Waste of space

3 min read

The problem of having to transport vast quantities of water and oxygen into space could be solved by a system that recycles an astronaut’s waste. Jon Excell reports

A European-developed processing plant designed for recycling human waste could be at the heart of future manned space missions to Mars and beyond, The Engineer has learned.

Inaugurated earlier this month at Barcelona’s Autonoma University, the so-called Melissa system (Micro-Ecological Life Support System Alternative) uses a suite of technologies largely borrowed from the process industry to recover food, water and oxygen from waste products, including faeces, urine, and carbon dioxide.

Partly funded by the European Space Agency (ESA), the project could get around one of the fundamental stumbling blocks to a prolonged presence in space: the problem of transporting vast quantities of water and oxygen into orbit. Melissa coordinator, ESA’s Dr Christophe Lasseur explained its potential: ‘If we want to have a long duration presence in space, life-support consumables will be a very important issue. To stay alive you need 5kg per day per person of consumables — water, food, oxygen — if you have a crew of six on a 500-day mission you will reach tonnes very easily.’ He added, that if you add non-essential but highly desirable products for washing to this mix, the amount of mass you need to lift into orbit for longer trips rapidly becomes untenable.

Lasseur explained that the current pilot plant — the result of more than 20 years of research — is effectively an artificial ecosystem.

Based on a mixture of off-the-shelf systems and technology developed specifically for the project, the facility consists of five interconnected compartments.

The first three compartments employ a number of techniques to progressively break down the waste.

In the first chamber — the liquefying compartment — a variety of bacteria are used to anaerobically transform urine, faeces and other waste to ammonium, volatile fatty acids and minerals. A complementary process oxidises the fibrous material in the waste. In the second compartment organic carbon is removed while in the third a process based on a fixed-bed reactor uses nitrosomas and nitrobacter bacteria to oxidise the ammonium to nitrites, then to nitrate. The products of these processes — CO2, nitrate, and other minerals — are pumped into a fourth compartment where, along with sunlight, they can be used to grow algae or plants to generate food, oxygen and water.

The final and fifth chamber is where the crew lives, in the case of the Melissa project a group of 40 rats whose combined oxygen consumption is, said Lasseur, roughly equivalent to a single human being.

Currently, the compartments are being tested independently, but Lasseur hopes to connect them up and close the loop within the next couple of years. Once this happens the waste generated by the ‘crew’ will then be fed back into the first chamber and the benefits of the system will become ever more apparent. Lasseur added that according to simulations the current system will recycle around 70 per cent of the waste it generates. The longer-term aim, however, is to have a 100 per cent efficient system,

While the incorporation of a full-scale Melissa system onto a spacecraft is some years away, Lasseur said that elements of the programme are already beginning to bear fruit. ‘Today we already have technology that we can use coming from the Melissa research,’ he said. Indeed, microbial detection systems developed as part of the project have already been used on the Automated Transfer Vehicle (ATV) used to supply the International Space Station. While closer to home, water treatment systems developed through Melissa are currently used to process around 1.8 million cubic metres of water a day across Europe.

The project has also led to the development of two spin-off companies: Ipstar, which is devoted to general technology transfer from the programme; and Ezcol, which is exploring the potential of a cholesterol lowering micro-organism used in Melissa.

Lasseur puts much of this success down to the multi-disciplinary nature of the team: a wide-ranging alliance of engineers, biologists, and mathematicians drawn from across industry and academia. ‘On a daily basis you will inevitably have some indirect return by bringing a large European community around the table,’ he commented.

Lasseur added that the system is very different from anything that has been attempted in the past and goes further, for instance, than recycling systems used on Mir or the International Space Station (ISS) that purify water and recycle urine and exhaled carbon dioxide. ‘Today on board the ISS they mainly recover the water condensate; around a month ago they brought a urine recycling machine, but there is nothing in terms of air and food,’ he said. The chief difference though, is that such systems are relatively piecemeal, and employ standalone units that perform specific functions. Melissa is the only project that attempts to connect all of these systems together in a closed artificial ecosystem. The closest equivalent to Melissa is the CEEF (closed ecology experiment facility) in Aomori, Japan, which is employing a similar approach not for space applications but to monitor the possible effects on ecosystems of nuclear fallout.

It’s taken the Melissa project around 20 years to get to its current stage, and Lasseur said that it may be another 20 years before the technology finds its way onto flight hardware. When it does make this leap, the scientists on the Melissa programme will have achieved something of great significance: the technology necessary to sustain human life in the depths of space.