Design and Test of an Anaerobic Prototype Reactor Coupled with a Filtration Unit for the Liquefying Compartment of the MELiSSA Loop

MELiSSA or the Micro-Ecological Life Support System Alternative is a closed loop system consisting of 5 compartments in which food, water and oxygen are produced out of organic waste and carbon dioxide. In the first compartment, the organic waste material is liquefied by a thermophilic anaerobic microbial community mainly to volatile fatty acids, ammonium and CO2. Methanogenesis is inhibited. In this paper, the results obtained with testing a prototype reactor, in terms of operational performance and degradation efficiencies will be presented. An anaerobic reactor of 25L was build to demonstrate the selected design and process at prototype scale. Since only the soluble products of the biodegradation, mainly VFA and ammonium are of interest in the rest of the Melissa loop, an external ultra-filtration unit was foreseen in order to separate particles and biomass. Therefore the inoculum can be kept in the reactor and an effluent free of solids and micro-organisms can be obtained. The operation of the prototype allowed to validate and optimize the concept of the compartment. Different strategies for filtration and membrane types (organic and ceramic) were tested. It was shown that ceramic membranes working in continuous filtration under flux control was well suited for this application. Regarding the microbial process, a global efficiency for organic matter biodegradation of 65% was achieved. The dry matter content of the reactor was stabilized around 40 g/L with an average drain of 0.5% of sludge per day, implied by the solids accumulation.