Adsorption Of Humic Substances Research Articles

Application of carbon nitride nanosheets for adsorption of various humic substances from aqueous solutions

Humic substances (HSs) cause serious problems such as membrane fouling and disinfection by-products. Particularly, HSs as the main UV-quenching substances in landfill leachate pose great challenges. In this study, we evaluated the application of carbon nitride nanosheets (CN-Ns) for adsorption of various HSs, as well as leachate nanofiltration concentrates (LNCs). The characterization revealed that as increasing thermal oxidation temperature, the properties of CN-Ns were affected, such as morphology, porosity, and crystallinity. The surface area of CN-N at 575 °C (CN-N-575) was 145.3 m2·g−1, resulting in an enhanced adsorption performance. The adsorption capacity of CN-N-575 for lignite humic acid (LHA) and soil fulvic acid (SFA) was considerably greater than that of bulk CN; the maximum adsorption amounts of LHA and SFA were 143.11 and 63.27 mg C·g−1, respectively. Upon adsorption, the removal rate of LHA and Elliott soil humic acid was about 90 %. Among HSs and LNCs, the humic-like components showed superior affinity; in some cases, the removal rate reached 100 %. The adsorption preference of aromatic compounds in HSs and LNCs was ascribed to π-electron interactions. The adsorption of LHA was more pH-dependent than that of SFA, attributed to the interactions (electrostatic, hydrogen bonding, and complexation) along with a specific conformation effect. The findings proved the great potential of CN-Ns in HSs adsorption, especially in the treatment of landfill leachate.

Change in adsorption behavior of aquatic humic substances on microplastic through biotic and abiotic aging processes

Interactions between microplastics (MPs) and humic substances (HS) are inevitable in MP-contaminated aquatic environment because of the ubiquitous presence of HS. In this study, we explored the effects of abiotic and biotic aging processes on the adsorption behavior of aquatic HS on MPs. Aging experiments were conducted using polyethylene (PE) as a representative MP, in which UV irradiation and microbial incubation were applied for 15 to 18 days to mimic the natural abiotic and biotic aging processes. Surface modifications after the aging treatments were evidenced by the appearance of CO, CO, O-C=O, and -OH groups; the formation of grooves on UV-aged PE; and the formation of biofilms on the surface of bio-aged PE. The specific surface areas of both treated PE MPs increased with aging. Higher HS adsorption on PE surface was observed after the aging treatments, with a highest kinetic rate for UV-aged PE than that for bio-aged PE. The adsorption isotherm models revealed that the aging processes enhanced the HS adsorption tendency, as evidenced by the highest adsorption capacity for UV-aged PE (~187 μg C/m2), followed by bio-aged PE (~157 μg C/m2) and pristine PE (~87.5 μg C/m2) for a comparable extended aging period (15–18 days). The difference was more pronounced at a lower pH. The enhanced HS adsorption was mainly attributed to the formation of hydrogen bonds, whereas HS adsorption on pristine PE was dominated by hydrophobic interactions and weak van der Waals interactions. Among the two identified fluorescent components (terrestrial humic-like C1 and protein-like C2), C1 exhibited a higher affinity for adsorption onto PE irrespective of aging. Our findings provide insights into the substantial changes that occur in the interactions between MPs and aquatic organic matter with aging processes, which may alter the fate and environmental impacts of MPs in many aquatic systems.

Prediction of polarity-dependent environmental behaviors of humic substances (HS) using a HS hydrophobicity index based on hydrophilic interaction chromatography

