Methane yield from SS-AD: Experiences to learn by a full spectrum analysis at laboratory-, pilot- and full-scale

Solid-state anaerobic digestion (SS-AD) takes place when solid content of the substrate is higher than 15%. Some advantages of this technology have been recognized as e.g., less required water added to raw feedstock and consequently minimized digester size and cost, higher volumetric organic loading rates (OLR) that may lead to higher efficiency methane yield and better acceptance of a wide range of feedstocks. However, scientific studies of SS-AD at pilot- and full-scale are very few and difficulties have been reported in operating SS-AD, especially when the system undergoes a scale-up, where methane production is the purpose. As a result, this review gives a summary of scientific studies for SS-AD processes at laboratory-, pilot- and full-scale, where a great diversity of substrate composition, reactor design and operational parameters have been categorized, and their performances in terms of methane yield have been analyzed. This, in turn, helps to identify that factors affecting methane yields at different scales arise mainly from operational conditions as well as the characteristic of feedstocks. This review even contributes to suggest several strategies for improvement of methane yield at full-scale.