This case study details the retrofit of an existing Rotating Biological Contactor (RBC) system to a Moving Bed Biofilm Reactor (MBBR) configuration for Wabaseemoong Independent Nations, located near the Ontario–Manitoba border. The upgrade addressed stringent effluent requirements—TSS <25 mg/L, cBOD₅ <25 mg/L, and TAN <10 mg/L—within a design flow of 438 m³/d, while minimizing civil works and footprint. The solution leveraged existing headworks and secondary clarification, incorporating twelve stainless steel coarse-bubble diffusers per tank to optimize oxygen transfer and reduce maintenance associated with membrane replacement. Media backflow prevention was achieved through influent piping modifications. The MBBR provided intensified nitrification and BOD removal within the RBC basins, ensuring compliance with nutrient limits and operational simplicity. Commissioned in January 2024, the system demonstrated stable performance and energy efficiency, validating MBBR retrofits as a cost-effective approach for decentralized wastewater treatment facilities