A variety of analytical methods have been applied to describe the properties of aquatic humic substances (HS). However, there are only a few methods available to probe HS hydrophobicity because of the heterogeneous character of HS. In this study, hydrophilic interaction chromatography (HILIC) equipped with a UV detector was employed to describe the heterogeneous distribution of HS with respect to its hydrophobicity and to suggest a representative HS hydrophobicity index. To this end, various mobile phases were explored to achieve the optimal separation capability of HILIC. The highest resolution was obtained with a mobile phase comprising acetonitrile and water at a ratio of 70:30 (v:v). A calibration curve was successfully constructed using eight different HS precursor compounds, which allowed for the successful conversion of the retention time (RT) into the octanol-water partition coefficient (Kow) (log Kow = −2.83 × (RT) + 17.44, R2 = 0.950). Several possible HS hydrophobicity indices were derived from the HILIC chromatogram. Among those, the weight-average log KOW value exhibited the strongest negative correlation with the well-known polarity index, (O + N)/C ratios, of seven reference HS samples. This new HILIC-based index (i.e., average log KOW) also presented a good relationship with the HS binding coefficients with pyrene as well as the extent of HS adsorption onto kaolinite at a given solution chemistry (i.e., at a high ionic strength and a neutral pH), both of which are known to be largely governed by the hydrophobic nature of HS. This study demonstrated that the average KOW value based on HILIC is an intuitive and robust HS hydrophobicity index to fully represent the heterogeneous distribution of hydrophobicity within a bulk HS and could be applied to predict many environmental behaviors related to HS hydrophobicity or HS polarity.

Insights into Adsorption of Humic Substances on Graphitic Carbon Nitride.

Graphitic carbon nitride (CN) has been widely used in environmental pollution remediation. However, the adsorption of organic compounds on CNs, which has practical significance for the environmental application of CNs, is poorly understood. For the first time, this study systematically investigated the adsorption behaviors and mechanisms of humic substances (HSs), i.e., humic acid (HA) and fulvic acid (FA), on CNs derived from four typical precursors. Intriguingly, CN derived from urea (CN-U) showed a great capacity for HS adsorption due to its porous structure and large surface area, with maximum adsorption amounts of 73.24 and 51.62 mgC/g for HA and FA, respectively. The formation, influencing factors, and relative contributions of multiple interactions to HS adsorption on CNs were thoroughly elucidated. HS adsorption on CNs was mainly mediated by electrostatic interactions, π-π interactions, and H-bonding. The dominance of electrostatic interactions resulted in HS adsorption being highly dependent on pH and ionic strength. HS components with high aromaticity and high molecular weight were preferentially adsorbed due to π-π interactions. These multiple interactions were largely affected by amino groups and tri-s-triazine units of CNs, as well as the moieties of aromatic rings and oxygen-containing groups of HSs.

Adsorption of humic substances on ferrihydrite affects its use as iron source by plants

Poorly crystalline Fe oxides are sources of Fe to plants. The adsorption of humic substances (HS) on these oxides alters its reactivity and stability in soils, and thus may affect Fe mobilization and uptake by plants from these compounds. This work aimed at studying how the adsorption of HS on Fe oxides affects its use as Fe source by two plant species with different Fe acquisition strategies, white lupin (Strategy I) and wheat (Strategy II). To this end, two completely randomized experiments, one with each plant, were carried out using a calcareous growing media and involving increasing amounts of HS adsorbed on ferrihydrite (0, 16, 60, and 97 mg C g–1) which was used as Fe source. The highest HS rate was the only treatment that significantly increased Fe uptake in wheat relative to control without HS. This was related to a decreased concentration of Fe in poorly crystalline oxides in the growing media. On the contrary, HS did not affect significantly Fe uptake by lupin. However, in this crop, the highest HS rate decreased the concentration of Fe in oxides relative to the lowest HS rate, without significant differences with other treatments. Thus, the effect of adsorbed HS on Fe uptake differed in two plants with different Fe acquisition strategies. The increased Fe uptake in wheat at the highest HS rate can be explained at least in part by an increased Fe mobilization from oxides by plant roots. These findings provide new insights on the role of soil organic matter on plant Fe nutrition.

Tritium labelling to study humic substance-nanodiamond composites

Nanodiamonds produced by the detonation method are used as lubricants, polishing compositions, polymer composites, etc. To reveal how nanodiamonds differ in terms of surface properties and interact with natural organic matter, we used tritium-labelled humic substances to quantitively describe their adsorption onto the nanodiamond surface. It was shown that the adsorption of humic substances onto nanodiamonds resulted in fractionation of humic substances that was strongly dependent on the zeta potential of nanodiamonds in water but did not significantly affect the uptake of nanodiamonds by wheat seedlings. The uptake of nanodiamond particles by plants was determined by the functional composition of the particle surface.

