Humic Research Articles

Influence of Organic Fertilizers on the Reactivity of the Low-Grade Phosphate Rock in a Sandy Soil: Incubation and Release Experiments

ABSTRACT Foods’ increasing demand, agricultural intensification, and affordable fertilizer drive low-grade phosphate rock (LGPR) use in farming. Incubation and release-batch experiments were conducted to investigate the phosphorus (P) availability as the LGPR was added to a coarse-textured alkaline soil. Incubation of the treated soil for 12 weeks was applied. The influence of co-application of LGPR with compost, poultry manure (PM), humic acid (HA), or farmyard manure (FYM) on P availability was evaluated. The changes in available P, soil pH, and exchangeable calcium (Ca) were quantified during the incubation. The released P was measured overtime at the end of the 12 weeks of incubation. Statistical analyses were conducted to assess the significant differences between treatments and identify the association of the available P with soil pH and the exchangeable Ca. Results revealed that the LGPR addition of 4.76 ton ha−1 increased the available P from 5.74 mg kg−1 to 11.57 mg kg−1 in the soil. However, the co-application of compost resulted in the highest available soil P (28.84 mg kg−1). Accurate predictions of the available P based on soil pH or exchangeable Ca were realized. The results demonstrate the beneficial impact of using LGPR in alkaline sandy soil.

INFLUENCE OF HUMIC ACIDS ON RHEOLOGICAL PROPERTIES OF COMPOSITE SUSPENSIONS BASED ON PYROCARBON

The possibility of utilizing technical pyrocarbon obtained as a result of pyrolysis of waste tires into composite suspension fuel was investigated. It was determined that the surface of unmodified pyrocarbon has a positive surface charge in the pH range of 2-10. The addition of humic acid causes a change in the surface charge of pyrocarbon and an overcharge of the surface. The influence of stabilizer additives on the rheological properties of composite suspension fuel based on pyrocarbon was studied. Carboxymethyl cellulose, OP-10, and humic acids were used as stabilizers. It is shown that the composite suspension fuel based on pyrocarbon has a synergistic effect of the addition of OP-10 with sodium humate to reduce the effective viscosity and fluidity of suspensions. A composite suspension fuel consisting of [0.5% C3 + 0.25% OP + 3% HA] at a solid phase concentration of 51.7% was proposed. The effective viscosity of the obtained suspensions does not exceed 0.9 Pa‧sec, and the sedimentation stability is 28-30 days. This allows us to recommend the obtained suspensions as liquid suspension fuel for liquid fuel units.

Soil-Easily Extractable Glomalin: An Innovative Approach to Deciphering Its Molecular Composition under the Influence of Seasonality, Vegetation Cover, and Wildfire.

Easily extractable glomalin (EEG) is a fraction of soil organic matter thought to contain mainly glomalin-related soil glycoproteins produced by mycorrhizal fungi. The EEG has an impact on various soil ecological functions, primarily related to soil aggregation formation and stability as well as water repellence. Here, analytical pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was used for studying the molecular composition of soil EEG, and a detailed description of the chemical composition is reported. Samples extracted from Mediterranean soils under different vegetation covers (Pinus halepensis and shrubland species, Rosmarinus officinalis, and Brachypodium spp, predominantly), impacted or not by forest fires and collected at different times, were studied. A total of 139 compounds were identified and grouped based on their probable biogenic origin. The EEG chemical composition is dominated by lipids, aromatic compounds, steranes, and hydroaromatics with a remarkable abundance of compounds from plant origin. Significant EEG structural changes can indicate environmental disturbances such as those after a wildfire. The EEG soil organic fraction is found to be a stable and heat-resistant material in nature if soil temperatures remain below 200-250 °C. This study advances the understanding of EEG by providing a detailed molecular characterization and highlighting its role as a stable, heat-resistant component of soil organic matter in Mediterranean ecosystems. The main findings indicate that while EEG is structurally resilient and mostly originates from plant material, its composition is more similar to that of humic acids than to that of glycoproteins.

