High Humic Acid Content Research Articles

Construction of a multiple reactive species-mediated Co9S8/NBC-PMS Fenton-like system for tetracycline degradation with broadened adaptability to water background

A Fenton-like system based on peroxymonosulfate (PMS) oxidant has high potential for antibiotic degradation, However, various complex water background factors, including pH, coexisting ions, and dissolved organic matter, can adversely affect degradation efficiency. This work constructed a PMS oxidative Fenton-like system activated by cobalt polysulfide/N-doped biochar composite (Co9S8/NBC) for the degradation of tetracycline (TC) and achieving approximately 99 % removal of TC. Furthermore, the removal efficiency was maintained above 90 % across a broad pH range (3−11), in the presence of various coexisting anions (Cl−, NO3− and CO32−), even at high concentrations of humic acid. The characterization of Co9S8/NBC through various techniques confirmed that Co9S8 nanoparticles were uniformly loaded within the porous NBC structure. Electron paramagnetic resonance and reactive oxygen species (ROSs) quenching experiment revealed that the effectiveness of TC degradation in the Co9S8/NBC/NBC-PMS system arises from the cooperation of radical and non-radical species rather than the single mechanism. Moreover, the analysis of the contribution ratios of ROSs to TC degradation indicates that the contribution of non-free radicals exceeds that of free radicals, and it is capable of adapting to changes in pH. The characterization of the post-reaction catalyst suggested that Co9S8 and NBC synergistically participated in the activation of PMS. Moreover, the practical examination proved that the disabled Co9S8/NBC catalyst can recover the catalytic activity via a reheat treatment, the leaching concentration of Co ions was lower than the emission limit of China. The river water and lake water as the matrix water have little negative impact on the degradation of TC. The Co9S8/NBC-PMS system is expected to provide a practical pathway for the treatment of antibiotic wastewater.

Insights into the synergistic effects between deposited Fe oxides and dissolved organic matter in influencing perfluorooctanoic acid transport in saturated porous media

Perfluorooctanoic acid (PFOA) transport in the subsurface environment is relevant to drinking water safety, while the compounding effects of soil components on PFOA migration are poorly understood. Laboratory miscible-displacement experiments were conducted using saturated sand columns to explore how metal oxide surfaces and dissolved organic matter (DOM) jointly affect PFOA transport in porous media. Retardation factors indicated that Fe oxide coating inhibited PFOA migration due to electrostatic interaction. However, PFOA recovery rates changed insignificantly, decreasing by less than 4 % when the proportion of Fe oxide-coated sand reached 50 %. DOM (1 mg/L humic acid) in the pore water slightly decreased PFOA recovery rates (by about 10 %) in quartz sand, indicating the effect of hydrophobic interaction on PFOA migration. When the PFOA solution containing 1 mg/L humic acid was injected into the column containing Fe oxide-coated sand, PFOA recovery was significantly decreased by nearly 20 %, and the retardation factor was more than doubled. This could be attributed to the stronger hydrophobic effect provided by the higher DOM deposition on the Fe oxide surface. These results, supported by SEM-EDS, zeta potential, and model fitting data, highlight the microscopic mechanisms by which interactions between metal oxides and DOM influence PFOA transport. However, this inhibitory effect disappeared at higher humic acid concentrations (20 mg/L), indicating the risk of PFOA re-migration when the DOM concentration greatly exceeds the adsorption capacity of the media for it. The findings of this work have implications for predicting or controlling the environmental risks of PFOA in soil and groundwater.

Density modification of DNAPL using self-demulsifying colloidal biliquid aphron: Kinetics, mechanisms and influencing factors

