Concentrations Of Humic Substances Research Articles

Sustainable control of invasive plants: Compost production, quality and effects on wheat germination

Invasive plant species pose significant ecological threats worldwide, affecting the stability and biodiversity of local ecosystems. As a result of their control, a considerable amount of plant biomass is produced, which can be used to produce various value-added products. Five different composts were prepared from three invasive plant species found in Latvia – Reynoutria japonica, Solidago canadensis, Lupinus polyphyllus. The stages of composting have been investigated and recommendations for process optimization have been made based on the quality characterization of the final compost. The quality of the prepared invasive plant biomass composts has been evaluated based on the main plant nutrient concentration, humic substance concentration, and mineral contents. The allelopathic lupin alkaloid concentration throughout the composting process has been evaluated and shows a consistent reduction. Obtained compost quality complies with the EU regulations for fertilizing products and soil amendments thus it can be considered equivalent to industrially produced compost and vermicompost. Seed germination tests confirm that compost prepared from invasive plants is suitable for plant growth and comparable to commercial composts. Based on pilot-scale composting results, recommendations for invasive plant composting have been suggested.

Changes in Soil Humin Macromolecular Structure Resulting from Long-Term Catch Cropping.

The aim of this study was to assess the effect of long-term catch crop application on the structural properties of humin, which is considered the most recalcitrant fraction of soil organic matter. Soil samples from a 30-year field experiment on triticale cultivated with and without catch crops were analysed to determine the total organic carbon content and fractional composition of humic substances. Meanwhile, humin isolated from bulk soil was analysed to determine its elemental composition and spectroscopic properties measured with UV-Vis, fluorescence, and 13C-CPMAS-NMR. It was found that catch crop farming enhanced the formation of highly reactive humus substances, like low-molecular-weight fractions and humic acids, while decreasing the humin fraction. The higher H/C and O/C atomic ratios of humin and the UV-Vis, fluorescence, and 13C-CPMAS-NMR results confirmed a higher share of oxygen-containing functional groups in humin isolated from the soil with catch crop rotation, also corroborating its greater aliphatic nature. Under the conditions of our field experiment, the results indicated that organic residues from catch crops quickly undergo the decay process and are transformed mainly into highly reactive humus substances, which can potentially improve soil health, while mineral fertilisation alone without catch crops favours the stabilisation and sequestration of carbon.

The impact of reservoirs on the soils of adjacent areas: overview of global and local aspects

AbstractThis study aims to analyze the impact of reservoirs on the soils of surrounding areas to elucidate potential ecological consequences. To achieve this goal, a territorial analysis of the soil surrounding such reservoirs as the Kyiv, Kaniv, Kremenchuk, and Kakhovka, which constitute the Dnieper Cascade of Reservoirs, was conducted. The study found that the average soil pH changes in reservoirs range from 6.0 to 7.5, while nitrogen and phosphorus content in the soil varies from 0.2% to 1.5% and from 0.1% to 0.5%, respectively. Average changes in the content of humic substances and fulvic acids in the reservoirs range from 1.0 to 3.5 and from 0.2 to 1.5 mg/L, respectively. Furthermore, it was found that the creation of large reservoirs on the Dnieper River is accompanied by significant consequences for shoreline soils. The geomorphological study of the reservoirs within the Dnieper Cascade revealed their diversity in terms of shoreline types. Some have more erodible shores, indicating vulnerability to erosion, as observed in the Kakhovka Reservoir, while others have more neutral shores less susceptible to erosion, such as the Kremenchuk Reservoir. The distribution of humic substances in the reservoirs of the Dnieper Cascade is determined by the hydrological structure and water inflows, with the highest concentrations in the upper regions. Decreased flow velocity in the lower part of the cascade leads to the deposition of humic substances in bottom sediments. The threat to ecological systems is exacerbated by incidents such as the catastrophe at the Kakhovka Hydroelectric Power Station in 2023, which triggered a serious ecological crisis with a wide range of consequences. Consequently, the application of a comprehensive approach to water resource management and environmental protection becomes crucial. This entails meticulous planning of construction, implementation of ecological technologies, and engaging the public in the water resource management process.

Typical Heterotrophic and Autotrophic Nitrogen Removal Process Coupled with Membrane Bioreactor: Comparison of Fouling Behavior and Characterization.

