Modeling of forward osmosis for microalgae harvesting

Abstract

In this study, a novel forward osmosis (FO) process coupled with microalgae cultivation process and its model were developed as a means for energy-efficient microalgae harvesting. The use of draw solution that conventionally necessitated the energy-intensive regeneration is no longer required by using microalgal culture medium, leading to direct utilization of diluted nutrients into microalgal cultivation. Its feasibility was proven by the way of glucose as draw solute, a common carbon source for heterotrophic microalgae cultivation, in microalgae harvesting. To mathematically predict the behavior of the newly proposed FO process for microalgae harvesting, a model was constructed. The model was first established in ideal environment, where there are no foulants within feed solution, to predict significant physicochemical phenomena including concentration polarization and solute diffusion. Dynamic model was then used to focus on the process itself, in addition to phenomenal perspective. Lastly, the model was extended to the fouling model that is applicable to microalgae harvesting process. Based on the developed model, Latin-hypercube one-at-a-time (LH-OAT) sensitivity analysis framework was adopted for evaluating the impact of model parameters. Model parameters, namely the physiochemical properties of the FO membrane, glucose solution, and microalgal solution, were estimated on the basis of experimental and theoretical methods. With the estimated model parameter, the proposed model adequately described the significant physicochemical phenomena for harvesting microalgae, including internal concentration polarization (ICP), external concentration polarization (ECP), reverse solute diffusion (RSD), cake layer growth, and the cake-enhanced concentration polarization (CECP). As a result, the simulated data from the model exhibited good agreement with the experimental data in batch FO operation.