The effect of temperature on the activity of microorganisms in the area of the Bureiskiy Landslide

The manuscript presents the results of experimental studies of the adaptive potential of microorganisms that are part of the bacterioplankton of the surface and bottom water layers of the Bureiskoe Reservoir in the zone of the landslide that descended in the winter of 2018. In the summer of 2022, the structure and activity of microbial complexes from area near the landslide were studied. More than 60 strains of microorganisms of different physiological groups were isolated. On the example of 4 strains isolated from different habitats (above and below the landslide body, surface and bottom layers of water) after 30 days of freezing at a temperature of –18°C, their viability and activity in the utilization of easily available nitrogen-containing organic substances were shown. In experimental cyclic freezing-thawing, two variants of thawing were used: slow thawing in a refrigerator from –18°C to +4°C; fast defrosting over a wide temperature range from –18°C to +23°C (at room temperature). Regardless of location, all strains grew vigorously in vitro with use of a readily available peptone carbon source before and after freezing. The maximum activity on peptone was shown by strain 40 BB (below the landslide body, bottom water) in the absence of substrate change. Utilization of peptone as a source of amino acids and peptides could be accompanied by activation of the protective function against cold stress. The selected strains of microorganisms differed in their ability to transform sodium humate molecules depending on the conditions of the freeze/thaw cycles. According to the spectral characteristics, significant changes in the aliphatic and aromatic components of the humate molecule occurred with the participation of strains 45 AB and 40 BB isolated from the bottom water. These strains were more active at low thawing temperatures, which actually corresponded to the in situ temperature of the bottom water layers, which is 4–6°C. Strain 13 BS from surface water sampled below the landslide body is characterized by active transformation of the aromatic component of humic substances in a wide range of thawing temperatures (from –18 to +23°C). The results indicate that in different regions during the thawing of permafrost and the influx of specific organic substances the specific mechanisms of formation of the quality of natural waters may manifest.

Chemodiversity and Molecular Mechanism Between Per-/Polyfluoroalkyl Substance Complexation Behavior of Humic Substances in Landfill Leachate

Landfill leachate contains a range of organic and inorganic pollutants, including per-/polyfluoroalkyl substances (PFASs), which can infiltrate into surrounding soil and groundwater through leaching processes, and can pose a threat to human health via food chains and drinking water processes. Thus, the transport of PFASs in landfill leachate is a research hotspot in environmental science. This study investigates the complexation and adsorption mechanisms between humic substances and PFASs in landfill leachate at the molecular level. Experimental results demonstrate that the binding constant logKsv of humic substances with PFASs correlates positively with specific ultraviolet absorbance (SUVA254), absorbance ratio (A250/A365), humification index (HIX), and fluorescence index (FI), while it exhibits a negative correlation with the biological index (BIX). These findings indicate that high aromaticity is a prerequisite for molecular interactions between humic substances and PFASs, with polar functional groups further facilitating the interaction. Molecular-level analysis revealed that humic substances undergo complexation and adsorption with PFASs through hydrophobic interactions, van der Waals forces, hydrogen bonding, ionic bonding, and covalent bonding, by functional groups such as hydroxyl, aliphatic C-H bonds, aromatic C=C double bonds, amides, quinones, and ketones. Future efforts should focus on enhanced co-regulation and mitigation strategies addressing the combined pollution of PFASs and humic substances in landfill leachate.

