It is of significance to reduce the total operational cost of seawater reverse osmosis (SWRO) system through the system engineering approach. In this work

based on the formulation of the full flowsheet model including process equations and total operational cost equation

an operational optimization strategy with time varying parameters was proposed. First

according to the solution-diffusion principle and variable parameter characteristics of the whole system

the RO process model

storage tank model and related parameter equations were established. Then

based on full flowsheet of SWRO process and composition of operational cost

the model of total operational cost was obtained as well as the full flow sheet's cost per cubic meter water. The optimization problem was formulated with the objective function to minimize total operational cost

and with the equations and various bound constraints. And then simultaneous approach wherein the differential and algebraic variables were fully discretized leading to a large-scale nonlinear programming (NLP) problem was used for the solution technique

and interior point optimizer (IPOPT) was used as the large scale solver. A case study was then performed to demonstrate the effect of the proposed strategy; computing results demonstrated that the proposed strategy could largely reduce the total operational cost of the SWRO system. Through solutions of the optimization problem

the optimal operating pressure and flowrate curve as well as the key performance profiles were obtained under different environmental parameters. This work is of significance to improve the performance and reduce the operational cost of the SWRO system.