RS
R. Shang
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1
Recently, the use of atomic layer deposition (ALD) technique for depositing thin films of metal oxides on membrane substrates has proved to be an effective way to fabricate commercially available UF or NF membranes to get tight UF/NF ceramic membranes. The main advantage of this technique is controlled deposition of a monolayer of metal oxides. This project was done to study the effect of ALD on 0.5 m long tubular membranes. TiO2 was deposited on the membranes by means of atmospheric pressure atomic layer deposition (APALD). This is different from most of the reported studies that use vacuum-based ALD. TiCl4 and H2O were used as the main precursors for depositing TiO2 through 2, 3 or 4 cycles of APALD. The growth rate of the deposited layer per cycle under different experimental conditions was measured indirectly using silicon wafers through ellipsometry. The effect of ALD was determined by measuring the membrane permeability and molecular weight cut-off (MWCO) values of the membranes before and after coating. The results obtained showed a variation in growth rate per cycle (GPC) of the deposited layers for different experimental conditions. APALD was performed on 6 membranes and the GPC rate was acceptable for only 2 membranes (0.14 nm/cycle and 0.03 nm/cycle), whereas the GPC for the other membranes was very high (more than 1 nm/cycle). After deposition, the 2 membranes with acceptable GPC rate showed a decrease in MWCO value by 627 Da and 405 Da respectively. These results demonstrated that APALD could be used to fabricate ceramic membranes, but only at proper experimental conditions for TiO2 deposition. An improved Carman-Kozeny model was also developed based on the MWCO value and on the GPC value, in order to predict the porosity and the permeability of the membranes. The results of the model and the measured permeability were compared; for some membranes, the model predicted correctly the permeability after coating.
...
Recently, the use of atomic layer deposition (ALD) technique for depositing thin films of metal oxides on membrane substrates has proved to be an effective way to fabricate commercially available UF or NF membranes to get tight UF/NF ceramic membranes. The main advantage of this technique is controlled deposition of a monolayer of metal oxides. This project was done to study the effect of ALD on 0.5 m long tubular membranes. TiO2 was deposited on the membranes by means of atmospheric pressure atomic layer deposition (APALD). This is different from most of the reported studies that use vacuum-based ALD. TiCl4 and H2O were used as the main precursors for depositing TiO2 through 2, 3 or 4 cycles of APALD. The growth rate of the deposited layer per cycle under different experimental conditions was measured indirectly using silicon wafers through ellipsometry. The effect of ALD was determined by measuring the membrane permeability and molecular weight cut-off (MWCO) values of the membranes before and after coating. The results obtained showed a variation in growth rate per cycle (GPC) of the deposited layers for different experimental conditions. APALD was performed on 6 membranes and the GPC rate was acceptable for only 2 membranes (0.14 nm/cycle and 0.03 nm/cycle), whereas the GPC for the other membranes was very high (more than 1 nm/cycle). After deposition, the 2 membranes with acceptable GPC rate showed a decrease in MWCO value by 627 Da and 405 Da respectively. These results demonstrated that APALD could be used to fabricate ceramic membranes, but only at proper experimental conditions for TiO2 deposition. An improved Carman-Kozeny model was also developed based on the MWCO value and on the GPC value, in order to predict the porosity and the permeability of the membranes. The results of the model and the measured permeability were compared; for some membranes, the model predicted correctly the permeability after coating.
