Mushrooms may be on the menu for astronauts to Mars, thanks to a scientist at NUI Maynooth. Dick Ahlstrom reports
Freshly picked mushrooms are usually a treat, but how would you feel about them if they had been grown in human waste? Researchers hoping to send astronauts on a future mission to Mars are trying to learn how to use excrement to produce food, oxygen and clean water - with the help of the humble mushroom.
As nothing will be thrown away on the three-year flight to Mars, a team of European Space Agency researchers are developing ways to convert the waste into something useful. They have set up a pilot waste digester outside Barcelona.
Dr David Martin of NUI Maynooth's department of computer science unexpectedly became involved because of his recent PhD thesis, which was on mushrooms' ideal growing conditions.
"Mushrooms are very sensitive about their climate," says Martin. "Air conditioning for mushrooms is trickier than air conditioning for humans."
He became an expert in mushroom comfort while pursuing a Walsh Fellowship arranged by Teagasc. "My original research was on climate control for mushrooms," he says. He worked in Holland, Europe's largest mushroom producer, then Paris, studying air-control systems.
His thesis attracted the attention of the European Space Agency, which is involved in a project called Micro-Ecological Life Support Alternative, or Melissa. This complex recycling system is designed to go further than those on Mir or the International Space Station, which purify water and recycle exhaled carbon dioxide but do not attempt to recycle organic waste for food production.
The Melissa team designed a multistage processor. The first three stages use aerobic and anaerobic bacteria to break down the waste material. The fourth is meant to support algae or plants that will grow in the decomposing waste to produce food, oxygen and water, but problems arose. The waste at that stage was rich in lignin, a tough plant polymer as rugged as cellulose that resists breakdown.
Martin was immediately at home with the problem. "They needed something to biologically process lignin," he says. Mushrooms and other fungi, which you can see at work in wet and dry rot in wood, are ideal for the purpose. He was also asked about providing the best possible environment for them. "The idea is to replicate the processes of nature but at a much faster pace."
Martin is using computer simulations of bioreactor designs. He is looking at overall reactor design and the control of reactor climate, as well as advising Melissa's biological group on waste inputs and mushroom species. He has studied two species in this context: Agaricus bisporus, the familiar white mushroom, and a more exotic species, Pleurotus ostreatus, or the oyster mushroom. "That one turns out to be a better lignin processor."
Mushrooms act like humans when they are growing, taking in oxygen and releasing carbon dioxide and water vapour. "The biggest problem from a climate perspective is water vapour," says Martin. "They like it very, very wet." Yet the waste substrate on which they will grow tends to be too wet while the atmosphere in the reactor tends to be too dry. The response was to dehumidify it, to help make the substrate less soggy, but then try to bump up humidity around the growing mushrooms.
Dehumidifying is a chilling process that causes water to condense from the air, but the air is then too cold and dry to reintroduce around the mushrooms. It usually needs to be reheated and rehumidified before returning to the bioreactor.
"One of the reasons it is so difficult to control is you have three processes. It is energy- inefficient," he says.
The goal is to encourage fast growth and lignin breakdown to bring the waste further along the path of decomposition. Strange territory indeed for a computer scientist.