During long duration human space missions the re-supply of food and water from Earth is restricted. The presence of a life support system, which enables the regeneration of oxygen, recycling of water and processing of waste streams, is therefore essential. In this context ESA designed MELiSSA, a bioregenerative life support system for the complete recycling of gas, liquid and solid waste products. This nutrient recycle system consists of a sequence of compartments

A major challenge, at this moment, for the MELiSSA loop is closing the carbon cycle, by completely oxidizing the carbon in the organic waste and non-edible parts of the plant into CO2 for the higher plants and algae to fix again and thus to produce food. A wide range of physical, chemical and biological processes has be been tested. However, the oxidation of fibrous material (mainly cellulose, lignin
and hemicellulose) remains challenging. In the fermentation step (CI) operated as a membrane bioreactor to improve biodegradation, the fibre degradation efficiency is only between 15-30%. With the help of high temperature and pressure, sub-or near critical water conditions proved to be promising for degradation of fibrous material. The addition of an oxidant (hydrogen peroxide, H2O2) under sub-or near critical conditions further enhanced the oxidation to CO2. In this project, the aim is to demonstrate that sub-, near-or supercritical oxidative water conditions are able to convert organic compounds completely into CO2.