Humic Acid Solution Research Articles

Enhanced formation of iodinated trihalomethanes in a mixed chlorine/chloramine system and attenuation by UV-activated process

Iodinated trihalomethanes (I-THMs) have drawn increasing concerns due to their higher toxicity than those of their chlorinated and brominated analogues. In this study, I-THM formation was firstly evaluated for three treatment scenarios - (i) chlorine alone, (ii) chloramine alone, and (iii) mixed chlorine/chloramine - in the presence and absence of UV irradiation for the iodide-containing humic acid solution or natural water. The results indicated that I-THM formation decreased in the order of mixed chlorination/chloramination > chloramination > > chlorination, which fitted the trend of toxicity evaluation results using Chinese hamster ovary cells. Conversely, total organic halide concentration decreased in the order of chlorination > > chloramination ≈ mixed chlorination/chloramination. Besides, I-THM formation can be efficiently controlled in a UV-activated mixed chlorine/chloramine system. Influencing factors including pH values and Br-/I- molar ratios were also systematically investigated in a mixed chlorine/chloramine system. Enhanced I-THM formation was observed with increasing pH values (6.0–8.0) and Br-/I- molar ratios (1: 1–10: 1). The results obtained in this study can provide new insights into the increasing risk of I-THM formation in a mixed chlorine/chloramine system and the effective control of I-THMs in the iodide-containing water using UV irradiation.

Sorption of Cs+ and Eu3+ ions onto sedimentary rock in the presence of gamma-irradiated humic acid

The influence of humic acid (HA) and its radiological degradation on the sorption of Cs+ and Eu3+ by sedimentary rock (obtained from the Horonobe Underground Research Laboratory in Japan) was investigated to understand the sorption process of metal ions and humic substances. Aldrich HA solution was gamma-irradiated assuming a strong radiation from a highly radioactive waste to be disposed of in deep geological formations. Batch sorption experiments were performed to evaluate the effect of gamma-irradiated HA on the sorption of Cs+ and Eu3+ ions. The addition of non-irradiated HA weakened the Eu sorption because of the lower sorption of the negatively charged Eu-HA complexes compared with free Eu ions. The sorption of Cs ions was barely affected by the presence of HA and its gamma irradiation. The concentration ratio of metal complexed and non-complexed species in the solid and liquid phases was evaluated by sequential filtration and chemical equilibrium calculations. The ratios were low in both phases for Cs and supported the minimal contribution of HA to Cs sorption. However, the concentration ratio for Eu3+ in the liquid phase was high, indicating that the complexing ability of HA to Eu3+ was higher than that of HA to Cs+.

Understanding the Effect of pH on the Solubility and Aggregation Extent of Humic Acid in Solution by Combining Simulation and the Experiment.

Molecular dynamics (MD) simulations were performed to investigate the dynamics of humic acid (HA) in an aqueous solution and the influence of pH, temperature, and HA concentration. The HA model employed in MD simulations was chosen and validated using experimental chemical composition data and Fourier transform infrared (FTIR) spectra. The simulations showed that the HA molecule has a strong propensity to adopt a compact conformation in water independent of pH, while the aggregation of HA was found to be pH-dependent. At high pH, the ionized HAs assembled into a thread-like structure, maximizing contact with water. At low pH, the neutral HAs formed a droplet-like aggregate, minimizing contact with the solvent. The simulation results are consistent with experimental data from dynamic light scattering (DLS) measurements and transmission electron microscopy (TEM) imaging. This work provides new insight into the folding and aggregation of HA as a function of pH and a molecular-level understanding of the relationship between the acidity and the structure, solubility, and aggregation of HA, with direct implications for HA-based remediation strategies of contaminated sites.

Development of Antifouling Polysulfone Membranes by Synergistic Modification with Two Different Additives in Casting Solution and Coagulation Bath: Synperonic F108 and Polyacrylic Acid.

