One, Inlet Pressure
Reverse osmosis equipment uses reverse osmosis membrane for physical separation. However, the original water needs to have a certain pressure to pass through the reverse osmosis membrane. However, the common water pressure is very small. But the water pressure required for the reverse osmosis equipment to work must be greater than the permeation pressure of the permeable membrane. In this case, a high-pressure pump can be used to add pressure to the water to ensure the normal operation of the reverse osmosis equipment. This can make up for the insufficiency of the water pressure of the tap water and ensure the normal operation of the reverse osmosis equipment to produce water. It may also increase the discharge rate of wastewater.
The inlet pressure will affect the water flux and salt rejection rate of the reverse osmosis membrane. The permeation flux increases with the increase of the inlet pressure. However, the reverse osmosis membrane cannot completely retain the dissolved salts in the feed water. Therefore, there will always be a certain amount of permeation with the increase of the pressure. Because the permeation rate of water is faster than the transmission rate of salts, this salt rejection rate increases rapidly and is quickly suppressed. Therefore, the inlet pressure of reverse osmosis membrane should be considered based on the performance of various membranes. The selection of inlet pressure also depends on the permeability of the membrane and the water recovery rate.
The unit of pressure K=1000, M=1000000
1psi=6.895 kPa
1MPa=10 kg/cm^2
Note: High inlet pressure will accelerate scaling and shorten the service life of the reverse osmosis membrane.
Recommended inlet pressure (for reference only):
Ultra-low pressure membrane: 6-8 kg/cm^2
Low-pressure membrane: 8-10 kg/cm^2
High-pressure membrane: 12-15 kg/cm^2
Seawater desalination membrane: 40-45 kg/cm^2
Two, pH value operating range
At pH 7, the reverse osmosis membrane has the highest salt rejection rate. The salt rejection rate of the membrane system also increases with the change of pH. The change of pH has a significant impact on the electrical conductivity. The wider the pH range of the reverse osmosis membrane, the more intense, faster, and effective the chemical cleaning method can be. However, excessively high or low pH values are likely to cause membrane damage.
Three, water inlet temperature
The permeate flow rate of the membrane increases with the rise of the feedwater temperature and decreases with the drop of the feedwater temperature. Some membranes can increase the permeate flow rate by about 2.7% per degree Celsius when the water temperature rises. However, when the temperature is too high, it will accelerate the rate of membrane hydrolysis. Generally, organic membranes become softer when the temperature rises, followed by an increase in membrane compaction. However, when the temperature is too low, it will also affect the normal water production of the reverse osmosis membrane. Therefore, the inlet water temperature of general organic membrane should be controlled at around 20~30℃.
Four, flushing the membrane element
During the reverse osmosis process, due to the continuous passage of water through the membrane, the solution concentration on the membrane surface increased, forming a concentration gradient from the membrane surface to the feed solution. If the solution concentration on the membrane surface continues to increase, the osmotic pressure of the solution on the membrane surface due to this concentration polarization phenomenon will increase greatly, causing the resistance to water passing through the membrane to increase, so the permeate flow rate and salt rejection rate will decrease accordingly. Some insoluble salts will precipitate out on the membrane surface. In order to avoid the concentration polarization phenomenon, the reverse osmosis membrane should be flushed periodically to prevent the increase in the concentration on the membrane surface.
Five, pH value usage range
Since the water to be treated usually contains inorganic matter, organic matter, microorganisms, particulate matter, and colloidal matter, etc., pretreatment must be carried out before the reverse osmosis process. Typically, methods such as quartz sand filters, activated carbon filters, and ion exchangers are used. The pretreatment scheme depends on the composition of the raw water and the application conditions of the source water, with well water, surface water, and municipal wastewater being treated differently. Well water quality is generally stable and has a low risk of contamination, so the pretreatment method is simple. However, some sediments may be severe, and if not properly treated, they can damage the membrane. Surface water, on the other hand, is a direct source that is affected by seasonal changes and has a high risk of microbial and colloidal pollution. Therefore, the pretreatment of surface water is more complex than that of well water and requires additional pretreatment steps, including chlorine disinfection, flocculation/coagulation, clarification, multi-media filtration, dechlorination, and adding acid or scale inhibitors.
Six, Security Filter
A security filter must be installed before the reverse osmosis membrane to prevent large particles from entering the membrane element and causing damage to the membrane element. The filter cartridge in the security filter should be replaced every 3-6 months.
