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

A process to produce renewable biogas and cellulosic fiber from a cellulose-rich feedstock, said process comprising:

• (a) obtaining a starting cellulose-containing feedstock and removing impurities to generate a cellulose-rich feedstock that is reduced in concentration of said impurities compared to said starting cellulose-containing feedstock, wherein said impurities comprise metals, plastics, glass, dirt, sand, and grit, and wherein said cellulose-rich feedstock is characterized by an average maximum length scale less than 5 inches;
• (b) feeding said cellulose-rich feedstock and starting water to a vacuum steam-explosion vessel, wherein said cellulose-rich feedstock and said starting water are mixed within said vacuum steam-explosion vessel, wherein a rapid depressurization takes place via vacuum applied to said vacuum steam-explosion vessel, and wherein water is removed as extracted vapor out of said vacuum steam-explosion vessel via vacuum drying, thereby generating a first cellulose-rich intermediate stream;
• (c) feeding said cellulose-rich intermediate stream to a secondary separation vessel to remove at least 50 wt % of the remainder of said impurities present, thereby generating a second cellulose-rich intermediate stream;
• (d) feeding said second cellulose-rich intermediate stream to an enzymatic-hydrolysis vessel operated in the presence of cellulase enzymes to convert said second cellulose-rich intermediate stream to low-viscosity cellulosic fibers comprising cellulose oligomers;
• (e) feeding said low-viscosity cellulosic fibers to an anaerobic digester operated in the presence of microorganisms capable of fermenting said low-viscosity cellulosic fibers to biomethane, thereby generating a biogas stream comprising said biomethane and a solid stream comprising residual fiber;
• (f) optionally, recycling said residual fiber to said enzymatic-hydrolysis vessel and/or to said anaerobic digester;
• and
• (g) recovering said residual fiber from said solid stream as a co-product comprising said cellulosic fiber.