Humic acid formation during subcritical water extraction of food by-products using accelerated solvent extractor

Efficient recovery and characterization of humic acids from municipal and manure composts: A comparative study

The recovery of humic acids from low-quality compost obtained in municipal solid waste treatment plants provides opportunities for its valorization. This study compares the recovery and properties of the humic acids obtained from municipal mixed waste compost (MMWC) and manure compost. The effects of temperature, time, and KOH concentration on the ratio of humic acids in the extracted liquid and the content of organic carbon of the precipitates were investigated by response surface methodology. Optimal conditions were 30 °C and 24 h for both composts, with a KOH concentration of 0.53 M for MMWC and 0.25 M for manure compost. The manure compost provided a liquid extract richer in humic acids than MMWC (76.6 % vs. 33.7 %), but the precipitates presented similar organic carbon contents (38.1 % vs. 42.4 %). Regarding composition, both humic acids presented higher organic carbon and nitrogen contents than the composts used as feedstock. The extraction and further precipitation of humic acids reduced the concentration of heavy metals. Humic acids from manure compost have a slightly higher average molecular weight (2650 Da) than those from MMWC (1980 Da), while both present similar C/N ratios and degree of aromaticity. Most contaminants of emerging concern present in the original composts were not detected in the humic acids. Thus, it was demonstrated that MMWC constitutes an attractive source of humic acids with properties similar to those obtained from a high-quality compost and, therefore, with potential economic value.

Flavonoid Extracts from Lemon By-Products as a Functional Ingredient for New Foods: A Systematic Review

This systematic review seeks to highlight, from the published literature about the extraction and application of lemon by-products rich in flavonoids, which works use environmentally friendly technologies and solvents and which ones propose a potentially functional food application, according to the Sustainable Development Goals (SDGs). WoS and SCOPUS were used as scientific databases for searching the documents, which were evaluated through 10 quality questions according to their adherence to our purpose (5 questions evaluating papers devoted to lemon flavonoid extraction and 5 concerning the application of such by-products in new foods). Each question was evaluated as "Yes", "No", or "does Not refer", according to its adherence to our aim. The analysis reported 39 manuscripts related to lemon flavonoid extraction; 89% of them used green technologies and solvents. On the other hand, 18 manuscripts were related to the incorporation of lemon by-products into new foods, of which 41% adhered to our purpose and only 35% evaluated the functionality of such incorporation. Conclusively, although the bibliography is extensive, there are still some gaps for further investigation concerning the extraction and application of lemon by-products to reduce food losses in an environmentally friendly way and the possible development of new functional foods, which must be performed following the SDGs.

Determination of Bioactive Components in Mandarin Fruits: A Review

During the last decade, there has been a continuous rise in the consumption of fresh easy-to-peel mandarins. However, the majority of the knowledge comes from other citrus fruit, like orange, while there are relatively few studies about mandarins and no comprehensive research on literature data about them. One of the most important steps in the analytical process is sample preparation. Its value is evident in analyzing the samples with complex matrices, such as in mandarin fruit. In addition, mandarin contains hundreds to thousands of various compounds and metabolites, some of them present in extremely low concentrations, that interfere with the detection of one another. Hence, mandarin samples are commonly pretreated by extraction to facilitate analysis of bioactive compounds, improve accuracy and quantification levels. There is an abundance of extraction techniques available, depending on the group of compounds of interest. Finally, modern analytical techniques, have been applied to cope with numerous bioactive compounds in mandarins. Considering all the above, this review aims to (i) list the most valuable procedures of sample preparation, (ii) highlight the most important techniques for extraction of bioactive compounds from mandarin fruit, and (iii) summarize current trends in the identification and determination of bioactive compounds in mandarin.

Liquid fertilizer production from organic waste by conventional and microwave-assisted extraction technologies: Techno-economic and environmental assessment

The use of mineral fertilizers in agriculture has significantly increased to support the growing global food demand. Organic fertilizers are produced from renewable waste materials to overcome the drawbacks of inorganic fertilizers. The development of novel production processes of organic fertilizers entails a significant advance towards the circular economy that reincorporates waste materials into the production cycle. In this work, the economic and environmental feasibility of an industrial plant with a treatment capacity of 300 kg/h of organic waste for the production of liquid fertilizers has been performed. Two extraction technologies (conventional and microwave) and two solvents (water and alkaline) have been compared to select the most sustainable and profitable scenario for scaling-up. The extraction process consists of 2 steps: extraction followed by a concentration stage (necessary only if water extraction is applied). The resolution of the mass balances shows that the fertilizer production under alkaline conditions is ten times higher than for water-based extraction. The economic analysis demonstrated that the total investment cost of microwave technology (>3.5 M€) is three times higher compared to the conventional extraction technology (<1.5 M€), mainly due to the higher complexity of the equipment. These facts directly impact the minimum selling price, because the fertilizers obtained by conventional extraction with alkaline solvent would have a lower selling price (about 1 €/L). As for environmental assessment, the indicators show that the environmental impact produced by water-based extraction is higher than alkaline-solvent extraction, mainly due to the necessity of a concentration stage of the liquid extract to meet the requirements of European regulations. In view of the results obtained in the economic and environmental evaluation, it could be concluded that the most favourable scenario for scaling up the production of liquid fertilizers from organic waste is the conventional extraction under alkaline conditions.