Use of nanoadvanced activated carbon, alumina and ferric adsorbents for humics removal from water: isotherm study

The adsorption of humic substances on three different adsorbents was investigated and adsorption isotherms were applied in this research. The three adsorbents studied include granular activated carbon (GAC), ferric oxihydroxide in its beta form (β-FeOOH) and iron-coated activated alumina (AAFS). Physical and chemical characteristics of the adsorbents were also fully investigated. Calcium was added to the HS solution in order to represent water with a hardness equivalent to water hardness typically found in London (UK). The examination of the GAC indicated a large microporous area with lower surface area associated with meso- and macropores. The AAFS and β-FeOOH did not present any microporous area. The overall surface area was high for GAC (980 m2 g−1) but lower for AAFS (286 m2 g−1) and β-FeOOH (360 m2 g−1). The Freundlich isotherm model was fitted to all adsorbent–adsorbate systems. It was shown that GAC offered a large adsorption capacity for removal of low molecular weight humics F1 (MW 0–5 kDa) but not for substances with molecular weight larger than 10 kDa (F3). The β-FeOOH adsorption capacity was only 0.43 mg g−1, compared with 9.11 and 2.55 mg g−1 on GAC and AAFS, respectively. On the contrary, F1 is not well adsorbed and only F2 (5–10 kDa) can be efficiently removed by AAFS and β-FeOOH. It was strongly suggested that precipitation/condensation occurred on the adsorbent surface.

Stimulated Adsorption of Humic Acids on Capped Plasmonic Ag Nanoparticles Investigated by Surface-Enhanced Optical Techniques.

The adsorption of humic substances on Ag nanoparticles (AgNPs) is of crucial environmental importance and determines the toxicity of these NPs and the structure of adsorbed organic matter. In this work, the adsorption of two standard soil andleonardite International Humic Substances Society humic acids was studied on AgNPs of different sizes, shapes (spherical and star-like), and interfacial chemical compositions. Surface-enhanced optical (Raman and fluorescence) spectroscopies were used to follow the specific chemical groups involved in this adsorption. By means of the latter optical techniques, information regarding the binding mechanism and the macromolecular aggregation can be deduced. The influence of the surface chemical composition induced by the different functionalizations of the interfaces of these NPs is highly important regarding the chemical interactions of these complex organic macromolecules. The surface functionalization with positively charged alkyl diamines led to a large increase in the adsorption as well as a strong structural rearrangement of the macromolecule once adsorbed onto the surface.

Adsorption of Humic Substances: The Effects of Heterogeneity and System Characteristics

Adsorption of Humic Substances: The Effects of Heterogeneity and System Characteristics

Using Two-Dimensional Correlation Size Exclusion Chromatography (2D-CoSEC) and EEM-PARAFAC to Explore the Heterogeneous Adsorption Behavior of Humic Substances on Nanoparticles with Respect to Molecular Sizes

The adsorption behaviors of different constituents within bulk humic substances (HS) on two nanoparticles, TiO2 and ZnO, were examined by using two-dimensional correlation size exclusion chromatography (2D-CoSEC) and excitation emission matrix-parallel factor analysis (EEM-PARAFAC), which separated bulk HS into different size fractions and fluorescent components, respectively. Subtle changes in the size distributions of HS with increasing adsorbents were successfully identified and tracked via the 2D-CoSEC. From adsorption isotherm experiments, three different HS constituent groups with respect to sizes and fluorescence features were identified by the 2D-CoSEC and EEM-PARAFAC, respectively. The chromatographically separated HS size groups presented dissimilar adsorption behaviors in terms of adsorption affinity and isotherm nonlinearity. The sequence orders of adsorption, interpreted from the 2D-CoSEC, was consistent with those of the isotherm model parameters individually calculated for different HS size subfractions, signifying the promising application of 2D-CoSEC in obtaining an insight into the heterogeneous adsorption of HS in terms of molecular sizes. EEM-PARAFAC results also supported the major finding of the 2D-CoSEC as shown by the preferential adsorption of the fluorescent components associated with large molecular sizes.

Combining Coagulation/MIEX with Biological Activated Carbon Treatment to Control Organic Fouling in the Microfiltration of Secondary Effluent.

