"Composting is a natural process that happens everywhere. At a basic level there's no effort required," explains Raven Recycling executive director Joy Snyder. "The key with a large-scale program is to manage the process so that it's quick and hot."

Heat kills the undesirable components including pathogens and weed seeds. A quick process is required to deal with the large volume at the municipal composting facility and to keep pace with northern summers.

Community composting started in Whitehorse in the 1990s and led to the formation of ROTS (Recycling Organics Together Society). ROTS initiated a commercial compost collection program and succeeded in having a compost facility included at the landfill. "Then the City of Whitehorse Waste Watch pilot program took off in 1995. Raven Recycling has operated the compost site at the landfill since the mid-1990s," says Snyder.

"Composting is in fact a very simple formula," Snyder explains, "It's about 50 per-cent carbon and 50 per-cent nitrogen, plus oxygen and water. Carbon comes from the 'browns' -- dry materials like paper, dead leaves or wood chips. Nitrogen comes from the 'greens' -- fresh, moist additions such as kitchen scraps, grass clippings and manure."

According to the composting manual from Olds College, an agriculture institute in Alberta, composting is 'a controlled biological process in which a succession of microbial populations convert organic material into a biologically stable product.' Composting is characterized by a microbially active period at high temperatures when easily digested materials are available, followed by a curing period at lower temperatures while more complex materials are slowly digested.

Composting is an aerobic process, meaning that the presence of oxygen is essential. Microorganisms that require oxygen work quickly to break down the plant materials to get the nutrients they need. But if the compost isn't turned and becomes compacted or too wet, anaerobic microorganisms will take over. These undesirable bacteria release methane gas and hydrogen sulfide, creating the 'rotten egg' smell often associated with compost piles.

To introduce air to the compost, the City uses a front-end loader to turn the piles. Workers ensure the piles stay uniformly moist because water allows bacteria to move around. Home composters can purchase compost accelerator with microbes in it, or they can do what Snyder does to achieve success in her own compost pile.

"The key to backyard composting is that I always put some of the last batch back in. It's like making sourdough or yogurt -- you retain some of the bacterial culture."

At the landfill, workers operate at a much larger scale and have to consider some different factors. "They build windrows using a mix of Waste Watch materials and yard waste -- the greens and browns. They store up some of the large volume materials so they can compose the makeup of the rows to get the right balance."

Snyder compares the exercise to a kitchen recipe, carefully executed to achieve a desired result. "The workers are always thinking about what they are adding in terms of nitrogen and carbon," she adds. "They take the temperature of the piles every day and test regularly for several things."

"The key is managing the temperature so that it's high enough to kill harmful pathogens but not too high to kill desirable bacteria. We maintain it at close to 70 degrees Celsius for at least twelve days," Snyder explains. To regulate the temperature, workers aerate the piles.

Waste Watch materials are continuously piled up through the winter in preparation for warm weather and composting season. "Sometimes the piles compost all winter long," says Snyder. "Microorganisms generate enough heat that they can thrive in piles from the previous summer -- even through our long winters."

The intense heat is why the Waste Watch program does not restrict many items that are usually eliminated from backyard compost bins. "Meat and dairy create concerns about salmonella and other pathogens. But at the city facility it's not an issue because the heat is so constant and intense, and we test it regularly," Snyder explains.

"Our compost meets Alberta Grade A standards for compost," says Snyder. "This means we test and monitor it for salinity, pH, the presence of heavy metals, fecal coliform, salmonella, as well as for nutrients-nitrogen, potassium, phosphate."

"In the past, compost at the Whitehorse landfill has not been properly screened. And we've outgrown the facility," she explains. But that's all going to change with the new compost facility the City of Whitehorse is building this summer.

"With the Waste Watch program being expanded city-wide, the upgraded facility will be able to handle the increased volume and solve all our problems," says Snyder. Compost will be screened and bagged, and will become a higher quality product.