Why avoiding odour nuisance in biogas production is important 

The arrival of a biogas production unit often leads to a lot of protest among local residents, for fear of odour nuisance. In Denmark, this theme is more intense than ever. In order to guarantee a harmonious relationship with local residents, a leading builder and operator of biogas plants decided to apply purification by activated carbon at the start-up and continuous operation of each plant. 

Acute odour nuisance caused by one specific plant, led to a storm of protest in Denmark,  which had a detrimental effect on the general public opinion on biogas plants. This opposition even resulted in the postponement and cancellation of new projects. A leading player in the Danish market realised that a comprehensive, lasting solution was required to tackle the problem vigorously and to re-establish a basis for such biogas plants with local resident.

Activated carbon, a better option than biofilters and bio scrubbers for the start-up of a biogas unit 

In the past, the company had already invested in biofilters and bioscrubbers to tackle odour problems. However, these systems do not provide an adequate solution at the start-up of a biogas plant. During those first weeks, organic matter is pumped into the digesters, after which the bacteria slowly start doing their work and ensure a strong scented gas emission, influenced, among other things, by the presence of hydrogen sulphide (H₂S). Because it takes a while for biofilters and scrubbers to run at full speed, they are unable to tackle this odour problem.

For the start-up of a new biogas unit on the island of Funen, the company decided to contact Desotec and solve the odour problem by means of mobile activated carbon filters. We supplied a ready-to-use AIRCON 2000 filter on a skid and with a fan. A flexible pipe from the digester is connected to the fan, which blows the gas flow into the filter at a flow rate of 330 m³/h. Thanks to an accurate selection of the right type of activated carbon, the H₂S concentration is reduced from 1,000ppm to 0 ppm.

Full odour removal with activated carbon improves public opinion of biogas plants 

Because of the urgency of the project, Desotec had to react quickly. The mobile installation was delivered in mid-April 2019 from the head office in Roeselare and was put into operation two weeks later. It is now generating a wave of customer satisfaction, which will now apply this approach to the start-up of every new biogas plant. In addition,  the company wants to carefully define all the odour sources of biogas plants at every (new) site in the future, and also treat them with activated carbon filtration.

At DESOTEC’s facilities, all used carbon is analysed so the right measures can be taken for handling and removing the saturated carbon out of the mobile filters. All molecules that were adsorbed on the activated carbon at the customers’ site, are desorbed inside DESOTEC’s reactivation furnaces. These contaminants are then fully destroyed, in accordance with National and European legislation, by an incineration and neutralisation setup. The entire installation and it's emissions are under continuous on-line monitoring, which guarantees that only harmless water vapour is seen exiting the chimney.