Humic Research Articles

Application of an ozone-activated peroxymonosulfate process to effectively degrade tetramethylammonium hydroxide (TMAH) in semiconductor wastewater

In this study, ozone-activated peroxymonosulfate (O3/PMS) was used to remove tetramethylammonium hydroxide (TMAH) from artificial semiconductor wastewater. The rate constant for the O3/PMS process was approximately 14.4 times higher than that for the process employing only O3. This was attributed to the explosive production of hydroxyl radicals (•OH) in the process, the contribution of which was confirmed using a scavenger test. The degradation efficiencies were the highest at pH 7.0 (1.80 × 10−2 min−1) and 40 °C (2.18 × 10−2 min−1). Alkalinity and humic acid, which are potent scavengers of •OH, significantly reduced the degradation of TMAH. Remarkably, removal efficiencies of 64.4 % for TMAH and 43.7 % for the total organic carbon (TOC) were achieved at a relatively high initial concentration of 100 μM. However, approximately 27 % of the nitrogen was converted to the final byproducts, NH4+ and NO3−, indicating that a considerable number of nitrogen fragments remained as intermediates. Degradation pathways and intermediates were proposed based on the spectrometry data. Given that the toxicity of the demethylated intermediates was roughly 20–30 times lower than that of TMAH, the acute toxicity to A. fischeri was reduced by approximately half (46.4 ± 2.57 %). The results of this study demonstrated the substantial potential of the O3/PMS process for treating wastewater containing TMAH.

Insights into transition metal encapsulated inside carbon aerogel for accelerated electro-peroxone oxidation: Activity evaluation and reactive oxygen species generation

Transition metals have critical influences on the generation of reactive oxygen species in activating O3 and H2O2, as the binary oxidant sources in electro-peroxone (EP). To evaluate the catalytic activity of different metals and reveal the reactive oxygen species generation in heterogeneous EP, series of metals encapsulated inside carbon aerogel spheres (M@CS, M=Fe, Co, Ni, Zn) were fabricated for strengthening EP. Atrazine was used as model pollutant due to its low reactivity with O3, and the abatement trends followed Co@CS > Fe@CS > Ni@CS > Zn@CS. Co@CS exhibited the superior catalytic activity with maximum metal active site utilization (1.28 × 103 min-1 mol-1 per mole Co atom sites at pH 7) and minimum electric energy consumption (0.106 kWh/m3-log). The catalytic activity of M@CS was related to the adsorption energies for O3 and H2O2 (Fe@CS > Co@CS > Ni@CS > Zn@CS) and the graphitization degree (Co@CS > Fe@CS > Ni@CS > Zn@CS). Verified by theoretical calculation and in-situ Fourier transformed infrared, the metal effectively promoted the adsorption and decomposition of O3 and H2O2 into the surface oxygen intermediates, finally generating ·OH/·O2-/1O2. The carbon layer was conducive to the reduction of internal metal, ensuring catalyst durability. Electronic paramagnetic resonance and kinetic model revealed the occurrence, ratio and transient concentration of ·OH/·O2-/1O2 in M@CS/EP. M@CS/EP showed good performance for pollutant removal in coexistence of anions, humic acid and real water. This study provides guidance for selecting the metal–carbon catalyst in heterogeneous EP.

Synergistic mechanism of pH control by CO2 and CaO2 pre-oxidation to enhance algae dehydration

This study investigated the improvement of algal dehydration efficiency through CO2 pH adjustment and moderate pre-oxidation with CaO2 to enhance coagulation. Adjusting the pH of algal water to 6.0–9.5 with CO2 significantly affected zeta potential and photosynthesis, enhancing aluminum hydrolysis product aggregation. At pH 6.5, the composition of algal organic matter closely matched the original water, indicating minimal impact on algae and optimal cell activity. CaO2 pre-oxidation effectively reduced residual aluminum content and DOM release after coagulation. The DOM removal rate reached 44.50 % at pH 6.5, with the highest dehydration efficiency of 44.34 % and the lowest cell rupture rate of 5.55 %. Small molecular aromatic proteins decreased, while humic substances increased significantly. The chemical bonding between the EPS membrane and CaO2 improved system density and elasticity, enhancing dehydration performance. This study provides new insights and guidance for the ongoing study of pH and CaO2 enhanced algal dehydration.

