When to clean membranes

When the system’s flux reduce by 10-15%;

When the operate pressure increase by 10-15%;

When the operate pressure of each stage increase by 10-15%;

When the TDS of the permeate water increase by 10-15%;

When the system has been operating continually for 3-12monthes or the total time for period operation gather up to 6-12monthes;

Before the long stop of system, the membranes need to be cleaned before injecting protected liquid.

Mark: The standard should be settled before comparing the above data, the standard data for comparing is the one of operating 25-48hours.

RO membrane, NF and Spiral UF shall not take backwash, flush membranes with its permeate water. If there is necessary to clean the membrane, choose the cleaning chemicals according to different problems as following:

1.    Membranes are polluted by metal oxide or hydroxide of a metal

Suggested cleaning chemical: 2.0% Citric acid + ammonia water(pH3) or 1.0% sodium bisulfite (pH11.5) liquid.

2.    Polluted by scale incrustation( such as CaCO3)

Suggested cleaning chemical: 2.0% Citric acid liquid or dilute hydrochloric acid liquid(pH2-3).

3.    Polluted by all kinds of colloids

Suggested cleaning chemical: Liquid(pH11) mixed with 2.0%STPP and 0.8% EDTA-2Na.

4.    Polluted by CaSO4, BaSO4, SrSO4

Suggested cleaning chemical: Liquid(pH11) mixed with 2.0%STPP and 0.8% EDTA-2Na.

5.    Polluted by organic matters

Suggested cleaning chemical: Liquid(Ph12) mixed with 2.0% STPP and 0.25% DDBS.

6.    Polluted by microbe

   Suggested cleaning chemical: First be cleaned with liquid mixed with 0.1%NaOH and 0.2%EDTA-2Na, then be cleaned with 0.1%formol.

7.    Polluted by SiO2

   Suggested cleaning chemical: for compound membranes, it’s better to move Si scale with alkali-liquid with pH10-12 and high temperature of 40℃.