Are they the BEST
Manure Handling Problems?
Bruce T. Bowman
(last Updated: 2009-02-20)
Stanton Bros. dairy manure digester (under construction)
near Ilderton, ON Photo:
The adoption of manure anaerobic digesters is much more advanced in
Europe than in North America, and especially more so than in Canada. In
searching for technical information on operating digesters, the majority
of the information (particularly on pilot plants), is of European
origin. This practical long-term European experience indicates that
manure digesters can operate well and are of economic value in cooler
climates, similar to Canada's. We have documented several installations
on this web site which are in Sweden and Denmark.
Manure digesters, especially those with co-generation capabilities,
may deserve another look in Canada, especially with increasing volatile
energy costs, and increasing concerns about greenhouse gas emissions,
odour and pathogens in manure.
The technology of anaerobic manure digestion has the potential to
accomplish the following:
- Greatly reduce odour levels during manure processing,
creating a relatively odour-free end product (closed vessel
processing confines odourous compounds which are converted to other
compounds). Digested manure, which could be subsequently applied to
land, would not have more odour associated with it than would composted manure.
- Reduce pathogen levels in the final products. Anaerobic
digestion greatly reduces pathogen levels. Additional pre- or
post-digester technologies can ensure pathogen-free end products.
- Conserve nutrients - more than 90% of nutrients entering
anaerobic digesters are conserved through the digestion process. By
conserving nitrogen during digestion, the N:P ratio of the treated
manure is more favourable for plant growth. Reducing the demand for
additional mineral nitrogen helps decrease the use of natural gas
for production of new mineral nitrogen, as well as reduce greenhouse
gas emissions associated with nitrogen fertilizer production.
- Reduce greenhouse gas [ghg] emissions - Since
anaerobic digestion operates in a closed system, substantial
reductions in greenhouse gas emissions (methane, nitrous oxide) are
achieved. Ammonia losses, while not of direct ghg
concern, are also reduced. Ammonia is now on the list of toxic
substances under the Canadian
Environmental Protection Act (CEPA).
- Kill Weed Seeds and Reduce Herbicide Use - It has been
observed that weed seeds lose their viability while passing through
an anaerobic digester. In conventional manure management systems,
weed seeds maintain most of their viability as they pass through
animal guts and as well as through the storage and handling steps,
so that the seeds are repeatedly cycled back to the fields. After a
few years with A.D. processing, weed pressures are substantially
reduced, thus reducing herbicide requirements.
- Co-generation and Energy Independence - Anaerobic
digesters produce biogas (approx. 65% methane, 35% CO2)
which can be captured for supplying energy (heat, electricity) for
the operation, thereby achieving substantial cost recovery. With the
increasing privatization of power generation utilities, the "net
cost" of power delivered to the farm is steadily increasing, and
energy independence for the farmer is becoming a more attractive
option. Often the delivered cost of electrical power can be at least
double the original generating costs. The decision to
co-generate electricity should initially be driven by the savings
for meeting the farm's power requirements, rather than based on
potential sales of excess power back to the grid, if allowed.
However, in Ontario, several significant developments have changed
the economics for considering A.D. Systems for farmers:
Feed-In Tariff (FIT) Program pays for electricity generated from farm digesters at 19¢/kwh
(≤ 100 kW), 18.5¢/kwh (>100 kW to ≤ 250 kW), & 16¢/kwh (>250 kW
to ≤ 500 kW) when put into the grid, with a multiplier of 1.35 for
for peak-time generation. Being able to store biogas for
peak-demand generation offers farm-based A.D. systems an
important advantage over other less predictable sources of
renewable energy, such as wind or solar, both in terms of income
for the farmer as well as increased efficiency/stability for the
grid (decreased line losses, distributed generation).
- OMAFRA introduced the
Ontario Biogas Systems Financial Assistance Program
which provides financial assistance with some of the
capital costs associated with the design, construction and
startup of farm A.D. systems (program now closed).
Nutrient Management Act Regulation 267/03 (OMAFRA)
permits the importation of up to 25% food-grade organic
wastes from off-farm sources (e.g. fats, oils, greases) under
specified conditions, which can significantly boost the biogas
output efficiency and substantially improve the profitability of
the digester for the farmer.
In some other jurisdictions,
laws are now starting to be implemented, which may improve
the economics for co-generation on smaller farms. In this
scenario, the farmer can only off-set his on-farm electricity
costs by exporting surplus electricity to the grid.
- More predictable as sources of plant nutrients - The
final products of anaerobic digestion are quite homogenous and are
more predictable as sources of plant nutrients since they are in a
more mineral form (50% of carbon (labile) is converted to biogas -
methane & CO2). If there is treated manure in excess of
land base requirements, this homogenous product lends itself well to
further processing for off-farm "value-added" products (adding
supplemental nutrients can make this a valuable "organic
fertilizer"). If the end product is dried and pelletized, it can be
stored, transported and applied with existing fertilizer application
Recycling of livestock
nutrients back to cereal production sources should be an
essential part of any long-term agricultural sustainability plan.
Because of the large initial capital costs associated with the
design, testing and construction of an on-farm digester plant, very
careful planning is essential. The most efficient design is likely to be
unique and quite dependent upon the operation. The digester option is
likely to be more attractive to larger operations, or to
well-established existing operations wanting to expand and modernize
their manure management systems. One of the greatest challenges in
Canada for the A.D. industry is the lack of experienced design-build
companies with a proven track record.
When considering manure digesters as an option, it may enhance the
chances of success if local municipalities or other agricultural
industries (vegetable or fruit processing, slaughter houses) or
commercial industries (distillers, bio-fuel production) are considered
as potential partners.... any industry generating non-toxic organic
wastes as by-products of their operations. This appears to be the trend
of several European digesters documented in the
Digester Compendium. The addition of off-farm fatty wastes, animal rendering
wastes or vegetable/cooking oils can act as an accelerant for methane production,
increasing outputs by up to 4-fold.
One of the key benefits to the farmer for generating and
exporting renewable energy is that it provides new type of revenue
stream, one that is relatively independent from the cyclic nature of
crop and livestock commodities, and thus can provide some degree of
stabilization of farm income, especially when commodity prices are
depressed. Livestock will continue to generate manure regardless of
what farm commodity prices are!
Since farm-based energy systems can operate 7/24, they make an
important contribution to "distributed baseload capacity" for the
electrical grid, complimenting less-reliable wind and solar power
sources, as noted above. Electrical transmission losses are
typically in the 5-7% range, and having the generating capacity
distributed across the countryside increases overall grid stability,
while reducing transmission losses.
The buyers of green power may not always be governments, but also
private industry looking for emissions credits. A positive
consequence of such a policy would be that farmers would coincidently
solve quite many of the current environmental issues associated with
livestock manure management through economic avenues, rather than as a
result of prescriptive regulations (e.g. odours, pathogens, greenhouse
gas emissions). As noted above in Sect. 7, treated manures lend
themselves very well to value-added processing which is essential for
developing a new business activity for recycling livestock nutrients.
See related articles:
- Making manure processing a
- Changing the Paradigm for Manure
- Sustainable Nutrient Management
in Agriculture and Closing the Loop on Large-Scale Nutrient Flows
- Commentary on
Nutrient Recovery Systems
- A New
Paradigm for Agriculture: "FOOD + BIO-ENERGY PRODUCTION" [pdf]
Bruce T. Bowman,