RS
R. Shang
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1
The adsorption mechanisms of organic micropollutants on high-silica zeolites causing S-shaped adsorption isotherms
An experimental and Monte Carlo simulation study
Journal article
(2020)
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Nan Jiang, Mate Erdös, Othon Moultos, Ran Shang, Thijs J.H. Vlugt, Sebastiaan G.J. Heijman, Luuk C. Rietveld
The adsorption of organic micropollutants (OMPs) on high-silica zeolites is characterized by adsorption isotherms with various shapes. The occurrence of an S-shaped adsorption isotherm indicates the lack of adsorption affinity for OMPs at low, environmentally relevant equilibrium concentrations. In this study, S-shaped isotherms were observed during batch experiments with 2,4,6-trichlorophenol (TCP) and FAU zeolites. This is the first time that an S-shaped isotherm is reported for the adsorption of OMPs on high-silica zeolites. Monte Carlo (MC) simulations in the grand-canonical ensemble were used to obtain a better understanding of the mechanism of the S-shaped adsorption isotherms. From the MC simulation results, it was observed that multiple TCP molecules were adsorbed in the supercages of the FAU zeolites. It was found that the π-π interactions between TCP molecules give rise to the adsorption of multiple TCP molecules per supercage, and thus causing an S-shaped adsorption isotherm. Simulations also revealed that water molecules were preferentially adsorbed in the supercages and sodalite cages of the FAU zeolites. FAU zeolites with a higher Al content adsorbed a higher amount of water molecules and a lower amount of TCP, and showed less pronounced S-shaped isotherms.
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The adsorption of organic micropollutants (OMPs) on high-silica zeolites is characterized by adsorption isotherms with various shapes. The occurrence of an S-shaped adsorption isotherm indicates the lack of adsorption affinity for OMPs at low, environmentally relevant equilibrium concentrations. In this study, S-shaped isotherms were observed during batch experiments with 2,4,6-trichlorophenol (TCP) and FAU zeolites. This is the first time that an S-shaped isotherm is reported for the adsorption of OMPs on high-silica zeolites. Monte Carlo (MC) simulations in the grand-canonical ensemble were used to obtain a better understanding of the mechanism of the S-shaped adsorption isotherms. From the MC simulation results, it was observed that multiple TCP molecules were adsorbed in the supercages of the FAU zeolites. It was found that the π-π interactions between TCP molecules give rise to the adsorption of multiple TCP molecules per supercage, and thus causing an S-shaped adsorption isotherm. Simulations also revealed that water molecules were preferentially adsorbed in the supercages and sodalite cages of the FAU zeolites. FAU zeolites with a higher Al content adsorbed a higher amount of water molecules and a lower amount of TCP, and showed less pronounced S-shaped isotherms.
Adsorption of triclosan, trichlorophenol and phenol by high-silica zeolites
Adsorption efficiencies and mechanisms
High-silica zeolites can be used for adsorption of organic compounds (OCs) from water. The adsorption efficacy could vary with the properties of OCs, as well as the porous and surface features of high-silica zeolites. In this study, the adsorption of triclosan, trichlorophenol (TCP) and phenol by ten high-silica zeolites were investigated. The plateaus of adsorption isotherms were observed in the adsorption of triclosan. The maximum adsorption capacity of triclosan could be related to the surface area and volume of micropores. The adsorption of TCP by FAU zeolites gave an S-shaped isotherm due to the possible lateral interactions of TCP molecules in the specific pore topology of FAU zeolites. The adsorption of phenol by high-silica zeolites had no adsorption plateau. Zeolites with channel structures, e.g. MFI zeolites, possess closely fitted pores for phenol, which slightly promoted its adsorption efficacy. The active adsorption sites of zeolites, i.e. Brønsted acid sites (BAS) and Lewis acid sites (LAS) failed to promote phenol adsorption. Phenol adsorption was favoured by carbon-based adsorbents with aromatic rings and functional groups, e.g. carboxyl and carbonyl, while the lack of active adsorption sites limited the phenol adsorption by high-silica zeolites, especially at the low concentration range.
