Humic Acid Solution Research Articles

Characterizing membrane fouling formation during ultrafiltration of high-salinity organic wastewater

High-salinity organic wastewater usually consists of diverse highly concentrated ions such as Na+, Ca2+ and Al3+ etc., which may significantly influence the fouling propensity when membrane technique is employed for contaminants removal. The current work investigated the effects of high salinity especially high-concentration Na+, Ca2+ and Al3+ on UF fouling characteristics, where 2 M Na+ and 0.5–1.0 M Ca2+ or Al3+ were applied according to the general composition of high-salinity wastewater. The results demonstrated that the presence of high-concentration Na+ alone benefited the ultrafiltration of bovine serum albumin (BSA) solution, but posed adverse effects on the ultrafiltration of humic acid (HA) solution. Further addition of Ca2+ or Al3+ on the basis of Na+ was found to aggravate the development of BSA fouling. Such differentiated behaviors were further elucidated by the comprehensive fouling characterizations in terms of foulant properties, specific resistances, filtration modelling and fouling layer observations. Correlation analysis suggested that irreversible fouling had strong relationship with Al3+ addition, while reversible fouling seemed to be primarily influenced by foulant size. Meanwhile, membrane rejection in the presence of various salts remarkably decreased, which was negatively correlated with zeta potential. Consequently, this study should shed light on the membrane fouling formation for treating high-salinity organic wastewater using membrane techniques.

Effect of coagulation treatment on antifouling properties of PVC nanocomposite membrane in a submerged membrane system for water treatment

A submerged membrane system was used in this work to investigate the effect of the polyaluminum chloride (PAC) coagulant on the antifouling performance of the polyvinyl chloride/alumina (PVC/Al2O3) nanocomposite membrane. The prepared nanocomposite membranes were characterized with field emission scanning electron microscopy (FE-SEM), atomic force microscopy, contact angle, porosity measurement, and pure water flux. The results revealed that the membrane containing Al2O3 nanoparticles (the mass ratio of PVC to Al2O3 was 98.5/1.5) had a higher hydrophilicity, porosity, and pure water flux than other membranes. The FE-SEM images showed that when Al2O3 nanoparticles were present in the PVC membrane, large pores and macrovoids formed on the surface and cross-section of the membrane. The fouling behavior of membranes was investigated through the filtration of humic acid (HA) solution with and without the PAC coagulant. Without PAC addition, the PVC/Al2O3 membrane significantly decreased the irreversible fouling ratio from 60.7% to 19.4% and showed a high HA removal efficiency of approximately 90.5%. The Hermia model confirmed that the cake formation mechanism best described the experimental data for the neat PVC and nanocomposite membranes with the presence and absence of the PAC coagulant. This confirms that the PAC coagulant can significantly mitigate fouling and improve HA removal in the submerged membrane system.

Photodegradation of fragrance materials and triclosan in water: Direct photolysis and photosensitized degradation

The present study aims to assess the photodegradation of three polycyclic musk compounds (OTNE, HHCB, and AHTN) and one disinfectant (triclosan) under simulated sunlight irradiation using a halogen lamp in pH-adjusted DI water, natural waters, and humic acid solution. The degradation induced by hydroxyl radical was examined with the addition of 2-propanol. The targeted compounds were considerably decreased in several days under irradiation, except for triclosan for blank water, with the pseudo-first-order rate constants in the order of one per day at the maximum. They were degraded with the paths of both direct and indirect photosensitized processes, with the hydroxyl radical and others. The main findings were that OTNE direct photolysis was possibly influenced by pH. HHCB photosensitized pathway was more eminent than that of AHTN, and triclosan was degraded mostly by the photosensitized process. The major influential factors were found to differ with the compounds and solution conditions, which intensifies the importance of the consideration of key factors for predicting the degree of photodegradation in water environments. • Direct photolysis and photosensitized degradation were evaluated simultaneously. • Triclosan was mostly degraded by photosensitized pathway, not by direct photolysis. • ONTE direct photolysis was influenced by pH.

