Powdered activated carbon (PAC) adsorption has been widely applied prior to ultrafiltration membrane for potable water production. However, the impact of PAC adsorption on membrane fouling was still ...controversial. To solve this problem, combined PAC and peroxymonosulfate (PMS) pretreatment was proposed in this study. The application of PAC/PMS for mitigating membrane fouling by natural organic matter (NOM) has been evaluated, and compared with PMS oxidation or PAC adsorption alone. The influence of NOM fractions on the control efficiency was also investigated using humic acid (HA), bovine serum albumin (BSA), sodium alginate (SA), and their mixture (HA-BSA-SA). The performance was examined through normalized flux decline, fouling resistances analysis, scanning electron microscopy, and model fits. The results indicated that PAC and PMS exhibited a remarkable synergistic effect in the reduction of NOM, with the DOC reduction rates of 53.6%, 24.3%, 27.1% and 31.4% for HA, BSA, SA and HA-BSA-SA, respectively. PAC adsorption exhibited limited influence on mitigating membrane fouling, and the co-existence of PAC and HA even exacerbated fouling due to the synergistic fouling effect between them. By contrast, PAC/PMS pretreatment efficiently reduced both reversible and irreversible fouling resistances. The control efficiency was closely associated with the NOM fractions in the feed water, and followed the order of SA > HA-BSA-SA > BSA > HA. The fouling mitigation by PAC/PMS was attributed to both PAC adsorption and oxidation with SO4− and OH. The experimental results are expected to provide a feasible strategy of PAC/PMS for fouling mitigation, and simultaneously solve the problem faced by PAC adsorption.
Display omitted
•PAC/PMS pretreatment was used to control UF fouling by different NOM fractions.•PAC adsorption exhibited limited influence on membrane fouling control.•PAC/PMS showed significantly higher control efficiency than PAC or PMS alone.•The control efficiency of PAC/PMS was closely associated with the NOM fractions.•The presence of PAC in the feed reduced the efficiency of PAC/PMS.
The wet oxidation of aqueous humic acids García, Manuel; Collado, Sergio; Oulego, Paula ...
Journal of hazardous materials,
09/2020, Letnik:
396
Journal Article
Recenzirano
Odprti dostop
Display omitted
•Higher temperatures enhanced formation of acetic and oxalic acids.•No effect of oxygen pressure (65−95 bar) on the removal.•Alkaline medium: higher HA removal but more refractory ...intermediates.•Alkaline medium favours the formation of formic, lactic, maleic and pyruvic acids.•A lumped kinetic model was successfully fitted to the experimental data.
Humic acids are highly distributed in aqueous environments. This article examines in depth the advanced oxidation of humic acid aqueous solutions, in order to understand more complex oxidation processes such as those of the sewage sludge or landfill leachate, or the matrix effects triggered by the humic acids of natural organic matter (NOM) in the oxidation of other aqueous compounds as herbicides.
Humic acids were efficiently oxidized; higher temperatures (180−220 °C) involved higher mineralization, the formation of intermediates with lower colour and also led to a higher concentration of organic acids at the end of the treatment, particularly acetic and oxalic ones. Nevertheless, humic acid wet oxidation was not sensitive to changes in the pressure, at least in the range tested (65−95 bar), but the initial pH (4–13) was found to be a key factor. Thus, alkaline media accelerated the humic acid removal, but more refractory intermediates were generated, and the organic acids, excepting malic acid, were more stable than in neutral or acidic media. Eventually, a lumped kinetic model was proposed and successfully fitted to the experimental data, including the effect of all the operating variables studied.
