Electrically enhanced ultrafiltration of industrial enzyme solutions
Advancing the chemical engineering fundamentals
Filtration - II (T2-11b)
Keywords: Fouling, Electrophoresis, Electric field
Introduction
Fouling and concentration polarization are major problems in ultrafiltration of industrial enzyme solutions. Usually the flux decreases a factor of 10 from its initial value –large membrane areas are therefore required. During production it is also necessary to use a high crossflow to enhance the shear rate at the membrane surface and thereby reduce concentration polarization.
Concentration polarization can also be reduced by applying a DC electric field across the membrane. The electric field imposes an electrophoretic force on the charged enzymes dragging them away from the membrane surface. The result is an enhanced flux. Electroosmosis also assists this enhancement but its effect is secondary.
By using an electric field it is also possible to operate at a much lower crossflow compared to conventional ultrafiltration; since the electric field has replaced the need of a high shear rate at the membrane surface.
Electro-ultrafiltration (EUF) has been successfully used on biomolecules [1], proteins [2], cleaning of wastewater [3], inorganic metallic compounds [4] and water soluble polymers [5].
In this work crossflow electro-ultrafiltration (EUF) is carried out on industrial enzyme solutions from Novozymes A/S, Denmark. The aim is to investigate the use of EUF in industrial production.
Experimental
The electro-ultrafiltration rig consists of 3 membranes. Two cation exchange membranes that shield the electrodes, and prevents direct contact between them and the feed and permeate solutions. A 10 kDa ETNA membrane from Alpha Laval is placed between the two ion exchange membranes.
Case studies were carried out on two different amylase solutions.
The solutions were diafiltrated before use. A transmembrane pressure of 1.5 bar and a crossflow of 0.075 m/s were used.
Results
EUF has been tested on two amylase solutions and a significantly flux enhancement was achieved. The relative flux increases with increasing concentration. The effect of salt concentration, TMP and crossflow were also studied. An increased TMP and crossflow did not improve the flux remarkably -since the process is controlled by the strength of the electric field.
Increasing the conductivity of the enzyme solution by adding CaCl2 did not change the flux, but the power consumption increased proportional to the conductivity.
The economy of the process is controlled by the conductivity of the enzyme solution and charge of the enzyme. At a certain conductivity the production costs of EUF exceeds the costs of conventional ultrafiltration.
No loss in enzyme activity was observed.
Conclusion
Results show that it is possible to use electro-ultrafiltration when concentrating enzyme solutions from Novozymes A/S. For enzyme solutions with low conductivities the operation costs is lower than for conventional ultrafiltration. The feasibility of the process will be a trade-off between production cost and investment.
References
[1] W. R. BOWEN, Pulsed electrophoretic filter-cake release in dead-end membrane processes,
AIChE journal, 43 (1997) 959-970.
[2] S. Oussedik, Enhanced ultrafiltration of bovine serum albumin with pulsed electric field and
fluidized activated alumina, Desalination, 127 (2000) 59-68.
[3] G. C. C. Yang, Reclamation of high quality water from treating CMP wastewater by a
novel crossflow electrofiltration/electrodialysis process, Journal of membrane science,
233 (2004) 151-159.
[4] T. Weigert, Crossflow electrofiltration in pilot scale, Journal of membrane science, 159 (1999) 253-
62.
[5] G. Akay, Electric field enhanced crossflow microfiltration of hydrophobically modified
water soluble polymers, Journal of membrane science, 131 (1997) 229-236.
Presented Tuesday 18, 08:45 to 09:05, in session Filtration - II (T2-11b).
