How the Calgary Composting Facility works
How the composting process works
Although the science is similar to backyard composting, here's an in-depth look at how industrial scale composting is different and why you can compost so many more materials with your Green Cart. From start to finish it takes approximately 60 days to produce nutrient-rich compost.
Two varieties of compost
The composting facility produces two compost varieties from two different sources. They are processed separately at different times of the year. They are:
- A Category A compost made from Green Cart food and yard waste; and
- A nutrient-rich biosolids based compost that meets Category A or B criteria.
Both add valuable nutrients to the soil. The composting process and testing for each variety is the same.
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The composting process
Step 1 - Shredding the material
Food and yard waste arrives by trucks to the composting facility. The material is shredded to create a recipe for optimum decomposition.
During the winter months dewatered biosolids are brought to the compost facility. Biosolids are a nutrient-rich, organic material produced by advanced wastewater treatment. Biosolids are blended with various types of wood chips to create the ideal mix to enhance the composting process.
Front end loaders and conveyors move material into composting vessels. Biosolids material and Green Cart food and yard waste are kept separate.
Step 2 - In-vessel composting
The material stays in the composting vessels for 21 days. During this time the pipes that extend beneath each vessel pump air into the material, keeping the microorganisms that break down the material active. Vessels are monitored for things such as temperature, moisture content and oxygen levels. This keeps the decomposition process running smoothly.
- Odour control
Odour management is one of our main priorities. We've invested in odour control systems to filter them out. Large biofilters are used to reduce odours before exhausting air from the building. Air from both the active composting and curing phases is directed through the biofilters.
- Eliminating pathogens
The compost pile reaches temperatures of at least 55 degrees Celsius for at least 3 days in a row. These sustained temperatures are difficult to achieve in backyard composters. This step is important because it kills off pathogens like e-coli and salmonella that might be found in materials like uncooked meats and pet waste.
Step 3 - Screening
The compost is screened producing top quality compost. This allows us to remove any contaminants that still remain and take them to the landfill.
Step 4 - Curing and cool down
After screening, the compost material enters the curing building where it remains for another 21 days. The material is turned over and mixed every five days to introduce oxygen and encourage further decomposition. Pipes in the floor draw air in and through the material to further enhance break down. After curing, the material is moved to the compost storage facility.
Step 5 - Final product testing
The composting facility produces Category A compost from green cart material that is safe to use anywhere, including farms, gardens, parks and nurseries.
To ensure it meets this compost standard, samples are sent to a Compost Quality Alliance (CQA) accredited lab for analysis to ensure it passes the criteria set by the Canadian Council of Ministers of the Environment.
Step 6 - Sales
Once certified, the compost is ready for distribution. Compost is a sustainable, nutrient-rich soil amendment used to enrich our soils.
The majority of the finished compost is sold in bulk to companies such as landscape soil blenders and compost baggers. The proceeds from the sale of the compost help reduce the processing cost and lower the Green Cart program fee.
A portion of the finished Category A compost from Green Cart is made available to the community for free. This includes being made available for community gardens and through select giveaway days to the public.
The City of Calgary's goal is to divert 70 per cent of waste from City landfills by 2025. Learn more about the City's waste goals.