Compartment III: The nitrifying compartment

This compartment is the gathering pool for the organic waste collected during mission i.e. food waste, urine, paper, the nonedible output of the higher plant compartment (straw, roots...) and the non-edible microbial biomass. Its essential task is to anaerobically transform this waste to ammonium, CO2, volatile fatty acids and minerals. For biosafety reasons, as well as degradation efficiency, the compartment operates in thermophilic conditions (i.e. 55°C). In terms of degradation, three main functions are expected in this compartment:

This compartment is responsible for the elimination of the terminal products of the liquefying compartment. In the original MELiSSA concept, it is divided into two separate and independent compartments (i.e. a photoautotrophic and an photoheterotrophic compartment). This separation was mainly due to an expectation of high H2 production from the first compartment. Although the specific treatment of hydrogen is still being kept in mind, the very wide results for substrate degradation obtained with R. rubrum lead to simplification of the loop to only one second compartment (that is, a photoheterotrophic one). Regarding the past researches on this compartment, they are driven by two major factors:the demonstration of the validity of the preliminarily established metabolism in the presence of one or several carbon sourcesthe improvement of the light transfer model

The nitrifying compartment's main function is to cycle NH4+ evolved from waste to nitrates, which is the most favourable source of nitrogen for higher plants. The compartment is composed of a mix Nitrosomas and Nitrobacter which oxidise NH4+ to NO2– and NO2– to NO3– respectively.

The fourth compartment is split into two parts:the ‘Algae’ compartment colonised by the cyanobacteria Arthrospira platensisthe Higher Plant (HP): plants that have lignin material to conduct water and minerals throughout the plantThese two compartments are essential for the regeneration of oxygen and the production of food.