How should the ceramic membrane be treated if it is "dirty"?

Ceramic membrane separation is an advanced technology that can be widely used for impurity separation and product purification in fields such as chemical engineering, food, medicine, and environmental protection. However, pollution and blockage may occur during its use, leading to a gradual decrease in membrane permeation flux, especially in ceramic membranes used in wastewater treatment, where fouling and blockage can occur at any time. How should we deal with the problem of ceramic membrane "fouling"?

1. The forms of pollutants on ceramic membrane surfaces

Ceramic membrane fouling refers to the adsorption and deposition of certain components in the treated liquid onto the membrane surface, or their entry into the membrane pores, or even the blockage of the membrane pores, resulting in a significant increase in membrane permeability resistance.

Generally speaking, the forms of membrane surface pollutants can be divided into the following two layers:

1. Dirt layer: It is composed of a filter cake layer formed by the accumulation of suspended solids in the extracted water on the membrane surface, a scale layer formed by the accumulation of scale generated by inorganic salts on the membrane surface, and an adsorption layer formed by the adsorption of colloidal substances or microorganisms on the membrane surface. It becomes dense under pressure, and the dirt overlaps with the membrane to form a dual membrane structure.

2. Gel layer: This layer exists with the filtration process. For example, during the filtration process in the produced water system of the oil field, the concentration of emulsified oil near the membrane surface increases continuously, especially in the case of low flow rate and high solute concentration, and gradually reaches the gel concentration. Above the dirt layer, a three-layer structure with series resistance is formed.

Controlling membrane fouling mainly considers two aspects. On the one hand, special preparation processes or application methods are used to reduce membrane fouling caused by ceramic membranes during use. On the other hand, physical or chemical methods are used to clean (preserve), wash (nourish) the contaminated ceramic membranes to restore their permeation flux.

2、 Cleaning methods for ceramic membranes

There are currently two commonly used methods for cleaning contaminated membranes: physical methods and chemical methods. Physical methods refer to the use of liquid flow flushing or mechanical action to remove dirt, usually including hydraulic methods, gas-liquid pulse methods, backwashing methods, and cyclic cleaning methods; Chemical methods refer to the use of reactions between chemical agents and dirt to achieve the goal of removing dirt. Commonly used cleaning agents include acids, bases, oxidants, surfactants, chelating agents, enzymes, and mixtures of chemical agents.

1. Physical cleaning

There are many methods for physical cleaning, which will be briefly analyzed below:

① Backwash method. This is one of the most common cleaning methods. It uses liquid or gas as a recoil carrier to apply pressure in the direction of the permeate on the ceramic membrane. In order to reverse the action of the permeate, pollutants on the surface and inside the pores of the membrane are removed through the ceramic membrane, thereby achieving the effect of restoring membrane flux.

② Low pressure and high flow rate cleaning. This method requires the use of low operating pressure to accelerate the flow rate of the liquid and reduce the possibility of solute molecules remaining on the membrane surface for cleaning. ƒ

③ Negative pressure cleaning. It requires the use of vacuum suction operation to create negative pressure on the functional surface of the membrane, thereby achieving the effect of cleaning pollutants inside and outside the membrane.

④ Mechanical scraping. This method requires the use of soft foam balls, sponge balls and other media to clean the inner surface of the membrane. By using water pressure to clean the membrane multiple times with sponge balls and other materials, the goal of removing impurities can be achieved. Using this method to remove dirt has excellent results. At the same time, this method is also suitable for cleaning organic adhesive impurities.

2. Chemical cleaning

In the process of using ceramic membranes, in order to maintain the initial flux, physical cleaning alone is far from enough. Chemical cleaning must also be used in conjunction to completely remove impurities and dirt. Given the extremely diverse materials used for ceramic membrane treatment, there are also significant differences in the substances adsorbed externally by ceramic membranes, resulting in varying degrees of pollution. So the selected chemical cleaning agents should also be targeted.

3. Ultrasonic cleaning

Ultrasonic cleaning utilizes ultrasound as a medium to fully utilize its cavitation and acceleration effects in liquids, combined with its direct flow effect, to separate and detach pollutants and achieve the goal of cleaning. This cleaning method can not only monitor the cleaning results in real-time, but also penetrate the membrane components.

For example, in the process of membrane filtration, the accumulation of inherent substances on the membrane surface can cause scaling. Researchers have found through experimental research that under specific process conditions, ultrasound can be used to prevent fouling and achieve membrane cleaning, as well as effectively clean ceramic membranes at a frequency of 130kHz.

4. Electric field cleaning

Electric field cleaning uses an electric field as a medium to place one side of the membrane inside the electric field, allowing the charged particles in the dirt to move with the electric field. When the ceramic membrane is filtered, a corresponding electric field is applied to move the particles on and near the membrane surface in the direction of the electric field, thereby cleaning up the charged impurities deposited on the membrane surface.

Different filtration systems have different characteristics of membrane fouling. Therefore, the application of pollution film cleaning technology needs to consider the combination of universality and pertinence; Secondly, the effective combination of chemical cleaning methods and physical cleaning methods can have a synergistic effect, which can restore the membrane permeation flux of ceramic membranes to a greater extent.

NanoMem® is a high-tech enterprise integrating R&D, production and service of plate ceramic filtration membrane products. We are professional supplier of flat ceramic filtration membrane, plate ceramic filtration membrane unit and MBR system. If you are interested in our products, please contact us at 0086 512 6638 9461 and email: export01@szdasen.com.