Hydrothermal carbonization (HTC) is a thermochemical process carried out in an aqueous medium. It is capable of converting biomass into a solid, carbon-rich material (hydrochar), and producing a liquid phase (process water) which contains the unreactive feedstock and/or chemical intermediates from the carbonization reaction. The aim of this study was to evaluate the characteristics of process water generated by HTC from vinasse and sugarcane bagasse produced by sugarcane industry and to evaluate its toxicity to both marine (using Artemia salina as a model organism) and the terrestrial environment (through seed germination studies of maize, lettuce, and tomato). The experiments showed that concentrated process water completely inhibited germination of maize, lettuce, and tomato seeds. On the other hand, diluted process water was able to stimulate seedlings of maize and tomato and enhance root and shoot growth. For Artemia, the LC indicated that the process water is practically non-toxic; however, morphological changes, especially damages to the digestive tube and antennas of Artemia, were observed for the concentration of 1000 mg C L.

Humic acids (HA) play an important role in the distribution, toxicity, and bioavailability of metals in the environment. Humic-like acids (HLA) that simulate geochemical processes can be prepared by NaOH aqueous extraction from hydrochars produced by hydrothermal carbonization (HTC). HLA can exhibit properties such as those found in HA from soils, which are known for their ability to interact with inorganic and organic compounds. The molecular characteristics of HLA and HA help to explain the relationship between their molecular features and their interaction with metallic species.The aim of this study is to assess the molecular features of HA extracted from Terra Mulata (TM) and HLA from hydrochars as well as their interaction with metals by using Cu(II) ions as a model. The results from 13 C NMR, elemental analysis, FTIR, and UV-Vis showed that HA are composed mostly of aromatic structures and oxygenated functional groups, whereas HLA showed a mutual contribution of aromatic and aliphatic structures as main constituents. The interactions of HA and HLA with Cu(II) ions were evaluated through fluorescence quenching, in which the density of complexing sites per gram of carbon for interaction was higher for HLA than for HA. Furthermore, the HLA showed similar values for stability constants, and higher than those found for other types of HA in the literature. In addition, the average lifetime in both humic extracts appeared to be independent of the copper addition, indicating that the main mechanism of interaction was static quenching with a non-fluorescent groundstate complex formation. Therefore, the HLA showed the ability to interact with Cu(II) ions, which suggests that their application can provide a new approach for remediation of contaminated areas.

We have imaged the particles of Brazilian soils at multiple length scales, from a few microns to millimeters, and soil particle size distributions were calculated with unmatched precision. The analysis included the Amazonian soil "Terra Mulata de Índio" (TMI), an anthropogenic soil (Anthrosol) with sustained fertility and a large amount of stabilized organic matter. Firstly, the soils were imaged ex situ, without any chemical processing, with sequential electron scanning of the pelletized soil samples, covering a total area of 8 × 8 mm. Secondly, it was performed a computational analysis of the large-field X-ray images assembled from hundreds of adjacent elemental maps, thus resulting in high-definition images (4800 × 4800 pixels). This analytical approach provides a large sampling with the identification of > 10,000 particles over the scanned area. The particles identified consisted of Al, C, Ca, Cr, F, Fe, Mg, Mn, Na, O, P, S, Si and Ti. A significantly larger concentration of C-, Ca-and P-based particles, of up to 100 μm 2 of cross-section area, was found in TMI samples in comparison with oxisol and ultisol soils. While the mean distance between neighboring C, Ca and P particles in TMI was of 40-70 μm, the value was of hundreds of microns in oxisol and ultisol. Furthermore, mapping of micrometric carbon particles by Raman spectroscopy indicated that they have a graphitic structure with a large amount of defects, partially associated with particle oxidation, although a well-preserved sp 2 graphitic structure is also present. From a technological perspective, improved soil amendments, such as biochar, can be rationally designed from the "fingerprint" described here for soil particles of Amazonian Anthrosols (i.e., morphological and structural characteristics), which can result in an increase in fertility and the optimization of carbon sequestration in the future.

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Hydrochar is a carbon-based material that can be used as soil amendment. Since the physical-chemical properties of hydrochar are mainly assigned to process parameters, we aimed at evaluating the organic fraction of different hydrochars through 13C-NMR and off-line TMAH-GC/MS. Four hydrochars produced with sugarcane bagasse, vinasse and sulfuric or phosphoric acids were analyzed to elucidate the main molecular features. Germination and initial growth of maize seedlings were assessed using hydrochar water-soluble fraction to evaluate their potential use as growth promoters. The hydrochars prepared with phosphoric acid showed larger amounts of bioavailable lignin-derived structures. Although no differences were shown about the percentage of maize seeds germination, the hydrochar produced with phosphoric acid promoted a better seedling growth. For this sample, the greatest relative percentage of benzene derivatives and phenolic compounds were associated to hormone-like effects, responsible for stimulating shoot and root elongation. The reactions parameters proved to be determinant for the organic composition of hydrochar, exerting a strict influence on molecular features and plant growth response.

Vinasse is a residue of ethanol production from sugarcane. In view of the problems associated with its disposal, this study aimed to propose a treatment for vinasse by hydrothermal carbonization. The influence of temperature (100 to 200 o C), acidity (1.7 to 8.3%) and reaction time (12 to 48 h) on the hydrothermal treatment was evaluated, as well the characteristics of the solid (hydrochar) and liquid (process water) products. For the solid product, two hydrothermal carbonization conditions stood out as leading to higher carbonization and yields. These conditions were 200 o C, 8.3% acidity and times of 12 and 48 h. For the process water, the carbonization reaction at 200 o C, 8.3% acidity and 48 h produced the highest discoloration and 77% reduction of total organic carbon. Thus, hydrothermal carbonization proved to be an efficient method to treat vinasse, and the hydrochar presents potential for use as fertilizers / soil conditioners, and also the process water after pre-treatment.

Fulvic acids (FA) are one of the components of humic substances and play an important role in the interaction with metallic species and, consequently, the bioavailability, distribution and toxicity of metals. However, only a few studies have investigated these FA properties in specific environment, such as anthropogenic soils. Therefore, knowledge about FA molecular composition as well as the FA-metal interaction is essential to predict their behavior in the soil. For this reason, the aim of this study was to investigate the molecular composition of FA extracted from two sites in an anthropogenic soil (Terra Mulata), from the Amazon region, as well as their interactions with Cu(II) ions as a model. Results from 13 C NMR, infrared and elemental analysis showed that these FA are composed mostly by alkyl structures and oxygenfunctional groups, e.g., hydroxyl, carbonyl and carboxyl. The interaction with Cu(II) ions was evaluated by fluorescence quenching, in which the FA showed both high quantity of complexing sites per gram of carbon and good affinity to interact with the metal when compared with other soil FA. The results showed that the complexation capacity was highly correlated by the content of functional groups, while the binding affinity was largely influenced by structural factors. In addition, through the lifetime decay given by time-resolved fluorescence, it was concluded that static quenching took place in FA and Cu(II) interaction with the formation of a non-fluorescent ground-state complex. Therefore, this fraction of soil organic matter will fully participate in complexation reactions, thereby influencing the mobility and bioavailability of metal in soils. Hence, the importance of the study, and the role of FA in the environment, can be seen especially in the Amazon, which is one of the most important biomes in the world.

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