High Humic Acid Research Articles

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.

Co-activation of peroxymonosulfate activation with sunlight and tailored catalytic MnFe2O4/MWCNTs membrane to mitigate membrane fouling caused by NOM and synergistic oxidation mechanism analysis

Membrane fouling has been a major factor hindering the development of ultrafiltration membranes. Herein, a novel in situ oxidation system was constructed via introducing MnFe2O4/MWCNTs into polyvinylidene fluoride (PVDF) membranes, utilizing sunlight to synergistically activate persulfate (PMS) to mitigate ultrafiltration membrane fouling. The mechanism of mitigating membrane fouling in MnFe2O4/MWCNTs-PVDF ultrafiltration membranes was systematically explored under four system (single filtration, single sunlight irradiation, single PMS oxidation and sunlight co-activated PMS). The MnFe2O4/MWCNTs-PVDF membranes exhibited different fouling characteristics under the four systems, with the sunlight and MnFe2O4/MWCNTs membrane co-activated PMS filtration system showing the highest humic acid (HA) removal efficiency of 90.2 %, as well as the lowest Rr (0.2108 × 1012m−1) and Rir (0.4525 × 1012m−1). To further evaluate the practicality and effectiveness of the sunlight-MnFe2O4/MWCNTs-PMS system, the secondary effluent was selected to verify the treatment effect on natural organic matter (NOM) of actual water. By observing the microscopic morphology of the fouled membrane surface, it was evident that, compared with the other three filtration systems, the filter cake layer on the MnFe2O4/MWCNTs membrane surface of the sunlight co-activated PMS system was obviously reduced, and the structure of the cake layer was more loose. It can be concluded that the principle behind the synergistically activated system to alleviate the membrane fouling was to accelerate the mineralization rate of HA molecules, oxidize the HA into a smaller particle size that can pass through the membrane pores. The main reactive oxygen species and HA degradation mechanism in the synergistic activation system were further elucidated by electron paramagnetic resonance (EPR) analysis and density functional theory calculations (DFT). The results indicated that the degradation of HA by the synergistically activated PMS system involved a combination of free radicals (·O2−、SO4·− and ·OH) and non-free radicals (1O2). Overall, the in-situ oxidation system provided an alternative way to alleviate ultrafiltration membrane fouling.

Effectiveness of cigarette butt filters as eco-friendly cellulose acetate membranes for organic contaminant removal

Abstract Cigarette waste is a persistent environmental problem that requires innovative solutions due to the inadequacy of traditional recycling methods. This paper explores the conversion of cigarette butt filters (CBFs) into raw material for cellulose acetate (CA) membrane production. This study prepared two types of membranes: 12% CBF and 12% CA as a control variable. The resulting material was evaluated for its properties and performance as an ultrafiltration membrane for organic contaminant removal. The result demonstrates that the CBF-based membrane exhibits superior characteristics to a CA-based membrane. This improvement is evident in the increased presence of hydroxyl (-OH) groups and enhanced porosity CA 18,37% and CBF 19,66%. Furthermore, the permeability of the CBF membrane has also increased, making it an efficient tool for maintaining humic acid removal CBF 79,02% and CA 66,18% while achieving a high flux ratio recovery CA 65,25 % and CBF 87,97%. The findings in this paper emphasize the promising potential of reusing cigarette waste as an eco-friendly membrane with high humic acid rejection and good antifouling properties.

Investigation of hydrothermal depolymerization of lignite under different conditions by 13C NMR spectroscopy

Efficient depolymerization of lignite under mild conditions is the key to realizing its low carbon conversion and high value utilization. This study focuses on three Chinese lignites: Xilinguole lignite (XL), Xiaolongtan lignite (XLT), and Zhaotong lignite (ZT), investigating the inherent structures effect on their depolymerization processes when subjected to alkali depolymerization (AD) and oxidation depolymerization (OD) under hydrothermal condition. The parent lignites and their depolymerized products were characterized by solid 13C NMR, FTIR, TGA, and elemental analysis. It was found that both AD and OD effectively broke down the macromolecular structure of lignite into humic acid (HA) and small molecular products including water-soluble components, with the highest depolymerization activity observed for ZT followed by XLT and XL, regardless of the method used. Notably, by AD at 80 oC, 91.4 % of ZT was depolymerized, producing 69.4 % of HA as the major product, while higher temperatures were required to efficiently depolymerize XLT and XL by either AD or OD. More than 80% of XLT and XL can be converted by AD at 200 oC, yielding 54.8 % and 52.9 % of HA, respectively. OD at 140 oC resulted in a 57.7 % conversion of XL and an HA yield of 50.2 %. Characterization of the products demonstrated that alkali addition significantly promotes lignite depolymerization by breaking oxygen-containing linkages such as ether and ester bonds, with ether bond hydrolysis occurring predominantly at high temperatures. High-temperature AD of lignite is dominated by the cleavage of oxygen-containing linkages, whereas OD at lower temperatures mainly depolymerizes lignite through oxy-cracking of C−C and C−O weak linkages, reducing carboxyl decomposition to achieve higher HA yields. These findings offer a new perspective on the low-carbon utilization of lignite.