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High-silica zeolites can be used for adsorption of organic compounds (OCs) from water. The adsorption efficacy could vary with the properties of OCs, as well as the porous and surface features of high-silica zeolites. In this study, the adsorption of triclosan, trichlorophenol (TCP) and phenol by ten high-silica zeolites were investigated. The plateaus of adsorption isotherms were observed in the adsorption of triclosan. The maximum adsorption capacity of triclosan could be related to the surface area and volume of micropores. The adsorption of TCP by FAU zeolites gave an S-shaped isotherm due to the possible lateral interactions of TCP molecules in the specific pore topology of FAU zeolites. The adsorption of phenol by high-silica zeolites had no adsorption plateau. Zeolites with channel structures, e.g. MFI zeolites, possess closely fitted pores for phenol, which slightly promoted its adsorption efficacy. The active adsorption sites of zeolites, i.e. Brønsted acid sites (BAS) and Lewis acid sites (LAS) failed to promote phenol adsorption. Phenol adsorption was favoured by carbon-based adsorbents with aromatic rings and functional groups, e.g. carboxyl and carbonyl, while the lack of active adsorption sites limited the phenol adsorption by high-silica zeolites, especially at the low concentration range.
Using ceramic nanofiltration membranes for treatment of municipal sewage is upcoming. However, the knowledge on fouling control methods for this application are very limited. The most commonly used fouling control method, chemical cleaning, has disadvantages. Chemical cleaning negatively impacts (i) the glass seal layer of tubular ceramic nanofiltration membranes and (ii) the environment, especially when using sodium hypochlorite for removal of organic fouling. Therefore, the use of chemical cleaning should be limited as much as possible. In this research, first, the well-known fouling control methods for polymeric micro- and ultrafiltration membranes, were studied on ceramic nanofiltration membranes: hydraulic backwash and forward flush. Second, a precoat method was combined with a chemical reaction to aid the detachment of the formed cake layer. In this method, a precoat layer was filtered atop of the membrane surface before the start of filtration. The precoat layer then acts as a barrier between the foulants and the membrane surface. After filtration, the precoat layer reacts with the cleaning reagent underneath the fouling layer to enable fast removal of fouling. Results showed that hydraulic backwash was not effective to be used for this type of membranes. Forward flush was able to maintain a higher flux but the relative production downtime was high. Reaction based precoat was most effective in maintaining a high flux and resulted in the highest net water production. Two reaction based precoat methods were tested of which the reaction of calcium carbonate with citric acid was more effective than a Fenton reaction.
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Using ceramic nanofiltration membranes for treatment of municipal sewage is upcoming. However, the knowledge on fouling control methods for this application are very limited. The most commonly used fouling control method, chemical cleaning, has disadvantages. Chemical cleaning negatively impacts (i) the glass seal layer of tubular ceramic nanofiltration membranes and (ii) the environment, especially when using sodium hypochlorite for removal of organic fouling. Therefore, the use of chemical cleaning should be limited as much as possible. In this research, first, the well-known fouling control methods for polymeric micro- and ultrafiltration membranes, were studied on ceramic nanofiltration membranes: hydraulic backwash and forward flush. Second, a precoat method was combined with a chemical reaction to aid the detachment of the formed cake layer. In this method, a precoat layer was filtered atop of the membrane surface before the start of filtration. The precoat layer then acts as a barrier between the foulants and the membrane surface. After filtration, the precoat layer reacts with the cleaning reagent underneath the fouling layer to enable fast removal of fouling. Results showed that hydraulic backwash was not effective to be used for this type of membranes. Forward flush was able to maintain a higher flux but the relative production downtime was high. Reaction based precoat was most effective in maintaining a high flux and resulted in the highest net water production. Two reaction based precoat methods were tested of which the reaction of calcium carbonate with citric acid was more effective than a Fenton reaction.
Journal article
(2020)
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Niels van Linden, Ran Shang, Georg Stockinger, Sebastiaan Heijman, H. Spanjers
The application of zero liquid discharge (ZLD) results in the generation of solid residual streams, which are often not fit for reuse. In this study, we assessed the separation of natural organic matter (NOM) and sodium chloride (NaCl) by nanofiltration (NF), electrodialysis (ED) and ion exchange (IEX) in reverse osmosis brine (RO-brine) and by the extraction of impurities from salt (SALEX) in the generated mixed solids of a full-scale ZLD water treatment plant. The NaCl recovery by NF, ED and IEX ranged 69-99% and the rejection of NOM ranged 18–19%, 43–65% and 53–76%, respectively. The recovery of NaCl by SALEX ranged 52–99%, while the rejection of NOM ranged 59–92%. The results show that NOM and NaCl can be sepa-rated both in RO-brine and mixed solids, opening opportunities for recovery of reusable salt from brines in ZLD.
