If certain heavy metals are present in the mixture when acid is added, they can create severe downstream problems in fermentation and product formation. Batteries should not be a part of the waste stream. In this process, garbage is introduced into a large, cylindrical, horizontal autoclave that is slowly rotated on its side while steam treatment takes place. The plastic materials collapse, and the fibrous materials for a pulp. Autohydrolysis Autohydrolysis is the process of converting lignocellulose into fermentable sugars by exposure to high temperature steam.
Many lignocellulosic materials contain significant quantities of acetylated hemicellulose.
Steam releases these in the form of acetic acid which subsequently carries out a partial hydrolysis of the hemicellulosic and cellulosic sugars. Acid hydrolysis is often used as a pretreatment because it can be adapted to a wide variety of feedstocks. Use of the concentrated acid however, allows lower temperature and pressure hydrolysis with fewer byproducts produced. Hydrolysis with concentrated hydrochloric acid gives one of the highest sugar yields of any acid hydrolysis process. It is carried out at room temperature.