Connection Between Different Compartments of the MELISSA Biological Life Support System 2001-01-2132

The MELISSA (Micro Ecological LIfe Support System Alternative) project of the European Space Agency (ESA) is a tool for the development of a simplified biological life support system. In order to achieve this purpose a loop of four interconnected bioreactors and a higher plant compartment has been designed. The target of the loop is to recycle the wastes, mainly CO₂ and organic materials, generated in a closed environment such as in manned space missions, into oxygen, water and edible material. Light is the only energy source used to reach this goal. As a part of the development of the project, a Pilot Plant laboratory has been set up. The role of this pilot plant is to demonstrate the feasibility and robustness of the Melissa concept.

In order to study the system two kinds of experiments are required. On one hand, each compartment has to be well characterized and, on the other hand, the performance of the connection between compartments has to be evaluated. Different experiments dealing with the connection between compartments II (photoheterotrophic bacteria degrading volatile fatty acids resulting from the hydrolysis of wastes), III (nitrifying bacteria transforming ammonium into nitrate) and IV (photoautotrophic bacteria Spirulina platensis providing edible material) are presented in this work.

The experiments with the interconnected bioreactors are of key importance in order to assure the satisfactory operation of the system, not only at optimal conditions but also taking into account possible deviations in the behaviour of any of them. Two different deviations from the optimal conditions in the connection of these compartments have been studied: the income of volatile fatty acids in compartment III and the income of nitrite in compartment IV. None of these two deviations produced any significant modification on the performance of these bioreactors. These results assure that the normal operation of the loop is not significantly affected by a temporal malfunction of one of its components.