Hydrothermal carbonization of microalgae biomass produced in agro-industrial effluent: Products, characterization and applications

Hydrothermal carbonization is a thermochemical treatment whose objective is to convert carbohydrate components of a given biomass into carbon-rich material in an aqueous medium. Biomass of wastewater grown microalgae is among the various potential biomasses for this route. However, operational parameters of hydrothermal carbonization for different types of biomass are still being investigated. In general, larger temperature ranges (180-260 degrees C) are applied to woody biomasses, which have fibrous and/or ligneous structures and, therefore, are more thermally stable than algae biomass. This study presents the hydrothermal carbonization of microalgae biomass cultivated in an agro-industrial effluent. For this purpose, a Parr reactor was operated at different temperatures (130. 150 and 170 degrees C) and retention times (10, 30 and 50 min). Results showed improvements in the properties of the hydrochar, mainly energy yield and carbon concentration, after the thermochemical treatment. Energy recovery was improved, as well as hydrophobicity of the carbonized material. It was observed that in the retention time of 10 min, the increase in temperature provided an increase of 7.53% in the yield of solids. On the other hand, in the retention times of 30 and 50 min, when the temperature was increased, the solid yield decreased 6.70% and 0.92%, respectively. Thus, the highest yield of solids (77.72%) and energy (7821%) was obtained at the temperature of 170 degrees C and retention time of 10 min. There was a high ash content in the raw biomass (32.99%) and an increase of approximately 3% in the carbonized material, regardless of the applied treatment With the exception of potassium and sodium, the other macro and micronutrients were concentrated in the hydrochar after thermochemical treatment, indicating the potential of the material for agriculture application, in addition to energy use. Results showed that the retention time was the most significant operational parameter of the process. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Hydrothermal carbonization is a thermochemical treatment method to convert carbohydrate components of biomass into carbon-rich material. This study demonstrated the hydrothermal carbonization process of microalgae biomass from agricultural effluent, showing improved properties of the hydrochar and energy recovery. The retention time was found to be the most significant operational parameter influencing the process performance.