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Principle of ultraviolet disinfection and TOC removal
作者: 时间:2019-03-21

1. How to disinfect ultraviolet light?

Ultraviolet (UV) is an electromagnetic wave with a wavelength between 100 and 400 nanometers (nm). Bactericidal disinfection wavelength in the 200-300nm spectral region. The low-pressure mercury lamps emit single-frequency rays of 253.7nm. The medium-pressure mercury lamps emit multi-frequency rays of different wavelengths that can be sterilized.

Under the irradiation of ultraviolet light, microbial photochemical reaction destroys microbial nucleic acid and makes it inactivated.

The cell's DNA and RNA absorb the high energy emitted by the short-wave union V. Absorption wavelengths are mostly between 240 and 280nm(253.7nm for low-voltage lamps), forming new binders between neighboring nucleosides and creating double structures or dimmers within the nucleic acid.

DNA thymine after photochemical damage, the adjacent pyrimidine dimer. The formation of most thymine dimmers (T=T) in the DNA of bacterial and viral mycetin prevents replication and ultimately cell death.

2. Reasons affecting ultraviolet disinfection

The UV dose transmitted through the disinfection system is the product of the V strength (milliwatts per square centimeter) and the retention (exposure) time.

UV dose = intensity x time

The units of dose are milliwatts per second per square centimeter (mw.s /cm2) or millijoules per square centimeter (mJ/cm2).

UV disinfection is affected by the following factors

Wastewater quality

Microbial inactivation mechanics

Disinfector lamp structure

Lamp life and casing fouling

3. Mechanism of ultraviolet removal of TOC

In high purity water systems, uv devices are usually connected to ion exchangers to reduce the amount of organic matter in the water, called TOC(total organic carbon).

High-energy ultraviolet lamps emit ultraviolet light with a wavelength below 200nm (185nm), which can stimulate the light decomposition of water and produce hydroxide ions (OH) with extremely high energy. These hydroxide ions attack organic compounds, and when TOC is completely oxidized, it breaks down into carbon dioxide and water. Some organic compounds are broken down into easily oxidized acid groups that can be easily removed by a polished mixed-bed ion exchanger

The TOC + UV185nm - CO2 + H2O

Generally, this system can reduce the TOC of tap water or underground water source to below 1.5 PPB, which can completely meet the high pure water standard

4. Ultraviolet rays remove ozone

Ozone is unstable. It absorbs ultraviolet light at 254nm and breaks down into dissolved oxygen.

O3 + UV185nm - Q2 + O