Combining patterned membrane filtration and flocculation for economical microalgae harvesting. (15th June 2021)

• Record Type: Journal Article
• Authors: Zhao, Zhenyu; Muylaert, Koenraad; Vankelecom, Ivo F.J.
• Is Part Of: Water research. Volume 198(2021)
• Publication Date: 2021-06-15
• Subjects: Flocculation -- Patterned membranes -- Economic analysis -- Microalgae harvesting -- Membrane filtration -- Phase inversion; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2021.117181
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: Flocculation combined membrane filtration can decrease microalgae harvesting cost. Surface patterning can significantly enhance flux, while reducing energy input. Very low energy consumption and harvesting cost were achieved. Patterned membranes showed a lower filtration resistance than flat membranes. 28w% PEG in the casting solution was optimal for patterned membrane preparation. Abstract: Membranes have a lot of potential for harvesting microalgae, but mainly membrane fouling and high harvesting costs linked to low fluxes are hampering their breakthrough. Patterned membranes can reduce fouling by enchancing local turbulences close to the membrane surface on one hand, and by increasing the active area per m 2 of installed membrane on the other. Flocculation can further increase membrane permeance by increasing microalgal partical size and reducing the fraction of free organic matter in the feed. In current study, the effect of polyethylene glycol (PEG) in the casting solution of patterned polysulfone membranes was investigated to better tune the performance of the patterned membranes, together with the effects of cross-flow velocity and chitosan dosage on membrane fouling. The energy consumption and total harvesting cost, extrapolated to a full-scale microalgal harvesting, were then estimated. The patterned membrane prepared with a 28w% PEG concentration showed the highest clean water permeance (900±22 L/m 2 h bar) and membrane permeance in a microalgal suspension (590±17 L/m 2 h bar). Patterned membranes showed a lower filtration resistance (15% permeance decline at the end of filtration) than flat membranes (72%) at a cross-flow velocity of 0.0025 m/s. Increasing cross-flow velocity could increase membrane permeance in most cases. The highest stable membrane permeance (110±17 L/m 2 h bar) and the lowest filtration resistance were achieved when combining patterned membrane filtration with flocculation at optimized chitosan dosage. A very low energy consumption (0.28 kWh/kg) and harvesting cost (0.16 €/kg) were achieved under these conditions. Graphic abstract: Image, graphical abstract