Membrane fouling is posing a critical obstacle limiting the widespread application of ultrafiltration (UF). Among the numerous membrane foulants, natural organic matter (NOM) is one of the most ...problematic since it exists ubiquitously in natural waters and can cause severe membrane fouling. This study investigated the removal of NOM in surface water and the mitigation of membrane fouling using heat-activated peroxydisulfate (PDS) as a pretreatment for UF process. The results demonstrated that the NOM was efficiently removed, with ultraviolet absorbance (UV254) and dissolved organic carbon (DOC) decreasing by approximately 71% and 52%, respectively, at a PDS dose of 0.8 mM within 60 min (80 °C). The chromatograms of high performance size exclusion chromatography (HPSEC) indicated that some high molecular weight humic substances with a peak at approximately 10 kDa were oxidized to low molecular weight organic matters distributed in the range of < 100 Da during the pretreatment process. Moreover, three-dimensional fluorescence parallel factor analysis (PARAFAC) indicated that humic-like substances were much more easily degraded by heat-activated PDS pretreatment than protein-like substances. These results indicated that some unsaturated NOM fractions were first degraded and then mineralized to carbon dioxide during pretreatment. Meanwhile, the destroyed structure of humic substances might hinder its binding with high valence cations to reduce the possibility of high valence cations deposited on the membrane surface, thereby reducing membrane fouling. Therefore, membrane fouling could be significantly mitigated due to the shifts of NOM concentration and structure by heat-activated PDS pretreatment in the surface water treatment.
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•The heat-activated peroxydisulfate was adopted as a pretreatment prior to ultrafiltration.•Suitable temperatures for mitigating membrane fouling by pre-oxidation were above 50 °C.•Structural destruction and mineralization of natural organic matter occurred simultaneously in oxidation process.•The destroyed structure of humic substances might hinder its binding with high valence cations.
Combined processes of light-emitting diodes ultraviolet (LED UV) and chlorination (Cl2) are alternative disinfection technologies in drinking water, while the formation of disinfection by-products ...(DBPs) needs to be evaluated. This study investigated the impacts of critical water matrix factors on the DBP formation in the combined processes. Moreover, the correlation between the degraded natural organic matter (NOM) and the formed DBP was studied. Simultaneous UV/Cl2 outperformed single Cl2 and sequential combined processes in degrading humic acids (HA) and resulted in the highest DBP yield. Iodide at 5–20 μg/L and bromide at 0.05–0.2 mg/L slightly affected the degradation of organics, while increased the formation of brominated DBPs up to 36.6 μg/L. pH 6 was regarded as the optimum pH, achieving high efficiency of HA degradation and a lower level of total DBP formation than pH 7 and 8 by 11 % and 24 %, respectively. Compared to HA samples (46.8–103.9 μg/L per mg/L DOC), NOM in canal water were less aromatic and yielded fewer DBPs (19.6 and 21.2 μg/L per mg/L DOC). However, the extremely high bromide in site 1 samples (18.6 mg/L) shifted the chlorinated DBPs to their brominated analogues, posting around 1 order of magnitude higher levels of toxicities than HA samples. The reduction of absorbance at 254 nm (UV254) correlated with all DBP categories in HA samples, while the correlation coefficients were compromised when included in the canal samples. For the first time, this study found that parallel factor analysis (PARAFAC) would neglect the fluorescence change caused by iodide/bromide in UV/Cl2, while the changes could be captured by self-organising map (SOM) trained with full fluorescence spectra. Fluorescence Ex/Em pairs were proposed to predict DBP formation, suggesting a potential method to develop an online monitoring system for DBPs.
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•Simultaneous LED UV/Cl2 yielded more DBPs than Cl2 alone from humic acids.•0.05–0.2 mg/L Br− increased the yield of Br-DBP in LED UV/Cl2 up to 36.6 μg/L.•EEM change neglected by PARAFAC was highlighted in SOM trained by full spectra.•UV254 was less correlated with DBPs when included in canal water samples.•Ex/Em pairs in whole fluorescence spectra were suggested to predict DBPs.
