Cost evaluation for a two-staged reverse osmosis and pressure retarded osmosis desalination process

This research provides an analysis of energy efficiency and cost evaluation for three types of two-staged reverse osmosis (RO) and hollow fibre pressure retarded osmosis (PRO) hybrid process; one without direct feed flow (Hybrid A), one with direct feed flow (Hybrid B) and one with direct feed flow and a turbine (Hybrid C). Firstly, models are built from first principles assuming multi-staged RO-PX (pressure exchanger) has equal stage recovery considering the effect of booster pumps and pressure drop in the RO system. Then, all simulations are implemented by MATLAB 2018b, and energy efficiencies are assessed based on the normalised specific energy consumption, NSEC. All hybrid processes are found to have higher total water prices (TWP) when the electricity price is 0.10 US$/kWh; however, they show certain advantages under different electricity prices when wastewater pretreatment and delivery of wastewater are neglected. Hybrid C is especially attractive even in countries where water prices are low, and electricity prices are high due to its insensitiveness to electricity prices. The requirement of wastewater pretreatment and wastewater pump and the further development of PRO membranes are the keys to practical operations.