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Introduction
In 1997, the swine industry and
especially the intensive swine operations (ISO) have had to face
opposition from rural communities. This social attitude results from
four major developments.
Large modern livestock operations
concentrated the production of waste, creating a stress on the
environment. In parallel, there has been a major increase in the number
of dwellings in and around agricultural areas (Ecologistics Ltd, 1996).
Swine producers have increased their production to respond to new Asian
Markets. The local agricultural producers have supported the effort
against the larger swine producers fearing that the livelihood of their
own operation is at stake (Thu et al. 1996).
The environmental legislation has not
adequately dealt with the environmental problems in some cases because
the dirty operator still pollutes while respecting the laws and bylaws
while the clean operator is penalized and there is a discrepancy between
the requirements of the laws and bylaws and the science of manure
management.
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The Canadian odour control legislation for
livestock operations
In Canada, the provincial governments
are responsible for the protection of the general soil, air and water
resources against livestock operations. Accordingly, livestock
legislation varies greatly among Canadian provinces. Some provinces,
such as British Columbia, Alberta, Manitoba, Ontario and Nova Scotia,
operate from Codes of Practices. In British Columbia, Alberta and
Ontario, a livestock producer can be fined for polluting if he does not
observe the Code of Practice. In Saskatchewan, Manitoba and Québec, the
present legislation requires that a livestock producer obtain a
certificate of authorization before proceeding with a new construction,
changing the type of livestock in an existing barn or increasing the
size of an existing shelter. New Brunswick, Nova Scotia and Prince
Edward Island have guidelines for the management of livestock manures.
In Provinces operating from a Code of
Practice, municipalities have introduced laws governing livestock
operations. Ontario is changing its Law on the Right to Farm to prevent
municipalities from legislating against livestock operations, provided
that these respect the Code of Practice. In other provinces such as
Québec, municipalities have enforced more demanding regulations and this
has prompted the introduction of a Law on the Right to Farm with
modified environmental laws to insure the protection of the rural
environment. British Columbia was able to introduce a law on the Right
to Farm with more ease.
In all Canadian provinces, odours are
controlled by requiring livestock producers to respect separation
distances. These distances are established provincially and thus vary
depending upon land use and availability of space. But, these separation
distances have never been based on Canadian nor North American criteria
and are not flexible enough to include the effects of various management
techniques nor to solve existing urban/agricultural conflicts. The
present separation distances used for odour control give producers no
incentive to clean up their operations, on one side, and on the other,
do not protect neighbouring dwellings from preferential air streams and
dirty operations. The separation distances are not flexible enough to
account for the new odour control technologies being developed. There is
a need to improve these separation distances by using a more direct
approach.
Livestock separation distances could be
better adapted to Canadian conditions by evaluating the sensitivity of
the Canadian population to swine manure odours and evaluating the level
of odour produced from Canadian swine operations using various types of
manure management techniques.
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Odour control techniques for the swine
operations
There is a pressing need to introduce
odour control techniques especially for the swine industry. In North
Carolina, people living near swine operations were found to show
significantly more anger, confusion, tension, depression, fatigue, mood
disturbances and less vigour than people living in the absence of such
operations (Schiffman 1995). Physiological and learned response may have
contributed to the mood alterations of these people. The human olfactory
acuity to mal-odours has also increased because of the more frequent use
of therapeutic drugs and food chemicals (Schiffman 1994). Humans are now
under more pressure and their health can suffer under the additional
stress of having no control over their exposure to mal-odours (Cunnick
1995).
As opposed to other livestock
operations, it seems that swine operations emit odours producing more
human response. Swine excretions are the most liquid of all excretions
leading to their anaerobic decomposition and producing stronger and more
toxic odours as opposed to solid manures (Spoelstra 1980; Sobel 1988;
Ritter 1989). Swine manure odours are richer in reduced gases containing
sulphur, such as the thiol group which is detectable by the human
olfactory sense at levels of 3 x 10-7 mg/m3 of air (Neil and Phillips
1992). In contact with the human nose, these gases oxidize and create
strong sulphur base acids which irritate the sense (Hobbs et al. 1995).