There is limited research on the relationship between membrane fouling and microbial metabolites in the nitrogen removal process coupled with membrane bioreactors (MBRs). In this study, we compared anoxic-oxic (AO) and partial nitritation-anammox (PNA), which were selected as representative heterotrophic and autotrophic biological nitrogen removal-coupled MBR processes for their fouling behavior. At the same nitrogen loading rate of 100 mg/L and mixed liquor suspended solids (MLSS) concentration of 4000 mg/L, PNA-MBR exhibited more severe membrane fouling compared to AO-MBR, as evidenced by monitoring changes in transmembrane pressure (TMP). In the autotrophic nitrogen removal process, without added organic carbon, the supernatant of PNA-MBR had higher concentrations of protein, polysaccharides, and low-molecular-weight humic substances, leading to a rapid flux decline. Extracellular polymeric substances (EPS) extracted from suspended sludge and cake sludge in PNA-MBR also contributed to more severe membrane fouling than in AO-MBR. The EPS subfractions of PNA-MBR exhibited looser secondary structures in protein and stronger surface hydrophobicity, particularly in the cake sludge, which contained higher contents of humic substances with lower molecular weights. The higher abundances of Candidatus Brocadia and Chloroflexi in PNA-MBR could lead to the production of more hydrophobic organics and humic substances. Hydrophobic metabolism products as well as anammox bacteria were deposited on the hydrophobic membrane surface and formed serious fouling. Therefore, hydrophilic membrane modification is more urgently needed to mitigate membrane fouling when running PNA-MBR than AO-MBR.

Degradation of extracellular antibiotic resistance gene through singlet oxygen produced by carbon nanotubes-activated persulfate

Extracellular antibiotic resistance gene (eARG) has emerged as a global crisis in recent years, yet commonly used disinfectants have proven ineffective for their elimination. Seeking to enhance the degradation efficiency of eARG, this study explored the potential of carbon nanotubes-activated persulfate (CNTs + PS) system as a novel method for eradicating eARG. Our findings demonstrated that CNTs + PS effectively disrupted the intact structure of eARG, inhibited their genetic replication and horizontal transfer capability, achieving remarkable degradation of eARG contamination. Further experiments revealed that 1O2 played a predominant role in eARG degradation, while electron transfer played minor roles in the degradation process. The carbonyl groups served as the primary sites for activating PS to generate 1O2. CNTs can enhance the efficiency of electron transfer from eARG to PS. Moreover, the degradation efficacy of eARG by CNTs + PS was influenced by various factors including the dosage ratio between CNTs and PS, initial concentrations of eARG, pH values, inorganic anions and humic substances and water matrix. Reusability experiment demonstrated that CNTs + PS exhibited stable degradation performance after multiple uses. These findings offer a new perspective for the efficient degradation of eARG in environmental remediation.

Enhanced humification attributed by the integration of Fenton reagent and oxalic acid during a co-composting of swine manure and corn straw: Impacts and the possible mechanisms

To illustrate the role and mechanism of using oxalic acid (OA) and Fenton reagent to enhance carbon transformation and humification in the co-composting of swine manure and corn straw, four different treatments, SW1 (Control), SW2 (Fenton reagent), SW3 (10 % OA), and SW4 (Fenton reagent + 10 % OA) were set up for an 80-day pilot-scale composting. Compared with the Fenton pretreatment, the contents of Fe (II) and hydroxyl radicals (·OH) in the SW4 treatment increased by 20.25 %-54.55 % and 6.39 %-71.00 %, respectively. This confirmed the role of OA in protecting Fe (II) and maintaining the generation of ·OH during the composting. Compared with Control, Fenton-like reagent amendment facilitated decomposition of dissolved organic carbon and total organic matter by 20.53 % and 25.37 %, respectively, which led to a higher content of humic substances (141.81 mg/g) and a higher degree of polymerization (3.51) in SW4. Among all, the dissolved organic carbon in the compost substrate of SW4 treatment showed the highest level of aromatization and more refractory organic matter decomposition. The compact microbial co-occurrence network analysis exhibited the high-metabolic activity in Fenton-like treatment (SW4). Therefore, the probable mechanism of humification facilitation by Fenton-like reagent amendment in co-composting could be controlled by several processes: 1) generation of ·OH for facilitating the decomposition of organic matter, 2) disintegration of refractory lignocellulose substances by promoting the lignin pathway of humification, and 3) increasing the quantity and activity of microbes (i.e., Proteobacteria, Actinobacteriota, Chloroflexi, Ascomycota and Basidiomycota) involved in humification. This study provided a profound understanding of Fenton-like reagent amendments in co-composting of agricultural solid wastes and proposes a solution for enhancing the humification degree of compost products for agricultural use.

