The direct drinking water system belongs to the category of dual water supply. It is the existing source water or the source water that meets the standard of drinking water, firstly deep treated to remove organic matter, bacteria, viruses and residual chlorine, then disinfected by ozone and ultraviolet light to become direct drinking water and finally delivered to the users through quality tubing.     

.Common Pollutants in Water:     

Solid suspended solids : sediment, rust, visible materials.     

Microorganisms: dissolved inorganic substances such as bacteria, viruses, algae; magnesium carbonate, copper sulfate, chloride, nitrate.    

Heavy metals: mercury, arsenic, lead, cadmium, etc.     

Organic substances: pesticides, fertilizers, various industrial solvents, fuels, detergents, disinfectants.     

Radiation particles: Radiation particles produced by the nuclear industry and nuclear medicine.   

.Process Introduction     

Ultrafiltration (UF):      

Between microfiltration and nanofiltration, with a pore size of 0.01-0.1 um and a molecular weight cut-off between 500 and 200,000 D. Principle: The separation mechanism relies mainly on physical sieving and the physicochemical interaction between membrane materials and contaminants. Small molecules can pass through the membrane while macromolecules are blocked out of the membrane.     

Features:      

It can trap fine-sized impurities, remove suspended solids, colloids, particles, bacterial viruses and some macromolecular organics in water, but does not treat inorganic ions, thus retaining trace elements beneficial to the human body. In line with the concept of healthy drinking water.     

Scope of application:      

There are many colloids in raw water, a large number of bacterial viruses, moderate hardness, and when organic pollution and inorganic pollution are low, and the height of the water station building can meet the process requirements. It is often used for deep treatment with drinking water in residential areas.     

Nanofiltration (NF):      

The pore size of the membrane is between the ultrafiltration membrane and the reverse osmosis membrane and is derived from the reverse osmosis membrane. Also known as ultra low pressure reverse osmosis and loose reverse osmosis. The membrane pore size is generally about 1 nm and the molecular weight cut off is 200-500D.     

Principle:      

A pressure-driven membrane separation technique between reverse osmosis and ultrafiltration.      It has separation properties for the electrodeless ions in water and small organic molecular components with a molecular weight of several hundred, and the membrane surface itself has a large amount of negative charge.    

Features:     

Compared with reverse osmosis, nanofiltration membranes have higher salt rejection at low pressures. Moreover, it has ion selectivity and different release rates for different ions. Due to its dual advantages of ultrafiltration and reverse osmosis, it is a promising and widely used membrane for advanced treatment of water.     

Scope of application:      

The raw water hardness is higher, the number of bacterial viruses is more, and the organic pollution and inorganic pollution are higher. It is often used for the deep treatment of drinking water in public buildings such as residential quarters and office buildings.     

Reverse osmosis (RO):      

The pore size of the membrane is less than 1 nm.     

Principle:      

It is a reverse migration movement of permeation, under the pressure push, the process of forcing the solvent in the solution to separate from the solute by the interception of the translucent membrane. The reverse osmosis membrane generally has a pore size of less than 1 nm.     

Features:      

Almost all of the solute in the water has a high removal rate. It can effectively remove the divalent and monovalent ions in the water, and the removal rate is 95%-99%. It can effectively remove the non-polar pollution and organic pollution and make the effluent Ames test is negative.     

Scope of application: 

Seawater desalination, brackish water desalination, etc. It can be used when the effluent water quality meets the requirements of the pure water standard and the electrical conductivity is strictly required (such as industrial pure water, experimental pure water), it can also be used for the deep treatment of drinking water in public buildings such as office buildings.     

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