Magnetite nanoparticles (MNPs) with varied organic coatings (OCs) which improved their stability have broad environmental applications. However, the adsorbed amounts and layer thickness of varied OCs ...onto MNPs during the synthesis were generally not or poorly characterized, and their interactions with natural organic matter (NOM) were still in progress. In this study, acetic (HAc), citric (CA), and polyacrylic acid (PAA) were selected as model OCs, the adsorption behaviors of OCs on MNPs were characterized under varied aqueous C/Fe ratios, and the aggregation behaviors of MNPs with varied OCs (OC-MNPs) at neutral pH (7.0 ± 0.2) with NaCl (5–800 mM) in the presence/absence of NOM were systematically investigated. Under low aqueous C/Fe ratio, the adsorbed amounts of model OCs as –COOH/Fe ratio followed the order: CA ≈ PAA > > HAc. With high aqueous C/Fe ratio, the maximum adsorbed masses of OC-MNPs were similar. The adsorbed layer thicknesses of OC-MNPs were thoroughly characterized using three different methods, all showing that the adsorbed layer of PAA was thicker than that of CA and HAc. Derjaguin–Landau–Verwey–Overbeek (DLVO) and extended DLVO (EDLVO) calculations showed that electrostatic and van der Waals forces were dominant for CA-MNPs and HAc-MNPs stabilization; while steric repulsion played major roles in stabilizing PAA-MNPs, probably due to a thicker PAA layer. In the presence of NOM, stability behaviors of all OC-MNPs were similar, ascribing to the much greater amounts of NOM adsorbed than the OCs, causing greater steric repulsion. This study provides new mechanistic insights which could help better understand the effects of varied OCs on MNPs' colloidal stability.
Display omitted
•The maximum adsorbed –COOH/Fe was similar for varied coatings on MNPs.•HAc and CA stabilized MNPs mainly by electrostatic and van der Waals forces.•Steric forces controlled PAA-MNPs stabilization due to a thicker layer.•In presence of SRNOM, SRNOM adsorption controlled stability of OC-MNPs.
Display omitted
•Tannin biocoagulants and iron sulphate were effective in vanadium removal.•Quebracho-derived tannin removed above 88% of vanadium over a wide pH range.•Charge density influenced ...vanadium removal by tannin coagulants.•Tannin coagulants produced larger flocs than iron sulphate.•Floc regrowth was significant for the coagulants at acidic pH.
This study compared the performance of tannin (quebracho and spruce) and iron sulphate (FS) coagulants for the removal of vanadium from effluent derived from an abandoned vanadium mine. The efficacy of the materials was studied at the natural pH of the mine effluent (7.4), and at adjusted pH levels of 4 and 9. The quebracho tannin coagulant (QT) recorded impressive turbidity and vanadium removals of above 88% over a wide pH range. However, the spruce tannin coagulant (ST) was not as effective at pH 9 (39%) although it showed an improved vanadium removal of 46% and 70% at pH 7.4 and 4, respectively. This was attributed to the lower charge density of ST than that of QT, and to a loss of cationic properties at pH 9. FS performed better in terms of vanadium removal (pH 4: 86%, pH 7: 98%, pH 9: 100%) with lower coagulant doses, although effective turbidity removal required precise pH control. QT produced the largest flocs and the highest floc regrowth at pH 4 and 7. Under alkaline conditions, tannin coagulants exhibit no regrowth, which implies that a careful flocculation and floc separation step is needed. The natural organic matter fractionation results revealed that FS effectively removed hydrophilic carbon (76%) in a pH-controlled mine effluent better than tannin coagulants (QT: 12% and ST: 22%) from the pH 4 effluent; however, ST removed hydrophobic carbon entirely. All coagulants adequately removed humic substances, with FS being the most efficient (88%), followed by ST (53%) and QT (47%). X-ray photoelectron spectroscopy (XPS) analysis of jar test residues showed that some of the vanadium removed existed in the V(IV) oxidation state.
•Molecular spectroscopy is a key platform to characterize and monitor NOM.•Advances/innovations on spectroscopic studies of NOM are summarized.•Limitations of spectroscopic approaches for NOM ...interpretation are criticized.•Perspectives on spectroscopic developments in NOM-related topics are envisaged.
