Characterization of biochars produced from residues from biogas production

• Residues from biogas production (RBP) were pyrolyzed at a different temperatures.
• Physico-chemical properties of biochars were determined.
• The origin of RBP has a significant effect on the properties and quality of biochar.

In the present study an evaluation of the properties of biochars produced from residues from biogas production (RBP) at a temperature range of 400–800 °C was investigated. RBP originated from three different biogas plants using different biogas production methods. Physico-chemical properties (pH, electrical conductivity – EC, elemental composition – CHN, the X-ray fluorescence – XRF, X-ray diffractometer – XRD, Raman spectroscopy) and surface properties (Surface area – SBET, Fourier Transform Infrared Photoacoustic Spectroscopy – FTIR-PAS) of RBP and RBP – derived biochars were studied.The values of the individual parameters were primarily dependent on the type of residue used (separated/unseparated). Furthermore, the temperature conditions (thermophilic/mesophilic) in these biogas plants and the type of substrates used for biogas production were observed to affect the specific surface area of the biochar. Generally, the pH (10.42–12.76), EC (2.91–23.80 mScm−1), ash (14.12–43.56%) and macro- and micronutrient content as well as aromaticity of the biochars increased with increasing pyrolysis temperature. For pyrolysis yield (45.27–27.16%), contribution of H (3.22–0.71), N (2.55–1.40%) and O (16.73–8.07%), O/C (polarity of the biochars), (O + N)/C mole ratios, an opposite trend was found.