Critical process design issues in the selection of the TF/SC process for a large secondary treatment plant

The Greater Vancouver Sewerage and Drainage District (GVS&DD) is a major regional wastewater agency serving Vancouver, Canada and surrounding municipalities. It was recently required to upgrade its largest treatment plant from primary treatment to secondary treatment. After initial screening of 17 processes, three were given detailed examination: the oxygen activated sludge process (OAS), the air activated sludge process (AAS), and the trickling filter/solids contact process (TF/SC). A comprehensive alternative analysis was completed consisting of process designs, plant layouts, and contractor-type construction cost estimates. Operations and maintenance costs were prepared from staffing plans, and estimates were made for energy and chemical use. Plants were surveyed and visited to address questions such as ease of operations and reliability. The TF/SC process was selected based upon its lower present value and O&M costs, ease of operation, robustness, and lower energy usage.