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Water Treatment Plant Piloting

Saint Johnsbury, VT

The Town of St. Johnsbury water system is supplied by a surface water source that is treated by Trident® clarifier/filters.  The clarifier/filter tanks were installed in 1990 and have not been repainted since installation.  The tanks have deteriorated due to corrosion and needed replacement.


The St. Johnsbury Water Treatment Plant Piloting project was done in conjunction with the State of Vermont Department of Environmental Conservation, Drinking Water and Groundwater Protection Division (DWGWPD) in order to determine possible alternatives for rehabilitating or replacing the severely corroded Trident® clarifier/filter tanks.


A Preliminary Engineering Report was completed with the recommendation of ultrafiltration membranes to replace the existing clarifier/filters.  Due to the condition of the existing tanks and in the interest of time, a pre-selection proposal process was completed to identify the manufacturer that would pilot their ultrafiltration membrane system.  A pilot unit from Suez Water Technologies & Solutions was chosen, and through testing it was found that the pilot unit performed as well as, if not better than, the existing Trident® unit in all the areas of analysis. 


This Pilot study was performed over the course of approximately 115 days.  Testing was done both on-site and in a certified laboratory.  On-site operational testing included temperature, total manganese, turbidity, and pH.  Laboratory testing included total iron, total organic carbon, and trihalomethane and haloacetic acid formation potential.

Key Features

  • This will be the first ultrafiltration membrane system serving a Public water supply in Vermont

  • A membrane manufacturer pre-selection process was utilized

  • The originally planned acid for cleaning the membranes, hydrochloric acid, was evaluated and replaced with sulfuric acid to improve operator safety

  • Eight different coagulants along with raw water only were evaluated under different pre-treatment conditions to determine operational and performance effects and identify final design parameters and sizing

Chad Whitehead, Town Manager
51 Depot Square, Suite 3
St. Johnsbury, VT 05819
Phone: 802.748.3926

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