Natural organic matter (NOM) is ubiquitous in environment and plays a fundamental role in the geochemical cycling of elements. It is involved in a wide range of environmental processes and can significantly affect the environmental fates of exogenous contaminants. Understanding the properties and environmental behaviors of NOM is critical to advance water treatment technologies and environmental remediation strategies. NOM is composed of characteristic light-absorbing/emitting functional groups, which are the “identification card” of NOM and susceptive to ambient physiochemical changes. These groups and their variations can be captured through optical sensing. Therefore, spectroscopic techniques are elegant tools to track the sources, features, and environmental behaviors of NOM. In this work, the most recent advances in molecular spectroscopic techniques, including UV-Vis, fluorescence, infrared, and Raman spectroscopy, for the characterization, measurement, and monitoring of NOM are reviewed, and the state-of-the-art innovations are highlighted. Furthermore, the limitations of current spectroscopic approaches for the exploration of NOM-related environmental processesand how these weaknesses/drawbacks can be addressed are explored. Finally, suggestions and directions are proposed to advance the development of spectroscopic methods in analyzing and elucidating the properties and behaviors of NOM in natural and engineered environments.
Display omitted
Ferrous iron/peroxymonosulfate (Fe(II)/PMS) oxidation was employed as a pretreatment method for ultrafiltration process to control membrane fouling caused by natural organic matter, including humic ...acid (HA), sodium alginate (SA), bovine serum albumin (BSA), and their mixture (HA-SA-BSA). To evaluate the mechanism of fouling mitigation, the effects of Fe(II)/PMS pretreatment on the characteristics of feed water were examined. The degradation of atrazine (ATZ) was also investigated and the species of generated radicals were preliminarily determined. Under the test exposure (15 and 50 μM), Fe(II)/PMS pretreatment effectively mitigated membrane fouling caused by HA, SA and HA-SA-BSA mixture, and the performance improved with the increase of Fe(II) or PMS dose; whereas aggravated BSA fouling at lower doses and fouling alleviation was observed only at a higher dose (50/50 μΜ). The fouling mitigation was mainly attributed to the effective reduction of organic loadings by coagulation with in-situ formed Fe(III). Its performance was comparable or even slightly higher than single coagulation with Fe(III), most likely due to the oxidation by Fe(II)/PMS process. Fe(II)/PMS oxidation showed better performance in reducing DOC and UV254, fluorescence intensities of fluorescent components and UV-absorbing compounds than single coagulation. In addition, Fe(II)/PMS pretreatment was efficient in ATZ degradation due to the generation of sulfate and hydroxyl radicals, whereas coagulation was ineffective to remove it.
Display omitted
•Fe(II)/PMS oxidation was employed as a pretreatment for ceramic UF membrane.•Fe(II)/PMS with proper doses significantly mitigated membrane fouling by NOM.•Lower doses of Fe(II) or PMS aggravated membrane fouling by BSA.•Fe(II)/PMS pretreatment was more effective in atrazine degradation than coagulation.
Estrogens are endocrine disrupting chemicals that have been frequently detected in diverse water matrices (e.g. surface water, wastewater and drinking water) and caused a series of health risks. This ...study was aimed at investigating the photochemical degradation of free estrogens estrone (E1), 17β-estradiol (E2), estriol (E3), and 17α-ethyl estradiol (EE2) upon the monochromatic irradiation (253.7 nm). Concerning the practical installation of photolysis treatment, exposing the impacts of photoreactor operation mode (stationary or up-flow) and the water matrix (ultrapure water or natural surface water) on the photolytic behaviour of estrogens was of high importance. The pseudo-first-order rate constants showed that E1 was the most susceptible to UV radiation among chosen estrogens due to its high molar absorption coefficient of 402.4 M−1 cm−1 and quantum yield of 0.065 mol E−1 at λ = 253.7 nm. Moreover, the up-flow mode and the surface water matrix collected from a lake in Regent's Park (London) were found to favour the photodegradation of estrogens due to the introduction of more dissolved oxygens and promotion of reactive oxygen species (ROS) formation. These findings may shed light on the photochemical behaviour of estrogens in some specific scenarios.
Display omitted
•Photolytic behaviour of estrogens under the radiation of 253.7 nm was investigated.•Estrone (E1) was the most sensitive to the UVC radiance among the studied estrogens.•The continuous flow mode favoured photolysis of estrogens compared to stationary mode.•The surface water matrix taken from a local lake promoted photolysis of estrogens.