•The PMS activation by N-MWCNTs and UF membrane filtration were synergistic.•The N-MWCNTs-modified membrane/PMS system showed improved catalytic activities.•The nonradical processes are dominant in ...the N-MWCNTs-modified membrane/PMS system.•This coupling system effectively mitigated the UF membrane fouling.
The synthesized catalyst nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) were introduced into membrane technology for peroxymonosulfate (PMS) activation. The enhanced permeability of the N-MWCNTs-modified membrane might be attributed to the increase in hydrophilicity and membrane porosity. The catalytic degradation and membrane filtration performance for the N-MWCNTs-modified membrane/PMS system in treating different types of natural waters were evaluated. The removal of phenol by the N-MWCNTs-modified membrane was 83.67% in 2 min, which was greater than the phenol removal by the virgin membrane (3.39%) and N-MWCNT powder (41.42%), respectively. Moreover, the resultant membrane coupled with PMS activation exhibited outstanding removal effects on the fluorescent organics in the secondary effluent and Songhua River water. The combination effectively reduced the total membrane fouling caused by the secondary effluent, Songhua River water, and three typical model organics by 28.19–61.98%. Electron paramagnetic resonance and classical quenching tests presented that the active species (SO4·−, ·OH, and 1O2) and other non-radical processes generated by N-MWCNTs activated PMS decreased the foulants deposition on the membrane surface. Meanwhile, the membrane interception accelerated the aggregation of pollutants and PMS towards the membrane surface through applied pressure, facilitating their mass transfer to the N-MWCNTs surface for the catalysis exerted more effectively. This study demonstrated the potential application of the coupling of N-MWCNTs catalytic oxidation and the UF, which offers a promising prospect to improve the permeate quality and simultaneously overcome the membrane fouling barriers.
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Atenolol (ATL), a kind of largely used beta-blockers, has been widely detected in the aquatic environment, which could cause adverse impact on human beings. In this study, bismuth oxychloride (BiOCl) ...photocatalyst was synthesized and applied to remove ATL in the aqueous system under simulated natural light. Emphasis was laid on the reaction kinetics and the impact of natural organic matter (NOM) (0–20 mg/L). Possible transformation pathways were systematically investigated based on identification of reaction products via liquid chromatography-mass spectrometry (LC-MS). As a consequence, BiOCl presents highly photocatalytic efficiency yielding up to nearly 100% ATL conversion after 60 min of interaction, together with fairly high photostability evidenced by considerably efficient removal of ATL after 10 catalytic cycles. Four kinds of possible products are detected using LC-MS in the process of reaction, indicating possible transformation ways of ATL photocatalysis. NOM has an inhibiting impact on the removal of ATL and influences the products distribution. This study provides an emerging nanocatalyst for ATL photodegradation and could eventually lead to development of novel methods to control pharmaceutical contamination in water.
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•Effective utilization of as-synthesized BiOCl on the removal of atenolol can be achieved during the process.•Performance of BiOCl photocatalyst declines with the addition of natural organic matter.•A conformational pathway for atenolol photodegradation by BiOCl is proposed.•Photocatalyst is easy to recycle and can be efficiently used for more than 10 times.
Nanofiltration (NF) membranes featuring high water permeance, excellent antifouling properties, and selective organic matter/minerals separation for drinking water are highly desirable in the ...environmental water treatment process. In this work, an ultra-permeable NF membrane was tailored via a low temperature-assisted interfacial polymerization (LTIP) method. The surface morphologies, structural compositions, and separation performances of the NF membranes were further regulated by changing the addition of the aqueous monomer. The optimized NF membrane (NFM-0.2) showed ultrahigh water permeance of 31.8 L m−2 h−1 bar−1 and 95.1 % Na2SO4 rejection while maintaining superior antifouling behaviors. During the filtration of natural surface water, NFM-0.2 presented 75.5 % higher removals of DOC, UV254, and bisphenol A. The application of NFM-0.2 for filtrating ground water indicated that NFM-0.2 could remove 50.0 % and 62.9 % of organic matter and total hardness, respectively. The permeate water not only had no potential to form scaling after boiling but also preserved mineral ions, which was helpful for providing high-quality drinking water. Combined with the feasibility and practicability of the LTIP method, the facile strategy provides a facile way for tailoring ultralow pressure NF membranes featuring both highly selective separation of organic matter/minerals and superior antifouling abilities for practical water treatment.
