Winter Temperatures,…

Winter Temperatures, Insulation, and Biological Treatment Performance

The design brief does not mention insulation of tanks or process components, aside from noting in the Napier Reid documentation that insulation is excluded from their scope.

Insulation is an important consideration for maintaining wastewater temperatures within the biological treatment system. Colder temperatures slow down biological processes, including BOD removal and nitrification, which could affect the plant’s ability to meet effluent limits—particularly ammonia.

Physical and chemical processes associated with solids removal and phosphorus removal are generally less sensitive to cold temperatures, provided that equipment is protected from freezing. However, the biological processes in the SBRs are temperature dependent, and maintaining adequate wastewater temperature is essential for consistent performance.

The expert review noted that Napier Reid’s design calculations do consider both winter and summer conditions, including biological treatment performance at wastewater temperatures as low as 5°C. If the tanks are buried and insulated, achieving a winter wastewater temperature of approximately 5°C is reasonable, and the modelling appears to appropriately account for the process implications of winter conditions.

However, because insulation is not described in the design brief, it is unclear how the proponent intends to maintain the temperatures assumed in the modelling. Without insulation or equivalent construction measures, actual winter temperatures could fall below the design basis, potentially compromising biological treatment performance.

I respectfully request that MECP require the proponent to:

1. Clarify how wastewater temperatures will be maintained to match the assumptions used in the Napier Reid design calculations.

2. Confirm whether insulation or other thermal protection measures will be included in the detailed design of buried tanks and process components.

3. Demonstrate that the plant can reliably achieve the required biological treatment performance under realistic winter operating conditions.

These steps are necessary to ensure that the winter temperature assumptions used in the design are achievable and that the plant will perform as intended throughout the year.