A controlled air stream (2) is applied to biogas contaminated with hydrogen sulfide H2S (1).

In the desulphurization tower (3) hydrogen sulfide is oxidized to sulfate and elemental sulfur by bacteria.

After H2S and moisture removal the biogas (4) is ready for utilization as energy source.

Process water (5) or digester effluent supernatant (6) is added to provide a flushing media and moist environment for the bacteria. Surplus flushing liquid (7) is discharged to sewer or digester effluent holding tank. Warm water (8) is supplied to maintain an operating temperature greater than 25°C.

Operating principle

The raw biogas stream (H2S contaminated biogas) is dosed with a controlled stream of air before entering the desulphurization tower.

The tower is filled with media providing surface area for hydrogen sulfide oxidizing bacteria. These bacteria gain energy from H2S oxidation for cell maintenance and growth.

Microbial H2S oxidation results in approx. 75% elemental sulfur and approx. 25% sulphate production.

H2S oxidation products are rinsed from the media by the flush water.

Depending on the pH value of the flush water process water or digester effluent supernatant is added on demand.

To maintain a constant flush water inventory, flush water and reaction products are drained from the tower dependent on the amount of process water added.

H2S oxidizing bacteria are present in the supernatant of the digested sludge and start growing on the desulphurization tower media with 14 to 20 days.

This process does not require any chemicals. The only input materials are electrical power, warm water, process water or digester effluent supernatant and nutrient solution.

Operating costs are insensitive to H2S content of raw biogas stream.

Plant size ranges from 250 - 2.000 m³/h with H2S content of raw biogas stream up to 10.000 ppm.

Depending on customer demand, H2S reduction in treated biogas stream in excess of 99% can be achieved.