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 maj or regional wastewater agency serving Vancouver, Canada and surroundin g municipalities. It was recently required to upgrade its largest trea tment plant from primary treatment to secondary treatment. After initi al screening of 17 processes, three were given detailed examination: t he oxygen activated sludge process (GAS), the air activated sludge pro cess (AAS), and the trickling filter/solids contact process (TF/SC). A comprehensive alternative analysis was completed consisting of proces s designs, plant layouts, and contractor-type construction cost estima tes. Operations and maintenance costs were prepared from staffing plan s, and estimates were made for energy and chemical use. Plants were su rveyed and visited to address questions such as ease of operations and reliability. The TF/SC process was selected based upon its lower pres ent value and O&M costs, ease of operation, robustness, and lower ener gy usage.