1. Article title: Simulation and optimisation of a medium scale industrial reverse osmosis desalination system. 2. Article Author or Authors: Al-Obaidi, M.A., Alsarayreh, A.A. and Mujtaba, I.M. 3.Name of journal and date of publication:Computer Aided Chemical Engineering, 2023 4. Article abstract: Desalination is one of the techniques used for meeting increasing water demand around the world. However, as the technology is energy intensive, the increasing energy price around the globe will force the practitioners to optimise the process from the point of minimising water production cost. The motivation of this study is to carry out simulation and optimisation of a reverse osmosis (RO) system to estimate and minimise the freshwater production cost. For this purpose, a detailed mathematical model of the process is developed using a combination of an earlier model of RO developed by the authors and a set of cost model equations collected from the open literature. The mediumscale industrial brackish water RO desalination system of Arab Potash Company in Jordan is selected as a case study. The model is first used in simulation mode which provides the detailed insight of the process and feasible operation envelope. The model is then embedded in a single objective non-linear optimisation framework to determine the best operating parameters in order to minimise the freshwater production cost while optimising several operating parameters and meeting the desired water quality specification in terms of salinity. Sensitivity of energy cost on the optimum operating conditions will also be presented in detail.