UV disinfection for ozone treatment plants ensures pathogen removal and bromate concentration reduction
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To comply with new drinking water regulations on pathogens and bromate restrictions, Ozonia equipped existing water treatment plants in Joinville and Orly, France, that currently utilize ozone with Aquaray H20 ultraviolet (UV) reactors. The addition of these UV light disinfection units brings these two ozone plants to full compliance. With a capacity to treat up to 80 million gal per day (mgd) of drinking water per plant, the project is the largest drinking water UV contract in Europe.
Levels of bromate ions in drinking water recently have come under scrutiny. These are commonly formed by the reaction between ozone and bromide ions, which often are present naturally in water.
The addition of UV disinfection to ozone treatment plants, however, helps ensure only the safest and highest-quality water is delivered—and well under limits imposed by new regulations for both pathogen removal and bromate concentration reduction.
The chosen UV reactors act as a final barrier in the disinfection process by inactivating pathogenic microorganisms such as viruses, bacteria and parasites. Under proper conditions, UV light is particularly effective for inactivating chlorine-resistant microorganisms such as Cryptosporidium and Giardia, even at low doses. UV-treated water also fully meets the new maximum limits for bromate concentrations, which were lowered to 10 μg/L (from 25 μg/L) in December 2008.
Ozonia was selected not only for the efficiency of the Aquaray H20 UV disinfection reactors but also due to the company’s long experience and ability to retrofit existing sites while maintaining full operation.
Careful consideration was given to the design and modeling of the UV reactors to guarantee compliance with the project’s specifications and the development of an installation plan that would keep the operation of the treatment lines already in place intact. The project consisted of:
- Replacing the regulation valve;
- Adding a shut-off valve;
- Installing the UV reactors in the existing plant while minimizing headloss, after a functional analysis of the filters/UV reactor combination; and
- Guaranteeing a dose of 40 mJ/sq cm under the most unfavorable conditions (maximum flow, minimum transmittance).
After validation of the specific operating conditions at the Orly and Joinville sites by Degremont North America Research and Development, the company developed highly advanced hydraulic modeling parameters—based on computational fluid dynamics (CFDs) using Fluent software—to precisely calculate and quantify the effects of hydraulic disturbances and pressure losses.
This preliminary study demonstrated that installation of these inline cross-flow UV reactors would have no significant impact on the hydraulics of the plant and, given the low pressure losses, they could be easily retrofitted to the main piping system at the outlet of the activated carbon filters.
The study also established the 20-in. diameter as the most appropriate choice for the plants. The reactor/valve combination guarantees the specified headloss and performance of the hydraulic regulation.
“The CFD modeling step was crucial and confirmed the UV reactors could be installed without any negative impact on the activated carbon filters. The technical teams of SAGEP [the Paris water management company Société Anonyme de Gestion des Eaux de Paris] and Degremont greatly contributed to success of this project through active collaboration,” said Vincent Pilmis, Ozonia project manager.
Proven & Recognized
UV treatment does not alter the physiochemical characteristics of the water. Bioassays, or biological tests, conducted on specific organisms in an operating plant provide the ultimate validation of the effectiveness of these UV medium pressure reactors.
The Aquaray H20 UV water disinfection reactors (20-in. Mono and 20-in. Duplex) are certified by the German Technical and Scientific Association for Gas and Water and the U.S. Environmental Protection Agency, and they guarantee consistent compliance with the prescribed amount of 40 mJ/sq cm defined in conjunction with SAGEP. In France, when used to prevent parasitic risks, UV treatment solutions also must be approved by the French Ministry of Health.
Currently, Ozonia is the only manufacturer to have obtained this approval for this specific range, following a recommendation from the French Food Safety Agency to manage flow rates such as those treated by these two 20-in. UV reactor ranges.
Reliability in a Small Footprint
These UV reactors use high-density medium pressure lamps to offer a compact footprint and reduce capital costs. Powered by electronic ballasts, these lamps are inserted in pure quartz sleeves that isolate them from the water. They can be changed without draining the reactor, and due to the variable output electronic ballast, total power consumption can be adjusted based on demand. In addition, a dedicated and calibrated UV sensor is installed for each lamp to monitor UV intensity and ensure optimum reliability.
Engineered with advanced CFD modeling software to determine the optimal lamp spacing, the system provides consistent and reliable disinfection with minimum headloss. As a result, the powerful dose of UV light delivered requires fewer lamps. Only six UV lamps were needed in each reactor for Joinville and 12 lamps per reactor for Orly to achieve a production of 80 mgd at each plant. This significantly decreases operating and maintenance costs.