Some measures can be taken to prevent and control the fouling process of ceramic membrane in the filtration process, but the membrane fouling can not be completely avoided. With the extension of the operation time, the permeation flux of ceramic membrane decreases rapidly, and it can not meet the requirements of industrial design. For a long period of time, the pollutants adhered to the membrane surface and existed in the pores, which may have chemical effects with the membrane and reduce its service life. Therefore, in order to restore the performance parameters of the membrane as much as possible, the ceramic membrane must be cleaned regularly.
Prevention and control of membrane pollution
The pretreatment and improvement of the properties of the material have a great effect on the prevention and control of the ceramic membrane pollution. The feed liquid often contains impurities such as organic matters, organic matters, microorganisms and colloids, which have adverse effects on the ceramic membrane. Therefore, the feed liquid should be pretreated, and the corresponding pretreatment process should be added in the process to remove the dominant pollutants, so as to minimize the pollution of the ceramic membrane.
Improve the properties of ceramic membrane, and improve the hydrophilicity of ceramic membrane. The results show that the hydrophilicity of the ceramic membrane material has a great influence on the anti pollution performance of the ceramic membrane, and the hydrophilic membrane is less affected by adsorption and can produce a greater membrane permeation flux.
Optimize the operating conditions of ceramic membrane separation
. The operating conditions are closely related to ceramic membrane pollution. The operating conditions, such as ceramic membrane flux, operating pressure, cross flow velocity, hydraulic retention time, solid retention time and operating temperature, have a direct impact on ceramic membrane pollution. There are two basic modes of ceramic membrane filtration, namely cross flow filtration and terminal filtration. According to Huang Xianhuai and others, the energy of terminal filtration is fully utilized, but it is easy to cause rapid ceramic membrane pollution; cross flow filtration is proposed for the shortcomings of terminal filtration, but the energy consumption is large.
Cleaning of membrane
At present, there are two common methods for cleaning the polluted membrane, physical method and chemical method. Physical method refers to the method to remove the dirt by liquid flow flushing or mechanical action, usually including hydraulic method, gas-liquid pulse method, back flushing method and circulation cleaning method; chemical method refers to the method to remove the dirt by the reaction between the chemical agent and the dirt, and the commonly used cleaning agents are: acid, alkali, oxidant, surfactant, complexing agent, enzyme and chemical agent A mixture of chemicals, etc.
There are many methods for physical cleaning, and they will be simply analyzed as follows:
① backwashing method. This is one of the most common cleaning methods. It uses liquid or gas as a recoil carrier to press the direction of the ceramic membrane through the liquid, in order to make the reverse effect of the liquid through the ceramic membrane. Clean out the pollutants on the surface of the membrane and in the hole, and then achieve the effect of restoring the membrane flux.
② low pressure and high flow rate cleaning. In this way, it is necessary to speed up the flow rate of the liquid with the help of low operating pressure, so as to reduce the possibility of retention of solute molecules on the membrane surface.
③ negative pressure cleaning. It needs vacuum suction operation to make the functional side of the membrane form negative pressure, so as to achieve the effect of cleaning the pollutants inside and outside the membrane.
④ mechanical scraping. This method requires the use of soft foam balls and sponge balls and other media to clean the inner surface of the membrane. Through water pressure, the sponge ball and the like can clean the membrane for many times, and then achieve the goal of removing impurities. The effect is excellent by using this way to remove dirt. At the same time, this method is also suitable for cleaning up organic gum impurities.
In the process of using ceramic membrane
, in order to keep the initial state of membrane flux, only physical cleaning is not enough, and chemical cleaning must be used together to completely remove impurities and dirt. In view of the diversity of the materials treated by ceramic membrane, the substances adsorbed by ceramic membrane are also quite different, and the pollution degree is also different. Therefore, the selected chemical cleaning agent should also be targeted.
Different filtration systems have different characteristics of membrane fouling. Therefore, the combination of universality and pertinence should be considered in the application of fouling membrane cleaning technology; secondly, the effective combination of chemical cleaning method and physical cleaning method can play a synergistic effect, and can restore the membrane permeability of ceramic membrane to a greater extent.