Swine manures have a high Biological Oxygen Demand (BOD) and start
decomposing anaerobically within 24 hours of excretion (Loerh 1984).
Therefore, manure odour problems are associated with all stages of
handling, from the barn to the storage and the disposal operation on
land. Approximately 20% of the manure odour complaints can be related to
barn venting, while 35% and 45% can be related to storage and field
spreading, respectively (Hardwick 1986).
The techniques now available for the
control of livestock odours will therefore be discussed with the
exception of:
1) aeration because of its high cost and
high nitrogen losses;
2) adoption of solid manure systems
because liquid systems are clean, practical and economical, especially
when dealing with large volumes;
3) soil injection of manure during land
spreading because this is a well known technique which takes twice as
much time and energy, requires well drained soils resistant to
compaction but reduces ammonia losses through volatilization by 50 to
90% (Negi et al. 1978).
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Manure management practices
Clean waste management, good animal care
practices, hygienic housing conditions and the frequent removal of the
manures are key odour control techniques in the barn. Often,
insufficient livestock space and poor ventilation leads to animal
stress, dirty habits and manure excretion all over the floor rather than
solely over the slats (Barrington et al. 1995a). The general recommended
practices for the shelters are:
1) designing manure gutters for minimum
air-manure surface contact (Voermans, 1994). Below-ground gutters keep
the manure cool and slows its decomposition. Manure gutters should also
offer minimal obstructions, such as lips and cross sectional beams, to
reduce the surface exposure of manures and the accommodation of flies;
2) using mechanical scrappers instead of
gravity flow because the manures can be removed before they start
releasing toxic gases;
3) reducing ammonia losses by handling
the waste with enough water to reduce the total solids content below 9%
(Barrington 1995a);
4) handling the waste as little as
possible but removing it from the building as quickly as it is produced
(Burton and Beauchamp 1986);
5) giving adequate space to the animals,
based on body weight, and housing them in groups of 12 and even 8 if
possible.
The spilling and over-flowing of storage
facilities can be avoided by using a safety depths of 300 mm above the
maximum (99% probability) rainfall depth. Manures should be introduced
at the tank bottom, under the liquid surface. This technique can reduce
nitrogen losses by 30%, on a yearly average (Muck and Steenhuis 1982).
In the field, application rates should
respect plant uptake and spreading should be performed close to the soil
surface. Incorporation is recommended within a few hours following the
manure application and injection is preferred where conditions are
suitable.
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Filters to treat the air vented from barns and
manure reservoirs
Biofilters are among the oldest
technique introduced to deodorize contaminated air vented from livestock
buildings. A biofilter consists of a box filled with a 500mm deep
mixture of 50% peat moss and 50% chopped reeds. The air ventilated from
the building is screened for dust and pressurized at 150Pa through the
biofilter material at a velocity of 300m/h. Odours are reduced from 60
to 80% (Noren 1986). The biofilter is kept moist by spraying with water
and microbes fixed on the biofilter are said to oxidize the odorous
gases. Because the biofilter material must be replaced after 5 years (Voermans
1994), it costs, per 100 finished hogs, $30 to $60 to install and $5 to
$10 to operate.
In Canada, biofilters such as peat moss
and straw are successfully used as floating covers over manure in
storage. In early spring, the organic material is blown, using a forage
harvester, over the liquid manure in storage and the manure is added
under the floating biofilter throughout the season. Odour and ammonia
emissions are reduced as a diffusion barrier is created between the
manure and the atmosphere. Peat moss offers the additional advantage of
absorbing ammonia and reducing nitrogen losses in storage by 40 to 60%,
as well as improving plant nutrient uptake in the field by 50%
(Barrington et al. 1995b). But peat, as straw, can only reduce the
diffusion of S containing gases as it does not absorb this element
(Barrington and Blais 1989; Al-Kanani et al. 1992).