This study deals with the development of antifouling ultrafiltration membranes based on polysulfone (PSF) for wastewater treatment and the concentration and purification of hemicellulose and lignin in the pulp and paper industry. The efficient simple and reproducible technique of PSF membrane modification to increase antifouling performance by simultaneous addition of triblock copolymer polyethylene glycol-polypropylene glycol-polyethylene glycol (Synperonic F108, Mn =14 × 103 g mol−1) to the casting solution and addition of polyacrylic acid (PAA, Mn = 250 × 103 g mol−1) to the coagulation bath is proposed for the first time. The effect of the PAA concentration in the aqueous solution on the PSF/Synperonic F108 membrane structure, surface characteristics, performance, and antifouling stability was investigated. PAA concentrations were varied from 0.35 to 2.0 wt.%. Membrane composition, structure, and topology were investigated by Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The addition of PAA into the coagulation bath was revealed to cause the formation of a thicker and denser selective layer with decreasing its pore size and porosity; according to the structural characterization, an interpolymer complex of the two additives was formed on the surface of the PSF membrane. Hydrophilicity of the membrane selective layer surface was shown to increase significantly. The selective layer surface charge was found to become more negative in comparison to the reference membrane. It was shown that PSF/Synperonic F108/PAA membranes are characterized by better antifouling performance in ultrafiltration of humic acid solution and thermomechanical pulp mill (ThMP) process water. Membrane modification with PAA results in higher ThMP process water flux, fouling recovery ratio, and hemicellulose and total lignin rejection compared to the reference PSF/Synperonic F108 membrane. This suggests the possibility of applying the developed membranes for hemicellulose concentration and purification.

Fabrication of Polyvinylidene Difluoride Membrane with Enhanced Pore and Filtration Properties by Using Tannic Acid as an Additive.

Potential use of tannic acid (TA) as an additive for fabrication of polyvinylidene difluoride (PVDF) membrane was investigated. The TA was introduced by blending into the dope solution with varying concentrations of 0, 1, 1.5, and 2 wt%. The prepared membranes were characterized and evaluated for filtration of humic acid (HA) solution. The stability of the membrane under harsh treatment was also evaluated by one-week exposure to acid and alkaline conditions. The results show that TA loadings enhanced the resulting membrane properties. It increased the bulk porosity, water uptake, and hydrophilicity, which translated into improved clean water flux from 15.4 L/m2.h for the pristine PVDF membrane up to 3.3× for the TA-modified membranes with the 2 wt% TA loading. The flux recovery ratio (FRR) of the TA-modified membranes (FRRs = 78–83%) was higher than the pristine one (FRR = 58.54%), with suitable chemical stability too. The improved antifouling property for the TA-modified membranes was attributed to their enhanced hydrophilicity thanks to improved morphology and residual TA in the membrane matric.

The Fate of Atrazine in Tropical Environments: Photolysis, Acute Toxicity and Endocrine Disruptor Potential

Triazine herbicides are widely used both in Brazil and internationally and are frequently detected in natural environments and drinking water. This study assesses atrazine degradation through solar radiation under tropical conditions and determines the toxicity of the intermediates. Atrazine degradation is tested through ultrapure water, humic acid solution and natural water experiments, with exposure to sunlight to simulate a natural environment. A yeast estrogen screen (YES) assay and Artemia salina test are carried out during the abiotic degradation. The atrazine degradation depends on the radiation intensity, since the experiments conducted in the summer reached 50% after ca. 17 days. No significant variations in this herbicide concentration are observed after 90 days of exposure in the fall. Atrazine degradation is observed only in humic acid and is responsible for indirect photolysis. Intermediates, namely, desethylatrazine (DEA) and deisopropylatrazine (DIA), are identified and quantified at the μg L–1 level. Thus, with the degradation of atrazine in water, the medium toxicity may decrease, since DEA and DIA have mean effective concentrations that kill 50% of Artemia salina (EC50) similars to atrazine (13 mg L–1). No estrogenic activity in the YES is detected for atrazine and its metabolites. These findings evidence that radiation intensity and organic substances in tropical countries influence the half-life of pesticides in aquatic environments.