Coagulation, magnetic ion exchange resin (MIEX) and biological activated carbon (BAC) were examined at lab scale as standalone, and sequential pre-treatments for controlling the organic fouling of a microfiltration membrane by biologically treated secondary effluent (BTSE) using a multi-cycle approach. MIEX gave slightly greater enhancement in flux than coagulation due to greater removal of high molecular weight (MW) humic substances, although it was unable to remove high MW biopolymers. BAC treatment was considerably more effective for improving the flux than coagulation or MIEX. This was due to the biodegradation of biopolymers and/or their adsorption by the biofilm, and adsorption of humic substances by the activated carbon, as indicated by size exclusion chromatography. Coagulation or MIEX followed by BAC treatment further reduced the problematic foulants and significantly improved the flux performance. The unified membrane fouling index showed that the reduction of membrane fouling by standalone BAC treatment was 42%. This improved to 65%, 70%, and 93% for alum, ferric chloride and MIEX pre-treatment, respectively, when followed by BAC treatment. This study showed the potential of sequential MIEX and BAC pre-treatment for controlling organic fouling and thus enhancing the performance of microfiltration in the reclamation of BTSE.

Analysis of electrokinetic properties of NiFe2O4 nanoparticles synthesized by DC thermal plasma route and its use in adsorption of humic substances

The paper reports the influence of electro-kinetic properties of nanoparticles of NiFe2O4 on the adsorption of humic substances (HS); with an aim of understanding their adsorption behavior. Crystalline single phase magnetic nanoparticles of NiFe2O4 are synthesized by gas phase condensation method using DC thermal plasma reactor. Due to the high temperature and steep temperature gradient this method helps in producing highly crystalline nanoparticles with sufficiently large number of surface states suitable for adsorption. These particles possessed high value of zeta potential, reducing their agglomeration and resulting into an enhanced adsorption capacity. However no significant influence of plasma parameters is observed on their zeta-potential and iso-electric values. The adsorption kinetics is studied and fitted to non-linear kinetic models and the best fit is observed for the pseudo first-order model. The analysis of adsorption isotherms suggests that the non-linear Langmuir model fits better as compared to Freundlich adsorption model. The adsorption of HS onto the nanoparticles is seen to depend on the pH value of the solution. A maximum adsorption of 5.2mg/g is obtained at pH value of 3.64. These results suggest that plasma synthesized nanoparticles of NiFe2O4 have high colloidal stability and can be employed as efficient adsorbents for the removal of humic substances from water sources.

Treatment of secondary effluent with biological activated carbon to reduce fouling of microfiltration membranes caused by algal organic matter from Microcystis aeruginosa

Wastewater stabilisation lagoons frequently suffer from cyanobacterial blooms which can negatively impact subsequent water reclamation due to fouling of membranes by the resultant algal organic matter (AOM). Biological activated carbon (BAC) was investigated as a pre-treatment for reducing the fouling in the microfiltration (0.1µm PVDF) of biologically treated secondary effluent (BTSE) to which AOM had been added. The AOM was extracted from Microcystis aeruginosa in stationary phase which had been grown in either MLA growth medium or BTSE and so had different organic composition. Although the DOC concentration was the same, the feedwater containing AOM from the MLA culture led to a greater flux decline than the AOM from the BTSE culture due to its higher biopolymer content (MW≥20,000Da). BAC treatment substantially reduced the fouling potential of the BTSE (with and without the added AOM) due to biodegradation of biopolymers by the microorganisms and adsorption of humic substances by the activated carbon. When the BTSE was spiked with the cyanotoxin microcystin-LR, the BAC treatment gave a microcystin reduction of more than 90%. This study demonstrated the potential of BAC for mitigating the impact of AOM and removing cyanotoxin when treating cyanobacterially impacted secondary effluent using low pressure membranes.

Effect of soil fulvic and humic acid on binding of Pb to goethite–water interface: Linear additivity and volume fractions of HS in the Stern layer