Surface-constructing of visible-light Bi2WO6/CeO2 nanophotocatalyst grafted PVDF membrane for degradation of tetracycline and humic acid

The synthesis of Bi2WO6 and CeO2 photocatalytic nanomaterials exhibit a great ability to photodegrade the antibiotics and shown excellent oxidation of various organic pollutants. Heterostructure 1:1 & 2:1 Bi2WO6/CeO2 nanocomposite was successfully synthesized via the facile sono-dispersion method and exquisite photocatalytic activity. The 0.5 wt% of nanocomposites were well-grafted on PVDF membrane surface via an in-situ polymerization method using polyacrylic acid. The fourier transform infrared (FTIR) spectra demonstrated that the network formation in PVDF induced by the -COOH functional group in acrylic acid. The grafted membrane morphology and strong binding ability over the membranes were validated by scanning electron microscope with energy dispersion (SEM-EDS) and X-ray photoelectron spectroscopy (XPS), respectively. The permeate flux of 49.2 L.m−2 h−1 and 41.65 L.m−2 h were observed for tetracycline and the humic acid solution respectively for 1 wt% of PVP and 0.5 wt% of photocatalytic nanomaterials in PVDF membrane. The tetracycline and humic acid photodegradation rate of 82% and 78% and total resistance of 1.43 × 1010 m−1 and 1.64 × 1010 m−1, 83.5% and 77% flux recovery ratio were observed with N5 membrane. The 2:1 Bi2WO6/CeO2 nanocomposite grafted membrane showed a high permeate flux and better photodegradation ability of organic pollutants in the wastewater.

The role of natural organic matter in the silver release from sludge generated from coagulation of wastewater spiked with silver nanoparticles

Sludge is an integral part in the migration pathway of silver nanoparticles (AgNPs) from manufacture to the terrestrial environment. However, the detailed information on the role of natural organic matters (NOMs) remains limited. In this study, the sludge generated from coagulation of wastewater spiked with AgNPs (denoted as sludgeC-AgNPs) was taken as the model. Effects of humic acid (HA), alginate (AA) and bovine serum albumin (BSA) on the release amount, dynamics and speciation of silver from the sludgeC-AgNPs were investigated by a series of leaching experiments. The results showed that HA, AA and BSA in the leaching solution could enhance the silver release from the sludgeC-AgNPs. The concentrations of the dissolved and colloidal silver in the BSA solution were the highest at the initial stage of dynamic leaching. The controlling step of the silver release was internal diffusion in the HA and AA solution, while the release of dissolved silver was controlled by both chemical reaction and internal diffusion in the BSA solution. In addition, the released colloidal silver fractions in the BSA solution contained more particles with size >50 nm compared with the HA and AA solutions. The results suggested that the properties of NOMs may be the key factor affecting the transfer of AgNPs from the sludge to the terrestrial environment.

Intensified ozonation in packed bubble columns for water treatment: Focus on mass transfer and humic acids removal

Ozonation has been widely applied for the oxidation of contaminants in wastewater, and the disinfection of water. However, low ozone (O3) mass transfer efficiency in common ozonation reactors requires high O3 doses and causes high energy consumption. In this study, to intensify the O3 mass transfer and oxidation of humic acids (HA) solution, a lava rock packed bubble column (LBC) and a metal pall ring packed bubble column (MBC) were developed and evaluated. In comparison with non-packed bubble column (BC), both LBC and MBC enhanced the O3 mass transfer efficiency and the generation of hydroxyl radicals, thereby increasing the HA removal from an aqueous solution. At applied O3 dose of 33.3 mg/(Lcolumn h), the HA removal efficiency in BC was only 47%. When MBC and LBC were applied, it increased to 66% and 72%, respectively. Meanwhile, the O3 utilization efficiency in LBC reached 68%, which was higher than that in MBC (50%) and BC (21%). Consequently, LBC has the lowest energy consumption (EEO) for HA removal (1.4 kWh/m3), followed by MBC (1.6 kWh/m3) and BC (2.9 kWh/m3). LBC had better performance than MBC due to the adsorptive and catalytic roles of lava rock on the ozonation process. This study demonstrates the advantages of using lava rocks as packed materials in O3 bubble column over metal pall rings in intensifying O3 mass transfer and organic matters removal, which provides some insights into promoting the industrial application of O3.