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•An ultrathin and ultra-smooth PA NF membrane was constructed by an LTIP strategy.•Tailored NF performances and antifouling behaviors were achieved for NF membranes.•Water permeance of 31.8 L m−2 h−1 bar−1 and 95.1 % Na2SO4 rejection was achieved at 2 bar.•Selective separation of NOM and minerals was obtained in treating both natural surface water and ground water.•The involved mechanisms of LTIP-assisted NF membranes were studied by stopped-flow spectroscopy.
Natural organic matter (NOM) is present in underground and surface waters. The main constituents of NOM are humic substances, with a major fraction of refractory anionic macromolecules of various ...molecular weights. The NOM concentration in drinking water is typically 2–10 ppm. Both aromatic and aliphatic components with carboxylic and phenolic functional groups can be found in NOM, leading to negatively charged humic substances at the pH of natural water. The presence of NOM in drinking water causes difficulties in conventional water treatment processes such as coagulation. Problems also arise when applying alternative treatment techniques for NOM removal. For example, the most significant challenge in nanofiltration (NF) is membrane fouling. The ion exchange process for NOM removal is an efficient technology that is recommended for the beginning of the treatment process. This approach allows for a significant decrease in the concentration of NOM and prevents the formation of disinfection byproducts (DBPs) such as trihalomethanes (THMs). This article provides a state-of-the-art review of NOM removal from water by ion exchange.
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•Application of ion exchange for NOM removal is reviewed.•From 30 to 90% of NOM can be removed from drinking water by ion exchange treatment.•Studies demonstrated that MIEX is one of the most promising resins for NOM removal.
Notre article est le deuxième d’une série qui se propose d’étudier, d’abord, la manière dont les expressions idiomatiques comprenant des noms d’animaux en français peuvent être traduites en roumain ...et de réfléchir, ensuite, à une démarche didactique visant la compréhension et l’emploi approprié de celles-ci. Le but est d’identifier les embarras des étudiants non spécialistes en langues et de proposer des activités ciblées pour l’atteinte de trois objectifs : reconnaître, comprendre et employer des expressions idiomatiques (EI) dont le terme central est un nom d’animal.
The orthokinetic coagulation of irregularly shaped polystyrene micro-particles (PS-MP) was investigated in solutions of inorganic cations with different valence (NaCl, CaCl2, LaCl3) using a ...coagulation jar test set-up combined with light extinction particle counting. The stabilizing effect of model natural organic matter (NOM from reverse-osmosis (RO-NOM), humic (HA) & fulvic acid (FA)) and of surface water components (SW-NOM) was studied. Collision efficiencies were calculated from the decrease in particle concentration applying first order reaction kinetics. The coagulation of PS-MP followed Derjaguin-Landau-Verwey-Overbeek (DLVO) theory with regard to ionic charge in solution. Highest collision efficiencies were obtained close to the suspected critical coagulation concentrations for CaCl2 (12 mM) and LaCl3 (5.5 mM) whereas for NaCl no CCC was found within the applied concentration range (10–1000 mM). The addition of NOM effectively stabilized PS-MP at low ionic strength (10 mM NaCl) in the order HA > RO-NOM > FA > SW-NOM at concentrations of dissolved organic carbon (DOC) as low as 0.2–0.5 mg/L DOC through electrostatic repulsion. PS-MP were effectively stabilized in 6.1 mg DOC/L of SW-NOM even at high ionic strength (100 mM MgCl2). Coagulation at intermediate ionic strength (10 mM MgCl2) was only observed for SW-NOM concentrations below 0.6 mg/L DOC. The results showed that even low NOM concentrations prevent PS-MP from orthokinetic coagulation in the presence of high ion concentrations. The study provides further insight in the orthokinetic coagulation behavior of PS-MP in the presence of NOM and highlights the importance of NOM for the stabilization of microplastics in aquatic suspensions. Further research is needed to elucidate the behavior of MP in turbulent systems to predict the mobility MP in aquatic systems such as rivers.