High flux Fe/activated carbon membranes for efficient degradation of organic pollutants in water by activating sodium persulfate

Efficient removal of organic pollutants in water is an important task and difficult problem in environmental treatment. In this paper, activated carbon supported Fe ions catalyst (Fe/AC) was prepared by a modulated hydrothermal approach for catalytic activating sodium persulfate (PS) to remove trace of humic acid (HA) in water. The effect of the dosage of Fe/AC and PS, the initial content of HA, pH, temperature, inorganic salt on the degradation of HA were analyzed. At the optimum condition, the advanced oxidation system achieved removal efficiencies of HA, TOC and chromaticity of 99.92%, 70.50% and 96.43%, respectively by adding 1.0 g/L Fe/AC and 0.30 g/L PS into 30 mg/L HA solution for 2 h. With increasing temperature and ionic concentration, the degradation rate was promoted. The regeneration efficiency of the catalyst was 66.70% as the reduction of active sites in AC. Electron paramagnetic resonance (EPR) and quenching tests were used to investigate the mechanism and both sulfate radicals (SO4−) and hydroxyl radicals (OH) were verified as dominant force responsible for HA degradation. Furthermore, a constant HA solution with PS was cross-flow filtrated by Fe/AC membrane within 20 h with excellent rejection of HA (93.33%) and high flux (298.8 L·m−2·h−1) under 0.1 MPa. The loaded Fe/AC effectively reduced the membrane fouling by HA and the coupled technology improved activation capacity of the Fe/AC. Other pollutions including amoxicillin, rhodamine B and methyl orange were employed to investigate the performance of the catalytic membrane. The combined technology exhibits an excellent performance of removing organic pollutants from water and provides a new idea for water environmental management.

Freeze-Thaw Cycle-Enhanced Transformation of Iodide to Organoiodine Compounds in the Presence of Natural Organic Matter and Fe(III).

The formation of organoiodine compounds (OICs) is of great interest in the natural iodine cycle as well as water treatment processes. Herein, we report a pathway of OIC formation that reactive iodine (RI) and OICs are produced from iodide oxidation in the presence of Fe(III) and natural organic matter (NOM) in frozen solution, whereas their production is insignificant in aqueous solution. Moreover, thawing the frozen solution induces the further production of OICs. A total of 352 OICs are detected by Fourier transform ion cyclotron resonance mass spectrometry in the freeze-thaw cycled reactions of Fe(III)/I-/humic acid solution, which are five times as many as OICs in aqueous reactions. Using model organic compounds instead of NOM, aromatic compounds (e.g., phenol, aniline, o-cresol, and guaiacol) induce higher OIC formation yields (10.4-18.6%) in the freeze-thaw Fe(III)/I- system than those in aqueous (1.1-2.1%) or frozen (2.7-7.6%) solutions. In the frozen solution, the formation of RI is enhanced, but its further reaction with NOM is hindered. Therefore, the freeze-thaw cycle in which RI is formed in the frozen media and the resulting RI is consumed by reaction with NOM in the subsequently thawed solution is more efficient in producing OICs than the continuous reaction in frozen solution.

Improvement of Properties and Performances of Polyethersulfone Ultrafiltration Membrane by Blending with Bio-Based Dragonbloodin Resin.

Polyethersulfone (PES) is the most commonly used polymer for membrane ultrafiltration because of its superior properties. However, it is hydrophobic, as such susceptible to fouling and low permeation rate. This study proposes a novel bio-based additive of dragonbloodin resin (DBR) for improving the properties and performance of PES-based membranes. Four flat sheet membranes were prepared by varying the concentration of DBR (0–3%) in the dope solutions using the phase inversion method. After fabrication, the membranes were thoroughly characterized and were tested for filtration of humic acid solution to investigate the effect of DBR loading. Results showed that the hydrophilicity, porosity, and water uptake increased along with the DBR loadings. The presence of DBR in the dope solution fastened the phase inversion, leading to a more porous microstructure, resulted in membranes with higher number and larger pore sizes. Those properties led to more superior hydraulic performances. The PES membranes loaded with DBR reached a clean water flux of 246.79 L/(m2·h), 25-folds higher than the pristine PES membrane at a loading of 3%. The flux of humic acid solution reached 154.5 ± 6.6 L/(m2·h), 30-folds higher than the pristine PES membrane with a slight decrease in rejection (71% vs. 60%). Moreover, DBR loaded membranes (2% and 3%) showed an almost complete flux recovery ratio over five cleaning cycles, demonstrating their excellent antifouling property. The hydraulic performance could possibly be enhanced by leaching the entrapped DBR to create more voids and pores for water permeation.

