Membrane fouling is a recognized obstacle for the application of ultrafiltration (UF) for drinking water treatment. In this study, ultraviolet/persulfate (UV/PS) oxidation was employed as a ...pretreatment to control membrane fouling caused by natural organic matter (NOM) in surface water. The effects of UV/PS pretreatment on amounts and characteristics of NOM were investigated in terms of dissolved organic carbon, fluorescent spectrum, molecular weight distribution and hydrophobicity. UF membrane fouling during filtration of raw and pre-oxidized water was compared with transmembrane pressure development, and the fouled membranes were further characterized using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results indicate that NOM was considerably degraded and partially mineralized (∼58%) by UV/PS pretreatment at a PS dose not exceeding 0.6 mM and a UV irradiation time within 120 min, which was attributed to the generation of sulfate and hydroxyl radicals. The fluorescent compounds in NOM were almost completely degraded (>98%) by the UV/PS pretreatment at a PS dose of 0.4 mM, except for tyrosine-like proteins (∼80%). Moreover, UV/PS pretreatment decreased the ratio of macromolecular compounds and increased the hydrophilic fractions, resulting in reduced NOM adhesion to the membrane. Hence, irreversible fouling by NOM was significantly retarded (∼75%) by the UV/PS pretreatment due to reduction in NOM, and more importantly by preferential degradation of fluorescent, macromolecular and hydrophobic compounds. Fouling control performance was considerably improved at increased PS doses and extended UV irradiation time.
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•UV/PS pre-oxidation was applied to retard UF membrane fouling by NOM.•UV/PS substantially degraded and partially mineralized NOM (<58%) in surface water.•Hydrophobic and fluorescent fractions of NOM were preferentially degraded by UV/PS.•NOM fouling was notably retarded (∼75%) by UV/PS, particularly at higher doses.•Fouling control was due to reduced NOM and improved characteristics.
To deeply assess the feasibility of sewage sludge-based biochars for use in soil applications, this review compared sewage sludge-based biochars (SSBBs) with lignocellulose-based biochars (LCBBs) in ...terms of their pyrolysis processes, various fractions and potential soil applications. Based on the reviewed literature, significant differences between the components of SSBB and LCBB result in different pyrolysis behavior. In terms of the fractions of biochars, obvious differences were confirmed to exist in the carbon content, surface functional groups, types of ash fractions and contents of potential toxic elements (PTEs). However, a clear influence of the feedstock on labile carbon and polycyclic aromatic hydrocarbons (PAHs) was not observed in the current research. These differences determined subsequent discrepancies in the soil application potential and corresponding mechanisms. The major challenges facing biochar application in soils and corresponding recommendations for future research were also addressed. LCBBs promote carbon sequestration, heavy metal retention and organic matter immobilization. The application of SSBBs is a promising approach to improve soil phosphorus fertility, immobilize heavy metals and provide available carbon sources for soil microbes to stimulate microbial biomass. The present review provides guidance information for selecting appropriate types of biochars to address targeted soil issues.
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•Feedstock composition affected pyrolysis processes and fractions of SSBB and LCBB.•Appropriate applications in soils were suggested for SSBB and LCBB.•Strategies for reducing PTEs and PAHs in biochars were proposed.
Bromide is universal in surface water influenced by salt tide and brackish water. It is harmless to human until transferring to bromate (a kind of disinfection byproducts) under certain conditions ...such as oxidation. Though both of them are not easily removed by conventional water treatment, nanofiltration seems to be an efficient way to solve the problems. In this study, the removal of bromate and bromide by nanofiltration membranes were systematically investigated, considering the system pressure (0.2–0.3–0.4 MPa), pH (5–7–9), ionic strength (0.005–0.05–0.1 mM), membrane type (NF270 and NF90), and the influences of organic matters (humic acid and sodium alginate). The membrane flux and the removal efficiency of anions were taken into consideration. According to the results, the membrane flux increased along with the system pressure, but slight influence on the removal of bromate and bromide was observed. Rising pH and ionic strength could not obviously deteriorate the flux. However, the removal of these anions was enhanced by increasing pH as well as decreasing ionic strength. Compared with humic acid, severer flux decline and deterioration of anion removal were achieved when sodium alginate was added in feed solution. Regardless of the operating conditions, bromate was more easily removed by nanofiltration membranes than bromide, which could result from different steric hindrance. Compared with NF270, NF90 can reject bromide and bromate more efficiently. The findings in the present study would contribute to the deep understanding of the factors affecting removal of bromate and bromide by nanofiltration and provides guidance about application of it.
