This bioscrubber technology digests hazardous organic emissions generated by soil, water, and air decontamination processes. The bioscrubber consists of a filter with an activated carbon medium that supports microbial growth. This unique medium, with increased microbial population and enhanced bioactivity, converts diluted organics into carbon dioxide, water, and other nonhazardous compounds. The filter removes biomass, supplies nutrients, and adds moisture. A pilot-scale unit with a 4-cubic-foot-per-minute capacity is being field-tested (see figure below).
In addition to efficient degradation, the bioscrubber provides an effective sink to mitigate feed fluctuations. During an 11-month bench-scale test, the bioscrubber consistently removed contaminants such as petroleum hydrocarbons, alcohols, ketones, and amines from the waste feed at levels ranging from less than 5 to 40 parts per million (ppm).
The bioscrubber provides several advantages over conventional activated carbon adsorbers. First, bioregeneration keeps the maximum adsorption capacity constantly available; thus, the mass transfer zone remains stationary and relatively short. The carbon does not require refrigeration, and the required bed length is greatly reduced, reducing capital and operating expenses. Finally, the chromatographic effect (premature desorption) common in an adsorber is eliminated because the maximum capacity is available constantly. The bioscrubber's advantages are fully exploited when the off-gas contains weakly adsorbed contaminants, such as methylene chloride, or adsorbates competing with moisture in the stream. The bioscrubber may replace activated carbon in some applications.
The bioscrubber technology removes organic contaminants in air streams from soil, water, or air decontamination processes. The technology is especially suited to treat streams containing aromatic solvents, such as benzene, toluene, and xylene, as well as alcohols, ketones, hydrocarbons, and others. The technology has several applications to Superfund sites, including (1) organic emission control for groundwater decontamination using air strippers, (2) emission control for biological treatment of ground and surface water, and (3) emission control for soil decontamination. These primary treatment processes have not been designed to prevent volatile organic compound discharges into the atmosphere. The bioscrubber is an ideal posttreatment for these processes because it handles trace organic volatiles economically and effectively.
This technology was accepted into the SITE Emerging Technology Program in July 1990. Bench-scale bioscrubbers operated continuously for more than 11 months to treat an air stream with trace concentrations of toluene at about 10 to 20 ppm. The bioscrubbers accomplished a removal efficiency of greater than 95 percent. The filter had a biodegradation efficiency 40 to 80 times greater than existing filters. The project was completed in June 1993. Based on results from the Emerging Technology Program, the bioscrubber technology was invited to participate in the SITE Demonstration Program.
Evaluation results have been published in the report "Bioscrubber for Removing Hazardous Organic Emissions from Soil, Water and Air Decontamination Processes" (EPA/540/R-93/521). This report is available from the National Technical Information Service. The Emerging Technology Bulletin (EPA/540/F-93/507) and the Emerging Technology Summary (EPA/540/SR-93/521) are available from EPA. An article was also published in the Journal of Air and Waste Management, Volume 44, March 1994, pp. 299-303.
The pilot-scale unit has also been tested on discharge from an air stripping tower at a flow rate of 2 standard cubic feet per minute. The discharge contained from less than 10 ppm up to 200 ppm toluene. The unit demonstrated the effectiveness, efficiency, and reliability of its design. Additional tests are underway to confirm results at higher flow rates and with other contaminants.
EPA PROJECT MANAGER:
Paul dePercin
U.S. EPA
National Risk Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7797
Fax: 513-569-7105
E-Mail:
dePercin.Paul@epamail.epa.gov
TECHNOLOGY DEVELOPER CONTACT:
Paul Liu
Media and Process Technology, Inc.
1155 William Pitt Way
Pittsburgh, PA 15238
412-826-3711
Fax: 412-826-3720