The Basin Creek Reservoir in Butte, Mont., served its community with water from both sides of the Continental Divide for nearly 100 years. In 2010, a pine beetle infestation killed most of the trees surrounding the reservoir increasing the natural organic matter (NOM) level. As a result, Butte-Silver Bow (BSB) Water Utility received a violation notice from the Montana Department of Environmental Quality for exceeding its Maximum Contaminant Level (MCL) for a type of disinfection byproduct (DBP). This violation prompted the construction of the Basin Creek Water Treatment Plant (WTP).
To maintain the use of the reservoir, filtration needed to be added to reduce the NOM and in turn, the DBPs. Initial efforts focused on site selection, pilot testing, hydraulic analysis, distribution system modeling and process selection. Based on these efforts, a pressurized membrane filtration process was selected and an Aqua MultiBore C-Series ceramic membrane system was procured by BSB to produce safe and secure drinking water.
The elevation difference between the reservoir and the distribution system allowed the opportunity to use gravity as the driving power to run the filtration plant. The C-series ceramic membrane offers high pressure ratings, allowing BSB to better capitalize on the gravity power. The reservoir pushes water through the membrane and directly into town, so when users in the city turn on their showers or water their lawns, more water flows through the Basin Creek WTP.
“It’s very unique in that it is on-demand, but it is also powered by gravity,” said Nathan Kutil, HDR’s project design manager.
“It saved a lot of infrastructure cost, and a lot of pumping cost. That was a big advantage of this design,” said Jim Keenan, chief operator of the new plant.
In addition, the Basin Creek WTP was designed to be efficient. Most water treatment plants waste about 10% of the water, but this treatment plant wastes less than 0.5% of the water it treats—an overall plant recovery of about 99.98%. At the 7 mgd design flow, the plant wastes less than 14,000 gal, close to zero liquid discharge.
“It’s the first ceramic membrane gravity-powered, on-demand plant in the country,” Keenan said. “We’ve been really pleased with how well the system works and how efficient it is. I really think that we have the most durable, longest-lasting, superior-quality product and I am really excited about that. I think it’s the future of water plants and the example is right here in Butte, Mont.”
Butte’s primary membrane system consists of four trains, each with 100 modules arranged in 10-module rows. The backwash water from this system is settled and treated with a backwash recovery train consisting of two 6-module rows. For both systems, each row has a complete set of valves so it operates independently of the other rows. Therefore, backwashes and cleanings are performed on one row at a time with the other row(s) in the train remaining in filtration.