Toronto invests in green technology with biogas digesters

Imagine a streetcar running on orange peels, the traffic lights running on leftover dinner scraps and your home powered by cow manure? One day the city of Toronto hopes to be sustained by renewable energy from the organic waste we throw in our green bins, with the use of biogas digesters.

A biogas digester (also known as anaerobic digester) is technology that converts organic waste into methane gas. It has two primary components for it to work at its highest efficiency. Most typically biogas digesters are equipped with cogeneration systems, the reciprocating motor fuelled by biogas which turns the generator to produce electricity.

Biogas digesters aren’t new in fact, the first commercial biogas system originated in1850 in Bombay, India. Most commonly you’ll find home versions of digesters in developing countries such as China where there is presently six to seven million single home biogas systems in use.

Brian Van Opstal, of Toronto’s Solid Waste Management Services, says the city collects 120,000 tonnes of green bin waste each year. That’s enough waste to produce 15 million cubic metres of biogas, enough energy to power up to 2, 000 homes for a year.

In 2002, Toronto commissioned its first anaerobic digester at the Dufferin Waste Management Facility. Its large septic tank 17 meters in diameter and 20 meters tall presently processes 30 to 35 tonnes of green bin waste each year. That’s enough to generate seven million kilowatt hours of electricity a year. According to Toronto Hydro, the annual electrical consumption of an average home is 10, 000 kilowatt hours a year.

The city has a $69 million plan to build two more anaerobic digestion plants by spring of 2011. One will be replacing the existing plant at the Dufferin site; the other will be built at the Disco Transfer Station at 120 Disco Road in Etobicoke. According to Van Opstal, the new biogas digesters will have conversion devices able to refine the gas into reusable energy, no different from the natural gas that flows through the present distribution system.

At the Dufferin site, pulped organics with a solids content of six percent are fed into the digester, a glass-lined steel septic tank with a working volume of 3,000 m3. Optimum temperature of the infeed material is 37°C (98.6 F), during colder months, a device known as a heat exchanger is used to maintain the optimum temperature.

Waste material is continuously withdrawn from the pulp and a screw press is used to separate the liquids and solids. Liquids are recycled back into a device in the digester known as a hydropulper. The capital costs for biogas utilization equipment can range from hundred of thousands of dollars to millions depending which gas utilization option is chosen. The operating costs can range from $48,000 per year to $82,000 per year, also depending on which gas utilization option chosen.

Although the anaerobic digester at the Dufferin site does produce large volumes of quality gas but there’s currently no cogeneration system installed to convert that gas into useable energy. Instead the gas is set ablaze. Van Opstal said this was due to the great deal of skepticism at the time regarding if anaerobic digestion would work to overcome the high costs involved with what was an “experimental” project.

“It’s a fact it was included in the original design but never installed…decisions were made between the design and construction phases of the project to remove it, said Van Opstal. “And that would have only been done to reduce project cost.”

Graemae Millen of CH Four Biogas, a leading developer of anaerobic digesters and biogas technology, believes biogas technology can supply whole communities with a viable source of sustainable energy from the volume of organic material the city generates.

“With the growing movement for green bin programs all across Canada, the applicability of community-based (biogas) systems is just exploding because a majority of that waste would be a viable feedstock, said Millen.”

Since 2005, all single family households – about 500,000 – in Toronto received curbside collection of organic materials. This represents tonnes of food scraps, soiled paper, disposable diapers, pet waste and other biodegradable residuals. Another 15,000 tonnes are being diverted from small commercial establishments.

Dairy farmer George Heinzle, owner of Terryland Farms in St. Eugene, has

George Heinzle's biogas digester at Terryland Farms, St. Eugene, Ontario.

 already seen the benefits. The manure from the 140 cows on his farm and his two anaerobic digesters each produce 180 kilowatts per hour generating 4,000 kilowatt hours per day. That’s enough electricity to power more than a 100 homes for a year and he says he’ll double that by Christmas.

Heinzle was the first of a handful of farmers generating renewable energy using biogas digesters and then selling it back to the province at a fixed rate. Heinzle has already invested $600,000 in his digester and said that figure could go as high as $1 million as soon as his second digester is “fully operational” by December of 2009.

One of the benefits of anaerobic digestion is once the manure is processed through the digester it becomes odorless, and can be reused as fertilizer. He also said the digestion process kills pathogens, reduces methane emissions, generates heat and electricity and is will always be a sustainable source of energy. He was the first in Ontario to sell energy back to the province under the Renewable Standard Offer Program (RESOP), but many seen that system as flawed with long queuing times and high fees for energy producers waiting to connect to the grid.   

Millen said the new Green Energy Act makes Canada “a continental leader when it comes to renewable energy development policy” and part of the new legislation would facilitate the development of renewable energy on a scale unseen anywhere else in North America.

Van Opstal said Toronto’s Waste Management Services initial focus was set on “waste diversion” which is processing the waste before it’s shipped to landfills. But says he recognizes the profitability of investing in projects such as biogas digesters that produce renewable forms of energy.

“One incentive for the production of electricity from renewable sources is the Feed-in Tariff program in the Green Energy Act by the Ontario Power Authority…it will pay an increased rate for producers of electricity from renewable sources,” said Van Opstal.

The electricity produced by biomass projects is purchased at 12 cents per kilo hour which is about double the base rate. The problem for biogas producers such as Heinzle is that they’re currently locked into a 20 year contract with the Ontario Power Authority (OPA) and are unable to reap the benefits that the new Green Energy Act has to offer. Although Heinzle believes the Green Energy Act is “a push in the right direction” he feels it’s time for the federal government to intervene.

“The problem is all the early adopters of biogas digesters, the ones who took the risks by signing with the Ontario Power Authority (OPA) we’re getting paid 12 cents per kilowatt an hour, now with the Feed-in Tariff program (FIT) everyone else is getting between 16 and a half to 21 cents,” said Heinzle.

Heinzle said if the government doesn’t quickly intervene to amend legislation of the Green Energy Act that the rising costs and inflation will put Ontario farmers out of business.

“I’m convinced that before the end of our 20 year term (with the OPA) we’ll have to shut down…unless the government admits they made a mistake,” said Heinzle. “It’s only fair that they allow us to be able to switch to the Feed in Tariff program…because with biogas digesters, we can produce electricity at a lower cost than other sources of renewable energy.”

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