Enhancing the content of biologically active components in cluster tomatoes using organic fertilizers

Tomatoes (Solanum lycopersicum L.) are a vital agricultural crop with significant nutritional value, attributed to their high content of vitamins, minerals, and antioxidants. The antioxidant properties of tomatoes contribute to reducing the risk of cardiovascular and oncological diseases, positioning them as an important component of a balanced diet and beneficial for public health. The application of organic fertilizers containing fulvic and humic acids is particularly relevant to ensure the production of high-quality and nutritious tomatoes. These compounds, recognized as bio stimulants in plant cultivation, enhance physiological processes in plant cells. They stimulate protein and nucleic acid synthesis, activate enzymatic activity, and regulate metabolic pathways, thereby improving the biochemical composition of tomato fruits, increasing their nutritional quality, and enriching the content of bioactive compounds. The objective of this study is to evaluate the accumulation of bioactive compounds such as lycopene, total phenols, vitamin C, total sugars, and dry matter in cluster tomato fruits using an Armenian fertilizer containing fulvic and humic acids. Additionally, the research aims to provide practical insights into sustainable agriculture by identifying optimal agronomic practices that enhance the accumulation of these bioactive compounds in cluster tomatoes. The research was conducted on greenhouse-grown cluster tomato hybrids: Syune F1 (Armenian breeding), Prodezo F1 (Rijk Zwaan), Santiano F1 (Rijk Zwaan), Adventure F1 (Rijk Zwaan), and Climbo F1 (Syngenta) during the spring growing seasons from the years 2022 to 2024. The experiment utilized an organic fertilizer, and applied by abiding the following treatment scheme: 1. Control (St) — no organic fertilizer application, 2. Root treatment (RT), 3. Foliar treatment (FT), 4. Combined root and foliar treatment (RT-FT). Biochemical analyses of the tomato fruits were performed to quantify lycopene, total phenols, ascorbic acid, and total sugars using spectrophotometry, while dry matter content was determined via refractometry. Statistical data analysis was conducted using analysis of variance (ANOVA). The study demonstrated that all treatment types with fulvic-humic fertilizer contributed to improving tomato fruit quality and the accumulation of biologically active components. The most effective treatment was the combined root and foliar application (RT-FT), which resulted in the highest values across all measured parameters. Depending on the hybrid, lycopene content increased by 11.1–15.9%, total phenols by 14.7–22.8%, when vitamin C by 13.1–15.9%, total sugars by 13.5–21.7%, and dry matter by 14.6–22.5% compared to the control. The 'Syune' and 'Climbo' hybrids exhibited the highest accumulation of lycopene and phenols, highlighting their potential for enhancing antioxidant properties. The 'Santiana' and 'Adventure' hybrids were notable for their elevated ascorbic acid content, making them particularly valuable for improving nutritional quality. The best results for sugar and dry matter accumulation were observed in the 'Syune' and 'Prodezo' hybrids, indicating improved flavor profiles in these tomato varieties. Keywords: tomatoes, lycopene, total phenols, ascorbic acids, total sugars, dry matter, organic fertilizer, fulvic acids, humic acids

Reducing Cd and Pb Accumulation in Potatoes: The Role of Soil Passivators in Contaminated Mining Soils

This work aimed to explore safe techniques for the utilization of farmland surrounding mining areas contaminated with heavy metals—specifically cadmium (Cd) and lead (Pb)—in order to achieve food security in agricultural production. A potato variety (Qingshu 9) with high Cd and Pb accumulation was used as the test crop, and seven treatments were set up: control (CK), special potato fertilizer (T1), humic acid (T2), special potato fertilizer + humic acid (T3), biochar (T4), calcium magnesium phosphate fertilizer (T5), and biochar + calcium magnesium phosphate fertilizer (T6). The remediation effect of the combined application of different passivators on the accumulation of cadmium and lead in potatoes in the contaminated soil of a mining area was studied. The results showed that, compared with CK, all passivator treatments improved the physical and chemical properties of the soil and reduced the available Cd and Pb content in the soil and in different parts of potatoes. The T6 treatment yielded the most significant reduction in the available Cd and Pb content in the soil, the Cd and Pb content in the potato pulp, and the enrichment factor (BCF) and transfer factor (TF) of the potatoes. Compared with T4 and T5, the content of available Cd in the soil decreased by 1.22% and 4.71%, respectively; the soil available Pb content decreased by 3.13% and 3.02%, respectively; the Cd content in the potato pulp decreased by 68.08% and 31.02%, respectively; and the Pb content decreased by 31.03% and 20.00%, respectively. The results showed that the application of biochar combined with calcium magnesium phosphate fertilizer had a better effect in terms of reducing the available Cd and Pb content in the soil and the Cd and Pb content in the potato flesh compared to their individual application. Biochar and calcium magnesium phosphate fertilizer can synergistically increase the content of soil available nutrients and reduce the activity of heavy metals in the soil to prevent the transfer and accumulation of cadmium and lead to potatoes, as well as improve their yield and quality. The results of this study provide technical support for safe potato planting and agricultural soil management.

