Characteristics Of Humic Acids Research Articles

Lignocellulose hydrothermal artificial humic acid production: Reaction parameters screening and investigation of model/real feedstock

Utilizing relatively mild hydrothermal conversion technique (under optimized conditions, 200 °C, 4 h, 1:10 solid-liquid ratio, 0.5 M NaOH), lignocellulosic biomass can be efficiently transformed into humic acids, thereby significantly enhancing its utilization. Additionally, this approach provides a means for precise manipulation of the composition and properties of the resulting humic acids. In this comprehensive study, lignocellulosic biomass, comprising various attributes like coniferous, broadleaf, and grassy species, as well as model components like cellulose, hemicellulose, and lignin, underwent hydrothermal reactions to produce humic acids. Firstly, a systematic evaluation was conducted to determine the influence of operational parameters on the formation of humic acids. Subsequently, the characteristics of humic acids derived from diverse lignocellulosic biomass sources were analyzed and benchmarked against commercial humic acids. Based on the empirical findings, a mechanistic pathway for the generation of humic acids was figured out. The results indicate that the primary stages in the hydrothermal conversion of lignocellulosic biomass to humic acids involve initial hydrolysis into smaller molecular components, followed by further reactions leading to the formation of humic acids. Notably, the interplay between cellulose, hemicellulose, lignin, and other minor components, such as tannins and pectins, plays a pivotal role in the synthesis of humic acids. The characterization of the derived humic acids revealed several noteworthy distinctions from commercial products. In the infrared spectroscopy (FTIR) and elemental analysis (EA) characterization, the synthetic humic acid has more oxygen functional groups, alkane groups and aromatic structures. In the X-ray photoelectron spectroscopy (XPS), the synthetic humic acid has more diverse forms and proportions of elements. In thermogravimetric analysis (TGA), the synthesized humic acid has higher thermal stability. The synthetic humic acid has a rougher surface microstructure. The synthetic humic acid has higher fluorescence intensity in three-dimensional fluorescence spectrum (3D EEM). Lignocellulose biomass raw materials with high wood quality content can obtain higher humic acid yield, but the interaction of cellulose, hemicellulose, lignin and other group components (such as tannins, pectin, etc.) in the hydrothermal process plays an important role in the generation of humic acid. This research offers valuable insights into the chemically driven production of humic acids and the strategic control of their properties, based on the structural and compositional nuances of the raw materials.

Characterization of Humic Acid Using E4/E6 Ratio in Various Land Uses in Jatiarjo Village, Prigen District, Pasuruan

Different land uses can influence the characteristics of humic acid in the soil. The study aimed to characterize humic acid in soil from various land uses in Jatiarjo Village, Prigen Distict, Pasuruan Regency of East Java. Soil sampling was carried out on three land uses, namely mixed gardens, bush lands, and dry lands. Sampling was carried out using the purposive random sampling method, where seven points were taken in each land use. Analysis of soil samples included soil chemical characteristics (pH, organic-C, and CEC) and characterization of humic acid using E4/E6 ratio. The results showed that the land use of bush land provided the best soil fertility indicated by the content of humic acid and C-organic in the soil that were higher than that of other land uses. All land uses in Jatiarjo Village, Pasuruan have advanced humification levels, as evidenced by low E4/E6 ratio values (<5).

Variations in structure and adsorption characteristics of humic acid during pressure oxidation process

Humic acid extraction from carbonaceous pressure-oxidized gold ore was carried out. The structure of humic acid was analyzed utilizing elemental analysis, FTIR, UV–Vis, Raman spectra and XPS. Also, the kinetic and isotherm models of the gold-adsorbing process were established to calculate the thermodynamic parameters and isosteric heat of adsorption. The results showed that affected by pressure oxidation, the aliphatic structure, C=O and other oxygen-containing groups were destroyed. Most importantly, new bonds, such as C—O—Clx, C—Clx and Me4N—Cl, were formed in the humic acid extracted from pressure-oxidized gold ore. The adsorption test results showed that, pressure oxidation made a profound impact on the gold-adsorbing performance of humic acid. The adsorption rate of humic acid decreased to (42.78±1.05)% for the pure gold solution and (28.63±1.11)% for the gold leaching solution after pressure oxidation. Adsorption findings conformed to the pseudo-second-order and Langmuir isotherm models. The isosteric adsorption heat of humic acid increased with the increase of the adsorption amount.

