OPTIMAL PLANNING OF COASTAL WASTE-WATER TREATMENT AND DISPOSAL SYSTEMS

Coastal wastewater treatment and ocean outfall facilities are usually planned as two separate subsystems in the traditional design strategy The choice of a primary or secondary wastewater treatment process is intimately related to financial land availability, and managerial factors. On the other hand, the design features of ocean outfall pipes are usually arranged based on the assimilative capacity in the nearby ocean environment and the given effluent quality from the wastewater treatment plant The technical efforts in planning wastewater treatment and ocean outfall subsystems can be combined by considering the minimization of system costs and the maximization of utilization rate of environmental assimilative capacity. Moreover, the fluctuations of the speed of coastal currents over seasons may further minimize the long-term operating costs. This strategy is especially effective for cities close to the deeper ocean. A nonlinear programming model is developed in this study to facilitate combined planning of wastewater treatment plants and their ocean outfalls.