Secondary & Tertiary Effluent Treatment

TrojanUV systems are installed in secondary and tertiary wastewater treatment plants around the world

About Secondary & Tertiary Wastewater Treatment

  • The vast majority of wastewater treatment plants around the world provide secondary treatment through conventional activated sludge processes
  • Secondary processes are effective upstream of UV treatment since they remove particles and improve water quality
  • Some wastewater treatment plants have tertiary treatment processes that use an additional filtration process to further improve water quality

Wastewater treatment plants utilizing secondary and tertiary treatment processes typically require a microorganism-treatment step prior to discharging effluent into receiving waters.

The microorganism-treatment limits for wastewater systems are typically measured in the number of colony forming units (CFU) per 100 mL of effluent. The CFU measured is typically fecal coliform, but some regulatory bodies require measurement of Escherichia coli (E .coli), total coliform or enterococci.

Treatment is Critical

The main objective of microorganism-treatment is to reduce the number of microorganisms to permissible levels.

UV is an ideal treatment solution for wastewater treatment plants using secondary and tertiary treatment processes. It is effective against chlorine-resistant microorganisms Cryptosporidium and Giardia.

Wastewater in aeration basins

Upstream Processes

The type and size of UV treatment system is influenced by upstream secondary and tertiary treatment processes. Generally, higher quality effluent requires less UV equipment due to its higher UV transmittance (UVT) and lower total suspended solids (TSS).

UVT is the ratio of light entering the water to that exiting the water. Simply put, water with high UVT (e.g., 85%) is relatively clear, whereas water with lower UVT is more turbid.

Upstream ProcessTypical UVT
Primary Treatment10% - 45%
Lagoon30% - 55%
Fixed Film (Trickling Filter, Rotating Biological Contractor)45% - 65%
Activated Sludge/Suspended Growth55% - 75%
Media Filtration60% - 80%
Membrane Filtration65% - 85%

Suspended solids are microorganism-laden particles of varying number and size. TSS levels are directly related to the concentration of particle-associated microorganisms and are more difficult to treat than free-floating microorganisms. Particles reduce the UV intensity by absorbing and scattering UV light.

The UV dose required for system sizing will depend on the standard to be achieved and regulatory requirements.

UV in Action

Kansas Wastewater Treatment Plant Makes a Long-overdue UV System Replacement 

The Water Pollution Control Department of the Unified Government of Wyandotte County and Kansas City, KS provides wastewater and stormwater services for more than 150,000 residents. Their top priority is protecting public health and the environment, and they work tirelessly to ensure that both wastewater and stormwater are treated and returned safely to the Missouri River.

So, when they were informed that it would take approximately $150,000 to keep the aging UV system operational, Unified Government and its Water Pollution Control Department decided to look into other UV equipment suppliers and investigate another UV solution. They were looking for a UV solution that would provide them with a better user experience and be easier to maintain.

Case study about a wastewater treatment plant in Kansas that replaced an aging UV system with the TrojanUV3000Plus  

UV Kind of Town, Chicago is

The Metropolitan Water Reclamation District of Greater Chicago (MWRD) – of which the Terrence J. O’Brien Water Reclamation Plant (WRP) is part of – has made a number of upgrades to its treatment process in recent years. The addition of UV has been a critical part of these upgrades; it played a key role in improving water quality throughout the Chicago Area Waterway System (CAWS).

Case study about the TrojanUVSigna installation at the Terrence J. O’Brien Water Reclamation Plant in Chicago  

Systems for Secondary & Tertiary Effluent Treatment

TrojanUVSigna Bank


The TrojanUVSigna® incorporates innovations, including TrojanUV Solo Lamp® Technology, to reduce the total cost of ownership and drastically simplify operation and maintenance. It is the ideal solution for treatment plants in need of revolutionary UV technology.

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TrojanUVFlex 100 Series Chamber


The TrojanUVFlex® is ideal for non-potable reuse and other wastewater applications where the treatment of filtered tertiary effluent is required. It is designed with features to make installation and operation simpler, faster and more cost-effective than ever before. Built on the TrojanUV Solo Lamp Technology platform, TrojanUVFlex allows for energy-efficient high-intensity delivery of UV light in an extremely compact footprint.

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TrojanUV3000PTP Module


The TrojanUV3000®PTP is pre-engineered for quick, inexpensive installation and is ideal for small wastewater applications. The system can be equipped with prefabricated stainless steel channels and transition boxes for integration with existing flanged piping.

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TrojanUV3000B Module


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

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TrojanUV3000Plus Module


The TrojanUV3000Plus® is one of the reasons why UV is now a favored technology in wastewater treatment. Often touted as a flagship UV system, it has demonstrated effective and reliable performance around the world. In fact, over 2,000 municipalities rely on it to treat over 30 billion gallons of wastewater every day.

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TrojanUVFit Chamber


Depending on site and design conditions, wastewater treatment plants producing filtered effluent sometimes prefer a solution using in-pipe (also called closed-vessel) UV chambers. The TrojanUVFit® offers an effective, compact, and energy-efficient solution for non-potable reuse.

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