Humic Acid Concentration Research Articles

Simultaneous removal of lead(II) and cadmium(II) from acidic wastewater by Fe-modified sludge biochar

In natural environments, heavy metal water pollution often involves simultaneous presence of various heavy metal ions (HMs), posing significant challenges for their removal. In this study, Fe-modified sludge biochar was synthesized via the co-precipitation method, and the effects of various environmental factors on simultaneously removing lead(II) and cadmium(II) by Fe@SBC were investigated. Batch adsorption experiments showed that Fe@SBC has a higher removal capacities for Pb(II) than for Cd(II) in both single or binary solutions. Increasing solution pH promoted the HMs removal on Fe@SBC. Coexisting divalent cations (Mg2+ and Ca2+) exhibited stronger inhibitory effects on HMs removal by Fe@SBC than monovalent cations (K+ and Na+). The presence of humic acid (HA) did not affect Pb(II) removal on Fe@SBC in either single or binary systems. In single systems, increasing HA concentration enhanced Cd(II) removing on Fe@SBC, while in binary systems, increasing HA concentrations inhibited the Cd(II) removal on Fe@SBC. The sorption of Pb(II) and Cd(II) on Fe@SBC followed the pseudo-second-order kinetic model and the Langmuir model. The removal mechanisms involved electrostatic interactions, complexation with O-containing group, and mineral dissolution-precipitation. After three regenerations, the adsorption capacity of Fe@SBC for Pb(II) and Cd(II) decreased by approximately 5–10 %. In summary, this environmentally friendly composite material has great potential for simultaneously remediating of Pb(II) and Cd(II).

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.

Enhanced diclofenac adsorption and degradation using iron‐loaded modified spent bleaching earth carbon in the presence of clofibric acid: mechanistic insights and toxicity assessment

AbstractBACKGROUNDThe presence of pharmaceutical active substances such as diclofenac (DCF) and clofibric acid (CA) in aquatic environments poses significant ecological threats. Existing treatments have not fully explored the impact of CA on DCF removal efficiency. This research introduces nZVI/CTAB‐SBE@C, a novel adsorbent developed from industrial spent bleaching earth (SBE), modified with cetyltrimethylammonium bromide (CTAB) and nano zero‐valent iron (nZVI), enhancing both adsorption and degradation of DCF and CA.RESULTSThis study investigated the impact of CA on the removal capabilities of nZVI/CTAB‐SBE@C for DCF in a coexisting system. Systematic examinations were conducted on the effects of various parameters, including reaction time, dosage, temperature, actual wastewater, humic acid content and coexisting ions. Results indicated that the presence of CA significantly enhanced the DCF removal efficiency, achieving an optimal rate of 87.3% under conditions of reaction time 2 h, adsorbent dosage 5 g L−1 and temperature 25 °C. Moreover, interactions between Al3+ ions and the adsorbent matrix notably improved removal efficiencies for both DCF and CA. Analysis revealed that CA facilitated new degradation pathways for DCF, including hydroxylation and decarboxylation reactions. Additionally, the presence of CA reduced the toxicity of degradation intermediates, enhancing environmental safety compared to systems containing only DCF.CONCLUSIONThis study effectively transforms industrial waste into the efficient nZVI/CTAB‐SBE@C adsorbent. The presence of CA not only boosts DCF removal efficiency but also promotes its safer degradation, thereby reducing the ecological impact of contaminants. © 2024 Society of Chemical Industry (SCI).

Hemostatic Gelatin-Alginate Hydrogels Modified with Humic Acids and Impregnated with Aminocaproic Acid

The work is devoted to the development of safe and biocompatible multicomponent gelatin-alginate hydrogels modified with humic acids (HA) and impregnated with the antifibrinolytic agent aminocaproic acid (АА).These hydrogels are designed to be effective hemostatic materials with anti-inflammatory properties and the ability to deliver in less than 30 seconds to deep and hidden areas of hemorrhages. Studies of the crystal structure by X-ray diffraction analysis and non-covalent interactions of molecules by Fourier transform infrared spectroscopy of the developed hemostatic gelatin-alginate hydrogels modified with bactericidal and anti-inflammatory humic acids made it possible to identify the optimal concentrations of HA from 2.5 wt.%. up to 5 wt.%. At such concentrations of HA, gelatin-alginate hydrogels have a semicrystalline structure. Due to non-covalent bonds between polymer chains, they are thermo-responsive with a gel-sol transition temperature of about 37 °C. Impregnation of these hydrogels with aminocaproic acid led to an almost threefold increase in their swelling, which facilitated the dissolution of AA in the hydrogels and its subsequent delivery to the wound. Experiments simulating the transmembrane transport of aminocaproic acid from the developed gelatin-alginate hydrogels confirmed their ability to rapidly deliver up to 494± 3 mg of AA from 5 ml of hydrogel to the wound.

