With the fast development of textile industry, the increasing discharge of textile wastewater is posing a grand challenge to the environmental safety. Graphene oxide (GO) nanosheet with excellent ...physicochemical properties and lamellar structure, is regarded as an ideal membrane material for the rejection of dyes. However, the selectivity and long-term course of GO-based membranes are largely limited due to the narrow interlayer distance as well as poor aqueous solution stability. To address such situations, a series of GO-based membranes (Fe/GO-TAx) were prepared using coordinated tannic acid-functionalized GO (GO-TA) nanosheets with FeIII ions in this study. The results indicated that Fe/GO-TAx membranes exhibited greater interlayer distance and higher hydrophilicity, as well as a decreasing trend of negative surface charge. Furthermore, the Fe/GO-TA20 conferred a superior dye/salt selective sieving mechanism with a high separation factor and a permeability of 61.2 L m−2 h−1 bar−1 (approximately 6-times higher than the pristine GO membrane). Importantly, the fabricated Fe/GO-TA20 membrane exhibited inherent removals for organic dyes, and more than 99% removals were achieved in the test. These findings were expected to provide some simple but practical strategies for the fast fabrication of two-dimensional laminar structure GO separation membranes to achieve excellent sieving of high-salinity textile wastewater.
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•Metal-polyphenol complex was incorporated into graphene oxide (GO) interlayer.•Hydrophilicity and permeability of the Fe/GO-TAx membranes improved dramatically.•The Fe/GO-TAx membranes exhibited excellent organic dyes removal performance.•The Fe/GO-TAx membranes conferred a superior dyes/salts selective sieving mechanism.
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•CO2 stripping volume was investigated in different aeration intensities.•CO2 stripping is the main cause of massive algae death during high-intensity aeration.•A certain CO2 blow-off ...will be beneficial to the stability of the ABS system.•A certain CO2 stripping can alleviate the competition between nitrifying bacteria and algae.
Utilizing additional aeration to enhance the pollutants removal in the ABS system has been extensively studied. It is widely accepted that that higher aeration rate poses limitations in algae growth. However, this phenomenon is always attributed the phenomenon to the high dissolved oxygen (DO), and the CO2 blow-off that results in inorganic carbon (IC) deficiency is often ignored. In this research, different aeration rates were set under the same DO condition to prove that CO2 stripping, and not DO, is the main cause of algae growth limitation. It was apparent that ideal algae growth conditions, at an aeration intensity of 100 mL/min, was deteriorated due to CO2 stripping, leading to a large amount (15.62 mg/L) of unused NO2− and NO3−. Meanwhile, algae death caused by CO2 stripping damaged the phosphate assimilation process. Furthermore, insufficient IC resulted in competition between autotrophic bacteria and algae, inducing the drastic decline of nitrifying bacteria (whose growth cycle is especially long) numbers. For the relatively lower aeration rate (20 mL/min), the ABS system presented a more stable condition and higher pollutants removal efficiency than both the non-aerated group (0 mL/min) and the high-aeration group (50 mL/min and 100 mL/min). This finding demonstrates that CO2 stripping in the aeration process is the main cause of damage to the ABS system, which guides the ABS application.
This study investigated the fouling and scaling behaviors in a capacitive deionization (CDI) system in the presence of iron and natural organic matter (NOM). It was found that the salt adsorption ...capacity (SAC) significantly decreased when treating Fe-containing brackish water, with higher Fe concentrations leading to severer SAC reduction. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis demonstrated that Fe2O3 appeared to be the predominant foulant attached on the electrode surface, which was difficult to be removed via backwashing, indicating the irreversible property of the foulant. Further characterizations (e.g., N2 sorption-desorption isotherms, electrochemical impedance spectroscopy and cyclic voltammetry) revealed that the CDI electrodes suffered from obvious deterioration such as specific surface area loss, resistance increase and capacitance decline with the occurrence of Fe scaling. While the presence of NOM alleviated the Fe scaling through NOM-Fe complexing effects, NOM itself was found to have negative impacts on CDI desalination performance due to their strong interactions with the carbon electrodes.
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•Iron scaling caused a significant decrease in desalination performances of CDI.•Fe2O3 was the predominant component of iron scale.•CDI fouled suffered from resistance increasing and capacitance losing.•NOM reduced precipitation of Fe on electrodes due to coagulation effect.
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•Combined PAC adsorption and chlorination reduced the fouling rate effectively.•The presence of PAC increased the removal of natural organic matter (NOM).•Chlorination postponed the ...accumulation of foulants on membrane surface.
The goal of this study was to quantify and demonstrate the combined effects of powdered activated carbon (PAC) adsorption and in situ chlorination on the performance of a coagulation and submersed hollow-fiber ultrafiltration (UF) membrane system at the pilot scale. The real-time levels of natural organic matter (NOM), including dissolved organic carbon (DOC) and trichloromethane formation potential (TCMFP), were quantified to evaluate NOM removal in different hybrid UF systems. The fouling behavior of the UF membranes after combined adsorption pre-treatment and in situ chlorination was systematically investigated in terms of membrane filtration resistance. The results showed that the presence of PAC during the coagulation–flocculation process increased the removal of NOM, particularly the fractions of proteinaceous substances and humic-like substances, as indicated by excitation emission matrix (EEM) spectroscopy, which contributed to the retardation of membrane fouling. In situ chlorination postponed membrane fouling to some extent owing to small modifications to the molecular structure of NOM, which demonstrated that the portion of humic acid (HA) that reacted with sodium hypochlorite penetrated the UF membrane, avoiding adsorption to the membrane pores. Combining adsorption enhancing coagulation pre-treatment and in situ chlorination in the hybrid UF system led to further alleviation of membrane fouling.
