Remarkable odour control
It’s difficult to find a large-scale composting facility operating in Canada today that doesn’t experience at least a handful of odour complaints each year but a reasonably-well designed and operated AD plant should be able to operate with zero off-site odours, since most operations are carried out in gas-tight piping and tanks.
The Bio-En Power facility in Elmira, Ontario processes 70,000 tonnes of organics per year, and does so on a small, urban lot just larger than three acres. More than 20 single-family homes are located within 300 metres of the centre of the plant, yet the facility has never experienced a single odour complaint.
The City of Toronto’s Disco Road AD facility processes 75,000 tonnes of curbside organics every year, and likewise has a sterling odour- control record, though there are many commercial, office, and industrial properties within a short distance.
Higher tolerance for contaminants
The City of Toronto strongly encourages residents to use as many layers of plastic bags as necessary to deal with the ‘yuck’ factor in packaging their curbside organics because its AD plant has a pre-processing system capable of separating those materials (not to mention button batteries, cutlery, ceramics, and oyster shells) from the organics before the material even gets to the digester.
Likewise, the Bio-En Power plant in Elmira, which processes municipal green bin organics, is simultaneously able to take in large loads of off-spec, spoiled, and recalled commercial organics in original packaging, including foam meat trays and glass bottles. It’s widely-established that the pre-processing systems available, especially with ‘wet’-type AD plants, allow them to routinely work with feedstock streams no composting facility could responsibly consider.
Of particular interest to municipalities is diversion numbers. A higher tolerance for inorganic contaminants means it’s easier to look at adding diapers and similar materials to the definition of
organics. Likewise, municipalities who move into sourcing organics from the multi-unit residential sector know they can count on AD systems to handle a high level of contaminants. Both Ontario’s Regional Municipalities of Peel and of Durham have recently embarked on procurement processes for AD capacity, premised on this very goal.
Some propose AD is more costly to build and operate than a comparable composting facility. Based on Bio-En’s experience, this conventional wisdom will soon be turned on its head. AD’s trump card is that every plant produces biogas, which can be used to generate energy revenue.
Obtaining lower costs requires preliminary design considerations. If the only goal is to process organics with energy as a by-product, the plant could end up expensive. But if the over-arching objective is a great, low-cost facility that doesn’t produce odours and deals well with the organics, design and operational decisions can indeed achieve this result.
For instance, if the plant is designed to maximize biogas production, even if that marginally increases capital cost, and is operated to take advantage of this potential, we know that the all-in system cost per tonne can be significantly lower than comparable costs of enclosed composting facilities.
Make Your Own Low-carbon Fleet Fuel
An option when deciding how to use biogas produced by an AD plant is whether to scrub it, produce natural gas, or burn it to produce electricity. Natural gas produced in this way (or from a landfill gas project, for instance), is called renewable natural gas (RNG), as it is being manufactured from a completely-renewable source – the organic wastes – rather than being pulled out of the ground. It can be used for any purpose natural gas can be used for, but an increasingly popular strategy is use to power municipal vehicle fleets.
The City of Surrey, BC is building an AD plant that will process curbside organics and produce biogas to make RNG for the city’s waste collection fleet. That’s the same fleet that picks up the organics in the first place. Talk about closing the loop.
The City of St-Hyacinthe, Quebec is developing a staged project that will produce RNG from curbside organics, biosolids in its wastewater treatment plant digester, and an abundance of local dairy-industry organic wastes, and hopes to eventually power its entire municipal fleet this way, right down to pickup trucks and street sweepers.
Revenue from selling RNG on par with today’s street price for diesel is enough to allow your AD plant to cover most of its operating costs if the plant is thoughtfully designed and operated with that goal in mind.
A municipality that uses its own RNG to power its vehicle fleet can get off of the world fuel price roller-coaster. Include an inflationary adjuster so the AD plant has a steady and predictable source of revenue, and you have a locked-in and predictable fuel cost for that vehicle fleet for years to come.
Several Canadian municipalities have already switched their waste collection fleets to natural gas because it is a much lower-carbon fuel than diesel, and the Ontario government has recently announced aggressive funding and other incentives to try and push heavy truck and transit vehicles off of diesel and into natural gas engines as a key plank in that province’s climate change strategy.
AD Market Tips
If you are thinking of building an AD plant, here are some key considerations in that procurement:
Seek a Low-cost Solution
To keep costs reasonable, design and build a plant to squeeze as much energy as possible out of the waste. Some facilities actually produce 50% more energy from the same waste because they were designed with that goal in mind.
Decide on the revenue goals and energy use before procuring the plant. This is easy for a municipality, since the biogas can operate the vehicle fleet as RNG. To do the procurement process properly, you need to set a price for the RNG, so bidders can assume the same level of revenue. We recommend 85 cents per diesel-litre equivalent—enough revenue to cover most of the plant’s operating costs and a competitive cost for truck fuel.
Be sure to link capital recovery and net operating costs to derive the lowest possible lifetime cost for the plant. Technology providers will respond to this if they’re given a specific target.
Demand a Super-clean End Product
Canada’s approximately 60 AD plants commonly direct market digestate as an agricultural soil amendment and apply it to farm lands without further processing.
Some others (the City of Toronto’s Disco Road plant, for instance), first de-water the digestate and market the resulting solids as compost. This latter approach will be used in large municipal plants planned for construction in Quebec.
We recommend buyers insist that the digestate meet the highest prevailing Canadian compost quality standards for pathogens, foreign and sharp foreign matter, and heavy metals. Standards vary widely from province to province, and between compost and digestate. To last 20–25 years, a plant should be built to where standards may be tomorrow.
The Bureau de Normalisation du Quebec (BNQ) is responsible for creating the ‘parent’ standards for compost quality in Canada, and issued its latest version earlier this year. In time, provinces will likely adopt this standard, including that for municipal organics-derived digestate.
Think Hard about Liquid Organics
Most Canadian AD plants process both solid and liquid organic wastes as feedstocks. There are also suitable liquid wastes out there looking for a home: fats, oils, and greases, and a broad range of food industry process waters and sludges. Including liquids brings three distinct advantages, all of which help to further reduce costs:
- Energy-rich liquids mean more power can be produced by the plant
- Most AD plants need large quantities of input water to produce a slurry from solid waste feedstocks. Displacing water with liquid wastes saves on water costs
- Liquid wastes will come with additional tipping fees
Think Hard about Commercial Organics
There are, of course, many commercial organic wastes that need management. Limiting a facility to processing municipally-collected organics will force these materials elsewhere, taking their energy and tipping fees with them. Build a slightly larger facility to accommodate these materials and take advantage of the economies of scale.
One Design and Operation Vendor
AD facilities can be complex to manage and operate. Have yours operated by an experienced operator with a track record that impresses, and ensure the plant is designed, built, and operated
by the same group, as a single package. That way, the plant will be designed and built to be practical and ensure success.