Traditional polyamide-based interfacial polymerized nanofiltration (NF) membranes exhibit upper bound features between water permeance and salt selectivity. Breaking the limits of the permeability ...and rejections of these composite NF membranes are highly desirable for water desalination. Herein, a high-performance NF membrane (TFC-P) was fabricated via interfacial polymerization on the poly(vinyl alcohol) (PVA) interlayered poly(ether sulfone) (PES) ultrafiltration support. Owing to the large surface area, great hydrophilicity, and high porosity of the PES–PVA support, a highly cross-linked polyamide separating layer was formed with a thickness of 9.6 nm, which was almost 90% thinner than that of the control membrane (TFC-C). In addition, the TFC-P possessed lower ζ-potential, smaller pore size, and greater surface area compared to that of the TFC-C, achieving an ultrahigh water permeance of 31.4 L m–2 h–1 bar–1 and a 99.4% Na2SO4 rejection. Importantly, the PVA interlayer strategy was further applied to a pilot NF production line and the fabricated membranes presented stable water flux and salt rejections as comparable to the lab-scaled membranes. The outstanding properties of the PVA-interlayered NF membranes highlight the feasibility of the fabrication method for practical applications, which provides a new avenue to develop robust polyamide-based NF desalination membranes for environmental water treatment.
Herein an investigation on the performance and structural properties with aspects of stability, composition, functional group, and three-dimensional distribution were approached to evaluate the ...influence of nanobubble aeration to the two most common microbial aggregates, activated sludge and biofilm. This study found that applying nanobubble effectively provided extra oxygen for microbial aggregates and achieved a 10.58% improvement in total nitrogen removal. The structure of microbial aggregates was enhanced, where extracellular protein and polysaccharides respectively increased as maximum as 3.40 and 1.70 times in biofilm and activated sludge, accompanied by the development of activated sludge floc size and the thickness of biofilm. Further investigation on extracellular polymeric substance and surface of microbial aggregates showed the composition of functional substances of microbial aggregates were shifted by the application of nanobubble, especially the oxygen-sensitive ones. Confocal laser scanning microscopy imaging visualized that the nanobubble changed the morphology of biofilm to a more evenly one. However, an adaptive process was more needed for activated sludge rather than biofilm, it suggested application of NB optimized the distribution of functional microorganisms in-depth and the metabolism pathway of them by accelerating the structure development of microbial aggregates, especially for biofilm.
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•Responses of AS and biofilm was compared under various NB dosage.•Microbial aggregates required an adaptive process for NB, which is shorter in biofilm.•NB application enhanced the structural development of microbial aggregates.•Selected functional groups were shift via NB in AS and biofilm.
Low pressure membrane (LPM) filtration is a promising technology for drinking water production, wastewater reclamation as well as pretreatment for seawater desalination. However, wider implementation ...of LPM is restricted by their inherent drawbacks, i.e., membrane fouling and insufficient rejection for dissolved contaminants. Pretreatment of feed water is a major method to improve the performance of LPM, and pre-oxidation has gained extensive attention because it can significantly alter compositions and properties of feed water through chemical reactions. This paper attempts to systematically review efficiency and mechanisms of pre-oxidation in membrane fouling control and permeate water quality improvement. On the basis of briefly discussing major foulants and fouling mechanisms of LPM, advantages and disadvantages of pre-oxidation in mitigating organic fouling, inorganic fouling and biofouling are discussed in detail. Impacts of pre-oxidation on removal of micropollutants, bulk organic matter and inorganic pollutants are summarized, and potential by-products of different oxidants are presented. As a prerequisite for the integration of chemical oxidation with LPM filtration, compatibility of membrane with oxidants at low concentration and long exposure time are highlighted. Finally, the existing challenges and future research needs in practical application of chemical oxidation to improve performance of LPM are also discussed.
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•Effect of pre-oxidation on fouling and permeate quality of LPM is reviewed.•Pre-oxidation effectively mitigates fouling caused by high-MW organics and bacteria.•Pre-oxidation enhances removal of micropollutants and inorganic pollutants.•Compatibility of polymeric membrane with oxidants requires further investigation.
This paper focused on the membrane fouling caused by extracellular organic matters (EOM) which was extracted from lab-cultured Microcystis aeruginosa in stationary phase. The characteristics of EOM ...such as molecular weight distribution, hydrophobicity and fluorescence were measured. It was found that high molecular weight (MW) and hydrophilic organics accounted for the major parts of algal EOM which was comprised of protein-like, polysaccharide-like and humic-like substances. Ultrafiltration (UF) experiments were carried out in a stirring cell and hydrophobic polyethersulfone (PES) membranes which carried negative charge were used. Prefiltration, calcium addition and XAD fractionation were employed to change the interfacial characteristics of EOM. Then the effects of these interfacial characteristics on flux decline, reversibility and mass balance of organics were compared. Algal EOM proved to cause serious membrane fouling during UF. The fraction of algal EOM between 0.45 μm and 100 kDa contributed a significant portion of the fouling. Hydrophobic organics in EOM tended to adhere to membrane surface causing irreversible fouling, while the cake layer formed by hydrophilic organics caused greater resistance to water flow due to hydrophilic interaction such as hydrogen bond and led to faster flux decline during UF. The results also indicated that the algal EOM was negatively charged and the electrostatic repulsion could prevent organics from adhering to membrane surface. In term of fouling mechanisms, cake layer formation, hydrophobic adhesion and pore plugging were the main mechanisms for membrane fouling caused by algal EOM.