Density-modification remediation of dense nonaqueous phase liquid (DNAPL) using colloidal biliquid aphron (CBLA) is an efficient means of enhancing flushing and avoiding the risk of downward migration of DNAPL. However, the use of demulsifier is currently necessary for CBLA to achieve density modification. This leads to issues such as low modification efficiency and the risk of secondary contamination. In this work, we developed a self-demulsifying CBLA (PO-CBLA-S) for density-modification remediation of DNAPL, eliminating the need for external demulsifiers. The self-demulsification process exhibited pseudo-secondary reaction kinetics, achieving densities below 1 g/cm3 for various DNAPLs. Groundwater chemistry parameters (pH, anions, cations, temperature, and humic acid (HA) content) were investigated for their impact on perchloroethylene (PCE) density modification. Cations were found to enhance PO-CBLA-S density modification more than anions. Both strong acidic and alkaline environments promote the density regulation of PCE by PO-CBLA-S, and temperature positively correlates with the efficiency of density modification. High concentrations of HA also have a favorable facilitating effect on the density modification. The mechanisms of self-demulsifying density modification were clarified at the microscale. Surfactant entanglement caused by internal surfactant-solvent interaction decreased the stability of PO-CBLA-S, leading to self-demulsification. This study addresses density modification challenges and provides a theoretical foundation for its groundwater remediation applications.

Strengthened Removal of Tetracycline by a Bi/Ni Co-Doped SrTiO3/TiO2 Composite under Visible Light

A two-step hydrothermal method was used to first obtain a SrTiO3/TiO2 composite then to dope the composite with Bi, Ni and Bi/Ni. Morphology, crystalline structures, surface valances and optical features of SrTiO3/TiO2 and Bi-, Ni-, Bi/Ni-doped SrTiO3/TiO2 were assessed. XRD and XPS analysis showed that Bi and Ni were successfully doped and existed in Bi(3+) and Ni(2+) oxidation state. UV–vis analysis further revealed that the bandgap energies of TiO2 and SrTiO3/TiO2 were calculated to be 3.14 eV and 3.04 eV. By comparison, Bi, Ni and Bi/Ni doping resulted in the narrowing of bandgaps to 2.82 eV, 2.96 eV and 2.69 eV, respectively. The removal ability of SrTiO3/TiO2 and doped SrTiO3/TiO2 were investigated with tetracycline as the representative pollutant. After 40 min of exposure to visible light, Bi/Ni co-doped SrTiO3/TiO2 photocatalyst was able to remove 90% of the tetracycline with a mineralization rate of about 70%. In addition, first-order removal rate constant was 0.0074 min−1 for SrTiO3/TiO2 and increased to 0.0278 min−1 after co-doping. The strengthened removal by co-doped photocatalyst was attributed mainly to the enhanced absorption of visible light as co-doping resulted in the decreases of bandgap energies. At the same time, the co-doped material was robust against changes in pH. Removal of tetracycline was stable as pH changed from 5 to 9. Tetracycline removal was inhibited to a certain degree by the presence of nitrate, phosphate and high concentration of humic acid. Moreover, the co-doped material exhibited strong structural stability and reusability. In addition, a photocatalysis mechanism with photogenerated holes and ·O2− radicals as main oxidative species was proposed based on entrapping experiments and EPR results.

Sulfur vacancies form charge transport channels on the S-type heterojunction engineered interface to enhance photocatalytic performance

This article presents the synthesis of an S-type heterojunction photocatalyst through a straightforward hydrothermal process, which involves the combination of FeWO4 with Zn0.5Cd0.5S containing sulfur vacancies (Zn0.5Cd0.5Ssv). The study delves into the intrinsic role of sulfur vacancies in enhancing the photocatalytic performance of the S-type heterojunction. The creation of sulfur vacancies effectively controls charge separation and triggers a rapid charge transfer pathway at the heterojunction, improving light absorption and permitting the formation of more photoinduced charges. The material demonstrates an impressive degradation efficiency, capable of breaking down 79.38% of IOH within just 40 minutes. It exhibits robust catalytic activity under both mildly acidic and mildly basic conditions, showing notable resistance to various anions and cations present in water, as well as a significant tolerance to high concentrations of humic acid. Further, trapping experiments reveal that hydroxyl radicals (•OH) and superoxide radicals (•O2⁻) are the predominant reactive species driving the photocatalytic process. This research sheds new light on the modulation of photogenerated charge carrier dynamics at the heterointerface, offering valuable guidance for the development of high-performance S-type photocatalysts.

