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Trojan ECT CaseStudy CornwallEnvironmental Contaminant Treatment
Site Example:
Treating Taste & Odor and Disinfecting Drinking Water with UV
Cornwall, Ontario
Cornwall is a city of nearly 60,000 people in Ontario, Canada. It is located on the St. Lawrence River, approximately 1,700 km from the Atlantic Ocean and 2,000 km from Lake Ontario.
The city draws its drinking water from the St. Lawrence, a reliable and generally good-quality source. However, in the late summer and early fall, dying algae from algae blooms during the warmest months often leave an earthy and musty taste in the water. The city’s conventional treatment process, consisting of coagulation, sedimentation, and mixed-media filtration, is at times unable to remove sufficient quantities of geosmin and 2 methylisoborneol (MIB), the compounds responsible for the difficult-to-treat taste and odor (T&O) problem. The city uses granular activated carbon in its filter beds to address taste and odor (T&O) issues.
However, this treatment method requires large amounts of carbon and is unable to completely treat the T&O problem. In addition, frequent carbon change-outs are required due to relatively rapid break-through of geosmin and MIB.
Cornwall has a need to meet additional disinfection rules set forth by the Ontario Ministry of the Environment. These rules were developed to protect the public from chlorine-resistant pathogens. The existing chlorine disinfection system is inadequate to meet the new rules. The city made a decision to install UV disinfection to accomplish an additional 1-log reduction of Giardia and earn additional disinfection contact time (CT) credit.
 The Trojan Solution
In the summer of 2004, the City of Cornwall, Ontario selected the TrojanUVSwift™ECT to meet their disinfection requirements and to treat the intermittent T&O problem. The completed system will consist of:
- Four 24" TrojanUVSwift™ECT reactors placed downstream of mixed-media filters
- Available supply of NSF-grade hydrogen peroxide, delivered as needed
- Trojan’s patent-pending control system that optimizes the UV-oxidation process in real time
The TrojanUVSwift™ECT will operate in two modes, disinfection-only mode and T&O control mode. In disinfection mode, the UV system will operate at lower energy levels sufficient for inactivation of any microorganisms. This is the normal operating mode for year-round drinking water treatment. While in disinfection mode, only a fraction of the total UV lamps and/or reactors installed will be operated thereby keeping the operating costs at a minimum to meet disinfection requirements.
Figure 1: Trojan UV-Oxidation of MIB in Cornwall Water
This graph shows the effectiveness of Trojan’s proven application of UV-oxidation for reducing concentrations of the chemicals that are responsible for T&O events. The Trojan UV system was designed to deliver a >1-Log reduction of MIB and geosmin. The log-linear degradation curve generated using bench scale analysis indicates that any required level of treatment can be achieved, even 4+ logs.
During a Taste & Odor event, the UV system mode changes from Disinfection-Only to Disinfection + Taste & Odor control. In this mode, additional UV lamps/reactors are energized and hydrogen peroxide is dosed into the water upstream of the UV system. The combination of UV and hydrogen peroxide initiates a powerful oxidation reaction that destroys T&O-causing chemicals and increases the level of disinfection. Figure 1 shows the degradation of MIB in a sample of Cornwall’s water.
Installation and startup will be completed in 2006.
Peak Flowrate: 26.4 mgd (100,000 m3/day)
Primary contaminant: Geosmin
Secondary contaminant: 2-Methylisoborneol (MIB)
Design Influent Concentration of Geosmin: 50 parts per trillion (ppt)
Design Geosmin reduction: > 1-log
Disinfection requirement: Minimum dose of 40 mJ/cm2 (>1-log of Giardia inactivation)
Key Benefits of Cornwall’s TrojanUVSwift™ECT System:
- Year round disinfection and simultaneous elimination of seasonal contaminants.
- Validated disinfection in accordance with upcoming LT2ESWTR (i.e. 2-log Crypto credit).
- Produces no disinfection by-products (DBPs), such as bromate.
- Dual operating modes minimize O&M costs (approx. 1 cent/1,000 gallons in disinfection mode).
- Compact reactor minimizes footprint and simplifies installation.
- Reduced reliance on chlorine for disinfection.
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