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► We examine the effects of interfacial characteristics of EOM on UF membrane fouling. ► The fraction of EOM between 0.45μm and 100kDa contributed a major portion of fouling. ► Hydrophobic organics in EOM tended to cause irreversible fouling by adhesion. ► Cake layer formed by hydrophilic organics caused faster flux decline. ► Negative surface charge could prevent organics in EOM from adhering to membrane.
The effects of pre-ozonation on ultrafiltration (UF) membrane fouling caused by different natural organic matter (NOM) fractions were investigated. Three typical organic model foulants, humic acid ...(HA), sodium alginate (SA) and bovine serum albumin (BSA) were selected as representatives of different NOM fractions in natural waters. Moreover, Songhua River water (SRW) was employed as a natural surface water. To predict membrane fouling, the dissolved organic carbon (DOC), ultraviolet absorbance (UV254) and the maximum fluorescence intensity (Fmax) were used to establish correlations with total fouling index (TFI) and hydraulic irreversible fouling index (HIFI). In addition, the fouling mechanisms were preliminarily analyzed. The results indicated that pre-ozonation significantly alleviated membrane fouling caused by HA, SA and SRW. Maximum ozone dose (4.0mg/L) showed the best performance with approximately 39%, 78% and 42% TFI reduction, and 26%, 73% and 39% HIFI reduction for HA, SA and SRW, respectively. However, pre-ozonation exerted little influence on BSA fouling under the tested ozone exposure (0.5, 1.5 and 4.0mg/L). TFI and HIFI were poorly correlated with the DOC contents of HA, SA, BSA and SRW, and the Fmax of BSA, whereas positively correlated with the UV254 of HA and SRW, and the Fmax of HA and each component of SRW. The fouling mitigation mechanisms were attributed to the changes of NOM properties after pre-ozonation. The results are expected to provide relevant information on predicting and controlling UF membrane fouling according to the composition and characteristics of NOM.
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•Effects of pre-ozonation on membrane fouling by diverse NOM fractions were studied.•Pre-ozonation significantly mitigated HA, SA and SRW fouling, rather than BSA.•DOC, UV254 and fluorescence EEM were utilized to predict UF membrane fouling.•It was the UV254 rather than the DOC content related to membrane fouling.•Fluorescence EEM might be invalid to predict membrane fouling after pre-ozonation.
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.
Extracellular organic matter (EOM) of cyanobacteria was classified into the dissolved EOM (dEOM) which was released into culture solution and the bound EOM (bEOM) which surrounded the cells. The dEOM ...and bEOM extracted from Microcystis aeruginosa in stationary phase were used to study their characteristic differences and then their impacts on ultrafiltration (UF) membrane fouling. Component analyses showed that dEOM was comprised of proteins, polysaccharides and humic-like substances, while that bEOM contained only proteins and polysaccharides. Additionally, polysaccharides dominated in dEOM with a polysaccharide/DOC ratio of 1.11 mg mg−1, while proteins were the primary components of bEOM with a protein/DOC ratio of 1.08 mg mg−1. Results of size fractionation and XAD resin fractionation revealed that bEOM was mainly distributed in the high-MW and hydrophobic fractions, while that dEOM was more hydrophilic. Result of UF experiments indicated that dEOM which had a higher organic content and stronger hydrophilicity caused more severe flux decline and reversible fouling, and that bEOM led to slower flux decline but more irreversible fouling due to less electrostatic repulsive and more hydrophobic adhesion. The impacts of these two kinds of EOM on the UF fouling caused by cyanobacterial cells were also investigated. It was found that both flux decline and irreversible membrane fouling caused by the cells were aggravated when cells were together with EOM, especially for bEOM which might increase the surface hydrophobicity of the cells.
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► EOM of cyanobacteria are classified into dissolved EOM (dEOM) and bound EOM (bEOM). ► bEOM contains more proteins and were more high-MW and hydrophobic than dEOM. ► dEOM causes more serious flux decline than bEOM due to larger organic amounts. ► bEOM causes more irreversible fouling due to hydrophobic adhesion of proteins. ► Both dEOM and bEOM can aggravate the membrane fouling caused by cyanobacterial cells.
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