Author: Site Editor Publish Time: 2022-10-18 Origin: Site
Ceramic membrane separation technology is one of the very advanced membrane separation technologies in the international arena in recent years and is widely used in chemical, food, pharmaceutical and environmental protection industries. Ceramic membrane is a new material of inorganic membrane, which has the advantages of good chemical stability, strong anti-microbial ability, high mechanical strength and long service life, so it has started to be promoted and applied in the transformation of industrial wastewater treatment in thermal power plants. However, due to the poor water quality and complex composition of industrial wastewater in thermal power plants and the low track record of practical application of ceramic membrane ultrafiltration, the technical reserve is insufficient, resulting in poor results of ceramic membrane ultrafiltration in practical use.
Membrane contamination refers to the adsorption, deposition or blockage of particles, colloids or solute macromolecules on the membrane surface or in the membrane pores, resulting in irreversible changes in the permeation flow and separation characteristics of the membrane. Whether organic or inorganic membranes, there is widespread mechanical retention, adsorption and concentration polarisation caused by different membrane pore sizes and different hydrophilic membrane materials. Ceramic membranes are mainly made of metal oxides and other materials, and alumina ceramic membranes, for example, are also contaminated by charge adsorption due to the amphoteric nature of the hydroxyl groups on the surface of the membrane after contact with the aqueous medium. Studies have shown that cations (Fe2+, Ca2+, Al3+) and anions (S2-, SO42-, PO43-) in solution above the divalent level are susceptible to charge adsorption contamination on the surface of ceramic membranes.
For ceramic membranes, the control and recovery techniques for general suspended matter, microorganisms and organic contamination are relatively mature, so the key is how to control the charge adsorption contamination on the ceramic membrane surface. Through extensive research and testing, we have found that by adding the appropriate amount of coagulant to the ceramic membrane feed water, we can significantly improve the charge adsorption contamination on the ceramic membrane surface. The mechanism of action is not yet clear, but relevant research shows that coagulants can significantly reduce the colloidal charge of clay-type impurities in water, which reacts with contaminants in raw water, through the process of electrical neutralisation, adsorption, bridging, etc., to form a more loose, more permeable filter cake on the membrane surface, which can effectively prevent the adsorption of colloidal charges on the membrane surface, but also effectively clean off the accumulated contaminants through backwashing. This prevents adsorption of colloidal charges etc. on the membrane surface and effectively cleans away accumulated contaminants by backwashing.
As ceramic membranes rely on a loose flocculent filter cake on the membrane surface to trap the colloidal charge, the stability of this flocculent filter cake has a significant impact on the operational effectiveness of the ceramic membrane.
The amount of coagulant added depends on whether a complete flocculation alum can be formed, which varies slightly depending on the system design, but studies have shown that coagulation can effectively improve membrane filtration flux, and the more coagulant is added, the more significant the flux improvement. Through a large number of practical operation tests, it was found that the coagulant addition (in the case of polyaluminium chloride) in the range of 1.0-5.0mg/L (in AL) can maintain the stable operation of ceramic membrane ultrafiltration.
When the system design is reasonable, the added coagulant can be mixed evenly and there is sufficient reaction time, the lower dosing amount can be maintained; when the system design is not perfect, the coagulation reaction time is short or the reaction is not sufficient, the dosing dose should be increased appropriately to maintain the normal operation of ceramic membrane ultrafiltration; if the subsequent system has high requirements for water quality or membrane equipment such as reverse osmosis, the reasonable dosing amount should be determined through on-site commissioning In order to ensure that the effluent water quality meets the requirements or to prevent the formation of post-flocculation and other phenomena, which will affect the normal operation of the subsequent system.