The existing Dufferin anaerobic digester facility (left) and rendering of the upgraded plant (right).

July 14, 2016 | General

Toronto Moves Ahead With AD Plant Upgrade

Peter Gorrie
BioCycle July 2016

The City of Toronto, Ontario, Canada is embarking on expansion of its original anaerobic digester facility, highlighted by innovative technology for pretreating feedstock from its curbside collection of Green Bin organics. The redevelopment of the Dufferin Organics Processing Facility, to be commissioned in September 2018, will enable it to process up to 60,000 tons of residential organics annually, a significant increase from the 27,500 tons in its original configuration.
This development proceeds as the city’s Solid Waste Management Services Division seeks City Council approval of a new Long Term Waste Management Strategy, which calls for further steps to reduce food waste and encourage residents to use waste diversion programs already in place.

The existing Dufferin anaerobic digester facility (left) and rendering of the upgraded plant (right).

The existing Dufferin anaerobic digester facility (left) and rendering of the upgraded plant (right). (Images courtesy of City of Toronto)

The Council awarded the contract to revamp the Dufferin facility to W.S. Nicholls Construction Inc. of Cambridge, Ontario. A budget of $73.8 million was approved for the design, build and commission contract. The pretreatment process in W.S. Nicholls’ proposal was developed by Ontario-based Anaergia Inc. As part of the same competitive procurement process, W.S. Nicholls won the contract to operate and maintain the facility.
The Dufferin facility opened 13 years ago as a prototype to demonstrate the potential for processing organic material from what was then the city’s fledgling residential Green Bin organics program. Since then, the program has achieved a 90 percent participation rate among Toronto’s single-family residences. The Green Bin program is also now available to all multiresidential buildings serviced by city collection.
As the program developed, a second digester, the 83,000 tons/year Disco Road Organics Processing Facility, went into operation in 2014. Meanwhile, the Dufferin facility was shut down for the major expansion now in progress.
The Nicholls group competed for the Dufferin contract against a group headed by AECOM Inc., with operators Veolia North America and CCI BioEnergy. CCI designed and operated the Dufferin prototype and continues to be involved in the Disco Road plant. While both bidders met the contract requirements, W.S. Nicholls came out ahead on technical merit and cost, says Neil MacDonald, manager of capital delivery with the Toronto Solid Waste Management Services Division. However, both exceeded the budget estimate of $53.1 million (CDN). City Council approved the additional funding last fall.

Organics Pretreatment

Pretreatment is a crucial element in processing organics collected through Toronto’s Green Bin program, which allows residents to put their organic materials in conventional plastic bags, and also accepts materials prohibited in many other programs, including cat litter, pet wastes and sanitary products such as diapers. The system removes the bags as well as other light plastics and heavy contaminants before the feedstock enters the digester.
The Dufferin facility will be outfitted with Anaergia’s BIOREX pretreatment equipment, which features an extrusion system. After going through a bag shredder and filter, the feedstock is loaded into a perforated steel box, where it is squeezed by a heavy ram. The pressure pushes the relatively liquid organics through the holes in the box while most of the unwanted materials stay inside, to be disposed in a landfill.
The organic fraction, still containing a small amount of contaminants, undergoes two additional cyclonic stages to separate out the remaining light and heavy nonorganics. The polished feedstock then enters a buffer tank, and flows in a steady, stream into the anaerobic digesters, which will operate 24 hours a day, seven days a week..
The Dufferin facility, like the Disco Road operation, will use an internal mixing system in the anaerobic digesters that compresses some of the biogas and pumps it through lines running deep down into the digesting material so that it bubbles back up to the top. Both facilities will produce about 3,524 cubic feet of biogas per ton of feedstock.
A centrifuge will be added to the existing screw press to dewater the Dufferin facility’s processed digestate output before it is trucked to a third party vendor to be combined with leaves and yard trimmings and composted. The centrifuge will do most of the dewatering, with a screw press retained as a backup.
The Dufferin expansion also includes installation of a wastewater treatment system, using a FibrePlate® membrane developed by Fibracast, an Anaergia subsidiary. Under the contract with W.S. Nicholls, the facility is to be operated by the Ontario Clean Water Agency, a provincial agency that provides water and wastewater services to municipalities, First Nation communities, institutions and private sector companies across Ontario.
The city is exploring the possibility of energy recovery from both the Disco Road and Dufferin plants, either by burning the biogas to generate electricity or upgrading it to renewable natural gas for injection into the natural gas pipeline and use as a fuel. Currently, biogas produced at the Disco plant is flared.
Toronto’s final recommended Long Term Waste Management Strategy, to be considered by City Council this summer, maps out waste management needs and solutions for the next 30 to 50 years. The Strategy outlines the need to improve organics diversion from multiresidential buildings and the IC&I sector, a crucial matter as Toronto’s population grows and high-rise condominium projects proliferate.
About one-third of the existing multiresidential buildings receive collection services from private waste haulers instead of City services. The strategy doesn’t set out a detailed plan. Instead, it proposes focusing on legally permissible options to increase organics diversion in multiresidential buildings serviced by the city and explore options for those served by private haulers and the IC&I sector.
Toronto remains committed to increasing waste reduction and diversion from landfill disposal, MacDonald notes: “By approving expansion of the Dufferin facility, it recognizes the vital contribution organics processing makes towards achieving this goal.”
Peter Gorrie is a Contributing Editor to BioCycle.

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