Synthesis and evaluation of a novel cross-linked biochar/ferric chloride hybrid material for integrated coagulation and adsorption of turbidity and humic acid from synthetic wastewater: Implications for sludge valorisation

The deep removal of organic pollutants is challenging for coagulation technology in drinking water and wastewater treatment plants to satisfy the rising water standards. Iron (III) chloride (FeCl3) is a popular inorganic coagulant; although it has good performance in removing the turbidity (TB) in water at an alkaline medium, it cannot remove dissolved pollutants and natural organic matter such as humic acid water solution. Additionally, its hygroscopic nature complicates determining the optimal dosage for effective coagulation. Biochar (BC), a popular adsorbent with abundant functional groups, porous structure, and relatively high surface area, can adsorb adsorbates from water matrices. Therefore, combining BC with FeCl3 presents a potential solution to address the challenges associated with iron chloride. Consequently, this study focused on preparing and characterizing a novel biochar/ferric chloride-based coagulant (BC–FeCl3) for efficient removal of turbidity (TB) and natural organic matter, specifically humic acid (HA), from synthetic wastewater. The potential solution for the disposal of produced sludge was achieved by its recovering and recycling, then used in adsorption of HA from aqueous solution. The novel coagulant presented high TB and HA removal within 10 min of settling period at pH solution of 7.5. Furthermore, the recovered sludge presented a good performance in the adsorption of HA from aqueous solution. Adsorption isotherm and kinetics studies revealed that the Pseudo-second-order model best described kinetic adsorption, while the Freundlich model dominated the adsorption isotherm.

Investigating the Adsorption of Humic Acid from Water Using CTS/PAM and CTS/PAM/EDTA Adsorbents

In recent decades, reports from around the globe indicate an increase in natural organic matters (NOMs) in surface waters, which has a negative impact on drinking water purification and causes problems such as the taste and color of water, reducing the amount of dissolved oxygen in water, causing membrane fouling in the filtration process, and acting as a precursor for the formation of an antiseptic by-product. This work used the adsorption process to evaluate the elimination of natural organic compounds in aquatic environments. Ethylenediaminetetraacetic acid (EDTA) as a crosslinker for chitosan (CTS) and N, N-methylenebisacrylamide as a crosslinker for polyacrylamide (PAM) were used to prepare humic acid (HA) adsorbents utilizing a two-step procedure. The FTIR spectroscopy proved the EDTA cross-linking agent was effective with the semicrosslinking CTS/PAM hydrogel. CTS/PAM/EDTA double network (DN) hydrogel exhibited a higher HA adsorption capacity (qe = 107.7 mg/g) than CTS/PAM (qe = 59.3 mg/g) at pH = 7 and an initial concentration of 60 mg·L−1 during 60 min. Also, results demonstrate that CTS/PAM/EDTA DN hydrogels showed faster adsorption kinetics than CTS/PAM.

Carbon sequestration potential of biochar in soil from the perspective of organic carbon structural modification

Application of biochar derived from biomass resources in soil is an encouraging method to decelerate global warming via carbon sequestration. While there has been extensive research on the priming effect of biochar on the mineralization of native soil organic carbon (nSOC), its correlation with soil organic carbon (SOC) structural variations remains poorly understood. A series of incubation experiments with soils amended with biochar prepared at 300 °C, 450 °C, and 600 °C were performed to explore the shifts in nSOC structure and reveal the interconnections among soil properties, SOC structural variation, and the priming effect induced by biochar. Biochar exhibited an “inhibitory concentration” on soil microorganisms, where 1 % biochar enhanced bacterial and fungal richness and diversity, while 3 % biochar reduced bacterial richness and diversity although soil nutrient conditions were improved. Biochar-treated soil had higher humic acid- and humin-like fractions (HAL and HML) but lower fulvic acid-like components (FAL). Moreover, bulk SOC, FAL, HAL, and HML of soils with 300 °C and 450 °C biochar contained more aromatic-type species (e.g., lignin). Such changes were related to improvement of the soil nutrient condition and shifts in microbial community structures, in addition to the “accumulation of biochar-derived OC in the nSOC pool”. Stable carbon isotopes indicated that the inhibitory effect on SOC mineralization (−94.5 to −8.0 mg CO2-C kg−1 soil) induced by biochar was significantly explained by the change in FAL and HAL contents. The findings improved the understanding of the carbon sequestration potential of biochar in soils for SOC structural modification.

