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Planning and Design of Desalination Plants Effluent Systems


Increasing demand for water in urban areas and agricultural zones in arid and semi-arid coastal regions has urged planners and regulators to look for alternative renewable water sources. Seawater reverse osmosis desalination (SWRO) plants have become an essential supply source for the production of freshwater in such regions. However, the disposal of hypersaline wastes from these plants in many of these regions has not been fully and properly addressed. This study aims to develop and present a strategy for the analysis and design of an optimal disposal system of wastes generated by SWRO desalination plants.

After current disposal options were evaluated, the use of multiport marine outfalls is recommended as an effective disposal system. Marine outfalls are a reliable means for conveying wastes from process plants, to include wastewater treatment and power plants, into the coastal waters. Their proper use, however, in conjunction with SWRO desalination plants is still in its beginning stage.

A simulation-optimization approach is proposed to design a system for safe disposal of brine wastes. This disposal system is comprised of a marine outfall that is equipped with a multiport diffuser structure. A hydrodynamic model (CORMIX) is used to assess the initial dilution of hypersaline effluent discharged into coastal waters. A regression model is developed to relate the input and output parameters of the simulation model. This regression model replaces the simulation model. A mixed-integer linear programming (MILP) optimization model is then formulated to determine the design of the multiport marine outfall. The design parameters are the length, diameter and number of ports of the disposal system. Given the uncertainty of some parameter, such as current speed, wind speed and ambient temperature, a chance-constrained programming model is used to properly incorporate these stochastic parameters into the model. This simulation-optimization framework provides planners with effective tools that preserve a healthy coastal environment, meet environmental permitting requirements and restrictions, while achieving cost savings and adequate hydrodynamic performance. A case study demonstrates the applicability of the proposed methodology.

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