Keeping the biofilter floating is the
greatest challenge. Oil is added to the straw while being blown over the
manure. At least 2 barrels of oil are required to treat 90 tons of straw
covering 2800m2 of storage (Filson 1995). Peat moss will float also if
it is very dry, applied to a depth of 200mm and contain a 50%/50%
mixture of particles greater and finer than 0.85mm. Fine particles
absorb N while the larger particles help float the filter.
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Manure additives for odour control
A number of biological agents have
successfully controlled manure odour emissions for some farms, while
they have generally failed in others and during initial laboratory tests
(Warburton et al. 1980; Patni and Jui 1993). Later, they were found to
work if applied at very specific rates and under initial aeration
(Barrington et al. 1995c). Operating conditions for biological additives
are not fully understood and before adopting an agent, a livestock
enterprise should find other successful operations with a manure
handling system similar to theirs. Control agents liquefying the manure
help reduce agitation time when removing the manure from storage and
thus, reduce odour emissions at that time. In general, livestock
producers use these biological agents for some time and then stop as no
economic benefits are observed (Tandem Trade Corporation, 1995).
Odour reducing feed additives have also
been tested. When added to the feed of grower hogs at the rate of 5%,
zeolite improved feed conversion by 0.25 kg/kg of weight gain, including
the weight of the zeolite. It also reduced air odours and ammonia levels
in the barn and improved carcass value by 0.05$/live kg (Barrington and
El Moueddeb 1995a). De-odorase (Yuka extract) proved helpful in reducing
ammonia levels in piggeries but had no effect on odour level and
livestock productivity (Amon et al. 1995). Acid salts can be added to
the feed of grower hogs to reduce the pH of their faeces from 7 to 5 and
the ammonia volatilization from 1.74 to 0.85 kg/pig place/year. These
salts were also found to improve feed conversion from 2.80 to 2.67 kg of
feed per kg of live weight, but to increase production costs by
6$/finished hog (Hendriks et al. 1997).
Fly ash has been tested as a stabilizing
agent inhibiting the production of odorous gases (Barrington et al.
1988; Bundy 1995). Rich in calcium, these ashes increase the manure pH
to 12 where all microbial activity ceases and sulphur compounds become
fixed. Large quantities of ash are required (250kg per m3 of wet manure)
and ammonia is released initially during the incorporation process. The
high pH tends to fall after one month of treatment and odour production
is re-initiated.
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Manure treatment for odour control
Oligolysis, an electric current induced
through manure which enhances the fixation of sulphur to the iron
electrodes. This treatment costs 0.56kWh/m3 of manure treated for 7 days
or $5.65 per pig grown. It was found to reduce the emission of sulphur
gases but not to reduce the overall odour effect (Feddes 1996). It is
being sold by a popular equipment dealer.
Cold temperature anaerobic fermentation
is a technique which has been tested by Agriculture Canada (Massé 1997).
It requires the use of a sealed cover over the storage tank. The low
volumes of gas produced have a high methane content.
Dryers with improved efficiency are
being introduced on the market. The efficiency is improved by running
the slurry in thin layers over a belt and by recirculating the dryer
air. The manure has to be dried down to 5% moisture content and the cost
is still about $5.00/hog. Drying using cold outside temperatures is a
promising technology which is being tested in the Prairie Provinces.
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Acknowledgement
This research was made possible through
the financial help of Atara Corporation of Montréal, Québec, Canada,
Scicorps Systems Inc. of Burlington, Ontario, Canada, Whitehorse
Minerals Ltd of Calgary, Alberta, The National Research Council of
Canada, Agriculture Québec and the Natural Sciences and Engineering
Research Council of Canada.
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