Why does reverse osmosis cleaning often put alkaline cleaning after acid cleaning?

Every reverse osmosis system is subject to contamination and requires cleaning. Since contamination usually occurs with more than one type of contaminant, the typical cleaning process usually includes two major steps, low pH cleaning and high pH cleaning, as required.

Different contaminants should be cleaned using different cleaning agents, with alkaline cleaning mainly used to remove microbial or organic contaminants and acid cleaning mainly used to remove fouling. Cleaning agents should be selected according to the type of contaminant and membrane type to avoid damage to the membrane.

The order in which the cleaning agents are used should be determined according to the actual problem. The usual cleaning order is to carry out acid cleaning first, followed by alkaline cleaning.

In some cases, if the contamination is mainly organic or microbial, an alkaline wash can be carried out first, followed by an acid wash and then a final step of alkaline wash.

The important reason for making lye washing the last step is that it allows the membrane pores to open sufficiently after acid washing to restore produced water flow.

If the conventional pickling followed by alkaline cleaning procedure is not used, you will need to consult a membrane specialist to help you make the right choice.