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UV Disinfection Knowledgebase for Reuse Applications

Project: 14-11
Estimated Release: 2016
Type: Decision Making Tool

Program: Tailored Collaboration
Funding Partner: Carollo Engineers
Total Investment: $395,138 (Cash: $135,000, In-Kind cash and service: $260,138)

Principal Investigator: Harold Wright, PE, Carollo Engineers

Background

UV disinfection systems used for reclaimed water applications are typically designed and operated in accordance to the NWRI Guidelines. The Guidelines specify that UV systems must deliver a validated UV dose of 100 mJ/cm2 with mediafiltered effluents, 80 mJ/cm2 with membrane filtered effluents, and 50 mJ/cm2 with reverse osmosis (RO) effluents. The guidelines also state that UV systems used after media filtration must also deliver a UV dose sufficient to meet coliform requirements. For example, reclaimed water used for public reuse in California must have a 7-day median total coliform of 2.2 MPN/100 mL, and those in Florida must have non-detect fecal coliform as 75th percentile over 30 days with no samples greater than 25 CFU/100 mL. The NWRI Guidelines focus on non-potable reclaimed water applications of UV disinfection, and guidelines for potable reclaimed water applications have not yet been developed. It is expected that UV systems will be used to achieve 6-log pathogen reduction.

Goals and Objectives

The project will benchmark the performance of UV systems used in reclaimed water applications, develop recommendations for UV implementation for non- and direct potable reuse, and develop troubleshooting tools that utilities can use to quantify and optimize UV system operation.

Research Approach

Task 1. UV System Audits. The research team will conduct UV system performance audits at 18 participating UV facilities located around the country. The approach for the UV audit will be based on techniques developed through previous Water Research Foundation (WRF) projects (Wright et al., 2012) and successfully applied with reuse UV systems (Wright et al., 2013).

Task 2. Evaluation of UV System Efficiency. The research team will use the UVCAT simulation tool to evaluate the efficiency of UV dose monitoring and control with each UV system. The simulations will use historic plant flow and UVT data collected by SCADA and the UV dosemonitoring algorithm programmed into the UV system PLC. We will define lamp aging and fouling based on the data observed with Task 1, as well as with values expected based on UV vender warranties. The simulations will predict UV dose delivery, power consumption, component replacement, and O&M costs. The simulations will also predict fecal or total coliform inactivation using the UV dose-response data measured in Task 1.

Task 3. Development of CFD-based UV Troubleshooting Tools

During the site audit, drawings and measurements will be collected, which will allow the development of a CFD-based UV dose models for the utilities. Fluent software (ANSYS Inc.) will then model UV reactor hydraulics and predict trajectories of virtual microbes. UVXPT software (Carollo Engineers) will predict UV intensity fields within the UV reactor. Particle trajectory and UV intensity information will be combined to predict UV dose distributions, which in turn will be used to predict microbial inactivation and Reduction Equivalent Doses. The results will be incorporated within a simple Excel-based software tool where the plant operator can enter reactor flow rates, UVT, ballast power setting, and predict UV dose delivery. In particular, the software will be able to predict UV dose delivery accounting for lamp failure. Our team will evaluate the impact of lamp failure on UV dose delivery with each UV system, providing recommendations for system maintenance that will minimize risk of indicator microbe excursions.

Task 4. Guidelines for UV System Troubleshooting, Optimization, and Implementation. The research team will use the results of Tasks 1 to 3 to develop a UV System Troubleshooting and Optimization Guide that plant operators can use to evaluate and improve the performance of their UV systems. The troubleshooting guide will define step-by-step approaches for evaluating the impact of lamp aging and fouling, wiper operation, hydraulic short-circuiting, biofilm and algae growth, and water quality on UV system performance, including UV dose delivery and indicator microbe inactivation.

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