Reevaluating biostimulation strategies: the impact of humic acid on ofloxacin bioadsorption

The exogenous addition of humic acid (HA) is often seen as a biostimulation strategy to expedite the bioremediation of various pharmaceutical pollutants. Nevertheless, the impact of HA on the bioadsorption of ofloxacin (OFL), the main pathway for OFL removal in activated sludge, remains unknown. In this study, the presence of 10 mg/L HA notably decreased the theoretical OFL adsorption capacity from 8.94 to 7.95 mg/g. The inhibitory effect persisted across varying pH and ionic strengths and became more pronounced with increasing HA concentration. The morphological changes on biosolid (BIO) induced by HA indicated that HA was bioadsorbed, which in turn competed with OFL for metal binding sites like Ca and Mg on BIO. Further analysis of the OFL-HA interaction reveals the involvement of hydrogen bonding and electrostatic attraction. The study also demonstrates the bridging role of HA between OFL and BIO through consecutive desorption and re-absorption processes of OFL in the presence of HA. To quantify the direct and indirect adsorption ratios, a new approach was proposed, which determined the mass ratios of direct (OFL:BIO) and indirect bioadsorption (OFL:HA:BIO) as 1:192 and 1:21:854, respectively. These findings suggest that the indirect OFL adsorption through the HA bridge could not compensate for the adverse effects caused by the reduction of metal binding sites. Overall, this study calls for a reassessment of the addition of HA in the bioremediation process of OFL. Considering that HA widely coexists with antibiotics in wastewater, the study also provides valuable insights into OFL removal mechanisms in WWTPs.

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.

Effects of humic acid fertilizer on the growth and microbial network stability of Panax notoginseng from the forest understorey

Humic acid (HA) can substantially enhance plant growth and improve soil health. Currently, the impacts of HA concentrations variation on the development and soil quality of Panax notoginseng (Sanqi) from the forest understorey are still unclear. In this study, exogenous HA was administered to the roots of Sanqi at varying concentrations (2, 4, and 6 ml/L). Subsequently, the diversity and community structure of bacteria and fungi were assessed through high-throughput sequencing technology. The investigation further involved analyzing the interplay among the growth of sanqi, soil edaphic factors, and the microbial network stability. Our finding revealed that moderate concentrations (4 ml/L) of HA improved the fresh/dry weight of Sanqi and NO3-−N levels. Compared with control, the moderate concentrations of HA had a notable impact on the bacterial and fungal communities compositions. However, there was no significant difference in the α and β diversity of bacteria and fungi. Moreover, the abundance of beneficial bacteria (Bradyrhizobium) and harmful bacteria (Xanthobacteraceae) increased and decreased at 4 ml/L HA, respectively, while the bacterial and fungal network stability were enhanced. Structural equation model (SEM) revealed that the fresh weight of Sanqi and bacterial and fungal communities were the factors that directly affected the microbial network stability at moderate concentrations of HA. In conclusion, 4 ml/L of HA is beneficial for promoting Sanqi growth and soil quality. Our study provides a reference for increasing the yield of Sanqi and sustainable development of the Sanqi-pine agroforestry system.

