WCW26

The Saskatoon Wastewater Treatment Plant is piloting the Mobile Organic Biofilm (MOB) process as a strategy for process intensification within its biological nutrient removal system. Initial piloting demonstrated improved nitrification reliability and reduced secondary clarifier solids loading, leading to refinement of the operating strategy to better balance suspended and attached growth.
In the second year, the pilot focused on sustained low solids retention time (SRT) operation to intentionally shift ammonia oxidation capacity toward the biofilm fraction. By operating at lower mixed liquor suspended solids (MLSS) concentrations, the team aimed to strengthen biofilm development, reduce solids loading to the secondary clarifiers, and increase overall system resilience.
A key objective was to evaluate system behaviours during extended cold-weather conditions. Low-SRT operation reduced suspended nitrifier populations and increased reliance on attached growth on the mobile carriers. This operating strategy provided insight into how much nitrification capacity could be maintained within the biofilm fraction and how the system responded under varying seasonal and loading conditions.
Results from the second year highlight the operational opportunities and constraints associated with low-SRT operation, including the importance of managing dissolved oxygen, solids inventory, and carrier distribution to maintain consistent performance.
This presentation will share second-year performance results, lessons learned from winter and low-SRT operation, and key considerations for full-scale implementation of the MOB process as a long-term capacity and resilience strategy.