Evaluation of an element-scale plate-type forward osmosis: Effect of structural parameters and operational conditions

This is the first study investigating a plate-type forward osmosis (FO) element in two different operating modes: FO and pressure assisted FO (PAFO). A baseline test was conducted to assess the FO process under different structural parameters and operating conditions. For the PAFO, both the naturally occurring pressure and artificially applied hydraulic pressure in at the feed solution (FS) were considered. FO water flux increased with an increase in the temperature (from 20 to 30 °C) and the draw solution (DS) concentration (0.4 to 0.7 M). In addition, when the flow rate of the FS increased, the water flux increased and the inlet pressure at the FS side also increased. In the PAFO mode, the water flux increased with an increase in the hydraulic pressure, but the water flux decreased with a 1.5 bar hydraulic pressure. The increase in the water flux became smaller as the flow rate difference between the FS and DS increased, which is not the same as the FO mode. This may due to that as the flow rate increases, and the hydraulic pressure is further increased, the central portion of the membrane comes into contact with the spacer at the DS side (bowing phenomenon).