Engineers have taken a novel approach to the design of a $34-million wastewater treatment plant under construction in Thompson, Man., a nickel mining town 740 kilometres north of Winnipeg.
Rather than design the plant with multiple buildings over a large area, the consultant chose to integrate the administration and multi-use areas of the plant on top of the treatment tanks, creating a three-level wastewater facility.
“It is a unique design that keeps the site (facilities) compact,” says Saibal Basu, a project manager and technical lead with Stantec Consulting Ltd., the prime consultant for the project.
The compact footprint also “optimizes energy usage and retains space for future expansion,” he says. Furthermore, it will result in “significant cost savings” over a conventional plant design spread over a larger area of land.
The new plant will service the city’s 13,000 residents. The treatment process uses Sequencing Batch Reactors (SBR) that discharge the effluent in batches, unlike conventional treatment systems. It is designed for a maximum month flow of 8.1 million litres per day, with a capacity to handle up to 13.7 million litres per day, says Basu.
The SBR is based on the principle of an activated sludge process system. The new plant will replace two 50-year-old treatment systems that are in poor condition, says Basu.
The old primary treatment plant handles 70 per cent of the waste flow, while a single-cell continuous discharge aerated lagoon handles the remainder. Neither treatment system disinfects effluent discharged into the Burntwood River. The anaerobic digesters at the primary plant are prone “to process upsets” causing significant odour problems in town, Basu states.
The new plant will address both issues. Bio-filters will mitigate odours and UV disinfection will be used prior to final discharge to the river, says Basu.
The new plant also includes: a sewage pump station to divert flows from the existing lagoon; six millimetre fine screens; a high-efficiency grit removal system; centrifuge sludge dewatering; and a new outfall to the Burntwood River.
The plant is a sustainable design with a number of energy-saving features, including high efficiency motors; blowers/pumps equipped with variable frequency drives; and independent mixing and aeration. Heat recovery ventilation will capture rejected heat from blowers for heating elsewhere and the complex will maximize the use of natural light.
Basu says before selecting the SBR, Stantec evaluated three wastewater treatment options based on population growth, flows and effluent criteria. The consultant also evaluated an option to upgrade and expand the two existing treatment systems.
“We concluded that a single centralized facility would be more cost effective on a life cycle basis, although capital costs were comparable” to upgrading the existing facilities, says Basu, adding it would have been a challenge for the existing plant to get regulatory approvals.
The old treatment systems will be decommissioned.
The new complex is being constructed adjacent to the old primary plant. A new lift station will allow for transfer flows — currently done by the lagoon — to the proposed centralized plant by a dedicated forcemain.
One of the construction challenges Bird Construction, the general contractor, faces is the weather. Winter ambient temperatures of -30 to -35 C in Thompson are not unusual so covering and heating new concrete is a standard practice, Basu says.
The new process tanks, including for the SBR, post equalization and aerobic digesters, are designed with common walls. To prevent process tanks from freezing, they will be covered with a combination of cast-in-place concrete and precast concrete slabs.
“That is unique to Manitoba as most treatment plants across Western Canada are left open,” says Basu.
The project is funded under a tri-partite agreement through the New Building Canada Fund’s Provincial-Territorial Infrastructure Component-National and Regional Projects. The project underwent a lengthy environmental approval process through Manitoba Sustainable Development. The plant is scheduled for completion in early spring of 2019.