Darko M. Krstić

Membrane fouling during cross-flow microfiltration of Polyporus squamosus fermentation broth

The application of microfiltration to biological systems is hindered by membrane fouling that results in a decrease in the filtrate flux and solute transmission with time. In this work, the effects of transmembrane pressure, cross-flow feed velocity, biomass structure and feed composition, on membrane fouling during cross-flow microfiltration of Polyporus squamosus fermentation broth, were investigated. The results of cross-flow trials with 0.2 μm aluminum oxide membrane showed the existence of the optimal operation transmembrane pressure and cross-flow velocity, in respect of membrane fouling, for examined range of operation conditions. It was noticed that the process of membrane fouling was moved from a predominantly surface layer phenomenon to internal membrane fouling as the cross-flow velocity was increased. Comminution of the fungal biomass prior to microfiltration to reduce particle size showed a beneficial effect on the transient flux. The steady-state flux and the transmission of solutes were not significantly affected by the biomass comminution. The observations of the filtrate flux and the transmission of solutes indicated a decrease in the rate of fouling with decreasing content of soluble components with large molecular weights in the feed.

Kenics Static Mixer as Turbulence Promoter in Cross-Flow Microfiltration of Skim Milk

The efficiency of cross-flow membrane filtration processes is limited by membrane fouling and concentration polarization. The question of membrane fouling and membrane pore blocking during microfiltration is much more important than in the traditional ultrafiltration, not only for the maintenance of acceptable flux but also for the adequate recovery of the permeate components. The objective of this study was to demonstrate that use of a static mixer as turbulence promoter results in enhanced cross-flow microfiltration of skim milk. Experimental investigations were performed on 50-nm and 100-nm ceramic tubular membranes. The use of a static mixer provided a significant reduction of membrane fouling and an increase of more than 700% in permeate flux for both membranes compared with that obtained without a static mixer at the same feed flow rate. The similar flux enhancement indicates that surface layer resistance dominates the overall fouling resistance. Although the power consumption was significantly increased by using a static mixer, a decrease of more than 25% in specific energy consumption for both membranes was achieved with static mixer as compared to arrangement without static mixer in experiments performed at the same cross-flow velocity.