Master thesis
(2019)
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Yundan Wang, Niels van Linden, H. Spanjers, Ran Shang, Jules van Lier, Xuerui Wang
Nitrogen (N) removal is one of the key tasks for every wastewater treatment plant under the growing pressure of environmental protection. Prevailing applied N treatment technologies are mostly energy-intensive. This dilemma triggers a rethinking of the way to approach N management. “N2kWh-From pollutant to power” is a project that aims at creating an energy-positive 푁 treatment system by exploiting the energy potential stored in reduced N compounds. Both thermal and electrical energy needed in this scheme will be provided by Solid Oxide Fuel Cell (SOFC) using the ammonia recovered from wastewater. To guarantee a proper function of the SOFC a minimum of 5 wt% of ammonia in the gas mixture is a prerequisite, whereas, the reject water of anaerobic digester only typically contains 0.15 wt%. Therefore, selectively stripping NH3 in waste streams is the main technical bottleneck of this project.This study aims at contributing to the understanding of selective transport of NH3 by pervaporation. A comprehensive literature study indicates silica-based ceramic membrane is able to perform this selective transport. Therefore, the task of this research was to test the feasibility of selective transport of NH3 by commercially available silica-based pervaporation membranes (hydrophobic PDMS and hydrophilic Hybrid Si AR). The objective was to find the optimum operating condition for maximizing the selective transport of NH3 by silica-based ceramic pervaporation membrane. To this end, the impact of flow regime (laminar and turbulent flow), temperature (35 oC and 45 oC), presence of additional salt (NaCl and Na2CO3) and TAN concentrations (total ammonium nitrogen; 1.5, 12.0 and 20.0 g TAN·L-1, respectively) was assessed through a series of systematic experiments.It was found that the PDMS membrane was unable to selectively transport NH3 from liquid solution because both H2O and NH3 are polar molecules while the hydrophobic PDMS was nonpolar. Besides, the PDMS membrane tested was not stable under solutions used in this study.The results of Hybrid Si pervaporation membrane showed that the optimum operating conditions for selective transport of NH3 was 35 oC, Re=2,400, 20.0 g TAN·L-1 ammonium bicarbonate solution (pH adjusted to 10). For these conditions, the highest perm-selectivity (ratio of mass transfer coefficients of NH3 and H2O) was 0.5 indicting NH3 was less selectively transported than H2O.The impact of flow regime on selective transport of NH3 was related to polarization effects and depended on TAN concentration in feed solution. In the tested temperature and TAN concentration range, perm-selectivity was independent on both parameters. In addition, the effect of both temperature and TAN concentration on the ammonia was mainly due to the driving force, so their influence on the perm-selectivity was limited. Presence of salt seemed to have a positive impact on the perm-selectivity. Although salt has little impact on the mass transfer coefficient of NH3, it decreased the mass transfer of H2O resulting in a better selective transport of NH3.As for energy consumption, it was inversely related to TAN content. At the optimum operating condition 7 MJ·kg-1 - N was consumed by pervaporation in this study. Compared with the energy consumption of air stripping, pervaporation is a promising technology for NH3 recovery.
...
Nitrogen (N) removal is one of the key tasks for every wastewater treatment plant under the growing pressure of environmental protection. Prevailing applied N treatment technologies are mostly energy-intensive. This dilemma triggers a rethinking of the way to approach N management. “N2kWh-From pollutant to power” is a project that aims at creating an energy-positive 푁 treatment system by exploiting the energy potential stored in reduced N compounds. Both thermal and electrical energy needed in this scheme will be provided by Solid Oxide Fuel Cell (SOFC) using the ammonia recovered from wastewater. To guarantee a proper function of the SOFC a minimum of 5 wt% of ammonia in the gas mixture is a prerequisite, whereas, the reject water of anaerobic digester only typically contains 0.15 wt%. Therefore, selectively stripping NH3 in waste streams is the main technical bottleneck of this project.This study aims at contributing to the understanding of selective transport of NH3 by pervaporation. A comprehensive literature study indicates silica-based ceramic membrane is able to perform this selective transport. Therefore, the task of this research was to test the feasibility of selective transport of NH3 by commercially available silica-based pervaporation membranes (hydrophobic PDMS and hydrophilic Hybrid Si AR). The objective was to find the optimum operating condition for maximizing the selective transport of NH3 by silica-based ceramic pervaporation membrane. To this end, the impact of flow regime (laminar and turbulent flow), temperature (35 oC and 45 oC), presence of additional salt (NaCl and Na2CO3) and TAN concentrations (total ammonium nitrogen; 1.5, 12.0 and 20.0 g TAN·L-1, respectively) was assessed through a series of systematic experiments.It was found that the PDMS membrane was unable to selectively transport NH3 from liquid solution because both H2O and NH3 are polar molecules while the hydrophobic PDMS was nonpolar. Besides, the PDMS membrane tested was not stable under solutions used in this study.The results of Hybrid Si pervaporation membrane showed that the optimum operating conditions for selective transport of NH3 was 35 oC, Re=2,400, 20.0 g TAN·L-1 ammonium bicarbonate solution (pH adjusted to 10). For these conditions, the highest perm-selectivity (ratio of mass transfer coefficients of NH3 and H2O) was 0.5 indicting NH3 was less selectively transported than H2O.The impact of flow regime on selective transport of NH3 was related to polarization effects and depended on TAN concentration in feed solution. In the tested temperature and TAN concentration range, perm-selectivity was independent on both parameters. In addition, the effect of both temperature and TAN concentration on the ammonia was mainly due to the driving force, so their influence on the perm-selectivity was limited. Presence of salt seemed to have a positive impact on the perm-selectivity. Although salt has little impact on the mass transfer coefficient of NH3, it decreased the mass transfer of H2O resulting in a better selective transport of NH3.As for energy consumption, it was inversely related to TAN content. At the optimum operating condition 7 MJ·kg-1 - N was consumed by pervaporation in this study. Compared with the energy consumption of air stripping, pervaporation is a promising technology for NH3 recovery.