Coagulation performance and mechanism analysis of humic acid by using covalently bonded coagulants: effect of pH and matching mechanism of humic acid functional groups.

Conventional inorganic coagulants (Al, Fe) and Al/Fe-based covalently bonded flocculants (CAFMs) had different hydrolysis species at different pHs, which subsequently led to differences in their binding sites and complexation ability with humic acid (HA). Studying the binding sites and interactions between CAFMs, AlCl3 (Al), and FeCl3 (Fe) hydrolysates and HA molecules is critical to understanding the coagulation mechanism. The results found that CAFM 0.6, Al, and AlCl3 combined FeCl3 (Al/Fe) removed more than 90% of HA at pH 6, and CAFMs showed higher HA removal rate than that of Al, Fe, and Al/Fe under the same reaction conditions. The flocs of CAFMs contained abundant -NH2/OH as well as the large particle size, compact structure, and excellent settling performance. The hydrolyzed species of Al and Fe were predominantly Alb and Feb at pH 6, but the hydrolyzed species of CAFMs were primarily (Al + Fe)c. Moreover, the hydrolyzed species of Al and Al/Fe were found to complex with HA functional groups such as -COOH, C = O, C-H/C-C, C = C, and C-OH to form ligand bonds, while the hydrolyzed species (Al + Fe)c of CAFMs could deeply interact with HA functional groups including C-O, -COOH, C = O, C-H/C-C, C = C, and C-OH by the adsorption and sweeping.

MnFe2O4 composited polyvinylidene fluoride catalytic ultrafiltration membrane via peroxymonosulfate activation for humic acid treatment: Exploration of synergistic mechanisms

Membrane separation has become the most promising technology in the field of wastewater purification, but there will inevitably be membrane fouling. Catalytic polymer membranes combining membrane filtration and advanced oxidation technologies (AOPs) offered an alternative for mitigating membrane fouling. This work successfully synthesized a MnFe2O4 catalytic polyvinylidene fluoride (MnFe2O4-PVDF) ultrafiltration membrane and systematically investigated the performance of peroxymonosulfate (PMS)/MnFe2O4 membrane oxidation filtration system for removing humic acid (HA). The results showed that the PVDF@MnFe2O4/PMS synergistic system oxidized HA into small molecules and further repelled them to the membrane surface by size exclusion to form a filter cake layer. The PVDF@MnFe2O4/PMS system exhibited the lowest irreversible fouling (0.414 × 1010m−1) and the highest HA removal efficiency (83.4 %) compared with PVDF single filtration. After hydrodynamic cleaning, PVDF@MnFe2O4 can achieve 73.2 % water flux recovery. The membrane fouling mitigation mechanisms were investigated by the Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory and the combined pore blockage-cake filtration model. Quenching experiment and density functional theory calculation (DFT) revealed the HA degradation as a result of the synergistic action of free radicals (SO4⋅-, ⋅OH) and non-free radicals(1O2) in PVDF@MnFe2O4/PMS system. Additionally, we evaluated the effectiveness of the system in the removal of natural organic matter (NOM) from surface water. The results suggested that the PVDF@MnFe2O4/PMS system could validly remove the main fluorescent matters from surface water. In conclusion, this work provides a promising route for solving the membrane fouling caused by NOM in water.

