Explanation of Basic Pure Water Treatment Processes

1. Coarse Filtration: This refers to mechanical filtration, removing suspended solids, colloids, turbidity, color, and odor from water. Main filtration methods include clarifiers, rapid filters, sand filters, sand filters, multi-media filters, activated carbon filters, disc filters, and high-efficiency fiber filters.

2. Fine Filtration: This uses filter membranes made of special materials, achieving higher filtration precision. Common methods include microfiltration membranes and cartridge filters.

3. Reverse Osmosis (RO): Developed in the 1960s, reverse osmosis is a membrane separation technology. Its principle involves passing raw water through a reverse osmosis membrane under high pressure. The solvent in the water diffuses from a high concentration to a low concentration, achieving separation, purification, and concentration. Because it is the opposite of natural osmosis, it is called reverse osmosis. Reverse osmosis can remove bacteria, viruses, colloids, organic matter, and over 98% of dissolved salts from water. This method features low operating costs, simple operation, high automation, and stable effluent quality. Compared to other traditional water treatment methods, it has significant advantages and is widely used in various industries related to water treatment. Reverse osmosis water treatment is essentially a physical desalination method, possessing numerous superior characteristics not found in traditional water treatment methods.

4. Ultrafiltration: This is a membrane filtration process that removes large molecules, colloids, bacteria, etc. It offers high filtration precision, with ultrafiltration membranes being the most common. Ultrafiltration membranes cannot remove ions from water, meaning they do not have desalination capabilities. They are used for pretreatment of reverse osmosis or fine treatment after reverse osmosis, and can also be used alone. Ultrafiltration is a tangential flow and pressure-driven filtration process that separates particles according to their molecular weight. The pore size of ultrafiltration membranes is approximately in the range of 0.002-0.1 micrometers. Dissolved substances and substances smaller than the membrane pore size can pass through the membrane as permeate, while substances that cannot pass through the membrane are concentrated in the effluent. Therefore, the product water contains water, dissolved solids, and low molecular weight substances, while colloids, suspended particles, high molecular weight organic matter, bacteria, viruses, and protozoa are filtered out.

5. Ion Exchange: Various inorganic salts in water ionize to generate cations and anions. When these cations pass through a hydrogen-type ion exchanger layer, the cations in the water are replaced by hydrogen ions; this is the desalination principle of a cation exchange bed. Similarly, various inorganic salts in water ionize to generate cations and anions. When these anions pass through an OH-type ion exchanger layer, the anions in the water are replaced by OH- ions; this is the desalination principle of an anion exchange bed. A mixed bed is an ion exchange device in which cation and anion exchange resins are mixed in a certain proportion and packed into the same exchange column. The uniformly mixed resin layer has cation and anion resins arranged closely and alternately. Each pair of cation and anion resin particles is similar to a multi-bed, so a mixed bed can be regarded as an infinite number of multi-beds operating in series. Because hydrogen ions and hydroxide ions entering the water after mixed-bed ion exchange immediately generate water molecules with very low ionization, it is unlikely to form counterions as in cation or anion exchange. This allows the exchange reaction to proceed very thoroughly. Therefore, the effluent quality of a mixed-bed ion exchange system is superior to that of a combined ion exchange system consisting of cation and anion exchange systems, producing finished water with a very high purity.

6. EDI: EDI technology is a new desalination process that combines electrodialysis and ion exchange. This equipment combines the advantages of both electrodialysis and mixed-bed ion exchange, compensating for their respective shortcomings. It utilizes ion exchange for deep treatment without the need for chemical regeneration. The H+ and OH- generated by ionization are used to regenerate the resin. EDI has high requirements for the influent water, which must be reverse osmosis permeate or equivalent in quality. It features: continuous production of qualified ultrapure water that meets user requirements, stable permeate quality, no need for chemical regeneration, compact structure, and small footprint.