Soil Mineral Nitrogen and Mobile Organic Carbon as Affected by Winter Wheat Strip Tillage and Forage Legume Intercropping

Diversifying crop rotations by incorporating legumes is recommended to enhance the resilience of agricultural systems against environmental stresses and optimize nitrogen utilization. Nonetheless, ploughing forage legumes or grass-legumes poses a significant risk of nitrate leaching. The study aimed to assess the impact of strip tillage intercropping management on soil mineral nitrogen, water-extractable organic carbon, mobile humic substances content, and winter wheat (Triticum aestivum L.) grain yield compared to forage legume and winter wheat monocropping with conventional tillage. In the intercropping systems, the following bicrops were used: black medick (Medicago lupulina L.) with winter wheat, white clover (Trifolium repens L.) with winter wheat, and Egyptian clover (Trifolium alexandrinum L.) with winter wheat. Research was conducted in two experiments. The results indicated that after implementing strip tillage and winter wheat intercropping, the soil mineral nitrogen content was similar to or lower than that observed in conventional tillage and winter wheat sowing after forage legumes. Winter wheat grain yield in intercrops decreased compared to the legumes monocultures that were ploughed before winter wheat sowing. The highest amount of water- extractable organic carbon was in intercropping growing white clover and winter wheat bicrops or in all fields (except Egyptian clover and winter wheat bicrops) after applying strip tillage. During the research period, the quantities of mobile humic substances and mobile humic acids exhibited similar changes. Their content increased substantially in fields with white clover and Egyptian clover, regardless of whether the legumes were ploughed or grown with winter wheat.

What Is the Molecular Weight of "High" Molecular Weight Dissolved Organic Matter?

The use of ultrafiltration to isolate high molecular weight dissolved organic matter (HMWDOM) from seawater is a fundamental tool in the environmental organic chemist's toolbox. Yet, important characteristics of HMWDOM relevant to its origin and cycling, such as its molecular weight distribution, remain poorly defined. We used diffusion-ordered NMR spectroscopy coupled with mixed-mode chromatography to separate and characterize two major components of marine HMWDOM: acylpolysaccharides (APS) and high molecular weight humic substances (HS). The molecular weights (MWs) of APS and HS both fell within distinct, narrow envelopes; 2.0-16 kDa for APS and 0.9-6.5 kDa for HS. In water samples from the North Pacific Ocean the average MW of both components decreased with depth through the mesopelagic. However, the minimum MW of APS was >2 kDa, well above the molecular weight cutoff of the ultrafilter, suggesting APS removal processes below 2 kDa are highly efficient. The MW distribution of APS shows only small variations with depth, while the MW distribution of HS narrowed due to removal of HMW components. Despite the narrowing of the MW distribution, the concentration of HS did not decrease with depth between 15 and 915 m. This suggests that HMW HS produced in surface waters was either degraded into lower MW compounds without significant remineralization, or that HMW HS was remineralized but replaced by an additional source of HS in the mesopelagic ocean. Based on these results, we propose potential pathways for the production and removal of these major components of HMWDOM.

Investigating the effect of Fenton-like pretreatment-clay mineral addition on humic substance during straw composting

Lignocellulose is difficult to directly degrade and mineralize during composting, which further leads to low humic substance content. Therefore, we investigated the effect of the combined Fenton-like pretreatment of the straw materials with clay minerals addition on humic substance during composting. We created six different treatments as CK, Z, FeZ, CK+, Z+, and FeZ+. The results showed that FeZ treatment increased the humic substance precursors content (31.3 %). The addition of clay minerals promoted the humic substance precursors formation, and the order of their content was as follows: FeZ+ > FeZ>Z+ > Z>CK+ > CK. The Fenton-like pretreatment with clay minerals addition increased humic substance (120.0 mg/g in CK, 141.6 mg/g in CK+, 135.8 mg/g in Z, 160.4 mg/g in Z+, 165.2 mg/g in FeZ and 180.9 mg/g in FeZ+ treatment). Upon coupling treatment increased the diversity of microbial communities, changed the composition of dominant genera, thus resulting in complex microbial structure. The structural equation model confirmed that the combined Fenton-like pretreatment with clay minerals addition could affect the content of humic substance by promoting their precursor formation. In addition, it could change the structure of microbial community structure to promote humic substance production and fixation. Our study provides new insights and theoretical support for the stable increase of humic substance content and humic substance fixation.

