TIGHT TREATMENT

The sequencing batch reactor plant in a downtown wastewater treatment facility in Quebec is pie-shaped to save on costs.

BCD Consultants of Valleyfield, Quebec were asked to double the capacity of the wastewater treatment plant in the nearby city of Vaudreuil-Dorion, west of Montreal. The site was very tight as the plant is located in the heart of the city near a residential zone and on a school complex. The treatment plant was originally built in the 1960s as a training facility. Consequently, it had an unusual variety of treatment processes and equipment, though it had been converted to an activated sludge process in 1984. By 1997 the plant was overloaded, smelly, and using too much energy.

LBCD developed a software program to study the options for expansion, and of 70 different possibilities found it was best to build a new plant alongside the existing one. While the two facilities use different treatment processes, their operations are integrated.

The new plant handles the bulk of the in-flow (12,000 cubic metres per day) and the variations. It uses the advanced Sequencing Batch Reactor (SBR) process whereby wastewater is sent to four cells in sequenced batches, and is treated by a system of aeration/decantation. The engineers designed the layout as a pie, with each of the four cells occupying a quarter of the pie. At the centre is the mechanical pit where all the equipment is installed. This unusual geometry reduces the quantity of concrete needed for construction, but also the amount of piping and other mechanical equipment.

The operation of the four cells in the Sequencing Batch Reactor is controlled by a Dissolved Oxygen (DO) sensor, which saves 20% energy. The odour from the influent and sludges is treated by an active carbon air purification system.

About $500,000 was spent on retrofitting the old plant with equipment like new diffusers and blowers. Its processes have been simplified so that the inflow bypasses the existing primary settling tanks and goes directly to the aeration tanks.

The project was completed in 21 months from studies to start up, and the plant can now service 29,000 people as well as local industries. It was built within budget at a total of $3.5 million or $294/m3 — a cost that is much less than that of similar projects in other Quebec towns. Latest results show that it is working efficiently. — BL

Client: City of Vaudreuil-Dorion

Prime consultant: LBCD; Pierre Beauchamp, P.Eng., Michel Lalande, P.Eng., Hui Wang, P.Eng., Denis LemieuxCCE