Use of Sphagnum Moss As a New Growth Medium in Advanced Life Support Systems

Advanced Life Support technologies are used in regenerative life support systems to enable human flight beyond Earth’s atmosphere. On long duration missions such as the establishment of a permanent base on the Moon or Mars, humans will require a continual food, water and air supply. For these flights it is not economical or practical to re-supply elements from Earth, therefore, the development of an integrated energy efficient technology to produce food, purify water, and scrub the air is paramount. Such a technology could for example involve hydroponic systems contributing to water purification, air revitalisation and resource recovery from organic waste, all the while operating under restrictions of minimising volume, mass, energy, and labour. This research investigated the use of Sphagnum moss in a hydroponic/ resource-recovery system for this purpose.

Sphagna leaves are nerveless, lack vascular tissue and are composed of two main cells, ‘living’ narrow green cells and inflated colourless ‘dead’ cells. The enormous water holding capacity of the plant is attributed to these dead cells. Sphagnum cuspidatum was selected for this investigation, based on its resilience to nutrient and environmental fluctuations. A salad crop trial using lettuce cv.  Flandria was initiated and observed for 28 days with the sphagna as the growth medium. Five trays were set up: Rockwool control + ½ Hoagland’s; Sphagna ‘living’ + ½ Hoagland’s; Sphagna ‘dead’ + ½ Hoagland’s; Sphagna ‘living’ + Urine Simulate & Sphagna ‘dead’ + Urine Simulate.  The effectiveness of the Sphagna to buffer the lettuce against nutrient overload was measured in both the Hoagland’s and urine simulate tests. The benefit of ‘living’ Sphagna versus ‘dead’ was also determined. Microbial characterization was completed using plate counts and PCR, while elemental analysis was carried out on both the lettuce & sphagna tissue to determine nutrient concentrations.

Lettuce in all 4 test trays with Sphagna showed healthy growth and nutrient concentration within the tissue was higher than that observed in the control. The urine simulate test trays, while causing stress to the live sphagna plants, exhibited a higher nutrient load than the Hoagland’s, with some leaf burning of the lettuce evident as the trial proceeded. We found that the ‘dead’ Sphagna plants performed similar to the live Sphana, making it a suitable choice for space flight, as it can be dehydrated before flight to reduce weight and rehydrated for use.