Solid Waste & Recycling

Feature

The New State of the Art

New compost plants have begun popping up in central Canada like mushrooms after a spring rain. Using proven European technology, several look like they may become the model for various communities wor...


New compost plants have begun popping up in central Canada like mushrooms after a spring rain. Using proven European technology, several look like they may become the model for various communities working to increase organics processing and beneficial re-use as part of their plans to go beyond the blue box and attain the provincial goal of diverting 60 per cent or more of waste from landfill by 2008. I toured several plants this spring to understand how the processes work and make notes about what specific equipment is being used.

Toronto’s Dufferin organics plant

The City of Toronto’s Dufferin Organics plant is an interesting facility. Most of the current organics processing equipment is housed within a fairly large building from the 1970s formerly known as the Dufferin Experimental Resource Recovery Plant. The building has hosted a number of experiments in mechanical/biological treatment (MBT) for processing mixed and organic wastes, namely a first-generation reactor known as the Hardy-Fairfield digester which was operated by the province. The end product would not satisfy today’s standards.

The current $10-million BTA system was commissioned in May 2004 to process source-separated organics (SSO) collected by the city, initially from a collection program in Etobicoke (that started in 2002). Overall, Toronto generates about 100,000 tonnes per year (tpy) of SSO material from its roughly half-million single-family homes. The city collects an additional 10,000 to 12,000 tpy of SSO from roughly 2,000 commercial establishments via its special “yellow bin” program. About 25,000 tpy (or a quarter of the total) is processed at the Dufferin plant. (Of the remainder, 15,000 to 18,000 tpy is shipped to Halton Recycling’s plant in Newmarket and the rest goes to plants in Quebec.)

The city will eventually issue a request for proposal (RFP) for another local plant for Toronto SSO. Staff have indicated they’d like to build another plant like the Dufferin facility, perhaps in the east end of town. Of course, the RFP will be open to other private sector bids and partnership ideas. The long-term vision is a combination of systems to process all the city’s single-family and multi-residential organics (plus some commercial organics) which it’s estimated will total 180,000 tpy by 2020. The city would like to manage 110,000 tpy itself and have the private sector manage the rest (70,000 tonnes).

The city owns the Dufferin plant, but the plant is operated by a partnership between Canada Composting Inc.’s company CCI Toronto and the TBN consortium (made up of Trow consultants, BTA, and Nichols Construction). Just five people run the plant working weekday shifts. It’s a testament to the robust performance of the digester that it can avoid upset over the weekends when no new material is being added.

Organics from the SSO program are lifted from the tipping floor by a CAT loader and conveyed to a hydro-pulping machine. The wet separation system allows for the removal of plastic bags at the top of the machine; gravity, torque and water work their magic on the organic materials and, in a second stage, heavy contaminants such as glass and grit are removed from the bottom.

The liquid material is pumped to the large outdoor digester where it’s retained for about 15 days at a temperature of 37C. Heat exchangers help maintain the mesophilic conditions, and gas is produced that actually exceeds the needs of the plant. The material is dewatered in a Huber press and shipped to an offsite facility for composting and blending with other organic materials (otherwise it would stay anaerobic). Bulking agents such as leaf and yard waste are added and the material is ready for market after about four to six months of curing.

Offsite composting allows the Dufferin plant to maintain a very small urban footprint. A biofilter takes care of emissions and the plant has had few odor problems. Capturing energy is another advantage of the system. The system works well and has avoided many process problems that have plagued other in-vessel facilities in Ontario.

Hamilton’s Central Composting Facility

Hamilton’s technologically-advanced Central Composting Facility opened in the first week of June on a 45-acre parcel of land on Burlington Street East. The northern third of the lot has been reserved for future waterworks infrastructure; the compost facility was purpose-built on a former Firestone Tire parking lot. The site already had a Certificate of Approval for use as a material recovery facility (MRF), but needed a C of A for air emissions.

The facility is the first large-scale compost plant built since the province’s environment minister announced the 60 per cent waste diversion goal, and it’s the first in the world to meet the new European standards (that strictly separate all dirty and clean stages in the system). It uses a Dutch in-vessel technology and is highly automated and SCADA computer controlled. (When I was there, technicians were directly performing tests on the system from Holland over the Internet.) In fact, four people (not including administrative staff) operate the plant during a day shift; this will rise to seven people and additional shifts when the plant is at capacity. The loaders are the only equipment that must be manually operated.

The $30-million facility (the size of three football fields) was built as a design/build/ operate project by Maple Reinders Contractors Ltd, who formed a partnership with other companies. These include: the Christiaens Group (the technology provider from Holland); Associated Engineering (which did the facility design and engineering work); and AIM Environmental Group of Stoney Creek (which operates the facility). Overall, this group is partnered with the City of Hamilton in a 15-year operating relationship. Peter Klaassen of Klaassen & Associates led the team that evaluated the different bids and technologies.

