Design and Selection Approach for an Open Channel UV Disinfection Systems for Wastewater Treatment

Ultraviolet (UV) systems are an effective technology used at wastewater treatment plants (WWTPs) to disinfect wastewater to meet and exceed permit limits for E. Coli, Enterococci, and similar disinfection requirements. UV disinfection offers several benefits, including the elimination of chemical handling and a smaller footprint. However, selecting and sizing UV systems for each application is critical and must be done based on regulatory requirements, client preferences, and site-specific factors. There are multiple ways to design and procure a UV disinfection system, each with specific advantages and disadvantages based on the requirements of the project.

In this article, we explore key considerations in designing and selecting UV disinfection systems for wastewater treatment, including:

• The basics of UV disinfection theory
• An overview of UV system components
• Project-specific criteria to consider
• How to perform an alternative analysis to preselect UV systems
• Considerations for procurement (e.g., two competing designs or preselection)

Sizing UV Disinfection Systems

UV systems are sized to meet a certain Reduction Equivalent Dose (RED) for each project to deactivate microorganisms and disinfect wastewater. The dose needed to disinfect the wastewater sample is reduced using two reduction factors (typically one for quartz sleeve fouling and one for end of lamp life) to determine the RED used for design. The RED and the UV system sizing can be influenced by many interconnecting factors, including bioassay validation (third-party validation of UV system models), UV transmittance (i.e. pre-UV influent wastewater quality), desired log inactivation effectiveness and effluent permit requirements, and the dosage reduction factors.

Designing Open Channel UV Disinfection Systems

UV systems are either open channel systems or closed vessel systems. This article is specific to open channel systems. There are a variety of open channel UV disinfection system makes and models but most of them have the following common basic components:  UV lamps and Quartz Sleeves, UV banks/modules, Ballast/drivers, cleaning systems, lifting mechanism, level control device, sensors, SCADA/control panels, and influent flow conditioner plates. 

The design and selection of UV system is highly specific to the unique characteristics of each site, project goals, and client/operator preferences.

Key factors to consider include:

• Site conditions (greenfield vs. rehabilitation)
• Process design criteria (upstream treatment and permit effluent limits)
• Redundancy needs
• Channel geometry
• WWTP hydraulics and level control requirements
• Available space for associated lifting, electrical, and controls equipment

Additionally, local service availability ensures reliable maintenance and is a factor that shouldn’t be overlooked. Finally, owner and operator preferences significantly influence the selection process. All of these factors influence project capital costs and operations and maintenance (O&M) expenses, with lifecycle costs typically governing the selection of a UV system.

Designs and products on the market for open channel UV disinfection technology vary significantly between manufacturers, and these differences extend past manufacturers selection and impact other aspects of design, such as channel geometry, hydraulics, electrical requirements, cleaning and lifting mechanisms, and other site layout considerations as well as the O&M of the system.

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Selecting and Procuring UV Disinfection Systems

Given the lack of “swappable equipment characteristics”, there are two common approaches to selecting and procuring UV disinfection systems. The first approach – allowing multiple manufacturers to compete during the bid phase which may lead to the need for separate designs for each manufacturer. Approach two – selecting a manufacturer through a preselection process or predesign engineering alternative analysis. Following are the advantages and disadvantages of the two approaches:

Approach 1: Allowing Multiple Manufacturers to Compete during Bid Phase

Advantages:

• Cost Competition: Encourages competitive pricing on bid day for a traditional design-bid-built project, potentially lowering overall project costs.
• Diverse Options: Provides a wider range of technologies and designs to choose from, which may lead to innovative project specific solutions.
• Flexibility: Allows for adjustments based on the best available technology and market conditions (lead times, contractor preferences, etc.).

Disadvantages:

• Design Complexity: May require separate designs for each manufacturer, complicating the overall system integration. This generally results in increased engineering effort and design fees.
• Increased Time: Lengthens the bidding, evaluation, and construction submittal review processes, as each proposal needs thorough review.
• Potential for Confusion: Different design approaches can lead to inconsistencies and challenges in coordination. As well contractors’ bids are not apples to apples comparison if contractors choose different UV systems.

Approach 2: Preselecting a Manufacturer via Alternative Analysis

Advantages:

• Systematic approach: Allows competition and comparison between manufacturers against the established project criteria, often using qualitative and quantitative measures. Making selection for the most suitable project specific option based on the alternative analysis.
• Streamlined Design: Facilitates a cohesive design process tailored to a specific manufacturer’s technology, enhancing integration.
• Faster Implementation: Reduces the time spent on bidding and submittal review process, generally allowing for quicker project execution.
• Clearer Expectations: Simplifies communication and alignment between the project team, the selected manufacturer, and the Contractor.

Disadvantages:

• Limited Bid-Day Competition: Generally, this approach reduces the competitive bidding environment, potentially leading to higher costs if equipment is not preselected.
• Dependency on One Manufacturer: Creates a reliance on a single manufacturer, which could pose risks if issues arise with their technology or personnel support.
• Inflexibility to Change: If project requirements evolve, it may be challenging to adapt when bound to a single manufacturer’s solutions.

Optimizing UV System Selection for Effective Wastewater Disinfection

UV disinfection systems play a vital role in helping wastewater treatment plants meet stringent regulatory standards for pathogen removal. Selecting the right system requires careful consideration of site-specific factors, project goals, and operator preferences, as these choices significantly impact capital and operational costs. Both procurement approaches—allowing multiple manufacturers to compete or preselecting a single manufacturer—come with their own advantages and disadvantages that must be weighed against project requirements. Ultimately, a thorough understanding of UV disinfection theory and system components is essential for making informed decisions. By optimizing the selection process, WWTPs can enhance disinfection efficiency while maintaining compliance and minimizing lifecycle costs.

Partner with HR Green’s Water Team to implement innovative wastewater treatment solutions. HR Green works with municipalities and utilities to design, construct, and implement wastewater treatment engineering solutions. Whether you’re looking to upgrade existing facilities or develop new facility designs, our proactive approach includes energy-saving initiatives that strategically invest dollars into upgrades, helping your facilities meet service and permit needs for the future. Contact us today to discuss how we can support your next project.

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