Located near Denver International Airport, the South Adams County Water & Sanitation District (SACWSD) and their customers rely on a group of 12 alluvial wells as their primary water source. These wells contain extremely hard water that has required local homeowners to frequently replace their plumbing and water heaters as well as to pay for in-home water softeners. These water softeners, however, release corrosive brine waste to the sewer and contribute to high dissolved solids in the local wastewater treatment plant’s discharge.
In 2017, SACWSD convened a Hardness Advisory Committee (HAC) to assess and select an affordable water-softening technology that could effectively improve water quality for their 66,000 customers. After extensive evaluations, the HAC decided to build the new John Ennis Water Softening Facility, a full-scale water-softening and filtration facility that utilizes a powerful technology that’s still new to the United States: Pellet softening.
Pellet softening reduces water hardness by capturing calcium carbonate that precipitates out of source water. These minerals attach onto seed materials in a pellet-softening reactor to ultimately form free-draining calcium-carbonate pellets that not only consist of environmentally benign solids but can also be reused and even monetized to earn utilities new revenue streams and off-set landfill disposal costs.
Advancements in Water Softening
Although pellet-softening treatment processes have been used throughout Europe for decades, this technology was further advanced and modified to serve the John Ennis Water Softening Facility, which contends against raw water hardness and subsequent finished water goals that are notably more aggressive than most European installations.
Carollo pilot-tested and designed SACWSD’s new facility with pellet softening using sodium hydroxide, stabilization using carbon dioxide, chlorine contact for 4-log virus inactivation, and dual-media filtration. Technology integration, equipment automation, and operator training enable the plant to operate unattended daily from 6 pm to 6 am.
During its first year of operation, the John Ennis Water Softening Facility ran at maximum capacity to effectively reduce water hardness from 380 milligrams of calcium carbonate per liter of water (mg/L) down to 60 mg/L. When operated at full capacity, the pellet-softening process can produce 27 tons of calcium carbonate pellets every day, which can be beneficially reused in the Denver Metro area.
Results and Highlights
The rise rate in a pellet softener is 20 times higher than that of conventional lime softening. Pellet softening installations take up a smaller footprint inside a building, allowing for facility hardening.
The pellet reactor has no moving parts and, when sodium hydroxide is utilized, boasts low turbidity (<0.3 NTU). As a result, it only consumes 1/2 of the alkalinity of lime softening.
Pellet softening can be constructed and maintained at approximately half the construction cost of conventional lime softening facilities and yield better process control.