First of Its Kind: The Power of Gravity With Ceramic Filtration
It’s not every day that you get to work on a project that is the first of its kind. Yet here I am, getting the opportunity to tell you about the first gravity-powered ceramic membrane water filtration plant in the United States. And thanks to this video by Butte. Elevated., I can give you a peek inside Butte’s new state-of-the-art Basin Creek drinking water treatment plant (WTP).
Butte, Montana, is a mining town with a long history of water needs that have resulted in a complicated municipal system. The forward-thinking community invested heavily in this new WTP facility to ensure the best treatment possible for its citizens. There was no “go-by” example for this project; it truly is the first of its kind in so many ways.
The primary treatment operation uses a ceramic membrane filter that has roots in Japan and is fairly new to the United States. In fact, this is only the second ceramic drinking WTP in the United States, and it is the first for this manufacturer. The chemical-resistant nature of the ceramic, coupled with its physical strength, makes it difficult to damage and therefore very reliable, with an impressive 20-year warranty on the filter.
Other membrane WTPs have used gravity as the driving force, but very few operate on-demand. The facility is designed to react to changes in the distribution system rather than anticipate them. It is unnecessary to pump water to the distribution system except in very extreme demand conditions. This concept has allowed the WTP to use the raw water reservoir as storage rather than having a downstream clear well, and it comes with cost savings as well as increased dependability. There are differences from the traditional polymeric membranes that we are accustomed to in the U.S. The ceramics have a higher pressure threshold, which is great when trying to capitalise on the maximum amount of gravity head available. Also, the clean-in-place interval is much longer, at an outstanding six months between required cleanings.
A proof pilot was an instrumental step for the design of this WTP. HDR’s Water Institute is a firm believer in proof of concept, and this project demonstrates that thorough research can impact design. For example, the proof pilot uncovered the need to add a higher dose of coagulant than originally planned. This resulted in the design of larger chemical storage tanks so the longer six-month cleaning interval was realised.
Another feature of this facility is the backwash recovery system. All filters require a periodic reverse flow to flush off material that adheres to the surface, and this process results in waste that affects the overall recovery of the treatment plant. Recovery would be defined as the amount of waste generated divided by the amount of raw water brought in, and typical values range from 85 to 95 percent. At Basin Creek, the backwash is collected and filtered through a separate ceramic recovery membrane, and the result is an overall recovery for the WTP of around 99.95 percent.
This new WTP is one that the City and County of Butte-Silver Bow and HDR can be proud of. It is destined to get a lot of attention throughout our industry and will provide low-cost, high-quality water for the residents of Butte long into the future. “First of its kind” is exciting, and I love talking about the details, but safe drinking water is always No. 1.