Replacing the filters in a water treatment plant is a routine piece of maintenance that occurs every 15 to 20 years.
And time’s just about up for the existing 8-inch layer of sand and 20-inch layer of anthracite coal particles that line the 16 filter beds at Denver Water’s Foothills Treatment Plant.
This also signals an opportunity for Denver Water’s experts to check out the latest technology on the market and consider the best way to improve the plant’s operation.
“In an effort to be the best utility in the nation, we’re looking to see what’s out there in new technology for the water industry and testing what works for us,” said Dave Swendensky, who manages the Foothills plant.
Denver Water is currently testing a new generation of materials that may be part of the new filter layers, including testing proprietary clay material mined in Norway and a ceramic material made by an American company. Technicians and scientists also are running tests to see if using deeper layers of sand and anthracite coal particles would be more efficient.
Finding a more efficient way to treat water could save money by reducing the cost to operate the plant.
The plant, the newest and largest of Denver Water’s treatment plants, started operating in 1983. New layers of sand and anthracite coal particles were installed in the plant’s 16 filter beds in 1999 through 2003, four beds every year. Those existing layers are scheduled to be replaced starting in 2019, with four beds replaced every year.
“The technology changes, and this is a chance to consider our options,” said Matt Bolt, a Denver Water engineer who is part of the team testing new filter technology.
At the Foothills plant, about five miles south of Chatfield Reservoir, the team has set up a miniature treatment plant to test various materials used to filter water.
The Foothills plant can treat up to 280 million gallons per day, while the miniature test plant typically treats about 7 gallons per minute. The mini-plant previously was set up at Denver Water’s Moffat Treatment Plant, where it helped engineers design the new Northwater Treatment Plant, where construction started in September.
The process to make safe, clean drinking water includes using gravity to run water through filter beds, made up of layers of material that trap and hold dirt and debris, before flowing to the next steps of the process.
The filter beds are cleaned out every day or two, depending upon usage, by reversing this process. Water is pumped backward through the filter beds to flush the trapped contaminants up and out of the filter materials.
This flushing process takes time, water and energy. It also physically knocks around the grains of sand and coal, which over time makes them smaller, reducing their ability to efficiently filter water.
At that point, it’s time to clean out the filter beds and start fresh.
“The question for the new beds is whether a different configuration or media would work better — or if the existing configuration is the best choice,” Bolt said.
The team is using the mini-plant to test if a new generation of materials can perform better than the existing combination of sand and anthracite coal. They’re also testing to see if deeper layers of material can make a significant difference.
The existing filters include a layer of sand particles, which are round. On top of that is a layer of anthracite coal particles, which are square-ish.
The mini-plant is testing layers of sand and a new line of products that under a microscope look like lava rocks used in some landscapes — with holes, nooks and crannies that can trap more particles compared to traditional, angular anthracite coal particles.
One product, called Filtralite, is a proprietary “expanded clay” material mined in Norway by Leca Norge AS, a Norwegian company. The material is made by heating clay to extremely high temperatures, to the point where the grains pop and expand into a jagged, pocked material.
It’s like heating corn kernels until they pop and become popcorn, Bolt said.
The team also is testing Ceralite, a new ceramic material manufactured by Wateropolis, based in Ohio. That material also has tiny pock marks that you need a microscope to see.
According to Bolt, the theory behind the jagged, pock-marked material such as Filtralite and Ceralite is that the expanded surface area offers more surface area to trap contaminants in the water.
Filtralite currently isn’t used in any other treatment plant in the United States, although it is used in plants in Canada, Europe and Asia. Ceralite is used in other U.S. plants.
“If we decide to go with the expanded clay material for Foothills, either Filtralite or Ceralite, it would be one of the largest drinking water treatment plant applications of this type of filter material in the world,” Bolt said.
A decision on what materials will be used for Foothill’s next set of filter beds is expected in early 2019. The work is expected to be underway by the end of next year.