Dewatering algal suspensions is an important step in the extraction of oil and other useful substances from algae. In this study, sphericalNannochloropsissp. and ellipsoidalMonoraphidiumsp. suspensions were dewatered in the presence of different amounts of 350‐nm magnetite particles using a microfiltration membrane with 360‐nm pores in cross‐flow mode. Magnetite functions as a filter aid by reducing the deformation of the cake of filtered algae on the membrane and providing paths for water to flow through the filtration cake of algae. In the case ofNannochloropsissp., the highest dewatering rate was obtained when the number ratio, defined based on the size and ideal density, betweenNannochloropsissp. and magnetite was 1:12.5, but the addition of magnetite had no observable effect on the filtration of ellipsoidalMonoraphidiumsp. suspensions through the membrane. After dewatering, magnetite was effectively separated from the concentrated algal suspension by the application of a magnetic field in an open flow system. Magnetite has the potential to enhance dewatering performance using a cross‐flow membrane system.
A 120-nm silica suspension was permeated through a porous polyethylene (PE) hollow-fiber membrane, as was a solution of deformable elastic particles of poly(N-isopropylacrylamide) (PNIPAM) gel and dextran. The amount adsorbed and flux of permeation were analyzed with ordinary differential equations to obtain adsorption coefficients, maximum amounts adsorbed, and pore-narrowing factors. The thickness of the “silica-deposited layer” on the membrane was 1 μm. In a batch adsorption mode, 5.0 mg of PNIPAM gel and 30 mg of dextran were adsorbed on the PE membrane, with no adsorption on the silica. The PE membrane pores were narrowed by a secondary layer of adsorbed PNIPAM gel. When filtered through the silica-deposited layer, PNIPAM gel occupies gaps, resulting in a reduced permeation flux. Dextran passed through the silica-deposited layer and was partially adsorbed on the PE membrane. The modified membrane can control adsorption, filtration, and flux permeation, which leads to dynamic membrane separations.
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