In The Circulating Water Treatment Of Swimming Pools, We Must Know The Steps And Precautions Of The Chemical Cleaning Method Of Reverse Osmosis Equipment In Advance.

Standards for chemical cleaning

When the following situations occur, physical washing can no longer restore the performance of the reverse osmosis membrane, then chemical cleaning is required.

The water production under standardized conditions decreased by 10-15%;

The system pressure difference between the inlet water and the concentrated water is increased to 1.5 times the initial value;

The quality of produced water drops by 10-15%.

Frequency of chemical cleaning

When the membrane element is slightly polluted, the membrane element should be cleaned in time. Severe pollution will affect the cleaning effect due to factors such as the difficulty of chemical agents from penetrating deeply into the contaminated layer, and the difficulty of pollutants being 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 restore the original performance of the membrane system.

The cleaning cycle of the diaphragm is determined according to the actual pollution situation on site. The normal cleaning cycle is every 3-12 months. If it is cleaned more than once in 1 month, it is necessary to improve the pretreatment such as additional investment or redesign the membrane system; if the cycle of cleaning 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 polluted 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, often the incompletely reacted inorganic salt does not form a filterable floc. The user should ensure that no excess flocculant enters the membrane system. Excessive flocculant can be measured by the SDI test device. For example, the iron on the SDI film is 3 μg / piece, and it should not exceed 5 μg / piece at any time.

In addition to turbidity and SDI measurement, the particle counter can also accurately measure whether the RO / NF influent is qualified. Particles larger than 2μm should be <100 particles / ml.

Selection of cleaning agents

Different pollutants should use different cleaning agents. When pollution occurs, there is usually not only one kind of pollutant, so conventional chemical cleaning needs to include two steps, high pH cleaning and low pH cleaning. See Table 4 for general chemical cleaning agents that can be used. Which cleaning agent is used for chemical cleaning can be judged as follows:

-Judging by the quality of the reverse osmosis water;

-Before the whole system membrane element cleaning, one or two membrane elements can be taken out from the system, and the best cleaning chemicals can be selected by performing a cleaning test.

In general, high pH cleaning solution should be used to clean oil and microbial contamination, and then low pH cleaning solution should be used to clean inorganic scale or metal oxide pollution. Sometimes it is also acid-washed and then alkali-washed, or only one agent is used for cleaning, such as iron pollution of groundwater sources, and simple low-pH cleaning is sufficient. Sometimes detergents are added to the cleaning solution to remove microorganisms and organic contaminants; some chelating agents such as EDTA are added to better remove colloids, organics, microorganisms and sulfate scale. Improper selection of cleaning agents or improper cleaning sequence may worsen contamination.

Reverse osmosis equipment

Precautions and preparations before cleaning

 Before using the drug, read the MSDS and the drug description from the drug company carefully;

Wear safety glasses, protective gloves and work clothes when operating;

Calibrate the pH meter before use;

Estimate the volume of cleaning solution used;

Ensure that all cleaning chemicals are completely dissolved and mixed before the cleaning solution enters the system;

 The temperature and pH range of the cleaning solution conform to the specified values.

cleaning method 

General chemical cleaning steps are shown below. The specific matters are determined according to the working conditions and cleaning requirements on site.

1.Rinse the membrane element. Rinse with reverse osmosis water or ion-exchanged water for several minutes.

2.Configure medicines. Ensure that the drug is completely dissolved.

3.Cycle. The water in the membrane element is replaced with a low flow rate, and a part of the cleaning liquid is discharged, and then circulated. The circulating flow is based on the range in Table 8. If the pollution is serious, if you choose a large flow cycle, there may be a problem that the pressure difference is too high, which will damage the membrane element (the maximum pressure drop of a single membrane element is 0.07 MPa). At this time, the following methods are more reliable for operation:

-5 minutes from the start of the cycle operation, cycle by 1/3 of the set flow;

-Cycling between 5-10 minutes, according to the circulating flow of set flow 2/3;

 After 10 minutes, cycle according to the flow requirements.

The cycle time should be decided according to the specific situation. Generally 1 hour shall prevail. During this period, it is necessary to check whether the pH value changes at any time. The pressure should be kept as low as possible and no water produced as much as possible. At the same time, the pressure difference is monitored for changes.

4. Soak and recycle. Slowly close the valve at the inlet of the reverse osmosis membrane element. When the circulation volume is close to zero, turn off the circulation pump. In order to prevent the liquid from flowing out of the pressure vessel, the relevant valve can be closed when soaking. The immersion time depends on the degree of contamination. Usually in the range of 1-12 hours. After soaking, open the relevant valve and cycle.

5. Rinse. Rinse the medicinal solution in the membrane element and the cleaning device with reverse osmosis water or ion exchange water. At this time, the system is replaced from the cyclic state to the discharge state. Rinse the membrane system with the supply water. The rinse time is approximately 20–60 minutes. You can determine whether the washing is thorough by measuring the pH and conductivity of the drainage. The values of pH and conductivity are similar to the values of the water, and the washing can be stopped when it no longer changes.

6.Test run. The system is started normally, and the initial water production is discharged until the water quality reaches the required level. In order to obtain stable water quality of reverse osmosis, the recovery time sometimes takes several hours to several days. Especially after washing with alkaline solution (high pH value), water quality recovery takes a long time.