Lithium production has become increasingly critical for sustainable development. The extraction of lithium from aqueous sources, particularly salt-lake brine, has become a trend in the lithium ...recovery industry because of its low cost and abundant reserves. Among various technologies applied for lithium recovery, membrane processes driven by pressure, electrical field, and thermal gradient have received considerable attention in the past few decades because of their high energy efficiency and low environmental impact. This paper presents a comprehensive review of the advantages and challenges of the current membrane-based technologies applied to the recovery of a water lithium resource. Here, we highlight that the combination of membrane processes (e.g. nanofiltration, selective electrodialysis, and membrane distillation crystallization) with a conventional lithium precipitation process will lead to higher performance efficiency and lower cost. Although the membrane-based separation technology is technically feasible, it is restricted by its high capital and operating costs. Therefore, the future development of membrane-based technologies should include efforts for the improvement of the separation efficiency, material stability, and some engineering aspects such as membrane fouling control, module design, and process optimisation.
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•Membrane-based technologies for lithium recovery from water resource are reviewed.•Technologies covered in review include NF, SLM, IIM, LISM, MDC, S-ED and PSMCDI.•The advantages and challenges of these membrane-based technologies are explained.•The techno-economic feasibility of these technologies is evaluated.•The diresssssctions for future research and development are identified.
Superhydrophilic-underwater superoleophobic (SUS) membranes have been demonstrated to be promising materials for oily wastewater treatment. However, development of facile, low cost and robust SUS ...membrane with high flux and less membrane fouling is still challenging. In this study, we reported a simple electrospinning/in-situ growth strategy to prepare SUS SiO2@PVA nanofibrous membrane for gravity-driven separation of oil/water mixture. In specific, a highly porous PVA nanofibrous membrane was first fabricated by electrospinning technique, followed by an in-situ growth of silica nanoparticles on the pristine PVA nanofibers through a modified Stöber reaction. The abundant hydroxyl groups on PVA nanofibers enabled uniform and stable deposition of silica nanoparticles, thus simultaneously realizing high surface energy surface (hydrophilic nature of PVA and silica) and multi-scale roughness. As expected, the resultant membrane exhibited excellent in-air “water-loving” (instantaneous in-air water wetting) and underwater “oil-hating” properties (underwater oil contact angle of 161.8° and sliding angle of 6.2°). The SUS SiO2@PVA membranes exhibited efficient separation of both free oil/water mixture and a variety of surfactant-stabilized oil-in-water emulsions in a gravity-driven filtration process. In addition, oil density played an important role during the separation process, due to superior separation performance was achieved for lighter-than-water oil when compared to heavier-than-water oils. Moreover, the membrane showed robust reusability that it maintained stable oil rejection and permeate flux in cyclic experiments.
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•In situ silica growth on PVA nanofibers to achieve superwetting property.•Excellent in-air water-loving and under-water oil-hating properties achieved.•The membrane realized efficient oil-in-water emulsion separation under gravity.•Oil density plays an important role in the oil/water separation process.•The membrane maintained stable rejection and flux in cyclic experiments.
In recent decades, nanofiltration (NF) is considered as a promising separation technique to produce drinking water from different types of water source. In this paper, we comprehensively reviewed the ...progress of NF-based drinking water treatment, through summarizing the development of materials/fabrication and applications of NF membranes in various scenarios including surface water treatment, groundwater treatment, water reuse, brackish water treatment, and point of use applications. We not only summarized the removal of target major pollutants (e.g., hardness, pathogen, and natural organic matter), but also paid attention to the removal of micropollutants of major concern (e.g., disinfection byproducts, per- and polyfluoroalkyl substances, and arsenic). We highlighted that, for different applications, fit-for-purpose design is needed to improve the separation capability for target compounds of NF membranes in addition to their removal of salts. Outlook and perspectives on membrane fouling control, chlorine resistance, integrity, and selectivity are also discussed to provide potential insights for future development of high-efficiency NF membranes for stable and reliable drinking water treatment.
