Characterization and ammonia adsorption of biochar prepared from distillers' grains anaerobic digestion residue with different pyrolysis temperatures

BACKGROUND Increasing attention is being paid to find an alternative way to handle biogas residue from biogas production which is important for sustainable development of biogas project. In this study, biochars from distillers’ grains anaerobic digestion residue (BRC) in the pyrolysis temperature range of 300 to 800 °C were prepared. Subsequently, elemental analysis, thermal stability, specific surface area (SSA), scanning electron microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and the performance of ammonia (NH4+) adsorption were studied. RESULTS BRC produced at 700 °C exhibited the highest SSA (251.47 m2 g−1). Generally, the pH (6.2-8.4), ash (17.58-36.93%), carbon (48.09-56.18%) and the NH4+ adsorption capacity (1.95-5.86 mg N g−1) of BRC increased with pyrolysis temperature increasing (300-700 °C). However, for pyrolysis yield (76.39-40.44%), volatile matter (48.72-4.69%), phenolic (0.85-0.01 mmol g−1), total acidity (1.39-0.21 mmol g−1) and the contribution of H (4.92-1.13%), O (29.41-5.76%), O/C (0.61-0.10), H/C (0.10-0.02), (O + N)/C (0.65-0.13), an opposite trend was found. CONCLUSIONS Pyrolysis temperature has a significant effect on the physicochemical properties of BRC and thus on their quantity of NH4+ adsorbed. The BRC, especially produced at 700 °C, could serve as a highly efficient material for NH4+ removal, therefore present a high value-added application for biogas residues.