Platte groundwater, Beebe Draw groundwater, and RO brine
sources achieving up to 73%, 72%, and 77% hardness removal,
respectively. Hardness removal was strongly dependent on pH.
Optimization curves were generated at pH values between 8 and
10.5 for all sources. Both groundwater sources showed that a pH
near 10.1 provided the most efficient hardness removal, whereas
the RO brine source optimal pH was shown to be between 10.5
and 11.4.
Hydraulic residence time also had a positive impact on hardness
removal. Two hydraulic residence times were evaluated for
both the South Platte and RO brine sources. Increasing the
hydraulic residence time for the South Platte source from
1.2 to 1.9 minutes enhanced maximum hardness removal by
11%. Similarly, increasing the hydraulic residence time for the
RO brine source from 1.9 to 3.1 minutes improved maximum
hardness removal by 20%.
Pellet size distribution was evaluated by changing the frequency
and volume of pellets extracted and added to the pellet reactor.
Hardness removal was optimized when the size of pellets was
evenly distributed between smaller sand-sized particles and fully
developed pellets. Smaller pellets offer increased surface area
for the precipitation of calcium and magnesium to occur. Pellets
increase in density as they grow; larger pellets migrate toward
the bottom of the reactor where they are eventually extracted.
In addition to hardness removal, pellet softening routinely
removed at least 90% of manganese present in the Beebe Draw
source. Extracted pellets from this source were light brown in
color as a result of removed manganese, in contrast to the typical
white color of extracted pellets.
Pilot testing has shown that pellet softening is effective for
Brighton’s two groundwater sources and RO brine source. Pellet
softening proved to be an overall operator-friendly process
consistently meeting project goals for hardness and manganese
removal in multiple sources tested.
Katie Hicks is an Environmental Engineer at Brown
and Caldwell, specializing in buried infrastructure and
drinking water treatment. She is a pilot operator of the
City of Brighton pilot study program.
Steven Shiokari is an Environmental Engineer at
Brown and Caldwell with expertise in bench and pilot
testing for water treatment and design, and a lead pilot
operator for the City of Brighton program.
Laurie Sullivan is a national expert in water treatment
piloting and processes for Brown and Caldwell and led
the technical process evaluation and pilot testing to assist
the City of Brighton in selecting a robust treatment pro-cess
to meet both current and future regulations.
FEATURE
ROCKY MOUNTAIN WATER SEPTEMBER 2020 | 17
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