Ammonia Limits,…

Ammonia Limits, Nitrification Capacity, and Concerns About Underestimated Influent Nitrogen

The proposed summer ammonia limits for this facility are quite low. While these limits are technically achievable, the expert review emphasized that reliable nitrification performance depends heavily on the accuracy of the influent nitrogen assumptions used in the design.

A well operated biological nitrification process can achieve total ammonia nitrogen (TAN) concentrations below 1 mg/L, and comparable facilities in Ontario routinely achieve even better performance. For example:

• Havelock WWTP and Teeswater Formosa WWTP (both using similar Napier Reid SBR systems) regularly achieve average effluent ammonia levels in the range of 0.1–0.2 mg/L.

These examples demonstrate that the proposed ammonia limits are achievable if the plant is designed based on accurate influent nitrogen concentrations and has sufficient aeration and alkalinity to support full nitrification.

However, the expert noted that the influent nitrogen concentration used in the design appears to be underestimated, particularly given the significant contribution of wastewater from restaurants and commercial kitchens. If actual influent TKN is higher than assumed, the plant may not have:

• adequate aeration capacity
• sufficient alkalinity
• appropriate SBR cycle timing
• enough biological volume

to achieve the required ammonia removal.

In the expert’s words:
“If the influent nitrogen concentration has been underestimated, modifications may be needed to the nitrification calculations/design.”

The expert also confirmed that alkalinity is essential for nitrification and that the Napier Reid design appropriately includes chemical alkalinity addition if natural alkalinity is insufficient.

However, the adequacy of this provision depends on the accuracy of the influent nitrogen assumptions.
Given the sensitivity of the receiving watercourse and the importance of meeting low ammonia limits, I respectfully request that MECP require the proponent to:

1. Reassess influent nitrogen concentrations, particularly TKN, to ensure the design basis reflects realistic conditions.

2. Demonstrate that aeration capacity, alkalinity supply, and SBR cycle design are sufficient to achieve full nitrification under peak loading conditions.

3. Confirm that the nitrification design has been evaluated for higher influent nitrogen scenarios, given the likelihood that commercial wastewater will increase nitrogen loading.

These steps are necessary to ensure the WWTP can reliably meet ammonia limits under real world operating conditions.