A mixed integer program was structured to identify the least cost combination of recycling and treatment alternatives that can be used to control the liquid, solid, and gas waste streams produced from a 750-megawatt coat fired steam electric power plant. The model compared methods of liquid stream recycle and waste discharge treatment to meet given air and water quality standards. The model was then used to study the effects on the optimal solution of changes in capital, operation and maintenance, and energy and water costs. In addition, the effects on optimum system design of changes in particulate and sulfur oxide emission standards and stream discharge standards were evaluated. Nonlinear cost functions for system components were structured with binary integer variables to define the ordinate intercept and with continuous variables to define the slopes of total cost curve segments. The binary and continuous variables were associated with each other in pairs to approximate nonlinear total cost functions of alternative pollution control units. The optimal plant design was sensitive to increases in capital, operation and maintenance, and energy costs as well as air emission standard changes. The model indentified the optimal treatment until alternatives and their sizes when segments of the total costs and environmental standards were changed. The optimal solutions always indentified water recycle, rather than stream discharge, as the optimal production strategy
