Description:

Figure 4-50b Typical Filtration System

Figure 4-50c: Typical Freeze Crystallization System

Figure 4-50d Typical Membrane Pervaporation/Reverse Osmosis System  

Separation processes seek to detach contaminants from their medium (i.e., ground water and/or binding material that contain them). Ex situ separation of waste stream can be performed by many processes: (1) distillation, (2) filtration/ultrafiltration/microfiltration, (3) freeze crystallization, (4) membrane pervaporation and (5) reverse osmosis.

Distillation

Distillation is a chemical separations process involving vaporization and condensation that is used to separate components of varying vapor pressures (volatilities) in a liquid or gas stream. Simple distillation involves a single stage operation in which heat is applied to a liquid mixture in a still, causing a portion of the liquid to vaporize. These vapors are subsequently cooled and condensed producing a liquid product called distillate or overhead product. The distillate is enriched with the higher volatility components. Conversely, the mixture remaining in the still is enriched with the less volatile components. This mixture is called the bottoms product. Multiple staging is utilized in most commercial distillation operations to obtain better separation of organic components than is possible in a single evaporation and condensation stage.

Filtration/Ultrafiltration/Microfiltration

Filtration is the physical process of mechanical separation based on particle size whereby particles suspended in a fluid are separated by forcing the fluid through a porous medium. As fluid passes through the medium, the suspended particles are trapped on the surface of the medium and/or within the body of the medium. Ultrafiltration/ microfiltration occurs when particles are separated by forcing fluid through a semipermeable membrane. Only the particles whose size are smaller than the openings of the membrane are allowed to flow through.

Freeze Crystallization

Freeze crystallization processes removes purified solvent from solution as frozen crystals. When a solution containing dissolved contaminants is slowly frozen, water ice crystals form on the surface, and the contaminants are concentrated in the remaining solution (called "mother liquor"). The ice crystals can be separated from the mother liquor, washed and melted to yield a nearly pure water stream. The contaminated waste stream, mother liquor, and any precipitated solids, are generally more amenable to subsequent treatment by conventional destruction and stabilization technologies due to the higher concentrations.

Membrane Pervaporation

Membrane pervaporation is a process that uses permeable membranes that preferentially adsorb volatile organic compounds (VOCs) from contaminated water. Contaminated water first passes through a heat exchanger, raising the water temperature. The heated water then enters the pervaporation module, containing membranes composed of a nonporous organophilic polymer, similar to silicone rubber, formed into capillary fibers. VOCs diffuse by vacuum from the membrane-water interface through the membrane wall. Treated water exits the pervaporation module, while the organic vapors travel from the module to a condenser where they return to the liquid phase. The condensed organic materials represent only a fraction of the initial wastewater volume and may be subsequently disposed of at a cost savings.

Reverse Osmosis

The membrane pervaporation process can be modified by using reverse osmosis. In reverse osmosis water is forced through the pervaporation module under pressure. The module containing the membrane(s), of which there are many types depending on the application, allows water free of contaminants to pass through. The water containing the contaminants that were not able to pass through the membrane is recirculated back to the pervaporation module for further treatment, where the organic vapors (called permeate) are extracted by vacuum, condensed and vented downstream of the condenser, thus minimizing air releases.

Synonyms:

NA

Applicability:

Limitations:

• Membrane pervaporation and freeze crystallization are limited to only aqueous waste streams.
• The presence of oil and grease contaminants may interfere with these processes by decreasing flow rate.
• Space must be adequate for distillation and freeze crystallization treatment systems. Distillation units are comparatively tall and can cover large areas.
• Compounds that decompose or polymerize at the operating temperature and are explosive are not desirable in distillation.
• In freeze crystallization, eutectic mixtures form as solutions become more concentrated; feed stream must be dilute enough to accomplish significant volume reduction before a eutectic mixture forms.

Data Needs:

Performance Data:

A pilot-plant was evaluated using membrane pervaporation at Wastewater Technology Centre (WTC) by ZENON Environmental Inc. and field tested in 1992. The technology had a removal efficiency of 99 percent. A cost comparison performed in 1992 by WTC and ZENON showed that pervaporation can be competitive with air stripping and activated carbon to treat low VOC concentrations.

Cost:

Additional cost information can be found in the Hazardous, Toxic, and Radioactive Wastes (HTRW) Historical Cost Analysis System (HCAS) developed by Environmental Historical Cost Committee of Interagency Cost Estimation Group.

References:

Innovative Remediation Technologies:  Field Scale Demonstration Project in North America, 2nd Edition

Abstracts of Remediation Case Studies, Volume 4, June 2000, EPA 542-R-00-006

Guide to Documenting and Managing Cost and Performance Information for Remediation Projects - Revised Version, October, 1998, EPA 542-B-98-007

Canning, P. and Chris L., 1995. "Cross-flow Pervaporation System", Zenon Environmental Inc.

EPA, 1990. Dupont/Oberlin Microfiltration System, series includes Technology Evaluation, EPA/540/5-90/007, PB92-153410; Applications Analysis, EPA/ 540/A5-90/007; Technology Demonstration Summary, EPA/540/S5-90/007; and Demonstration Bulletin, EPA/540/M5-90/007.

EPA, 1990. Innovative and Alternative Technology Assessment Manual, EPA, Office of Water Program Operations, EPA/430/9-78/009.

EPA, 1992. Atomic Energy of Canada Limited Chemical Treatment and Ultrafiltration, Emerging Technology Bulletin, EPA/540/F-92/002.

EPA, 1992. SBP Technologies-Membrane Filtration, Demonstration Bulletin, EPA/540/MR-92/014; and Applications Analysis, EPA/540/AR-92/014.

EPA, 1993. Microfiltration Technology EPOC Water, Inc., Demonstration Bulletin, EPA/540/MR-93/513.

Federal Remediation Technologies Roundtable, 1998. Remediation Case Studies: Innovative Groundwater Treatment Technologies, EPA/542/R-98/015.

• PerVap™ Membrane Separation Groundwater Treatment at DOE's Pinellas Northeast Site, Largo, Florida

Turner, R., 1995. "Update on Zenon Pervaporation", Ground Water Currents, Issue No.13.

• Wastewater Technology Center
• EPA & DOE Demo Rocky Flats Facility, CO
• EPA Demo American Creosote Works, FL
• DOI Demo Birmingham, AL; Manassas, VA
• DOI Demo Bureau of Mines and USAEC (Cooperative effort) Buffalo, NY
• EPA SITE Demo Selma Pressure Treating Selma, CA
• DOE Integrated Demo,4 DOE sites:
  (1) Hanford
  (2) Fernald, ID
  (3) Oak Ridge
  (4) Savannah River
• DOI, Army, EPA Demo Saginaw Bay Confined Disposal Facility, MI; Toronto, Canada
• EPA Demo Palmerton Zinc Superfund Site, PA
• Naval Air Station North Island, San Diego, CA
• DOE's Pinellas Northeast Site, Largo, FL (PerVap Membrane Separation)
• 

General FRTR Agency Contacts

Government Web Sites

Non Government Web Sites

A list of vendors offering Ex Situ Physical/Chemical Water Treatment is available from  EPA REACH IT which combines information from three established EPA databases, the Vendor Information System for Innovative Treatment Technologies (VISITT), the Vendor Field Analytical and Characterization Technologies System (Vendor FACTS), and the Innovative Treatment Technologies (ITT), to give users access to comprehensive information about treatment and characterization technologies and their applications.

Government Disclaimer

Hazard Analysis