Continuous controlled long-term operation and modeling of a closed loop connecting an air-lift photobioreactor and an animal compartment for the development of a life support system

© 2019 Elsevier B.V. The MELiSSA (MicroEcological Life Support System Alternative) project is developing a closed regenerative life support system for long-term space missions by considering the integration of six biological compartments tested in a dedicated pilot plant. The technological effort of building such a closed and sustainable ecological system can also have relevant applications for intensive circular resources reutilization at terrestrial level. In this work, the continuous operation and gas phase connection of two elements of the loop (83 L air-lift Limnospira indica photobioreactor (PBR) and a rat isolator (mock crew)) is performed and modelled. The model includes PBR hydrodynamic characterization, gas-liquid mass transfer and cyanobacteria growth, crew consumption and a control system adjusting light intensity according to oxygen demand. The model is validated in a series of tests where crew compartment oxygen setpoints are sequentially changed to test the global dynamics. The obtained results show a good model performance, as indicated in the low relative error (≤ 0.06) and the high Pearson correlation coefficient and Willmott-d-index obtained for the main variable of the system (0.98–1.00), oxygen concentration, in all cases.