Fabrication and performance of polysulfone/H2O2-g-C3N4 mixed matrix membrane in a photocatalytic membrane reactor under visible light irradiation for removal of natural organic matter

The coupling of photocatalysis with membrane technology, which is known as photocatalytic membrane reactors (PMRs), has received great consideration in recent years and become a promising approach with the high potential to improve the fouling of membranes. In this paper, the photocatalyst of g-C3N4 treated with H2O2 was incorporated with a polysulfone membrane to enhance the anti-fouling properties of the membrane. AFM, FE-SEM images, porosity, and contact angle analysis indicated that the membrane properties like hydrophilicity, porosity, and surface roughness were improved. Also, UV–visible DRS, PL spectra, EIS analysis confirmed that the treated g-C3N4 (H2O2-g-C3N4) had high light absorption and low electron-hole recombination rate. The polysulfone/H2O2-g-C3N4 membrane with photocatalytic influences improved the removal of humic acid and anti-fouling properties under light conditions. Also, this incorporating was enhanced the water permeability from 266.6 to 412.1 L m−2 h−1 bar−1 in the optimum condition. To a considerable extent, the modified membranes maintained the humic acid solution fluxes during long-time experiments under visible light irradiation, so that after a 10 h run, the flux decline of the modified membrane was 21.9% compared to the initial flux, while for the pristine membrane was 53% in the same condition. The unique properties of polysulfone/H2O2-g-C3N4 membrane, like photocatalytic activity, led to a reduction in fouling resistances, especially block resistance. These results demonstrated the high potential of the polysulfone/H2O2-g-C3N4 mixed matrix membrane exposed to light irradiation for treating humic acid solution.

Annealing of grain-like poly (vinylidene fluoride-trifluoroethylene) membranes with a single-crystalline electroactive phase and high anti-fouling activity

Electroactive membranes are attracting attention due to their piezo-, pyro-, and ferro-electric properties. Here we report the fabrication of electroactive membranes from poly (vinylidene fluoride-trifluoroethylene) P(VDF-TrFE), i.e. co-polymers of vinylidene fluoride and trifluoroethylene. A new P(VDF-TrFE)/Polyvinylpyrrolidone (PVP)/Dimethylacetamide (DMAc)/water system was used to tailor the membranes’ structure. Since hot treatment in the air could induce defect on membrane structure (i.e., fracture, shrinkage, and rolling), the annealing was conducted in the glycerin. Thanks to the high boiling point and moderate surface tension of glycerin, the integrity of P(VDF-TrFE) membranes was preserved during the annealing process. X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy experiments revealed that the relative abundance of the β–crystalline phase increased with the annealing temperature when the latter was above the Curie temperature. P(VDF-TrFE) membranes annealed at 130 °C exhibited high crystallinity with grain-like surface, which resulted from multiple stacks of edge-on lamellae, and possessed excellent physicochemical properties of filtration. The anti-fouling performance of pristine and annealed P(VDF-TrFE) membranes was tested by dead-end filtration with a 13.5 mg/L humic acid (HA) solution. Annealed P(VDF-TrFE) membranes achieved greater fluxes and had superior anti-fouling properties, which was attributed to the weaker hydrophobic attraction between HA and the aligned β–phase crystals. This work provides a facile method for designing highly crystalline P(VDF-TrFE) membranes with potential applications in filtration systems, smart wearable devices, and medicine.

Development of polysulfone ultrafiltration membranes with enhanced antifouling performance for the valorisation of side streams in the pulp and paper industry

One-stage method of polysulfone (PSf) membrane modification by the addition of polyacrylic acid (PAA, Mn = 250 kg·mol−1) to the coagulation bath during membrane preparation via non-solvent induced phase separation (NIPS) was proposed. The effect of PAA concentration on the membrane structure, hydrophilicity, zeta potential, separation performance and antifouling stability in ultrafiltration of lysozyme, polyvinylpyrrolidone (PVP K-30, Mn = 40 kg mol−1) and humic acid model solutions as well as thermomechanical pulp mill process (ThMP) water was studied. Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), measurements of the tangential flow streaming potential and water contact angle were used for membrane characterization. It was found that addition of PAA into coagulation bath resulted in decreasing pore size and porosity of the selective layer as well as the formation of a thicker and denser selective layer. Water contact angle of the modified membranes was found to decrease significantly and zeta potential of the selective layer was shown to become more negative in the studied pH range 3–10, all compared to the reference membrane. It was revealed that pure water flux (PWF) decreased and lysozyme and PVP K-30 rejection increased with the increase in PAA concentration in the coagulation bath. It was found that membranes modified with PAA demonstrated better antifouling stability in ultrafiltration of humic acid solution and ThMP process water. Modified membranes were found to have higher flux, fouling recovery ratio and hemicelluloses rejection in ThMP process water ultrafiltration compared to the reference PSf membrane that allows application of these membranes for hemicelluloses concentration and purification.

