Numerical and experimental investigation on the forward osmosis (FO) process for the operational conditions and spacer configuration optimization in microalgae dewatering

Microalgae (Scenedesmus obliquus) dewatering using forward osmosis membrane has received considerable attention for its possible application in biofuel generation. To investigate the filtration performance by analyzing permeate water flux, five different velocities (0.23 m/s, 0.31 m/s, 0.40 m/s, 0.55 m/s, 0.66 m/s) were selected in a bench-scale experiments. The results showed that the optimal flux was with 0.55 m/s velocity. Moreover, the same velocities (0.23 m/s, 0.31 m/s, 0.40 m/s, 0.55 m/s, 0.66 m/s) and three various spacer positions (0.3 mm, 1 mm and 2 mm away from the membrane) were simulated employing the computational fluid dynamics (CFD) approach. The results showed that the pressure and velocity distribution were affected by the velocities at the module inlet and the spacer configuration. And the 0.55 m/s velocity was confirmed, while the CFD revealed that the velocity distribution was relatively uniform and exerted a higher pressure on the membrane, and 0.55 m/s velocity agreed with the experiment in optimal operation. As for the spacer configurations, they were evenly distributed in the channel and the optimum structures occurred when the spacers were 1 mm away from the membrane. The spacer is beneficial for alleviating external concentration polarization (ECP) during osmosis process.

Automated summary

The study revealed that a velocity of 0.55 m/s was optimal for microalgae dewatering using forward osmosis membrane, with spacers positioned 1 mm away from the membrane providing the best results. The presence of spacers was found to alleviate external concentration polarization during the osmosis process.