Start up of a pre-industrial scale Solid State Anaerobic Digestion Cell for the treatment of zootechincal and agricultural residues

A Pre-Industrial Scale Anaerobic Digestion Cell, working in batch mode at the Solid State (i.e. Total Solids content higher than 25% w/w) has been built for the co-treatment of Zootechnical and Agricultural Residues. The anaerobic cell has a gross volume of about 170m3 and is able to treat about 95 tonnes of biomass per cycle. The aim of this technology is to perform the Anaerobic Digestion process with an high solids content for reducing, or eliminate at all, the waste liquid fraction usually produced by other Anaerobic Digestion technology. This will lead to produce renewable electrical energy from Zootecnhical manure and other Agricultural Residues in a more sustainable way. The cell has been built in an existing Italian farm that breeds about 135 tonnes per year of live weight swine, producing also other residues from its agricultural activity. The problem of starting the Anaerobic Digestion inside the cell has been analyzed and different strategies have been evaluated. The one based on the aerobic pre-treatment of the mixture before anaerobic process inside the cell seems to give interesting results both for the rapidity of the methanogens phase start, and also for the quality of the biogas produced. The results shows that after 15 days of aerobic treatment, in 7 days of anaerobic treatment, the biogas rate achieves about 1.3 Nm3 per day per kg of Volatile Solids, with a methane content higher than 55% v/v.