Desulphurization of coal by using of Thiobacillus ferrooxidans and Thiobacillus thiooxidans bacteria

A new solution aiming at coal biodesulphurization has been developed based on the use of bacteria. The most frequently used species of bacteria for removal of inorganic sulphur compounds are Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Thiobacillus acidophilus. In this study the coal sample was decomposed initially and desulphurization experiments was carried out in pure and mixed cultures of Thiobacillus ferrooxidans and Thiobacillus thiooxidans. Microbial oxidation of pyrite, the main source of inorganic sulphur in coal, is a complex multistage process that the rate of this process is about 1000 times higher than that of the analogous chemical process. The achieved results of using bacteria on coal desulphurization shown when using T. thiooxidans 0.36 mmol sulphuric acid is produced without sulphur and 7.43 mmol with elementary sulphur. Amount of this acid in pure culture of T. ferrooxidans were 0.19 and 1.37 mmol respectively. Content of sulphuric acid produced by mixed cultures of bacteria were 0.92 and 7.86 mmol respectively. The sulphric acid produced by mixed cultures of T.ferrooxidans and T.thiooxidans was higher than the pure cultures of each bacterium. The optimum conditions for the highest desulphurization were shown that solid weight percent less than 3 percent, temperature 30°C to 35°C, pH =2 and the times were sixty days. The best efficiency of removing sulphur was shown on mixed cultures of T. ferrooxidans and T. thiooxidans. Studies of these kinds of microorganisms are of great economical importance and may provide a solution to the ecological problems many countries are facing.