Adsorption of micropollutants onto realistic microplastics: Role of microplastic nature, size, age, and NOM fouling

This work aims at evaluating the role of nature, size, age, and natural organic matter (NOM) fouling of realistic microplastics (MPs) on the adsorption of two persistent micropollutants (diclofenac (DCF) and metronidazole (MNZ)). For such goal, four representative polymer types (polystyrene (PS), polyethylene terephthalate (PET), polypropylene (PP) and high-density polyethylene (HDPE)) were tested. MPs were obtained by cryogenic milling of different commercial materials (disposable bottles, containers, and trays), and fully characterized (optical microscopic and SEM images, FTIR, elemental analysis, water contact angle and pHslurry). The micropollutants hydrophobicity determined to a high extent their removal yield from water. Regardless of the MP's nature, the adsorption capacity for DCF was considerably higher than the achieved for MNZ, which can be related to its stronger hydrophobic properties and aromatic character. In fact, aromatic MPs (PS and PET) showed the highest adsorption capacity values with DCF (~100 μg g−1). The MP size also played a key role on its adsorption capacity, which was found to increase with decreasing the particle size (20–1000 μm). MPs aging (simulated by Fenton oxidation) led also to substantial changes on their sorption behavior. Oxidized MPs exhibited acidic surface properties which led to a strong decrease on the adsorption of the hydrophobic micropollutant (DCF) but to an increase with the hydrophilic one (MNZ). NOM fouling (WWTP effluent, river water, humic acid solution) led to a dramatic decrease on the MPs sorption capacity due to sorption sites blocking. Finally, the increase of pH or salinity of the aqueous medium increased the micropollutants desorption.

Phosphate alters the compositional characteristics of humic acid adsorbed onto goethite

The adsorption of organic matter and phosphate on minerals is a common natural process that has an important impact on the migration and burial of carbon and phosphorus. Previous studies have focused mainly on the influence of organic matter on the adsorption of phosphate. Yet, the influence of phosphate on the adsorption of different pools of organic matter is not well understood. This study evaluates changes in different organic matter pools during their adsorption to minerals in the presence of phosphate. Firstly, the adsorption behaviors of natural organic matter (i.e., humic acid) and phosphate on goethite were evaluated separately. Secondly, humic acid and phosphate were added to goethite at different orders to elucidate the effect of phosphate on the fractionation of humic acid components adsorbed to goethite. The results showed that when phosphate and humic acid were added simultaneously, goethite was preferentially combined with phosphate. In the absence of phosphate, SUVA254 of the humic acid solution decreased and E2/E3 of the solution increased during the adsorption. Among the six EEM-PARAFAC (excitation-emission matrix fluorescence coupled with parallel factor analysis) components of the humic acid, C1, C2, and C4 (terrestrial humus-like substances) decreased significantly and exhibited strong adsorption, C3 (microbial fulvic-like substance) showed weak adsorption, whereas C5 (photodegradation products) and C6 (tyrosine-like component) did not show evident adsorption. In the presence of phosphate, phosphate inhibited, and replaced the adsorbed C1, C2, and C4, but promoted the adsorption of C5, which increased the aromaticity and the molecular weight of the humic acid solution. Our results reveal that phosphate influences the fractionation of humic acid components adsorbed onto goethite, suggesting that phosphate can alter the chemical composition of natural organic matter interacting with minerals and thus impact the burial and fractionation of natural organic matter at the mineral-water interface.