Changes in the Physicochemical Characteristics of Humic Acids in a Hydrodynamic Rotor-Pulsation Apparatus

The work presents research results of the change comparison of brown coals and the study of the physicochemical properties of humic substances obtained from brown coals of the Karazhyra, Ekibastuz, and Kyzyl-Kiya deposits after hydrodynamic treatment in a rotary-pulsation apparatus. It is shown that the hydromechanical effect on humic acids leads to a change in their composition, accompanied by a decrease in the degree of aromaticity and an increase in the content of oxygen-containing fragments. Mechanical treatment of brown coals under oxidizing conditions maximizes the efficiency of extraction of water-soluble components and humic acids. The structural parameters and functional composition of humic acid molecules during the treatment of brown coals under oxidation-reduction conditions change depending on the conditions. The elemental and functional composition (using IR spectroscopy and potentiometry) of humic substances in brown coals and their molecular weight distribution using size-exclusion chromatography were studied. The influence of the content of metal-binding centers, dispersity, and ash content of humic substances was studied before and after treatment. At a temperature of 70 ºC a rotation time of 10 s, 98.7% of humic acids passes into the solution, which is the best indicator.

Humus component of pedosediments at the end of the Sartan cryochron in the Nadym River basin (West Siberia)

The aim of the study. To assess the potential of humus substances from the pedosediments in the polygonal ice wedges pseudomorphs as indicators of the paleoecological conditions of their formation during the period of their functioning within the surface soil, using the case of the Razduv object of the end of the Sartan cryochron (corresponding to MIS-2) in the basin of Nadym River (West Siberia). Important comment: In this paper the terms “humus”, “humus component of soils” and the “system of humus substances” are used as synonyms. Location and time of the study. The research was conducted in the Nadym district of the Yamalo-Nenets Autonomous Okrug (YaNAO), at the Razduv site 15 km to the north-east of the Nadym city, during the late summer 2018. Methods: The study is based on a new methodological approach to the diagnostics of the bioclimatic conditions at the end of Sartanian cryochron in one of the northern territories of West Siberia, based on the humus substances of pedosediments which serve as indicators of paleoenvironment. Main results. It was established that the applied indicator features of the formation conditions of the studied pedosediments, based on indicators of the composition and spectral properties of their humus component, correlated well with each other, in their totality reflecting the cold humid conditions of soil formation, similar to those for modern soils of different tundra subzones of the West Siberia. Conclusions. The study of the specific features of composition, structure and properties of humus substances from the pedosediments in the pseudomorphs after polygonal ice wedges, dated back to the end of the Sartanian cryochron at the key section of Razduv and revealing the indicators of their formation conditions, demonstrated that the characteristics of the humus substances system and in particular one of its components, i.e. humic acids, obtained by independent methods, have high diagnostic significance for reconstructing paleoclimatic and paleoecological conditions of their formation. Characteristics of modern soils and paleosols from various parts of North Siberia, from northern Trans-Urals to the coastal lowlands in the north of Yakutia, were used as a recent reference dataset for diagnostics and reconstruction of the bioclimatic conditions of paleosol development on the land surface during MIS 2. It was confirmed that the studied samples, attributed to redeposited soil materials, i.e. pedosediments, due to their morphology in fact had undergone the phase of pedogenesis that is evidenced by the presence of humus substances, including humic acids with their typical outline of FTIR-spectra with a characteristic set of the absorption bands, individual ratio of the main structural elements and similar variation of the quantitative parameters of the fluorescence emission. The closest similarity of the composition and proportion of the main components of the humus substances system was found between the samples of the Sartanian pedosediments and the modern soils formed in the tundra conditions of West Siberia. The similarity of the main humus substances ratio, as well as the main structure-forming elements and values of all fluorescence characteristics of humic acids, especially for the samples with higher humus content and those affected by permafrost, was revealed. These results confirm that at the end of the Sartanian cryochron the pedogenesis in the vicinities of Razduv section was similar to that is now going on in the region located to the north of the study site.

