Membrane cleaning: Chemically enhanced removal of deposits formed during yeast cell harvesting

Cleaning strategies have been evaluated for a microfiltration membrane fouled during cell harvesting. The membrane selected was a flat sheet of hydrophilic polyethersulphone with a nominal pore size of 0.1 mu m. Baker's yeast was selected as a model microorganism. During microfiltration, a constant transmembrane pressure of 2 bar, cross-flow velocity of 1 m s(-1), and suspension temperature of 34 degrees C produced a steady state flux within 90 minutes. A water rinse removed the majority of the cellular cake revealing tenacious noncellular and cellular deposits. Chemically enhanced cleaning of the rinsed deposit was investigated using dilute solutions of sodium hydroxide, nitric acid and P3 Ultrasil II. Cleaning temperature effects were investigated over the range 30 degrees C to 60 degrees C and laminar and turbulent flow regimes were compared. A combination of measured flux recovery and microscopic visualization was used to assess cleaning performance. Effective two-stage cleanings was achieved with sequential alkali and acid treatments while effective single-stage cleaning was achieved using the formulated detergent P3 Ultrasil 11.