Mechanism and toxicity evaluation of catalytic ozonation over Cu/Ce\u2013Al2O3 system aiming at degradation of humic acid in real wastewater

Humic acid (HA) is the main component of organic matter in effluent from wastewater treatment. The effective removal of HA is significant. In this study, a novel catalyst was prepared using a transition metal oxide as the active component and Al2O3 as a granular carrier. The mechanism of catalytic ozonation of HA under neutral pH conditions and its efficiency were investigated. Under the chosen conditions (an ozone concentration of 2.2 mg/L, 50 mg/L HA solution, catalyst dosage of 5 g/L and initial pH of 6.49), the Cu/Ce–Al2O3 bimetallic catalyst led to 54.79% TOC removal rate after 30 min; the removal rate by ozone alone was only 20.49%. The characteristics of organic compounds determined by FT-IR and GC–MS showed that organic compounds were degraded significantly by the catalytic treatment. The addition of catalysts could effectively degrade toxic intermediates and reduce the acute toxicity produced by ozonation. Humic acid substances were largely removed and transformed into biodegradable intermediates. This study proposes a new and efficient ozonation catalyst for practical applications in advanced wastewater treatment.

Study of Turbulence Promoters in Prolonging Membrane Life.

Nanofiltration membrane technology is an effective method for secondary treated sewage purification. However, membrane fouling, which is inevitable in the membrane-separation process, can reduce membrane performance and shorten membrane life. Installing a turbulence promoter is a promising means of improving the hydraulic conditions inside the membrane chamber. In this study, the effect of turbulence promoter on prolonging membrane life was studied for the first time. Flat-sheet polyethersulfone nanofiltration membrane was used to filter humic acid solution, used for simulating secondary treated sewage. By comparing photographs and SEM images of the membrane before and after the simulated secondary treated sewage filtration, it was found that humic acid tended to be deposited on the low-velocity region, which was reflected by COMSOL simulation. After incorporating a turbulence promoter, the reduction of the humic acid deposition area and membrane fouling resistance indicated that the turbulence promoter could reduce membrane fouling due to the improved hydraulic conditions. Additionally, the turbulence promoter also increased the flux and reduced the flux decay rate. The turbulence promoter was then place in the crossflow flat-sheet membrane filtration module, and the variation of flux with time was tested in simulated secondary treated sewage with different concentrations. The results showed that the membrane life for the filtration of simulated secondary treated sewage comprising 50, 250, and 500 ppm humic acid increased by 23.1%, 80.4%, and 85.7%, respectively. The results of this article can serve as a reference for the prediction of membrane life and the performance enhancement mechanism of membranes containing a turbulence promoter.

Effect of Composite Composition in Nanofiber for Degradation of Humic Acid Solution

One of the basic needs for human is clean water. Many lowlands and marshy areas in larger islands in Indonesia such as Sumatra and Kalimantan are the source of peat water. This type of water is harmful for people living in such areas and it cannot be used directly for drinking and living. According to the standard quality of good water, peat water does not meet the requirements as a source of water for daily life. Peat water is acidic, red-brownish coloured, and it contains higher organic matters especially humic acid and its derivatives. Photocatalysis process is one of the promising way to treat solution that contains humic acid. This research aims to pre-eliminary study activity of PVDF-TiO2/ZnO nanofiber for degradation of humic acid solution. Photocatalytic activities were studied inside photoreactor system with artificial UV radiation with 254 nm wavelength. The percentage of degradation after contacting humic acid solution to photocatalyst was determined by measuring humic acid solution before and after degradation by using UV-Vis spectrophotometer with maximum lambda in 219 nm. The rate constants were calculated and the results were 0,03909 min-1 and 0.02832 min-1 respectively for PVDF-4%TiO2/ZnO and PVDF-8%TiO2/ZnOnanofibers and it is in pseudo first order kinetic model.