The Quantity and Quality of Humic Substances following Different Land Uses in Karst Peak-Cluster Depression in Guangxi, China

There were some ecological and environmental problems in limestone soil in the karst peak-cluster depression in Pingguo City of Guangxi, such as the destruction of soil structure, soil acidification and soil fertility decline, and these problems were closely related to soil organic matter. The soil in this site was classified as Cambisols. Therefore, this project took soil under five major land uses (grassland, afforestation, sugarcane field, corn field and pitaya field) in the karst area of Guangxi as the research object. The contents and molecular structure properties of humic acids, fulvic acids and humins in soils were studied by solid-state 13C nuclear magnetic resonance spectroscopy and elemental composition. From the perspective of the chemical structure of humic substances, the differences in the quantity and structural characteristics of humic acids, fulvic acids and humins in different land uses were revealed. The results showed that the organic carbon content of both afforestation (34.83 g kg−1) and natural restored grassland (31.67 g kg−1) were significantly higher than that of sugarcane field (17.60 g kg−1), corn field (16.35 g kg−1) and pitaya field (14.31 g kg−1) (p < 0.05). The contents of three humic fractions in grassland were relatively high, and the contents of three humic fractions in sugarcane field were relatively low (p < 0.05). The structural characteristics of humic substances showed that the protein components of the three humic fractions in the afforestation were high, indicating that the humic substances in the afforestation contained more unstable components. The Alkyl C/O-alkyl C and Hydrophobic C/hydrophilic C ratios of the three humic fractions of corn field were high, indicating high stability and maturity in humic substances in corn field.

Chemical and Spectroscopic Characteristics of Humic Acids Under No-Tillage and Forest Systems

ABSTRACT This study aims to evaluate the no-tillage system (NT) with different implantation times and vegetation cover on changes in the chemical and structural compositions of soil humified organic matter. Five areas with different NT management histories were studied; for 6 (NT6), 14 (NT14), 22 (NT22) years with succession of soybean/corn crops; for 12 years and 4 more years with corn and Brachiaria (NT+B), pasture for 39 years and native forest. Soil samples were collected at the depths of 0.0–0.05 and 0.05–0.10 m. The changes in the quality of humic acid (HA) were evaluated by several chemical techniques (total organic carbon (TOC), fulvic acid fraction (FA), humic acid fraction (HA) and humin fraction (HU), ionizable functional groups, elemental composition) and spectroscopic techniques (UV–Vis absorption, fluorescence, and Fourier transform mid-infrared photoacoustic spectroscopy, called FTIR-PAS). On the surface, the TOC, carbon of the HA and HU fractions, total acidity, phenolic acidity, Carbon, Nitrogen, Sulfur, Hydrogen and Hydrogen/Carbon ratio were higher in the areas of forest, pasture and NT22. On the subsurface, the responses are the same as on the surface. However, the NT22 system presents higher FA, HA, carboxylic acidity and humification degree (HD). UV–Vis absorption spectroscopy, fluorescence spectroscopy and FTIR-PAS can discriminate soils under different managements and under natural conditions. Agronomic practices have strongly affected the soil organic matter, in which the NT promotes the formation of HA with characteristics closer to those of the forest, as the implantation time increases, such as 22-year-old NT and pasture. This indicates that care must be taken in managing the no-till system to maximize its potential to promote stabilization of organic matter, thereby contributing to carbon sequestration.

Enhanced Sorption Performance of Natural Zeolites Modified with pH-Fractionated Humic Acids for the Removal of Methylene Blue from Water.

This work explores the effect of humic acids (HA) fractionation on the sorption ability of a natural zeolite (NYT)-HA adduct. HA were extracted from compost, fractionated via the pH fractionation method, and characterized via UV-Vis spectroscopy and gel permeation chromatography. The HA samples were immobilized onto NYT via thermal treatment. The resulting adducts (NYT-HA) were tested for their ability to remove methylene blue (MB) from an aqueous solution. It was found that the sorption performance of NYT-HA strongly depends on the chemical characteristics of humic acids. Sorption capacity increased with the molecular weight and hydrophobicity degree of the HA fractions. Hydrophobic and π-π interactions are likely the primary mechanisms by which MB interacts with HA. The sorption kinetic data conform to the pseudo-second-order model. The Freundlich isotherm model adequately described the sorption equilibrium and revealed that the uptake of MB onto NYT-HA is endothermic in nature.

