Start up of a pre-industrial scale solid state anaerobic digestion cell for the co-treatment of animal and agricultural residues

A Pre-Industrial Scale Anaerobic Digestion Cell, working in batch mode in the Solid State (i.e. Total Solids content higher than 25% w/w) was built for the co-treatment of Animal and Agricultural Residues. The anaerobic cell has a total volume of about 170m3 and is able to treat about 95 tonnes of biomass per cycle. The aim is to perform the Anaerobic Digestion process with a high solids content to reduce, or completely eliminate, the waste liquid fraction usually produced by other types of Anaerobic Digestion technology. This could lead to the production of renewable electrical energy from animal manure and other agricultural residues in a more sustainable way. The cell was built on an existing Italian farm that raises about 135 tonnes per year of live weight swine, and also produces other agricultural residues. The problem of the starting the Anaerobic Digestion inside the cell without inoculum was analysed and different strategies were evaluated. The one based on aerobic pre-treatment of the mixture before the anaerobic process inside the cell seems to give interesting results both for the rapidity of starting the methanogens phase as well as for the quality of the biogas produced. The results show that 15 days of aerobic pre-treatment led to the production of a biogas with a biomethane concentration of about 50%v/v after 10 days of anaerobic treatment. Further, the whole anaerobic process can be considered practically finished after about 65 days.