Effective adsorption performance and mechanism of methylene blue from dye wastewater by humic acid sucrose-modified red mud

Effective adsorption performance and mechanism of methylene blue from dye wastewater by humic acid sucrose-modified red mud

The modulatory influence of humic acid on cognitive impairment and neurobehavioral changes induced by colitis in adult male Wistar rats

The modulatory influence of humic acid on cognitive impairment and neurobehavioral changes induced by colitis in adult male Wistar rats

Effects of exogenously added humic acid on the fate of aminoglycoside antibiotics and humification process during aerobic compost

Efficient elimination of antibiotics, particularly aminoglycosides, and Antibiotic resistance genes (ARGs) from agricultural and livestock waste, as well as enhancing the level of humification, remains a major challenge in the pursuit of high-value utilization of agricultural waste. Here, the roles of bacteria and fungus in the dissipation of aminoglycoside antibiotics, ARGs and the enhancement of humification with the addition of humic acid (HA) to compost systems were investigated. Compared to the control, the contents of humus (HS) and HA were increased by 41.3 and 143.3 %, respectively, and the content of fulvic acid (FA) was decreased by 74.1 % with HA addition. Interestingly, the abundance of aminoglycoside ARGs was decreased significantly (p < 0.05) as well as the abundance of functional genes involved in oxidative stress response and type IV secretion system (T4SS). The bacterium Nocardiopsis related to carbon cycle, and the fungi Ascomycota and Basidiomycota associated with ligocellulose degradation were significantly enriched (p < 0.05). Structural equation models revealed that the decrease in aminoglycoside ARGs abundance was attributed to bacteria promoting HA synthesis, thereby inhibiting the multiplication of aminoglycoside ARGs and ultimately mitigating oxidative damage to microbial cells. These findings shed light on the mechanism by which HA removes aminoglycoside ARGs, and provide valuable insights into enhancing the biosafety of compost products.

Synthesis and mechanism of Bi/SnO2 for enhanced photocatalytic activity in the degradation of humic acid under visible light

Humic acid (HA) is a typical refractory organic matter, widely existing in natural water and many types of wastewaters. In this study, Bi/SnO2 composites were synthesized by a simple one-step hydrothermal method for photocatalytic degradation of HA. Due to the surface plasmon resonance (SPR) effect of Bi, the light absorption of Bi/SnO2 composites expands from UV to visible light compared to pure SnO2. Under visible light irradiation for 120 min, the UV254 removal reached 93.58 %, color number (CN) removal reached 94.41 %. The degradation rate constant of Bi/SnO2 (0.0178 min−1) is 14.83 times higher than that of SnO2 (0.0012 min−1), indicating the superior photocatalytic degradation efficiency of Bi/SnO2 composites. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was found that photocatalysis mainly degraded most CHO-containing organic matter and reduced the amount of organic matter (from 7240 to 3886). The molecular number of organic compounds with m/z of 400–500 and 500–600 exhibited a significant decrease, specifically by 1052 and 770, respectively. This observation suggests that the photocatalytic process effectively eliminates low and moderate molecular weight organics. The molecular number, aromaticity and molecular weight of dissolved organic matter (DOM) were reduced mainly by carboxylic acid reaction, dealkylation reaction and oxygen addition reaction.