In this study, the effect of high concentration of Mn2+ on the aerobic granular sludge (AGS) systems for aniline wastewater treatment was systematically investigated in terms of AGS formation and ...pollutant removal efficiency. Two parallel sequencing batch reactors were operated to treat the aniline-rich wastewater with and without 20 mg L−1 of Mn2+. In the presence of Mn2+, the time to granulation was prolonged from 23 d to 30 d due to the toxicity of the high concentration of Mn2+. However, the mature granules with Mn2+ produced more protein and polysaccharides, and had a larger size (870 μm) than that without Mn2+ (740 μm). The extracellular polymeric substances of the granules in the two reactors had similar protein compositions, but some functional groups increased with Mn2+. The reactors showed high overall removal efficiency of chemical oxygen demand, NH4+-N, and total nitrogen with average concentrations below 40, 1.0, and 19 mg L−1, respectively, in the effluents. In one typical operating cycle, however, Mn2+ retarded nitrification and the degradation of aniline, while promoted denitrification. The microbial community analysis revealed that the growth of Terrisporobacter, Pseudomonas, and many other bacteria responsible for aniline degradation was inhibited by Mn2+, and so were the strains involved in nitrification. In contrast, Mn2+ facilitated the growth of denitrifying bacteria.
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•High concentration of Mn2+ prolonged the granulation time and enhanced EPS secretion.•Mn2+ retarded nitrification and aniline degradation while promoted denitrification.•The layered structure of AGS led to opposite effects of Mn2+ on functional bacteria.
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.
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.
Cu(II) is one of the most widely-existed heavy metal ions in industrial effluents. A high concentration of Cu(II) leads to strong toxic effects on microorganisms and sludge for treating industrial ...wastewater which often contains aromatic pollutants. Granular sludge has different characteristics compared with floc sludge, and it may exhibit unique responses to the high concentration of Cu(II). Therefore, in this study, the variations of sludge properties and pollutant removal were investigated in the aerobic granular sludge (AGS) system with 0, 5, and 10 mg L−1 of Cu(II). The results suggested that both levels of Cu(II) promoted protein secretion and bounded with extracellular polymeric substances; thus, led to more compact granules with better settleability. Cu(II) had limited impacts on the overall organic degradation and denitrification efficiency, while it exerted significant negative effect on nitrification. The average NH4+-N concentration reached 1.4 ± 0.5, 6.7 ± 3.1, and 8.4 ± 1.5 mg L−1 in the effluent when the influent contained 0, 5, and 10 mg L−1 of Cu(II), respectively. The microbial community succession showed that no reduction was observed for the total relative abundance of main groups involved in organic removal such as Pseudoxanthomonas, Acidovorax, Acinetobacter, and Thauera. However, the growth of some functional groups such as Saccharibacteria for nitrification was inhibited by the toxic effect of Cu(II). These findings suggested that AGS could resist to the long-term toxic effects of Cu(II) by multiple rationales.
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•5 and 10 mg L−1 of Cu(II) promoted the settleability and stability of granules.•Protein secretion increased while carbohydrate production decreased with Cu(II).•Cu(II) had limited impacts on overall organic removal while retarded nitrification.•The Cu(II)-tolerance strains for removal of organics and nitrogen were enriched.
This study focused on the effects of membrane pore size and surface hydrophobicity on ultrafiltration (UF) membrane fouling caused by extracellular organic matter (EOM) from Microcystis aeruginosa. A ...hydrophilic membrane (cellulose acetate) with a molecular weight cutoff (MWCO) of 100kDa and hydrophobic membranes (polyethersulfone) with MWCO of 100, 30 and 10kDa were employed for UF experiments. The results indicated that the hydrophobic membrane suffered more adsorptive fouling, faster flux decline and worse fouling reversibility than the hydrophilic membrane when treating EOM solution. The membrane with larger pores exhibited worse flux reduction but less adsorptive fouling and superior flux recovery. Mass balances of dissolved organic carbon (DOC) content implied that more EOM passed through the hydrophilic membrane owing to a lack of hydrophobic adsorption and that the larger pore membrane allowed for higher EOM retention and a greater capacity for irreversibly deposited EOM. Fluorescence excitation-emission matrix (EEM) spectra coupling with regional integration were used to further analyze the fates of protein-like and humic-like substances during UF. Membrane pore size and surface hydrophobicity apparently influenced the transportation of protein-like substances, but they were of less importance for humic-like substances. In addition, four classic filtration models were introduced to analyze the fouling mechanisms. Cake formation was identified as the main mechanism for flux decline caused by EOM in this study, independent of membrane pore size and surface hydrophobicity.