Algae Removal and Release of Algal Organic Matter During Ozonation of Synechococcus sp.

Pre-ozonation can enhance the removal of algae in source water during cyanobacterial blooms; however, little is known about the influence of the co-existing allochthonous natural organic matter (NOM) on algal removal and algal organic matter (AOM) behavior during ozonation. This study aims to elucidate in the presence and absence of allochthonous NOM and the effects of varying ozone doses on Synechococcus sp. cell removal, membrane integrity, and dissolved organic matter (DOM) release and removal. The results indicate that ozone effectively disrupted algal cell membranes, reducing algal density; however, the presence of allochthonous NOM delayed cell rupture by competing for ozone due to aromatic humic-like substances. Pterin-like and protein-like fluorescent compounds were released upon cell disruption. Due to that, excess ozone led to the oxidation of the released pterin-like compounds, with characteristic fluorescence changes correlating to ozone dosage; these changes are potential to be used as an indicator to determine the optimized ozone dosage, avoiding more adverse release of intracellular AOM to form disinfection byproducts.

Simultaneous Recovery of Vivianite and Humic Acids from Waste Activated Sludge via Ferric Trichloride Flocculation and Enzymatic Hydrolysis Co-Treatment

Synchronously recovering phosphorus as vivianite and humic acids (HAs) from waste activated sludge (WAS) is of great significance for the carbon neutralization of wastewater. In this study, flocculation, enzyme degradation (lysozyme/protease/amylase/cellulase in a 1:1:1:1 ratio), and pH adjustment were used to reclaim vivianite and HAs. After FeCl3 coagulation–precipitation and enzymatic hydrolysis of the sludge for 11 h, the supernatant was enriched with Fe2+ and PO43−, with the molar ratio of Fe2+:PO43− of 2.21. To improve the purity of the vivianite, the crude protein was separated at pI 6.0. The purity of the crystals reached a peak of 97.44 ± 0.04% at pH 7.5. HAs extracted from the residuals had a high affinity for metal adsorption, and the adsorption process was both endothermic and efficient. Overall, this study demonstrates the feasibility and effectiveness of the joint reclaiming of vivianite and HAs, providing new insights into multiple resource recovery from WAS.

Efficient Phosphorus capture from treated sanitary wastewater using a waste-derived SiO2@FeOOH composite: Robustness, Ca2+ interactions, and recovery perspectives