Spray coating of 2D materials in the production of antifouling membranes for membrane distillation

Membrane surface coatings with 2D materials have been shown to exhibit antifouling properties for water-treatment applications; however, synthesis methods currently based on vacuum filtration are not easily scalable. This study describes a scalable method for coating membranes with a range of 2D materials including graphene oxide (GO), hexagonal boron nitride (hBN), molybdenum disulphide (MoS2) and tungsten disulphide (WS2). Isopropyl alcohol solutions containing each class of the 2D flakes were spray-coated onto commercial polyvinylidene fluoride (PVDF) using a pyrolyser. The nanomaterials were secured with polydopamine (PDA) as a crosslinker in a method that could easily be integrated into a scalable roll-to-roll process. Changes in morphology, surface roughness, hydrophobicity, mechanical durability and chemical composition were evaluated using scanning electron microscopy, atomic force microscopy, contact angle, tensile strength measurements and Fourier-transform infrared spectroscopy. The 2D nanomaterials-coated membranes were tested in membrane distillation (MD) experiments over 72 h and compared to pristine PVDF and PDA/PVDF membranes. Salt rejection and MD performance stability were evaluated using feedwaters with high concentrations of humic acid (150 ppm) and paraffin oil (200 ppm) simulating simple organic wastewater from oil and gas extraction. The flux decline ratio was measured in terms of percentage permeate loss per hour (%/h), to allow for future comparisons with studies with different experimental times. The pristine PVDF membrane failed after 10 h by pore-wetting due to fouling while the PDA/PVDF membrane had the largest flux decline ratio (0.3 %/h). The membranes coated with GO and hBN had flux decline ratios orders of magnitude lower (0.0021 ± 0.005 and 0.028 ± 0.01 %/h, respectively). All membranes had a high salt rejection (>99.9 %). The GO-coated membrane was the only membrane type that was able to treat both surfactant-containing and foulant-containing feedwaters. The improved performance is attributed to the decrease in both surface roughness and hydrophobicity, which reduces the adsorption of foulants onto the membrane surface. This work shows a facile, scalable method to overcome fouling limitations in MD.

Deciphering the anammox microbial community succession with humic acid exposure to optimize large anammox granules for robust nitrogen removal

The robustness of the anaerobic ammonia oxidation (anammox) process in treating wastewater with high concentrations of humic acids (HAs), including landfill leachate and sludge anaerobic digestion liquid, has been paid great attention. This study revealed that the anammox sludge granule size of 1.0–2.0 mm could be robust under the HA exposure with high concentrations. The total nitrogen removal efficiency (NRE) was 96.2% at the HA concentration of 20–100 mg/L, while the NRE was 88.5% at the HA concentration of 500 mg/L, with reduced by 7.7%. The increased extracellular polymeric substances (EPS) content which was stimulated by the HA exposure favored the formation of large granules (1.0–2.0 mm) by enveloping medium and micro granules (0.2–1.0 mm). The abundance of anammox bacteria Candidatus Brocadia was found to be higher (14.2%) in large anammox granules sized 1.0–2.0 mm, suggesting a potentially high anammox activity. However, the abundance of denitrifiers Denitratisoma increased by 4.3% in ultra-large anammox granules sized >2.0 mm, which could be attributed to the high EPS content for heterotrophic denitrifiers metabolism as organic matter. The feedback mechanism of the anammox community for maintaining the ecological function under the HA exposure resulted in a closely related microbial community, with positive and negative correlations in the ecological network increased by 64.3%. This study revealed that the HA exposure of the anammox system resulted in the anammox granules of 1.0–2.0 mm size being the dominant granules with robust nitrogen removal, providing significant guidance for the optimization of anammox granules for an efficient treatment of HA-containing wastewater in anammox applications.

A holistic insight on stability and transport of hematite colloid: Role of various environmental factors

