Large Scale Composting

Grow Calgary Accelerated Composting Program 

Market Gardening, Urban Farming, & Commercial Organics Collection for Composting at Grow Calgary contribute to the health of our soil resulting in increased yields for the Calgary Food Bank Fresh & Local hamper program.

Grow Calgary works with many local companies to acquire the materials for our large scale compost program. We source from local restaurants and food producers to access their commercially produced compostable materials. We receive grass, leaves, sod and chips from local landscapers and arborists. We assist 20+ Calgary companies with diversion of organic resources from the landfill for use in Grow Calgary's Accelerated Composting Program. This is part of Grow Calgary's commitment to sustainable agriculture.

Compost is organic matter that has been decomposed and recycled many times over, and is used as fertilizer and as a soil amendment. Essentially composting requires a large amount of wet organic matter (known as green waste or raw materials), which include leaves, food wastes, grass clippings, etc., and waiting for it to decompose and break down into humus (the black soil found on top of an A horizon aka organic matter).

Decomposition can be sped up by shredding the plant matter, adding water, and ensuring proper aeration by turning the organic matter. Worms, fungi further break up the material, and aerobic bacteria converts the inputs into heat, ammonium, and carbon dioxide. 

Compost is rich in nutrients and can be beneficial to the soil. It acts as a fertilizer, soil conditioner, and can aid in the reduction of erosion, reduce landfill input, and save you money!

* Fun fact: over 60% of what we put into landfills each year is organic waste, and can be recycled through composting! 

Compost is composed of 4 ingredients: carbon, nitrogen, oxygen, and water. A combination of these ingredients makes the perfect conditions for breakdown of materials.

Composting on a small scale is quite manageable, however, on a large scale requires more thought and planning. There are two different methods for large scale composting: wind-row composting and in-vessel composting.

Wind-row composting has three different methods:

• Turned wind-rows
• Passively aerated wind-rows
• Aerated static pile

Turned wind-rows

Turned wind-rows are essentially long narrow rows of compost that are turned or agitated on a regular basis. This turning/agitation mixes the organic matter and enhances passive aeration of the mixture. 

Passively aerated wind-rows are a little more complicated. With this method, air is supplied to the decomposing material via perforated pipes that are embedded into each wind-row. This therefore eliminates the need for turning or agitation. The ends of the pipe are open to allow for air flow in and out. Since the materials are not turned, it is important that the materials are thoroughly mixed before the are placed on top of the pile. 

Aerated Static Pile

Aerated static piles take passively aerated wind rows to the next level by using a blower to supply air to the organic matter. This method provides control of the airflow and therefore allow for larger piles. Just like passively aerated wind-rows, no turning or agitation is needed. 



In-vessel composting refers to several methods that comprise of confining the organic matter within a vessel, building, or container. These methods consist of turning the material sometimes and forced aeration to speed up the composting process. Some of these methods include:

• Bin composting
• Rectangular agitated beds
• Silos
• Rotating drums

Bin composting is the simplest in-vessel method. The organic materials are confined by walls and a roof and allow for higher stacking of materials. This method also eliminate weather problems, odour issues, and provide better temperature control inside. Bin composting operates in similar fashion to aerated static pile method. There is some forced aeration and little to no turning of the materials, although occasional remixing and turning of materials can speed up the process.

Rectangular agitated beds is a combination of controlled aeration with periodic turning of the material. The composing is done in beds (long, narrow channels surrounded by walls). A channel or rail on top of the surrounding walls supports and guides a compost-turning machine. Raw material is loaded at the front of the bed. As that turning machine moves forwards, it mixes the compost in the bed and discharges the compost behind itself. With each turn, the turning machine moves the compost towards the end of the bed at a set distance.


Silos are another technique (which resembles a bottom-unloading silo), which involves an auger (large screw that functions as a conveyor belt) that removes the compost from the bottom of the silo, while a mixture of new raw materials is added to the top. There is an aeration system that blows air up into the silo from the base. A downfall of this method is the fact that stacking of the raw materials increases compaction, reduces temperature control, and increases air flow challenges. Since the materials in the silo do not experience significant mixing, raw materials must be thoroughly mixed before being loaded into the silo.

Rotating drums is another method that employs a horizontal rotary drum to mix, aerate, and move the raw materials through the system. The drum is mounted on large bearings and its rotated through a bull gear. Air is supplied via the discharge end and incorporates into the material as it is tumbling, and moves in the opposite direction of the material. 


References: 
http://www.exmouth.wa.gov.au/composting.aspx
http://en.wikipedia.org/wiki/Compost
http://www.fao.org/docrep/007/y5104e/y5104e07.htm