Different cleaning agents should be used for different pollutants. When pollution occurs, there is usually not only one type of contaminant, so conventional chemical cleaning needs to include two steps: high pH cleaning and low pH cleaning. See Table 4 for general chemical cleaning agents that can be used. Which cleaning agent is used for chemical cleaning can be judged as follows:
- judged by the quality of reverse osmosis water;
- Before performing a system-wide membrane element cleaning, one or two membrane elements can be removed from the system and a cleaning test can be performed to select the best cleaning drug.
In general, high-pH cleaning solutions should be used to clean oil and microbial contamination, and then low-pH cleaning solutions are used to clean inorganic scale or metal oxide contamination. Sometimes it is acid washed and then washed with alkali, or only with one agent, such as iron contamination from groundwater sources, using simple low pH cleaning. Sometimes detergents are added to the cleaning solution to remove microbes and organic contaminants; some are added to chelating agents such as EDTA to better remove colloids, organics, microorganisms and sulfate scales. If the cleaning agent is chosen improperly or the cleaning sequence is not correct, the contamination may be deteriorated.