Tarentum Water Plant
The Tarentum Water treatment plant provides drinking water to the Borough of Tarentum, PA, from the Allegheny River. While plant capacity already met the community’s needs, plant management wanted to evaluate the opportunity to achieve operational cost savings from increased plant flow. If they could double sedimentation basin capacity, they could operate the plant in two shifts, instead of three.
Having long trusted the Xylem Leopold brand for reliable filtration, Tarentum Water explored the possibility of using Leopold’s Texler™ lamella clarifier to increase clarification capacity, as it could be easily retrofitted into the plant’s existing rectangular sedimentation basins. They agreed to participate in a pilot program.
The innovative Texler design uses lamella sheets made from high strength, UV resistant, NSF/ANSI/CAN 61 and 372 certified woven HDPE material. While strong, these sheets are also lightweight for easy installation. Plus, the material’s repellant and flexible nature prevents sludge accumulation, which simplifies maintenance.
Plant and pilot design
The water treatment plant (WTP) at Tarentum currently uses four sedimentation basins for the clarification process. Before entering the basins, the source water undergoes chemical dosing to address color, odor, manganese, biological growth, and pH balance. After the chemical addition, the water passes through a three-stage coagulation and flocculation process to improve settleability. Once in the sedimentation basins, the water has a detention time of approximately eight hours. The clarified water then flows by gravity to a Leopold dual-media gravity filtration system, which produces filtrate with turbidity less than 0.02 NTU. The filtered water passes through a final disinfection and fluoride process before it is supplied to the borough.
The Texler solution was evaluated in two phases to help determine the best configuration for Tarentum. The phases utilized different plate sizes to determine the effect of the length-to-width ratio on performance. In phase one, the plates were 8 feet long by 3 feet wide; in phase two, they were 5 feet long by 3 feet wide. In both phases, the Texler pilot unit was installed within one of the plant’s existing basins, with a minimal quiescent zone. Effluent flow was controlled to provide an industry-standard plate loading rate (PLR) of 0.3 gpm/ft2.
The pilot operated 24 hours a day, seven days a week, with minimal supervision.
During the first phase of testing, May to July 2021, the Texler pilot unit provided an average turbidity reduction of 89% with an average river water turbidity of 9 NTU. The effluent turbidity from the Texler unit (0.85 NTU) was comparable to that provided by the sedimentation basin (0.88 NTU). During periods of higher river water turbidity (16 NTU), the turbidity reduction from the Texler unit reached 96%.
During the second phase, August 2021 through March 2022, the Texler design demonstrated effective performance under a variety of conditions. From August to January, when the source water had typical turbidity levels (averaging 9 NTU), the Texler lamella clarifier provided an average turbidity reduction of 91%.
During this period, the Texler unit’s average effluent turbidity (0.69 NTU) was lower than that of the sedimentation basin (1.03 NTU). It was also lower than the Texler unit’s effluent in phase one. Because the Texler unit in phase two had a lower flow rate to maintain the 0.3 gpm/ft2 PLR with the shorter plates, it also had a lower surface overflow rate (SOR), which likely contributed to the better effluent quality.
In January and February 2022, the Texler lamella clarifier proved itself under cold weather conditions. The river water temperature was 3 to 4°C (37 to 39°F), and while colder conditions adversely affect particle settling, the Texler lamella clarifier continued to provide effective turbidity reduction.
In mid-February, the Allegheny River experienced a high turbidity event, peaking at 160 NTU. Again, the Texler lamella clarifier proved resilient. The turbidity reduction was as high as 99% during this peak event.
Across all four seasons, the Texler pilot consistently matched the sedimentation basin in performance, while having higher flow rates.
Potential capacity increase
With its ability to provide effective turbidity reduction at a higher flow rate, the Texler lamella clarifier can significantly increase the Tarentum WTP’s capacity.
If Tarentum Water were to retrofit the Texler system in two of the plant’s four existing sedimentation basins (and decommission the other two basins), the plant could double its capacity from 1 mgd to 2 mgd, without any new infrastructure. The basin detention time could drop from the current eight hours to a mere two hours.
The larger quiescent zone that would be part of a largescale installation of the Texler lamella clarifier would further improve effluent quality.
Additional plant capacity, beyond the 2 mgd, would be available with a retrofit of the Texler system in the decommissioned sedimentation basins.