Evaluation of various factors influencing dynamic membrane formation and performance using metal oxide adsorbent

A dynamic membrane (DM) comprises a layer of particles deposited onto a conventional membrane, which minimizes fouling of the primary membrane to enhance permeate fluxes. Because DMs are involved in adsorption, the size and material of the adsorbent significantly affect DM performance. However, the comprehensive effects of these factors on DMs remain unclear. Herein, the factors influencing DM morphology and performance were investigated by varying the size of two different DM adsorbent materials: heated aluminum oxide particles (HAOPs) and heated iron oxide particles (HIOPs), deposited on polymeric and ceramic (CE) membranes. The density of the dynamic layer increased as the adsorbent particle size decreased. All DMs exhibited approximately 30 % improved flux and higher humic acid (HA) removal efficiencies (HAOP-DM:90 %, HIOP-DM:82 %) than the virgin membranes. Adsorbent size significantly affected DM performance; a five-fold size reduction resulted in an approximately 25 % increase in HA removal. A membrane resistance model was employed to quantitatively analyze the DM performance. HIOP-DM exhibited 80 %–90 % reversible fouling, whereas HAOP-CE displayed 70 %–80 % irreversible fouling. Because reversible fouling was the dominant mechanism of HIOPs, the DMs were reused after chemical treatment. However, HAOP DMs required replacement, despite their high water flux retention and HA removal efficiency.

Study of the effectiveness of a ZnO–TiO2 formulation in the degradation of humic substances in mature leachate by solar photocatalysis Brazil

Treatment of landfill leachate is an important environmental issue, especially in developing countries such as Brazil. Advanced oxidation processes (AOPs) have been considered interesting treatment alternatives. In this study, ZnO–TiO2 mixtures were incorporated into a paint polymer matrix and fixed onto supports. Paints were applied by overlapping coat layers on plates, resulting in high film thickness (600 ± 80 µm). Treatment of mature leachate by an AOP was conducted in a plug flow reactor connected to a stirred tank under solar irradiation. The objective was to evaluate the degradation of humic acid (HA) and fulvic acid + humins (FAH). The highest HA and FAH removal efficiencies were 62% ± 4.9% and 16% ± 4.2%, respectively. The kinetic model provided a coefficient of determination (R2) of 0.974. Rate constants for HA and FAH removal were 2.96 and 1.03 × 10−3 min−1, respectively. Statistical models for HA and FAH degradation had R2 values of 0.96 and 0.99, respectively. Both approaches indicated that HA degradation is greater at acidic pH and higher TiO2 concentrations. FAH degradation was favored by acidic pH and higher ZnO concentrations. Statistical models showed the same mean difference in conversion between replicate runs of HA and FAH, suggesting a uniform diffusion of fractions through catalysts.
 Keywords: heterogeneous photocatalysis, humic and fulvic acid, landfill leachate treatment, titanium dioxide, zinc oxide.

Characterization of a Commercial Grade Humic Acid (HA) and Its Impact on Soil Properties and the Yield of Maize

The study was conducted at the Prince Audu Abubakar University Research and Demonstration Farm, Anyigba, during the 2020 farming season. The broad objective of this research was to determine the effect of humic acid (HA) on soil properties, growth and yield of maize in southern guinea savannah. The parameters measured includes, plant height (cm), number of leaves, stem girth (cm), fresh cob weight (g), dry cob weight (g), fresh biomass (g), dry biomass (g), cob length (cm) cob diameter(cm), 100 grains weight (g) and total yield (kg). The experiment had eight (8) treatments (T1 = Control, T2 = HA10, T3= HA20, T4= HA30, T5= RNPK, T6= 1/3RNPK+HA30, T7= 1/2RNPK+HA30 and 2/3RNPK+HA30) which were replicated three (3) times and the experimental design was randomized complete block design (RCBD). From the result obtained, the HA concentrate has high pH (10.07), high in carbon (36.48) and high HA percentage (92.00). Pre-cropping soil analyses confirm the soil to be acidic (4.85), low in nutrient and the textural class is sand. Post-cropping soil analyses showed HA10 helped reduce soil pH the most (5.22) and application of HA generally help increase the concentration of micronutrients. The application of HA on maize had no significant (p<0.05) influence on the plant height, number of leaves, stem girth and most of the yield parameters tested with the exception of 100grain weight and total yield. Treatment 2/3RNPK+HA30 had a seed weight (21.50) which is statistically same with treatment RNPK (21.67).The total yield of maize gotten in this study showed that treatment HA10 had the highest yield (2.93) after treatment RNPK (3.53).Therefore, long term studies are required in the study location to know if positive responses will be observed on soil properties and growth of crops with the application of HA.

Combined Application of Organic Fertilizer with Microbial Inoculum Improved Aggregate Formation and Salt Leaching in a Secondary Salinized Soil.

