The ferrite process is an established method for treating wastewaters containing dissolved toxic ... more The ferrite process is an established method for treating wastewaters containing dissolved toxic metals, using precipitation at temperatures above 65 • C. Various ambient-temperature operation methodologies have also been proposed, but the effects of temperature reduction on product stability, and on the extent of isomorphous substitution (in terms of x in Me x Fe 3-x O 4 , Me representing a non-iron metal), have not been adequately quantified. At ambient temperature precipitation, maximal x of Zn 2+ , Co 2+ , Ni 2+ and Cd 2+ was found in the current study to be approximately 0.73, 0.67, 0.39 and 0.17, respectively. These values are 73% to 50% of the corresponding values attained by precipitation at 90 • C. The chemical stability of the ferrites produced under ambient temperatures was found to deteriorate upon high Me 2+ incorporation levels, in stark contrast with the trend observed in ferrites precipitated at 90 • C. Both observations were ascribed to the increased importance of Fe 2+ -Fe 3+ interaction under ambient conditions in driving spinel ordering. In the presence of high Me to Fe ratio in the initial solution, this interaction is weaker, resulting in impeded dehydration.
Removal of heavy metals (HM) from industrial wastewater is of primary environmental importance. T... more Removal of heavy metals (HM) from industrial wastewater is of primary environmental importance. The seeded ambient temperature ferrite process, in which heavy metals are removed from solution by their incorporation into a magnetite structure, is an attractive alternative for both complete metals separation and generation of stable magnetic sludge. Despite its potential, the effects of various operational parameters on the composition and stability of the final product are not fully understood to-date. The current paper addresses the combined effect of selected operational parameters on Co 2+ incorporation efficiency. Co 2+ , which is used in many industries (e.g., plating, alloys manufacturing, catalytic converters, and paint pigments) and hence may pose a significant environment risk, was shown previously to be incorporated successfully into ferrite structures. Co 2+ -bearing ferrites were synthesized from Fe(II) solutions at ambient temperature (20 and 30°C), applying slow oxidation, pH 10.5, 20 g (as Fe) l -1 ferrite seed, and different Fe 2+ to Co 2+ influent ratios. Pure magnetite was used as an initial seed, which was gradually exchanged, as the reaction proceeded, by the Co 2+ -bearing ferrite generated within the reactor (until full exchange at steady state). Under all conditions investigated >99% of the Co 2+ was removed from solution (yielding Co 2+ levels below 20 μg/l in the effluent) while the generated precipitates were composed predominately of magnetite/ferrite (based on XRD analysis). Favorable results in terms of Co 2+ incorporation efficiency and sludge stability were obtained when the following operational conditions were applied: 1:10 Co 2+ :Fe 2+ molar influent ratio, 30°C, 1,500 mgFe 2+ l -1 metal intermediate concentration, and 16 h aging period (pH 10.5).
A lab-scale activated-sludge type reactor was used to induce denitrification by using the organic... more A lab-scale activated-sludge type reactor was used to induce denitrification by using the organic solid waste of a typical Recirculating Aquaculture System (RAS) as the electron donor ('Single-sludge denitrification'). The results were compared with the predictions of a stoichiometry-based model. As predicted by the model, reactor's performance was found to be strongly related to the mean solids retention time (SRT) employed. Measured denitrification rates conformed very well to model predictions. High nitrate removal rates of up to 590 mg N (L reactor d d) -1 were recorded at a relatively low SRT of 4 d. Oxygen, that entered the reactor via both atmospheric diffusion and with the stream used to simulate the influent from a fish tank, reduced the amount of organic matter available for denitrification, resulting in lower denitrification rates. This interference was more significant when the system was operated at the longer SRTs. Most of the excess ammonia released to the aqueous phase through ammonification was oxidized (presumably by anammox bacteria) under the prevailing anoxic conditions, resulting in very low effluent TAN concentrations. Phosphate release to the aqueous phase was significantly lower than predicted, suggesting above-typical microbial P assimilation. Reaction kinetics was found to be zero order with respect to nitrate at concentrations of above 1.5 to 2.0 mg N L -1 . Taken together the findings indicate that intensive single-sludge denitrification for treating RAS effluents is technically feasible, and that the process appears to be a cost-effective solution to reducing both the nutrient and the organic loads generated by intensive fish farms. The main advantages of the method include minimal formation of undesired by-products, small reactor volume and simple control and operation. Furthermore, the process is well described by a conceptual mathematical model, allowing its application as a part of any RAS design.
h i g h l i g h t s g r a p h i c a l a b s t r a c t Kinetics of seeded aeration softening in re... more h i g h l i g h t s g r a p h i c a l a b s t r a c t Kinetics of seeded aeration softening in real desalination concentrate was assessed. Reaction followed zero,1st, or 2nd order kinetics, depending on aeration rate. Aeration rate and seed concentration increased mass transfer constant linearly. Up to 73% of calcium was removed as calcite at up to 1.05 g-CaCO 3 L À1 h À1 . Calcite may be recovered to reduce operational costs.
