Processes and systems to produce renewable energy and fiber from cellulose-rich waste materials

Abstract

Some variations provide a process to produce renewable biogas and cellulosic fiber from a cellulose-rich feedstock, comprising: obtaining a cellulose-rich feedstock that is reduced in concentration of impurities and has a length less than 5 inches; feeding the cellulose-rich feedstock and water to a vacuum steam-explosion vessel, thereby generating a first cellulose-rich intermediate stream; feeding the cellulose-rich intermediate stream to a secondary separation vessel to remove remaining impurities, thereby generating a second cellulose-rich intermediate stream; feeding the second cellulose-rich intermediate stream to an enzymatic-hydrolysis vessel to convert the second cellulose-rich intermediate stream to low-viscosity cellulosic fibers comprising cellulose oligomers; feeding the low-viscosity cellulosic fibers to an anaerobic digester, thereby generating a biogas stream and residual fiber; optionally, recycling residual fiber to the enzymatic-hydrolysis vessel and/or to the anaerobic digester; and recovering some or all of the residual cellulosic fiber from the solid stream as a co-product.