Greenhouse vegetable production provides significant quantities of vegetables throughout the year and improves farmers' income. However, over-fertilization with mineral fertilizer causes soil secondary salinization and decreases the stability of the soil structure. To improve aggregate formation and decrease salt accumulation in the soil profile, bio-organic fertilizers (Protaetia brevitarsis larvae frass with Bacillus amyloliticus and/or Trichoderma harziensis) were applied to partially substitute mineral fertilizer in a salinized vegetable soil. Soil nutrient condition, aggregate stability, and salt movement in the soil profile were measured in a greenhouse double-cucumber system. The results showed that soil organic matter (SOM), total nitrogen (TN), and available phosphorus (AP) increased significantly under bio-organic fertilizer treatments compared with control. Soil electrical conductivity (EC) and total salt content (TSC) decreased by 15.74-24.20% and 19.15-29.05%, respectively, with bio-organic fertilizers (p < 0.05). Cl-, NO3-, and SO42- content under double inoculation with B. amyloliticus and T. harziensis reduced by 31.19%, 26.30%, and 53.11%, respectively, compared to CK (p < 0.05). In addition, double inoculation was more efficient in reducing nitrate content in the soil profile than single inoculation. Soil microaggregates of 0.25-0.053 mm increased by 75.87-78.51% with bio-fertilizers compared with control, and double inoculation was the best for aggregate formation. In conclusion, the inoculation of plant-growth-promoting and salt-tolerant microorganisms with high humic acid larvae frass can alleviate salinization in vegetable soil, enhance soil nutrient content, and improve the soil structure.

New insights into membrane fouling in coagulation-ultrafiltration by cake characteristics analysis: A case study with PACl-Al13 and PACl

Membrane fouling is a bottleneck issue that hindered the further application of ultrafiltration technology. To alleviate membrane fouling, coagulation-ultrafiltration (C-UF) process using polyaluminum chloride (PACl) and PACl-Al13 with high proportion of Al13O4(OH)247+ as coagulants, respectively, were investigated at various pH conditions. Results indicated that an increase in solution pH contributed to larger floc size and looser floc structure for both PACl and PACl-Al13. It was conducive to the formation of more porous cake, as evidenced by mean pore area and pore area distribution of cake, leading to lower reversible fouling. Furthermore, humic acid (HA) removal presented a trend of first increasing and then decreasing with the increase of pH. The optimal HA removal was achieved at pH 6 regardless of coagulant type, suggesting that the slightest irreversible fouling should be occurred at this point. Interestingly, the irreversible fouling with PACl coagulant achieved a minimum value at pH 9, while the minimal irreversible fouling with PACl-Al13 was observed at pH 6. We speculated that the cake formed by PACl could further intercept HA prior to UF process at alkaline pH. Furthermore, compared with PACl, PACl-Al13 had a stronger charge neutralization ability, thus contributing to more compact floc structure and higher HA removal at various pH conditions. By UF fractionation measurement, higher HA removal for PACl-Al13 was due to higher removal of HA with molecular weight less than 50 kDa.

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

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

Alloying effect of PdCu-TiO2 in photocatalytic membrane reactor for efficient removal of humic acid foulant

Photocatalytic membrane reactor (PMR), coupling photocatalysis and membrane separation, has shown a considerable potential in foulant removal. However, the serious membrane fouling and fragile membrane stability still limit the application of current PMR systems. Here, we report a strategy that PdCu alloy deposited on TiO2, which is incorporated with polyvinylidene fluoride membrane, achieves high humic acid (HA) rejection efficiency (100%) with enhanced membrane permeation and anti-fouling performance. Detailed characterizations demonstrate that alloying effect of PdCu-TiO2 plays multiple roles in improving PMR performance: (1) providing the paired Pd-Cu sites for enhancing HA adsorption and transferring electrons from Pd-Cu sites to HA to improve photocatalytic HA removal; (2) inducing the photothermal effect due to the carrier damping, which directly enhances membrane permeation. The remarkable properties of PdCu-TiO2 membrane in PMR confirm the significance of alloying effect for treating aqueous organic pollutants.