Separation and Purification Technology, Sep 1, 2013
ABSTRACT Selenate (SeO42-) is a toxic soluble compound and its presence in the environment should... more ABSTRACT Selenate (SeO42-) is a toxic soluble compound and its presence in the environment should be minimized. Reduction of selenate ions by elemental iron is a promising approach for treating contaminated waters. However, uncertainty exists regarding both the favorable conditions required and the associated mechanisms. In this study, the kinetics and mechanisms of selenate removal using Fe degrees at different pH and aeration rates was investigated using quantitative measurement of reactants and products. Under acidic anaerobic conditions, selenate was reduced directly by Fe degrees. Limited aeration increased removal rates by up to four times due to formation of reactive Fe(II)-bearing solid intermediates on the iron surface. Further increase in aeration rate decreased removal rates but also decreased iron release and acid consumption. Under basic conditions, selenate by Fe degrees was negligible under anaerobic conditions and low under limited aeration. Selenate removal rates were shown to be dependent on Se concentration, on available reducing solid surface and on competition with oxygen over electrons. (c) 2013 Elsevier B.V. All rights reserved.
Supercapacitors are energy storage devices that have the ability to be charged and discharged muc... more Supercapacitors are energy storage devices that have the ability to be charged and discharged much faster than batteries but suffer from low energy density. In researching the influence of pore dimensions of activated carbon to increase energy storage, we reported earlier that there can be a significant fraction of charge held in activated carbon that has a very long redistribution time constant, at least for the carbon source with which we were working. This implies that the energy density could be increased if we can understand the reasons for charge redistribution. In this paper, the research has been extended to include other commercial carbon sources and similar charge redistribution phenomenon has been found. The effect of temperature has been studied to understand the phenomenon of charge redistribution in activated carbon supercapacitors.
In the near future, the discharge of nitrate from recirculating aquaculture systems (RAS) to rece... more In the near future, the discharge of nitrate from recirculating aquaculture systems (RAS) to receiving water bodies is expected to be constrained by environmental regulations. Following wastewater treatment terminology, nitrate removal that makes use of the organic solid wastes generated within the RAS as the energy source for denitrification, may be termed 'single-sludge denitrification'. In this approach, the costs associated with the addition of an external carbon source, the treatment of solid-wastes generated in the RAS, and the supplementation of alkalinity are reduced. The simple and economical operation of such a process can be realized by adopting the conventional activated sludge (AS) methodology. Organic solid-wastes taken from the solids-filter of a RAS growing gilthead seabream were characterized for their chemical and biodegradation properties. The results were used to generate a conceptual model to predict the performance of single-sludge denitrification in RAS. The model was run under typical operational conditions, employing the mean solids retention time (SRT) as the key operational parameter. Results indicated that in order to attain high denitrification rates, the ratio of the flux of organic solids (as COD) supplied to the denitrification reactor to the flux of NO 3 -reduced should be between 4.0 and 6.0 g COD (g NO 3 -N) -1 and the SRT values should be lower than 10 d. At these conditions, sludge production was estimated to be between 40% and 60% of the solids feed mass (in terms of COD), and NH 3 -N production as a result of ammonification was estimated to be less than 10% of the NO 3 --N removed. Empirical verification of the model is presented elsewhere. The model can be used as a design tool and for predicting the performance of the process at any operational conditions.
The ferrite process is an established method for treating wastewaters containing dissolved toxic ... more The ferrite process is an established method for treating wastewaters containing dissolved toxic metals, using precipitation at temperatures above 65 • C. Various ambient-temperature operation methodologies have also been proposed, but the effects of temperature reduction on product stability, and on the extent of isomorphous substitution (in terms of x in Me x Fe 3-x O 4 , Me representing a non-iron metal), have not been adequately quantified. At ambient temperature precipitation, maximal x of Zn 2+ , Co 2+ , Ni 2+ and Cd 2+ was found in the current study to be approximately 0.73, 0.67, 0.39 and 0.17, respectively. These values are 73% to 50% of the corresponding values attained by precipitation at 90 • C. The chemical stability of the ferrites produced under ambient temperatures was found to deteriorate upon high Me 2+ incorporation levels, in stark contrast with the trend observed in ferrites precipitated at 90 • C. Both observations were ascribed to the increased importance of Fe 2+ -Fe 3+ interaction under ambient conditions in driving spinel ordering. In the presence of high Me to Fe ratio in the initial solution, this interaction is weaker, resulting in impeded dehydration.
