Membrane elements can not be exposed to sunlight, even in their original packaging, due to reasons below:

Material performance damage: Most membrane elements are made of polymer materials, such as common polyamide composite membranes. The high energy of ultraviolet rays in sunlight can cause photo-oxidation reactions in these polymer materials, and even breakage and degradation of the molecular chain. This destroys the microstructure of the membrane including changes in the pore size, affecting the membrane's selectivity for substance separation. In addition, it reduces the mechanical strength of the membrane, embrittling the membrane elements and making it more prone to breakage during installation or operation.

Acceleration in aging: Exposure to sunlight significantly accelerates the aging of membrane elements. Under the combined effects of high temperature and ultraviolet rays, the physical and chemical properties of the membrane material may be deteriorated rapidly. Membranes with good flexibility and stability originally become less flexible and more rigid after aging, which shortens their normal service life and increases replacement costs.

Induced thermal deformation: Sunlight exposure can cause a rapid increase in the temperature on the surface of membrane elements, uneven heating in different areas and potential thermal deformation of the membrane elements. For example, the mebrane may bulge or twist locally, which disrupts the flow channel structure within the membrane element, thereby affecting the uniform distribution of fluid therein and reducing the overall performance and operating efficiency of the membrane system.

Microbial growth: If there is residual moisture on the surface of the membrane element, the elevated temperature in a sunlit environment provides suitable conditions for microbial growth, which can easily lead to microbial growth. Microorganisms reproduce on the membrane surface to form biofilms, which further clog membrane pores, increase operating resistance of the membrane, and reduce water production and desalination rate.

(The answer is for reference only. Please consult VONTRON engineers for actual conditions)

Decrease in water production: If the water production significantly decreases compared to that during the initial normal operation under stable system pressure, temperature, and other operating conditions, it is likely that the membrane system has been contaminated.

Increase in feed water pressure: When pollutants are accumulated on the membrane surface, the resistance of water flow passing through the membrane increases, requiring higher feed water pressure for maintaining fixed water production. It indicates that the membrane system may have been contaminated.

Increase in pressure difference between sections: In a multi-stage membrane system, the contamination can be effectively determined by monitoring the pressure difference between sections. If the pressure difference in a certain section is significantly higher than the normal level, it indicates that the membrane element therein may be contaminated.

Significant change in desalination rate: The desalination rate is an important indicator of judging a RO membrane system. If the desalination rate significantly increases or decreases compared to the initial value, it indicates that the membrane may be contaminated.

Increase in the weight of the membrane element.

(The answer is for reference only. Please consult VONTRON engineers for actual conditions)

The type of pollutant can be determined by analyzing the water quality of the feed water, change in operating parameters, appearance of membrane elements, and analysis and test methods, thereby selecting the appropriate cleaning solution.

Inorganic scale pollution: Common inorganic scales include calcium carbonate, calcium sulfate, barium sulfate, and magnesium silicate. The calcium carbonate scale can be cleaned by acidic solutions such as citric acid and hydrochloric acid.

Metal oxide pollution: The metal oxide pollution such as iron and manganese are generally cleaned by acidic solutions.

Microbial pollution: When bacteria, fungi, and other microorganisms grow on the membrane surface to form a biofilm, biocides and alkaline cleaners are generally used for cleaning.

Organic pollution: Alkaline cleaning solutions are recommended for cleaning.

(The answer is for reference only. Please consult VONTRON engineers for actual conditions)

The water transmission is closely related to the viscosity of water in the reverse osmosis process. As the temperature rises, the viscosity of water decreases, while the activity of water molecules increases. Under the same pressure conditions, it is more easily for water molecules to pass through the RO membrane, thereby increasing the water production; conversely, when the temperature decreases, the viscosity of water increases, and the movement of water molecules is restricted, causing a decrease in the  water production. Under normal circumstances, the water production of the RO system increases by about 2%-3% as water temperature increases 1℃.

(The answer is for reference only. Please consult VONTRON engineers for actual conditions)

Glycerin is commonly used. Glycerin has good lubricating performance and stable chemical properties, with no chemically react with membrane elements, adverse effect on the  membrane performance, and contamination to the subsequent treated liquids. In addition, it is relatively safe and environmentally friendly. It it prohibited to use any other reagents or industry and household detergents with unknown physical and chemical properties.

(The answer is for reference only. Please consult VONTRON engineers for actual conditions)

The cleaning frequency of the RO system is not determined by a fixed standard, depending on factors such as raw water quality, pretreatment effects, and system operating conditions. The detailed analysis is as follows:

1. Based on changes in operating parameters

Flux decline: When the normalized flux decreases by 10% to 15%, it indicates that the RO system may be contaminated and requires cleaning. For example, if the system originally produced pure water with a fixed amount per hour but with significantly decreased output now, it may need cleaning.

Decrease in desalination rate: If the system's desalination rate drops by 10% to 15%, it means the membrane's filtration efficiency has deteriorated, and the amount of salts and other impurities passing through the membrane has increased, requiring the cleaning of the system.

Increase in pressure and pressure differential: When the operating pressure and inter-stage pressure differential increase by 10% to 15%, the water flow resistance within the system has increased possibly due to fouling on the membrane surface, requiring the cleaning of the system.

2. Referring to raw water quality and pretreatment

SDI15 below 3: If the silt density index (SDI15) of raw water is less than 3, the water quality is relatively good. The cleaning frequency thereof may be 4 times per year.

SDI15 around 5: When the SDI15 is around 5, the water quality is relatively poor. The cleaning frequency may need to be doubled, i.e., about 8 times per year.

(The answer is for reference only. Please consult VONTRON engineers for actual conditions)