AWARD OF EXCELLENCE – WATER RESOURCES Oxford Pollution Control Plant Expansion

Maintaining clean waterways while building wastewater infrastructure to meet the needs of growing populations is a challenge facing many regions.

Stantec designed an expansion to the Oxford Pollution Control Plant in London, Ontario that demonstrates it is possible to design an affordable wastewater treatment plant with both expanded processing capacity, and a higher quality effluent, without increasing the footprint of the physical structure.

The existing plant was built in 1960 and needed expanding to service new residential developments in the northwest quadrant of the city.

The upgrades have made it one of the largest membrane bioreactor (MBR) municipal pollution control plants in Canada. But more importantly, the expansion has doubled the plant’s capacity to treat sewage flows from average 10,000 to 20,000 m3/day, all while costing the city less money for a better quality of filtering.

A membrane bioreactor (MBR) is a wastewater treatment process that combines the physical filtration of matter from water through a porous barrier (membrane) with a biologically active environment which breaks down bacteria (bioreactor). The MBR system provides tertiary-level filtration, while traditional means would only provide secondary levels for the same amount of space. It also provides a lower capital cost for tertiary filtration than secondary filtration via traditional means, with improved effluent quality, and lower sludge thickening costs.

Located on the banks of the Thames River, the plant sits beside Oxford Road, a major arterial roadway into the city. The site is also near new residential areas and the prestigious Hunt Club golf course. As an MBR plant requires a much smaller footprint, the use of the system eliminated the need to expand into the sensitive neighbouring lands and was a logical fit for this site.

Meeting effluent limit targets was a concern, specifically achieving the low monthly limit of total phosphorus at less than 0.5 mg/L and summer total ammonia at less than 1.0 mg/L. By using MBR technology, the plant was able easily to achieve the phosphorus limit, and alkalinity concerns were addressed by including anoxic zones in the aeration tank.

The new preliminary treatment process eliminated the conventional de-gritter systems by implementing above-grade fine mesh (2 mm) rotary drum screens for the removal of fibrous materials and grit from raw wastewaters. To the best of Stantec’s knowledge, this design concept has not been used at any other pollution control plant, but it is necessary at this facility to allow the membranes to function more efficiently. The fine screening will extend the life of the membrane in this cold climate application.

Stantec also developed an activated sludge thickener employing membrane filtration systems to achieve a 4.5% sludge density.

Two existing structures were repurposed: the existing de-gritter tanks were converted into a pump station and a flow splitter box, and secondary clarifiers were converted into membrane tanks using a novel pump layout.

The engineering involved many other features, including an oversized raw sewage lift station, a new headworks building (120,000 m³/d capacity), expanded primary clarifiers, a new aeration tank and the conversion of two aeration tanks (doubling their capacity from 2,200 to 4,000 m³/day each), a new electrical system and a 1-MW emergency generator.

A new chemical storage system and new administration building were also designed and constructed. cce