Ceramic membranes are gaining more and more attention due to their inherent advan- tages compared with polymeric membranes. Their high thermal, mechanical and chem- ical stability make them more applicable in treating e.g. corrosive and hot wastewater. With their small pore sizes, the ceramic tight ultrafiltration (tight UF) membranes show a greater selectivity than ceramic UF or microfiltration (MF) membranes. However, low permeability and unstable membrane quality were observed using most commercially available ceramic tight UF membranes.
Atomic layer deposition (ALD), have come up as an important technique for deposit- ing thin films, and have turned out to be a good potential alternative to produce tight UF ceramic membranes from ceramic UF or MF membranes, due to its capability of con- trolled deposition of a one single atom layer film.
In this study, we explored the potential of ALD in the fabrication of tight UF ceramic membranes from normal sol-gel made UF ceramic membranes with various initial pore sizes. Since the resistance against flux within a porous membrane is mainly from the separation layer, we primarily focused on the coating depth of the coated membranes by the ALD technology. In addition a relation was found between the coating depth and the performance of the coated membranes.
The results of the experiments demonstrate that ALD method could successfully be used in the fabrication of tight UF ceramic membranes and, to some extent, cure the defects in the original membranes. By applying different ALD settings, different coating depths in the membrane filtration layer were achieved, which influenced the water per- meability and solute rejection. Further, membranes with larger pore sizes tended to have a deeper effective coating depth since the precursors could diffuse more easily through the larger pores. The Carmen Kozeny model, used to determine the permeability and porosity for each studied membrane, showed results in the same order of magnitude with most of the measurement data, being thus able to predict permeability as a func- tion of porosity and layer thickness. ...
Atomic layer deposition (ALD), have come up as an important technique for deposit- ing thin films, and have turned out to be a good potential alternative to produce tight UF ceramic membranes from ceramic UF or MF membranes, due to its capability of con- trolled deposition of a one single atom layer film.
In this study, we explored the potential of ALD in the fabrication of tight UF ceramic membranes from normal sol-gel made UF ceramic membranes with various initial pore sizes. Since the resistance against flux within a porous membrane is mainly from the separation layer, we primarily focused on the coating depth of the coated membranes by the ALD technology. In addition a relation was found between the coating depth and the performance of the coated membranes.
The results of the experiments demonstrate that ALD method could successfully be used in the fabrication of tight UF ceramic membranes and, to some extent, cure the defects in the original membranes. By applying different ALD settings, different coating depths in the membrane filtration layer were achieved, which influenced the water per- meability and solute rejection. Further, membranes with larger pore sizes tended to have a deeper effective coating depth since the precursors could diffuse more easily through the larger pores. The Carmen Kozeny model, used to determine the permeability and porosity for each studied membrane, showed results in the same order of magnitude with most of the measurement data, being thus able to predict permeability as a func- tion of porosity and layer thickness. ...
Ceramic membranes are gaining more and more attention due to their inherent advan- tages compared with polymeric membranes. Their high thermal, mechanical and chem- ical stability make them more applicable in treating e.g. corrosive and hot wastewater. With their small pore sizes, the ceramic tight ultrafiltration (tight UF) membranes show a greater selectivity than ceramic UF or microfiltration (MF) membranes. However, low permeability and unstable membrane quality were observed using most commercially available ceramic tight UF membranes.
Atomic layer deposition (ALD), have come up as an important technique for deposit- ing thin films, and have turned out to be a good potential alternative to produce tight UF ceramic membranes from ceramic UF or MF membranes, due to its capability of con- trolled deposition of a one single atom layer film.
In this study, we explored the potential of ALD in the fabrication of tight UF ceramic membranes from normal sol-gel made UF ceramic membranes with various initial pore sizes. Since the resistance against flux within a porous membrane is mainly from the separation layer, we primarily focused on the coating depth of the coated membranes by the ALD technology. In addition a relation was found between the coating depth and the performance of the coated membranes.