Hematite colloids (Hem) could carry pollutants into deep underground environments and its potential ecological risk needs to be evaluated. This study investigated the aggregation and transport behavior of Hem under different solution pH, electrolyte concentration and humic acid (HA) concentration. Rising the electrolyte concentration would shrink the double electric layer of Hem, weaken the electrostatic repulsion and promote the aggregation of Hem. The critical coagulation concentration (CCC) of Hem was higher at pH 5 (48.83 mM) than pH 10 (24.70 mM), implying that Hem were more stable under acidic conditions than under alkaline conditions. The addition of HA increased the negative charge of Hem and improved the electrostatic repulsion between colloid and sand surface, thus intensifying the stability and mobility of Hem. High HA concentration (≥ 0.5 mg/L) had little effect on the surface charge of Hem, indicating that electrostatic repulsion was not the dominant, however increasing HA significantly improve the stability and transport of Hem by stimulating the steric hindrance interaction. The effect of HA on the transport of Hem under acidic condition was significantly higher than that under alkaline condition because HA changed the surface charge of Hem from positive to negative under acidic condition, so that the electrostatic repulsion between the colloid and sand surface increased sharply and accompanied by a significant penetration. This study exhibited a holistic view on the aggregation and transport behavior of Hem in typical soil environment, and extended the understanding of co-transport potential mechanisms of colloids with contaminants and/or nutrients.

Перспективы переработки угля с низкой степенью метаморфизма

Introduction. The relevance and significance of this work is due to the fact that the soils of Kazakhstan are about 48% salt marshes. The reasons for their occurrence are different: harsh climatic conditions, the drying Aral Sea, the Baikonur cosmodrome, numerous test sites, etc. With an increased content of water-soluble salts in the root layer of soils, most cultivated plants develop poorly and yield a reduced yield. To solve the above problem, the technology of processing brown coal from the Kiyakty deposit and its substandard part for the production of drugs-growth stimulants for agricultural plants, high-calorie fuel briquettes and coal-alkali reagents is proposed. Materials and methods. Development of technology for the production of a humic preparation from brown coal deposits in Kazakhstan. It is known that these coals are amorphous polymers containing bitumen, humic acids, residual organic substances and moisture. Laboratory experiments were carried out by the method of biotesting according to B.P. Strogonov in glasses with a capacity of 0.5 liters in accordance with the requirements of GOST (GOST 10250–80, GOST 12038–84). The methodology for conducting research on the manufacture of briquettes, carbon-alkali reagents based on the humic acid hypothesis and various local binding materials with the involvement of certified CeLSIM laboratories is substantiated. The most optimal binder is a liquid bardic concentrate. Results. As a result of the application of new methods of pre-sowing treatment of rice seeds with a 2.5 % aqueous solution of the preparation from coal, its yield increased by 9.5–12.1 quintals per 1 ha, or by 33.8–41 % compared with the control. Discussion. The works of a number of foreign and domestic researchers on this topic have proved the possibility of using humic substances from brown coals to obtain organo-mineral fertilizers, and a comparative study of the chemical composition has been conducted. However, according to our technology, it is clear that we do not get fertilizer, but plant growth stimulants. It should be noted that the technology developed by the authors makes it possible to obtain a humic preparation, the use of which on low-yielding soils of Kazakhstan ensures a stable increase in the yield of cereals and legumes. Conclusion. The developed technology for the production of humic preparations for various purposes can be used to increase crop yields on degraded soils, for the bio recultivation of man-made formations, the manufacture of a substrate for greenhouse farms, the production of fuel briquettes and coal-alkali reagents, as well as during the operation of other brown coal deposits of the Republic of Kazakhstan with a high content of humic acids in their composition. Suggestions for practical applications and directions for future research. The territory of Kazakhstan is considered to be arid zones of dry steppe soils without rains. In these conditions, agricultural technicians resort to plants of halophyte varieties, therefore, the prospects for using this technology are very large, for example, to suppress dust formation on the surface of tailings ponds with the cultivation of green mass of wild plant varieties. Preparations from brown coals can be used to purify water and wines, leach precious metals, etc.

