Ultraviolet (UV) light is a form of light that is invisible to the human eye. Specific wavelengths, between 200 and 300 nanometres (or billionths of a metre), are categorized as germicidal ? meaning they eliminate bacteria, viruses and protozoa. UV has been used to disinfect water since the early 1900s. Today, UV is applied to treat various water issues in municipalities all over the world. Applications for UV disinfection include:
- Disinfection of primary, secondary or tertiary wastewater effluent
- Disinfection of high quality wastewater for reuse purposes
- Treatment of storm water or combined storm sewer overflows
- Disinfection of ground water or surface water for drinking
- Advanced Oxidation (UV +hydrogen peroxide) for indirect potable reuse and destruction of chemical contaminants.
Environmental Contaminants and UV Treatment
The term ?environmental contaminants? refers to harmful chemicals present in soil, air and water. UV, either alone or in combination with hydrogen peroxide can destroy contaminants in a variety of applications including drinking water, wastewater recycling and groundwater remediation. Increasingly, water providers are taking advantage of this dual capability of UV light to simultaneously disinfect and treat contaminants (through UV photolysis and UV-oxidation ? also known as advanced oxidation) such as taste and odor-causing compounds, nitrosamines, pesticides and algal toxins.
Microorganisms in the water are exposed to ultraviolet light when they pass by special UV lamps. These lamps can be housed in a closed reactor, or submerged into an open concrete channel. The UV energy instantly destroys the genetic material (DNA) within bacteria, viruses and protozoa, eliminating their ability to reproduce and cause infection. Unable to multiply, the microorganisms die and no longer pose a health risk. With UV technology, it is possible to inactivate harmful microorganisms including E. Coli, Cryptosporidium and Giardia.
Drinking Water Treatment
UV Disinfection is the critical final step in the treatment of drinking water, inactivating microorganisms (especially chlorine-resistant Cryptosporidium and Giardia) to protect public health. Alternatively, UV and chlorine can be used simultaneously to provide protection against the full spectrum of microbes, providing reliable multi-barrier protection. Municipalities around the world ? from rural wells to cities serving millions of people ? have installed UV disinfection to protect their residents.
Wastewater Treatment
Disinfection is the final step in the wastewater treatment process. Bacteria, virus and protozoa populations are inactivated before wastewater is discharged into oceans, lakes and rivers.
The adoption of ultraviolet light for wastewater disinfection has grown significantly over the past few decades. Thousands of municipalities have converted from chemical-based disinfection, such as chlorine gas, to UV due to the significant safety advantages for their communities, plant employees and local water bodies. As new wastewater treatment plants are constructed around the world, UV is most often selected for disinfection because of the cost savings in both initial construction and long term operation.
Leading the Way
TrojanUV began in 1976 when a young entrepreneur named Hank Vander Laan bought Trojan Metal Works ? a small company located in London, Ontario, Canada. Although fabricating metal toolboxes was the company?s mainstay, what caught Vander Laan?s eye was the patent it held on a small, UV treatment unit for homeowners to purify their drinking water. He immediately recognized the benefits of ultraviolet (UV) light as a safer, more environmentally friendly alternative to chemical water treatment and had the idea of transforming the fledgling metal fabricator into a dynamic solution for water treatment.
Today, TrojanUV is recognized around the world as a leader in the design and manufacture of advanced UV water treatment technology, committed to protecting public health while delivering sustainable treatment solutions for a variety of water applications including drinking water, wastewater as well as environmental contaminant treatment. TrojanUV?s solutions are implemented in more than 7,500 municipal UV disinfection facilities operating in over 80 countries ? the largest installed base of UV systems in the world.
Here are a few examples of municipalities TrojanUV has partnered with to provide treatment solutions:
New York City Drinking Water Facilities
As many are aware, New York City is made up of five boroughs: the Bronx, Manhattan, Queens, Brooklyn and Staten Island, and is home to more than eight million people, making it the most populous city in the United States.
The city draws its drinking water from two protected surface water systems: the Catskill/Delaware and Croton watersheds. The majority of New York City?s drinking water is supplied by the Catskill/Delaware watershed, located approximately 100 miles outside the city. Historically, New York City has not filtered the water from this system nor did they require any additional barriers to microbial contaminants due to the pristine nature of the watershed. The total area of both watersheds is approximately 1,972 square miles and contains 19 reservoirs and three controlled lakes.
In 2006, the United States Environmental Protection Agency released the Long Term Enhanced Surface Water Treatment Rule (LT2ESWTR). This new rule requires surface water treatment facilities to either filter their water or install an additional barrier for microorganisms as a multi-barrier disinfection strategy. Engineers working on the Catskill/Delaware project evaluated a new filtration plant but the cost of installing a 2.2 billion gallon per day (BGD) filtration facility was significantly greater than other alternatives. After evaluation of available technologies, it was decided that UV was the most practical and cost-effective solution.
When completed, New York City will operate the largest drinking water UV installation in the world ? the Catskill/Delaware UV Facility ? with a capacity to treat 2.24 billion gallons per day (BGD). Combined, the Catskill/Delaware and Croton water plants will supply residents of New York City with over 2.8 BGD of high quality drinking water. In 2003, after evaluation of available lamp technologies, NYC chose to design a low pressure, high output (LPHO) lamp-based UV system over a medium pressure (MP) lamp-based system. The LPHO units are capable of disinfecting the water utilizing approximately one-third the power of MP lamp units. Trojan offered a high-flow capacity LPHO lamp solution ? the TrojanUVTorrent ? which minimizes electrical costs while maximizing disinfection efficiency.
Catskill/Delaware UV Facility
In 2005, Trojan was selected as the manufacturer for the UV portion of New York City?s drinking water project.
Figure 1: The TrojanUVTorrent, a high-flow capacity LPHO
lamp solution, minimizes electrical costs while maximizing
disinfection efficiency.
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In 2009 and 2010, Trojan delivered 56 TrojanUVTorrent UV units to the Catskill/Delaware UV Facility. Each unit is capable of delivering a 40 mJ/cm2 dose to 40 million gallons of water per day (MGD). This disinfection requirement, set by the New York City Department of Environmental Protection, delivers greater than 3-log reduction of microorganisms such as Cryptosporidium and Giardia. The TrojanUVTorrent was custom-designed by Trojan?s engineers and scientists in order to meet the challenging design parameters of this unique project. The Catskill/Delaware UV Facility is located in Valhalla, New York. The treatment train consists of screening, UV treatment and chlorination (for a residual disinfectant in the distribution system).
Croton Water Treatment Facility
In 2006, Trojan Technologies was selected to supply the UV equipment for the new Croton Water Treatment Facility. This facility has the capacity to treat up to 600 MGD of high quality drinking water. Trojan is supplying 20 TrojanUVTorrent UV units. Each unit is capable of producing a dose of 40 mJ/cm2 to treat a flow of 30 MGD.
Life Cycle Assessment
In separate work, Trojan assessed the relative carbon dioxide (CO2) emissions associated with both MP and LPHO solutions through a joint project with the University of Western Ontario. It was estimated that for the Catskill/Delaware Facility, the low pressure solution would lead to the release of approximately 13,700 fewer tons of carbon dioxide (CO2) annually than a medium pressure option (assuming that for typical conditions, the system operates at 70 percent of its peak capacity). Over 20 years, this equates to 274,000 fewer tons of carbon dioxide, making the TrojanUVTorrent the most environmentally-friendly solution for New York City (see Figure 2).
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Adam Festger is the market manager for Trojan?s Drinking Water and Environmental Contaminant Treatment (ECT) Divisions.?
