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The City of Toronto owns and operates the Ashbridges Bay Treatment Plant (ABTP), a 818,000 m3/day secondary treatment wastewater treatment facility, the largest in Canada.

Primary and secondary sludge are anaerobically digested and dewatered, generating approximately 50,000 dry tonnes of dewatered biosolids annually.

In 1998, the City of Toronto decided that incineration, the primary sludge disposal method at the time, was no longer acceptable for the City and embarked on a search for alternative disposal methods that could be classified as beneficial. Various biosolids beneficial use alternatives were investigated, among them, alkaline stabilization, direct application of dewatered product to agricultural land, composting and pelletization. With active participation of public through a Biosolids Multi-Stakeholder Committee, two options were selected for implementation – application to agricultural land and pelletization.

These options would provide the City of Toronto with a more diverse program, giving greater flexibility for biosolids beneficial use, and would consequently lead to the end of sludge incineration at the ABTP. However, because the incinerators have been used as a heat source for the treatment plant and for foul air combustion, alternatives for heating and for treatment of odorous air streams from the existing and new biosolids management facilities would be required after shutting-down the incinerators.

In order to implement the program, three projects were required, having a total construction value of 85 million had to be implemented. These were: Dryer Facility, Truck Loading and Odour Control Facilities, and Plant Wide Heating System. The latter was to replace the incinerator heat recovery boilers, and to convert the system from steam to hot water.

The City of Toronto established an extremely ambitious timeline to achieve the shutdown of the incinerators, leaving some 27 months for planning, bid document preparation, bid periods, evaluation, negotiation, award, detailed design, construction and commissioning of the required projects.

In view of the ambitious timeline, a design-build project delivery method was chosen. An “Open-concept” design-build approach was used for Dryer Construction project, where the Request For Proposal (RFP) document specified minimum performance criteria but did not include conceptual design. This “limited pre-design” approach was required to permit flexibility for the bidders to consider a range of options – for the type of technology, location, etc.

In the case of the Truck Loading and Odour Control Facilities as well as Plant Wide Heating projects, the potential solutions (technology, major equipment selection, location, etc.) were more restricted. Because of two different project drivers, a “Defined-concept” approach was selected.

Complete RFP documentation was prepared in just twelve weeks. It included reviews of various options, development of a conceptual design, outline design criteria, size and performance requirements, process and air flow diagrams, site selection and layouts of the buildings, major equipment and piping layouts, development of detailed specifications, and pre-selection of major equipment. This “Defined-concept” approach provided design-build proposal teams with a focused outlook, requiring no investigation of several options, but having the most suitable option, already reviewed by the City, ready for finalization.

The paper discusses advantages and disadvantages of two design-build approaches and the role of the Consultant and the City staff team in the administration of the design-build projects. The paper also discusses one of the major concerns with design-build approaches – securing final quality, while allowing sufficient latitude for innovation by the design-build proponent.
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Document Type: Research Article

Publication date: 2002-01-01

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