The results of the experiments demonstrate that ALD method could successfully be used in the fabrication of tight UF ceramic membranes and, to some extent, cure the defects in the original membranes. By applying different ALD settings, different coating depths in the membrane filtration layer were achieved, which influenced the water per- meability and solute rejection. Further, membranes with larger pore sizes tended to have a deeper effective coating depth since the precursors could diffuse more easily through the larger pores. The Carmen Kozeny model, used to determine the permeability and porosity for each studied membrane, showed results in the same order of magnitude with most of the measurement data, being thus able to predict permeability as a func- tion of porosity and layer thickness.
Atomic layer deposition (ALD), have come up as an important technique for deposit- ing thin films, and have turned out to be a good potential alternative to produce tight UF ceramic membranes from ceramic UF or MF membranes, due to its capability of con- trolled deposition of a one single atom layer film.
In this study, we explored the potential of ALD in the fabrication of tight UF ceramic membranes from normal sol-gel made UF ceramic membranes with various initial pore sizes. Since the resistance against flux within a porous membrane is mainly from the separation layer, we primarily focused on the coating depth of the coated membranes by the ALD technology. In addition a relation was found between the coating depth and the performance of the coated membranes.
The results of the experiments demonstrate that ALD method could successfully be used in the fabrication of tight UF ceramic membranes and, to some extent, cure the defects in the original membranes. By applying different ALD settings, different coating depths in the membrane filtration layer were achieved, which influenced the water per- meability and solute rejection. Further, membranes with larger pore sizes tended to have a deeper effective coating depth since the precursors could diffuse more easily through the larger pores. The Carmen Kozeny model, used to determine the permeability and porosity for each studied membrane, showed results in the same order of magnitude with most of the measurement data, being thus able to predict permeability as a func- tion of porosity and layer thickness.
Ceramic nanofiltration membranes
Rejection of salts and NOM at high ionic strength and modification of pore size by atomic layer deposition
Master thesis
(2018)
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Liying Feng, Luuk Rietveld, Sebastiaan Heijman, Irene Caltran, Ran Shang, Frank Dirne
Natural Organic Matter (NOM) is always present in the drinking water sources such as rivers, lakes and reservoirs. It causes several problems, including the unfavourable colour and odour of water, formation of disinfectant by-products and harmful microbial growth. In drinking water treatment, anion exchange (anion-IEX) is used for NOM removal. However, the regeneration of anion-IEX produces a brine, which is a high saline waste stream containing the desorbed NOM and anions (i.e. sulphate) as well as the residual sodium chloride added during the regeneration process.
One possible approach to manage the waste brine is to recover the valuable compounds from the brine, and consequently, reduce the brine volume that has to be disposed. The separation could be done by ceramic nanofiltration (NF) membranes. However, the separation performance of ceramic NF membranes at high salinity conditions is still not fully understood. Therefore, the use of ceramic NF membranes to treat the brine-like wastes that contain NOM and high salt concentrations were investigated.
Commercial 500 Dalton(Da) ceramic NF membranes were used in the salt experiments. Several experimental conditions such as pH and ionic strength were investigated to understand their influence on the rejection of sulphate (SO42-) and chloride (Cl-). The results show that the salt rejection was governed by charge effect, and it changed depending on pH and ionic strength. When ionic strength was 0.1M, the mitigated charge effect led to a low rejection of SO42- (<20%) and Cl- (<5%) by the 500Da membranes. On the other hand, the 560Da membrane used in salt&NOM experiments exhibited more than 95% rejection of NOM but less than 25% rejection of both SO42- and Cl- when ionic strength was 1M.
Since the 500Da membranes were unable to reject divalent ions at high ionic strength, it is suggested to decrease the membrane pore size to achieve the separation of SO42- and Cl-. The size of pores in ceramic membranes can be narrowed down by an approach called Atomic Layer Deposition (ALD) (Shang et al., 2017). In this study, the vacuum TiO2 ALD was applied to coat thin films on the commercial ceramic NF membranes that have Molecular weight cut-off (MWCO) ranging from 600Da to 900Da. After the first coating, the water permeability of the membranes decreased dramatically while the MWCO of the membranes decreased slightly. After the second coating, an increased MWCO was observed, which might be attributed to the plugging of small pores. In addition, the flux distribution and pore size distribution were theoretically analysed to investigate the change of the membrane pores before and after ALD.
