The use of ozone for pipeline disinfection is becoming more popular and widely accepted. Ozone is a useful tool to quickly disinfect new water pipelines without wasting significant amounts of water. Previously, high levels of liquid chlorine or other harsh chemicals were used to disinfect new water pipelines. This process involved hauling and handling chemicals, mixing with water, and disposing of the water upon completion and validation.
However, using ozone eliminates the need for chemicals and reduces the cost, as well as eliminating the concern of discharging the spent water safely. This approach saves both time and money.
Denver Water has been at the forefront of developing a disinfection method that saves millions of gallons of water and reduces staff time while almost eliminating expensive pipe replacements. Every year, Denver Water installs over 100,000 feet of new water main delivery pipes, which are typically located under a neighborhood’s streets. Before the newly installed pipes can be used, they must be cleaned and disinfected and then pass a test demonstrating that they can deliver clean, safe water to customers.
In 2019, Denver Water added gaseous ozone to its disinfectant arsenal, becoming one of the world’s first water utilities to do so. Previously, the water utility used liquid chlorine, liquid ozone, and/or pressure washing methods to clean and disinfect newly installed pipes. Then, the pipes were flushed for hours, sending thousands of gallons of water to the storm sewer before testing for harmful bacteria.
The use of gaseous ozone is considered the next evolution in disinfection methods, according to Ryan Gregg, Denver Water’s water quality supervisor. In 2013, water quality technicians were unable to get any traditional disinfection methods to work after crews had finished installing 1,000 feet of pipe. Tests showed that bacteria were present inside the pipe.
Even after replacing the pipe twice, the traditional disinfection methods could not pass the test. Technicians discovered that Pseudomonas aeruginosa, a type of bacteria that is extremely difficult to remove, had contaminated the pipe that failed to pass the repeated tests.
Consequently, Denver Water started searching for an alternative disinfection technique that could eliminate stubborn bacteria without wasting significant amounts of water. After conducting dozens of pilot studies for five years with the help of CDM Smith, an engineering firm, and Denver Water’s transmission and distribution group, the utility’s water quality operations techs found that ozone gas could work.
The custom-built ozone gas trailer used by Denver Water pulls outside air in, separating oxygen (O2) and nitrogen. The concentrated oxygen goes to the other side of the trailer, where high-voltage electricity creates ozone, or O3. After the disinfection process, the ozone is then purged and rendered ineffective. The process is fast, requires little flushing, and saves Denver Water 13.5 million gallons of water a year, reducing staff time by about 30 days annually. There is no concern with the public breathing ozone once the pipe has been disinfected.
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