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Innovative Membrane Removes Contaminants from Liquids

from Tech Trends June 1995

Innovative Membrane Removes Contaminants from Liquids

By Douglas Grosse, EPA National Risk Management Research Laboratory

The SITE (Superfund Innovative Technology Evaluation) Program evaluated the Disc Tube Module (DTM), developed by Rochem Separation Systems, Inc., at the Central Landfill in Johnston, Rhode Island. The DTM is an innovative membrane separation process that removes contaminants from liquid hazardous waste streams. The patented DTM can be the primary treatment for waste streams such as landfill leachate. Traditionally, membrane separation processes have been used as a secondary or polishing step in waste treatment schemes rather than as primary treatment. However, the DTM is designed to treat waste that is higher in dissolved solids' content, turbidity and contaminant levels than waste treated by conventional membrane separation processes. The patented DTM features larger feed flow channels and a higher feed flow velocity than other membrane separation systems.

Membrane material for the DTM is formed into a cushion with a porous spacer material on the inside. The membrane cushions are alternately stacked with hydraulic discs on a tension rod. The hydraulic discs support the membranes and provide flow channels to pass the feed liquid over the membranes.

After passing through the membrane material, permeate flows through permeate collection channels to a product recovery tank. A stack of cushions and discs is housed in a pressure vessel. Flanges seal the ends of the module in the pressure vessel and provide the feed water input and the product and the reject output connections. The number of discs per module, number of modules and the membrane materials can be custom designed to suit the application. Modules are typically combined in a treatment unit or stage. The DTM technology can use reverse osmosis, ultrafiltration or microfiltration membrane materials. The membranes are more permeable to water than to contaminants or impurities. The percentage of water that passes through the membranes is a function of the operating pressure, membrane type and concentration of the contaminants.

For the SITE demonstration, approximately 33,000 gallons of hazardous landfill leachate were treated by the DTM using reverse osmosis membranes. The leachate contained chlorobenzene and 1,2-dichlorobenzene at average concentrations of 21 milligrams per Liter (mg/L) and 16 mg/L, respectively, and lower levels of toluene, xylenes and ethylbenzene; total organic carbon at an average concentration of 460 mg/L; low levels of heavy metals ranging from 1.4 mg/L for barium to 48 mg/L for iron to 710 mg/L for sodium; and total dissolved solids at an average concentration of 4,900 mg/L. For treatment of this waste, a three-stage DTM process was utilized. Two stages in a series treated the landfill leachate and produced the final permeate. The third stage was a high pressure unit (HPU) which further treated the concentrate rejected by the first stage to increase the system water recovery. Media and cartridge filters were built into each unit to remove suspended particulates, and acid was added at the first stage and at the HPU for pH control.

The percentages of rejections were greater than the test criteria of: 99% for total dissolved solids; 92% for total organic carbon; and 99% for all target metals. In addition, the average percentage rejection for volatile organic compound was greater than the test criteria of 90%. The average water recovery rate for the DTM technology during the demonstration was approximately 75%, which met the test criteria.

For more information, call Doug Grosse at EPA's National Risk Management Research Laboratory at 513-569-7844. An Innovative Technology Evaluation Report, due August 1995, will present key findings from the demonstration, including complete analytical results, baseline test results and an economic analysis.


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