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To decrease consumable usage by current physico-chemical (P/C) air Trace Contaminant Control Systems (TCCS), there is an increased focus on developing regenerative TCCS technologies for long duration missions. This potentially includes reducing the need for disposable activated charcoal canisters (which pre-treat air prior to thermal catalytic treatment) as well as decreasing catalyst regeneration/replacement from eventual (and predictable) poisoning. Biofiltration is a low-energy, bio-regenerative air treatment technology capable of removing a variety of air contaminants and may substantially reduce loading to subsequent P/C TCCS components, thereby decreasing consumable usage. The design, operation and integration of biofilters are tightly coupled with waste stream characteristics. In particular, the inlet gas carbon to nitrogen ratio (C:N) will directly affect whether the system eventually becomes limited through nitrogen depletion or excess.

Composting is a biological solid waste treatment technology with potential use in the management of organic solid wastes generated within advanced life support (ALS) systems, such as planetary bases with extensive plant production. Composting can serve to decrease mass, volume and water content, as well as stabilize and sanitize waste materials. Composting may also serve as a pre-treatment system prior to aqueous extraction (for nutrient recovery) or incineration. Additionally, the compost produced may serve as a nutrient-rich plant growth substrate. Each of these treatment objectives exerts different compost quality requirements. It is necessary to accurately determine the processing time required for the specified treatment objectives prior to system design and analysis. For example, waste stabilization will require less processing time than production of composts suitable for plant growth.

Distant and/or long-term missions, particularly Mars and lunar bases, will require a high degree of regenerative systems utilization. Bio-regenerative systems inherently lend themselves to integrative application, and can serve multiple processing functions in Advanced Life Support (ALS) systems. Striving for maximal use of bio-regenerative systems can reveal possibilities and relationships difficult to conceptualize within the context of a “unit process” methodology common to physico-chemical (P/C) systems. The required regenerative functions of biomass production and solid, liquid, and air processing are discussed, and a potential integrated ALS system scenario including “soil'based” plant production is developed to illustrate potential ramifications of biological (and P/C) system integration.

The use of biofilters for the control of air contaminants in Advanced Life Support (ALS) systems is currently being investigated by the Waste Processing and Resource Recovery research team of the New Jersey - NSCORT (NASA Specialized Center of Research and Training). Ammonia (NH3) was selected as a test air contaminant as it presents special challenges to the sustained operation of a biofilter. Ammonia loading to the ALS atmosphere will likely be from waste treatment (biological treatment of human, plant and food wastes) and food processing operations. This NH3 has the potential of causing adverse effects on plant growth and humans.

A current study is investigating the feasibility of using air treatment biofilters to remove ethylene from atmospheres of Advanced Life Support (ALS) systems for spacecraft or planetary habitat environments. Ethylene was selected as the contaminant because: 1) it partitions poorly in water, thus challenging the limits of biofilter performance; and 2) it is a plant growth regulator that can adversely affect plant growth even at concentrations as low as 40 parts per billion (ppb). Thus control of ethylene in a biomass production chamber (BPC) is of direct concern. In laboratory scale studies ethylene was removed from air to below a target level of 20 ppb, with 4 ppb being the lowest exit concentration observed. This performance (<20 ppb) was observed for 12 days, with exit concentrations gradually increasing to 70 - 100 ppb by day 55. The decreased level of performance was apparently due to nutrient (nitrogen) limitation.

Biological treatment technologies used in removing air pollutants are reviewed from the perspective of an Advanced Life Support System (ALSS). These are based on the capability of microbial communities to biodegrade complex and variable mixtures of organic and inorganic compounds, typically to innocuous end products. The technologies considered are biofilters, biotrickling filters and bioscrubbers, with emphasis on biofilters. Theoretical design aspects are outlined. Different bed media (matrices) are described. A list of compounds treated successfully, solely or in complex mixtures, is provided. A brief summary of our current research on the removal of ethylene and ammonia (model compounds) through biofiltration is included.