Long-term effects of nitrogen and phosphorus fertilization on profile distribution and characteristics of dissolved organic matter in fluvo-aquic soil

Dissolved organic matter (DOM) drives numerous biogeochemical processes (e.g. carbon cycling) in agro-ecosystems and is sensitive to fertilization management. Nevertheless, changes in the quantity and quality of DOM in the vertical soil profile following long-term continuous nitrogen (N) and phosphorus (P) inputs remain unclear. In this study, the contents and optical characteristics of DOM along a 2-m soil profile were investigated using a 40-year wheat/maize rotation combined with experiments using different N and P fertilization rates in the North China Plain. The results revealed that the dissolved organic carbon (DOC) content decreased with an increase in soil depths. Compared with that in the control (no fertilization), 40-year N, P, and N + P additions increased the soil DOC content by 26%–69%, except for 270-kg N, and 67.5-kg P treatments. N + P application resulted in higher DOC contents than N-alone and P-alone applications. N, P, and N + P inputs increased or did not affect the aromaticity and hydrophobicity of DOM at 0–40 cm but reduced them from 40 to 200 cm. Compared with that in the control, N, P, and N + P inputs enhanced the content of humic acid-like substances (C1+C2+C3+C4) and decreased the content of protein-like substance (C5). C1 was the dominant component among the five DOM, representing the microbial humic component. Optical indices also indicated that soil DOM primarily originated from microbial sources. Nutrient addition accelerated transformation between complex C1 and simple C5 via promoting microbial activities. These results imply that N and P fertilizers increased the DOM content and altered its composition, thereby potentially affecting the stability of soil organic matter in the agroe-cosystems.

The use of the self-organizing map (SOM) methodology to study the dissolved organic matter (DOM) in different water body types.

This study investigated the characteristics of dissolved organic matter (DOM) in two distinct water bodies, through the utilization of three-dimensional fluorescence spectroscopy coupled with self-organizing map (SOM) methodology. Specifically, this analysis concentrated on neurons 3, 14, and 17 within the SOM model, identifying notable differences in the DOM compositions of a coal subsidence water body (TX) and the MaChang Reservoir (MC). The humic substance content of DOM TX exceeded that of MC. The origin of DOM in TX was primarily linked to agricultural inputs and rainfall runoff, whereas the DOM in MC was associated with human activities, displaying distinctive autochthonous features and heightened biological activity. Principal component analysis revealed that humic substances dominated the DOM in TX, while the natural DOM in MC was primarily autochthonous. Furthermore, a multiple linear regression model (MLR) determined that external pollution was responsible for 99.11% of variation in the humification index (HIX) of water bodies.

The fate of various organic compounds including pharmaceuticals in the treatment of landfill leachate and anaerobic digestate using deammonification

Studies focusing on the fate of organic compounds specifically recalcitrant organics and pharmaceuticals in a deammonification plant are scarce. This study downscaled a full-scale deammonification plant, which was being operated with the same wastewater streams of this study and evaluated for the first time the fate of different fractions of organic compounds in deammonification process along with the removal of nitrogenous compounds. Organic compounds in the feed and effluent were analyzed and their changes in the deammonification process were characterized. The results demonstrate that deammonification achieved over 90% of ammonium removal. COD monitoring revealed that around 11% of COD was reduced during the process mainly due to aerobic COD degradation and heterotrophic denitrifying bacteria. Analysis of the organic fractions revealed that high molecular weight components (around 11 kDa) are susceptible to removal and their concentrations tend to decrease in the reactor. Concentrations of humic substances, specifically fulvic acid-like substances, were reduced. Tracking nine different pharmaceutical residues revealed that morphine and cotinine were completely removed, while pregabalin and oxazepam which are known to be highly recalcitrant were more than 60% removed. The research finding can help in optimizing treatment processes by revealing the fate of different organic compounds, especially pharmaceuticals, within the deammonification process, thereby contributing to better effluent quality, regulatory compliance, and environmental protection.