Isotherm and thermodynamic studies of the biosorption of Humic acid from aqueous solution by pine sawdust-based activated charcoal

In this work, activated charcoal was prepared from pine tree sawdust by chemical activation using phosphoric acid (PSDP) that was applied for the biosorption of Humic acid from aqueous medium. The effect of sorbent mass, humic acid initial concentration and solution temperature on the adsorption process were investigated by batch experiments. The equilibrium sorption data were analyzed by Langmuir and Freundlich isotherm models. The maximum adsorption capacities of PSDP obtained from Langmuir were 170.9, 182.1 and 209.6 mg/g at 25 o C, 45 o C and 65 o C, respectively. The adsorption of humic acid onto PSDP was spontaneous, favorable at higher temperature and endothermic in nature. Activated charcoal from pine tree sawdust proves to have high capacity adsorptive to natural organic compound (humic acid).

Enhanced humic acid degradation by Fe3O4/ultrasound-activated peroxymonosulfate : Synergy index, non-radical effect and mechanism

In this study, Fe3O4/ultrasound (US) activated-peroxymonosulfate (PMS) was employed to degrade humic acid (HA). Magnetic nano-scale Fe3O4 particles were prepared via a co-precipitation method. The physical and chemical properties of Fe3O4 were characterized explicitly by a variety of methods, including scanning electron microscope-energy dispersive spectrometer (SEM-EDS), transmission electron microscope (TEM), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), Zeta potential, Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), and vibrating-sample-magnetometer (VSM). The synergy index of US and Fe3O4 activated PMS for humic acid degradation was calculated. After 20 min of reaction under the Fe3O4/Ultrasound/PMS system, 10 mg/L of HA solution was completely degraded. Batch experiments were conducted to determine the effect of PMS concentration, HA concentration, dosage of Fe3O4, and pH value on the degradation of HA in the absence and presence of US. The thermal and non-thermal effects of US on HA degradation were studied. Electron paramagnetic resonance (EPR) and quenching tests indicated that non-radical singlet oxygen (1O2) is the dominant contributor for HA degradation. This study provides a fast and cost-effective method for HA removal.

Novel polycarbonate membrane embedded with multi-walled carbon nanotube for water treatment: a comparative study between bovine serum albumin and humic acid removal

Flat sheet polycarbonate/multi-walled carbon nanotube (PC/MWCNT) nanocomposite membranes with different nanoparticle contents were prepared by applying the phase inversion method. The characteristics of the prepared membranes were analyzed by field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), water contact angle, porosity, pure water flux (PWF), and mechanical properties. The performance of the membranes was evaluated in a submerged membrane system for two cycles and also for the filtration of humic acid (HA) and bovine serum albumin (BSA). The obtained results revealed that nanocomposites containing 0.1 wt% of MWCNTs showed better hydrophilicity, porosity, PWF, and mechanical properties. The FE-SEM images from surface indicated that the density and pore size of membrane increased from 0 to 0.1 wt% of MWCNTs. Moreover, according to AFM images, the PC/MWCNT-0.1 membrane showed a smoother surface than other samples. The antifouling performance of the membranes in a submerged membrane system revealed that the BSA solution flux for all membranes was lower than that of the HA solution due to the pore blocking of membranes occurring in the initial filtration of BSA. Apart from that addition of the 0.1 wt% of MWCNTs led to significant improvement in the fouling recovery ratio in the filtration of both HA and BSA because of the lower roughness and high hydrophilicity of the membrane surface. The rejection results revealed that the neat PC membrane had the highest value in the removal of HA and BSA with respect to other samples due to the formation of a thicker and denser cake layer on the membrane surface.