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The application of zero liquid discharge (ZLD) results in the generation of solid residual streams, which are often not fit for reuse. In this study, we assessed the separation of natural organic matter (NOM) and sodium chloride (NaCl) by nanofiltration (NF), electrodialysis (ED) and ion exchange (IEX) in reverse osmosis brine (RO-brine) and by the extraction of impurities from salt (SALEX) in the generated mixed solids of a full-scale ZLD water treatment plant. The NaCl recovery by NF, ED and IEX ranged 69-99% and the rejection of NOM ranged 18–19%, 43–65% and 53–76%, respectively. The recovery of NaCl by SALEX ranged 52–99%, while the rejection of NOM ranged 59–92%. The results show that NOM and NaCl can be sepa-rated both in RO-brine and mixed solids, opening opportunities for recovery of reusable salt from brines in ZLD.
Journal article
(2019)
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Yunhua Zhu, Chun Zhao, Jialiang Liang, Ran Shang, Xuanmo Zhu, Lei Ding, Huiping Deng, Huaili Zheng, Timothy J. Strathmann
Electrolysis and permanganate (PM) oxidation are two commonly used technologies for water treatment. However, they are often handicapped by their slow reaction rates. To improve the removal efficiency of refractory contaminants, we combined electrolysis with PM using an activated carbon fiber (ACF) as cathode (E-ACF-PM) for the first time to treat diclofenac (DCF) in aqueous solution. Up to 90% DCF was removed in 5 min by E-ACF-PM process. In comparison, only 3.95 and 27.35% of DCF was removed by individual electrolysis and PM oxidation at the same time, respectively. Acidic condition was more conducive to DCF removal. Surprisingly, soluble Mn(III) ( aq) formed on the surface of ACF was demonstrated as the principal oxidizing agent in E-ACF-PM process. Further studies showed that all three components (electrolysis + ACF + PM) were necessary to facilitate the heterogeneous generation of reactive Mn(III) ( aq). Moreover, SEM images and XPS spectra of ACF before and after treatment revealed that the morphologies and elemental compositions of reacted ACF were nearly unchanged during the E-ACF-PM process. ACF can be remained active and utilized to the rapid degradation of DCF in E-ACF-PM process even after reused for 20 times. Therefore, the E-ACF-PM process may provide a novel and effective alternative on the generation of reactive Mn(III) ( aq) in situ for water treatment by green electrochemical reactions.
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Electrolysis and permanganate (PM) oxidation are two commonly used technologies for water treatment. However, they are often handicapped by their slow reaction rates. To improve the removal efficiency of refractory contaminants, we combined electrolysis with PM using an activated carbon fiber (ACF) as cathode (E-ACF-PM) for the first time to treat diclofenac (DCF) in aqueous solution. Up to 90% DCF was removed in 5 min by E-ACF-PM process. In comparison, only 3.95 and 27.35% of DCF was removed by individual electrolysis and PM oxidation at the same time, respectively. Acidic condition was more conducive to DCF removal. Surprisingly, soluble Mn(III) ( aq) formed on the surface of ACF was demonstrated as the principal oxidizing agent in E-ACF-PM process. Further studies showed that all three components (electrolysis + ACF + PM) were necessary to facilitate the heterogeneous generation of reactive Mn(III) ( aq). Moreover, SEM images and XPS spectra of ACF before and after treatment revealed that the morphologies and elemental compositions of reacted ACF were nearly unchanged during the E-ACF-PM process. ACF can be remained active and utilized to the rapid degradation of DCF in E-ACF-PM process even after reused for 20 times. Therefore, the E-ACF-PM process may provide a novel and effective alternative on the generation of reactive Mn(III) ( aq) in situ for water treatment by green electrochemical reactions.
