The food waste digesting AD sector is under pressure to reduce the level of plastics in their digestate before it can be used for land spreading. The annual disposal cost for plastic ‘screening’ waste - waste that has been through a trommel, or rotary, screen to separate materials - is £1m for Scotland alone.

Syngas, or synthesis gas, is a fuel gas mixture consisting primarily of hydrogen, carbon monoxide, and very often some carbon dioxide.

Biomethanisation is a process by which a natural selection of microorganisms decompose organic matter through anaerobic digestion.

Challenge

Owners of food waste AD plants are looking for alternative ways to valorise waste that contains both plastic and biobased substances. Carbogenics wanted to investigate whether fermentation from screening waste was possible and test a scaled-up version of their process for making biomethane from waste using bacteria.

Solution

With IBioIC funding, Carbogenics worked with Andrew Free and Leah Herrgen of the University of Edinburgh to see if Carbogenics’ new syngas fermentation technology could unlock the conversion of screening waste using pyrolysis and subsequent syngas biomethanisation, and if the new process reduced the build up of toxic gases and promote bacterial growth.

Carbogenics contributed expertise and equipment for syngas fermentation, chemical analysis and evaluation of the system and the University of Edinburgh group carried out analyses to determine the key microbial species and metabolic pathways important to the process.

The team trialled syngas fermentation in 3L reactors. The system was tested with technical and native syngas and samples were taken throughout the trial for gas and chemical analysis. Metagenomics was carried out on the fermentation using native syngas to identify which microbial communities were present and the performance parameters of the fermentation.

Outcome

The project showed that fermentation from screening waste derived syngas is principally possible. For Carbogenics this is an important milestone towards commercialisation.

Dr Free had the opportunity to work with syngas-fermenting microbial communities. It has opened the door to future collaborations in optimising the performance and delivery of such communities into anaerobic digestion systems.