Investigations on the fouling characteristic of humic acid and alginate sodium in capacitive deionization

Abstract Capacitive deionization (CDI) has been investigated for brackish water desalination, selective removal of ions, and water softening. We used humic acid (HA) and alginate sodium (SA) to simulate different kinds of natural organic matter to investigate the fouling phenomena during CDI operation. Adsorption amount and energy efficiency were studied. Results showed that both SA and HA could decrease the removal of NaCl during CDI operation. There existed a slight decrease of energy consumption in SA solutions which was opposite to that in HA solutions. HA can compete with ions adsorbed by electrodes and attach to electrodes adhesively, resulting in co-ion repulsion. SA is not sensitive to electrical field and its fouling is not obvious. The amount of adsorbed Mg2+ would increase from 0.927 mg/g to 1.508 mg/g in ten cycles' operation and the increment of Ca2+ was from 1.885 mg/g to 2.878 mg/g in SA solutions. This increase of adsorption was due to the complexation between SA and cations. Simultaneously, energy consumption was decreased. In HA solutions, energy consumption of Mg2+ and Ca2+ adsorption increased. In ten cycles' operations, both HA and SA could reduce the efficiency of CDI operation. The types of organic substances are important factors in fouling of CDI electrodes.

Interaction of Ca2+ and soil humic acid characterized by a joint experimental platform of potentiometric titration, UV–visible spectroscopy, and fluorescence spectroscopy

Rocky desertification has become a major environmental issue in the karst region of southwestern China. Karst rocky desertification was more severe in regions of limestone soil than in adjacent regions of other soils, despite the relatively higher soil organic matter (SOM) content in limestone soil. The underlying mechanism remains ambiguous. We speculated that the geochemical characteristics of limestone soils in the karst region plays an essential role, especially the high calcium content of limestone soil. To test this hypothesis, we collected limestone soil samples from a limestone soil profile in the southwestern China karst region and extracted humic acid (HA) from these limestone soil samples. We investigated the interaction of Ca2+ and three HA samples on a joint experimental platform, which consists of an automatic potentiometric titrator, a UV–visible spectrometer, and a Fluorescence spectrometer. HA solutions were titrated by Ca2+ and optical spectra of the HA solutions were monitored during the titration experiments. The results indicated that: (1) the interaction of Ca2+ and HA is a combined process of adsorption and complexation. Adsorption dominated the overall distribution behavior of Ca2+, which could be fit by Langmuir and Freundlich isotherm models. Complexation was distinguished only when the concentration of Ca2+ is low; (2) the changes of UV–visible spectroscopy and excitation–emission matrix fluorescence spectroscopy spectra of HA samples when they were binding with Ca2+ implied the apparent molecular size and structure of HA became larger and more complex; (3) the combination of Ca2+ and HA plays an important role in the SOM preservation of limestone soils but the stability of the Ca–HA association was relatively weak. The present study draws attention to maintaining the relatively higher Ca2+ concentration in limestone soils in ecologic restoration attempts in karst regions.

Efficient simultaneous removal of heavy metals and polychlorobiphenyls from a polluted industrial site by washing the soil with natural humic surfactants

We evaluated the effectiveness of natural organic surfactants such as humic acids (HA) from lignite to simultaneously wash heavy metals (HM) and polychlorobiphenyls (PCB) from a heavily contaminated industrial soil of northern Italy. Supramolecular HA promote in solution a micelle-like structure, where recalcitrant apolar organic xenobiotics are repartitioned from surfaces of soil particles during soil washing process. Concomitantly, the HA acidic functional groups enable a simultaneous complexation of HM. A single soil washing with HA removed 68 and 75% of PCB congeners for 1:1 and 10:1 solution/soil ratios, respectively. The same HA washing simultaneously and efficiently removed a cumulative average of 47% of total HM, with a maximum of 57 and 67% for Hg and Cu, respectively. We showed that washing a highly polluted soil with HA solution not only is an effective and rapid soil remediation technique but also simultaneously removes both HM and persistent organic pollutants (POP). Soil washing by humic biosurfactants is also a sustainable and eco-friendly technology, since, contrary to synthetic surfactants and solvents used in conventional washing techniques, it preserves soil biodiversity, promotes natural attenuation of unextracted POP, and accelerates further soil reclamation techniques such as bio- or phytoremediation.