Оценка химического состава сапропелей различных месторождений

Complex chemical composition and wide mining opportunities determine the use of sapropels and sapropel-based products in various sectors of national economy. The fullest potential of sapropel is revealed in agriculture, where it is used as fertilizer, a component of soils, raw materials for humic preparations production etc. The aim was to study the sapropels’ suitability for the production of humic fertilizers. Using validated methods we analyze chemical composition of sapropel sediments from 4 freshwater lakes located within the latitudinal section of 53–56° N in the temperate climate. Microbiological parameters of all studied samples are within the normal range. Dry matter content in the range of 46.1–51.3% corresponds to the normative indicators. The mass fraction of organic matter varies in the range of 31.8–39.9% DM. This allows classifying all samples as organo-clay, and determines the possibility of their use for soils of light granulometric composition. The relatively high content of humic (18.3–22.9% DM) and fulvic acids (3.7–6.4% DM) makes it possible to use the studied sapropel samples for the manufacture of humic preparations (especially, a sapropel sample of the lake Chervonoe, Belarus). Low P and K content (0.24–0.36% DM and 0.32–0.42% DM, respectively) can negatively affect the efficiency of fertilizers from these sapropel species; this can be avoided by mixing sapropel with manure or enrichment with mineral fertilizers. Indicators of heavy metal (Cu, Mn, Zn, Co, Pb and Cd) content in all studied samples meet the safety requirements. Samples from deeper layers of the Rusaki Lake (Altai Territory) and the Beloe Lake (Novosibirsk Region) refer to the 1st class of suitability, the rest (according to a number of indicators) – to the 2nd class. The content of trace elements in the studied sapropels is within the established norms and makes it possible to use them for replenishing the deficit of trace elements in soils. In general, all the studied samples can be used as environmentally friendly organomineral fertilizers, as well as production of humic preparations to increase in the biological and energy capacity of agrocenoses and to reproduce the soil fertility.

Removal of Metribuzin and Bentazon by LDH-HA Modified Material: Kinetic and Equilibrium Study

ABSTRACT This study investigates the adsorption behavior of herbicides Metribuzin and Bentazon using a soil model incorporating Layered Double Hydroxide (LDH) and humic acid. Mg3AlCl-LDH, synthesized at pH 10, was combined with humic acid to produce two distinct materials: Mg3–5%HA and Mg3–10%HA. These materials were characterized using FTIR, XRD, and SEM techniques. The research confirms that humic acid adsorbs onto the LDH surface without altering its structure, resulting in negatively charged materials. While both materials fully adsorb Metribuzin at 20 mg/L, their adsorption capacities diverge at higher concentrations, with Mg3–10%HA exhibiting a higher capacity than Mg3–5%HA. In contrast, Bentazon’s adsorption is unaffected by humic acid content, displaying identical adsorption capacities in both materials at different concentrations. Both herbicides exhibit rapid adsorption kinetics, reaching equilibrium in 15 minutes. The Avrami model accurately predicts equilibrium adsorption capacities, with Metribuzin primarily adsorbed through electrostatic attraction and hydrogen bonding, while Bentazon’s adsorption is limited due to electrostatic repulsion. The adsorption of both herbicides by Mg3-HA materials is not influenced by pH variations, likely due to the surface charge of the materials. Metribuzin retention in soil containing LDH and humic acid is effective, increasing with higher humic acid concentrations, whereas Bentazon demonstrates greater mobility and resistance. These findings provide valuable insights for developing efficient water decontamination techniques, with implications for environmental protection and public health. Policymakers, researchers, and professionals in water management and pollution control should consider these findings to enhance current practices and technologies.

Insight into the humification and carbon balance of biogas residual biochar amended co-composting of hog slurry and wheat straw.

The impact of biogas residual biochar (BRB) on the humification and carbon balance process of co-composting of hog slurry (HGS) and wheat straw (WTS) was examined. The 50-day humification process was significantly enhanced by the addition of BRB, particular of 5% BRB, as indicated by the relatively higher humic acid content (67.28 g/kg) and humification ratio (2.31) than other treatments. The carbon balance calculation indicated that although BRB addition increased 22.16-46.77% of C lost in form of CO2-C, but the 5% BRB treatment showed relatively higher C fixation and lower C loss than other treatments. In addition, the BRB addition reshaped the bacterial community structure during composting, resulting in increased abundances of Proteobacteria (25.50%) during the thermophilic phase and Bacteroidetes (33.55%) during the maturation phase. Combined these results with biological mechanism analysis, 5% of BRB was likely an optimal addition for promoting compost humification and carbon fixation in practice.

Unlocking the Therapeutic Potential of Freshwater Sapropel Extracts: In Vitro Analysis and Antioxidant Profiling for Skincare Applications.