Phosphorus uptake and recovery from sanitary wastewater have been considered a promising approach to producing more sustainable fertilizers, in addition to reducing environmental damage caused by the discharge of this nutrient into water streams. In this study, the Phosphorus adsorption/desorption dynamics exhibited by a tailored SiO2@FeOOH adsorbent, produced using quartz sand waste and Fe derived from the acid dissolution of scrap iron, were examined. The adsorbent’s behavior, robustness, and interaction with Ca2+ ions in simulated treated sanitary wastewater were systematically investigated. As a result, the behavior of the adsorbent under controlled conditions was successfully modeled, and relevant interactions between the material and Ca2+ ions were identified under simulated conditions. The performance of the adsorbent was not affected by the presence of nitrate, carbonate, sulfate, ammonium, fluoride, and humic substances in the simulated media. Additionally, the composite can adsorb humic substances and Phosphorus simultaneously, without interfering with its Phosphorus adsorption capacity. In simulated treated wastewater, the adsorption of the nutrient was enhanced in the presence of Ca2+; however, the formation of insoluble Ca/P deposits on the adsorbent surface significantly changed the adsorption dynamics and disturbed the recovery of Phosphorus using the usual alkaline desorption method. The adsorbent exhibited a robust Phosphorus adsorption capacity as high as 40 mg P/g in simulated treated wastewater, showing clear potential for Phosphorus uptake in Wastewater Treatment Plants. Based on the experimental evidence, future perspectives on the final disposal of the spent adsorbent were also discussed within a circular economy framework.

Humic acid effects on wind erosion control in sandy clay loam and clay loam soils: A wind tunnel study

Humic acid effects on wind erosion control in sandy clay loam and clay loam soils: A wind tunnel study

Microencapsulation of Bacillus megaterium in Humic Acid-Supplied Alginate Beads Enhances Tomato Growth and Suppresses the Root-Knot Nematode Meloidogyne javanica Under Greenhouse Conditions

In recent years, interest in using encapsulated plant growth-promoting rhizobacteria (PGPR) as a biocontrol agent against root-knot nematodes has increased. Root-knot nematodes are soil-borne parasites that mostly cause annual commercial losses globally by infecting tomato plants (Solanum lycopersicum). In this work, tomato plants (cv. GS) were grown in a greenhouse to test the effectiveness of encapsulated Bacillus megaterium with or without humic acid or in liquid form at different inoculum levels against Meloidogyne javanica and their impact on different growth parameters. A scanning electron microscope (SEM) was used to visualize the microencapsulation of B. megaterium as well as viability and protease production In vitro. In a greenhouse experiment, humic acid-encapsulated B. megaterium resulted in a significant decrease in nematode parameters compared to the control group. When compared to other inoculants, the use of 10 capsules/plant decreased nematode infestation and enhanced plant growth parameters, antioxidant enzymes, and photosynthetic pigments. These results are reflected in increased dehydrogenase activity, total bacterial count, and acidic and alkaline phosphatase in soil 30 and 60 days after transplanting. Therefore, to increase the development dynamics of tomato plants and reduce nematode infestation, we advise using B. megaterium capsules supplemented with humic acid.

Analysis of the fluorescence spectral characteristics of dissolved organic matter in a black soil with different straw return amounts

Straw return improves soil carbon pool and dissolved organic matter (DOM) characteristics in black soil. Optimal straw return rate is the key to promoting straw return practices in farmland in Northeast China. The experiment was conducted at the Science and Technology Park of China Grain Storage and Northern Corporation in NenJiang, Heilongjiang Province, straw return at 0 kg hm−2, 3000 kg hm−2, 4500 kg hm−2, and 9000 kg hm−2. In the seventh year of the experiment, we used three-dimensional excitation-emission matrices combined with Parallel Factor analysis to characterize the fluorescence characteristics of DOM of black soils. The results showed substantial improvement in soil physical characteristics and soil organic matter (SOM) following straw return, SOM content rises in proportion to the amount of straw returned, and a significant positive correlation coefficient between water-holding capacity (WHC) (p < 0.001, r = 0.82) and dissolved organic matter (DOC) (p < 0.01, r = 0.77). Moreover, straw return significantly increased the richness of three fluorescent components, namely fulvic acid (UV and visible fulvic acids), humic-like acid, and protein-like (short and long-wavelength tryptophan). The fluorescence intensities of these components were lower in straw treatments than in no straw return. The fluorescence intensities of fulvic and humic acids showed decreasing and increasing trends, respectively, with increasing straw return amount. The fluorescence spectroscopy data of DOC demonstrated the key role of high straw return amounts in enhancing substantially the metabolic activity of soil microorganisms. Overall, straw-returning practices improve soil fertility and can be beneficial for black soil farmlands, with the optimal return rate observed at 4500 kg hm−2.

