Electrofiltration

The electrostatic precipitation is a method in which the membrane filtration is combined with the electrophoresis in a dead-end process.

The electric filtration has been found to be a suitable method for the concentration and fractionation of biopolymers. Hindering the covering layer for the filtration assembly to the filter membrane can be reduced by an electric field or even prevented and thus the performance of the filtration, as well as their selectivity can be increased (for fractionation ). Thus, the cost in the range of the downstream process to significantly reduce bioprocesses.

Method

The electric filtration is a process for the separation or concentration of colloidal substances such as biopolymers. The principle of electrostatic precipitation is due to the fact that a conventional dead-end filtration, an electric field is superimposed. This affects swift polarity on the usually charged biopolymers an electrophoretic force acting opposite to the resistance of the flow of filtrate. Characterized the covering layer structure is drastically reduced to the micro-or ultra-filtration membrane and reduce the filtration time of several hours in the case of filtration for a few minutes in case of electric filtration. The electrofiltration shows in comparison to the cross-flow filtration not only a greater permeate flux, it is also due to the low shear stress on the often sensitive biopolymers a particularly gentle separation.

The use in the biotechnological product work is promising, as biopolymers one hand are difficult to filter, but are otherwise loaded due to the often existing amino or carboxyl groups. In the electric filtration, the goal is to counteract the cake structure to improve the filtration rate is difficult to filter products.

Is the filtration process, an electric field is superimposed, it comes to the electrophoresis particles and electroosmosis. In the filtration of the conventional electric filtering an electric field ( DC) superimposed on this which acts in parallel to the flow direction of the filtrate. Exceeds the flow of opposing electrophoretic force FE, the hydrodynamic resistance force FW, so wander charged particles away from the filter medium, so that significantly reduces the thickness of the filter cake on the membrane.

Are the separated solid particles are negatively charged, so they migrate toward the anode (positive pole) and are deposited on the filter cloth there. On the membrane on the cathode side (negative pole) based on which a very thin coating layer, so that virtually all the filtrate flows through the membrane.

Figure 1 is a schematic illustration of a chamber is shown with electric filtration rinsed electrodes. For the rinse cycle of a buffer solution used. For this operation, 2002, a patent was granted.

Basics

The drag force can be estimated using Stokes' law.

The electrophoretic force can be estimated using the Coulomb's law.

In these equations, rh is the hydrodynamic radius of the colloid, ν the electrophoretic migration velocity, η the dynamic viscosity of the solvent, ε0 is the permittivity of vacuum ( electric field constant ), εr is the relative permittivity of water at 298 K, ζ zeta potential, and E electric field. The hydrodynamic radius is the sum of the particle radius, and the stationary boundary layer of solvent.

In the stationary electrophoretic migration of a charged colloid, these are electric force and the drag force are in equilibrium, and we have:

These effects is also effective electric field strength in the electrostatic precipitation of the biopolymers, which may be charged, in addition to the hydrodynamic resistance. Looking at the cathode side, where it acts on negatively charged particles, the electric field force against the hydrodynamic drag force. This is hampered on this side of the structure of the filter cake, in the best case, no filter cake is formed. The field strength at which this occurs is called the critical field strength E crit. Also on the liquid acts an electric force, as this is loaded due to the neutrality condition. In addition to the applied hydraulic pressure difference thus affects the electroosmotic pressure Pe.

The extension of the fundamental equation of the cake -forming filtration, the Darcy's law using the electrokinetic effects by integrating under the condition of constant values ​​of the electroosmotic pressure Pe, the critical field strength E crit and the effective field strength E is obtained:

In this equation,? C mass specific cake resistance, c concentration, A filtration area, VL filtrate, ApH hydraulic pressure.

Previous work in the area of ​​Biochemical Engineering, Institute of Bio - and Food Technology at the University of Karlsruhe have shown that the electrostatic precipitation for the concentration of charged biopolymers works. Very good results have already been achieved in the purification of the charged polysaccharide xanthan. In Figure 2, a filter cake of xanthan is shown.