The effects of soil fulvic (JGFA) and humic acid (JGHA) on Pb binding to goethite were investigated with batch experiments and modeling. The CD-MUSIC and NICA-Donnan model could describe the Pb binding to, respectively, the binary Pb–goethite and Pb–HS systems. The adsorption of humic substances (HS) on goethite strongly depended on pH and was promoted by Pb binding. The mass amount of adsorbed JGFA (mg/g) was smaller than that of JGHA, but when expressed in number of particles/nm2 the JGFA adsorption was higher. At low pH and low initial Pb concentration the linear additivity rule always underestimated Pb adsorption to goethite–HS complex, which was caused by the strong effect of adsorbed HS on the electrostatic potentials in the Stern layer region. At other conditions except the 450mg/L JGHA in the 0.5mmol/L Pb system the additivity rule predicted the experimental results reasonably well, and at high pH nearly all Pb is bound to goethite. At the same mass adsorbed, the effect of JGFA on Pb adsorption to goethite is stronger than that of JGHA, due to the fact that the JGFA particles were primarily adsorbed in the Stern layer, whereas JGHA particles were present in both Stern layer and diffuse layer. Therefore, the electrostatic potential profile of the goethite-JGFA complex is considerably different from that of goethite-JGHA complex and affects Pb binding strongly.

Incidence of Adsorption Process on the Reduction of Trihalomethanes Precursory in Algerian Surface Water

The objective of our work is to test the performance of activated carbon on the elimination of humic substances by adsorption before chlorination in order to reduce the trihalomethane precursor of humic substances for two types of surface waters of Biskra region (South East of Algeria). During the chlorination, the results showed that the potential of consumption chlorine is very high for raw surface water tested and accompanied by a rather significant quantity of the trihalomethanes. The adsorption of humic substances on powder activated carbon showed that the activated carbon whatever its form effectively removes humic substances and the yield could reach 98%. For coupling adsorption / chlorination, the results showed that adsorption induced a significant and even a remarkable reduction in both of potential of chlorine consumption and the training potential of organochlorine compounds especially trihalomethanes.

Adsorption of Humic Substances by Using Coconut Copra

Nowadays, consumers are concern about the quality of water that being supplied in order to ensure the water supplied is free from any harmful substances for example like Humic Substances (HS). High concentration of HS in drinking water can cause disease for human such as stomach cancer. Thus, it is important to develop a new technique to improve the quality of drinking water. Therefore, the objective of this research is to investigate the potential of using coconut copra treated with citric acid as activated carbon in adsorbing HS contained in wastewater collected from Asajaya Treatment Plant situated in district of Samarahan, Sarawak. In this research, the optimum condition of adsorption process need to determined. As such, there are two types of parameters which are considered as constant; temperature and pH of activated carbon and variable; solid liquid ratio and residence time. As a result, this research has shown that coconut copra possess the capacity to adsorp 97.5% of HS contained in wastewater.

New insights into the dynamics of adsorption equilibria of humic matter as revealed by radiotracer studies

The mobility of contaminants in the subsurface hydrosphere can be governed by their interaction with aquatic humic substances, which may act as carriers. For modelling migration processes, retardation of humic molecules at mineral surfaces must be considered. There is, however, a lack of clarity concerning the reversibility of adsorption of these natural polyelectrolytes. In this work, evidence was provided that a dynamic adsorption equilibrium exists. For this purpose, adsorption of humic substances (purified Aldrich humic acid and an aquatic fulvic acid) onto kaolinite was examined in tracer exchange studies by means of 14C-labelled humic material. In addition, the kinetics of adsorption and desorption were investigated in batch experiments.Attaining the equilibrium state of adsorption took considerably longer for the humic acid than for the fulvic acid (24h and 4h, respectively). In desorption experiments, initiated by diluting the supernatant at constant pH, no net release was observed for both substances within a time frame of 4weeks. However, when introducing radiolabelled humic or fulvic acid as a tracer into pre-equilibrated adsorption systems in the state of surface saturation, quantitative exchange was found to take place. This indicates that adsorption of humic matter is in fact a reversible process, albeit an exchange time of more than 4weeks was required for both humic materials. Models for humic-bound contaminant transport (presuming dynamic equilibria) are thus applicable under appropriate conditions.

Dependence of microbial magnetite formation on humic substance and ferrihydrite concentrations

