Optimized physical parameters for high cell density cultivation of the indigenous Thiobacillus thiooxidans by response surface methodology

In this study, response surface methodology (RSM) was employed to determine the optimal physical parameters for high cell density cultivation of the indigenous Thiobacillus thiooxidans. Optimization of four parameters (temperature, shaking rate, initial pH, and inoculum size) was attempted by using a 2⁴ full-factorial central composite design (CCD) with a statistical method for experimental design and analysis. The experimental results showed that the shaking rate had a more significant effect than the other three variables on the yield of the microorganism, and that an optimal growth level was achieved when these physical parameters were optimized by fitting a second-order polynomial model. The optimized values of the tested parameters for the maximal production of sulfuric acid were as follows: temperature = 31°C, shaking rate = 114 rpm, pH = 3.98, and inoculum size = 9.6 %. The maximal predicted yields was achieved when the cell concentration and sulfuric acid production were 0.773 g/L and 65,296 ppm, respectively.