Gas equilibrium regulation by closed-loop photo bioreactor built on system dynamics, fuzzy inference system and computer simulation

• Microalgae were used as bioregenerative tool of gases equilibrium control in BLSS.
• Developing a valid mathematical model of photo bioreactor (PBR) by system dynamics.
• Closed-loop PBR with fuzzy logic controller is designed by digital simulation.
• Real-time simulation is conducted for validation, verification and accreditation.
• Closed-loop PBR could enhance the safety and reliability of BLSS on space mission.

It is vitally important to robustly stabilize gases (O2 and CO2) concentrations in the Bioregenerative Life Support System at nominal levels on space mission. The blue algae, Spirulina platensis, having special advantages of high growth rate, controllability and metabolism flexibility were therefore utilized to maintain gas equilibrium. In our research, photo bioreactor (PBR) cultivating S. platensis was built for investigation on effective design and optimization of advanced PBR. Firstly, a mathematical model expressed in terms of a set of parameterized nonlinear first-order differential equations for sufficient description of inner structure and processes of PBR was developed by system dynamics based on related mechanisms and experimental data. Secondly, a fuzzy inference system (FIS) was constructed and used as feedback fuzzy logic controller (FLC) of PBR. Finally, the parameters in PBR model and member functions were optimally specified by a predetermined response curve. The results demonstrated that FIS–FLC could effectively control and regulate the system’s inputs, light intensity and flow rate of air in aerating pipe, to robustly stabilize the system’s output at a target O2 /CO2 ratio of 214 in the gas phase of PBR with satisfactory dynamic process.