Characteristics of Humic Acids in Drained Floodplain Soils in Temperate Climates: A Spectroscopic Study

This study aims to assess the characteristics of humic acids (HAs) in floodplain soils. HAs were isolated from the Fluvisols located out of the embankment in the riparian forest (unflooded riparian forest) and within the embankment (inter-embankment), in the area periodically flooded. HAs from these soils were examined for quantity, structure, and humification degree using extraction methods as well as elemental analysis, UV-Vis, FTIR, EPR, and 1HNMR spectroscopies. In the soils after drainage, a significant decrease in HAs has been observed compared to the periodically flooded areas. Obtained results showed that organic matter from periodically flooded soils is more humified and contains HAs with a more aromatic, lignin-like structure compared to the humus matter from unflooded Fluvisols. Humic acids from periodically flooded soil contained a lower amount of C and H compared to those isolated from unflooded soils located out of the embankment, which resulted in a less aliphatic or more aromatic character of their molecules. A higher H/C ratio of HAs from the Fluvisols after drainage exhibits more condensed aromatic ring or substituted ring structures in the molecules. Soils with organic matter with a higher humification index contained HAs with lower radical concentration values in comparison to soils with less humified organic matter. Results obtained show that in flooded areas with periodically reductive conditions, humic acids do not lose as many -OCH3 groups as in better oxidized soils and therefore exhibit a lignin-like aromatic structure. It has been proven that the formation and dynamics of HA transformation may vary due to the water regime in soils.

Effect of Strong Acids on the Spectral Characteristics of Humic Acid Extracted from Biomethane Fermentation Peat Residue

Effect of Strong Acids on the Spectral Characteristics of Humic Acid Extracted from Biomethane Fermentation Peat Residue

Biostimulant activity of humic acids derived from goat manure vermicompost and lignite in relation to their structure and interaction with a PGPR strain under semiarid conditions

The use of humified organic matter (HOM)-based plant biostimulants and plant growth-promoting rhizobacteria (PGPR) has emerged as a promising approach to enhance agricultural productivity in arid and semiarid environments. However, the bioactivity of humic stimulants varies based on their chemical composition, and the synergistic effects of co-applying these biostimulants remain to be fully elucidated. In this research, we investigated the structural and bioactive characteristics of humic acids derived from goat manure vermicompost (HAVC) and lignite coal (HAC). Additionally, we explored the plant growth-promoting effects of each humic acid (HA) in conjunction with the Bacillus mycoides strain BSC25 (Bm) on corn plants in arid conditions. To assess the relationship between structure and bioactivity, we determined the supramolecular composition of the HAs and evaluated their effectiveness through a corn coleoptile elongation test. Subsequently, we conducted biostimulation tests on maize seedlings in a growth chamber and performed a field-based biostimulation test in a semi-arid region. Notably, HACs exhibited coleoptile elongation at lower concentrations (25-50 mg LC) compared to HAVCs, which required higher concentrations (100-200 mg LC) to achieve the same effect. These outcomes correlated with the supramolecular composition of HAs. The bioactivity of HACs was linked to their oxygen content, aromatic and carboxylic groups, whereas HAVCs' bioactivity was associated with their carbohydrate, aliphatic carbon, and hydrogen content. The application of both HAs, together with Bm, resulted in enhanced corn leaf biomass production in the growth chamber and under field conditions. This effect can be attributed to the hormone-like actions of HA and the PGPR activity of Bm. Interestingly, despite foliar application, HAs displayed bioactivity at the root level, as evidenced by increased root biomass in the field. These results indicate a PGPR effect of Bm that remained unaltered with co-application of HAVC. However, the joint application of Bm-HAC and Bm-HAVC reversed the positive effect of Bm on corn production under field conditions. This outcome likely relates to the hormone-like effects of HA and potential additive effects following Bm inoculation.