Carbon fixation mechanism of fungal community bypass strategy in rice straw composting combined with functional microbes: inhibition from cellobiose to glucose pathway

Composting offers an eco-friendly approach, converting organic solid waste into valuable soil enhancer products. Three experimental treatments were designed to explore the microbial mechanisms influencing lignocellulose loss in rice straw composting: CK (the control), B4 (inoculated with Bacillus subtilis), and Z1 (inoculated with Aspergillus fumigatus). The results showed significant increases in carboxymethyl cellulase, cellobiohydrolase, laccase, and xylanase activities during B4 and Z1composting. However, lignin peroxidase and manganese peroxidase were not significantly affected, and β-glucosidase was inhibited. Additionally, microbial inoculation stimulated lignin loss, with B4 and Z1 composting increasing degradation by 14.42% and 16.29%, respectively, compared to the CK. Simultaneously, humic substance content increased as microbial inoculation inhibited β-glucosidase, causing cellobiose to accumulate and divert into a pathway that forms humic substances. The random forest model showed that Symmetrospora and Phaeosphaeria significantly boosted lignocellulose loss in B4 and Z1 composting by promoting fungi functional aggregation, thus accelerating the degradation and transformation process. This study explored the microbial mechanism of lignocellulose loss and provided new insights into lignocellulose conversion and carbon fixation.

Short-term electrochemical stimulation induces sustained enhancement of extracellular pollutant degradation in anaerobic granular sludge

Electroactive bacteria (EAB) are advantageous for degrading the pollutants extracellularly, but the enrichment primarily restricts on the electrode surface of bioelectrochemical system and is challenging to scale up. To address this, a new strategy was proposed to electrochemically stimulate the anaerobic granular sludge (AGS) and employ the harvested electroactive granular sludge (EGS) to an electrode-free bioreactor for pollutant removal. Fast establishment of EGS was achieved after 7 days' electrochemical stimulation, with a maximum current output of 112.5 A/m3 achieved and the abundance of electroactive bacteria-like genera increased from 5% to around 20%. The electric conductivity of EGS improved by 1-fold, while the increased extracellular protein and humic acid substance but unchanged polysaccharide content in the extracellular polymeric substance suggested a more robust redox network. After assembling in a sequential batch reactor, the methylene orange (MO) and Cr(VI) removal rate by EGS was enhanced by 65–80% and 38–55%, respectively. Better oxygen tolerance was also observed. The comparative study with exogenous riboflavin and respiration inhibitors indicated the complete extracellular reduction achieved by EGS while almost half of MO was metabolically degraded by AGS, which was kinetically sluggish. More importantly, there is no performance and electroactivity decay in a 60 days' batch operation. Meanwhile, the characterization of microbial community revealed the further increased abundance of EAB-like genera (∼28%) but Acinetobacter became dominant (∼15%), suggesting the competition of EAB species in EGS. In brief, a simple 7-day electrochemical stimulation imposed diverse and sustained benefits on the performance and microbial community of granular sludge, which may inspire the application of EAB and their extracellular degradation capacity in real wastewater treatment.

The Use of Products from Leonardite to Improve Soil Quality in Condition of Climate Change

Abstract The principle of sustainable fertilisation in modern agriculture, which ensures that the soil is maintained in a fertile state requires the search for alternatives to manure fertilisation for products based on humic substances to increase the organic matter content of soils.The advantage of leonardite over conventional natural and organic fertilisers is mainly due to its high content of organic matter and humic substances (humic and fulvic acids). Leonardite, due to the presence of humic acids in it, can be suitable for soil amendment and yield of barley. In the conducted studies, the yield increase after adding Rosahumus fertilizer to the soil at a rate of 6 kg.ha−1 + NPK (Nitrogen, Phosphorus, Potasssium) was found to be 11% compared to the control (NPK).There were no changes in the Corg. content of the soil as a result of the application of Rosahumus fertilizer with NPK. The fertilizer only slightly modified the fractional composition of humus. In the future, we should expect an increase in the use of leonardite-derived humic substances in fertilizers and soil conditioners to stabilize soil organic matter.

Addition of Biochar and Fertiliser Drives Changes in Soil Organic Matter and Humic Substance Content in Haplic Luvisol

Humic substances (HSs) constitute a primary component of soil organic matter (SOM) and play a crucial role in soil formation and fertility. However, comprehensive information regarding quantitative and qualitative changes in HS following biochar’s application to soil still needs to be improved. This study reports on the impact of biochar application at rates of 0, 10, and 20 t ha⁻1 (B0, B10, B20), both with and without nitrogen fertilisation at varying levels (N0, N1, N2), on SOM and HS contents throughout the cropping seasons between 2014 and 2019. The findings reveal changes in SOM and HS contents due to biochar addition and fertilisation. Notably, the most substantial increase in soil organic carbon content was observed in the B20N1 and B10N1 treatments, in stark contrast with the reference B0N0 treatment. A decrease in humification of SOM was noted across all treatments involving biochar, whether alone or combined with different N fertilisation levels. An interesting positive change in HS contents was observed in B10N2, where an increase in humic acids and a decrease in fulvic acids enhanced HS stability and improved HS quality. These findings shed light on the intricate dynamics of SOM and HSs in response to biochar application and nitrogen fertilisation over multiple vegetation seasons of crops on loamy Haplic Luvisols in Central Europe.