Enhanced permeability and antifouling performance of polyether sulfone (PES) membrane via elevating magnetic Ni@MXene nanoparticles to upper layer in phase inversion process

In this study, magnetic Ni@MXene nanoparticles were firstly developed and then elevated to the upper layer of polyether sulfone (PES) membrane by an external magnetic field during the wet phase inversion process. Flux of the prepared PES-Ni@MXene membrane was 2.5 times of that of the control PES membrane. Moreover, PES-Ni@MXene membranes showed a significant promotion of antifouling ability, evidenced by the flux recovery rates (FRR) of 64.6% and 99.8% for bovine serum albumin (BSA) and humic acid (HA) solutions, respectively. The antifouling performance of the PES-Ni@MXene membrane was comparable or better than those in the literature studies. Meanwhile, the optimal PES-Ni@MXene membrane possessed an efficient decoloration ability for Congo red (CR) solution and colored emulsion. To analyze the anti-fouling mechanism, the interaction energies between the membrane surface and pollutants (BSA and HA) were computed via the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. The results showed that the total attraction energy between PES-Ni@MXene membrane and pollutant interface was smaller than that between the control PES membrane and pollutant interface. This study provided a new incentive to development of high-efficient Mxene-based membranes.

Polyaniline/polysulfone ultrafiltration membranes with improved permeability and anti-fouling behavior

To enhance the anti-fouling performance of polysulfone (PSF) membranes, polyaniline (PANI) nanofibers were used as additives in a facile method to prepare PANI/PSF blended membranes (PPMs). The fouling behavior between the membrane and natural organic matters (NOM) pollutant was further analyzed by implementing extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory. Overall, the performance of the PPMs was improved in comparison with that of the pristine PSF membrane. The pure water flux of the PPM increased to 2.4 times that of pristine PSF, reaching up to 169 L·m−2 h−1 bar−1. The tensile strength of the hybrid membranes also increased after the incorporation of PANI nanofibers. In particular, in anti-fouling measurement, the PPMs exhibited enhanced anti-fouling properties for filtration serum albumin (BSA), humic acid (HA) and sodium alginate (SA) solutions. The anti-fouling mechanism was analyzed by the interfacial interaction energy, which were obtained by applying the XDLVO theory. Results confirmed that there are reduced attractive interaction energies between the PPMs and NOM pollutants molecules in comparison to the interaction between the pristine PSF and NOM pollutants molecules.

Gamma-irradiation-induced molecular-weight distribution and complexation affinity of humic acid with Cs+, Sr2+, and Eu3+

Solutions of humic acid (HA) were irradiated with 0, 1, 5, 10, 50, and 100 kGy of gamma irradiation using a 60Co source. The non-irradiated and irradiated HA molecules were fractionated by ultrafiltration into four categories: > 100, 50–100, 10–50, and < 10 kDa. Total organic carbon measurements and potentiometric titration analysis suggested that (1) some gamma-irradiated HA molecules were degraded into smaller molecules and (2) radiolytic degradation caused phenolic –OH became the predominant functional group in the small molecular-weight fractions of HA. The effect of absorbed dose of gamma rays on the distributions of Cs+, Sr2+, and Eu3+ ions in the molecular-weight fractions of the metal–HA systems was examined to discuss the complexation affinity. The metal ions were distributed in the smaller molecular-weight fractions at different doses, which corresponded to the degradation of HA molecules. For a predetermined absorbed dose, Cs+ ions did not change the molecular-weight distribution of the total organic carbon content of the degraded HA molecules. Conversely, the Sr2+ and Eu3+ ions redistributed organic carbon toward the larger molecular-weight fractions.