August 16, 2011 | General

Digesting Septage And Food Waste

BioCycle August 2011, Vol. 52, No. 8, p. 57
With a pending ban on land applying untreated septage and abattoir waste, townships team up to build a mixed organics AD system.
Dan Sullivan

THE municipalities of Georgian Bluffs and Chatsworth in Ontario, Canada have teamed up to manage septage and other organic waste through investment in an anaerobic digester, which began operating in December 2010 and has been providing power to the grid since March 2011. The nearby municipality of Meaford, local businesses and institutions pay up to $45/metric ton to deposit organics such as postconsumer residential food waste, abattoir residuals, FOG (fats, oils and grease) and kitchen waste from the Owen Sound hospital. Even at the highest tipping fee charged, that’s still $55/metric ton in cost savings over going to the local landfill.
But processing food waste – or even producing electricity for the grid with the produced biogas – wasn’t the main driving force behind the two towns forming the Georgian Bluff/Chatsworth Biogas Energy Project. “We’re in a large rural area where septic tanks have to be pumped,” explains Chatsworth Chief Administrative Officer Will Moore. The comanaged facility accepts septage for $25/ton. Additionally, the digester receives agricultural residues such as corn stover and spoiled hay. “Food waste was kind of an afterthought,” Moore says, adding that the higher rate of $45/ton for residential food waste is partially due to having to deal with contaminants.
Residential organics are typically placed by homeowners into noncompostable plastic bags, which are collected by Miller Waste. The hauler is supposed to clean the material before it comes to the digester, Moore notes. “We have a screener as well. Miller does the first ‘rip-open,’ and we do our own screening at the plant. If the process was streamlined so that we didn’t end up with any waste, perhaps we could reduce the tipping fee.” While some septage contains material that can’t pass through the screen, it’s pretty much a nonissue, he adds.
Another impetus for the project was anticipated legislation that would prohibit the land application of untreated septage and animal bloods. Still another reason for taking food waste is to provide the 1,000 m3 digester with year-round feedstock. People don’t generally pump their septic tanks during the colder winter months, Moore explains, because heaving brought on by freezing and thawing can cause the empty tanks to crack. The site – built at Georgian Bluff’s septage lagoon and servicing around 9,000 households – has storage capacity for 5,000 tons of material.

The Maple Reindeers Group partnered with CH4 Biogas, Inc., to build the new $3.5 million plant. The digester, which operates at 42°C (107.6°F), required about 400 metric tons of seed sludge – a third of its capacity – to get going. Corn stover was used as an initial codigestion substrate. The project received $ 1,766,668 from the Build Canada Fund, which is funded 50 percent from the federal government and 50 percent from the Province of Ontario.
Current production of 100 kW via a Caterpillar genset is expected to triple soon. “We’re going to 300 kW,” says Moore, adding that the expansion requires a grid-interface upgrade from single-phase to three-phase power. “The current financial plan calls for tripling output by next year because it’s working so well. We designed the system to handle that knowing it was where we’d eventually end up.” Power is sold to Ontario Hydro via a microFIT feed-in tarrif program that pays a premium for green power and is also available to producers of wind and solar electricity. “Our Fit contract is structured so that we receive 22.4 cents per Kw during peak hours and 14.9 cents off peak hours,” says Moore. “The average rate we have received so far is 16.9 cents.” Current electricity production nets the project $142,000 annually. At current volume, an additional $220,000 is collected annually via tipping fees. “We had to manage septic sludge, and this was the perfect way to do it and make money,” he adds.
The liquid fertilizer produced out the back end of the digester contains about 4 percent suspended solids. It is a 99.9 percent pathogen-free material – the most-pure claim the facility can make by law, says Moore. Currently, the material is land applied to farmers’ fields, but the facility is looking for a partner, as it would like to make and market a dry fertilizer product. “We’ve got big plans,” says Moore, adding that the partners are also considering construction of a commercial greenhouse that would utilize the waste heat from the genset.

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