Water disinfection technologies using ultraviolet radiation: principles and efficiency

Today, finding truly clean water is becoming increasingly difficult. Even when buying it in stores, we cannot be completely sure of its quality. Therefore, more and more people are paying attention to purification systems that make ordinary tap water safe and suitable for drinking.

Water is an ideal environment for a multitude of microorganisms: protozoa, bacteria, viruses. They are invisible to the eye but can cause serious harm to health. That is why the disinfection stage is an essential part of any drinking water treatment system.

There are several disinfection methods: ultrafiltration, chlorination, ozonation. However, one of the most effective is treating water with an ultraviolet lamp. UV radiation destroys all known bacteria and viruses while not changing the chemical composition of water and leaving no foreign odors or taste. 

What is the technology of water disinfection using ultraviolet radiation?

Ultraviolet is electromagnetic radiation located in the spectrum between visible light and X-rays. This energy is invisible to the human eye, and the wavelengths range from 100–400 nm. The name comes from the Latin ultra (“beyond”) and the English violet (“violet”).

Low-pressure UV lamps emit light with a wavelength of about 254 nm — almost coinciding with the peak sensitivity of DNA and RNA in microorganisms (265 nm). The strongest biocidal effect is in the UV-C range (200–280 nm): this dose is sufficient to destroy bacteria, viruses, and protozoa, including chlorine-resistant pathogens (e.g., Giardia and Cryptosporidium).

Water disinfection using ultraviolet radiation is a physical method based on photochemical reactions that cause irreversible damage to the DNA and RNA of microorganisms. After exposure to ultraviolet light, cells lose the ability to reproduce and are considered inactivated. This method is used not only in water treatment and wastewater systems but also for air and surface treatment.

Principle of operation of ultraviolet disinfection units

UV disinfection works on a simple principle: water enters the reaction chamber and passes around a powerful mercury lamp enclosed in a durable quartz sleeve. The UV lamp emits ultraviolet light in a narrow range — about 253 nm. Even brief contact with this radiation triggers photochemical reactions that damage the DNA and RNA of microorganisms. Having lost the ability to reproduce, they are considered fully inactivated.

At the same time, the chemical composition of the water remains unchanged. Unlike chlorination or ozonation, which use strong oxidizers and may form unwanted by-products, UV treatment does not add any substances to the water and does not change its taste, smell, or color.

For maximum effectiveness of ultraviolet disinfection, water must be as transparent as possible. Impurities — iron, manganese, organic matter, hardness salts, suspended particles, and colloids — reduce the efficiency of UV radiation. They:

• absorb and scatter ultraviolet light;
• alter the wavelength;
• settle on the quartz sleeve of the lamp;
• prevent light from penetrating through the water.

Therefore, UV lamps are rarely used as a standalone purification system. They usually operate in combination with other water treatment stages: mechanical filters, water softeners, clarifiers, etc.

It should be noted that ultraviolet disinfects water only while it passes through the chamber. It does not create a residual protective effect like chlorine. Therefore, during long-term storage of treated water, microorganisms may reappear. This must be considered when designing water treatment systems.

Where UV disinfection is applied

Ultraviolet units are used not only in household filters. They are actively applied:

• at municipal water supply stations;
• in wastewater treatment;
• in aquaculture recirculation systems;
• for air and surface treatment.

The method is valued for its high efficiency, eco-friendliness, and safety for humans. Unlike chlorine, UV radiation does not produce toxic by-products and does not cause resistance in microorganisms.

Conclusion

Although ultraviolet disinfection cannot be called an absolutely universal method, it rightfully occupies an important place in water treatment systems. Its main advantages are high effectiveness against most bacteria and microorganisms, ease of use, cost-effectiveness, and no impact on the chemical composition of water.

The market offers a wide range of UV units of various power and capacity, allowing solutions for both household needs and industrial or municipal systems. Thanks to the combination of efficiency and eco-friendliness, ultraviolet remains one of the most in-demand and safe methods of water disinfection.