Co-composting sugar-containing waste with chicken manure–A new approach to carbon sequestration

Improving resource use is a pressing research issue because of the huge potential organic waste market. Composting is a recycling technique, treatment to achieve the dual effect of resource recovery and zero waste. Waste composition varies: for example, chicken manure is rich in protein, straw contains wood fibres, fruit and vegetables contain sugar, and food waste contains starch.When considering combining waste streams for composting, it is important to ask if this approach can reduce overall composting costs while achieving a more concentrated result. Chicken manure, in particular, presents a unique challenge. This is due to its high protein content. The lack of precursor sugars for glucosamine condensation in chicken manure results in lower humus content in the final compost than other composting methods. To address this, we conducted experiments to investigate whether adding sugary fruits and vegetables to a chicken manure composting system would improve compost quality. To improve experimental results, we used sucrose and maltose instead of fruit and vegetable waste. Sugars added to chicken manure composting resulted in a significant increase in humic substance (HS) content, with improvements of 9.0% and 17.4%, respectively, compared to the control. Sucrose and maltose have a similar effect on the formation of humic substances. These results demonstrate the feasibility of composting fruit and vegetable waste with chicken manure, providing a theoretical basis for future composting experiments.

Environmental condition-dependent effects of aquatic humic substances on the distribution of phenanthrene in microplastic-contaminated aquatic systems

Numerous studies have focused on the interaction between microplastics (MPs) and phenanthrene (PHE) in aquatic environments. However, the intricate roles of aquatic humic substances (HS), which vary with environmental conditions, in influencing PHE-MP interactions are not yet fully understood. This study investigates the variable and environmentally sensitive roles of HS in modifying the interactions between PHE and polyethylene (PE) MPs under laboratory-simulated aquatic conditions with varying solution chemistry, including pH, HS types, HS concentrations, and ionic strength. Our findings show that the presence of HS significantly reduces the adsorption of PHE onto both pristine and aged PE MPs, with a more pronounced reduction observed in aged PEs. This effect is highlighted by a notable decrease in the partitioning coefficient (Kd) of PHE, which falls from 2.60 × 104 to 1.30 × 104 L/kg on MPs in the presence of HS. The study also demonstrates that alterations in the net charge of HS solutions are crucial in modifying PHE distribution onto PEs. An initial decrease in Kd values at higher pH levels is reversed when HS is introduced. Furthermore, an increase in HS concentrations is associated with lower Kd values. In conditions of higher ionic strength, the retention of PHE by HS is intensified, likely due to an enhanced salting-out effect. This research highlights the significant role of aquatic HS in modulating the distribution of PHE in MP-polluted waters, which is highly influenced by various solution chemistry factors. The findings are vital for understanding the fate of PHE in MP-contaminated aquatic environments and can contribute to refining predictive models that consider diverse solution chemistry scenarios.

Ultrasound-Assisted Synthesis of Humic-Silica Composites by the Isolation of Humic Substances from Peat and Lignite.

The aim of the presented study was to evaluate an integrated, direct procedure for the synthesis of humic-silica composites (HSiC) by the isolation of humic substances (HS) from peat and lignite by the use of sodium silicate solution as an extractant. The obtained materials, because of the presence of humic functional groups, may potentially be used for removing contaminants from aqueous solutions. The quantitative assessment was based on experiments designed according to the Box-Behnken plan. The statistical analysis of the results allowed to determine the optimal conditions of the process tested, for which the isolation efficiency of humic substances (HS) was greater than 50 % for both raw materials. This made it possible to synthesize humic silica composites with a high content of HS, which have been qualitatively evaluated. This step was focused on the analysis of the humic structure using elemental analysis, spectroscopic methods, and differential thermal analysis coupled with thermogravimetry. On the basis of them, the presence of structures characteristic for HS in the HSiC tested was observed. Moreover, the results of the thermal analysis pointed to the higher thermal stability of the synthesized compounds, compared to the HS isolated with the use of a traditional extractant.

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.