Evaluating membrane cleaning for organic fouling in direct contact membrane distillation

To find an effective cleaning method for organic fouling in membrane distillation (MD), this work focused on the fouling characteristics of humic acid (HA), sodium alginate (SA), and bovine serum albumin (BSA), and the cleaning efficiency of deionized (DI) water flushing, NaCl flushing, NaOH flushing and DI water backwashing. The results showed that when Ca2+ was absent from the feed solution, severe fouling was observed for HA and BSA, while SA led to slight fouling due to its hydrophilicity. The addition of Ca2+ alleviated the fouling for HA, but intensified the fouling for SA and BSA. There was a transition from cake filtration to complete blocking in membrane fouling mechanism for most MD tests. NaOH flushing resulted in irreversible fouling ratio of 48–60% after fouling by HA and BSA, while DI water flushing can recover 70% of flux decline caused by SA without Ca2+ present in the feed. For the three organics, only 8–15% of fouling was removed after DI water backwashing. The differences in the cleaning efficiency of the four cleaning methods were further verified by the positive correlation between irreversible fouling ratio and surface energy parameter, as well as Scanning electron microscopy and Fourier transform Infrared analysis of the membranes used in this study.

Potential of Humic Acid from Soil to Reduce The Content of Heavy Metals

Humic acid is an important component for the qualities of soil with different properties or characteristics depending on the sources. The purpose of this study was to investigate the characteristics of humic acid produced from soil as a heavy metal adsorbent. This study used several methods to examine its adsorption pattern, including time incubations (20, 40, 60, 80, and 100 minutes), pH treatment (1-9), the adsorbent treatments (humic acid) with a weight ratio of adsorbent (1:2:3 and 4) also adsorption using five different heavy metals concentrations. The result showed that each treatment provides a different pattern of heavy metal uptake depending on the type of heavy metals. Humic acid from soil has good adsorption characteristics. They absorbed the greatest amount of heavy metals, particularly Pb (18.25%-98.06%), Cd (3.65%-70, 99%), and Cr (18.15%-97.52%). Furthermore, soil as a planting medium has potential to be used as a substance that can reduce heavy metal contain.

Effects of Corn Straw and Biochar Returning to Fields Every Other Year on the Structure of Soil Humic Acid

Returning straw and biochar to the fields can change the structure of humic acid in soil and affect the content of soil organic matter. However, returning straw and biochar to the fields in successive years also increases the insect pests of crops and causes nitrogen competition, thus increasing the soil burden. Therefore, to provide a theoretical basis for the study of the time effect of returning fields, three treatments were set in this paper to study the effects of straw and biochar returning every other year on the soil organic matter and humic acid (HA) structure. Elements, Fourier transform infrared spectroscopy (FTIR), thermogravimetric spectroscopy (TG), three-dimensional fluorescence spectroscopy, and solid state 13C-NMR spectroscopy were used to comprehensively investigate the structural characteristics of humic acid in soil. The results showed that after straw and biomass charcoal are returned to the field every other year, compared with 2018, after planting in 2020, the average content of soil organic carbon will increase by 29.49% and 36.14%, respectively. HA showed a phenomenon of increased aliphatic property and decreased aromaticity; aromatic carbon of HA decreased, while alkyl carbon and alkoxy carbon increased; the molecular structure of HA developed toward simplification. In the short term, the effect of biomass charcoal returning was more significant. This study can be used as a reference for the research on the time effect of returning straw and biomass carbon to the fields, and can also provide a basis for the research on the composition of humus after returning organic materials to the fields.

Multi‐proxy climate and environmental records from a Holocene eutrophic mire, southern taiga subzone, West Siberia

Palaeoenvironmental reconstructions from peat are strongly focused on ombrotrophic mires, but this study demonstrates that eutrophic mires can also be used. A multi‐proxy approach was applied to a eutrophic mire on a floodplain terrace in the southern taiga of West Siberia. The results of the reconstruction were considered in the wide geographic context of the surrounding regions, including Siberia and Central Asia. Different palaeoecological proxies (analysis of plant macrofossils, testate amoebae, oribatid mites, molluscs, peat humification, ash content and spectral characteristics of humic acids) were used in this study. The results of different proxies showed a high level of consistency among themselves, which allowed for a robust interpretation of Holocene mire development. Throughout the ~7800 years history of the mire, there was a high level of surface wetness. The presence of mineral matter in the peat between 7800 and 5100 cal. a BP indicates regular flooding caused by the intensive fluvial activity, apparently resulting from increased precipitation. This was followed by a trend towards a gradual decrease in surface wetness from conditions of high surface moisture (stagnant water) between 5100 and 3000 cal. a BP to present day conditions of moderate surface moisture with a water table slightly below the mire surface. This pattern is consistent with the well‐documented long‐term trend from palaeoecological records throughout the taiga and arctic zones in West Siberia and central arid Asia. Our data further support the idea that the westerlies were the dominant driver of climate for the southern taiga of West Siberia during the Middle to Late Holocene.