Comparing the effects and mechanisms of granular activated carbon and magnetite nanoparticles in dry anaerobic digestion: Focusing on microbial electron transfer and metagenomic evidence

Enhancing direct interspecies electron transfer (DIET) via granular activated carbon (GAC) and magnetite nanoparticles (MNPs) to promote methanation performance in dry anaerobic digestion (AD) systems has been extensively studied in recent years. However, the underlying mechanisms, particularly how GAC and MNPs influence DIET and extracellular polymeric substances (EPSs), remain poorly understood. In this study, the different effects and mechanisms of GAC and MNPs on dry AD fed with pig manure (PM) and corn straw were compared, with additions of 10, 20, and 50% of the volatile solid (VS) of PM. The results indicated that GAC improved the cumulative specific methane yields (CSMYs) by 18.8–20.9%, while a high dose of MNPs (50% of the VSPM) decreased the CSMY and hydrolysis rate constant by 27.0 and 75.4%, respectively. GAC provided microorganism attachment sites and functional groups for electron transfer, improving hydrolysis by enriching fermenters such as Fastidiosipila and Rikenellaceae. Nevertheless, MNPs stimulated intense dissimilatory iron reduction by Clostridium sp. in the early stage, competing with methanogens for substrates. Low and medium GAC doses (10 and 20% of the VSPM) increased the utilization of redox-active substances (e.g., humic substances and proteins) in EPS, while the high MNP dose stimulated their secretion due to microbial self-protection, impairing electron transfer. Metagenomic evidence showed that the medium GAC dose improved four methanogenic pathways and DIET mediated by microbial nanowires, while a high MNP dose impeded the final step of methanogenesis. These results provide deeper insights into the mechanisms of different conductive materials on dry AD.

Eco-corona enhanced the interactive effects of nanoplastics and 6:2 chlorinated polyfluorinated ether sulfonate in zebrafish embryos

Nanoplastics (NPs, < 1000 nm) interact with chemicals and biomolecules to produce chemical−/eco-corona, altering the environmental destiny, bioavailability, and toxicity of plastic particles and co-occurring chemicals. This study employs exogenous (humic acid, HA) and endogenous (bovine serum albumin, BSA) natural organic matter (NOM) to investigate the eco-corona formation on NPs and explore the interfacial effects of eco-corona and 6:2 chlorinated polyfluorinated ether sulfonate (Cl-PFESA, commonly named as F-53B) on zebrafish (Danio rerio) after 7 days of exposure. Our results indicated significant changes in growth and developmental indices of zebrafish embryos among all eco-corona groups (p < 0.05). Additionally, NFB (BSA-corona, 1 mg/L NPs + 200 μg/L F-53B + 10 mg/L BSA), NFH (HA-corona, 1 mg/L NPs + 200 μg/L F-53B + 10 mg/L HA) and NFHB (BSA-HA-corona, 1 mg/L NPs + 200 μg/L F-53B + 10 mg/L BSA + 10 mg/L HA) showed elevated bioaccumulation of NPs, ROS generation and induction of apoptosis. Transcriptomic analysis showed the number of differentially expressed genes (DEGs) in the following order: BSA-HA-corona (NFHB (2953) > HA-corona (NFH (2797) > NH (2721) > F-53B (2292) > NF (2033) > BSA-corona (NFB (687) > NB (450)), and no DEGs were detected in the single NP compared to the control. Further, the PI3K-AKT, immune system, endocrine system, digestive system, infectious diseases, and neurovegetative disease pathways showed sensitive responses in the NFH/NFHB groups compared to those in the NFB group. Therefore, the interactive effects of NPs and F-53B on zebrafish embryos were lower in the presence of BSA-corona than those in HA- or HA-BSA-coronas, indicating a relationship between the formation of diverse eco-coronas on NPs by multiple NOM and an associated increase in the interfacial toxicological effects of plastic particles and F-35B in freshwater organisms.

Degradation of tris(1,3-dichloro-2-propyl) phosphate (TDCPP) by ultraviolet activated hydrogen peroxide: Mechanisms, pathways and toxicity assessments