Iron mineral (trans)formation during microbial Fe(III) reduction is of environmental relevance as it can influence the fate of pollutants such as toxic metal ions or hydrocarbons. Magnetite is an important biomineralization product of microbial iron reduction and influences soil magnetic properties that are used for paleoclimate reconstruction and were suggested to assist in the localization of organic and inorganic pollutants. However, it is not well understood how different concentrations of Fe(III) minerals and humic substances (HS) affect magnetite formation during microbial Fe(III) reduction. We therefore used wet-chemical extractions, magnetic susceptibility measurements and X-ray diffraction analyses to determine systematically how (i) different initial ferrihydrite (FH) concentrations and (ii) different concentrations of HS (i.e. the presence of either only adsorbed HS or adsorbed and dissolved HS) affect magnetite formation during FH reduction by Shewanella oneidensis MR-1. In our experiments magnetite formation did not occur at FH concentrations lower than 5 mM, even though rapid iron reduction took place. At higher FH concentrations a minimum fraction of Fe(II) of 25–30% of the total iron present was necessary to initiate magnetite formation. The Fe(II) fraction at which magnetite formation started decreased with increasing FH concentration, which might be due to aggregation of the FH particles reducing the FH surface area at higher FH concentrations. HS concentrations of 215–393 mg HS/g FH slowed down (at partial FH surface coverage with sorbed HS) or even completely inhibited (at complete FH surface coverage with sorbed HS) magnetite formation due to blocking of surface sites by adsorbed HS. These results indicate the requirement of Fe(II) adsorption to, and subsequent interaction with, the FH surface for the transformation of FH into magnetite. Additionally, we found that the microbially formed magnetite was further reduced by strain MR-1 leading to the formation of either dissolved Fe(II), i.e. Fe 2+, in HEPES buffered medium or Fe(II) carbonate (siderite) in bicarbonate buffered medium. Besides the different identity of the Fe(II) compound formed at the end of Fe(III) reduction, there was no difference in the maximum rate and extent of microbial iron reduction and magnetite formation during FH reduction in the two buffer systems used. Our findings indicate that microbial magnetite formation during iron reduction depends on the geochemical conditions and can be of minor importance at low FH concentrations or be inhibited by adsorption of HS to the FH surface. Such scenarios could occur in soils with low iron mineral or high organic matter content.

Mobilization and deposition of iron nano and sub-micrometer particles in porous media: A glass micromodel study

Mobilization and deposition of iron nano and sub-micrometer particles (INSMP) in a porous medium were investigated using a water-saturated glass micromodel. The deposition and detachment of INSMP in the micromodel were visualized by taking serial images and experimentally verified by analysis of breakthrough curves. This first visualization study of INSMP fate showed that there were dense aggregations at the pores as the concentration of INSMP increased. The presence of dissolved humic substances (>1 ppm) significantly reduced deposition of suspended particles and enhanced detachment of the deposited particles. The mobility of INSMP in the presence of Pahokee peat fulvic acid standard II (PPFA) was higher than for Pahokee peat humic acid standard I (PPHA) due to the presence of more aromatic groups and the molecular weight in PPFA. Interfacial energy estimation based on the DLVO theory revealed that the adsorption of humic substances onto the INSMP increased the energy barrier and reduced the depth of secondary minimum between particles. The “affinity transition” in the initial deposition of INSMP within the micromodel was observed in the presence of Pahokee peat humic substances.

Effect of Humic Substance Photoalteration on Lead Bioavailability to Freshwater Microalgae

The present study provides results on the influence of humic substance (HS) photoalteration on lead availability to the freshwater microalga Chlorella kesslerii . The evolution of the free lead-ion concentrations measured by the ion exchange technique [Pb](IET) and intracellular lead contents was explored in the presence of Suwannee River humic (SRHA) and fulvic (SRFA) acids, as well as Aldrich humic acid (AHA) exposed at increasing radiance doses under a solar simulator. Modifications of HS characteristics highly relevant to Pb complexation and accumulation of HS to algal surfaces, including Fourier transform infrared spectroscopy, were followed. It was demonstrated that simulated sunlight exposure of HS increased [Pb](IET) in the medium for SRFA and SRHA, but had no effect for AHA. No clear relationship was observed between the changes in free lead-ion concentrations and intracellular content in alga for all studied HS, suggesting that HS photodegradation products also exhibit Pb complexation properties, and that direct interactions between HS and alga are affected. Indeed, photoalteration of humic substances reduced the adsorption of HS to the algal surface; the effect was more pronounced for SRFA and AHA and less significant for SRHA. The bioavailability results were consistent with the characterization of the phototransformation of humic substances: Pb speciation changes followed the modification of the relative abundance of the carboxylic groups and their molecular environment, while the reduced HS adsorption to the alga correlated with losses of the double bond abundance and aromaticity.