Potential Hydrothermal-Humification of Vegetable Wastes by Steam Explosion and Structural Characteristics of Humified Fractions

In this work, steam explosion (SE) was exploited as a potential hydrothermal-humification process of vegetable wastes to deconstruct their structure and accelerate their decomposition to prepare humified substances. Results indicated that the SE process led to the removal of hemicellulose, re-condensation of lignin, degradation of the cellulosic amorphous region, and the enhancement of thermal stability of broccoli wastes, which provided transformable substrates and a thermal-acidic reaction environment for humification. After SE treatment, total humic substances (HS), humic acids (HA_s), and fulvic acids (FA_s) contents of broccoli samples accounted for up to 198.3 g/kg, 42.3 g/kg, and 166.6 g/kg, and their purification were also facilitated. With the increment of SE severity, structural characteristics of HA_s presented the loss of aliphatic compounds, carbohydrates, and carboxylic acids and the enrichment of aromatic structures and N-containing groups. Lignin substructures were proved to be the predominant aromatic structures and gluconoxylans were the main carbohydrates associated with lignin in HA_s, both of their signals were enhanced by SE. Above results suggested that SE could promote the decomposition of easily biodegradable matters and further polycondensation, aromatization, and nitrogen-fixation reactions during humification, which were conducive to the formation of HA_s.

Physicochemical characteristics of chitosan from swimming crab (Portunus trituberculatus) shells prepared by subcritical water pretreatment

The physicochemical properties of chitosan obtained from the shells of swimming crab (Portunus trituberculatus) and prepared via subcritical water pretreatment were examined. At the deacetylation temperature of 90 °C, the yield, ash content, and molecular weight of chitosan in the shells prepared via subcritical water pretreatment were 12.2%, 0.6%, and 1187.2 kDa, respectively. These values were lower than those of shells prepared via sodium hydroxide pretreatment. At the deacetylation temperature of 120 °C, a similar trend was observed in chitosan molecular weight, but differences in chitosan yield and ash content were not remarkable. At the same deacetylation temperature, the structures of chitosan prepared via sodium hydroxide and subcritical water pretreatments were not substantially different. However, the compactness and thermal stability of chitosan prepared via sodium hydroxide pretreatment was lower than those of chitosan prepared via subcritical water pretreatment. Compared with the chitosan prepared by sodium hydroxide pretreatment, the chitosan prepared by subcritical water pretreatment was easier to use in preparing oligosaccharides, including (GlcN)₂, via enzymatic hydrolysis with chitosanase. Results suggested that subcritical water pretreatment can be potentially used for the pretreatment of crustacean shells. The residues obtained via this method can be utilized to prepare chitosan.

Rapid leaching and recovery of valuable metals from spent Lithium Ion batteries (LIBs) via environmentally benign subcritical nickel-containing water over chlorinated polyvinyl chloride

This study presents the development of an effective and environmentally friendly method to leach and to recover valuable metals, such as lithium (Li) and cobalt (Co) from the spent lithium-ion batteries (LIBs) using subcritical water assisted by nickel catalyst and waste chlorinated polyvinyl chloride (CPVC). The effects of reaction parameters, such as Ni²⁺ concentration, temperature, time, and liquid-solid ratio on the leaching efficiencies of Li and Co were carefully investigated. The solid residues obtained thereof were characterized by XRD and SEM-EDS analyses, while the leachates were analyzed by ICP-OES. The ICP-OES results showed that about 99.05% of Li and 98.08% of Co were effectively leached from the spent LiCoO₂ powder under the following optimized reaction conditions: temperature of 240 °C, reaction time of 40 min, Ni²⁺ concentration of 0.04 M, and the liquid-solid ratio of 25:1 mL/g, respectively. Finally, based on the precipitation method, the Li and Co were recovered from the leachate as Li₂CO₃ and Co(OH)₂. The results and the method applied in this research suggest that the leaching and recovery of Li and Co from the spent LIBs using subcritical nickel-containing water is an inexpensive, efficient, sustainable and eco-friendly technology.

Chlorinated polyvinyl chloride (CPVC) assisted leaching of lithium and cobalt from spent lithium-ion battery in subcritical water

The objective of this study was to determine leaching efficiency of Li and Co from spent lithium-ion batteries (LIBs) by using waste chlorinated polyvinyl chloride (CPVC) in hydrothermal subcritical water process. Waste CPVC was used as the source of HCl to speed up leaching efficiency. Effects of temperature, time, LiCoO₂: CPVC mass ratio and liquid-solid ratio on leaching efficiencies of Li and Co were investigated. Solid residues were characterized by XRD and SEM-EDS elemental mapping to predict chemical compounds remained after leaching. Results showed that more than 98.71 % of Li and 97.69 % of Co were effectively leached from LiCoO₂ powder under the following conditions: temperature of 250 °C, reaction time of 60 min, and LiCoO₂: CPVC mass ratio of 1:3. Results of this study suggest that recovery of Li and Co from spent LIBs using hydrothermal subcritical water is an efficient, environmental friendly and sustainable technology.