Zero-Waste Biorefinery: Pyrolysis of Fermentation Residues into Catalytic Biochar for Circular Biohydrogen Systems

TL;DR

This paper develops a sustainable biorefinery process that converts fermentation residues into functional biochar catalysts, improving biohydrogen production efficiency and supporting circular bioeconomy goals.

Contribution

It introduces a novel pyrolysis-based upcycling method for fermentation residues, producing tailored biochar catalysts that enhance biohydrogen yields and process efficiency.

Findings

Biochar from fermentation residues increases hydrogen yield.

Pyrolysis restores porosity and tailors biochar properties.

Integrated process produces syngas, bio-oil, and biochar.

Abstract

This study presents a closed-loop biorefinery strategy that thermochemically upcycles fermentation residues (FRs) from photo-fermentative biohydrogen production (PFHP) into functional biochar catalysts, thereby enhancing the efficiency of the initial PFHP process. Four FRs derived from hydrothermal and ethylene glycol-pretreated corn stover were pyrolyzed at 700{\deg}C. Multi-model kinetic analyses revealed diffusion-controlled mechanisms with activation energies ranging from 157 to 278 kJ/mol, while thermodynamic profiling highlighted the influence of feedstock composition on reaction spontaneity and entropy. Pyrolysis effectively restored porosity compromised during fermentation, yielding biochar with tailored properties: microporous BC3 (185 m2/g) from oxygen-rich precursors and mesoporous BC4 (76.58 m2/g) from graphitized residues. When reintroduced into PFHP, BC3 maximized cumulative hydrogen yield (570 mL) via pH buffering, and BC4 achieved the highest production rate (14.91 mL/h) through electron shuttle mechanisms. The integrated process concurrently generated syngas, bio-oil, and catalytic biochar, enabling waste valorization, renewable energy output, and process enhancement within a circular bioeconomy framework.