wastewater treatment aerial view

Municipal Wastewater Treatment

How Tertiary Treatment of Wastewater Works

While there are many steps that take place in a municipal wastewater treatment plant, the final step in the process is inactivation. Inactivation is required to reduce microorganisms in the wastewater before it’s discharged into a receiving body of water. These microorganisms are typically microbes that may cause disease in humans when they come into contact with local bodies of water while swimming, fishing or taking part in other recreational activities. This is why it is crucial for wastewater to be treated before it is discharged back into a lake or river.

TrojanUVSigna treating wastewater at a wastewater treatment plant in Ohio

Alternatives to Chemical Treatment of Wastewater

With growing awareness of potential long-term negative impacts and generation of toxic by-products caused by chemical wastewater treatment, the creation of alternative treatments, like UV is becoming increasingly popular. UV wastewater treatment systems can treat municipal drinking water and wastewater to ensure communities meet their water quality goals.

How Ultraviolet (UV) Light Works

UV light is a form of light that is invisible to the human eye. It occupies the portion of the electromagnetic spectrum between X-rays and visible light and is uniquely able to inactivate microorganisms such as E.Coli and Fecal Coliforms. This capability has led to widespread adoption of UV light as a highly effective way to treat wastewater and drinking water.*

Microorganisms are inactivated by UV light when nucleic acids are damaged. When nucleic acids are exposed to certain wavelengths of UV light via UV lamps, they are instantly unable to reproduce. If a microorganism can’t reproduce, it is unable to cause infection. UV light has proven efficient in inactivating a variety of different microorganisms, including the ones responsible for cholera, polio, typhoid, hepatitis, along with other diseases.*

UV light is also effective at inactivating Cryptosporidium and Giardia, two microbes that chlorine is unable treat. Treating these two chlorine-resistant microbes is extremely important as they are often found in bodies of water that communities use as a source of drinking water and for recreational use.

* An Introduction to UV Treatment for Municipal Wastewater eBook by Trojan Technologies (February 2024)

UV Applications for Municipal Wastewater

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Benefits of UV for the Treatment of Wastewater

Chlorine was initially introduced to treat municipal wastewater because it was able to reduce microbes that had the potential to cause illness in humans. However, limits on the levels of chlorine discharged in treated wastewater were introduced in 1976 because residual chlorine is toxic to plant and animal life. These regulations accelerated the development and adoption of UV for tertiary treatment of wastewater since it produces no by-products and inactivates Cryptosporidium and Giardia.


Chlorine Treatment

UV Treatment

No Treatment By-products (DBP’s)

No Chemical Residue

No Chemical Spill Risk

Effective Against Cryptosporidium and Giardia

Well-Suited for Changing Regulations

When a wastewater treatment plant uses chlorine in the tertiary treatment of wastewater, a reducing chemical can be used to help dechlorinate the wastewater. Precise dosing and control of the reducing chemical is extremely important to protect plant and animal life – but this takes time and a great deal of vigilance.

UV treatment of wastewater takes place in seconds, reducing the physical footprint and capital costs of installing a UV system. 

The below system illustrates the differences in different types of wastewater treatment systems:

TUV disinfection alternatives diagram

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Systems for UV Wastewater Treatment

A photo of a TrojanUVSigna bank in a raised position


The TrojanUVSigna® uses innovative technology to reduce the total cost of ownership and simplify operation and maintenance for treatment plants.

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A photo of a TrojanUV3000Plus module


The TrojanUV3000Plus® is a flagship UV system used by over 2,000 municipalities around the world to treat over 30 billion gallons of wastewater every day.

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A photo of a TrojanUV3000PTP module


The TrojanUV3000®PTP is pre-engineered for quick, inexpensive installation and is ideal for small wastewater treatment applications.

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A photo of a TrojanUV3000B module


The TrojanUV3000®B is a simple, yet robust, wastewater treatment system for small communities and towns.

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A photo of a TrojanUVFit chamber


The TrojanUVFit® is a closed-vessel system that offers an effective, compact and energy-efficient solution for non-potable reuse applications.

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A photo of a TrojanUVFlex 100 Series chamber


The TrojanUVFlex® offers high-intensity delivery of UV light for non-potable reuse and other wastewater applications where the treatment of filtered tertiary effluent is required.

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