Magnetic seeding to aid recovery of biological precipitates

A new approach to solid/liquid separation for biological precipitates is presented. The precipitate is seeded with small dense and/or magnetic particles to increase the density difference between precipitate and liquid or to make the precipitate amenable to magnetic separation. Experiments on seeding of ammonium sulphate precipitates of casein and separation of the seeded precipitate by gravity settling and batch centrifugation have shown that the approach holds promise. Seeded precipitates exhibit hindered settling under gravity with typical settling velocities of 0.6 cm/min for iron oxide seed and 2.4 cm/min for nickel seed. Calculations indicate that seeding of these precipitates causes a 23 fold increase in density difference between precipitate particle and supernatant liquid. The design of a magnetic seeding step for use in an enzyme isolation process is discussed.