Soil Solution Properties of Tropical Soils and Brachiaria Growth as Affected by Humic Acid Concentration

The soil solution is the compartment where plants uptake nutrients and this phase is in equilibrium with the soil solid phase. Changes in nutrient content and availability in the soil solution can vary among soil types in response to humic acid concentrations, thereby affecting Brachiaria growth. However, there are no studies demonstrating these effects of humic acid application on different soil types and how they affect Brachiaria growth. Thus, the aim of this study was to evaluate the effects of humic acid concentrations (0, 5, 10, 25, and 60 mg kg−1 carbon-humic acid) on Brachiaria brizantha growth and soil solution properties of contrasting tropical soils. Plants were grown for 35 days in greenhouse conditions in pots containing Sandy Entisol, Clayey (Red Oxisol), and Medium Texture (Red-Yellow Oxisol). Soil solution was assessed for pH, electrical conductivity (EC), carbon, and nutrient content. Shoot and root dry matter, as well as macro and micronutrients accumulation in the shoot, were determined. In a soil type-dependent effect, pH, EC, and concentrations of nutrients in solutions changed in response to carbon-humic acid concentration. In the less-buffered soils, Sandy Entisol and Red-Yellow Oxisol, the addition of 30–40 mg kg−1 carbon-humic acid increased root proliferation by 76–89%, while Brachiaria biomass produced in all soils increased by approximately 30%. Levels of carbon in solution were high (>580 mg L−1) and varied depending on the investigated soil type. Though solution carbon contents did not appear to be a driving factor controlling the positive effects of humic acid concentrations on Brachiaria dry matter, there was a direct relationship between other properties and nutrient content in the soil solution, and Brachiaria dry matter production.

Biostimulation of humic acids on Lepidium sativum L. regulated by their content of stable phenolic O⋅ radicals

BackgroundHumic acid affects plant growth. Its source and structure may play a central role to its functionality. The relationship between humic acid and plant bioactivity is still unclear. This study investigated the biostimulation effects of two natural humic acids derived from soil (SHA) and lignite (LHA) on Lepidium sativum in comparison to a synthetic humic acid model (HALP) with known structure.ResultsAll humic acids positively affected cress seed germination and root elongation. Greater root hairs density and dry matter, compared to control, were observed using concentration of 5 mg L−1 for HALP, 50 mg L−1 for LHA, and 100 mg L−1 for SHA. The germination index was the largest (698% more effective than control) with 50 mg L−1 of SHA, while it was 528% for LHA, and 493% for HALP at 5 mg L−1. SHA contained the lowest aromatic and phenolic C content, the largest pK2 value of 9.0 (7.7 for LHA and 7.6 for HALP), the least ratio between the aromaticity index and lignin ratio (ARM/LigR) of 0.15 (0.66 for LHA and 129.92 for HALP), and at pH 6.3 the lowest amount of free radicals with a value of 0.567 × 1017 spin g−1 (1.670 × 1017 and 1.780 × 1017 spin g−1 for LHA and HALP, respectively), with the greatest g value of 2.0039 (2.0035 for LHA and 2.0037 for HALP).ConclusionsThe overall chemical structure of humic acids exerted a biostimulation of cress plantlets. The level of the intrinsic stable free radicals identified by EPR in the humic acids resulted well correlated to the ARM/LigR ratio calculated by NMR. Our results suggested that HA biostimulation effect is related to its applied concentration, which is limited by its free radical content. The modulation of the humic supramolecular structure by ROS and organic acids in root exudates can determine the release of bioactive humic molecules. When the content of the intrinsic humic free radicals is high, possible molecular coupling of the bioactive humic molecules may hinder their biostimulation activity. In such cases, a low humic acid concentration appears to be required to achieve the optimum biostimulation effects.Graphical

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.

Influence of macromolecules and electrolytes on heteroaggregation kinetics of polystyrene nanoplastics and goethite nanoparticles in aquatic environments

Fate and transport of nanoplastics in aquatic environments are affected by their heteroaggregation with minerals in the presence of macromolecules. This study investigated the heteroaggregation of polystyrene nanoplastics (PSNPs) with goethite nanoparticles (GNPs) under the influence of macromolecules [humic acid (HA), bovine serum albumin (BSA), and DNA] and electrolytes. Under 1 mg C/L macromolecule, raising electrolyte concentration promoted heteroaggregation via charge screening, except that calcium bridging with HA also enhanced heteroaggregation at CaCl2 concentration above 5 mM. At all NaCl concentrations and CaCl2 concentration below 5 mM, 1 mg C/L macromolecules strongly retarded heteroaggregation, ranking BSA > DNA > HA. Raising macromolecule concentration strengthened such stabilization effect of all macromolecules in NaCl solution and that of DNA and BSA in CaCl2 solution by enhancing steric hindrance. However, 0.1 mg C/L BSA slightly promoted heteroaggregation in CaCl2 solution due to stronger electrostatic attraction than steric hindrance. In CaCl2 solution, raising HA concentration strengthened its destabilization effect via calcium bridging. Macromolecules having more compact globular structure and higher molecular weight may exert greater steric hindrance to inhibit heteroaggregation more effectively. This study provides new insights on the effects of macromolecules and electrolytes on heteroaggregation between nanoplastics and iron minerals in aquatic environments.