Humic acid promotes pathway of chloronitrobenzene cathodic reduction shunting from atomic H* to direct electron transfer

Progress mechanism of humic acid (HA) interacting with chloronitrobenzenes (ClNBs) and affecting their reduction and degradation was investigated. A two-stage chamber with graphite felt as cathode and anode was constructed, and 2,4-dichloronitrobenzene (2,4-DCNB) was target pollutant. Result showed that HA increased 36.15% of 2,4-DCNB removal efficiency at pH 5.0 after 4-h cathodic reduction, while at pH 7.0 and 10.0, it showed much less effect. Meanwhile, HA reduced cathodic H2 and atomic H* production via competing electron with H+. Combined with result of HA alleviating inhibition of tert-butyl alcohol on 2,4-DCNB removal, it was supposed that HA shunted dominant pathway of cathodic reduction of 2,4-DCNB from atomic H* to direct electron transfer (DET). This was proved by HA increasing electron transfer efficiency (k) of 2,4-DCNB reduction from 0.50±0.01 to 0.63±0.01, which indicated rate-limiting step of 2,4-DCNB reduction changed from electron transfer (ET) to bond breaking kinetics. HA-mediated DET pathway initially reduced nitro group, followed by dechlorination, while atomic H* pathway was randomly dechlorinated and nitro reduced. The pH significantly affected agglomeration of HA and 2,4-DCNB. Molecular dynamics simulation showed that hydrogen bond and Van der Waals force dominated agglomeration of HA and 2,4-DCNB in acidic condition, while electrostatic force was main driving force in alkaline condition. Less effect of HA on 2,4-DCNB removal efficiency at high pH could be related to its reduced conductivity and weaker molecular interactions with 2,4-DCNB. This study provides comprehensive insight into role and impact of HA in remediation of ClNBs-contaminated sediment and water by (bio)electrochemical technology.

Characterization of atmospheric humic-like substances (HULIS) at a high elevation in North China: Abundance, molecular composition and optical properties

The optical absorption of large molecular compounds HULIS (humic-like substances) can significantly impact the aerosol light absorption and radiative forcing, influencing cloud condensation nuclei formation and thus the climate and atmospheric environment. This study collected aerosol (PM2.5) samples from the summit of Mount Tai in North China to investigate the concentration, molecular composition, and optical properties of HULIS. The average concentration of HULIS in the PM2.5 in this study was 1.26 ± 0.54 μg/m3, comprising for 56 % of the water-soluble organic carbon (WSOC), with levels lower than urban areas but higher than other mountainous regions. Mass spectrometry revealed that CHO and CHON components, with high aromaticity and phenolic groups, are major contributors to absorption and fluorescence. These results indicate that HULIS is mainly composed of lignin and proteins/amino sugars, derived from combustion and secondary formation, and possesses a high light absorption capacity (with MAE365 (mass absorption efficiency) and AAE (Ångström exponent) indices of 0.62 m2/g and 4.99, respectively). Parallel factor analysis identified three fluorescence components of HULIS, with proportions of 60.8 % for less oxygen humic-like substances, 21.0 % for high oxygen humic-like substances, and 18.2 % for protein-like substances. Our study highlights the significance of the light-absorbing capacity and secondary formation of HULIS at Mount Tai, laying the groundwork for investigation into the climate effects, formation mechanisms, and sources of HULIS generation.

