Redundancy, Multi Train SBR…

Redundancy, Multi Train SBR Design, and the Need for Additional Flexibility

The expert review noted that the proposed SBR system is divided into four parallel trains, which is a strong design feature. This multi train configuration provides several operational advantages:

• It allows the operator to run multiple trains simultaneously while keeping each train at a different point in the treatment cycle to accommodate incoming flow.
• It provides flexibility during start up and during seasonal variations in flow and loading.
• It offers built in redundancy, allowing the system to remain operational if one train requires maintenance or repair.

However, the same level of redundancy and operational flexibility is not provided for the tertiary filter or the UV disinfection system. The design includes:

• one single tertiary filter, and
• one single UV disinfection unit,

each sized for maximum flow.

This creates two single points of failure. If either unit requires maintenance or experiences an equipment issue, the plant would have no ability to filter or disinfect effluent, which could result in non compliance and increased environmental risk.

The expert recommended that the proponent consider splitting the filtration and UV systems into two parallel units, if feasible based on equipment sizing. This would provide:
• operational flexibility,
• redundancy during maintenance, and
• improved reliability during peak flow periods.

The expert also noted that while the Napier Reid SBR design does not require up front equalization due to the multi train configuration, the proponent should still consider some form of flow equalization. Equalization would help:
• manage seasonal and weekend/holiday flow variations,
• stabilize influent loading,
• improve chemical dosing consistency, and
• support more reliable performance across the treatment train.

Given the sensitivity of the receiving watercourse and the importance of system reliability, I respectfully request that MECP require the proponent to:

1. Evaluate the need for redundancy in the tertiary filter and UV disinfection systems, including the feasibility of using two parallel units.

2. Assess whether up front flow equalization is warranted, given the expected variability in flows and loadings from a resort based development.

3. Demonstrate that the treatment system can maintain compliance during maintenance events or equipment downtime.

These steps are necessary to ensure the WWTP has adequate operational flexibility and redundancy to protect the receiving watercourse under real world conditions.