# Optimized Dissolved Oxygen Fuzzy Control for Recombinant _Escherichia coli_ Cultivations
## 5 Conclusions  
The findings have shown the feasibility of applying fuzzy reasoning for DOC control in a bioreactor. Regarding the classical control strategies-based on complex equations and mathematical modeling-fuzzy logic overcame the high DOC non-linearity by translating the expert's knowledge into a linguistic, rule-based controller. Moreover, from its concept up till its operation, the fuzzy controller proved to be less complicated than the classical strategies. With few selected input and output variables and cultivation data, the optimized fuzzy controller proved to be robust (regarding its parameters) and adaptable (as modifications could be easily performed during the implementation step in the SUPERSYS_HCDC software). Simulation results have shown smoother behavior of the manipulated variables (air and oxygen flow rates) compared with the previous controller (decision tree), leading to an attenuation of DOC peaks. These findings were confirmed based on _E. coli_ cultivations results. Furthermore, experimental QairVar and QO2 Var range values were close to the simulation results, with mild adjustments during the experiments, proving the robustness of the fuzzy controller parameters.  
Overall, the results lead not only to an increase in the flow meter lifespan (due to its sensitivity to abrupt oscillations in air and oxygen flow rates) but also point toward a possible reduction in the metabolic stress suffered by the _E. coli_, given its sensitivity to oscillations in dissolved oxygen concentration. Further investigations, based on this new strategy of DOC control, can lead to a productivity increase and cost reduction in microorganism cultivations.  
Computation-wise, the fuzzy controller proved to be flexible, as it was implemented in two wide-known types of programming software (MATLAB and LabVIEW). In addition, the fuzzy controller is an important update in the SUPERSYS_HDCD program that could  
Figure 10: _E. coli_ cultivation tests results. Fuzzy controller was activated around the 10 th h. Cell mass, carbon source consumption and acetic acid production during the cultivation (**a**), dynamics of air (**b**) and oxygen (**c**) flow rates, dissolved oxygen behavior (**d**), and experimental adjustment in limits for QairVar and QO2 Var (**e**) during the _E. coli_ cultivation test.  
benefit different research studies on microorganism cultivation. Although fuzzy reasoning applicability has been proven successful in different fields, its implementation on bioreactor control is still timid. This work is one of the few recent attempts to readdress DOC control issues in bioreactors, an area that requires different solutions for complex problems.  
Conceptualization, R.A.A. and R.d.S.J.; methodology, R.A.A., A.C.L.H. and R.d.S.J.; software, R.A.A. and R.d.S.J.; validation, R.A.A., M.L.H., A.C.L.H. and R.d.S.J.; formal analysis, R.A.A. and R.d.S.J.; investigation, R.A.A., M.L.H., A.C.L.H. and R.d.S.J.; resources, A.C.L.H. and R.d.S.J.; data curation, R.A.A. and A.C.L.H.; writing--original draft preparation, R.A.A.; writing--review and editing, R.A.A., A.C.L.H. and R.d.S.J.; visualization, R.A.A. and R.d.S.J.; supervision, R.d.S.J.; project administration, R.d.S.J.; funding acquisition, A.C.L.H. and R.d.S.J. All authors have read and agreed to the published version of the manuscript.  
This study was financed in part by the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior-Brasil (CAPES)-Finance Code 001. Authors would also like to thank CNPq and FAPESP.  
The authors declare no conflict of interest.