Bioenergy is a renewable energy source that is derived from biomass, which is organic matter such as plants, algae material, or animal waste. The energy can be generated by burning biomass, or harnessing methane gas produced by natural decomposition. It is produced in large plants, or it can be produced using personal systems, such as biodigesters or other on-farm systems. The use of bioenergy has been steadily increasing and currently accounts for approximately 6% of Canada’s total energy supply. The three most common types of biofuels are biodiesel, ethanol, and biogas.
Biodiesel
Biodiesel is fuel derived from vegetable oils such as soybean, canola, and palm oils. Biodiesel is an incredibly safe renewable energy source that can extend the lifespan of engines. The burning of biomass can also be used to heat buildings, dry crops, and produce steam to generate electricity.
Small-scale biodiesel production can cost $2.50 to $3.50 per gallon for production and can cost small farms $5.30 to $7.00 per gallon, which is higher than the cost of regular diesel. In terms of kWh, a biomass system can range from 6 to 29 cents in price.
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A canola field with farm buildings in the background
Ethanol
Ethanol is a renewable fuel option that is made up of various organic materials, or biomass, the most common being corn. It can also be made from other cellulosic feedstocks, such as crop residue, wood, or sugarcane. Ethanol is used in various ways, from being a main component of vehicle fuel, to the main and intoxicating ingredient in alcoholic beverages.
It is either produced through a starch- or sugar-based production, the majority with a starch base (corn) due to its lower costs. Using the starch-based method, the corn goes through either a dry- or wet-mill, where it is reduced to several different components, one of which being ethanol. One acre of corn can produce approximately 300 gallons of ethanol.
If using cellulosic feedstocks, or the sugar-based ethanol production method, the process involves more steps and is done using either a biochemical or thermochemical method. This method is less common for its increased cost and use of materials, as one ton of sucrose will produce approximately 163 gallons of ethanol.
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Red gas nozzle sitting in corn kernels, with two full ears of corn on either side of the nozzle
Biodigesters
A biodigester digests organic waste/materials to produce renewable energy called biogas (methane and carbon dioxide) and fertilizer. Most food, greases, or animal manure can be processed and broken down in a biodigester to create these elements. The system gives off no odor as it is airtight (eliminating pests like flies and rodents). Continual water flow is used to dilute the organic waste, which is then fermented by microorganisms. This process is anaerobic as it takes place without oxygen and the bacteria created decomposes the waste to produce biogas. The final product is an organic and pathogen-free fertilizer or manure.
These systems may be implemented in any rural or urban area that generate a significant amount of food or animal waste. They are useful on farms with livestock, or in cultivation areas where fertilizer is used, as the systems produces fertilizer that can improve soil fertility. They can be found is smaller sizes that digest smaller amounts of organic waste. These systems are easy to use and require little maintenance. They are also eco-friendly as they reduce a facility’s carbon footprint by diverting the organic waste that would potentially go to landfills, to instead produce biogas that can be widely used.
After putting organic waste such as manure or food scraps into the tank of the biodigester, microorganisms digest it, and then produce biogas. The biogas is then collected at the top of the tank (the bladder of the tank), where it will sit until it is released to be used as an energy source. As the volume of organic waste increase, so will the amount of biogas. For small farms or small-scale use, the biogas can be used for electricity purposes like cooking or heating, for a couple hours at a time.
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Infographic of a cow producing manure, the manure going to a biodigester, the biodigester then outputting gas, organic fertilizers, green energy, and warm
Biodigesters require an optimal temperate of 38 degrees Celsius and can range in price depending on tank size and digester type. The system is designed to produce 60% methane and 39% carbon dioxide, which is equivalent to 5 cubic meters (2 large garbage cans per hour) of biogas per day. To find the right biodigester, calculate the volume of organic waste being produced daily and select a biodigester that meets these requirements. There are various types of small-scale biodigesters for stand-alone or on-farm use. Stand-alone biodigesters are primarily used to process food waste, but they can also digest other organic materials, such as yard waste, manure, and wastewater solids. Some common biodigesters are:
Fixed Dome Biodigesters
This system is a closed, dome-shaped digester with an immobile gas holder that sits on top of the digester. It is relatively low in cost due to not having any moving parts. The system is underground, which saves space, and protects it from fluctuating weather conditions and extreme temperatures.
Floating Drum Biodigesters
This system is an underground cylinder or dome-shaped system with a moving gasholder. When biogas is collected, the gas drum will rise, depending on the volume of stored biogas. When the biogas is used the drum will then fall.
Balloon Biodigesters
This system has a heat-sealed plastic or rubber balloon bag. There is an inlet on one side of the system and an outlet on the other. The biogas is stored in the upper portion of the system and is release using a gas pipe. This system is low in cost, easy to maintain, and has high temperature digesters when used in warm climates.
Low-Cost Polyethylene Tube
This system has an inlet slurry where organic waste flows in and enters the main chamber. When combined with water, the organic matter begins its fermentation process. The biogas accumulates at the top of the system, and the fertilizer stays on the bottom.
There are various other biodigesters available for small farms. Different types of biodigesters will have different gas storage, gas pressure, materials, durability, size, and biogas production methods. Before choosing a biodigester, calculate the volume of organic matter being produced and find an appropriate system with sufficient retention, determine what type of organic matter is being used, and if it can handle a range of solid concentrations.