Tray-based air strippers inside Cheyenne's groundwater treatment plant reduce TCE levels to below 2ppb.Two recent projects involved stripping trichloroethylene (TCE) from groundwater so the water could be used for drinking. A low-profile tray-based air stripping system was used in the projects.
The air stripping process is governed by Henry's Law. The Henry's Law constant (H) of any dissolved contaminant can be used to predict how effectively that contaminant will be driven from the water into the air. Some contaminants are easier to strip than others, for instance, vinyl chloride strips easily, benzene less so, and MTBE is relatively difficult to strip. A pilot test may be required to determine the expected level of stripping if the mixture entering the air stripper contains free-phase organics, or non-volatile, polar organic chemicals since these contaminants impact H values for the full range of VOCs present in wastewater. Temperature also affects the stripping process – higher water temperature increases stripping.
Case Studies
The U.S. Army Corps of Engineers (USACE) – Omaha District has funded the design and construction of a new groundwater treatment plant in Cheyenne, WY, to treat groundwater from the city's Borie well field. This important groundwater supply was apparently contaminated with trichloroethylene in the late 1960s at the Former F.E. Warren Atlas Missile Site 4.
The new facility was designed, constructed and placed into long-term automatic operations by Boise, Idaho-based firm McMillen, LLC. The company selected a tray-based air stripper system offered by QED Environmental. The low-profile system was incorporated into the city's existing well field hydraulic profile at a location where repumping of the water was not required.
A total of four, 6-level E-Z Tray® Air Strippers, each with a treatment capacity of 1,000 gpm, were used in McMillen's design to insure that the TCE treatment goal of less than 2 ppb could be reached without pretreatment.
Matt Moughamian, McMillen's project manager, said the tray units chosen for the Cheyenne treatment facility have more than enough capacity to handle the city water's contamination load, "and there have been no issues so far."
In October 2011, the Cedarburg, WI, Light and Water Utility installed a similar system in a discreet addition to its existing production pump building. The E-Z Tray 72.6 with 4-stage trays handles a flow rate of 600 gpm and treats groundwater containing vinyl chloride that has been traced back to a nearby landfill. The current influent into the air stripper is drinking water with less than 1 ppb of vinyl chloride, and the goal is complete removal.
