The anaerobic digestion process can be realized simultaneously using more typologies of substrates (co-substrates): in this case, we talk about co-digestion.

The applicable co-substrates can be effluents from intensive animal breeding, agricultural residuals, bio-solids, agro-alimentary industry rejections, etc.

Co-digestion involves the use of complete mixing reactors, where the substrate is usually diluted to obtain a dry substance concentration that is between 8% and 15%. The use of co-digestion cannot be justified for higher bio-gas yields, but it results in the possibility of obtaining an extra income from the plant’s administration [2, 37, 38].