Community Water System
Greers Ferry, AR
Challenge
The Community Water System (CWS) in Greers Ferry, AR, provides drinking water to communities across North Central Arkansas. Its source water, Greers Ferry Lake, is one of the most pristine lakes in the United States, with an average turbidity of less than 2 NTU.
The CWS water treatment plant is a 10 million gallon per day (mgd) plant using clarification, dual media gravity filtration, and disinfection. Lake water is pumped to the plant and mixed with chemicals to improve the settleability of suspended solids before entering two cone-shaped clarification basins. From there, the water travels downstream to dual media gravity filters, and then to disinfection prior to distribution.
Greers Ferry starts with very good water, but reducing the turbidity further through clarification creates benefits for downstream processes. A lower NTU in the clarified water extends media filtration run times and reduces backwash water consumption. The CWS plant, however, is limited by available surface footprint.
Solution
In fall 2022, CWS piloted the Texler™ lamella clarifier from Xylem Leopold. The goal was to evaluate whether Texler lamella technology could help the plant increase flow capacity and reduce chemical usage.
Using a series of inclined plates (also called lamella sheets), a lamella clarifier provides a large settling area within a small footprint. The innovative Texler design uses lamella sheets made from high strength, UV resistant, NSF/ANSI/CAN 61 and 372 certified woven HDPE material. The repellant and flexible nature of the HDPE sheets prevents sludge accumulation, which reduces the need for regular cleaning compared to the traditional stainless steel plates. What’s more, the Texler design is modular and lightweight, for easy installation.
The “Big Blue” Texler pilot unit was installed at CWS in parallel to the clarification cones. “Big Blue” is a stand-alone unit with coagulation, flocculation and clarification stages, as well as all the necessary pumps, mixers, flow and turbidity instrumentation, and sludge removal equipment. It is controlled by its own independent PLC. The unit is designed to operate at a plate loading rate (PLR) of 0.3 gpm/ft2, but was operated up to 0.7 gpm/ft2 during its pilot at CWS.
Result
Over the pilot period, the Texler pilot unit delivered comparable or better effluent turbidity than the clarification cones, even when operating above the design PLR. A high plate loading rate resulted in reduced particle settling time.
Low influent turbidity like that coming from Greers Ferry Lake can make it difficult to achieve high turbidity reduction. Nevertheless, the Texler lamella clarifier was able to reduce turbidity by an average 74%.
Overall, the Texler lamella clarifier produced water of equal or better quality as the clarification cones, with a higher surface overflow rate.
