Anaerobic Digestion of Fallen Leaf Biomass for Methane and Hydrogen Generation: Comparison of Single- and Two-Stage Systems

Single- and two-stage anaerobic digestion (AD) of fallen tree leaves was conducted. The AD process was preceded by mechanical, chemical, and enzymatic pretreatment. The most efficient option was the use of sulfuric acid (1%) at 121 °C for 60 min, resulting in a reducing sugar yield of 28.2 g glucose/L. The highest methane yield for single-stage AD was achieved for the 1–2 mm leaf fraction, 1.5% H₂SO₄ at 121 °C for 90 min, at 115.54 dm³ CH₄/kg VS. For two-stage AD, 10.25 dm³ H₄/kg VS and 81.24 dm³ CH₄/kg VS were achieved for the variant fraction >2 mm, 1.5% H₂SO₄, 121 °C, 60 min. The AD process can be useful for utilizing fallen leaves. Therefore, fallen leaves from trees can be used as a renewable energy source.