For the cleaning of contaminated membranes, there are two main methods commonly used in physical methods and chemical methods. The physical method refers to a method of removing dirt by flushing or mechanical action of a liquid stream, and generally has a hydraulic method, a gas-liquid pulse method, a backwash method, and a circulation cleaning method. The chemical method refers to the method of removing the dirt by the reaction between the chemical agent and the dirt. The cleaning agents commonly used are: acid, alkali, oxidizing agent, surfactant, complexing agent, enzyme and a mixture of chemical agents.
1. Physical cleaning
There are many ways to physically clean, and they will be briefly parsed below:
①Backwashing method. This is one of the most common cleaning methods. It uses a liquid or gas as a back-up carrier to apply pressure to the ceramic membrane in the direction of the permeate. It is to reverse the action of the liquid, through the ceramic membrane
, the contaminants in the outer surface of the membrane and the pores are cleaned out, thereby achieving the effect of restoring the membrane flux.
② Low pressure and high flow rate cleaning. This approach requires a low operating pressure to speed up the flow of the liquid and thereby reduce the likelihood of solute molecules remaining in the membrane surface.
③ Negative pressure cleaning. It needs a vacuum suction operation to make the functional side of the membrane constitute a negative pressure, thereby obtaining the effect of cleaning the inside and outside of the membrane.
④Mechanical scraping. This method requires the cleaning of the inner surface of the membrane by means of a medium such as a soft foam ball and a sponge ball. The sponge ball or the like is washed several times by water pressure, and then the target of removing impurities is achieved. This method is used to remove dirt and the effect is excellent. At the same time, this method is also very suitable for cleaning organic impurities.
2. Chemical cleaning
In the process of using the ceramic membrane
, in order to keep the membrane flux in the initial state, only physical cleaning is not enough, and chemical cleaning must be used together to completely remove impurities and dirt. In view of the extremely diverse materials treated by the ceramic membrane
, the externally adsorbed substances of the ceramic membrane
are also greatly different, and the degree of contamination is also different. Therefore, the selected chemical cleaning agent should also be targeted.
3. Ultrasonic cleaning
Ultrasonic cleaning is the medium of ultrasonic wave, which fully exerts its cavitation and acceleration in the liquid, and cooperates with its direct flow effect to differentiate and dissociate the pollutants to achieve the goal of cleaning. This cleaning method not only enables real-time monitoring of the cleaning results, but also penetrates the membrane module.
For example, the accumulation of substances inherent in membrane filtration on the surface of the membrane can cause fouling. Under certain process conditions, ultrasonic waves can be used to prevent fouling and achieve film cleaning and effective cleaning of ceramic membranes
at a frequency of 130 kHz.
4. Electric field cleaning
The electric field cleaning uses the medium of the electric field to place one side of the film within the electric field, so that the charged particles in the dirt move with the electric field. When the ceramic membrane is filtered, a corresponding electric field is applied to move the surface of the membrane and nearby particles along the direction of the electric field, thereby cleaning the charged impurities deposited on the surface of the membrane.
Different filtration systems have different characteristics of membrane fouling. Therefore, the application of the pollution film cleaning technology needs to consider the combination of universality and specificity. Secondly, the combination of the chemical cleaning method and the physical cleaning method can synergistically effect, and the membrane permeation flux of the ceramic membrane can be restored to a greater extent.