Effect of humic acid on aerobic denitrification by Achromobacter sp. strain GAD-3

Humic acid (HA), a common natural organic matter, could affect conventional anoxic denitrification. Aim of this study was to investigate effect of HA on the process of aerobic denitrification in Achromobacter sp. GAD-3, an aerobic denitrifying strain. The findings demonstrated that an increase in HA concentrations (≥5mgL-1) promoted the aerobic denitrification process (excluding N2O reduction), manifesting as higher rates of nitrate removal (6.67-11.1mgL-1h-1) and lower levels of nitrite accumulation (30.2-20.7mgL-1). This was attributed to the increased electron transfer activities and denitrifying reductase activities (including NAR, NIR and NOR) facilitated by HA. Accordingly, the expression of denitrification genes such as napA, cnorB, and nirS was enhanced by HA. Nonetheless, the nosZ gene and N2OR activity underwent suppression by HA, which was accountable for N2O emission. It is crucial to understand the HA mechanism towards aerobic denitrifiers for wastewater treatment plants to enhance nitrogen removal.

Adsorption–desorption and leaching behavior of benzovindiflupyr in different soil types

Benzovindiflupyr is a succinate dehydrogenase inhibitor fungicide that targets mitochondrial function for disease control. In this study, we investigated the adsorption–desorption and leaching behavior of benzovindiflupyr in eight soil types using the batch equilibrium method and the soil column leaching method. A Freundlich model (r2 > 0.9959) was used to better characterize the adsorption-desorption process in eight soil types, with adsorption coefficients (KF-ads) ranging from 2.303 to 17.886. KF-ads was significantly and positively correlated (p < 0.05) with the organic carbon content. High temperatures and increased initial pH of aqueous solutions led to a decrease in benzovindiflupyr adsorption in the soil. The adsorption was also influenced by factors such as ionic strength, humic acid, surfactant type, microplastic type, and particle size and concentration. Moreover, benzovindiflupyr exhibited low leachability in all four soils selected, but different leaching solutions affected the risk of benzovindiflupyr migration to groundwater. Overall, this study provides insights into the adsorption characteristics of benzovindiflupyr in different soils and provides key information for environmental risk assessment.

Evaluation of chemical properties and humification process during co-composting of spent mushroom substrate (Pleurotus ostreatus) and pig manure under different mass ratios

Spent mushroom substrate (SMS) from Pleurotus ostreatus is high in salinity, susceptible to deterioration caused by mold, and not suitable for direct application in soil. Its high C/N ratio and low pH inhibit the humification process during composting. Pig manure (PM) possesses high density and low porosity, impeding microbial metabolism. Co-composting SMS and PM can overcome these challenges. A 120-day composting experiment was conducted with varying mass ratios of SMS and PM, supplemented with calcium bentonite and microbial inoculum. After composting, there was observed a significant rise in the N and K2O contents, ranging from 11.1% to 84.1% and 55.1%–296.8%, respectively. Additionally, there was a decrease in the C/N ratio by a range of 18.9%–60.1%. The total nutrient content of SMS post-composting solely was a mere 4.9%, failing to meet the 5% required by China's Professional Standard outlined for organic fertilizers (NY/T525-2021). Composting PM alone simplified the molecular structure of humic-extracted acid (HE) and reduced the C content of humic acid (HA) by up to 18.1%. In contrast, co-composting SMS and PM in equal proportions stimulated microbial consumption of water-soluble substances, resulting in increase in C contents of HE and HA by 11.5% and 18.7%, respectively, along with a 15.4% rise in the polymerization level of the composted materials. Furthermore, this combination facilitated the conversion of inert humic component, reducing C content of humin by 79.3%, lowering the electrical conductivity (EC) value by 23.0%, and boosting GI value by 154.1%. Increasing the proportion of SMS in co-compost proved advantageous in enriching its organic matter content. The composting process involved bio-degradation of O-containing functional groups like phenols and alcohols, utilization of polysaccharides by microorganisms, and development of carboxyl groups in the HA. Based on the above index analysis, the most effective compost ratio to achieve higher humification level and compost quality was determined to be a mass ratio of SMS to PM of 5:5, followed by 6:4.

