INNISFAIL, Alta. – Malodorous piles of municipal wastewater sludge have some rural communities holding their noses.
“Odors are a political thing, so we’re looking at alternatives,” said Innisfail town engineer Clayton Ross.
Composting the sludge with wood chips to reduce the smell and potential contamination from human sewage is one avenue under investigation.
Everything flushed down an urban drain or toilet goes through a wastewater treatment plant. The byproduct is a stinky, tar-like sludge.
Some communities haul sludge to landfills while others, including the City of Calgary, give it to farmers who spread it on their fields like manure. However, concerns have arisen regarding public health.
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Innisfail’s 6,800 people produce about 100 tonnes of dry sludge per year.
The town dries the sludge in concrete-lined beds. It takes about a month to dry. It is then spread on a 90-acre piece of land owned by the town.
Spreading requires a permit from Alberta Environment and the sludge can only be put on the same piece of land every three years. The sludge is also tested for nutrients to determine what rate to spread it.
Trial run
Recently, a composting demonstration project at Innisfail used the services of a Calgary oilfield company that specializes in cleaning drilling mud and other hydrocarbon-contaminated soils. The oil company’s process blends wood chips, known as hog fuel, with municipal waste sludge.
“We take municipal waste sludge from the water treatment plant to composting rather than sending it straight to farmers’ fields,” said Dave Hill of Unique Oilfield Technology Services.
“A number of rural communities are considering it,” he said.
Wood chips have about 40 percent moisture content, while the sludge is more than 80 percent moisture. When blended together, it creates a product with 60 percent moisture that composts within a month or two.
“As long as it is screened and it meets (environmental) standards you can do what you want,” said Hill.
Alberta Environment demands a permit to spread this type of composted material.
The process involves building a wood chip bed 30 centimetres deep in a concrete-lined windrow. Perforated pipes are laid at 60 cm intervals in the holding area so air can get in for proper composting.
Next, a blend of sludge and wood chips is added and then covered with another protective layer of hog fuel.
Wood chips work well because they are porous and the microbial action is more efficient. As the composting microbes do their work, the windrows heat up and kill pathogens present in human sewage.
By straining the sludge and blending it according to an exact recipe, the compost is suitable for farmland.
“Anybody can compost. It’s really hard to compost well.”
Alberta Environment has specific composting standards. If a town like Innisfail decides to compost its sewage, a new facility would have to be built to prevent leakage or other environmental problems.
