1、 Inlet pressure
Reverse osmosis equipment uses reverse osmosis membranes for physical isolation. But the raw water requires a certain pressure to pass through the reverse osmosis membrane. And ordinary water pressure is very small. However, the water pressure required to operate the reverse osmosis equipment must be greater than the permeate pressure of the permeable membrane. In this case, a high-pressure pump is needed to add a certain amount of pressure to the water to ensure the normal operation of the reverse osmosis equipment. This can fill the insufficient water pressure of tap water itself. Ensuring the water production efficiency of reverse osmosis equipment may also increase the speed of wastewater discharge. The inlet pressure will affect the water production flux and desalination rate of the reverse osmosis membrane. The permeability increases with the increase of inlet pressure. Since the reverse osmosis membrane cannot absolutely intercept the dissolved salts in the inlet water, there is always a certain amount of permeation with the increase of pressure. Because the rate of water permeation through the membrane is faster than the rate of salt transfer, this increase in permeability is quickly restrained. Therefore, the inlet pressure of reverse osmosis should be considered based on the performance of various membranes. The choice of inlet pressure also depends on the permeability of the membrane and the water recovery rate. Conversion of pressure units: K=1000 M=10000001psi=6.895kPa1MPa is equivalent to 10kg/cm ^ 2. Note that excessive inlet pressure of reverse osmosis membranes can accelerate fouling and shorten their lifespan. Recommended inlet pressure
Ultra low pressure membrane: 6-8kg/cm2 Low pressure membrane: 8-10kg/cm2 High pressure membrane: 12-15kg/cm2 Seawater desalination membrane: 40-45kg/cm2
2、 PH value usage range
At around pH 7, the reverse osmosis membrane has the highest desalination rate, and the desalination rate of the membrane system increases with the change of pH value. The change in pH has a significant impact on conductivity. A wide range of pH values for reverse osmosis membranes allows us to use stronger, faster, and more effective chemical cleaning methods, but excessively high or low pH values are likely to cause membrane damage.
3、 Inlet water temperature
The permeability of the membrane increases with the increase of raw water temperature and decreases with the decrease of raw water temperature. When the water temperature increases by 1 ℃, some membranes can increase their permeability by about 2.7%. But when the temperature is too high, it will accelerate the hydrolysis rate of the membrane. Generally, organic films become softer due to temperature increase, and the compaction of the film also increases. But when the temperature is too low, it also affects the normal water production of the reverse osmosis membrane. Therefore, the raw water temperature of organic membranes should generally be controlled at around 20-30 ℃.
4、 Rinse membrane components
In the process of reverse osmosis, due to the continuous permeation of water through the membrane, the concentration of the solution on the membrane surface increases, forming a concentration gradient from the membrane surface to the feed solution. If the concentration of the solution on the membrane surface increases, this concentration polarization phenomenon causes a significant increase in the osmotic pressure of the solution on the membrane surface, resulting in an increase in the resistance of water passing through the membrane. As a result, the permeability and desalination rate of the membrane decrease, and some insoluble salts will precipitate on the membrane surface. In order to avoid concentration polarization, the reverse osmosis membrane should be flushed after a certain period of operation to prevent an increase in membrane surface concentration.
5、 PH value usage range
Due to the presence of impurities such as inorganic, organic, microbial, granular, and gelatinous substances in the treated water, pre-treatment is necessary before the reverse osmosis process, typically using methods such as quartz sand filters, activated carbon filters, and ion exchangers. The pre-treatment plan depends on the composition and application conditions of the raw water source, and is treated differently for well water, surface water, and municipal wastewater. The water quality of well water is relatively stable, the possibility of pollution is low, and the pretreatment method is simple. However, some serious sediment and incomplete treatment can cause damage to the membrane. Surface water, on the other hand, is a water source directly affected by seasons and has the potential for high levels of contamination from both microorganisms and colloids. So pretreatment is more complex than well water, requiring other pretreatment steps including chlorine disinfection, flocculation/coagulation aid, clarification, multi-media filtration, dechlorination, acid or scale inhibitor addition, etc.
6、 Security filter
Before installing the reverse osmosis membrane, it is necessary to install a security filter to prevent large particles of impurities from entering the membrane element and avoiding damage to the membrane element. The filter element in the security filter should be replaced every 3-6 months.
