An extensive literature
review has been conducted to collect and analyze information
on technologies and practices in odour measurement and mitigation.
The review and analysis are focused on the following nine
areas: (1) odour measurement and odour evaluation technologies;
(2) odour production and odour release quantification; (3)
feed additives and dietary manipulation for odour reduction;
(4) manure additives; (5) in-barn manure handling systems;
(6) manure storage design and management; (7) biofiltration;
(8) dust control; and (9) emerging technologies for odour
measurement and control. The suitabilities of odour management
technologies to Manitoba are evaluated in terms of cost and
climatic conditions.
Over 168 odour compounds have been identified in livestock
odours. These individual odour compounds may be measured with
analytical instrument such as GC or GC/MS, but there is no
established correlation between the individual odour compounds
and the human perception of odour. The most reliable way of
measuring odour is using the human olfactory sense (nose).
Dynamic-dilution olfactometers with trained human assessors
are considered to be the industry standard for measuring odour
concentration. However, there are considerable inconsistencies
in the design and operation of olfactometers. A national standard
should be developed, or existing standards, such as the European
Union Standard, should be adopted, to provide guidelines for
conducting olfactometry measurements of livestock odours.
The human sniffing technique shows the potential of evaluating
odour directly in the field. This technology is relatively
inexpensive and may be adopted by various levels of regulatory
agencies for evaluating odour complaints.
Research on the quantification of odour emissions from swine
operations has been mainly focused on production buildings,
with limited information available on manure storage, land
application and mortality disposal. Odour emission rates vary
widely among different facilities and within the same types
of facilities. Reported odour emission rates range from 0.1
to 62 OU/s per m2 of floor area for various swine production
facilities. Limited data have shown that emission rates from
earthen manure storage (EMS) are mostly below 10 OU/s per
m2 of manure surface area. An EMS normally exposes a much
larger surface area than other storage types, and is therefore
commonly associated with more odour complaints. Odour emission
from land application could be minimized by proper injection.
Adoption of manure injection by producers has appeared to
shift odour complaints from land application to animal production
facilities and manure storage units. Field measurements should
be conducted to collect odour emission data from earthen manure
storage under Manitoba climate conditions. Scientific methods
should also be developed to assess the downwind impact of
odour sources from swine operations and to establish setback
requirements for Manitoba conditions.
Dietary manipulations have been shown to potentially reduce
odour generation in swine operations. Although much of research
to date has been done elsewhere, primarily in the Netherlands
and the Midwestern region of the US, the results of the majority
of the research can be translated to the Canadian situation
either directly or with further refinement. However, differences
in primary cereal crops used in feed and the associated differences
in chemical composition warrant further research in Manitoba.
Many chemical and biological products are being marketed
as manure additive for odour control. Research reported in
the literature is mostly focused on the evaluation of manure
additives, with little on the mechanism of action or the development
of products. Researchers have reported conflicting results
on the effectiveness of using manure additives. This is partially
due to the lack of universally accepted protocols for evaluating
manure additives. Although some existing manure additive products
have been shown to be effective in odour reduction under laboratory
conditions, they may not perform well in actual production
facilities. Many other factors, such as the building, ventilation,
manure handling, feeding, and the overall management practice,
may conceal the effect of manure additives in actual production
facilities.
The in-barn manure handling system plays an important role
in odour management. An effective manure handling system should
promote quick separation of manure from animals to minimize
odour generation. Properly designed slatted floor systems
provide an effective way of separating manure from animals
with minimum efforts. If manure is stored under the floors
in the barn, well-designed ventilation systems are necessary
to provide under-floor pit ventilation for minimizing odour
problems. Solid manure systems usually result in less odour
emission, but are more expensive and difficult to operate.
Research should be conducted to evaluate solid manure handling
systems for Manitoba conditions, in terms of their effectiveness
in odour reduction, economic feasibility, and agronomic impacts
of using solid manure as fertilizer.
Open-top manure storages such as earthen manure storage (EMS)
are a main source of odour from swine operations. Covering
the manure storage is an effective way of minimizing odour
emission. Biocovers, such as straw, provide a cost-effective
and farmer-friendly solution to odour problems associated
with EMS, however they have not been adopted on a widespread
basis by the swine industry. The straw cover is easy to apply,
but will sink over time, and thus reapplication is required.
Additional agitation and straw chopping are required for pump-out
if straw covers are used. Straw covers also increase the volume
of manure that must be transported. Synthetic plastic covers
that provide complete year-round odour control in a cost-effective
manner are commercially available. Research is needed to quantify
the odour reduction by using various covers under Manitoba
conditions.
Treating manure before or during storage may reduce odour
emission from manure storage. Some technologies that have
been studied are solid-liquid separation, anaerobic digestion,
and composting (for solid manure). Most odorous compounds
are contained in small manure particles. Therefore, removal
of fine particles is necessary for effective odour reduction
when using solid-liquid separation. Anaerobic digestion is
performed in closed digesters and it reduces odour emission
by converting odorous intermediate products of anaerobic decomposition
into odourless end products of carbon dioxide and methane.
Mesophilic and thermophilic anaerobic digestion seem hard
to be accepted in Manitoba because of associated high heating
cost during long and cold winter. Anaerobic digestion at lower
temperatures of psychrotrophic or psychrophilic range holds
some potential for Manitoba conditions.
Biofiltration is a potential technology for reducing odours
from livestock facilities. Open-bed biofilters are the most
common style for treating exhaust air from livestock facilities.
The open-bed filters usually use compost and wood chips as
filter medium and odour removal efficiencies of between 75%
and 90% may be achieved. Biofilters associated with livestock
operations generally do not need supplementary heat; the heat
from the exhaust air and exothermic microbial activity in
the filter bed is usually sufficient to keep the filter bed
in the right temperature range even under Manitoba climate
conditions. Despite the success of open-bed biofilters, there
is a need to continue research efforts to improve both the
economics and aesthetics of biofiltration systems for livestock
operations.
Dust may act as an important odour carrier. Odour compounds
attached to small dust particles stays in the air longer,
thus having a greater downwind impact. Furthermore, many of
the respirable dust particles are odorous because of their
fecal origin. Spraying oil or oil-water mixture inside the
building seems to be effective in reducing dust and odour
emissions. Other options, such as mechanical and electrical
dust removal, are expensive.
One of the greatest obstacles to the advancement of odour
management is the difficulty of measuring odour itself. Olfactometers
are only capable of measuring the odour concentration. The
electronic nose (e-nose) technology has the potential of measuring
both quality and quantity of odour. Research is needed to
correlate human perceptions of odours to e-nose measurements
and to develop portable e-noses for field measurements of
odour.
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