Journal article
(2019)
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F. C. Kramer, R. Shang, S. M. Scherrenberg, L. C. Rietveld, S. J.G. Heijman
One of the perceived benefits of ceramic membranes is their robustness, which makes them suitable for treating high organic load waste streams. In particular, ceramic tight ultrafiltration (tUF) and nanofiltration (NF) form an important barrier against small colloids and organic molecules. In order to achieve this barrier, the quality of the membranes should be uncompromised. An extension on a commonly used size exclusion method was developed in order to quantify defects in membranes and calculate the MWCO accurately excluding the defects. This approach gives a better representation of the membrane quality than the original method. The quality of a broad range of commercial ceramic membranes was investigated by determining the (i) hydraulic permeability, (ii) molecular weight cut-off, and (iii) quantitative defects. Several membranes – both tubular and disc membranes, selected from various suppliers – were tested to investigate their variability. Furthermore, the robustness of tubular NF membranes was studied by monitoring the effect of long-term exposure to sodium hypochlorite, which is commonly used to mitigate organic fouling. The results showed that batches of both tubular and disc membranes of different pore size and suppliers included membranes with defects. Furthermore, the long-term treatment of tubular ceramic membranes with sodium hypochlorite negatively affected, beyond expectation, the quality of the membranes. The separation layer in these membranes was not notably compromised by sodium hypochlorite exposure, but the end seal layer was damaged.
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One of the perceived benefits of ceramic membranes is their robustness, which makes them suitable for treating high organic load waste streams. In particular, ceramic tight ultrafiltration (tUF) and nanofiltration (NF) form an important barrier against small colloids and organic molecules. In order to achieve this barrier, the quality of the membranes should be uncompromised. An extension on a commonly used size exclusion method was developed in order to quantify defects in membranes and calculate the MWCO accurately excluding the defects. This approach gives a better representation of the membrane quality than the original method. The quality of a broad range of commercial ceramic membranes was investigated by determining the (i) hydraulic permeability, (ii) molecular weight cut-off, and (iii) quantitative defects. Several membranes – both tubular and disc membranes, selected from various suppliers – were tested to investigate their variability. Furthermore, the robustness of tubular NF membranes was studied by monitoring the effect of long-term exposure to sodium hypochlorite, which is commonly used to mitigate organic fouling. The results showed that batches of both tubular and disc membranes of different pore size and suppliers included membranes with defects. Furthermore, the long-term treatment of tubular ceramic membranes with sodium hypochlorite negatively affected, beyond expectation, the quality of the membranes. The separation layer in these membranes was not notably compromised by sodium hypochlorite exposure, but the end seal layer was damaged.
Ceramic nanofiltration is an emerging technology for the recovery of water and nutrients (including phosphate) from municipal sewage which becomes more imperative worldwide. In order to use ceramic nanofiltration for phosphate recovery from municipal sewage, more knowledge is needed. This is the first paper reporting the phosphate retention of ceramic nanofiltration membranes. Furthermore, the influence of pH, multivalent counter ions, and membrane fouling on phosphate retention is reported in this paper. Various experiments were executed to analyse the phosphate retention and zeta potential under varying conditions. During filtration of a salt solution including phosphate, the phosphate retention increased, from 76% to 99%, with a change in pH from 5 to 9. Furthermore, magnesium ions and organic fouling had a large influence on the phosphate retention: at pH 7 the phosphate retention dropped from 92% to 42–43% due to the presence of either magnesium ions or organic fouling.
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Ceramic nanofiltration is an emerging technology for the recovery of water and nutrients (including phosphate) from municipal sewage which becomes more imperative worldwide. In order to use ceramic nanofiltration for phosphate recovery from municipal sewage, more knowledge is needed. This is the first paper reporting the phosphate retention of ceramic nanofiltration membranes. Furthermore, the influence of pH, multivalent counter ions, and membrane fouling on phosphate retention is reported in this paper. Various experiments were executed to analyse the phosphate retention and zeta potential under varying conditions. During filtration of a salt solution including phosphate, the phosphate retention increased, from 76% to 99%, with a change in pH from 5 to 9. Furthermore, magnesium ions and organic fouling had a large influence on the phosphate retention: at pH 7 the phosphate retention dropped from 92% to 42–43% due to the presence of either magnesium ions or organic fouling.
High-silica zeolites have been found to be effective adsorbents for the removal of organic micro-pollutants (OMPs) from impaired water, including various pharmaceuticals, personal care products, industrial chemicals, etc. In this review, the properties and fundamentals of high-silica zeolites are summarised. Recent research on mechanisms and efficiencies of OMP adsorption by high-silica zeolites are reviewed to assess the potential opportunities and challenges for the application of high-silica zeolites for OMP adsorption in water treatment. It is concluded that the adsorption capacities are well-related to surface hydrophobicity/hydrophilicity and structural features, e.g. micropore volume and pore size of high-silica zeolites, as well as the properties of OMPs. By using high-silica zeolites, the undesired competitive adsorption of background organic matter (BOM) in natural water could potentially be prevented. In addition, oxidative regeneration could be applied on-site to restore the adsorption capacity of zeolites for OMPs and prevent the toxic residues from re-entering the environment.
