Engineering Technical Support Center (ETSC)
Biological Technologies ¹
Biological treatments are referred to as bioremedial approaches because they heal with life. The living organisms that heal are either microorganisms (algae, fungi, bacteria), or plants and trees (vegetation). Some plants absorb and store chemicals or metals in their cells or tissues, known as bioaccumulation.
- Physical/Chemical Technologies
- Thermal Technologies
Table of Contents
- Biochemical Reactor
- Evapotranspiration Cover
- Monitored Natural Attenuation
- Biochemical Dehalogenation
Phytoremediation means to heal with plants. Plants are useful if they successfully remove hazardous substances through their roots, increase biological activity around their roots, break down contaminants, or change the soil's chemical balance to restrain contaminants. A plant's ability to remove harmful substances largely depends upon how far below the surface its roots penetrate relative to the depth of the contamination.
A biochemical reactor, an Engineering Technical Support Center (ETSC)
emerging technology, relies on the constant interchange between chemical and biological processes.
Sulfate-reducing bacteria create basic sulfide species, which mix with free metals
to precipitate metal sulfides. The gas from this process may be captured, while the
precipitates settle into a less mobile sludge.
Advances in this technology show hope for the recovery of metals, like iron, from the sludge.
Conceptually, this system discharges clean water,
turns a liability into an asset, and is self-sustaining (passive).
ETSC staff evaluated solid substrate-free bioreactor treatment of aluminum, copper, iron, nickel, selenium and zinc in acid rock drainage from the Aspen Seep of the Leviathan Mine Superfund site. Compost-Free Bioreactor Treatment of Acid Rock Drainage, Leviathan Mine, California (PDF) (93 pp, 4.2M, EPA/540/R-06/009, Abstract) summarizes the research conducted from 2003-2005.
An evapotranspiration cover uses plants and soil to capture rainfall to later return it to the atmosphere by evaporation and transpiration, which prevents that moisture from reaching a contaminated area. Alternative Covers Assessment Program (ACAP)
This is a passive technique to track and observe pollutant levels without direct intervention. Technicians install and use monitoring systems to ensure that natural processes effectively control pollution levels.
Bioventing enhances the microbial degradation of subsurface contaminants by introducing a gas into the subsurface. Aerobic bioventing delivers oxygen through a gas delivery system, while an anaerobic system utilizes hydrogen and carbon dioxide.
Biochemical dehalogenation treats waste that cannot be alternatively broken down (recalcitrant waste) by both biological processes and chlorine. Since most organisms cannot thrive around chlorine, engineers carefully analyze and balance the biological and chemical characteristics of the area to be treated.
¹ Adapted from "In Situ Treatment Technologies for Contaminated Soil," (PDF) (35 pp, 939K, EPA/542/F-06/013).
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