...
Natural Organic Matter (NOM) is always present in the drinking water sources such as rivers, lakes and reservoirs. It causes several problems, including the unfavourable colour and odour of water, formation of disinfectant by-products and harmful microbial growth. In drinking water treatment, anion exchange (anion-IEX) is used for NOM removal. However, the regeneration of anion-IEX produces a brine, which is a high saline waste stream containing the desorbed NOM and anions (i.e. sulphate) as well as the residual sodium chloride added during the regeneration process.
One possible approach to manage the waste brine is to recover the valuable compounds from the brine, and consequently, reduce the brine volume that has to be disposed. The separation could be done by ceramic nanofiltration (NF) membranes. However, the separation performance of ceramic NF membranes at high salinity conditions is still not fully understood. Therefore, the use of ceramic NF membranes to treat the brine-like wastes that contain NOM and high salt concentrations were investigated.
Commercial 500 Dalton(Da) ceramic NF membranes were used in the salt experiments. Several experimental conditions such as pH and ionic strength were investigated to understand their influence on the rejection of sulphate (SO42-) and chloride (Cl-). The results show that the salt rejection was governed by charge effect, and it changed depending on pH and ionic strength. When ionic strength was 0.1M, the mitigated charge effect led to a low rejection of SO42- (<20%) and Cl- (<5%) by the 500Da membranes. On the other hand, the 560Da membrane used in salt&NOM experiments exhibited more than 95% rejection of NOM but less than 25% rejection of both SO42- and Cl- when ionic strength was 1M.
Since the 500Da membranes were unable to reject divalent ions at high ionic strength, it is suggested to decrease the membrane pore size to achieve the separation of SO42- and Cl-. The size of pores in ceramic membranes can be narrowed down by an approach called Atomic Layer Deposition (ALD) (Shang et al., 2017). In this study, the vacuum TiO2 ALD was applied to coat thin films on the commercial ceramic NF membranes that have Molecular weight cut-off (MWCO) ranging from 600Da to 900Da. After the first coating, the water permeability of the membranes decreased dramatically while the MWCO of the membranes decreased slightly. After the second coating, an increased MWCO was observed, which might be attributed to the plugging of small pores. In addition, the flux distribution and pore size distribution were theoretically analysed to investigate the change of the membrane pores before and after ALD.
Pressure driven membranes have become increasingly popular in removal of natural organic matter (NOM). With the purpose to tailor pore size of membrane to remove NOM effectively, atomic layer deposition (ALD) was applied on the ceramic nanofiltration (NF) membrane with a pore size of 1.3 nm. Ceramic membranes were chosen as the substrate membrane due to their high physical strength and high chemical resistance. TiO2 was deposited on the membrane by using TiCl4 and H2O as precursors. After deposition with 3 cycles, MWCO of the ceramic membranes was reduced by ~ 250 Da. The pore size of the ceramic membranes was correspondingly narrowed down by ~ 0.16 nm. The growth per cycle of TiO2 on the pore walls was ~ 0.272 nm/cycle. An improved Carman-Kozeny model was used to estimate water permeability. With the help of two scenarios, the model results are close to the results from water permeability experiments that the water permeability decreased from ~ 24 퐿 h%& m%( bar%& to ~ 6 퐿 h%& m%( bar%&. The application of the fabricated membrane in water treatment could be investigated in the further study.
...
Pressure driven membranes have become increasingly popular in removal of natural organic matter (NOM). With the purpose to tailor pore size of membrane to remove NOM effectively, atomic layer deposition (ALD) was applied on the ceramic nanofiltration (NF) membrane with a pore size of 1.3 nm. Ceramic membranes were chosen as the substrate membrane due to their high physical strength and high chemical resistance. TiO2 was deposited on the membrane by using TiCl4 and H2O as precursors. After deposition with 3 cycles, MWCO of the ceramic membranes was reduced by ~ 250 Da. The pore size of the ceramic membranes was correspondingly narrowed down by ~ 0.16 nm. The growth per cycle of TiO2 on the pore walls was ~ 0.272 nm/cycle. An improved Carman-Kozeny model was used to estimate water permeability. With the help of two scenarios, the model results are close to the results from water permeability experiments that the water permeability decreased from ~ 24 퐿 h%& m%( bar%& to ~ 6 퐿 h%& m%( bar%&. The application of the fabricated membrane in water treatment could be investigated in the further study.