The compound 2,2′,4,4′,5,5′-hexabrominated diphenyl ether (BDE-153) is an intermediate photolytic product in the degradation of highly brominated diphenyl ethers to lower brominated forms. Herein, we ...report the effects of two natural organic matter (NOM) sources, Suwannee River fulvic acid (SRFA) and Pony Lake fulvic acid (PLFA), on BDE-153 photolysis in water. The rate constant (k) and half-life of BDE-153 was 2.26 × 10−2 min−1 and 30.72 min under UV–Vis irradiation (direct photolysis at λ > 290 nm). The k value for BDE-153 decreased markedly in the presence of NOM with a larger decrease in the presence of PLFA than SRFA. Electron spin resonance (ESR) demonstrated generation of free radicals in the photolytic process that mainly involved 1O2 and OH. The biomolecular k values for reaction of 1O2 and OH with BDE-153 were 3.65 × 106 and 7.70 × 108 M−1 s−1, respectively. The contribution of OH (28.7–31.0%) to the indirect photolysis of BDE-153 was higher than for 1O2 (12.9–14.9%). The photolytic rate of BDE-153 in oxygen-rich (aerated) solution was much slower than in oxygen-poor (nitrogen-sparged) conditions, demonstrating that 3NOM* is a more effective reagent for degradation of BDE-153 than 1O2. Addition of sorbic acid (a 3NOM* quencher) significantly reduced the photolytic rate of BDE-153 confirming the important role of 3NOM* in indirect photolysis. In the presence of NOM, BDE-153 indirect photolysis was facilitated mainly by reaction with 3NOM* and OH. To the best of our knowledge, this is the first comprehensive investigation of indirect photolysis of BDE-153 in water containing NOM.
Generation of OH and 1O2 in process of BDE-153 photolysis in water by ESR technique. Sorbic acid (a 3NOM* quencher) and oxygenated or deoxygenated experiments showed that excited state NOM* played a key role in the photochemical transformation of BDE-153. Display omitted
•Generation of OH and 1O2 in process of BDE-153 photolysis in water by ESR technique.•The contribution of OH (28.7–31.0%) to the indirect photolysis of BDE-153 was higher than that of the 1O2 (12.9–14.9%).•The indirect photolysis of BDE-153 containing NOM is primarily attributable to OH and 3NOM*.
Display omitted
•Functionalized polymer chains grafted graphene oxide (GO) (SPK-g-GO) nanosheets.•Fabrication of a new type of charge tunable hybrid ultrafiltration membranes.•Tunable membrane ...surface charge, pore size and hydrophilicity with SPK-g-GO amount.•The flux of membrane with 4 wt% SPK-g-GO is 270% higher than pristine membrane.•Hybrid membranes display excellent NOM rejection and fouling resistance.
The unprecedented performance of fouling resistant, high flux and high rejection hybrid ultrafiltration polysulfone membranes with charge tunable channels using functionalized polymer chains grafted graphene oxide (SPK-g-GO) nanosheets for natural organic matter removal from aqueous feed is herein reported. The novel SPK-g-GO nanosheets were first prepared by esterification reaction at 55 °C using hydroxylated sulfonated poly(ether ether ketone) and graphene oxide. Then, polysulfone blend hybrid membranes with charge tunable channels were produced via the non-solvent induced phase separation method and optimized by varying the SPK-g-GO concentration from 1 to 8 wt.% in the casting solution. The membranes were characterized using scanning electron microscopy, Raman spectroscopy, atomic force microscopy, surface zeta potential and contact angle measurements. The surface texture and hydrophilicity of the membranes were altered due to the incorporation of SPK-g-GO. The hybrid membrane’s water flux was highly dependent on the amount of SPK-g-GO incorporated within the membrane matrix. The maximum water flux (485.7 L m−2 h−1), obtained using the membrane with 4 wt.% SPK-g-GO, was almost 270% higher than that of the membrane without SPK-g-GO (181.1 L m−2 h−1). The fouling resistance and natural organic matter retention capabilities of the membranes were examined via UF tests of synthetic natural organic matter solution at 1 bar feed pressure and neutral pH. The hybrid membrane with 4 wt.% SPK-g-GO loading exhibited remarkable improvement over the pristine one, rejecting more than 86% of the and recovering ~90% of its initial water flux after washing with a stable retention rate during a long-term filtration test.
PDF