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•Orthokinetic coagulation of polystyrene microparticles (PS-MP) was assessed.•Collision efficiencies were calculated to compare stabilization.•PS-MP were stabilized by natural organic matter (NOM) even at high ionic strength.•Stabilization differed between model and surface water NOM.
Membrane technology plays important roles in drinking water treatment in last decades; ultrafiltration (UF) is typically used to separate natural organic matters (NOM) and nanofiltration (NF) is used ...primarily to reject divalent ions, due to the different pore sizes of the used membranes. However, high water production rate at low energy consumption will be achieved if NOM and heavy metals can be simultaneously removed via UF-based water treatment process, which is necessary nowadays due to the carbon neutrality target worldwide. Here, a polyethersulfone (PES)-based UF membrane, modified chemically by grafting and crosslinking polyethylenimine (PEI, 25,000 Da) in two steps, was used to simultaneously remove humic acid (HA) and copper (Cu) from water. The molecular weight cut-off of the PEI-modified membrane was ∼110 kDa, and results showed that the efficiencies of HA and Cu2+ removal substantially increased because of the smaller pore size and additional adsorption effects compared to pristine PES membrane. Although the flux of the PEI-modified membrane was reduced, the membrane fouling was significantly alleviated compared with the pristine UF membrane. In comparison with Fe-based coagulants, Al-based coagulants as pretreatment performed better on removing HA and Cu2+, and the membrane flux greatly improved compared to only UF. The higher the coagulant dosage, the better the membrane performance was, particularly the pollutants removal efficiency. In addition, the PEI-modified UF membranes presented excellent pollutants removal after 4 months of storage in water. Besides, the as-modified UF membrane has only limited influence on removing mineral substances (e.g., Ca2+, Mg2+), indicating a potential application in actual water treatment. Furthermore, the PEI-modified membrane can be easily chemically cleaned; the removal efficiencies for hybrid Al-coagulation and UF process were as high as 88.2% ± 0.8% (HA) and 82.8% ± 0.1% (Cu2+) even after 4 cycles of filtration and subsequent chemical cleaning.
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•Modified UF membrane was used to simultaneously remove NOM and Cu2+.•Excellent membrane performance was observed after PEI modification.•Al-based salts performed better than that of Fe-based salts as pretreatment.•Modified membrane was stable and had little influence toward mineral substances.•Modified membrane can be easily chemically cleaned and performed well.
The present work compares the chemical properties of isolated biopolymers of different origins and their fouling potential during ultrafiltration (UF). The biopolymers were extracted from secondary ...wastewater effluent as effluent organic matter (EfOM) and from surface water as natural organic matter (NOM). Multiple analytical techniques were used to characterize the isolates. The characterization results revealed that EfOM biopolymers were more enriched in protein-type structures compared to the NOM organics, and they presented significant differences in the reversibility of membrane fouling. Dissolved in pure water, EfOM biopolymers led to more irreversible fouling than that caused by NOM isolates. Dosing divalent cations (e.g., Ca2+) into the solutions increased the irreversibility of both types of fouling, while aggravating NOM fouling more significantly. Further investigation was conducted to understand the interaction between EfOM and NOM biopolymers during formation of the fouling layer. The results showed that the interaction between these two types of organics was negligible in the absence of salts. These findings highlight the importance of a comprehensive understanding of biopolymers from different origins, considering their chemical properties and water chemistry, which have valuable implications for selecting suitable membrane fouling control strategies for treating water from different origins.
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•Chemical property & UF fouling of biopolymers from different origins are investigated.•Wastewater biopolymers present higher content of proteinaceous than surface water ones.•Surface water biopolymer fouling is more reversible than wastewater ones in pure water.•The interaction between different biopolymers is negligible in pure water.