Background and Objective: Sapropel, a biologically active sedimentary deposit, is high in organic matter and minerals and has been shown to offer health benefits. Its constituents, humic acid (HA) and fulvic acid (FA), have been found to have some therapeutic applications. The aim of this study was to determine the potential therapeutically significant properties of freshwater sapropel extracts: their polyacid content, antioxidative (AO) status, and biological activity in cell culture. Materials and Methods: Freshwater lakes from the southeast region of Latvia were investigated layer by layer. The total organic carbon (TOC) was determined through combustion using the catalytic oxidation method, HA and FA were measured via acid perspiration, and the total polyphenol content (TPC) and total antioxidant status (TAS) was analysed spectrophotometrically. Sapropel extracts' regenerative abilities were tested in vitro using a Cell-IQ real-time monitoring system on mouse BALB/c 3T3 fibroblasts and human keratinocyte HaCaT cell lines. Cytotoxicity was measured through neutral red uptake assessment as a concentration-dependent reduction in the uptake of neutral red dye relative to a vehicle control or untreated cells. Results: The highest AO activity was observed in sapropel extracts with elevated concentrations of HA and TPC from Audzelu Lake (1.08 ± 0.03 mmol/L), and the lowest activity was found in extracts from Ivusku Lake (0.31 ± 0.01 mmol/L). Correspondingly, the concentrations of HA in Audzelu and Ivusku Lakes were recorded as 45.2 and 27.4 mg/g, respectively. High concentrations of HA promoted in vitro cell growth upon short-term exposure (up to 6 h). Conclusions: The results show that high TPC correlates with AO status and sapropel extracts with higher concentrations of HA exhibit greater AO activity and promote in vitro cell growth, suggesting a perspective use for short-term topical therapeutic skin applications. However, higher concentrations over longer durations showed cytotoxic effects, indicating the need for further investigation.

Influence of humic acid on the bioaccumulation, elimination, and toxicity of PFOS and TBBPA co-exposure in Mytilus unguiculatus Valenciennes

Tetrabromobisphenol A (TBBPA) and Perfluorooctane sulfonate (PFOS) are emerging contaminants which coexist in marine environments, posing significant risks to ecosystems and human health. The behavior of these contaminants in the presence of dissolved organic matter (DOM), specifically the co-contamination of TBBPA and PFOS, is not well understood. The bioaccumulation, distribution, elimination, and toxic effects of TBBPA and PFOS on thick-shell mussels (Mytilus unguiculatus V.), with the absence and presence of humic acid (HA), a typical DOM, were studied. The results showed that the uptake of TBBPA decreased and the uptake of PFOS increased when exposed to 1 mg/L HA. However, at higher concentrations of HA (5 and 25 mg/L), the opposite effect was observed. Combined exposure to HA, TBBPA, and PFOS resulted in oxidative stress in the digestive gland, with the severity of stress dependent on exposure time and HA dose. Histological analysis revealed a positive correlation between HA concentration and tissue damage caused by TBBPA and PFOS. This study provides insights into the influence of HA on the bioaccumulation-elimination patterns and toxicity of TBBPA and PFOS in marine bivalves, offering valuable data for ecological and health risk assessments of combined pollutants in aquatic environments rich in DOM.

Oxidation of selected fluoroquinolones by ferrate(VI) in water: Kinetics, mechanism, effects of constituents, and reaction pathways

In this work, the oxidation of gatifloxacin (GAT), fleroxacin (FLE) and enoxacin (ENO) in aqueous solution by ferrate (Fe(VI)) was systemically investigated. Weak alkaline and high oxidant doses were favorable for the reaction. The pseudosecond-order rate constants were 0.18055, 0.29162, and 0.05476 L/(mg·min), and the activation energies were 25.13, 15.25, and 11.30 kJ/mol at pH = 8.00 and n(Fe(VI)):n(GAT) = 30:1, n(Fe(VI)):n(FLE) = 20:1, n(Fe(VI)):n(ENO) = 40:1 and a temperature of 25 °C. The maximum degradation rates of the GAT, FLE and ENO were 96.72%, 98.48% and 94.12%, respectively, well simulated by Response Surface Methodology. During the oxidation, the contribution of hydroxyl radicals (HO•) varied with time, whereas the final contribution was approximately 20% at 30 min. The removal efficiency was inhibited by anions by less than 10%, and cations by less than 25%, and significantly inhibited by high concentrations of humic acid. Moreover, two or three dominant reaction pathways were predicted, and the ring cleavages of quinolone and piperazine were mainly achieved through decarboxylation, demethlation and hydroxylation, and some pathways ended up with monocyclic chemicals, which were harmless to aquatic animals and plants. Theoretical calculations further proved that the reactions between FeO4− and neutral fluoroquinolone antibiotics were the major reactions. This work illustrates that Fe(VI) can efficiently remove fluoroquinolone antibiotics (FQs) in aqueous environments, and the results may contribute to the treatment of wastewater containing trace antibiotics and Fe(VI) chemistry.

