Cleaning of a RO system
|The cleaning system is an important part of a desalination installation. Membranes can become contaminated after they have been used for some time, with pollutants such as colloids, bio films and biological matter. These contaminants can absorb to the membrane surface and the pipes of the membrane system and consequentially, the performance of the system will decrease. The system may even be seriously damaged. That is why a system needs cleaning periodically. |
Cleaning of a Reverse Osmosis system is usually started when the following conditions are in order:
· The normalized flux has decreased 10-15%
· The normalized salt content of the permeate has increased 10%
· The pressure gradient in a pressure vessel has decreased 15%
The cleaning procedure of a Reverse Osmosis system consists of the following process steps:
1. Production of the cleaning fluid
The fluids that are used for the cleaning process need to be of a certain pH and all chemicals must be dissolved and mixed before the cleaning fluid is added in the membrane elements.
2. The removal of feed water from pressure vessels and elements with cleaning fluid
3. Low-flow recirculation through pressure vessels
The cleaning fluid is now in the drains and the feed water has been forced out of the system.
4. Soaking in the cleaning fluid
The pump is shut off and the cleansing fluid will soak into the membranes.
5. Drainage of the pressure vessels
The applied cleaning fluid is pumped out of the system. By sampling the cleansing fluid and analysing the samples, one can determine the amount of contamination.
6. Rinsing out the system
For the rinsing process, either permeate or good-quality water is used.
7. Starting up the cleaned system parts
The installation is started up according to the usual process parameters. When cleaning fluid is still present in the permeate, the system needs to be rinsed again, until permeate quality is satisfactory.