Ultrasmall copper-metal organic framework (Cu-MOF) quantum dots decorated on waste derived biochar for enhanced removal of emerging contaminants: Synergistic effect and mechanistic insight

This study proposes a novel one-pot hydrothermal impregnation strategy for surface decoration of waste derived pisum sativum biochar with zero‒dimensional Cu‒MOF Quantum dots (PBC‒HK), with an average particle size of 5.67 nm, for synergistic removal of an emerging sulfur containing drug pantoprazole (PTZ) and Basic Blue 26 (VB) dye within 80 min and 50 min of visible-light exposure, respectively. The designed Integrated Photocatalytic Adsorbent (IPA) presented an enhanced PTZ removal efficiency of 95.23% with a catalyst loading of 0.24 g/L and initial PTZ conc. 30 mg/L at pH 7, within 80 min via synergistic adsorption and photodegradation under visible-light exposure. While, on the other hand, 96.31% VB removal efficiency was obtained in 50 min with a catalyst dosage of 0.20 g/L, initial VB conc. 60 mg/L at pH 7 under similar irradiation conditions. An in-depth analysis of the synergistic adsorption and photocatalysis mechanism resulting in the shortened time for the removal of contaminants in the synergistic integrated model has been performed by outlining the various advantageous attributes of this strategy. The first-order degradation rate constant for PTZ was found to be 0.04846 min−1 and 0.04370 min−1 for PTZ and VB, respectively. Adsorption of contaminant molecules on the biochar (PS‒BC) surface can facilitate photodegradation by accelerating the kinetics, and photodegradation promotes regeneration of adsorption sites, contributing to an overall reduction in operation time for removal of contaminants. Besides enhancing the adsorption of targeted pollutants, the carbon matrix of IPAs serves as a surface for adsorption of intermediates of degradation, thereby minimizing the risk of secondary pollution. The photogenerated holes present in the VB is responsible for the generation of •OH radicals. While, the photogenerated electrons present in the CB are captured by Cu2+ of the MOF metal center, reducing it to Cu+, which is subsequently oxidized to produce additional •OH species in the aqueous medium. This process leads to effective charge separation of the photogenerated charge carriers and minimizes the probability of charge recombination as evident from photoluminescence (PL) analysis. Meanwhile, PL studies, EPR and radical trapping experiments indicate the predominant role of •OH radicals in the removal mechanism of PTZ and VB. The investigation of the degradation reaction intermediates was confirmed by HR‒LCMS, on the basis of which the plausible degradation pathway was elucidated in detail. Moreover, effects of pH, inorganic salts, other organic compounds and humic acid concentration have been investigated in detail. The environmental impact of the proposed method was comprehensively evaluated by ICP-OES analysis and TOC and COD removal studies. Furthermore, the economic feasibility and the cost-effectiveness of the catalyst was assessed to address the potential for large scale commercialization. Notably, this research not only demonstrates a rational design strategy for the utilization of solid waste into treasure via the fabrication of IPAs based on MOF Quantum dots (QDs) and waste-derived biochar, but also provides a practical solution for real wastewater treatment systems for broader industrial 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.

