Removal of Trace Concentrations of Ethylene from Air by Biofiltration: Preliminary Results

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. No ethylene removal by the biofilter receiving air containing 1 ppm ethylene was observed, perhaps, because the loading rate was insufficient to maintain an active culture. Work is underway to further investigate these limits to enable improvement in biofilter performance.