Structural similarity of humic substances from hydrochar obtained from vinasse and sugarcane bagasse with those of the Amazonian dark earth

Author(s)

Lucas Raimundo Bento

• Document type: Master's Dissertation
• Press: São José do Rio Preto. 2019-07-03.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências Letras e Ciências Exatas. São José do Rio Preto
• Defense date: 2019-06-26
• Advisor: Márcia Cristina Bisinoti

Abstract

Amazonian Dark Earth (ADE) is known for the higher fertility associated with the recalcitrant and reactive organic matter. It has been tried to mimic experimentally the chemical nature of the organic matter from ADE by the thermal treatment of biomass, employing the pyrolytic process and hydrothermal carbonization (HTC). Humic substances (HS) is part of soil organic matter and influences the chemical, physical and biological properties, playing an import role in the soil fertility. The main objective this study was to extract HS from ADE and humic-like substances (HLS) from hydrochar (HC), aiming to access the composition and to compare the chemical functionality. The HTC of sugarcane bagasse, vinasse and the mixture of sugarcane bagasse and vinasse were carried out with and without addition of phosphoric acid in the reaction medium. HLS were extracted from HC and HS from TPI and also from surrounding soil (SR) in depth. The samples were characterized by 13C nuclear magnetic resonance, thermal hydrolysis and methylation reactions coupled to gas chromatography and mass spectrometry (Thermochemolysis GC-MS), thermogravimetry, composition analysis, molecular fluorescence and were submitted to bioassays using maize seeds. The HTC process generated a HLS characterized by the presence of aromatic groups and aliphatic chains, and the addition of phosphoric acid in the medium reaction left the HLS more hydrophobic, with greater structural rigidity mainly by the aromatic content. HLS presented two supramolecular structures: 1-HLS composed by hydrophilic (O-Aryl and O-Alkyl) and hydrophobic (C-Aryl) moieties, which they have a flexible arrangement enabling the release of bioactive molecules; 2-HLS composed by more hydrophobic (Calkyl) moieties that did not showed bioactivity. The HS from ADE showed a greater structural complexity and hydrophobicity than SR. The HS presented different characteristics in depth; HS from ADE seems to be more humified on top layer, while the SR is in depth. The HLS of HC of sugarcane bagasse were the ones that presented the highest similarity to HS by the presence of phenolic compounds, which influenced the initial growth of the maize seeds and were different due to the greater presence of polysaccharide structures in the soil. The HLS generated employing the HTC process showed similarity with natural organic matter and bioactivity in maize seeds, depending on the raw material. (AU)

• FAPESP's process: 17/05575-2 - Structural similarity of the humic substances from hydrochar obtained from vinasse and sugarcane bagasse with the Black Earth (TPI)
• Grantee: Lucas Raimundo Bento
• Support Opportunities: Scholarships in Brazil - Master