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High-silica zeolites have been found to be effective adsorbents for the removal of organic micro-pollutants (OMPs) from impaired water, including various pharmaceuticals, personal care products, industrial chemicals, etc. In this review, the properties and fundamentals of high-silica zeolites are summarised. Recent research on mechanisms and efficiencies of OMP adsorption by high-silica zeolites are reviewed to assess the potential opportunities and challenges for the application of high-silica zeolites for OMP adsorption in water treatment. It is concluded that the adsorption capacities are well-related to surface hydrophobicity/hydrophilicity and structural features, e.g. micropore volume and pore size of high-silica zeolites, as well as the properties of OMPs. By using high-silica zeolites, the undesired competitive adsorption of background organic matter (BOM) in natural water could potentially be prevented. In addition, oxidative regeneration could be applied on-site to restore the adsorption capacity of zeolites for OMPs and prevent the toxic residues from re-entering the environment.
Journal article
(2017)
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Pengchao Xie, Yizhou Guo, Yiqun Chen, Zongping Wang, Ran Shang, Songlin Wang, Jiaqi Ding, Ying Wan, Wei Jiang, Jun Ma
A novel advanced oxidation process, combined zero-valent iron and sulfite (Fe0/sulfite) system containing oxygen, was firstly developed to efficiently degrade organic pollutants at weak acidic and neutral conditions by selecting X-3B as a target compound. The removal of X-3B was attributed to the formed reactive radicals, such as SO4 -, SO5 - and HO[rad], in the Fe0/sulfite system, and SO4 - was evidenced as the principal reactive species. The quite low removal efficiency of X-3B (less than 5%) after reaction for 90 min with purging nitrogen gas suggests oxygen to be an essential factor for producing SO4 - in the system. Optimal dosages of Fe0 and sulfite were suggested to be 0.5 mM and 1.0 mM, respectively, in the system as both the two chemicals would scavenge the reactive radicals at overdosing. The presence of 2 mM bicarbonate significantly inhibited the removal of X-3B from 74.1% to 37.5% in the system. Halide ions inhibited the removal of X-3B following a trend that Cl− <Br− <I−. HSO3 −, being effective in complexion of Fe(II) and transferring Fe(III) to Fe(II), is the main species during pHs 4–6, which results in the good reuse of Fe0 and the highest removal efficiency of X-3B at weak acidic condition. Fe0/sulfite system was also evidenced to be effective in the treatment of actual textile effluents along with improving biodegradability, and the removal of nitrobenzene, methylparaben, bisphenol A, imipramine and amitriptyline. Overall, this study provided a cheap and easy operational advanced oxidation process in treatment of aqueous organic pollutants.
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A novel advanced oxidation process, combined zero-valent iron and sulfite (Fe0/sulfite) system containing oxygen, was firstly developed to efficiently degrade organic pollutants at weak acidic and neutral conditions by selecting X-3B as a target compound. The removal of X-3B was attributed to the formed reactive radicals, such as SO4 -, SO5 - and HO[rad], in the Fe0/sulfite system, and SO4 - was evidenced as the principal reactive species. The quite low removal efficiency of X-3B (less than 5%) after reaction for 90 min with purging nitrogen gas suggests oxygen to be an essential factor for producing SO4 - in the system. Optimal dosages of Fe0 and sulfite were suggested to be 0.5 mM and 1.0 mM, respectively, in the system as both the two chemicals would scavenge the reactive radicals at overdosing. The presence of 2 mM bicarbonate significantly inhibited the removal of X-3B from 74.1% to 37.5% in the system. Halide ions inhibited the removal of X-3B following a trend that Cl− <Br− <I−. HSO3 −, being effective in complexion of Fe(II) and transferring Fe(III) to Fe(II), is the main species during pHs 4–6, which results in the good reuse of Fe0 and the highest removal efficiency of X-3B at weak acidic condition. Fe0/sulfite system was also evidenced to be effective in the treatment of actual textile effluents along with improving biodegradability, and the removal of nitrobenzene, methylparaben, bisphenol A, imipramine and amitriptyline. Overall, this study provided a cheap and easy operational advanced oxidation process in treatment of aqueous organic pollutants.
