Finding Gold at the Edmonton (Alberta) Gold Bar Final Clarifiers

Activated sludge plants are often limited by the performance of their secondary clarifiers. This is especially true when the process includes biological nutrient removal. The Gold Bar plant was no different. While the BNR process was capable of removing nitrogen and phosphorous to extremely low levels, the entire process was limited by the capacity of the clarifiers to produce an acceptable effluent when the temperatures were low and the MLSS levels were elevated to meet the nutrient removal process demands. In order to increase the capacity of the existing clarifiers, the plant staff embarked on an ambitious project to insert in-tank baffles to control the density currents. This paper discusses the field evaluation which included full-scale stress testing of a modified clarifier side-by-side with an unmodified clarifier. Using the methods adopted by the ASCE Clarifier Research Technical Committee, the results demonstrated the effectiveness of these trial baffles in reducing density currents and treating the anticipated high solids loadings.