Aerial view of a wastewater treatment plant

Primary & Low-quality Effluent Disinfection

TrojanUV systems are capable of disinfecting effluent with UV transmittance as low as 15%

About Primary Wastewater & Combined Sewer Overflow Treatment 

  • Some wastewater treatment plants only utilize a primary treatment process and do not use any form of secondary or tertiary steps

  • Primary treatment usually consists of bar screens, grit chambers, and sedimentation tanks – the goal of primary treatment is to remove large objects, particles, and suspended solids

  • Combined sewer systems are sewers that are designed to collect rainwater runoff and domestic wastewater in the same pipe – during periods of heavy rainfall or snowmelt, the wastewater volume in a combined sewer system can exceed the capacity of the wastewater treatment plant and overflow directly into nearby streams and rivers

  • The treatment and disinfection of combined sewer overflows (CSOs) is a growing regulatory requirement in many regions

High flow rates and volumes, combined with the inherently high suspended solids concentration, variable temperature, and disinfectant-resistant pathogens seen in low quality wastewater applications requires a disinfection technology with rapid oxidation and powerful pathogen-killing capabilities.

UV vs. Chlorine Disinfection

Traditional disinfection, such as chlorine, has rapid oxidation capabilities and is relatively low cost, however, effective treatment can require a lengthy contact time which can necessitate the need for substantial footprint expansion and construction costs. In addition, the high chlorine dosages applied can potentially result in a high level chlorine residual and disinfection by-products (DBPs) in receiving waters. This has prompted municipalities to look for more environmentally sound disinfection options, notably UV.

Low quality wastewater flowing through treatment process 

UV has an advantage compared to chemical disinfection because there are no health and safety concerns related to chemical storage and handling, it does not lead to environmentally harmful DBPs, and UV does not require the additional complexity and cost of subsequent chemical removal or treatment technologies (e.g., dechlorination, re-aeration) to ensure environmentally safe discharges.

Robust UV System Design

Low quality wastewater – such as that which has only received primary treatment – has low UV transmittance (UVT), thus the UV system design challenge is a greater one because a higher percentage of the UV light is absorbed in a shorter distance.

The key to proper UV system design is to optimize the effective water layer between the UV lamps for the transmittance of the water in consideration. In low transmittance wastewater, the effective water layers need to be smaller which can be accomplished with more powerful lamps, a narrower spacing, or with hydraulic devices to induce streamlines and direct flow toward the lamps.

New quartz sleeve with no fouling, and used quartz sleeve that shows a portion of it clean with a mechanical/chemical sleeve cleaning system compared to a portion of it not cleaned, the uncleaned portion has fouling on it

Also, the rate and degree of fouling on the quartz sleeves can be accelerated in low UVT applications. Fouling must be removed from the quartz sleeves to maximize the UV light transfer to the water.

A dual-action sleeve cleaning system that uses automatic mechanical wiping in conjunction with a cleaning solution – such as the ActiClean® system – is critical. This advanced system operates automatically, without operator involvement, reducing maintenance and ensuring maximum UV output every day. Quartz sleeves and intensity sensors are cleaned regularly without disrupting disinfection.



    UV in Action

    Treating Stormwater With UV

    Cog Moors Wastewater Treatment Works in South Wales services the areas of Barry and Penarth. Total population is approximately 240,000, and incoming flows can reach approximately five cubic metres per second. Discharge from the Cog Moors WwTW is adjacent to three bathing water beaches and due to the growing popularity of these beaches, the Environment Agency Wales introduced stringent stormwater spill limits and discharge consents.

    Officials decided to conduct an economic and environmental evaluation of adding more storage tanks vs. installing a UV system to the stormwater treatment train. 

    Learn More

    Case study about stormwater management at a wastewater treatment plant in South Wales

    UV Disinfection for Public Water Feature in Toronto

    Sherbourne Common is an innovative waterfront park that provides the public with green recreational space along Lake Ontario in a former industrial area. This park features three large art sculptures that rise almost nine meters from the ground.

    Water used in the art sculptures comes from either Lake Ontario or from stormwater collected at the park. Stormwater runoff is stored in underground tanks that allow the sedimentation of suspended solids. The clarified runoff is then sent for disinfection before exiting the water features.

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