Journal article
(2017)
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Wei Fang, Panyue Zhang, Ran Shang, Jie Ye, Yan Wu, Haibo Zhang, Jianbo Liu, Xiying Gou, Guangming Zeng, Shuqiong Zhou
In order to improve the efficiency of anaerobic sludge digestion, alkaline and high pressure homogenization (HPH) were combined to pre-treat the excess activated sludge. The effect of HPH operating parameters, including homogenization pressure and cycle number, on the performances of anaerobic sludge digestion was studied. The results demonstrated that the performances of sludge disintegration and anaerobic digestion were markedly enhanced by increasing the homogenization pressure. After pretreatment at a homogenization pressure of 60 MPa with one homogenization cycle combined with an alkaline dosage of 0.04 mol/L, the sludge TCOD, VS removal and cumulative biogas production in a mesophilic anaerobic digestion system increased by 24.68%, 18.95% and 95.81%, respectively, in comparison with that with the alkaline pretreatment alone. But the sludge disintegration and biogas production only slightly increased with the increase of homogenization cycle. Considering biogas production and energy-saving, the suitable homogenization operation was selected as homogenization pressure of 60 MPa with once cycle. Relationships between methane yield and sludge disintegration showed that the improved methane production was mainly attributed to the sludge disintegration resulted from combined sludge pretreatment.
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In order to improve the efficiency of anaerobic sludge digestion, alkaline and high pressure homogenization (HPH) were combined to pre-treat the excess activated sludge. The effect of HPH operating parameters, including homogenization pressure and cycle number, on the performances of anaerobic sludge digestion was studied. The results demonstrated that the performances of sludge disintegration and anaerobic digestion were markedly enhanced by increasing the homogenization pressure. After pretreatment at a homogenization pressure of 60 MPa with one homogenization cycle combined with an alkaline dosage of 0.04 mol/L, the sludge TCOD, VS removal and cumulative biogas production in a mesophilic anaerobic digestion system increased by 24.68%, 18.95% and 95.81%, respectively, in comparison with that with the alkaline pretreatment alone. But the sludge disintegration and biogas production only slightly increased with the increase of homogenization cycle. Considering biogas production and energy-saving, the suitable homogenization operation was selected as homogenization pressure of 60 MPa with once cycle. Relationships between methane yield and sludge disintegration showed that the improved methane production was mainly attributed to the sludge disintegration resulted from combined sludge pretreatment.
Journal article
(2017)
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Ran Shang, A Goulas, CY Tang, Xavier de Frias Serra, Luuk Rietveld, Bas Heijman
Tight ceramic nanofiltration (NF) membranes allow efficient separation of organic matter and ions for advanced water treatment. These membranes are typically produced by the sol-gel method. Recently, atomic layer deposition (ALD), a self-limiting gas phase coating technique, has been explored for membrane fabrication and modification. In this work, the synthesis of tight ceramic NF membranes is demonstrated using atmospheric pressure ALD (APALD), which is operated without a vacuum-generation system compared to the commonly reported vacuum-based ALD method. Titanium dioxide was coated on nano-porous membrane substrates using merely one to three cycles of APALD. The average size of active pores was effectively narrowed by 0.2 nm, from 0.7 to 0.5 nm. In addition, the size distribution of the active pores became more uniform after the APALD modification. The fabricated tight ceramic NF membranes had a molecular weight cut-off (MWCO) ranging from 260 to 380 Da while maintaining high water permeability at 11–16 L m−2 h−1 bar−1, which is notably higher than the commercial tight polymeric NF and sol-gel-made tight ceramic NF membranes. It was observed that conformal TiO2 thin films can be deposited on planar surfaces under the APALD with a growth rate of 0.39 nm per cycle, while the deposition in the membrane micropores was at a lower rate, estimated as 0.05 nm per cycle.
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Tight ceramic nanofiltration (NF) membranes allow efficient separation of organic matter and ions for advanced water treatment. These membranes are typically produced by the sol-gel method. Recently, atomic layer deposition (ALD), a self-limiting gas phase coating technique, has been explored for membrane fabrication and modification. In this work, the synthesis of tight ceramic NF membranes is demonstrated using atmospheric pressure ALD (APALD), which is operated without a vacuum-generation system compared to the commonly reported vacuum-based ALD method. Titanium dioxide was coated on nano-porous membrane substrates using merely one to three cycles of APALD. The average size of active pores was effectively narrowed by 0.2 nm, from 0.7 to 0.5 nm. In addition, the size distribution of the active pores became more uniform after the APALD modification. The fabricated tight ceramic NF membranes had a molecular weight cut-off (MWCO) ranging from 260 to 380 Da while maintaining high water permeability at 11–16 L m−2 h−1 bar−1, which is notably higher than the commercial tight polymeric NF and sol-gel-made tight ceramic NF membranes. It was observed that conformal TiO2 thin films can be deposited on planar surfaces under the APALD with a growth rate of 0.39 nm per cycle, while the deposition in the membrane micropores was at a lower rate, estimated as 0.05 nm per cycle.