Response of humification process to fungal inoculant in corn straw composting with two different kinds of nitrogen sources

Inoculation is widely used in composting to improve the mineralization process, however, the link of fungal inoculant to humification is rarely proposed. The objective of this study was to investigate the effect of compound fungal inoculation on humification process and fungal community dynamics in corn straw composting with two different kinds of nitrogen sources [pig manure (PM) and urea (UR)]. Structural equation modeling and random forest analysis were conducted to identify key fungi and explore the fungi-mediated humification mechanism. Results showed that fungal inoculation increased the content of humic acids in PM and UR by 71.76 % and 53.01 % compared to control, respectively. High-throughput sequencing indicated that there were more key fungal genera for lignin degradation in PM especially in the later stage of composting, but a more complex fungal (genera) connections with lower humification degree was found in UR. Network analysis and random forest suggested that inoculation promoted dominant genus such as Coprinus, affecting lignocellulose degradation. Structural equation modeling indicated that fungal inoculation could promote humification by direct pathway based on lignin degradation and indirect pathway based on stimulating the indigenous microbes such as Scedosporiu and Coprinus for the accumulation of carboxyl and polyphenol hydroxyl groups. In summary, fungal inoculation is suitable to be used combining with complex nitrogen source such as pig manure in straw composting.

Soil organic matter components and sesquioxides integrally regulate aggregate stability and size distribution under erosion and deposition conditions in southern China

Water erosion considerably affects the stability and particle size distribution of soil aggregates, but the underlying mechanisms of water erosion remain unclear. To this end, we selected four landscape positions (top-, up-, mid-, and toe-slope) with distinct erosion and deposition characteristics on a typical eroded slope in southern China to conduct experiments- aiming to investigate the main drivers of soil aggregate stability during erosion and deposition processes. Soil samples were collected from 12 sites, and 4 size classes (>2, 2–0.25, 0.25–0.053, and <0.053 mm) of soil aggregates were obtained using the wet sieving method. The composition and stability of the soil aggregates, as well as the contents of organic (organic matter components) and inorganic (iron-aluminum oxides) cementing materials of different particle sizes, were determined. The results indicated that erosion significantly reduced the aggregate stability and the >0.25 mm water-stable aggregate content (WR0.25) (P < 0.05). The mean weight diameter (MWD) and geometric mean diameter (GMD) values of the soil aggregates at the eroding site decreased, and the fractal dimension (FD) increased. Furthermore, erosion markedly reduced the humic acid (HA) and fulvic acid (FA) contents in the bulk soils and soil aggregates, while the HA content showed no obvious difference between the eroding and depositional sites. In addition to the presence of complexed iron/alumina oxides (Fep/Alp), erosion markedly reduced the contents of amorphous (Feo/Alo) and free-form (Fed/Ald) iron/alumina oxides in the bulk soils and size fractions. Moreover, Fed/Ald, Fep and Feo/Alo were present in the microaggregates, while Alp was found in the macroaggregates. Additionally, boosted regression tree (BRT) analysis indicated that FA (36.70 %), Feo (19.00 %), and Ald (12.71 %) were the crucial predictors of soil aggregate stability. These findings further confirm that the organic and inorganic cementing materials in red soils collectively contribute to aggregate stabilization under the impact of erosion. This study facilitates a deeper understanding of the mechanisms governing soil aggregate stability in eroded landscapes, and provides a theoretical basis for biogeochemical cycling processes.

Growth and flowering of gerbera (Gerbera jamesonii) as affected by different concentrations of micronutrients and humic acid under naturally ventilated polyhouse conditions of Prayagraj

Growth and flowering of gerbera (Gerbera jamesonii) as affected by different concentrations of micronutrients and humic acid under naturally ventilated polyhouse conditions of Prayagraj

Superoxide radicals dominated hydrogen peroxide activation using BiOI for boosting Fenton-like catalytic degradation of bisphenol A

Herein, flower-like BiOI micro-spherulites were successfully prepared via a solvothermal method, and it exhibited a remarkably Fenton-like catalytic efficacy in the degradation of BPA under dark condition without additional energy input. BiOI can function as an electron-poor center, facilitating the activation of H2O2 into •O2−, while simultaneously serving as an electron-rich center to reduce dissolved O2 to •O2−. This electron-rich and electron-poor centers of BiOI synergistically enhance the •O2− generation for highly Fenton-like catalytic performance. Moreover, the removal performance of BPA demonstrated a significant pH dependency, and the presence of low concentrations of halide ions and humic acid did not exhibit noticeable inhibitory effect on the degradation of BPA. Additionally, several intermediates have been identified to propose a comprehensive degradation mechanism for BPA. This study presents a novel BiOI Fenton-like catalytic system for the purification of recalcitrant organic pollutants in wastewater.