Portland Water District upgrades with UV treatment - By Elizabeth Richards

Earlier this spring, the Portland Water District celebrated the completion of a $12-million project, including the installation of a new UV system and upgrade of their ozone disinfection system at the Sebago Lake Water Treatment Facility. The project brought the facility into compliance with new EPA regulations, as well as adding efficiency to their operations.

Chief Operator Joel Anderson said the project began with new federal mandates for enhanced surface water treatment focusing on the pathogen cryptosporidium, a microscopic parasite which can cause severe gastrointestinal illness. 

 

The PWD is one of just a few water districts in the country that doesn’t employ expensive conventional filtration methods. “Because we have such a pristine source in Sebago Lake, we were granted a waiver from conventional filtration,” said Anderson. But this didn’t exempt them from the new rules, even though over a two year monitoring program, cryptosporidium was never detected in the water. “When the EPA writes these rules, they’re for everybody,” said Anderson.

The treatment facility in Standish has been using ozonation and chloramination to treat the water since its construction in 1994. When they began looking at how to best meet the new regulations, they took the opportunity to update the ozone system at the same time. “We know that you don’t run your primary treatment system into the ground. You get your useful life out of it – which we did – and then you move on,” said Anderson. 

The primary concerns when looking at the project with engineering consultant CDM Smith were cost effectiveness and safety for customers Anderson said. The rules stated that there had to be a second disinfectant if the water wasn’t being filtered, so they couldn’t just increase the ozone. They could have increased the dose of chlorine used, but Anderson said organic matter in unfiltered water reacts with chlorine to form disinfection byproducts, which are known carcinogens. Therefore, the PWD didn’t want to increase those numbers. Since UV is a physical process, not a chemical one, it does not have any known disinfection byproducts associated with it, Anderson said.

Looking at the existing technology available, they concluded that UV water treatment in combination with ozone disinfection was both the most cost effective and the safest method. The light process means that no more chemicals are added to the average 21.5 million gallons of water that are treated every day. The light penetrates the outer shell of the pathogen and disrupts the DNA so they cannot replicate. One cyst won’t make you sick, said Anderson. It’s when the cells find a host environment and multiply that causes problems, he said. Since UV isn’t very effective against viruses, ozone was also still needed, he added. 

Instead of using ambient air, the upgrades to the ozone system mean that now liquid oxygen is converted to gaseous oxygen and sent to ozone generators. This new process is much more efficient according to Anderson. “We’re using much less electricity to do the same work,” he said. The sustainable design allowed the PWD to receive a $300,000 competitive grant from Efficiency Maine Trust Competitive Program. The energy efficient upgrades are anticipated to save approximately $150,000 annually.

Once the type of system was selected, there were many decisions to be made. Anderson said they didn’t want to increase the footprint of the existing building, and they needed to decide what would come first in the complex treatment process. A series of pilot studies conducted over a six month period clearly showed that because the ozone works by increasing the clarity of the water, the UV was much more effective if it came second in the process. 

Because two of each system is required, finding space to fit it all in was another challenge. In water treatment, said Anderson, redundancy is critical. 

“You can’t afford to have just one ozone generator. You can’t afford to have one UV reactor. You’ve got to have at least two of everything,” he said. In fact, it is required as part of the waiver from filtration. If there are two that means that if something fails another unit can be put on line without missing a beat.

The new system took about two years from start to finish to construct. The biggest challenge, Anderson said, was trying to maintain the existing treatment system while trying to install the new one at the same time. “It was like trying to live in your house while someone is redoing the kitchen, and the bathroom, and the roof – it did present a lot of challenges,” he said. “Our staff here did a great job of meeting those challenges,” he added. 

There hasn’t been a public response to the project, since most people don’t even know that the system changed. This is a good thing, Anderson said. As long as the process is running smoothly and safely there’s no need to know. It is only when there are problems that people want to understand where something went wrong. “It has been an interesting couple of years, but since we never made the front page of the paper, apparently we met the challenge,” he said. “I’m pretty proud of that.” 

More information on the project can be found at http://www.pwd.org/pdf/UVFact%20Sheet.pdf.