Removal of Microcystis aeruginosa by UV-activated persulfate
Performance and characteristics
Cyanobacteria blooms in source waters have become a worldwide issue for drinking water production. UV-activated persulfate (UV/PS) technology was firstly applied to remove cultivated Microcystis aeruginosa (M. aeruginosa) in bench scale. The presence of persulfate significantly enhanced both cytoclasis and algal organic matter mineralization compared with UV-C inactivation alone. Around 98.2% of algal cells were removed after UV/PS process treatment for 2 h at a dosage of PS being 1500 mg/L (approximately 6 mM). Both sulfate and hydroxyl radicals were proven to contribute to the removal of algae and the loss of cell integrity. The cultivated M. aeruginosa in death growth phase were found to be more vulnerable to UV/PS treatment than those growing in log phase, thus a significant lower dosage of PS is needed to achieve the desired removal efficiency. This study suggested a novel application of UV/PS process in the removal of algae in source waters due to the high degradation efficiency of both algal cells and their derived organic matter.
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Cyanobacteria blooms in source waters have become a worldwide issue for drinking water production. UV-activated persulfate (UV/PS) technology was firstly applied to remove cultivated Microcystis aeruginosa (M. aeruginosa) in bench scale. The presence of persulfate significantly enhanced both cytoclasis and algal organic matter mineralization compared with UV-C inactivation alone. Around 98.2% of algal cells were removed after UV/PS process treatment for 2 h at a dosage of PS being 1500 mg/L (approximately 6 mM). Both sulfate and hydroxyl radicals were proven to contribute to the removal of algae and the loss of cell integrity. The cultivated M. aeruginosa in death growth phase were found to be more vulnerable to UV/PS treatment than those growing in log phase, thus a significant lower dosage of PS is needed to achieve the desired removal efficiency. This study suggested a novel application of UV/PS process in the removal of algae in source waters due to the high degradation efficiency of both algal cells and their derived organic matter.
The performance of UV-activated persulfate (UV/PS) technology as preoxidation process to enhanceMicrocystis aeruginosa removal by subsequent coagulation-sedimentation was firstly evaluated. Theresults demonstrate that UV/PS preoxidation could successfully promote coagulation of algae cellsthrough the effective neutralization of zeta potential, which was caused by the changes of cell mor-phology, size distribution and surface properties after simultaneous UV irradiation and formed reactivespecies (i.e. SO4•−and HO•) oxidation. Since excessive oxidation would cause cell rupture along withthe release of organics, which could deteriorate coagulation efficiency, optimal PS dose (60 mg/L) andUV dose (375 mJ/cm2) were proposed to exist in this study. The concentrations of extracellular algal∗
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The performance of UV-activated persulfate (UV/PS) technology as preoxidation process to enhanceMicrocystis aeruginosa removal by subsequent coagulation-sedimentation was firstly evaluated. Theresults demonstrate that UV/PS preoxidation could successfully promote coagulation of algae cellsthrough the effective neutralization of zeta potential, which was caused by the changes of cell mor-phology, size distribution and surface properties after simultaneous UV irradiation and formed reactivespecies (i.e. SO4•−and HO•) oxidation. Since excessive oxidation would cause cell rupture along withthe release of organics, which could deteriorate coagulation efficiency, optimal PS dose (60 mg/L) andUV dose (375 mJ/cm2) were proposed to exist in this study. The concentrations of extracellular algal∗
We report herein the use of ferric iron (Fe 3 + ) and sulfite (SO 3 2 −) to activate persulfate (S 2 O 8 2 −). Decolorization and mineralization of reactive Brilliant Red X-3B (a model azo dye) by an Fe(III)/sulfite/persulfate triple system have been investigated in aqueous solutions. Initial pH and dis- solved oxygen are important factors influencing X-3B decolorization in this system. The rapid decoloriza- tion process occurred in 30 min and about 85% of X-3B was decolorized in this triple system at initial pH 6.0. Moreover, about 66.4% of the TOC was removed through reaction for 36 h. The generation of SO 4 •−and HO •were identified through radical quenching experiments and by electron spin resonance (ESR), which contributed to 61.1% and 28.9% of the oxidation process. Degradation products of X-3B were iden- tified by LC-ESI-MS, and the degradation pathway was proposed. Furthermore, other organic pollutants, such as Orange II, metoprolol, imipramine, naproxen, estradiol, and amitriptyline, could also be efficiently degraded in this triple system. The results of the present work suggest that the Fe(III)/sulfite/persulfate triple system can be used for the rapid decolorization and partial mineralization of dyeing wastewater at near-neutral pH values.
