- Total cost for pilot system - $88,728, including pre-demonstration consultation, mobilization and demobilization, monitoring, sampling and analysis, treatment, and disposal. The total cost includes $29,000 in costs for MTR who agreed to provide the pilot system and engineering services to Lockheed Martin on a fixed-price basis ($5,000 for the first month and $3,000/month for eight months)
- Cost per unit of groundwater treated during the pilot test - $0.01-0.015/gallon
- Projected cost for full-scale - capital cost of $250,000 and operating cost of $0.01/gallon.
The Pinellas Northeast site, located at the DOE Pinellas Plant in Largo, Florida, includes the East Pond and was identified as a Solid Waste Management Unit in a RCRA Facility Assessment conducted by EPA Region 4. The East Pond was excavated in 1968 and used as a borrow pit. The area was used to store construction debris and waste, including solvents, in drums and containers. In 1986 shallow groundwater at the site was determined to be contaminated with a variety of VOCs . The predominant contaminants at the site were TCE, methylene chloride, and 1,2-dichloroethene, detected at levels as high as 360,000 ppb, 1,200,000 ppb, and 58,000 ppb, respectively. Vinyl chloride and toluene were also detected at relatively high concentrations.
The groundwater pump and treat system at the site includes seven recovery wells connected to an air stripper. Effluent is discharged to a POTW. Because the aquifer is anaerobic and contains high levels of dissolved solids and iron, the extracted groundwater must be pretreated prior to the air stripper. The purpose of the demonstration was to determine if the pervaporation system would be able to treat the groundwater directly without pretreatment and would be able to concentrate contaminants in a condensate that could be recycled, thereby reducing waste disposal costs as well as air emissions.
The MTR PerVap pilot system was a self-contained, field transportable pervaporation system that had been adapted for use in removing organics from aqueous liquid streams. Contaminated groundwater, pumped into a surge tank, was passed through a cloth filter into the 50 gallon process feed tank. The pervaporation cycle, begun when the feed tank was full, consisted of pumping a 50-gallon batch of water across a heater (to raise the temperature to 50 °C), through two membranes modules in series, then back to the feed tank. A vacuum was applied across the membrane modules creating a pressure gradient to facilitate the transfer of VOCs across the membranes. The resultant vapor stream or permeate (about 1,500 ml/batch) was then cooled to condense the liquid which was then sent to a chilled permeate storage container. The treated water was discharged to a POTW. The capacity of the pilot system was 1-2 gal/min and a typical pervaporation cycle was 1-2 hours. The residuals produced by the system were filters and permeate, which were disposed of as hazardous waste, and used membranes, which were returned to MTR.
Optimal operating parameters could not be established during the demonstration. Because of membrane clogging problems caused by precipitants from the groundwater, the removal efficiencies were highly variable during the demonstration. Several groundwater pretreatment methods were evaluated an attempt to alleviate the clogging, including nitrogen blanketing, adding a chelator, adding a dispersant, and changing the pH of the water. The use of a nitrogen blanketing and the dispersant produced the best results, but were not compatible with the existing groundwater treatment system. Therefore, while cost effective pretreatment was available, the applicability is subject to site- specific constraints. In addition, the POTW discharge limit was not achieved and the water was treated using the existing groundwater treatment system.