When applying reverse osmosis, if the water production rate of the equipment decreases by 10%, if the salt throughput increases by double, or if the pressure drop increases by double, it indicates that the reverse osmosis must be cleaned (but it should be noted that a decrease in temperature can also cause a decrease in water production rate, which is a normal situation. Except for regular cleaning, it is recommended to operate at low voltage for a few minutes before each operation to remove the concentrated water in the reverse osmosis device and discharge it without going to the next module).

1、 Chemical cleaning methods

① Citric acid solution, under high or low voltage, is used to continuously or cyclically clean the membrane with 1% -2% citric acid aqueous solution. This method has a very good cleaning effect on Fe (OH) 3 pollution.

② Ammonium citrate solution, sodium hydroxide can be added to the citric acid solution or a solution with a different pH value can be prepared. HCL can also be added to the ammonium citrate solution, adjusting the pH value to 2-2.5. For example, in 190L double distilled water, 277g of citric acid amine can be dissolved, and the pH value of the solution can be adjusted to 2.5 with HCL. This type of solution is circulated in the membrane system software car for 6 hours, and the actual effect is very good. If the solution is heated to 35-40 ℃, the cleaning effect is stronger. The cleaning effect of this solution on inorganic compound pollution is very good, but the cleaning time is relatively long.

③ Adding enzyme detergent, using a detergent containing one enzyme to solve membrane fouling, is particularly reasonable for organic compound pollution, especially for protein, raw oil and other organic compound pollution. If the cleaning effect is stronger at 50 ℃ -60 ℃, it is generally recommended to clean the membrane with 1% enzyme detergent at low voltage after 10 days or more of operation. Due to the lower concentration of commonly used enzyme detergents, a longer pre soaking time is required.

④ It is reasonable to use concentrated salt water to clean the membrane that punishes body pollution. This is because high concentrations of salt water can weaken the mutual influence between colloidal solutions and promote the coagulation of colloidal solutions to produce micelles.

⑤ Water soluble emulsified oil is very reasonable for cleaning membranes contaminated with oil and compounds, usually cleaning for 30-60 minutes.

⑥ A hydrogen peroxide solution, such as diluting 0.5L, 30% H2O2 with 12L double distilled water, and then cleaning the membrane surface, is particularly reasonable for organic compound contamination.

⑦ Calcium hydroxide and indoor formaldehyde solutions should adopt different solutions for bacterial contamination depending on the membrane. For aromatic acrylic resin membranes, a 1% (net weight) indoor formaldehyde solution can be used for cleaning. At the same time, it is necessary to regularly analyze and maintain a permanganate index of 0.2-0.5mg/l in reverse osmosis concentrated water to avoid bacterial proliferation.

⑧ Hydrochloric acid and EDTA solution should be used to clean the hydroxide deposition on the membrane.

2、 Physical cleaning methods

A simple physical cleaning method is to use a membrane made of low pressure and high flow rate to clean with water for 30 minutes. This can restore the water absorption performance of the membrane to a certain level, but over time, the permeability coefficient still decreases. Alternatively, a mixture of tap water and gas can be used to clean the surface of the membrane at low voltage for 15 minutes. It is reasonable to use this method to clean the membrane contaminated with organic compounds in the early stage.

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