Physical Cleaning Method of Membrane Filter
The physical cleaning method is to remove contaminants from the membrane filter surface by mechanical means. It would not bring new contaminants to the membrane filter with simple cleaning steps. It consists of a variety of methods, such as positive direction rinsing, backwashing, hydraulic methods, gas-liquid pulses cleaning, and cycle washing methods.
For instance, the backwashing method is to remove the contaminant on the surface by blowing gas or a liquid from the permeate side of the membrane filter. It should be carried out at a lower operating pressure (about 132kPa) to avoid membrane filter rupture. Generally, it takes 20~30min. However, the physical cleaning method is effective only for the membrane filter at the initial stage of contamination, and the cleaning effect cannot be sustained.
Chemical Cleaning Method of Membrane Filter
The chemical cleaning method employs the reactions between the chemical reagents and deposits and other contaminants that affect flux rates to remove contaminants from the membrane filter. These chemical agents include acids, bases, oxidizing agents, and formulated agents. The acid is effective in removing deposits, like calcium carbonate, iron oxide, and metal sulfide. The alkaline cleaning solution includes phosphates, carbonates, and hydroxides, which can loosen, emulsify, and disperse the deposits easily. When removing deposits such as silicates that are particularly difficult to remove, the alkaline and acid agents are alternately used.
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