LIGNITE AS A RAW MATERIAL FOR THE PRODUCTION OF WATER-SOLUBLE SORBENTS

Large lignite reserves are concentrated in the Dnipro lignite basin of Ukraine. It is profitable to extract it by open-pit mining, as the seams are shallow. Ukrainian lignite is predominantly earthy, subbituminous, which in turn is characterized by a high content of free humic acids. Despite the significant lignite reserves in Ukraine and favourable conditions, its production is insignificant. Most of the lignite is used as fuel, and a small part of it is used as raw material. We have studied the lignite of the Oleksandriya deposit of Ukraine, which contains a large amount (about 80 %) of humic acid, which is the basis to produce effective water-soluble sorbents. The article investigates and determines the efficiency of using lignite from the Oleksandriya deposit to produce humic substances, their elemental composition, and the yield of humic acids from them. The efficiency of the use of humic substances obtained from lignite of the Alexandria deposit in the binding of heavy metal ions (Pb2+, Cd2+) using the method of complexation - ultrafiltration - was determined. The performance of ultrafiltration membranes with a humate solution was determined. The retention coefficient of metal ions, which depends on the concentration of humic substances, was calculated. The conducted studies allow us to assert that the application of the ultrafiltration-complexation method using complexing agents based on humic substances of lignite from the Alexandria deposit can significantly increase the degree of purification of aqueous solutions from heavy metal ions. These studies are relevant and expand the possibilities of using lignite. It has been shown that Ukrainian lignite can be used to produce an environmentally friendly and cheap complexing agent. An important priority for the use of water-soluble humic substances is the large lignite reserves in Ukraine, which can also contribute to improving economic performance. Also, the studies conducted suggest that the application of a combined method that combines ultrafiltration with complexation when using complexing agents based on lignite humic substances can significantly increase the degree of purification from heavy metal ions.

Influence of organic matter on the photocatalytic degradation of steroid hormones by TiO2-coated polyethersulfone microfiltration membrane

Water treatment in photocatalytic membrane reactors (PMR) holds great promise for removing micropollutants from aquatic environments. Organic matter (OM) that is present in any water matrix may significantly interfere with the degradation of steroid hormone (SH) micropollutants in PMRs. In this study, the interference of various OM types, humic acid (HA), Australian natural organic matter (AUS), worm farm extract (WF), tannic acid (TA), and gallic acid (GA) with the SH degradation at its environmentally relevant concentration (100 ng/L) in a flow-through PMR equipped with a polyethersulphone-titanium dioxide (PES-TiO2) membrane operated under UV light (365 nm) was investigated. Results of this study showed that OM effects are complex and depend on OM type and concentration. The removal of β-estradiol (E2) was enhanced by HA at its levels below 5 mgC/L while the enhancement was abated at higher HA concentrations. The E2 removal was inhibited by TA, and GA, while no significant interference observed for AUS, and WF. The data demonstrated diverse roles of OM that acts in PMRs as a light screening agent, a photoreactive species scavenger, an adsorption alteration trigger, and a photosensitizer. The time-resolved fluorescence measurement showed that HA, acting as a photosensitizer, promoted the sensitization of TiO2 by absorbing light energy and transferring energy/electron to the TiO2 substrate. This pathway dominated the mechanism of the enhanced E2 degradation by HA. The favorable effect of HA was augmented as increasing the light intensity from 0.5 to 10 mW/cm2 and was weakened at higher light intensities due to the increased scavenging reactions and the limited amount of HA. This work clarifies the underlying mechanism of the OM interference on photocatalytic degradation of E2 by the PES-TiO2 PMR.

