Soil-Based Biofiltration for Air Purification:Potentials for Environmental and Space LifeSupport Application

Abstract

Soil biofiltration, also known as soil bed reactor (SBR), technology was originally developed in Germany to take ad- vantage of the diversity in microbial mechanisms to control gases producing malodor in industrial processes. The ap- proach has since gained wider international acceptance and continues to see improvements to maximize microbial and process efficiency and extend the range of problematical gases for which the technology can be an effective control. We review the basic mechanisms which underlay microbial soil processes involved in air purification, advantages and limitations of the technology and the current research status of the approach. Soil biofiltration has lower capital and operating/energetic costs than conventional technologies and is well adapted to handle contaminants in moderate con- centrations. The systems can be engineered to optimize efficiency though manipulation of temperature, pH, moisture content, soil organic matter and airflow rates. Soil air biofiltration technology was modified for application in the Bio- sphere 2 project, which demonstrated in preparatory research with a number of closed system testbeds that soil could also support crop plants while also serving as soil filters with airpumps to push air through the soil. This Biosphere 2 research demonstrated in several closed system testbeds that a number of important trace gases could be kept under control and led to the engineering of the entire agricultural soil of Biosphere 2 to serve as a soil filtration unit for the facility. Soil biofiltration, coupled with food crop production, as a component of bioregenerative space life support sys- tems has the advantages of lower energy use and avoidance of the consumables required for other air purification ap- proaches. Expanding use of soil biofiltration can aid a number of environmental applications, from the mitigation of indoor air pollution, as a method of reducing global warming impact of methane (biogas), improvement of industrial air emissions and prevention of accidental release of toxic gases.