Method for removal of harmful sulphurous compounds from gas mixtures

A method for treating a raw gas mixture which contains harmful sulphurous compounds, comprising

• i) introducing into a first unit:
• a raw gas mixture containing harmful sulphurous compounds, and
• an acidic aqueous medium containing nitrate;
• ii) contacting in said first unit said raw gas mixture with micro-organisms capable of degrading said harmful sulphurous compounds in said aqueous medium;
• iii) passing said aqueous medium with said nitrate and said raw gas mixture through a synthetic structure comprising a biofilm of said micro-organisms for facilitating diffusion between said medium and said raw gas mixture, and allowing, under anaerobic conditions, said micro-organisms to metabolize in said aqueous medium at least part of said harmful sulphurous compounds to sulphuric acid (H2SO4) and to metabolize at least part of said nitrate into nitrite such that a gas product comprising a lower content of harmful sulphurous compounds compared to the raw gas mixture and an aqueous medium containing H2SO4 are obtained;
• iv) discharging aqueous medium containing H2SO4, said nitrite and said gas product from said first unit;
• wherein, in the acidic aqueous medium introduced into said first unit, the nitrate level is controlled at a level which is sufficient to allow conversion of at least part of said harmful sulphurous compounds to H2SO4 under said anaerobic conditions;
• v) passing said aqueous medium containing H2SO4 and nitrite from said first unit to a second unit in which, under aerobic conditions, nitrate is regenerated by an oxidation reaction of nitrite to nitrate to obtain an aqueous medium containing H2SO4 and nitrate;
• and
• vi) recycling at least part of said aqueous medium containing H2SO4 and nitrate from said second unit back to said first unit to function as said acidic aqueous medium containing nitrate of step i);
• wherein in said aqueous medium throughout the method the pH is maintained below 2.