Conventional sulfuric acid production is tied heavily to the fossil fuel industry, where it is typically obtained from the desulfurization of fuels. Here, the biological production of sulfuric acid by Acidithiobacillus thiooxidans in a reactor setup was optimized using design of experiments methodology. The effects of initial sulfur dosage, phosphate (PO43−) concentration, and inoculum size were evaluated with respect to sulfate (SO42−) concentration, optical density, and pH. A significant effect was observed for sulfur dosage; the highest sulfur supplementation, 35 g L−1, yielded the highest SO42− concentration and lowest pH after 14 days of cultivation. A mean sulfur-to-SO42− conversion rate of 81 ± 9% was determined across all trials conducted with 35 g L− 1 of sulfur. Among all trials, a maximum SO42− molarity of 1.08 M was achieved, with a corresponding pH of 0.18. No significant effects were determined for PO43− and inoculum volume. The feasibility of using an industrial by-product as a sulfur source was demonstrated, in addition to establishing a strong correlation between the measured SO42− concentration and conductivity of the biological lixiviant. • Sulfur dosage correlated positively with SO42− concentration. • DoE revealed no significant effect for PO43− concentration and inoculum size. • Strong correlation between SO42− concentration and conductivity was established.
Frueholz et al. (Thu,) studied this question.