Microfiltration Of Yeast Suspensions Research Articles

Application of backflushing for fouling reduction during microfiltration of yeast suspensions

The results of microfiltration studies using inorganic TiO 2/Al 2O 3 membranes for solutions containing yeast are reported. The aim of the research was experimental as well as mathematical analysis of the permeate flux dependence on time for cross-flow filtration combined with backflushing using permeate. The effect of operating parameters such as cross-flow velocity, pressure difference across the membrane, and filtration time on permeate flux was experimentally investigated. The transmembrane pressure was changed in the range of 120–320 kPa. The feed was pumped to the membrane module at a cross-flow velocity in the range of 2.73–4.55 m/s. Microfiltration processes were performed at constant temperature (20°C) using feed with constant content of yeast, i.e. 510 mg/L. The backflushing runs were performed at constant operating parameters, ▵ P R=150 kPa; t R=60 s with frequency every 10 min. Experimental results were used for analysis in the frame of mathematical equation obtained using semiempirical models of the filtration and steady-state fluxes.

Using a yeast cell layer as a secondary membrane in microfiltration

Microfiltration of yeast suspensions ( Sacch. cerevisiae) was carried out to investigate the impact of a secondary membrane, composed of deposited yeast cells, on the filtration performance. Cross-flow filtration experiments with yeast–water suspensions in a rectangular channel showed the deposition of cells of different sizes, depending on the hydrodynamic parameters of the experiments. In dead-end filtration experiments with yeast–wort suspensions, the presence of the yeast layer provided, for constant filtrate flux, a slower increase in transmembrane pressure and for constant transmembrane pressure a slower decrease of filtrate flux. The positive effect of the yeast presence, which was observed, strongly depends on the yeast concentration. In cross-flow filtration experiments at a given filtrate flux the lower cross-flow velocity enables the formation of the yeast cell layer, which acts as secondary membrane and protects the primary membrane from the fouling agents of the wort, such as proteins and polysaccharides. At higher cross-flow velocity, there is no yeast layer formation, which results in blocking of the membrane through the fouling agents and the transmembrane pressure rises dramatically.

Comparison of Different Pitch Lengths on Static Promoters for Flux Enhancement in Tubular Ceramic Membrane

The use of turbulence promoters in membrane based processes have been investigated and are increasingly been used in industrial applications to minimize fouling and enhance the membrane flux. The efficiency of crossflow microfiltration is limited by membrane fouling and concentration polarization leading to flux decline during operation. A detailed study was carried out in the microfiltration of yeast suspensions using an in‐house rig and three different static turbulence promoters of varying pitch lengths. The design of the promoters incorporates a helical thread around the length of the insert, which induces turbulent flow through the membrane. This promotes good mixing of the feed fluid and minimizes concentration polarization effects. The testing of tubular membranes with the static inserts has been carried out and the results are included in the report. The pitch lengths used were 7 mm, 10 mm, and 14 mm and the parameters investigated included temperature, CFV, concentration of feed suspension and pressure. The flux decline data was recorded over a 50 minute filtration cycle and the cleaning protocol was employed after every cycle to restore the permeability of the membrane. A comparison of the membrane performance and efficiency of the three swirls inserts of varying pitch lengths together with a comparison of the degree of total, reversible, and irreversible fouling data amongst others are reported and discussed. The results obtained during the investigations of flux enhancement via static turbulence promoters into the tubular membranes are presented and are selected to differentiate the efficiency of the inserts and the degree of fouling associated with them.

Effects of colloidal fouling and gas sparging on microfiltration of yeast suspension

Cross-flow microfiltration is an important step in separating Baker's yeast (Saccharomyces cerevisiae) from aqueous suspension in many processes. However the permeate flux often declines rapidly due to colloidal fouling of membranes and concentration polarisation. The present work explores the possibility of maintaining acceptable permeate flux by co-current sparging of gas along with the feed, which would scour away colloidal deposits and reduce concentration polarisation of membranes. In this work, both washed and unwashed yeast were used to study the effect of washing to reduce protein fouling of membranes. It was found that permeate flux increased by 45% for liquid throughput of 75 kg/h for a feed concentration of 2.0 kg/m3 of washed yeast as compared with unwashed yeast suspension without gas sparging. For washed yeast suspension, the increase in gas flow rate from 0.5 lpm to 1.5 lpm (30 l/h to 90 l/h) had beneficial effect on permeate flux. It is concluded that in the present case, the gas flow rate should be less than or equal to the liquid flow rate for enhancement of permeates flux.

Microfiltration of yeast suspensions with self‐cleaning spiral vortices: Possibilities for a new membrane module design

A novel method of producing controlled vortices was used to reduce both concentration polarization and membrane fouling during microfiltration of Saccharomyces cerevisiae broth suspensions. The method involves flow around a curved channel at a sufficient rate so as to produce centrifugal instabilities (called Dean vortices). These vortices depolarize the build-up of suspended particles such as yeast cells at the membrane-solution interface and allow for increased membrane permeation rates. Various operating conditions under which such vortices effectively reduced cake build-up of suspended particles such as yeast cells at the membrane-solution interface and allow for increased membrane permeation rates. Various operating conditions under which such vortices effectively reduced cake build-up during microfiltration of 0 to 0.55 dry wt% yeast broth were investigated. Flux improvements of over 60% for 0.25 dry wt% yeast broth for flow with over that without Dean vortices were observed. This beneficial effect increased with increasing retentate flow rate and increasing transmembrane pressure and decreased with increasing concentration of suspended matter. Similar behavior was observed whether the cells were viable of killed. the improvement in flux in the presence over that in the absence of vortices correlated well with centrifugal force or azimuthal velocity squared. The relative cake resistances increased with reservoir yeast concentration. These values with vortices increased from 62% to 75% of that without vortices with increasing yeast concentration. The ratio of the cake thicknesses in the limiting case (at high feed concentration) was 3.25. These results suggest that self-cleaning spiral vortices could be effective in maintaining good and steady microfiltration performance with cell suspensions other than those tested.