Characteristics of humic acids in sod-podzolic soil under long-term exposure to different fertilization systems

The elemental composition and structure of humic acids in the soddy-podzolic heavy loamy soil of the Cis-Urals were studied during long-term application of organic, mineral and organo-mineral fertilizers under conditions of a long-term stationary experiment. Mineral fertilizers contributed to the formation of humic acids with increased content of aliphatic components, the ratio H : C = 1.45 and a high degree of oxidation (ω = 0.41). The low content of nitrogen in humic acids (from 2.0 to 2.6 at.%), with various fertilizer systems, is primarily due to its low content in the plant biomass of crops cultivated in crop rotation.The organic fertilizer system resulted in the enrichment of the structural aggregates of humic acids with aromatic groups and nitrogen. The high intensity of absorption of the >C=O group of carboxylic acids in the region of 1 717 cm-1 and double bonds of carbon atoms at 1 627 cm-1 confirms this position. Humic acids of the “manure 10 t/ha” and “manure 5 t/ha + equiv. NPK” have the largest number of carboxyl groups in their composition. The vibrations of the >C=O group of carboxylic acids are most weakly expressed in soil humic acids with a mineral fertilizer system. Organo-mineral fertilizer system demonstrates intermediate results in terms of the content of the main constitutional elements in humic acids. Mineral fertilizers application reduces the amount and thermal stability of the structural components of humic acids, thereby contributing to the degradation of the most stable part of macromolecule, which can lead to the loss of potential soil fertility. Тhe use of mineral fertilizers on sod-podzolic heavy loamy soil led to the enrichment of humic acids with aliphatic fragments, and of organic ones – increased the content of stable components of aromatic nature, but lowered their thermal stability. According to thermographic analysis the ratio of weight loss in the low-temperature zone and the weight loss in the high-temperature zone (Z) during long-term use of mineral fertilizers is 0.9, i. e. the proportion of components of aliphatic nature in the structure of humic acids increases in comparison with unfertilized or manure fertilized soil.

Characteristics of humic acids isolated from burned and unburned topsoils in sub-boreal Scotch pine forests by 13C-NMR spectroscopy

Postpyrogenic soil dynamics is an informative tool for studying soil elementary processes in extreme temperature conditions and for predicting short time environmental changes in conditions of catastrophic landscape changes. Soil organic matter (SOM) system evolution is the most rapid process of postpyrogenic soil development. In this relation, the focus on humus structure is important for understanding these important dynamics. Soil restoration after spontaneous forest fires near Togljatty City (Samara Region, Russia) was abandoned in 2010 and further monitoring over the next ten years was organised to evaluate the speed of humus accumulation dynamics. The aim of this study was to apply the 13C-NMR (nuclear magnetic resonance) spectroscopy to analyse the effect of forest fires on SOM degradation in Scotch pine forests on Psamment Entisols of the fragmented steppe in the Samara Region. Three key soil plots were studied for estimating SOM quality changes under the forest fire effect: surface forest fire, crown forest fire and control, i.e. 18 soil samples of top soil horizons were analysed in three replicates. The data obtained indicate that the humus molecular composition was substantially affected by the wildfires. Investigation of the humic acids’ (HAs) molecular structure by 13C-NMR showed a relative increase in aromatic compounds and decrease in aliphatic ones. The aromaticity degree of HA molecules increases in 5.7 and 3.8 times in cases of surface and crown forest fires, correspondingly. In general, crown and surface fires plots are not very different in terms of 13C-NMR spectra of HAs (p = 0.34); however, HAs of control plot have essential differences from pyrogenic ones (p < 0.05). 13C NMR spectra have shown a change in the proportion of oxygen-containing functional groups as well. One of the most important effects observed in wildfire-affected SOM is that the proportion of lignin-like structures increases as a concomitant effect of depletion of C,H-alkyl groups, especially in the case of crown fires.

