Harvesting algal biomass for biofuels using ultrafiltration membranes

The objective of this paper is to develop efficient technologies for harvesting of algal biomass using membrane filtration. Foulants were characterized using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Anti-fouling strategies were established, such as using air-assisted backwash with air scouring, and optimizing operational conditions. A model was also developed to predict the flux decline and final concentration based on a resistance-in-series analysis and a cake development calculation. The results showed that the buildup of the algal cake layer and adsorption of algogenic organic matter (AOM) (mainly protein, polysaccharides or polysaccharide-like substances) on the membrane caused membrane fouling. The cake layer buildup was removed by conducting an air-assisted backwash every 15 min. The adsorbed AOM could be removed by soaking the membrane in 400 mg/L NaClO for 1 h. In our experiment the algal suspension was concentrated 150 times, to give a final cell concentration of 154.85 g/L. The harvesting efficiency and average flux were 46.01 g/(m² h) and 45.50 L/(m² h), respectively. No algae were found in the permeate, which had an average turbidity of 0.018 Nephelometric Turbidity Units (NTU). The flux decline predicted by the model under different conditions was consistent with the experimental results.