Biogas Plant – Anerobic Digestion July 2015

We were asked to advise on a biogas plant where the off gases from the anaerobic digestion of greenwaste were being used to generate electricity.

According to Environment Agency Best Practice biofiltration is the preferred method of air treatment for greenwaste reception halls.The client was looking to replace the media in their existing biofilter with lava rock, as they wanted to benefit from the reduced whole life cost offered by the extended lifespan of lava rock.

The parameters of the gas to be treated were as follows:

  • Air flow volume: 46,000m3/hr
  • Air temperature: 20oC
  • Air humidity: 12g/kg dry air
  • Ammonia levels: 6-11 mg/m3
  • Hydrogen Sulphide levels: 100ppm

After meeting with the client the following was agreed upon:

For 46,000 m3/h flow rate they required a media volume of approximately 440m3.

Given the dimensions of the existing tank (surface area of 220m2) a media depth of 2.0m was agreed upon and therefore an approach velocity of 209m/h.

The empty bed contact time (EBCT) we recommended was 34 seconds.

The air to be treated was at 20oC and at this temperature we suggested an irrigation system would be required delivering 12-15 litres per m2 per hour across the bed.

After the client instigated the above and we supplied the corresponding quantity of our lava rock media we achieved removal rates of between 95% – 98% for ammonia and hydrogen sulphide.

For more information regarding our Pumice Odour Control Media or its benefits in anerobic  digestion please contact our Chief Process Engineer at