Investigating the Evolution of Structural Characteristics of Humic Acid Generated during the Continuous Anaerobic Digestion and Its Potential for Chromium Adsorption and Reduction

Humic acid (HA), as an important by-product, has been demonstrated to affect anaerobic digestion performance and subsequent land application of digestate via the batch anaerobic digestion process. However, the knowledge about the evolution of structure and function of HA during continuous anaerobic digestion (AD) is still unclear. Therefore, the current study examined the structural changes in HA produced during the continuous AD process and its metal-adsorption-reduction abilities. The results of three-dimensional fluorescence spectroscopy showed a general upsurge in humic-like components’ abundance (70–77%), with an increase in humification index (2.56–3.43). Likewise, the content of HA increased from 4.8 g L−1 to 6.9 g L−1 in the continuous AD process. The evolution of C-H, O-H, C=O, C=C, and C-O functional groups of HA was observed via the 2D COS FTIR analysis. Moreover, the concurrent dynamics of functional groups contributed to the higher adsorption (255.2 mg g−1) of Cr (VI) and reduction (60.3 mg g−1) of Cr (VI) to Cr (III) after 168 days of the continuous AD process. The findings of the current study not only advanced understanding of the evolution of HA during continuous anaerobic digestion and its metal remediation potential but also support further research toward developing an eco-friendly and innovative strategy for the remediation of heavy metals contaminated soils employing anaerobic digestate as an auxiliary agent.

Parameters optimization using an artificial neural networks and release characteristics of humic acids during lignite bioconversion.

The bioconversion of coal at ambient conditions is a promising technology for coal processing. However, there are few examples of the optimization of processes for industrial-scale use. In this work, the optimization of process parameters affecting lignite bioconversion by an isolated fungus WF8 using an artificial neural network (ANN) combined with a genetic algorithm (GA) was carried out for modeling of humic acids (HAs) yield and parameters. Kinetic models were used to understand the release characteristics of HAs from the bioconversion of lignite. The results of the present work indicate that the optimal process parameters (OPP) are 29°C, initial pH of 7, 180rpm, 0.6mmol·L-1 of CuSO4, 0.4mmol L-1 of MnSO4, and 6.4μmol·L-1 of veratryl alcohol (VA). The predicted experimental data obtained by ANN is similar to the actual and the significant correlation coefficient value (R2) of 0.99 indicates that ANN has good predictability. The actual yield of HAs are 5.17mg·mL-1. During bioconversion, the fungus WF8 could loosen and attack the structure of lignite. The release of HAs produced by bioconversion of lignite under the OPP via diffusion and swelling is fit to zero-order model independent on concentration. This provides support for the industrial bioconversion of lignite.

Roles of organic matter transformation in the bioavailability of Cu and Zn during sepiolite-amended pig manure composting

The application of clay minerals facilitates the bioavailability of heavy metals and the humification in livestock manure composting. However, whether the humification plays a critical role in the bioavailability of heavy metals is still unclear. Here, with the addition of sepiolite (SEP), the fractions of Cu and Zn, and the spectral characteristics of humic acids (HAs) during aerobic pig manure composting were investigated. The SEP-amended composting had a decreased peak temperature and an increased electrical conductivity, regardless of the SEP dosage. The seed germination index increased by 15.9 ± 0.5% (p < 0.05) with the appropriate dosage of SEP (6%), indicating a higher maturity and a lower phytotoxicity of the SEP-amended compost. The addition of SEP reduced the water-extractable organic matter (WEOM) content and increased the percentage of HAs by 2.8–10.7%. More interestingly, during SEP-amended composting, the reducible fraction of heavy metals was transformed into the oxidizable fraction, and the bioavailability of Cu and Zn decreased by 11.0–15.9% and 15.4–26.5%, respectively. Ultraviolet–visible (UV–vis) spectra and fluorescence spectra analyses showed that the SUVA254 and complex fluorescent components of HAs in the SEP-amended composting increased by 4.4–15.8% and 1.2–9.0%, respectively. Nuclear magnetic resonance (NMR) further confirmed that the addition of SEP increased the aromatic index and percentage of carbonyl-carboxyl C of HAs by 3.4–8.3% and 4.6–5.7%, respectively. The redundancy analyses (RDA) described the SUVA254, aromatic index and carbonyl-carboxyl C of HAs had a strong positive correlation with the oxidizable fraction of heavy metals, which was further confirmed by variance partitioning analysis (VPA). Overall, this work suggested that the HAs structure play an important role in the bioavailability of Cu and Zn during SEP-amended composting, potentially providing safe organic fertilizer.