AWWA WQTC69407

Water quality modeling was performed for the 13.2 million gallon per day (MGD) Gibson Island Advanced Water Treatment Plant (AWTP) in Brisbane, Australia. The AWTP includes high-rate clarification, microfiltration, reverse osmosis and advanced oxidation. The model incorporated differing influent water quality, multiple chemical injection points and multiple unit processes. The main objectives were to: understand how alkalinity and phosphorus levels would affect treated water stabilization; document the chemical system calculations; incorporate the addition of constituents into the water stream because of chemical injection; document the assumed operational control philosophy; and, optimize chemical costs, process performance and residual production. The AWTP Process included the following unit processes: chloramination and pH adjustment (sulfuric acid or caustic soda); coagulation with ferric chloride and polymer and high-rate clarification; microfiltration; pH adjustment; two-pass reverse-osmosis treatment; hydrogen peroxide/advanced oxidation ultraviolet light reactors; and, chemical conditioning with lime and carbon dioxide prior to storage or discharge. The AWTP processes were split into incremental systems, and each chemical injection point and treatment process was treated individually. A combination of project-specific spreadsheet models and a commercially-available, spreadsheet-based water quality model was used. Models were run sequentially, so one system's effluent water quality became the next system's influent water quality. For each treatment strategy, multiple influent water quality scenarios were modeled to determine the chemical dosing requirements and resulting treated water quality. Includes tables, figures.