Pretreatment of Lignocellulosic Materials to Enhance their Methane Potential

Lignocellulosic materials (LMs) are the most abundant residues on the planet and have a huge potential for methane production. Several strategies have been tested to enhance the methane potential of LMs, with a particular emphasis on environmentally friendly and economically convenient pretreatments. This chapter revisits the potential of two chemical, i.e. organosolv and N-methylmorpholine N-oxide (NMMO)-driven, and one physical, i.e. ultrasounds, pretreatments. Organosolv pretreatment enables to obtain a pure lignin fraction from LMs, leaving most of the fermentable sugars in the solid matrix. The result is a lignin-poor material with an increased porosity and a higher bioavailability of the sugar fraction. Another advantage is the cost-effectiveness and the easy recovery of the chemicals involved. NMMO pretreatment focuses on the cellulosic component of the biomass, aiming to reduce its crystallinity and to increase the porosity of the substrate. The main advantage of NMMO lies in its high recovery percentage, which reaches up to 99%. Ultrasound pretreatment involves ultrasonic waves that allow fractionating LMs, breaking the linkages between lignin, cellulose and hemicellulose, generally leaving cellulose and most of the hemicellulose in the solid fraction and dissolving the lignin in the liquor. Ultrasound pretreatment does not require chemicals and can be easily combined with other pretreatment methods to enhance its effectiveness.