Influence of dope composition of polyethersulfone membrane blend with cellulose nanocrystal and carboxylated multi-walled carbon nanotube on humic acid rejection

A full factorial experimental design was employed to investigate the dope composition of a membrane made of cellulose nanocrystal (CNC), multi-walled carbon nanotube (MWCNT), and polyethersulfone (PES) for its ability to reject humic acid (HA). Four factors were screened, including PES composition, polyvinylpyrrolidone content, CNC content, and carboxylated MWCNT content. The membranes were tested for HA rejection using a 10-ppm aqueous feed solution. The results indicated that the percentage of MWCNT had the most significant impact, contributing 72.31% to the overall contribution. The fabricated membranes exhibited high HA removal capacity of up to 90% for the membrane embedded with MWCNT. The model's predicted values agreed reasonably with the experimental data, indicating the model's validity. This study provides insights into the development of CNC/MWCNT/PES membranes for efficient HA rejection in water treatment applications.

Effects of Incorporating Different Proportions of Humic Acid into Phosphate Fertilizers on Phosphorus Migration and Transformation in Soil

Incorporating humic acid (HA) into phosphate fertilizers to produce HA-enhanced phosphate fertilizers (HAPs) can improve the migration and availability of fertilizer-derived phosphorus (P) in soil. However, the optimal proportion of HA remains inconsistent. Here, we investigated the effects of HAPs with different HA proportions (0.1–10% w/w) on water-soluble P fixation rate, P migration, P transformation, and soil microorganisms, and analyzed the main P forms in HAP using Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The results showed that incorporating 0.1% HA had no impact on P migration and transformation, whereas incorporating 0.5–10% HA increased the migration distance and cumulative migration of fertilizer-derived P by 0–5 mm and 17.1–30.3%, respectively, compared with conventional phosphate fertilizer (CP). Meanwhile, HAPs with 0.5–10% HA significantly reduced the water-soluble P fixation rate by 18.3–25.6%, and significantly increased the soil average available P (AP) content in 0–40 mm soil layer around the P application site by 6.2–12.9% relative to CP, partly due to the phosphate monoesters in HAPs. Clustering analysis revealed that 0.5% HA had similar effects relative to higher HA proportions (1% and 5%), and the inhibition of HAP with 0.5% HA on bacteria and fungi was also greater than that of CP due to the high concentration of soil P. Overall, 0.5% was determined to be the optimal amount of HA for HAP production, which provided a theoretical basis for the development of high-efficiency phosphate fertilizer.

Efficiency of Ag3PO4/TiO2 as a heterogeneous catalyst under solar and visible light for humic acid removal from aqueous solution

Nowadays, the presence of humic acid (HA) in water sources is highly regarded due to the production of extremely harmful byproducts such as trihalomethanes. In this study, the effectiveness of an Ag3PO4/TiO2 catalyst produced by in situ precipitation as a heterogeneous catalyst for the degradation of humic acid in the existence of visible and solar light was evaluated. The Ag3PO4/TiO2 catalyst's structure was characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS), after which the catalyst dosage, HA concentration, and pH parameters were adjusted. After a 20-min reaction, the highest HA degradation of 88.2% and 85.9% in presence of solar light and visible light were attained at the ideal operating conditions of 0.2 g/L catalyst, 5 mg/L HA, and pH 3, respectively. It was discovered that, based on kinetic models, the degradation of HA matched both Langmuir-Hinshelwood and pseudo-first-order kinetics at concentrations of 5 to 30 mg/L (R2 > 0.8). The Langmuir-Hinshelwood model had surface reaction rate constants (Kc) of 0.729 mg/L.min and adsorption equilibrium constants (KL-H) of 0.036 L/mg. Eventually, a real-water investigation into the process' effectiveness revealed that, under ideal circumstances, the catalyst had a reasonable HA removal efficiency of 56%.

Response of nitrogen removal and microbial community to high concentration of humic acid in the anammox biofilm system

The anaerobic ammonium oxidation (anammox) process is highly effective to remove nitrogen from the wastewater with high ammonia concentration, such as landfill leachate and anaerobic digestion. This kind of wastewater generally contains high content of humic acid, and its effect on anammox is not clear. Therefore, this study investigated the effect of humic acid with high concentration (100–1000 mg/L) on the anammox biofilm system. The nitrogen degradation rates were greatly decreased at the high concentration of humic acid and the reaction time was prolonged by 4 h compared with that lacking humic acid. In the anammox biofilm system, the relative abundance of anammox bacteria Candidatus_Brocadia and Candidatus_Kuenenia decreased from 2.1 % and 15.01 % to 0.6 % and 8.32 %, respectively, while the denitrifying bacteria Thauera increased from zero to 8.86 %. Overall, the high humic acid concentration did not obviously inhibit nitrogen removal performance of anammox system, but affected anammox bacteria activity and microbial community structure.