Automated electrophoretic membrane cleaning for dead-end microfiltration and ultrafiltration

doi:10.1016/S1383-5866(02)00066-7

Separation and Purification Technology

Volume 29, Issue 2, 1 November 2002, Pages 105-112

https://doi.org/10.1016/S1383-5866(02)00066-7 Get rights and content

Abstract

Membrane separation technology has been identified as a new and clean technology and as an alternative to the classical separation processes. Lately, it has been widely used in the wastewater treatment applications. However membrane fouling is a major bottleneck in this separation technology, as expected in the industrial application of such finely porous media. As the filtration process continues, the concentration of solute keeps building up on the membrane surface to form a filter cake. This results in a continuous declining of the flux. A number of methods are reported in preventing the membrane fouling. One of the established method is by using electric pulses known to be electrophoretic membrane cleaning, taking into account the effect of electroporeses, electroosmosis and the hydrodynamics forces during the application of the electric pulses. In the current study, an automated experimental rig has been developed to test this electrophoretic membrane cleaning. This rig enables to test the effectiveness of this method for electrophoretic membrane cleaning of dead-end microfiltration and ultrafiltration processes. The details of this rig will be presented and the process variables varied in this study are the strength of the applied voltage, pulse interval and pulse duration. An average flux is measured in each experiment as an indication of effectiveness of this method in reducing the membrane fouling. The experiments are controlled and monitored by a PC fitted with interface via an A/D converter which allows the collection of all the data automatically. Data are presented for microfiltration and ultrafiltration processes. In all cases, electrophoretic membrane cleaning for microfiltration and ultrafiltration processes has been successful by reducing the membrane fouling at different variables.

Introduction

Applying the electric field continuously (conventional electrofiltration) has been shown as an effective means in combating the deposition of materials on the membrane surface and thus, reduces the rate of fouling. The use of electric fields in controlling membrane fouling and filter cake formation has been studied by a number of researchers [1], [2], [3], [4], [5], [6]. This approach utilizes the inherent surface charge of dispersed materials when brought into contact with a polar (e.g. aqueous) solvent such as water. This may arise from a combination of a number of mechanisms, including ion association, ion adsorption or ion dissolution. The electrochemical properties of the membrane surface and the dispersed materials or solutes can have a significant influence on the nature and magnitude of the interactions between the membrane and the substances being used and their separation characteristics. The utilization of such properties by the application of external electric fields can potentially give substantial improvement in the performance of membrane separation. In particular, such processes make use of two electrokinetic phenomena, electrophoretic and electroosmosis. The conventional electrofiltration can be effective means of reducing both the concentration polarization and membrane deposition but it has some drawbacks which make this method uneconomical and difficult to handle for certain processes. The disadvantages of this process are:

a
Limitation of the process stream for relatively low conductivity of feed stream.
b
A high-energy requirement.
c
Substantial heat production.
d
Changes in the process feed due to reaction at the electrode.

For this reason, attention has been directed to the use of pulsed electric fields [4], [7]. This process has the same mechanism at work in preventing fouling as conventional electrofiltration. The only difference is that in pulsed electric fields, the electric field can be applied at certain intervals, which can be adjusted to suit the process. In some cases, this process can enhance the flux better than the conventional electrofiltration [8]. Applying the electric pulse on dead-end filtration has also been reported to reduce the rate of fouling [9], [10], [11], [12]. The advantages of dead-end filtration process over the cross-flow filtration are higher average percentage of water recovery and higher filter cake concentration while operating the process at acceptable permeation rate.

In order to run the experiments efficiently and to obtain meaningful data, an automated test rig has been designed, developed and constructed that enables the collection of reliable and reproducible data over a wide range of conditions. This paper describes the details of an automated experimental rig for microfiltration and ultrafiltration processes for electrophoretic membrane cleaning. TiO₂ and SiO₂ were used as the test system for microfiltration and ultrafiltration processes, respectively. Some parameters of experiment have been selected to investigate the effectiveness of cleaning the membrane surface using this method with respect to those parameters. The selected parameters are

a
Variation of the application of the pulse interval
b
Variation of the pulse duration
c
Variation of the electric field strength (V)

Section snippets

Materials and methods

The automated test rig was developed in order to test the electrophoretic pulse and filter cake release process for dead-end filtration processes. In this rig, the filtration rate, pressure, temperature and pH was monitored and recorded continuously throughout the experiment. The electric pulse was applied at certain intervals and for certain duration. Upon applying the pulse, the filter cake was released immediately after applying the pulse by opening the valve at the bottom of the filtration

Results and discussion

The average flux for normal filtration was 175 and 9.15 l/m² h for microfiltration and ultrafiltration process, respectively. As shown in Fig. 4(graph a) and Fig. 5(graph a), the flux dropped continuously with time throughout the whole experiment for both microfiltration and ultrafiltration processes. This was due to the building up of deposited particles on the membrane surface without any membrane cleaning. Whereas Fig. 4(graph b) and Fig. 5(graph b) show how the flux varied after application

Conclusion

Experimental data has been presented in cleaning the membrane surface using electric pulses with an automated rig. The automated rig developed has proven to reduce membrane fouling using electric pulse for both dead-end microfiltration and ultrafiltration processes. Therefore, the running of this experiments are more efficient and more accurate compared to the manual method. In all cases, it was found that the application of the electric pulse in the cleaning membrane surface is an effective

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View full text

Automated electrophoretic membrane cleaning for dead-end microfiltration and ultrafiltration

Abstract

Introduction

Section snippets

Materials and methods

Results and discussion

Conclusion

Chem. Eng. Sci.

A solid/liquid separation process base on cross flow and electrofiltration

AlChE J.

Cross flow electrofiltration for colloidal separation of protein

J. Chem. Eng. Japan

Electrical separation processes

Application of particles and colloidal membrane fouling in cross flow microfiltration

Sep. Sci. Technol.

Analysis of filtration mechanism of dead-end electroultrafiltration for proteinaceous solutions

Chem. Eng. Jpn