Surface- and substrate-coated catalytic membrane for mitigating interference of water matrix species in intensified micropollutant confinement oxidation

The integration of advanced oxidation processes (AOPs) with membrane technology offers benefits for catalyst recovery and reducing membrane fouling. However, the application of the hybrid process could be hampered by the background species in water matrix. This study addresses this challenge by developing catalytic ceramic membranes (CCMs) with dual mechanisms to intensify acetaminophen (ACT) removal in water. The CCMs effectively activated peroxymonosulfate (PMS), achieving ACT degradation of 85% and 93% in real water matrices (reverse osmosis retentate and settled water, respectively) and 99% in MQ water. The CCMs demonstrated consistent performance across multiple operational cycles, even in the presence of humic acid (HA) (96% ACT reduction). The CCM design features Co3O4 catalytic layer on CCM surface, facilitating surface oxidation, reducing fouling, and TiO2 intermediate rejection layers serving as barrier for bulk organic pollutants, achieving 50% HA removal through rejection and 70% with 1.5mM PMS. This design facilitates catalytic degradation at the membrane surface, allowing retention and degradation of bulk organic pollutants and intermediates, while ACT permeates into CCM substrate. The surface oxidation and rejection enhanced confinement oxidation within the Co3O4-coated macropores, minimizing interference from background species. LC-QTOF analysis identified multiple degradation pathways, including hydroxylation, acetyl-amino group cleavage, side chain oxidation and benzene ring cleavage, with intermediates showing reduced toxicity. Reactive oxygen species involved in the system were identified and PMS activation mechanism was proposed. This research highlights the potential of the hybrid process, enhancing micropollutant removal by mitigating interference from background species, providing practical implications in water treatment applications.

Coagulative removal of polyethylene microplastics using polyaluminum chloride in conjunction with laminarin

As emerging pollutants in water, microplastics pose potential risks to aquatic organisms and human health. Previous studies have shown that traditional metal coagulants are effective in removing microplastics from water, but they come with drawbacks such as high chemical dosage and metal residues. Therefore, it is important to explore more efficient coagulation systems. This study utilized laminarin (LA) as a coagulant aid in combination with polyaluminum chloride (PAC) to investigate its enhanced coagulation performance on polyethylene microplastics in water. The performance of coagulation systems for the removal of microplastics was evaluated for different agent dosages, pH, anion and HA content. Experimental results demonstrated that the compounded system (PAC-LA) significantly improved the removal efficiency of PE microplastics compared to the single PAC system, achieving a removal rate of 91.5% while reducing the dosage of PAC. The enhanced coagulation mechanism of LA was analyzed using various techniques including scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and zeta potential analysis. The results indicated that charge neutralization and sweep flocculation were the primary coagulation mechanisms in the presence of PAC alone. The effect of charge neutralization and adsorption was strengthened with the introduction of LA. The coagulation system of PAC-LA showed higher removal rates of PE microplastics under different environmental conditions such as varying pH levels, co-existing anions, and humic acid, suggesting a promising application for microplastic control in water.

Mechanism of action of persulfate activation based on humic acid modified sludge biochar: Enhancement of electron transfer mechanism

Humic acid (HA) was used to modify sludge biochar (SBC) in order to prepare HBC with higher defect structure and abundant oxygenated functional groups. The degradation of TC by HBC was up to 90 % much higher than that of SBC (30 %). HBC possessed a large number of defective structures and oxygenated functional groups, which contributed greatly to the activation of PMS. The co-regulation of highly exposed active sites such as CO, pyrrole N and pyridine N on HBC2, which played a key role in the activation of PMS. In addition, the results of electrochemical tests indicated that an active intermediate (Persistent free radicals PFRs). Oxygen-centered PFRs were implicated in the movement of electrons through conversion to carbon centers. The conductivity of the process was enhanced by the presence of graphite N. A large number of reactive radicals made sufficient preparations for the production of PFRs. Mutual electron transfer between the oxygen and carbon centers of PFRs was the main mechanism. In addition, the PFRs mechanism and the 1O2 mechanism were subjected, which yielded that both degrade TC by electrophilic addition attack and ring-opening reaction, respectively.