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We report herein the use of ferric iron (Fe 3 + ) and sulfite (SO 3 2 −) to activate persulfate (S 2 O 8 2 −). Decolorization and mineralization of reactive Brilliant Red X-3B (a model azo dye) by an Fe(III)/sulfite/persulfate triple system have been investigated in aqueous solutions. Initial pH and dis- solved oxygen are important factors influencing X-3B decolorization in this system. The rapid decoloriza- tion process occurred in 30 min and about 85% of X-3B was decolorized in this triple system at initial pH 6.0. Moreover, about 66.4% of the TOC was removed through reaction for 36 h. The generation of SO 4 •−and HO •were identified through radical quenching experiments and by electron spin resonance (ESR), which contributed to 61.1% and 28.9% of the oxidation process. Degradation products of X-3B were iden- tified by LC-ESI-MS, and the degradation pathway was proposed. Furthermore, other organic pollutants, such as Orange II, metoprolol, imipramine, naproxen, estradiol, and amitriptyline, could also be efficiently degraded in this triple system. The results of the present work suggest that the Fe(III)/sulfite/persulfate triple system can be used for the rapid decolorization and partial mineralization of dyeing wastewater at near-neutral pH values.
Integrating powdered activated carbon (PAC) into wastewater tertiary treatment is a promising technology to reduce organic micro-pollutant (OMP) discharge into the receiving waters. To take advantage of the existing tertiary filter, PAC was pre-embedded inside the filter bed acting as a fixed-bed adsorber. The pre-embedding (i.e. immobilization) of PAC was realized by direct dosing a PAC solution on the filter top, which was then promoted to penetrate into the filter media by a down-flow of tap water. In order to examine the effectiveness of this PAC pre-embedded filter towards OMP removal, batch adsorption tests, representing PAC contact reactor (with the same PAC mass-to-treated water volume ratio as in the PAC pre-embedded filter) were performed as references. Moreover, as a conventional dosing option, PAC was dosed continuously with the filter influent (i.e. the wastewater secondary effluent with the investigated OMPs). Comparative results confirmed a higher OMP removal efficiency associated with the PAC preembedded filter, as compared to the batch system with a practical PAC residence time. Furthermore, over a filtration period of 10 h (approximating a realistic filtration cycle for tertiary filters), the continuous dosing approach resulted in less OMP removal. Therefore, it was concluded that the pre-embedding approach can be preferentially considered when integrating PAC into the wastewater tertiary treatment for OMP elimination.
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Integrating powdered activated carbon (PAC) into wastewater tertiary treatment is a promising technology to reduce organic micro-pollutant (OMP) discharge into the receiving waters. To take advantage of the existing tertiary filter, PAC was pre-embedded inside the filter bed acting as a fixed-bed adsorber. The pre-embedding (i.e. immobilization) of PAC was realized by direct dosing a PAC solution on the filter top, which was then promoted to penetrate into the filter media by a down-flow of tap water. In order to examine the effectiveness of this PAC pre-embedded filter towards OMP removal, batch adsorption tests, representing PAC contact reactor (with the same PAC mass-to-treated water volume ratio as in the PAC pre-embedded filter) were performed as references. Moreover, as a conventional dosing option, PAC was dosed continuously with the filter influent (i.e. the wastewater secondary effluent with the investigated OMPs). Comparative results confirmed a higher OMP removal efficiency associated with the PAC preembedded filter, as compared to the batch system with a practical PAC residence time. Furthermore, over a filtration period of 10 h (approximating a realistic filtration cycle for tertiary filters), the continuous dosing approach resulted in less OMP removal. Therefore, it was concluded that the pre-embedding approach can be preferentially considered when integrating PAC into the wastewater tertiary treatment for OMP elimination.