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Green Cart composting facility and process

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About the composting facility

The Calgary Composting Facility is the largest of its kind in Canada. The facility is owned by The City of Calgary and operated by AIM Environmental Group.

The facility produces high quality compost from both food and yard waste collected from the Green Cart program and dewatered biosolids, a nutrient-rich by-product from wastewater treatment.

Three buildings make up the composting facility - main building, curing building and storage building. Together, the facility is 521,000 square feet. The facility will process upwards of 145,500 metric tons of residential food and yard waste and dewatered biosolids every year.

Green Cart compost giveaway

The City of Calgary will be offering free compost for residents to use in their yards and gardens this spring. To learn more about how the giveaway works, visit Green Cart Compost Giveaway.

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 new composting facility will produce two compost varieties from two different sources. They will be processed separately at different times of the year. They are:

Both add valuable nutrients to the soil. The composting process and testing for each variety is the same.


Green Cart Compost Facility Process Infographic
Please click the image to view a full size picture

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 all of the material into large 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 happy. 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 will reach temperatures of at least 55 degrees Celsius. 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 wa​ste.

Step 3 - Screening

The composted material is s​cre​ened to as small as 12 millimetres, 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 will produce a Category A compost from green cart material that is safe to use anywhere, including farms, gardens, parks and nurseries. Compost from biosolids meets Category A or B criteria. Category B compost is more suitable for agriculture and land reclamation uses.

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 Category A or B compost is ready for distribution. Compost is a sustainable, nutrient-rich soil amendment used to enrich our soils.

The majority of the finished compost will be 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 will be made available to the community for free. This includes being made available for community gardens and through select giveaway days to the public.

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