Objective. To optimize a nutrient medium based on fertilizers for the cultivation of Bacillus subtilis in an Airlift-type handcrafted bioreactor. Design/Methodology/Approach. Twenty-seven nutrient media, fixed by combining five factors with three levels, including sucrose, ammonium sulfate, triple superphosphate, UltraK® formula, and B. subtilis inoculum (Serenade® Max) were tested in a 50L handcrafted by the authors. The variables monitored in the media were absorbance, dissolved oxygen, pH,

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... d temperature. The first was the one that was considered for optimization as it is the indirect indicator of bacterial growth. On the statistical analysis, the option "Larger is better" was chosen for Signal/Noise for the ANOVA of the main effects according to the Taguchi method. Results. The highest level of sucrose, together with the lowest level of triple superphosphate were determinants for maximum growth of Bacillus in the time studied. On the other hand, the components such as ammonium sulfate, UltraK® formula, or the amount of inoculum were not significant, which means that they can be added from the mid to low levels. Study limitations/Implications. This new information can be scaled to bioreactors of 2500 L for B. subtilis that we have previously developed. Finding/Conclusions. Maximum bacterial growth depends on a good supply of sucrose, limiting triple superphosphate. Additionally, it is prudent to decrease additions of ammonium sulfate because it reduces dissolved oxygen in the nutrient medium.