Effects of aging of polyethylene microplastics and polystyrene nanoplastics on antibiotic resistance gene transfer during primary sludge fermentation

The increasing presence of nano and microplastics (NPs/MPs) in wastewater treatment plants and their inevitable accumulation in the sludge has raised serious concerns in recent years. This study investigated the effects of pristine and aged polyethylene microplastics (PEMPs), polystyrene nanoplastics (PsNPs), and their mixtures on the primary sludge fermentation process. Pristine MPs/NPs (150 μg/L and 2 g/L for PsNPs and PEMPs, respectively) underwent two weeks of weathering in the presence of humic and alginic acids. The results from a batch fermentation experiment (15 days, pH 10) revealed that the exposure to aged PEMPs/PsNPs experienced greater VFA production than pristine samples. Notably, the aged PEMPs/PsNPs mixture showed a 23.12% increase in VFA production over the pristine mixture. The relative abundance and total concentration of antibiotic resistance genes (ARGs) increased in all PEMPs/PsNPs batches compared to the control, with the most significant rise in total ARGs observed in the aged PEMPs sample. Aged PEMPs exhibited a 26.22-fold increase in tetA genes, while aged mix samples showed a 19.68-fold increase in tetM genes compared to their pristine counterparts. Both pristine and aged PEMPs/PsNPs, particularly the aged PEMPs adversely affected the microbial communities at the genus level and altered the microbial structure. Microbial richness and diversity were enhanced in samples exposed to pristine PEMPs/PsNPs and aged PsNPs but decreased in aged PEMPs and in the aged mixture group, suggesting a negative impact of aged polyethylene microplastics on microbial communities. Correlation analysis suggested that phyla Planctomycetes, Proteobacteria, and TM7 are potential hosts of ARGs. These findings manifest the substantial effects of aged nano/microplastics compared to their pristine forms, emphasizing the complex interplay between various forms of PEMPs/PsNPs and microbial dynamics in sludge fermentation processes.

Commercial organomineral fertilizer produced through granulation of a blend of monoammonium phosphate and pulp and paper industry waste post-composting

This study investigates a commercial granular organomineral fertilizer (GOF) produced by physically mixing landfill paper and cellulose industry waste composted over a long period with monoammonium phosphate (MAP), focusing on its morphological properties, and phosphate release into the water. The organic base used in the GOF composition is rich in humic and fulvic acids due to its long-term composting, rebalances the soil's organic matter, and eliminates a critical environmental liability. No studies have involved long-term lignocellulosic waste composting as the organic base of organomineral fertilizers. Most GOF and MAP granules range from 2 to 4 mm in size, with rough and macroporous surfaces observed through scanning electron microscopy. The specific surface area values of fertilizers are low compared to other fertilizers with different organic matrices. However, 2–4 mm granules exhibit similar values, indicating uniformity of granules. Infrared spectroscopy reveals bands from mineral and organic bases, with possible clay additives confirmed by the silicon detected in Energy Dispersive Spectroscopy analysis. Thermogravimetric curves exhibit improved thermal stability for GOF over the composted organic base, with a 31 °C increase in the second decomposition stage and delayed completion of the subsequent stages. However, this did not significantly alter the Tonset of the ammonium phosphate decomposition, as GOF presented a similar thermal behavior to MAP. GOF and MAP exhibit similar kinetic profiles, with rapid phosphorus release in the first 4 hours, reaching about 77 % of the available phosphorus. GOF shows an increase in specific surface area 29 times after 240 hours of contact with water, facilitating phosphorus release from the commercial mixture. MAP and GOF exhibit a release rate exceeding 84 %, indicating rapid phosphate availability. These values are comparable to those of other organomineral fertilizers. The results demonstrate that the GOF performs similarly to MAP, with lower phosphorus dosages, rebalance of soil organic matter, and increased nutrient application efficiency.