line of a facility. In
response to a 1997 odor complaint, the agency recorded
readings of 30-90 ppb H2S at the property line of
one hog facility, which resulted in the first documented
violation of the H2S standard. To comply, the
company installed a felt-like synthetic polymer material atop
its 7- to 9-acre lagoon (perhaps the largest in the state).
The cover substantially reduced H2S emissions.
Just between phew and me. Exhaust air
from hog barns is forced through barley straw biofilters
that absorb both odors and dust.
Photo credit: Energy
& Environmental Research Center, University of North
Dakota
Minnesota farmers have also tried the barley straw lagoon
covers and found them promising, especially on smaller
lagoons. On one 2-acre lagoon cover, Criswell noticed, "The
barley straw actually grew. You could see it had greened up."
This could mean that the straw is more likely to float and
stay intact. For larger lagoons, though, the area is harder to
cover and the straw cap is more likely to shift and crack.
More Hogs, More Odors, More Money
In North Carolina, the pork industry has grown faster and
with less regulatory oversight than in the Midwest. The number
of hogs in the state has nearly quadrupled since 1990 (from
2.5 million to 9.6 million), while the number of hog farms has
shrunk by nearly half (from about 10,000 to 5,800). "Fewer
people are raising more hogs on much bigger farms," notes Tom
Mather, a spokesman for the division of air quality in the
state's Department of Environment and Natural Resources. "The
mom-and-pop operations have largely gone by the wayside," he
says.
Unlike North Dakota, North Carolina currently has no
regulations specifically governing animal odors, but rather,
has a general odor standard that is hard to enforce.
"Complaints about odors have steadily increased as the
industry has grown," says Mather. In 1997, the North Carolina
General Assembly passed a bill directing NCSU to coordinate a
study on odor controls. The bill also directed the state's
Environmental Management Commission to draft regulations for
odor control in conjunction with the NCSU study. The NCSU
study's initial findings were released in September 1998.
The NCSU study was led by Mike Williams, director of the
university's Animal and Poultry Waste Management Center, which
has supported research on waste management and related issues.
The study describes several odor-control technologies the
center has evaluated, makes recommendations for establishing
odor standards, and includes an appendix of possible remedies
for odor sources. "We have evaluated several technologies with
promising results," says Williams, "but with the economic
realities in the current market, they have met with mixed
results from producers."
 |
Twin towers. Waste
separators in which odorous compounds are broken down by
bacteria are another promising technology.
Photo
credit: Ekokan |
Although pork exports were up 24.8% as of November 1998
over numbers for the same period in 1997, according to the
Foreign Agricultural Service, the prices for the exports are
falling. Paradoxically, the U.S. hog industry is expanding
despite the falling prices. A recent Foreign Agricultural
Service report states, "Structural change in the U.S. hog
industry has put many producers in the position of having to
expand hog numbers to efficiently use recently constructed
facilities. Hence, while in the past such low hog prices would
have brought on a contraction in inventories, today more
operations continue to expand, notably contract operations."
Among promising innovations evaluated by the NCSU study,
Williams notes windbreak walls, similar to those installed at
the EnviroPork facility but providing more of a physical
barrier for diverting airflow, because in North Carolina's
warmer climate, airflow rates from exhaust fans would have to
be higher than those in North Dakota. Barley straw is also
less readily available in North Carolina. The NCSU study
therefore assesses lagoon covers as effective but costly.
Williams says separators are another promising technology.
In one type, an upflow biofilter first separates solids from
liquid waste and then flushes the liquid manure through two
reactor towers about 15 feet tall. The towers contain layers
of porous plastic. These layers provide a large surface area
on which bacteria that have been added to the tower break down
odorous compounds and convert ammonia to nitrates. In a
second-stage anaerobic polisher process, the nitrates are
converted to nitrogen gas. "We're looking at numerous systems
that use that [denitrification] approach," says Williams. The
upflow biofilter system, manufactured by Ekokan, a company
based in Cary, North Carolina, is expected to cost about
$50,000 for a facility of 800-1,200 hogs.
North Carolina's pork producers are leery of new
technologies and their costs. "Over the past three years we've
had 800 companies call and say, 'We can solve your problem,'"
says Walter Cherry, executive director of the North Carolina
Pork Council. Cherry directs them all to NCSU for evaluation.
Moe agrees there are a lot of vendors with unsubstantiated
claims. For Cherry, the downturn in pork exports shifts the
frame for the debate to economics. He cites a two-year study
funded by the Pork Council that found that only about 25% of
the state's larger hog farms (2,500 or more animals) had odor
problems or potential odor problems.
Don Webb, a former hog farmer and head of the Alliance for
a Responsible Swine Industry, insists that the pork industry's
influence in North Carolina has slowed odor-control efforts
there. "The technologies to do something about odor are here
now," Webb says, but the industry doesn't want to invest in
them. Webb believes that the NCSU study team has been
pressured to avoid costly measures, and to instead seek out
technologies that convert the waste into usable commercial
products, such as potting soil. To the dictum of
nineteenth-century pork baron Gustavius Swift, who said, "We
use everything but the squeal," Webb adds: "They want to make
money off the squeal."
Still, there are signs that the winds of change are blowing
through the hog industry. "There are technologies to take care
of [odor]," says Schiffman, noting the lagoon covers, fan
exhaust biofilters, good management, and better facility
design. In November 1998, South Dakota voters approved a
constitutional amendment allowing only family-run farms to
operate in the state. (Family-run farms tend to be smaller
facilities with lower concentrations of animals that produce
lower levels of noxious odors.) And in North Carolina, new
provisional rules regulating animal farm odors are expected to
be in place by March 1, as directed by the state assembly. The
current version of the rules sets minimum standards for all
pork producers based on low-cost best-management practices.
Beyond that, complaints about a facility can prompt the state
to require a best-management plan for controlling odors.
Meanwhile, the state's Environmental Management Commission is
proceeding to develop permanent rules.
|
Suggested Reading
North Carolina State University Odor Control Task
Force. Control of odor emissions from animal operations.
Raleigh, NC:North Carolina Agricultural Research
Service, 1998.
Schiffman SS. Livestock odors: implications for human
health and well-being. J Anim Sci 76:1343-1355 (1998).
Thu K. Odor problems from large-scale agriculture:
nuisance or public health problem? Health Environ Dig
12(8):57-59 (1998).
FAS. Livestock and poultry: world markets and trade.
Circular series FLP1-98. Washington, DC:United States
Department of Agriculture, Foreign Agricultural Service,
1998. |
David Taylor
Last Updated: March 1 , 1999
