What are some methods for preparing pure water through water treatment?

The demand for ultrapure water has increased significantly with the development of the semiconductor industry and its increasingly stringent requirements for ultrapure water quality, greatly promoting the development of pure water technology. Membrane technology has been widely applied, with rapid advancements in advanced water treatment technologies such as microfiltration, ultrafiltration, electrodialysis, and reverse osmosis. Membrane-based pure water preparation has replaced traditional ion exchange systems, solving TOC problems and meeting the electronic industry's requirements for pure water quality.

I. Fine Filtration Pure Water Treatment

Filter membranes made of special materials with high filtration accuracy are used. Common types include microfiltration membranes and filter cartridges.

II. Coarse Filtration Pure Water Treatment

This refers to mechanical filtration, removing suspended solids, colloids, turbidity, color, odor, etc. from the water. Main filtration methods include clarification ponds, rapid filter beds, sand filter beds, sand filters, multimedia filters, activated carbon filters, disc filters, and high-efficiency fiber filters.

III. Ultrafiltration Pure Water Treatment

This is a membrane filtration process that removes macromolecules, colloids, bacteria, etc. It has high filtration accuracy and commonly uses ultrafiltration membranes. Ultrafiltration membranes cannot remove ions from water; that is, they do not have a desalination function. They are used for pretreatment before reverse osmosis or post-treatment after reverse osmosis, and can also be used independently. 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.

IV. Reverse Osmosis Pure Water Treatment

Reverse osmosis, abbreviated as RO, is a membrane separation technology developed in the 1960s. Its principle is that under high pressure, the raw water passes through a reverse osmosis membrane, and the solvent in the water diffuses from high concentration to low concentration to achieve separation, purification, and concentration. Because it is opposite to the direction 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 has the characteristics of low operating costs, simple operation, high degree of automation, and stable effluent water quality. Compared with other traditional water treatment methods, it has obvious advantages and is widely used in various industries related to water treatment. Reverse osmosis water treatment technology basically belongs to a physical desalination method, and it has excellent characteristics that traditional water treatment methods do not have in many aspects:
1. Reverse osmosis uses a phase-change-free physical method to desalinate and purify saline feed water at room temperature. Currently, the desalination rate of ultra-thin composite membrane elements can reach over 99.5%, and it can simultaneously remove colloids, organic matter, bacteria, and viruses from the water.
2. Water treatment relies only on water pressure as the driving force, and its energy consumption is the lowest among many treatment methods.
3. It does not use large amounts of chemical reagents and acid-base regeneration treatment, has no chemical waste liquid discharge, and no environmental pollution.
4. Reverse osmosis equipment can continuously produce water, the system is simple, the operation is convenient, and the product water quality is stable.
5. Reverse osmosis equipment has a high degree of automation, and the operation and maintenance and equipment maintenance workload is very small.
6. The equipment occupies a small area and requires less space.
7. It is suitable for a wider range of raw water qualities, suitable for the treatment of brackish water, seawater, and even wastewater, as well as low-salinity freshwater treatment. Our company, with years of experience in the process design, equipment manufacturing, system integration, and membrane application technology of industrial water treatment systems, selects reasonable process settings and design parameters to ensure the long-term stable operation of the equipment.

V. EDI Pure Water Treatment

A new desalination technology that combines electrodialysis and ion exchange. This equipment takes advantage of both electrodialysis and mixed-bed ion exchange, making up for each other's shortcomings. It can use ion exchange for deep treatment and does not require chemical regeneration. It uses H+ and OH- generated by ionization to regenerate the resin. EDI has higher requirements for feed water and must be reverse osmosis product water or water quality equivalent to reverse osmosis product water. It has the following characteristics:
1. It can continuously produce qualified ultrapure water that meets user requirements, and the water production is stable;
2. No chemical reagents are required for regeneration, and there is no chemical discharge, making it an environmentally friendly product;
3. Compact structure, small footprint, and low water production cost;
4. The device is debugged before leaving the factory, and on-site installation and debugging are simple;
5. Simple operation, extremely low labor intensity, and easy training.

VI. Ion Exchange Pure Water Treatment

Various inorganic salts in water ionize to form cations and anions. When passing through the hydrogen-type ion exchange layer, the cations in the water are replaced by hydrogen ions, which is the desalination principle of the cation bed.
Various inorganic salts in water ionize to form cations and anions. When passing through the OH--type ion exchange layer, the anions in the water are replaced by OH- ions, which is the desalination principle of the anion bed.
A mixed bed is an ion exchange device in which cation and anion exchange resins are mixed in a certain proportion and filled into the same exchange column. In the uniformly mixed resin layer, the cation resin and anion resin are closely intertwined, and each pair of cation and anion resin particles is similar to a set of double beds, so the mixed bed can be regarded as a number of double beds connected in series.
Because the hydrogen ions and hydroxide ions entering the water after mixed ion exchange immediately generate water molecules with very low ionization, it is unlikely to form counterions during cation or anion exchange, which can make the exchange reaction very thorough. Therefore, the water quality of the effluent from the mixed bed is superior to that of the multi-bed composed of cation and anion exchange in series, and water with a fairly high purity can be produced.