Reverse osmosis pretreatment
Reverse osmosis pretreatment design considerations
Membrane element type Inlet water quality (water source and its changes) Inlet water flow rate Reverse osmosis recovery (high recovery means better pretreatment is needed) Post-treatment equipment and requirementsReverse osmosis feed water contains insoluble salts and related components to the concentrations listed in the table below, should be taken in the pretreatment measures to prevent reverse osmosis membrane fouling.
1. Raw water tank (optional)
Storage of raw water, buffer raw water pipes in the water pressure instability of the water treatment system caused by the impact, while used to precipitate groundwater in the large sand particles and other precipitable substances.
2. Coagulant additive: mainly to remove the tiny particle size of the suspended colloids in the water. Because these tiny particles in the water will not be subject to the effect of gravity and settlement, but also difficult to remove in the subsequent filter, and thus the need for coagulation treatment of raw water. It is by adding coagulants to the raw water, so that the suspended solids and colloids in the water to generate larger flocs, and then filtered through the multi-media filter to remove. When the content of iron in the raw water is less than 0.3 mg / L, the content of suspended solids is less than 20 mg / L, pre-treatment can not use this device. When the content of suspended solids and colloidal substances in the water is relatively high, it is generally necessary to use coagulant addition device
3. Raw water pump
Constant system water supply pressure, stabilize the water supply.
4. Multi-media filter Using multiple filtration layers of the filter, the main purpose is to remove sediment, rust, colloidal substances, suspended solids and other particles in the raw water in the 20um or more of the material, you can choose to use a manual valve control or automatic controller for backwashing, positive flushing and a series of operations. Ensure that the quality of the water produced by the equipment to extend the service life of the equipment.
5. It can remove free chlorine and organic matter in water to protect reverse osmosis facilities.
Free chlorine can oxidize and destroy reverse osmosis membrane, reverse osmosis generally require water residual chlorine & lt; 0.1ppm; organic matter is not only the bait of microorganisms, and when it is concentrated to a certain extent, can dissolve the organic membrane materials, so that membrane performance deterioration. There are many kinds of organic matter in water, different organic matter on reverse osmosis membrane harm is not the same, thus in reverse osmosis pretreatment system design, if the content of total organic carbon (TOC) in the water is more than 2mg/L, generally need to be processed, for the purification system with tap water as the source of water, activated carbon adsorption is necessary because of the high content of organic matter in surface water.
Because the activated carbon adsorption method has the advantages of simple equipment, small investment, simple operation and easy control of treatment effect, it is widely used in water treatment and purification system.
6. Water softening equipment / dosing scale inhibitor: to prevent insoluble salts in the reverse osmosis membrane surface scaling.
Softening is the use of ion exchange resins and the exchange of calcium and magnesium ions in the water to remove the calcium and magnesium ions in the water. The advantage of softening is that it can remove the calcium and magnesium ions in the water more thoroughly, to avoid these ions in the reverse osmosis device scaling, the disadvantage is that the equipment investment is high, operation to a certain period of time after the need for regeneration.
Add scale inhibitor can delay the growth of salt crystals to delay the precipitation process, the use of this method can also prevent reverse osmosis scale pollution. But due to calcium and magnesium ions still exist in the water, reverse osmosis water will be higher than the use of calcium and magnesium ions to soften, and the use of dosing scale inhibitor is easier to achieve automated control, and equipment is simple and low cost. In addition, the use of scale inhibitors can also reduce silicon precipitation, while softening can not, which is very suitable for groundwater water treatment. The cost of softening facilities and flow proportional to the relationship between the cost of adding scale inhibitor facilities and flow rate relationship is not large, therefore, two-stage reverse osmosis and ware-type system, the use of scale inhibitor to add the system
7. Precision filters, also known as security filters, the role of which is to retain the raw water particles larger than 5 microns to ensure that the reverse osmosis membrane is not large particles of suspended solids scratches.
Because the thickness of the reverse osmosis membrane is about 10 microns or so, the larger particles in the raw water accelerated by the high-pressure pump is very easy to scratch the surface of the reverse osmosis membrane desalination epithelium or may penetrate the reverse osmosis membrane components, and thus the general reverse osmosis equipment before the installation of the 5 micron precision filter. The use of precision filters in the feed water residual suspended solids, non-curved particles and colloids and other substances to remove, so that the RO reverse osmosis equipment to run more safely and reliably.
8. After the above treatment of water in order to reach the reverse osmosis membrane water intake standards, water under pressure, water through the reverse osmosis membrane to become pure water; impurities in the water by the reverse osmosis membrane retention and by the concentration of water out of the water, the use of reverse osmosis technology can be effectively removed from the water of inorganic salts, ions, colloid, bacteria, viruses, bacterial endotoxin and most of the organic matter and other impurities. Reverse osmosis system desalination rate is generally 95-99%. A reverse osmosis equipment outlet water online monitoring conductivity is generally between 1-10us. Produced by the pure water indicators have reached the national standard GB17323 pure drinking water.
9. Ultraviolet sterilization (optional) kill bacteria produced by secondary pollution to ensure that the finished water health indicators.