The ubiquity and ecotoxicity of tri (1,3-dichloro-2-propyl) phosphate (TDCPP) in aquatic environments make it essential to develop efficient related treatment techniques. The present research aims to systematically explore the mechanisms and toxicity changes of TDCPP degradation through UV-driven hydrogen peroxide process (UV/H2O2). The results revealed degradation efficiency of TDCPP attained 95 % with 0.5 mM H2O2, corresponding to a reaction rate constant (k) of 0.04919 min−1. Furthermore, three typical chlorinated OPEs (Cl-OPEs) were simultaneously degraded by the UV/H2O2 process, with different degradation efficiencies, according to the following order: TCEP<TDCPP<TCPP. The degradation efficiency was restricted under alkaline condition and the presence of humic acid (HA), nitrate (NO3–), chloride (Cl-), sulfate (SO42-), and dihydrogen phosphate (H2PO4-). A total of 12 intermediates were identified, which were generated through different pathways, including bond breaking, hydroxylation, and oxidation reactions. The Toxicity Estimation Software Tool (T.E.S.T) results demonstrated stronger mutagenicity and developmental toxicity of the TDCPP intermediates than parent compound. According to RNA sequencing results, UV/H2O2-based TDCPP degradation for 20 min and 60 min still had negative effects on Escherichia coli (E. coli). Indeed, the Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis results further suggested the stronger negative effect (e.g., damaging effects on the cell membrane, energy metabolism, and vitality) of the 20-min oxidation solution on E. coli, followed by those observed in without treatment and 60-min oxidation solution. Therefore, longer oxidation times are required in the UV/H2O2 process to decrease the toxicity of TDCPP.

Nitrogen and magnesium codoped biochar activates periodate to remediate bensulfuron methyl-contaminated water at low temperature: Performance, mechanisms, and phytotoxicity

Bensulfuron methyl (BSM), a typical sulfonylurea herbicide, has been widely used worldwide for weed suppression and crop protection. Nevertheless, the long-term and prolonged usage led to residues in environment, resulting in the reduction of crop yields and even threatening food security. In this study, the nitrogen/magnesium codoped biochar (NMg-BC) was prepared via two-step pyrolysis method to activate periodate (PI) for BSM degradation. The results demonstrated BSM degradation rate was 87.9 % within 10 min by NMg-BC/PI system at 15 ℃. The system exhibited the favorable tolerance to environmental changes (pH, temperature, anions, and humic acids), presenting high removal efficiency of BSM. Radicals (IO3•) and non-radicals (1O2 and electron transfer) pathways contributed to the degradation of BSM, while the latter performed a crucial role in BSM degradation. Theoretical calculations further confirmed doped of N and Mg changed the electron configuration and electrostatic potential (ESP) distribution of biochar, which was beneficial to provide more active sites for PI activation. Hydroponic experiments showed that NMg-BC/PI system could effectively degrade BSM, and its residue had no significant effect on the length and weight of soybean. The study provides a promising approach for the pollutant remediation in cold regions.

Anoxic Manganese Bioleaching – Investigation of Scale-up Parameters in a Stirred Bioreactor

Presently huge operation costs arising from aeration and high electron donor requirements accompanied by low metal recovery rates are some impediments to the large-scale application of bioleaching for low-grade ores. The current study investigates key parameters for scaling up anoxic bioleaching, which overcomes some of the above shortcomings, on polymetallic manganese nodules using soil-based manganese-reducing bacterial consortia in a stirred bioreactor. Operating conditions such as carbon source concentration and pulp density were optimized. Parameters like pH, oxidation–reduction potential (ORP), and microbial growth were monitored in the bioreactor in both stirred and non-stirred conditions. The Mn(IV) reduction and dissolution in the bioreactor was 27 (±2.8)% over 30 days, which significantly enhanced to 43 (±1.5)% and 42 (±0.35)% in the presence of humic acid and anthraquinone sulfonic acid, respectively, in 15 days. A maximum dissolution of 21 (±4.1)% Cu, 10 (±3.0)% Ni, 18 (±4.7)% Co and 7 (±3.9)% Fe were also obtained with 100 µM humic acid from the agitated bioreactor in 15 days. The corresponding specific glucose consumption rate per unit mass of ore was found to be 27 mg g−1 day−1, which is 10 times lower than the rates reported previously for aerobic bioleaching methods. The investigation shows that mild agitation can significantly improve the anoxic bioleaching, especially with added electron shuttles, to enable better ore-bacteria interaction and prevent ore compaction during scale-up. The pH and ORP of the system point toward a reductive dissolution of Mn by the organisms.

