Site-specific raw seawater quality impact study on SWRO process for optimizing operation of the pressurized step

As a means of optimizing desalination processes, site-specificity in the determination of seawater quality conditions is a crucial point for improving the overall energy efficiency of a seawater reverse osmosis (SWRO) process. To this end, field studies were carried out at 16 sampling sites along the shoreline in South Korea to investigate the site-specific features of seawater quality. Also, two mathematical models were developed for the simulation of SWRO processes dependent on seawater quality in macroscopic and microscopic contexts, respectively. As a result, the microscopic dynamic model revealed that concentration polarization in the vicinity of the membrane surface and permeate concentration are affected by the feed seawater concentration and pressure. Then, the application of Fujairah SWRO plant operation data to the macroscopic simulation of a non-isobaric SWRO process model resulted in significant energy savings in terms of operational pressure savings, reducing 0.3 bar from the annual average value in the first pass operational pressure. These findings suggest that a cost-effective SWRO operation can be feasible using non-isobaric pressure controls by considering site-specific feed seawater concentrations. Results of the study presented here can be applied to improving the energy efficiency in SWRO plants through the optimization of pressurized systems.

This study confirmed that the site-specific raw seawater quality increased the complexity in SWRO processes. Thus, to reduce the complexity, understanding the seawater quality associated with regional and seasonal variations should precede any attempt at optimizing an SWRO process. In this study, we simulated an RO process from both macroscopic and microscopic viewpoints based on the salinity datasets of Fujairah and Korea. The simulation results show that permeate salinity is significantly dependent on feed salinity. This dependence indicates that site-specific properties can greatly affect SWRO systems and permeate salinity. Furthermore, the concentration polarization modulus decreased as the feed velocity (or feed pressure) increased, which means that feed pressure also plays a key role in the SWRO process performance. Contrary to thermal desalination plants such as MSF and MED, site-specificity in determining the seawater quality conditions should be regarded as a crucial point for improving the overall energy efficiency of SWRO processes. This study shows that non-isobaric operation has the potential to optimize the SWRO process according to site-specificity; cost-effective operation in SWRO process can be made feasible by using a non-isobaric pressure control that considers various feed seawater concentrations. The study presented above can be applied to improving the energy efficiency in SWRO plants through the optimization of the pressurized systems. In this paper, although we only applied seawater salinity in a simplified simulation, the SWRO process is related to other factors such as temperature, fouling, and scaling; therefore, further study is needed. In addition, a study investigating the relationship between the boundarylayer thickness in momentum transfer and the concentration polarization thickness in mass transfer as a means of optimizing feed concentration and velocity is also required.