Nitrate enhanced the carbon tetrachloride degradation in the UV/HCOOH reductive system

Catalytic hydrodechlorination is one of the most effective methods for remediating chlorinated organic wastewater. The influence of nitrate on the production capacity of the carbon dioxide radical anion (CO2·-) and the reduction efficiency of carbon tetrachloride (CT) in an ultraviolet/formic acid (UV/HCOOH) system was evaluated in this study. In the water distribution system, nitrate enhanced the degradation efficiency of CT (5 mg L−1) from 19.1 % to 95.2 % using formic acid (20 mM) under UV radiation, and the degradation rate was positively related to the nitrate concentration. Chloroform was the main by-product during the CT reduction and conversion and could be further dechlorinated to dichloromethane. Moreover, the environmental adaptability of UV/HCOOH/NO3 was better than that of UV/HCOOH over a wide pH range, and the degradation efficiency of CT in the UV/HCOOH/NO3 system was 83.4 % at pH 12. Except for the high concentrations of bicarbonate ions and humic acid, chloride and sulfate had little effect on the CT reduction efficiency in the UV/HCOOH/NO3 system. Experiments by electron paramagnetic resonance and quenching experiment showed that CO2·- radicals were primarily responsible for the CT reduction. In the water distribution system, the addition of nitrate enhances the rate of CO2·- radical generation in the UV/HCOOH system. The novel insights in this study highlight the significant potential of nitrate solutions to repair chlorinated solvents by enhancing the generation of CO2·- radicals in UV/HCOOH systems.

The influence of humic acid on metal(loid)s leaching in landfill leachate for enhancing landfill mining

The aim of this study was to investigate the effect of different concentrations of humic acid on the recovery rate of metal(loid)s in landfill leachate. The study focused on the release of 12 selected metal(loid)s, including critical raw materials (CRM) in landfills that were less than five years old and those that were more than ten years old. The experimental setup involved using different concentrations of humic acid (w/v) (0 %, 0.1 %, and 0.5 %) at pH 4 and 6. The results of the study showed that humic acid was effective in releasing Al, Cr, Co, Ni, Cu, Zn, As, Cd, and Pb. On the other hand, an increase in humic acid concentration led to a decrease in the release of Li, Mn, and Hg. The immobilization of Li, Mn, and Hg was due to the coordination and adsorption of humic acid. The presence of humic acid accelerated the release of metal(loid)s by carboxylic acidity compared to the recovery rate of metal(loid)s in landfill leachate without humic acid. However, a higher concentration of humic acid did not always result in a stronger recovery rate. The recovery rate of metal(loid)s was related to the solubility and concentration of humic acid. These findings can inform the development of more efficient and environmentally-friendly methods of recovering metal(loid)s using humic acid as a leaching agent.

THE COMPOSITION OF THE ORGANIC MATTER AND MICROELEMENTS OF SPHAGNUM PEATS IN THE NORTHERN PART OF THE VASYUGAN PEAT DEPOSIT AND DIRECTIONS FOR THEIR USE

The results of studies of sphagnum peats in the northern part of the Vasyugan peat deposit are presented. Peat sampling points were planned based on the materials of detailed exploration. The samples were collected in the form of mixed samples, which were taken at 3–4 points from the middle of the genetic layer of the peat deposit, the core height was 0.5 m. The peat quality assessment was carried out on the requirements for peat as a raw material for different uses. It is shown that the ash of different types of sphagnum peats may have elevated values of Ca, Mg and Fe. It is revealed that the elemental analysis of sphagnum peats has individual features of their content. It was found that the group composition of the organic matter of sphagnum peats is characterized by a high content of water-soluble and easily hydrolyzed matters and a low content of humic and fulvic acids. At the same time, in two samples, an increased content of bitumen was noted (samples 2 and 11), and in sample 9, a high content of humic and fulvic acids was detected and at the same time a low content of water-soluble and easily hydrolyzed matters. It is revealed that it is impossible to reduce all the variety of peat properties only to the species characteristic and the degree of decomposition due to the wide variability of the leading and subordinate peat-forming agents in the peat composition. It is shown that the properties of sphagnum peats of the oligotrophic type of the studied territory show their suitability for the production of many types of products, and the duration of operation of these reserves stretches up to 200 thousand years.