Presenting the treatments
Micro-scale Anaerobic Digestion
Micro-scale anaerobic digestion
Anaerobic digestion is a succession of processes in which biodegradable material is broken down in absence of oxygen, leading to the production of biogas containing methane and of a residue called digestate. Anaerobic digestion represents an interesting treatment process for bio-waste, allowing the production of energy trough the recovery of biogas and the generation of fertilizers from the digestate.
While centralised anaerobic digestion plants are common in Europe to treat municipal bio-waste, the DECISIVE project aims at developing an eco-designed, micro-scale anaerobic digestion treatment process with the objective to propose a local, inexpensive, flexibile and easy-to manage treatment option for urban bio-waste.
Currently, micro-scale anaerobic digestion plants are widely used in rural areas in China and India, as well as in farms across Europe. To be implemented in European urban reas where winter cold can be challenging for the AD process and to comply with the European environmental and sanitary regulation, several improvements need to be brought to the process.
The micro-AD units designed by the DECISIVE projects will be coupled with Stirling motors to maximise their energy recovery and produce a local source of renewable energy.
DECISIVE’s micro-AD: first specifications
Taking into account the main technical and legal constraints linked with urban bio-waste, a preliminary study detailing the general specification of the DECISIVE micro-AD process has been led by Irstea and is now available. These specifications include:
- The choice of a solid state anaerobic digestion process, motivated by the characteristic of food-waste as core substrate and by the need to come up with a compact technology that can be implemented in areas with heavy land pressure;
- The avoidance of pre-treatment of food waste (such as storage, sorting and shredding) to ensure a compact and cost-effective solution;
- An annual capacity ranging between 50 and 200 t/yr, allowing to be operated with bio-waste from a group of housing and small commercial catering sites;
- The requirement of a hygenisation process for digestate and of a separation step to obtain a solid digestate suitable for solid state fermentation.
These specifications entail significant challenges to be overcome for the system to be implemented: clean bio-waste collected at the source with as little impurities as possible, and the need to identify a recovery route for the liquid fraction of the digestate prior to set the micro-AD unit.