Organic onion biofortification using microalgae and humic acid

Biofortification can be understood as a strategy to raise nutrients levels in vegetables edible structures, which can positively interfere in human diet. Biofertilizers are an interesting option in alternative production systems, as they can increase food nutritional quality and contribute to plant development, while aiding environment sustainability as natural products. The use of microalgae and humic acid as biofertilizers points to improvements in nutrients and biomolecules content in plants, however, their combined application is still unexplored. In that scenario, it was carried a study with onions about the influence of applications via root immersion in microalgae Scenedesmus subspicatus (Sc) and humic acid (HA) solutions, analyzing possible alterations of macro and micronutrients, total sugars, reducing sugar, free total amino acids, , total soluble solids, soluble proteins and antioxidant capacity in the bulbs. Treatments consisted of one minute seedlings roots immersion from two onion cultivars in solutions containing microalgae and humic acid, and then transplanted to organic system field. There were used three concentrations: control, 0.3 g L-1 Sc + 0.3 g L-1 HA (3SH) and 0.6 g L-1 Sc + 0.6 g L-1 HA (6SH). Results show that the treatments with microalgae with humic acid association were able to increase the content of N, carbohydrates and soluble proteins, also elevating antioxidant activity in onion bulbs.

Priming with Humic Acid to Reverse Ageing Damage in Soybean [Glycine max (L.) Merrill.] Seeds

Soybean seed vigour declines with increase in storage duration, due to ageing, which can be alleviated through seed priming. The objective of this study was to investigate the effects of Humic acid (HA) priming on germination, vigour and seedling performance under laboratory and greenhouse conditions with two soil moisture level [50% and 80% field capacity (FC)]. Seeds stored for 12 months having 60% germination were primed either with 0.2 g/L HA solution or distilled water (hydro-primed) at 25 °C for 1, 3, 5 and 7 h. Non-primed dry seeds were used as control, giving nine treatment combinations. Various germination traits [mean germination time (MGT), final germination percentage (FG%), germination rate index (GRI), seedling emergence percentage (SEP)], mean emergence time (MET), seedling quality traits [seedling vigor index (SVI), shoot length, root length, root volume], antioxidant enzyme activities [catalase (CAT), peroxidase (POD)], lipid peroxidation [malondialdehyde (MDA)] and electrical conductivity (EC) were determined. A germination test in the laboratory was conducted as single factor (nine priming treatments), while the greenhouse experiment was conducted as two factors [2 soil moisture level (50 and 80% FC) and 9 priming treatments]. The results indicated that seeds primed with HA for 5 h was able to reinstate the CAT activities (25%), POD activities (50%) and reduced EC (51%) and MDA content (40%) compared with non-primed seeds, reduced the MET (from 4.3 to 3.5 days), increased FG% (from 62 to 71%), GRI (15.6–21.1) and SEP (from 35 to 54%) and (from 60 to 72%) at 50% FC level and 80% FC level, respectively. A strong negative correlation (r = −0.80 **) was found between MDA content and GRI, while CAT and POD activities had positive correlation with GRI r= 0.67 ** and r = 0.56 **, respectively. Thus, priming with 0.2 g/L HA for 5 h improved the vigour of minimally deteriorated soybean seeds resulting in increased emergence with more uniform field establishment.

Facile Fabrication of Multi-Hydrogen Bond Self-Assembly Poly(MAAc-co-MAAm) Hydrogel Modified PVDF Ultrafiltration Membrane to Enhance Anti-Fouling Property.

