Desulphurisation of Coal - Coal contains usually 0.2-8% sulphur, but in some cases it may exceed 11 %. Coal burning, therefore, liberates large amounts of S0₂- and S0₃ -, which dissolve in atmospheric moisture and give rise to 'acid rain'. The sulphur is present both in inorganic (iron pyrite, FeS₂) and organic forms.

Microbes can be used for desulphurisation of coal. Thiobacillus spp. may be used on pulverised coal to oxidise iron pyrite, but organic sulphur has to be oxidised using a bacterium like Sulfolobus acidocaldarius. Commercial application of this process may occur in the future.