AbstractA full‐scale RBC plant having two parallel trains and treating combined municipal and industrial dairy waste was used to investigate the effectiveness of supplemental aeration and an enlarged first‐stage in improving RBC performance. Enlarged first‐stage was created by removing the baffles between the first two stages. One RBC train was used as a control and the other train was used to evaluate the combined effectiveness of supplemental aeration and an enlarged first‐stage. Composite wastewater samples were collected from influent and effluent of each RBC stage in both trains. Samples were analyzed for soluble COD and BOD5, ammonia nitrogen, and suspended solids. Wastewater temperature, pH and dissolved oxygen levels were measured in each stage. The study results indicate that it is possible to achieve higher organic loading rates and removal rates when RBC units are provided with supplemental aeration and enlarged firs