In this work, a facile preparation method was proposed to reduce natural organics fouling of hydrophobic membrane via UV grafting polymerization with methacrylic acid (MAAc) and methyl acrylamide (MAAm) as hydrophilic monomers, followed by multihydrogen bond self-assembly. The resulting poly(vinylidene fluoride)-membranes were characterized with respect to monomer ratio, chemical structure and morphology, surface potential, and water contact angle, as well as water flux and organic foulants ultrafiltration property. The results indicated that the optimal membrane modified with a poly(MAAc-co-MAAm) polymer gel layer derived from a 1:1 monomer ratio exhibited superior hydrophilicity and excellent gel layer stability, even after ultrasonic treatment or soaking in acid or alkaline aqueous solution. The initial water contact angle of modified membranes was only 36.6° ± 2.9, and dropped to 0° within 13 s. Moreover, flux recovery rates (FRR) of modified membranes tested by bovine serum albumin (BSA), humic acid (HA), and sodium alginate (SA) solution, respectively, were all above 90% after one-cycle filtration (2 h), significantly higher than that of the pure membrane (70–76%). The total fouling rates (Rt) of the pure membrane for three foulants were as high as 47.8–56.2%, while the Rt values for modified membranes were less than 30.8%. Where Rt of BSA dynamic filtration was merely 10.7%. The membrane designed through grafting a thin-layer hydrophilic hydrogel possessed a robust antifouling property and stability, which offers new insights for applications in pure water treatment or protein purification.

Performance improvement of thin film nanocomposite membranes by covalently bonding with Janus porous hollow nanoparticles for nanofiltration applications

AbstractIncorporation of nanofillers into membranes is one of effective ways to improve the performance of membranes. Various nanofillers are induced into the polymeric matrices, including nonporous nanofillers, porous nanofillers, and hollow nanofillers. In this study, thin film nanocomposite (TFN) membranes covalently incorporated with Janus porous hollow nanoparticles with opposite surface charges are prepared by interfacial polymerization. The effects of the Janus porous hollow nanoparticles on performances of the composite membrane including surface hydrophilicity, surface charge, surface roughness, water permeability, salt rejection, and antifouling resistance are investigated. The incorporation of Janus porous hollow nanoparticles improves the overall performance of the membranes. The hydrophilicity and surface charge increase as the loading of nanoparticles increases, and the roughness increases firstly and then decreases. The flux of the TFN membranes (96.8 L·h−1·m−2 at 0.5 MPa) has more than doubled compared with unmodified composite membranes, mainly due to the additional channel provided by hollow structure of nanoparticles with porous shells, accompanied with high level rejections (>97%) against Na2SO4 and MgSO4. The NaCl rejection increases from 49.7% to 55.9% due to the synchronous rejection ability of cations and anions given by the dually charged composite nanoparticles. The chemically modified TFN membranes show improved stabilities in the pure water and the humic acid solution with decrements in flux about 2% and 6% respectively, due to the improved surface properties.

Effects of micro-flocculation pretreatment on the ultrafiltration membrane fouling caused by different dissolved organic matters in treated wastewater

Abstract This study investigated the efficacy of using micro-flocculation as a pretreatment approach in alleviating ultrafiltration (UF) membrane fouling caused by organic matter in treated wastewater. Three typical model dissolved organic matters (DOM), humic acid, fulvic acid, and sodium alginate, were employed to simulate membrane fouling. The results showed that micro-flocculation using poly aluminum chloride (PAC) or polymerized ferric sulfate (PFS) as flocculant could effectively enhance the treatment performance of the UF process on DOM. With 6 mg/L PAC, the removal efficiency of humic acid, fulvic acid, and sodium alginate by micro-flocculation combined UF process reached 79.95%, 63.25%, and 51.14%, respectively. Specifically, after micro-flocculation, micromolecular hydrophilic organic matter (e.g., fulvic acid) tended to form a compact cake layer. The macromolecular hydrophobic organic matter (e.g., humic acid) and macromolecular hydrophilic organic matter (e.g., sodium alginate) generally led to a loose cake layer. At PAC dosage of 6 mg/L, the membrane specific flux (J/J0) at the end was improved by 11.71%, 10.27%, and 2.2% for humic acid, sodium alginate and fulvic acid solutions, respectively, compared with the UF process alone. It could be inferred that micro-flocculation pretreatment can effectively mitigate the membrane fouling when treating wastewater containing humic acid, sodium alginate, or fulvic acid.

