Biogas (Anaerobic Digestion)
Table of Contents
When organic material breaks down in an oxygen-free environment a process called anaerobic digestion it produces a mix of methane and carbon dioxide called biogas, as well as a nutrient-rich slurry.
That biogas, in turn, can be burned as a fuel in a boiler or furnace, used to run a generator to create electricity and heat, or cleaned and concentrated for use as a natural gas replacement.
Manure is usually the primary feedstock in farm-based systems, but many other materials can be digested, including food industry products and by-products, organic wastes from municipalities and energy crops such as corn silage, haylage and grasses.
You'll find several digester models on the market, with designs that vary according to operating temperature, processing time, size, number of chambers and type of throughput (batch, continuous flow or plug flow).
Anaerobic digestion is widely used in Asia and parts of Europe. Ontario is a leader in North America, At least 20 biogas facilities will be operating in 2010 on farms and at (or near) food processing plants in Ontario. In the past, it served primarily as a method of treating manure, but now it is attracting interest as a way of generating renewable energy, especially as new technologies and control systems have improved performance.
The viability of a biogas system will depend on your access to materials: to create the right mix and volume, you may need to bring in materials from off-site.
Keep in mind that anaerobic digestion may not be cost-effective at a small scale, although you may wish to pursue it simply as a method of manure treatment.
See OMAFRA's factsheet Biogas Incentives and Requirements: Building a Farm-Based Biogas System in Ontario for information on how to start, where to get help and basic requirements for a biogas system.
OMAFRA estimates the capital costs for an anaerobic digestion system to be $6,700-10,000 per installed kilowatt. A digester should operate up to 8,000 hours per year although some operators may purposely run less time per year to focus on operation during hours when peak power prices can be obtained. The Ontario Power Authority facilitates the FIT program which offers a 20 year contract for electricity from renewable sources.
Prices for biogas ranges from 10.4 to 19.5 cents per kilowatt hour (kWh) plus community adder of 0.4 cents per kWh may be available.
A dairy herd of 100 cows produces enough manure to generate a continuous
25 to 30 kW. Adding 25 per cent good quality off-farm source material
such as grease trap waste from restaurants will triple the electrical
output. More information can be found using the Energy
Yields from a Farm-Based Anaerobic Digestion System infosheet.
Contact your local municipality to find out what permits and approvals are required. Keep in mind that zoning changes may be necessary. You should also find out how a farm-based anaerobic digester will be assessed for property tax purposes.
There are three routes to having biogas systems approved in Ontario.
If you're siting a biogas system at a livestock facility and building a Regulated Mixed AD Facility, you'll need to apply the Ontario Ministry of Agriculture, Food and Rural Affairs' Minimum Distance Separation Formulae.
If you plan to connect your system to the power grid, there are additional requirements you'll need to meet.
Finally, if you are using biogas as a fuel on-site, your system must be approved by the Technical Standards and Safety Authority.
Setting up a digester requires construction and electrical skills, so consider hiring a qualified contractor.
Once the system is installed, it may take some experimenting to achieve the right mix of materials and the right temperature to maximize digestion. Expect digester maintenance to take at least 1 hour per day.
Publications and Websites
The Ontario Ministry of Agriculture, Food and Rural Affairs has produced a number of publications on biogas, while the Integration of Renewable Energy on Farms website includes several pages of information on anaerobic digestion. As well, check the AgriEnergy Producers' Association of Ontarios Resource Kit for AgriEnergy Projects.
FarmEnergyOnline.com offers a business plan for anaerobic digestion systems.
For more information:
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