Fermentative hydrogen and methane cogeneration from cassava residues: Effect of pretreatment on structural characterization and fermentation performance

• Cassava residue was pretreated by microwave (or steam)-heated acid (MHAP or SHAP).
• MHAP generated many regular micropores and SHAP generated many irregular fragments.
• SHAP generated wider cracks (∼0.2 μm) in delaminated cell walls than MHAP (∼0.1 μm).
• MHAP resulted in a higher crystallinity index (33.00) than SHAP (25.88).
• MHAP with enzymolysis led to a higher H2 yield than SHAP, but CH4 yield reversed.

The physicochemical properties of cassava residues subjected to microwave (or steam)-heated acid pretreatment (MHAP or SHAP) were comparatively investigated to improve fermentative hydrogen and methane cogeneration. The hydrogen yield from cassava residues with MHAP and enzymolysis was higher (106.2 mL/g TVS) than that with SHAP and enzymolysis (102.1 mL/g TVS), whereas the subsequent methane yields showed opposite results (75.4 and 93.2 mL/g TVS). Total energy conversion efficiency increased to 24.7%. Scanning electron microscopy images revealed MHAP generated numerous regular micropores (∼6 μm) and SHAP generated irregular fragments (∼23 μm) in the destroyed lignocellulose matrix. Transmission electron microscopy images showed SHAP generated wider cracks (∼0.2 μm) in delaminated cell walls than MHAP (∼0.1 μm). X-ray diffraction patterns indicated MHAP caused a higher crystallinity index (33.00) than SHAP (25.88), due to the deconstruction of amorphous cellulose. Fourier transform infrared spectroscopy indicated MHAP caused a higher crystallinity coefficient (1.20) than SHAP (1.12).

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