Polycyclic Aromatic Hydrocarbon Sorption by Functionalized Humic Acids Immobilized in Micro- and Nano-Zeolites

Polycyclic aromatic hydrocarbons (PAHs) are hazardous compounds originating from anthropogenic activity. Due to their carcinogenic properties for humans, several technologies have been developed for PAH removal. Sorption with natural and organic materials is currently one of the most studied due to its low cost and its environmentally friendly nature. In this work, a hybrid sorbent involving functionalized humic acids (HAs) and nano-zeolite is proposed to entrap PAHs. The use of functionalized HAs immobilized in a porous support is designed to address the instability of HAs in solution, which has been already reported. HA functionalization was carried out to increase the non-polarity of HAs and aliphatic group formation. The HAs were functionalized by esterification/etherification with alkyl halides, and their chemical changes were verified by FTIR and NMR. The sorption isotherms of the functionalized HAs in micro- and nano-zeolites were used to assess the performance of the nano-zeolites in adsorbing these HAs. The hybrid support allowed the removal of anthracene and pyrene at percentages higher than 90%; fluoranthene, of angular molecular structure, was adsorbed at 85%. PAHs are ubiquitous in the environment, and a stable sorption of them in solid matrices will allow their removal from the environment through effective and environmentally friendly methods.

Facile synthesis of 2D TiO2@MXene composite membrane with enhanced separation and antifouling performance

While composite membranes with two-dimensional (2D) lamellar materials (e.g., graphene and MXene) have recently attracted increasing attention, fabrication of high-performance 2D membrane still faces a serious challenge. In this study, 2D TiO2@MXene nanomaterial was prepared and introduced to fabricate polyethersulfone (PES)-TiO2@MXene composite membrane. The composite membrane displayed superior separation and antifouling performance. When filtrating 1.0 g L−1 bovine serum albumin (BSA) solution, the flux of the optimal membrane (BSA rejection 95%) reached to 756.8 L m−2 h−1·bar−1, which is 185% higher than that of the original membrane (BSA rejection 70%). Moreover, the PES-TiO2@MXene composite membrane possessed excellent self-cleaning function under UV irradiation, which was verified by the flux recovery rate (FRR) values of 80.2%, 100%, 100% and 99.56% for BSA, sodium alginate (SA), humic acid (HA) and yeast (YE) solution, respectively. The excellent self-cleaning ability can be put down to the special 2D TiO2@MXene structure where there exists a synergy between MXene and TiO2 for self-cleaning. The composite membrane demonstrated a significant superiority in filtration performance over those in the literature. According to extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) approach, the PES-TiO2@MXene composite membrane displayed an optimal interface condition, significantly reducing the attractive interactions with foulants. The facile fabrication method, together with the efficient membrane performance, indicated good application prospects of the PES-TiO2@MXene composite membrane proposed in this study.

Response surface methodology to investigate the effects of operational parameters on membrane fouling and organic matter rejection in hard-shell encased hollow-fiber membrane

The response surface methodology (RSM) was found useful statistical tool for understanding combined effect of filtration, backwashing time and dosage of sodium hypochlorite (NaOCl) added into backwash water as three operational parameters on transient behavior of transmembrane pressure (TMP) and organic rejection efficiency. Here, encased, hollow-fiber ultrafiltration (UF) system was developed for treating synthetic humic acid (HA) solution. To carry out RSM analysis, experimental matrix was designed by Box-Behnken model. Results showed that the NaOCl dosage for the chemical enhanced backwashing (CEB) as single parameter played most dominant role in fouling mitigation. Effect of hydraulic cleaning by applying the permeate backwashing only without performing the CEB was almost negligible to flush the fouling layer from membrane. Considering two correlated parameters, backwashing time combined with NaOCl dosage was found much more important than combination of other parameter such as filtration time to reduce fouling rate. Regardless of the operational parameters, the organic rejection efficiency was maintained 30% only. The RSM analysis also found that 40.1 min of filtration, 1.1 min of backwashing and 834 mg/L of NaOCl were optimum operating parameters to enhance both permeate recovery and fouling mitigation.