The method of membrane cleaning  

In the operation, needed monitor for module, the suction pressure must not exceed a set value. When it exceeds a set value, will alarm, and then quickly clean the liquid and restore the pressure difference. 

There are 3 kinds of cleaning of medicines: maintenance cleaning; recovery cleaning; immersion cleaning.

Usually, to maintain the system function, combine with the maintenance cleaning - once a week, and the recovery cleaning - once every 3 months (or when the suction pressure exceeds the set value) .

The membrane contamination of the MBR system is mainly blocked by organic substances. Therefore, the cleaning liquid that is usually used is NaCIO. If it is used for a long time, there will be blockage of inorganic substances. So it is suitable to use acid cleaning. 

1.  Maintenance cleaning.

Maintenance Cleaning periodically clear the blockage of the membrane surface, to control the thickening on the adhesive layer and the TMP, achieving stable operation.  

The maintenance cleaning is once a week. The NaCIO, with effective chlorine concentration of 300~1000mg/L , for 15~30min. And the amount of liquid is 2L/m2 per unit membrane area . In the implementation, the aeration is stopped and the operation is automatic. 
2.  Resume cleaning. 

The cleaning is performed every 3 months. Or when the TMP rises. The purpose is to remove the blockage of the diaphragm and return the TMP to the initial value. Stopping the aeration, NaCIO ,which the effective chlorine concentration is 3000mg /L, in working for 30 min.

After maintaining the NaCIO for 30 - 90 minutes in the state, if the TMP is still high, it could be considered to be caused by the blockage of the inorganic substance. So the acid is required (1% oxalic acid, 1% citric acid). Online cleaning of 0.1~0.5mo/L sulfuric acid or hydrochloric acid). 
3. Offline cleaning 

When the recovery and cleaning cannot restore the TMP, the membrane module should be immersed in the chemical cleaning tank to remove the blockage, in order to restore the TMP in the initial value. 

Immersion cleaning is better than recovery cleaning.

In the immersion Cleaning, the membrane module is immersed in a solution containing an effective chlorine concentration of NaCIO (3000 mg/L) or sulfuric acid or hydrochloric acid (1% to 2% oxalic acid or citric acid, 0.1 to 0.5 mol/L). 

The immersion time in NaC1O is 6 - 24h; the acid is immersed for about 2h.