Optimization of operating variables in a pilot-scale reverse osmosis membrane process for reclamation of tunnel construction wastewater

The goal of this study was to investigate the individual and combined effects of temperature, salinity, and pressure on permeate flux and salt rejection of the reverse osmosis (RO) process used for reclamation of tunnel construction wastewater. Regardless of changes in temperature, higher operating pressures enhanced both permeate flux and salt rejection, while effects of temperatures on performance varied depending on the operating pressures. Increasing temperatures to less than 35 bar did not improve the permeate flux and salt rejection, while to more than 50 bar led to higher rejection as well as more permeate flux of reclaimed wastewater. Based on analysis of model equations developed, the extent of flux and salt rejection required for reuse of the reclaimed wastewater occurred under different optimal conditions depending on variations in seasons and salinity of wastewater. In particular, it was necessary to add additional pressure exceeding 50 bar or increase the temperature to over 20°C when wastewater of more than 20‰ salinity flows into the treatment system. Adjustment of influential variables can provide an implementable approach to improve operation of the RO process as well as optimize a process for practical construction on-site applications.