Microalgae harvesting from anaerobic membrane bioreactor permeate: Comparative performance of PVDF and PES ultrafiltration membranes

Membrane-based harvesting offers an effective approach for recovering microalgal biomass from anaerobic membrane bioreactor (AnMBR) permeate while improving effluent quality. In this study, laboratory-fabricated polyvinylidene fluoride (PVDF) and polyethersulfone (PES) ultrafiltration membranes were comparatively evaluated for harvesting mixed-culture microalgae cultivated in AnMBR permeates derived from mono-digestion of sewage sludge (SS) and co-digestion of SS with food waste. Prior to cultivation, the permeates were diluted with Bold's Basal Medium (BBM) to reduce ammonium concentration and mitigate inhibitory effects on microalgal growth. Membrane performance was evaluated in terms of relative flux (operational flux/pure water flux), biomass retention, and effluent quality, while post-filtration membrane characterization was performed using scanning electron microscopy and Fourier transform infrared spectroscopy. The PES membrane exhibited more stable filtration performance during harvesting, which was likely associated with its higher surface hydrophilicity and reduced tendency for organic matter adsorption and microalgal cell attachment compared with the PVDF membrane. Both membranes achieved high biomass retention and produced low-turbidity effluents with reduced residual nutrient concentrations. Surface analyses confirmed the formation of a fouling layer on both membranes after filtration. The harvested biomass was predominantly protein-rich under all tested conditions. Overall, the results demonstrate that membrane material significantly influences the filtration performance in integrated AnMBR-microalgae systems. Further studies should investigate membrane performance at higher volumetric concentration factors and under repeated filtration-cleaning cycles, supported by techno-economic assessment.