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.
.jpeg)
.jpeg)
.jpeg)