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•Effect of pore size and surface hydrophobicity on EOM fouling was investigated.•More hydrophobic and lower MWCO membranes suffer worse adsorptive fouling.•Stronger hydrophobicity leads to faster flux decline and worse reversibility.•Membrane with larger pores exhibits faster flux decline but better flux recovery.•Cake formation serves as the major mechanism of UF membrane fouling by EOM.
This research focused on the combined fouling by humic acid (HA) and powdered activated carbon (PAC) which possibly occurred in the PAC-ultrafiltration (PAC-UF) hybrid process. The membrane fouling ...and the HA transmission were systematically investigated with HA (Aldrich, 10mg/L) and PAC (with different sizes and dosages) in the presence and absence of 0.5mM calcium. Experimental results suggested that PAC and HA exhibited a significant synergistic fouling effect when they formed a fouling cake together. In the absence of calcium, the adsorption of HA on PAC surface increased the repulsive interaction between PAC particles, and thus a fragile cake layer was formed by the PAC–HA mixture. In the presence of calcium, however, a dense cake layer was formed due to particle bridging by HA–Ca–HA associations. The combined fouling effect increased as the PAC dosage increased and the PAC size decreased, both in the presence and absence of calcium, suggesting that the steric effect play an important role in the combined fouling. In the absence of calcium, an unexpected phenomenon that the HA transmission increased in the presence of PAC suggested that in addition to the steric effect, the hindered foulant back diffusion effect was also involved in the combined fouling.
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•HA and PAC had substantial combined influences on ultrafiltration fouling.•PAC size, PAC dosage and the presence of calcium greatly affected the combined fouling.•The main combined fouling mechanisms were steric effect and hindered back diffusion effect.
•Degradation of AOM by advanced oxidation processes were reported.•UV/PDS and UV/H2O2 process could convert the growth inhibitors into nutrient.•AOPs-treated media promoted algal growth in the ...recycled culture.•The economic comparison of UV/PDS and UV/H2O2 were investigated.
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Algae show great potential as sustainable feedstock for numerous bioproducts. However, large volume of water consumption during algal biomass production makes that the culture media recycling is a necessity due to economic and environmental concern. To avoid the negative effect of enriched organic matters in the harvested culture media, pre-treatment prior to medium replenishment and reuse is required. In this study, degradation of algenitic organic matters (AOM) in the culture media by UV-based photolysis processes (i.e., direct UV, UV/peroxydisulfate (PDS), UV/H2O2, and UV/NH2Cl) was explored. The results showed that UV, UV/PDS, UV/H2O2 and UV/NH2Cl caused a decrease of SUVA for 29.9%, 35.4%, 40.45%, and 22.6%, respectively, though the organic matter was almost not mineralized. Fluorescence excitation-emission matrix combined with parallel factor analysis indicated that UV/PDS and UV/H2O2 degraded 47.26%–56.31% of the fulvic-like and humic-like fractions in AOM. Powder activated carbon absorption and growth evaluation for the AOPs-treated media indicated that UV/PDS and UV/H2O2 processes not only could remove the growth inhibitors in the media, but were also beneficial to the algae growth. These results suggested that UV/PDS and UV/H2O2 could effectively degrade the hydrophobic components in AOM and converted the growth inhibition fraction of AOM in the recycled media into nutrient source for algal growth. Different from the general application of UV-based AOP in the wastewater treatment, this study provided an innovative idea about how to pre-treat AOM in the media recycling: utilization rather than removal, which was a more sustainable and environment-friendly technology.
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