Microalgae Concentration through Microfiltration and Forward Osmosis: Evaluation of Membrane Setup Design and Operating Conditions

Microalgae technology has the potential to take part to the transition from traditional wastewater treatment plants (WWTPs) toward innovative water resource recovery facilities. However, microalgae separation and concentration from treated wastewater (WW) is currently a major limitation because of energy costs. In this study, we compared microalgae (Chlorella vulgaris) concentration using two low-energy membrane processes, i.e., microfiltration (MF) and forward osmosis (FO) under two configurations, i.e., submerged and cross-flow membrane systems. The impact of turbulences promoters such as aeration in submerged operation and the impact of spacers in cross-flow mode were assessed; filtration cell orientation was also evaluated. All systems allowed for four times volumetric concentration of the microalgae batches, but the lack of turbulence promoters substantially impacted permeation flux and efficient microalgae recovery. The preferred configuration is submerged operation with aeration allowing for more than 90% microalgae recovery both using MF and FO membranes. The main limitation of FO is the high salinity of the concentrated microalgae batch that may alter downstream treatment. Despite higher initial flux observed in cross-flow filtration, severe flux decreases and important microalgae biomass losses on membrane surface or within spaced-filled channel did not allow for faster concentration and with recovery limited to 77%. These results demonstrate the importance of membrane configuration for efficient microalgae harvesting and recovery offering key insights toward industrial-scale algae production. Furthermore, it suggests the potential for integrating a membrane system into photo-bioreactors for simultaneous microalgae cultivation and concentration.