An optimized cleaning strategy of a thin-film composite membrane functionalized with zwitterionic poly(sulfobetaine methacrylate) brushes (TFC-PSBMA membrane) was investigated for a long-term ...forward osmosis (FO) treatment of polymer-flooding produced water (PFPW). Crude oil and anionic polyacrylamide (APAM) were used as the representative organic substances in the wastewater. The results showed that irreversible fouling was significantly aggravated by increasing the relative concentration of crude oil in the feed solution revealing it to be the major foulant. Then, five cleaning protocols were investigated such as deionized water washing, NaCl osmotic backwashing, chemical washing with acid, alkali, and surfactant cleaning, respectively. As the result, it was found that chemical cleaning with sodium dodecyl benzenesulfonate (SDBS) was the most effective method for removing foulants from the membrane surfaces. Meanwhile, PSBMA brushes grafted on the membrane exhibited excellent tolerance to the chemical stress caused by SDBS but not to NaOH.
•Adding GAC alleviated membrane fouling of a membrane-coupled EGSB process.•It reduced the concentrations of SMP, SMPps and SMPpr by 26.8%, 27.8% and 24.7%.•It primarily reduced tryptophan proteins, ...aromatic proteins and fulvic substances.•GAC addition mainly decreased the cake layer resistance proportion by 53.5%.
To mitigate membrane fouling of membrane-coupled anaerobic process, granular activated carbon (GAC: 50g/L) was added into an expanded granular sludge bed (EGSB). A short-term ultrafiltration test was investigated for analyzing membrane fouling potential and underlying fouling mechanisms. The results showed that adding GAC into the EGSB not only improved the COD removal efficiency, but also alleviated membrane fouling efficiently because GAC could help to reduce soluble microbial products, polysaccharides and proteins by 26.8%, 27.8% and 24.7%, respectively, compared with the control system. Furthermore, excitation emission matrix (EEM) fluorescence spectroscopy analysis revealed that GAC addition mainly reduced tryptophan protein-like, aromatic protein-like and fulvic-like substances. In addition, the resistance distribution analysis demonstrated that adding GAC primarily decreased the cake layer resistance by 53.5%. The classic filtration mode analysis showed that cake filtration was the major fouling mechanism for membrane-coupled EGSB process regardless of the GAC addition.
Water reuse is an effective way to solve the issues of current wastewater increments and water resource scarcity. Ultrafiltration, a promising method for water reuse, has the characteristics of low ...energy consumption, easy operation, and high adaptability to coupling with other water treatment processes. However, emerging organic contaminants (EOCs) in municipal wastewater cannot be effectively intercepted by ultrafiltration, which poses significant challenges to the effluent quality and sustainability of ultrafiltration process. Here, we develop a cobalt single-atom catalyst-tailored ceramic membrane (Co1-NCNT-CM) in conjunction with an activated peroxymonosulfate (PMS) system, achieving excellent EOCs degradation and anti-fouling performance. An interfacial reaction mechanism effectively mitigates membrane fouling through a repulsive interaction with natural organic matter. The generation of singlet oxygen at the Co-N3-C active sites through a catalytic pathway (PMS→PMS∗→OH∗→O∗→OO∗→1O2) exhibits selective oxidation of phenols and sulfonamides, achieving >90% removal rates. Our findings elucidate a multi-layered functional architecture within the Co1-NCNT-CM/PMS system, responsible for its superior performance in organic decontamination and membrane maintenance during secondary effluent treatment. It highlights the power of integrating Co1-NCNT-CM/PMS systems in advanced wastewater treatment frameworks, specifically for targeted EOCs removal, heralding a new direction for sustainable water management.
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•Cobalt single-atom catalysts coated ceramic membrane (Co1-NCNT-CM) is prepared.•Co1-NCNT-CM/PMS selectively removes phenols and sulfonamides.•1O2 is the key reactive species in the selective oxidation filtration system.•The O∗ intermediate is a rate-limit step for 1O2 generation.•Co1-NCNT-CM/PMS enhances the energy barrier between foulants and membrane.
The impact of sludge discharge on membrane fouling during ultrafiltration of surface water was investigated in this study. Discharge sludge and without discharge during UF were compared by measuring ...the increase of transmembrane pressure (TMP) and the accumulation of foulants with running time was studied. It was found that turbidity and dissolved organic carbon of retentate solution apparently increased as UF proceeded. Three-dimensional excitation/emission matrix fluorescence spectroscopy analyses of raw water and retentate solution demonstrated that UF could lead to the accumulation of humic and protein-like substances. Filtration experiments showed that membrane fouling could be alleviated by discharging the retentate solution after physical cleaning due to the reduced cake layer formation and concentration polarization. In addition, effects of sludge discharge intervals on the TMP and fouling characteristics were further investigated. Results indicated that short SDI would benefit control of both reversible and irreversible fouling. However, frequent discharge of retentate solution may increase the self-use water and decrease the water production rate of the UF system, leading to an expansion of running cost. In general, SDI was a critically important factor for both membrane fouling and water production rate.
•Effect of sludge discharge interval (SDI) on UF membrane fouling was studied.•Foulants including particles and organic matter accumulate in retentate solution.•Sludge discharge can alleviate both reversible fouling and irreversible fouling.•All fouling resistances involved can be reduced by decreasing SDI.•Both membrane fouling and production rate should be considered for choosing SDI.
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