Biological desulphurisation using a conventional biotrickling scrubber is a proven technology that has been successfully used for many years to remove hydrogen sulphide (H₂S) from biogas, sewage gas and landfill gas. The process is also known as microbial desulphurisation. Other names are scrubber, bio-scrubber, bio-trickling scrubber, bio-trickling reactor, bio-bed reactor.

The H2S hydrogen sulphide-containing biogas is passed through a vessel filled with packing material. Microorganisms colonise the surface of the packing material and, in the presence of oxygen, oxidise hydrogen sulphide into elemental sulphur and sulphate.

By adding nutrients for the microorganisms and continuously circulating water, sulphur and sulphate are washed out of the system. The resulting sulphur- and sulphate-containing suspension can be discharged to the inlet of a wastewater treatment plant or, in the case of biogas plants, to the digestate storage tank.

Microorganisms of the Thiobacillus (Thiooxidans) type are used. These bacteria are chemolithotrophic and use carbon dioxide as their carbon source. They require oxygen for their metabolism, which is supplied in the form of air.

The air supply is regulated according to the biogas flow rate. For this purpose, a 4–20 mA signal from the biogas flow measurement is required. Process air is supplied by a blower whose capacity is controlled by a frequency converter.

The vessels are made of PP (polypropylene). Heating of the system is not required. Due to the low pH value of the suspension, all process piping in contact with the medium is made of PVC or PP.

The control cabinet and the complete process equipment are installed in a technical room made of PP. A separate ATEX safety shutdown system is installed outside the technical room. The gas connections of the vessels are DN 350.

A major advantage of biological desulphurisation compared with other processes, such as activated carbon filters or chemical scrubbers, is that no additional chemicals are required for H₂S removal. Only small quantities of nutrients for the microorganisms need to be added.

The system achieves an H₂S removal efficiency of 96%, reducing the H₂S concentration from 2,500 ppm to as low as 100 ppm.

Equipment

• Towers (tanks) made of acid-resistant plastic (PP)
• Acid-resistant circulation pumps
• Air blowers with non-return valves and deflagration flame arresters
• Automatic water supply
• Nutrient solution storage tank and dosing system
• Spray lances inside the vessels
• Control cabinet with measurement, control and regulation equipment
• H₂S reduction from 2,500 ppm to as low as 100 ppm