Preliminary hydrothermal treatment and steam explosion of cellulosic feedstock for the subsequent biotechnological transformation: A review

   The use of renewable sources of cellulosic feedstock to produce high value-added products is a relevant issue. Cellulosic feedstock constitutes a natural matrix comprising cellulose (38–50 %), lignin (10–25 %), and hemicel-luloses (23–32 %). In order to break it down, pretreatment involving the removal of hemicelluloses and lignin is required. This process can change the chemical composition and structure of cellulose while increasing porosity. This review article provides an analysis of data on the hydrothermal treatment and steam explosion of cellulosic feedstock (sunflower straw, lawn grass, poplar sawdust, hay, reed, aspen, giant reed, silage, etc.) intended to convert it into substrates for the synthesis of biotechnological products (protein, biohydrogen, biogas, levulinic acid, methane, lactic acid, ethanol, and succinic acid). Hydrothermal treatment involves treating raw materials at 160–240 °С in water under high pressure. Pressure keeps water in a liquid state. During steam explosion, feedstock is treated with steam at a moderate temperature and pressure for a certain amount of time. Then, the pressure is rapidly released, and the fibers of cellulosic feedstock expand. The effectiveness of hydrothermal treatment and steam explosion depends both on the type of feedstock (chemical composition, solids concentration, and properties of solids) as well as on the conditions of hydrothermal treatment and steam explosion.