Natural organic matter (NOM) can increase the uptake fluxes of three critical metals (Ga, La, Pt) in a unicellular green alga

Critical metals such as gallium, lanthanum and platinum are considered essential in a modern economy and for the required energy transition. Their relatively recent and increasing use in new technologies have led to an increase in their environmental mobility. As they reach aquatic systems, these metals can interact with organic ligands and especially Natural Organic Matter (NOM). The formation of organic complexes would be expected to reduce metal bioavailability and uptake by living cells, according to the Biotic Ligand Model (BLM). However, exceptions to this model have been determined for several critical metals in the past. The present work compared internalization kinetics of Ga, La and Pt in the green alga Chlamydomonas reinhardtii in the presence of NOMs from different origins: humic and fulvic acids from Suwannee River as well as NOMs from Ontario (Bannister Lake and Luther Marsh). Complexation was determined using a partial ultrafiltration method allowing for a normalization of data based on speciation to compare all conditions based on the concentration of the metal that was not bound to NOM. While internalization metal fluxes varied greatly from one NOM source to the other, uptake was almost always significantly higher than expected based on metal speciation. Quite often, metal internalization fluxes were even significantly increased in the presence of NOM, for the same total metal exposure concentration. For instance, Pt internalization was twice greater in the presence of Bannister Lake NOM than it was in the absence of NOM. The assumption that such exceptions could be explained by NOM characteristics was contradicted by the variable results from one metal to another. To further explore this phenomenon, internalization mechanisms for these individual metals need to be elucidated. This is a necessary step to accurately estimate the risk posed by the presence of these metals in humic aquatic systems.

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

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

Improved humification and Cr(VI) immobilization by CaO2 and Fe3O4 during composting

The current research studied how Fe3O4 nanomaterials (NMs) and CaO2 affect humification and Cr(VI) immobilization and reduction during the composting of oil-tea Camellia meal and Cr-contaminated soil. The results showed that Fe3O4 NMs and CaO2 successfully construct a Fenton-like reaction in this system. The excitation-emission matrix-parallel factor (EEM-PARAFAC) demonstrated that this Fenton-like treatment increased the generation of humic acids and accelerated the humification. Meantime, RES-Cr increased by 5.91 % and Cr(VI) decreased by 16.36 % in the treatment group with CaO2 and Fe3O4 NMs after 60 days. Moreover, the microbial results showed that Fe3O4 NMs and CaO2 could promote the enrichment of Cr(VI) reducing bacteria, e.g., Bacillus, Pseudomonas, and Psychrobacter, and promote Cr(VI) reduction. This study gives a novel view and theoretical reference to remediate Cr(VI) pollution through composting.

Quality and Safety of Extracted Humic Substances as Fundamental Factor of Natural Regulation for the Sustainable Development

Humic substances as natural biogeochemical macromolecules have been formed over tens of millions of years as a result of the processes of natural destruction of biological systems with a high degree of chemical diversity. The prospects and realities of today’s use of humic substances by humans in agriculture, pharmaceuticals and medicine raise the issue of strict safety control of various drugs derived from these natural substances. These technologies for the extraction and purification of final humic preparations should be carried out in accordance with the balanced development of natural ecosystems and biosafety requirements. In this publication we raise the issue of creating a single standard for the quality and safety of purified humic substances on a global scale.

An Engineering Porous Spherical Carbon Cathode for High-Energy Sodium-Ion Capacitor.

Sodium-ion hybrid capacitors (SICs) are emerging as promising devices that can balance energy and power output. However, the lack of a high-capacity cathode that can match the anode has limited its further application. In this work, we develop an efficient method to prepare spherical porous carbons (SPCs) with great specific surface area and narrow pore size distribution from coal-based humic acid via spray drying and a subsequent chemical activation process. Thanks to this unique porous structure, the SPC cathode has a superb capacity of 223 F g-1 at 0.05 A g-1, as well as splendid rate performance and cycling stability. SICs constructed by an SPC cathode and hard carbon anode can exhibit a high energy density of 179.8 Wh kg-1 at 155 W kg-1 and achieved 89.4% capacity retention after 10 000 cycles at 0.5 A g-1. This outcome presents a viable approach to attaining high-capacity cathodes for constructing outstanding performance hybrid capacitors.

