In order to prevent the growth of organisms on the membrane surface during storage and the degradation of performance in subsequent operations, the membrane elements must be stored in a special solution.

New module:

(1) The membrane elements have been tested with water before leaving the factory, and stored with 1% sodium sulfite solution, and then sealed with oxygen and vacuum packaging;

(2) The membrane element must be kept wet at all times. Even if it needs to be opened temporarily to confirm the agreed quantity of packages, it must be carried out without damaging the plastic bag, and this state shall be saved until it is used;

(3) The membrane elements should be stored at a low temperature of 5 ~ 10 ℃. When stored in an environment with a temperature of more than 10 ℃, select a well ventilated place, avoid direct sunlight, and the storage temperature shall not exceed 35 ℃;

(4) If the membrane element is frozen, it will be physically damaged, so preservation measures shall be taken not to freeze it;

(5) When stacking membrane components, the packing box shall not exceed 5 layers, and ensure that the carton is kept dry.

Used modules:

(1) Membrane elements must always be kept in a dark place, the storage temperature shall not exceed 35 ℃, and direct sunlight shall be avoided;

(2) When the temperature is below 0 ℃, there is a risk of freezing, so anti freezing measures shall be taken;

(3) In order to prevent the growth of microorganisms during short-term storage, transportation and system standby of membrane elements, it is necessary to soak the elements with sodium sulfite (food grade) protective solution with concentration of 500 ~ 1000ppm and pH 3 ~ 6 in pure water or reverse osmosis produced water. Generally, Na2S2O5 is used, which reacts with water to form bisulfite: Na2S2O5 + h2o-2nahso3

(4) After soaking the membrane element in the storage solution for about 1 hour, take the membrane element out of the solution and package it in an oxygen isolation bag, seal the bag and label it with the packaging date;

(5) After the membrane elements to be stored are repackaged, the storage conditions are the same as those of the new membrane elements.

(6) The concentration and pH of the preservation solution shall be kept within the above range, which shall be checked regularly. If it may deviate from the above range, the preservation solution shall be prepared again;

(7) Under no circumstances shall the film be kept dry.

(8) In addition, formaldehyde solution with a concentration (mass percentage concentration) of 0.2 ~ 0.3% can also be used as the preservation solution. Formaldehyde is a stronger microbial killing agent of sodium bisulfate, and the component does not contain oxygen.

Re wetting of membrane elements

Irreversible loss of water flux may occur after the used membrane element is inadvertently dried. Please re wet the element in the following ways:

1. Soak in 50% ethanol aqueous solution or propanol aqueous solution for 15 minutes;

2. Pressurize the element to 10 bar and close the water outlet for 30 minutes, but remember to open the produced water outlet valve before the inlet pressure is relieved. This step can be carried out when the element is installed into the system. In this case, when the produced water outlet is closed, the pressure difference between the inlet end and the concentrated water end shall not be greater than 0.7 bar, otherwise the produced water back pressure will appear at the concentrated water end, The safest way to cause damage to the diaphragm is to turn down the water production outlet valve to make the water production pressure close to the concentrated water end pressure, so there is no need to care about the limitation of pressure drop;

3. Immerse the element in 1% HCl or 4% HNO3 for 1 ~ 100 hours, and the element must be immersed vertically to discharge the air in the element.

Cleaning organic pollution

The following cleaning procedures are specifically aimed at cleaning the membrane system polluted by organic substances such as humic acid and fulvic acid, scale inhibitor or oil. For all cleaning processes, the cleaning system configuration, pH, temperature range and recommended cleaning flow value are exactly the same. It is recommended to refer to the provisions of general cleaning guidelines.

Six steps are taken to clean the membrane element with organic pollution, but these six cleaning steps need to be repeated, one is high pH cleaning solution and the other is low pH cleaning solution:     

(1) Prepare cleaning solution according to table 7-9:     

(2) Low flow input cleaning fluid.     

When the cleaning water pump mixes the cleaning solution, the cleaning solution is preheated and the raw water in the element is replaced with the cleaning solution, it shall be carried out according to half of the flow value listed in table 7-1, that is, under the operating conditions of low flow and low pressure. The required pressure only needs to reach the pressure loss sufficient to supplement the water to the concentrated water. The pressure must be low enough not to produce significant osmotic water production. Low pressure can minimize the re precipitation of dirt to the membrane surface. Depending on the situation, some concentrated water should be discharged to prevent the dilution of cleaning solution.     

(3) Cycle.     

After the raw water is replaced, the cleaning solution should appear in the concentrated water pipeline. The cleaning solution can be circulated back to the cleaning solution tank. The cleaning solution can be circulated for 30 minutes. If the color of the cleaning solution still changes, release the cleaning solution and prepare a new cleaning solution according to step 1).     

(4) Soak.     

Stop the operation of the cleaning pump and let the membrane element completely soak in the cleaning solution. The soaking time of components is 1 ~ 15 hours (it will be better to soak overnight). In order to maintain the temperature of the soaking process, a very low circulating flow (about 10% of the flow shown in table 7-1) can be used. The soaking time depends on the severity of pollution. For mild pollution, soaking for 1 ~ 2 hours is sufficient.

(5) High flow water pump circulation.     

Cycle for 30 minutes according to the flow listed in table 7-1. The high flow rate can wash away the pollutants washed by the cleaning solution. If the pollution is serious, please use a flow rate higher than 50% specified in table 7-1 to facilitate cleaning. Under the condition of high flow rate, the problem of excessive high pressure drop will occur. The maximum allowable pressure drop of unit parts is 1bar (15psi), and the maximum allowable pressure drop of multi-element pressure vessels is 3.5bar (50psi), which shall be exceeded first.     

(6) Rinse.     

The pretreated qualified pretreated effluent can be used to flush the cleaning fluid unless there is a corrosion problem (e.g. static seawater will corrode stainless steel pipes). In order to prevent sedimentation, the minimum flushing temperature is 20 ℃, and the system flushing time is about 1 hour.     

(7) Repeat steps 2) to 6) with HCl solution with pH 2.     

(8) Restart the system.     

After the components and system reach stability, the operating parameters after system restart must be recorded. The time for system performance to return to stability after cleaning depends on the degree of original pollution. In order to obtain the best performance, multiple cleaning and soaking steps are sometimes required.

Additional information:

A. In order to maximize the cleaning efficiency, the temperature of the cleaning solution must be higher than 25 ℃. Increasing the temperature is helpful to help the cleaning solution remove organic pollutants from the membrane surface.

B. Some organics such as oils are very difficult to clean. In order to remove them, it is necessary to test various cleaning soaking times to obtain the best efficiency. In addition, the most effective cleaning solution usually contains surfactants such as Na SDS or some commercial cleaning agents contain surfactants and detergents, which can help remove oil pollution. Consult the chemical supplier.

C. If the organic pollution is caused by the addition of excessive flocculant in the pretreatment part, it is more effective to use the cleaning agent in the reverse order (use acidic cleaning solution first and then alkaline cleaning solution). In order to determine the appropriate cleaning solution sequence (first high pH and then low pH or vice versa), try to obtain the system pollutant sample, and use alkaline and then acidic solution for the sample or vice versa, Qualitatively identify which order is better. If the effect is equivalent, it is more appropriate to clean the organic matter with high pH cleaning solution first.