“Having a facilitator helped with out initial meetings and led to a smooth construction process,” says Craig Murdoch, the facility manager.

The facility is designed to take the 157,000 tpy of SSO generated by Hamilton residents and efficiently transform it into clean Grade A compost, without odor or dust problems. (The program doesn’t yet include the city’s roughly 30 per cent multi-residential sector.) The city collects the SSO via 140-litre IPL green wheeled carts it provided to residents, along with the same number of Rehrig minibins. The city started its collection program with an intensive public education program and a strict ban on plastic bags (and biodegradable bags). This has kept contamination levels low.

Material is initially lifted by a John Deere 744J loader into Komptech “Terminator” screening equipment (e.g., for glass and plastic), then passed under a magnetic overhead pulley before being transported via a transverse conveyer to the in-vessel aerobic tunnels. There are ten Phase One tunnels (37 metres long x 10 metres wide x 6 metres tall). Each tunnel holds 800 tonnes of wet incoming feedstock (which I was told equates to 120 BMW minis stacked nose-to-nose). Organic material stays in these vessels for 7-10 days, and then is transferred by loader to any of six Phase Two tunnels for further composting and size reduction for a similar 7-10 days. A separate, dedicated loader moves the composted material into a star screen and then onto a special enclosed tubular conveyor (designed in Japan) that takes it to a separate building for a further 20 to 30 days curing. (The two-step in-vessel composting process thus reduces curing time.)

The main plant buildings are maintained under negative pressure to control odors, and air is fed through a scrubber and biofilter. Liquids are collected in drains, sent to a cistern and then sprayed back onto the compost to maintain moisture; nothing is discharged to the sewer. All metal parts in the facility are galvanized or aluminum to prevent corrosion, and the exterior walls and some roof areas are made from freezer panels

(foam sandwiched between aluminum) to insulate against condensation.

Miller Compost

Miller Compost, a division of Markham, Ontario-based The Miller Group, has operated its flagship leaf-and-yard compost site — one of the largest outdoor windrow compost sites in the province — on Bloomington Road in Richmond Hill, Ontario since 1990. This summer the company built two additional composting facilities in the Durham Region. The first is an enclosed facility that uses in-vessel wide-bed technology; it opened on July 1. The second is an outdoor windrow site similar to the one on Bloomington Road that will open this fall.

The enclosed facility is in Pickering and uses the Ebara wide-bed in-vessel composting technology. It’s an aerobic process in which source-separated organics are fed via front-end loader to a series of conveyors that deliver the material to a sortation room. (This front-end separation system was supplied and installed by Machinex Industries.) The sort room consists of an environmentally controlled enclosure where sorters remove any foreign objects.

After passing through the sort line, the SSO is conveyed into an SSI slow-speed shredder. From there, the material is conveyed to a holding area within the active composting area of the facility. Once it’s in the holding area, the materials can be adjusted for C-to-N ratio, moisture content and bulk density. When the composting parameters are adjusted to within an acceptable range, the material is fed via front-end loader to the wide-bed composting vessel. Inside the vessel, the Ebara paddle fluffs the material and moves it toward the back of the facility. The stainless steel paddle is mounted on an overhead crane that spans the entire width of the vessel. (The paddle was manufactured for Miller by ABCO Industries of Nova Scotia.) The turning cycle is performed in off-peak hydro time periods and is completely automated. The compost is held in the composting bed for about 25 days.

Moisture is added via an overhead sprinkler system. Temperature is measured by probes in the composting vessel and monitored by the control system. The aeration for the composting process is a “draw down” or negative aeration system. Air flow through a series of aeration zones is utilized to ensure the composting system remains aerobic. The entire building operates under negative air pressure by drawing in fresh air and exhausting odourous air out through a biofilter. Prior to being fed to the biofilter, the odourous air is passed through a wet scrubber to ensure that it’s at 100 per cent humidity.

Phase One of the project will see 25,000 tonnes of material processed, and this will eventually rise to 50,000 tonnes per year. The facility contracts with municipalities, and will initially serve Durham Region’s green bin program After the material is cured it will be taken via trailer to Miller Compost’s new Clarington outdoor windrow facility for further curing and finishing. After three to six months, a Class A compost is expected to be produced.

The Clarington plant is a conventional windrow compost facility and can handle 70,000 tonnes of material annually. In addition to the processed material from the Pickering plant, other leaf and yard material could take six months to a year to fully cure.

Guy Crittenden is editor of this magazine.


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