In-situ atomic hydrogen generation: A key to elevating membrane cleaning via citric acid-modified Fenton-like system

Oxidation process has been widely used to clean irreversible membrane fouling, and the development of novel oxidative cleaning process has attracted worldwide attention. In this study, a novel cleaning process with the combination of sodium percarbonate (SPC), citric acid (CA), and ferrous ion (Fe(II)) was introduced to remove organic fouling derived from the complexation of humic acid (HA) and calcium ions (Ca2+) for the first time. Remarkably, both flux recovery and resistance removal could reach 99 % within one hour. The efficiency and durability of this novel cleaning system were confirmed through comprehensive characterization and cyclic cleaning test of the ultrafiltration membranes. Furthermore, it effectively removed various natural organic matter-induced fouling and performed well in long-term experiments. This outstanding performance is due to the synergy between oxidative hydroxyl radicals (HO) and reductive atomic hydrogen (H*) in SPC/CA/Fe(II). Analysis of intermediate/final products confirmed that H* is generated through the reaction of CA and HO and absorbed by HA. Confocal laser scanning microscopy (CLSM) revealed that this absorption makes HA more susceptible to HO attack, resulting in enhanced cleaning performance. This mechanism demonstrates the potential of advanced reduction–oxidation systems for membrane cleaning, offering new insights for the development of novel cleaning methods.

Heteroaggregation, disaggregation, and migration of nanoplastics with nanosized activated carbon in aquatic environments: Effects of particle property, water chemistry, and hydrodynamic condition

Nanosized activated carbon (NAC) as emerging engineered nanomaterials may interact with nanoplastics prevalent in aquatic environments to affect their fate and transport. This study investigated the effects of particle property (charge and concentration), water chemistry [electrolytes, pH, humic acid (HA), and sodium alginate (SA)], and hydrodynamic condition [wave (i.e., sonication) and turbulence (i.e., stirring)] on the heteroaggregation, disaggregation, and migration of NAC with positively charged amino-modified polystyrene (APS) or negatively charged bare polystyrene (BPS) nanoplastics. The homoaggregation rate of APS was slower than its heteroaggregation rate with NAC, with critical coagulation concentrations (CCC) decreasing at higher NAC concentrations. However, the homoaggregation rate of BPS was intermediate between its heteroaggregation rates under low (10 mg/L) and high (40 mg/L) NAC concentrations. The heteroaggregation rate of APS+NAC enhanced as pH increasing from 3 to 10, whereas the opposite trend was observed for BPS+NAC. In NaCl solution or at CaCl2 concentration below 2.5 mM, HA stabilized APS+NAC and BPS+NAC via steric hindrance more effectively than SA. Above 2.5 mM CaCl2, SA destabilized APS+NAC and BPS+NAC by calcium bridging more strongly than HA. The migration process of heteroaggregates was simulated in nearshore environments. The simulation suggests that without hydrodynamic disturbance, APS+NAC (971 m) may travel farther than BPS+NAC (901 m). Mild wave (30-s sonication) and intense turbulence (1500-rpm stirring) could induce disaggregation of heteroaggregates, thus potentially extending the migration distances of APS+NAC and BPS+NAC to 1611 and 2160 m, respectively. Conversely, intense wave (20-min sonication) and mild turbulence (150-rpm stirring) may further promote aggregation of heteroaggregates, shortening the migration distances of APS+NAC and BPS+NAC to 262 and 552 m, respectively. Particle interactions mainly involved van der Waals attraction, electrostatic repulsion, steric hindrance, calcium bridging, π-π interactions, hydrogen bonding, and hydrophobic interactions. These findings highlight the important influence of NAC on the fate, transport, and risks of nanoplastics in aquatic environments.

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.