Study of optimal residence time for degradation of solid particles in the first compartment of MELiSSA loop

摘要

In the Micro-Ecological Life Support System Alternative (MELiSSA), the liquefying compartment is the first step in the loop; the fraction of organic wastes that can be further recycled in the loop is determined by the efficiency of liquefaction. The first compartment is colonized by mixed group of bacteria which digests wastes by anaerobic process (hydrolysis, acidogenesis) knowing that the production of methane is not favoured by low pH and high temperature. The semi-continuous feeding of solid wastes in a perfectly mixed tank leads to consider that the residence times of the different solid particles are distributed with a mean (average age of the particles) and a variance which depend on hydraulic characteristics of the reactor. In order to make the solid particles residence time a controllable variable, a solid particles-recycled reactor has been imagined and operated. However, this calls for the rationale study of the influence of solid particles residence time on global efficiency of the reactor. This is the aim of this study. A reactor (RuSiTec: Rumen Simulating Technique) operating with controlled residence time of solid particles has been designed and built. The influence of residence time and of the degradability of solid particles is tested with pure culture of a rumen bacteria, Fibrobacter succinogenes. The results show that the mean residence time of solid particle can be shortened by using this kind of device in comparison with perfectly mixed conditions. This leads to a significant reduction of the volume of the reactor maintaining the same percentage of waste degradation. Furthermore, the kinetics of waste degradation can be assessed, enabling to define digestible and recalcitrant fractions of wastes.