Physical rinsing has not been able to restore the performance of the reverse osmosis membrane when the following conditions occur, and chemical cleaning is required.
1 The water production under standardized conditions is reduced by 10 – 15%;
2 The system pressure difference between the influent and concentrated water rises to 1.5 times the initial value;
3 The water quality of the produced water is reduced by 10-15%.
Frequency of chemical cleaning of reverse osmosis equipment
When the membrane element is slightly contaminated, the membrane element should be cleaned in time. Severe pollution may affect the cleaning effect due to the fact that chemical agents are not easily penetrated into the contaminated layer and the contaminants are not easily washed out of the membrane. If the performance of the membrane element is reduced to 30-50% of the normal value, it is difficult to clean and return to the initial performance of the membrane system.
The cleaning cycle of the membrane depends on the actual contamination on site. The normal cleaning cycle is once every 3-12 months. If it is washed more than once in one month, it is necessary to improve the pretreatment such as additional investment or redesign the membrane system; if the period of cleaning the reverse osmosis pure water equipment is once every 1-3 months, it should focus on adjusting and optimizing the operation of the existing system. parameter. Even if the system has not been contaminated for a long time, in order to better ensure the normal operation of the system, it is generally considered to perform chemical cleaning once every 6 months.
When an inorganic flocculant is used in the pretreatment process, the inorganic salt which is often incompletely reacted does not form a filterable floc. The user should ensure that no excess flocculant enters the membrane system. Excess flocculant can be determined by an SDI tester. For example, the iron on the SDI membrane is 3 μg/tablet and should not exceed 5 μg/table at any time.
In addition to turbidity and SDI measurements, the particle counter accurately measures RO/NF water intake. Particles with a particle size greater than 2 μm should be <100/ml.