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

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.