Journal of Technology and Science Education, Jul 29, 2021
Technology-enriched lessons can contribute to improving student engagement and learning in engine... more Technology-enriched lessons can contribute to improving student engagement and learning in engineering courses. In this study we systematically incorporated Kahoot!, a game-based response system, in two mandatory content-intensive undergraduate engineering courses. In both courses, short quizzes were incorporated regularly at the beginning of the lesson. The questions were mostly about concepts, and students earned bonus points. At the end of the course, the students filled in an anonymous survey regarding their perceptions of the Kahoot! part of the lessons. In addition, the students' grades in the final test were compared to their gains in the Kahoot! quizzes. We found that student satisfaction with the systematic incorporation of the Kahoot! quizzes was high in both courses. Most students were motivated to review the course content before class and about half were motivated to attend class. Most students perceived Kahoot! quizzes as contributing to their understanding of the course content. We also found a positive association between student success in the quizzes and their performance in the final exam in both courses. The frequent Kahoot! quizzes supplied continuous feedback to the students and lecturers, and the students became more engaged in the course content. Our findings indicate that technologyenriched strategies, specifically gamification techniques, contribute to increased student engagement, motivation, and performance in content-intensive engineering courses.
Removal of heavy metals (HM) from industrial wastewater is of primary environmental importance. T... more Removal of heavy metals (HM) from industrial wastewater is of primary environmental importance. The seeded ambient temperature ferrite process, in which heavy metals are removed from solution by their incorporation into a magnetite structure, is an attractive alternative for both complete metals separation and generation of stable magnetic sludge. Despite its potential, the effects of various operational parameters on the composition and stability of the final product are not fully understood to-date. The current paper addresses the combined effect of selected operational parameters on Co 2+ incorporation efficiency. Co 2+ , which is used in many industries (e.g., plating, alloys manufacturing, catalytic converters, and paint pigments) and hence may pose a significant environment risk, was shown previously to be incorporated successfully into ferrite structures. Co 2+ -bearing ferrites were synthesized from Fe(II) solutions at ambient temperature (20 and 30°C), applying slow oxidation, pH 10.5, 20 g (as Fe) l -1 ferrite seed, and different Fe 2+ to Co 2+ influent ratios. Pure magnetite was used as an initial seed, which was gradually exchanged, as the reaction proceeded, by the Co 2+ -bearing ferrite generated within the reactor (until full exchange at steady state). Under all conditions investigated >99% of the Co 2+ was removed from solution (yielding Co 2+ levels below 20 μg/l in the effluent) while the generated precipitates were composed predominately of magnetite/ferrite (based on XRD analysis). Favorable results in terms of Co 2+ incorporation efficiency and sludge stability were obtained when the following operational conditions were applied: 1:10 Co 2+ :Fe 2+ molar influent ratio, 30°C, 1,500 mgFe 2+ l -1 metal intermediate concentration, and 16 h aging period (pH 10.5).
A lab-scale activated-sludge type reactor was used to induce denitrification by using the organic... more A lab-scale activated-sludge type reactor was used to induce denitrification by using the organic solid waste of a typical Recirculating Aquaculture System (RAS) as the electron donor ('Single-sludge denitrification'). The results were compared with the predictions of a stoichiometry-based model. As predicted by the model, reactor's performance was found to be strongly related to the mean solids retention time (SRT) employed. Measured denitrification rates conformed very well to model predictions. High nitrate removal rates of up to 590 mg N (L reactor d d) -1 were recorded at a relatively low SRT of 4 d. Oxygen, that entered the reactor via both atmospheric diffusion and with the stream used to simulate the influent from a fish tank, reduced the amount of organic matter available for denitrification, resulting in lower denitrification rates. This interference was more significant when the system was operated at the longer SRTs. Most of the excess ammonia released to the aqueous phase through ammonification was oxidized (presumably by anammox bacteria) under the prevailing anoxic conditions, resulting in very low effluent TAN concentrations. Phosphate release to the aqueous phase was significantly lower than predicted, suggesting above-typical microbial P assimilation. Reaction kinetics was found to be zero order with respect to nitrate at concentrations of above 1.5 to 2.0 mg N L -1 . Taken together the findings indicate that intensive single-sludge denitrification for treating RAS effluents is technically feasible, and that the process appears to be a cost-effective solution to reducing both the nutrient and the organic loads generated by intensive fish farms. The main advantages of the method include minimal formation of undesired by-products, small reactor volume and simple control and operation. Furthermore, the process is well described by a conceptual mathematical model, allowing its application as a part of any RAS design.
h i g h l i g h t s g r a p h i c a l a b s t r a c t Kinetics of seeded aeration softening in re... more h i g h l i g h t s g r a p h i c a l a b s t r a c t Kinetics of seeded aeration softening in real desalination concentrate was assessed. Reaction followed zero,1st, or 2nd order kinetics, depending on aeration rate. Aeration rate and seed concentration increased mass transfer constant linearly. Up to 73% of calcium was removed as calcite at up to 1.05 g-CaCO 3 L À1 h À1 . Calcite may be recovered to reduce operational costs.
Separation and Purification Technology, Sep 1, 2013
ABSTRACT Selenate (SeO42-) is a toxic soluble compound and its presence in the environment should... more ABSTRACT Selenate (SeO42-) is a toxic soluble compound and its presence in the environment should be minimized. Reduction of selenate ions by elemental iron is a promising approach for treating contaminated waters. However, uncertainty exists regarding both the favorable conditions required and the associated mechanisms. In this study, the kinetics and mechanisms of selenate removal using Fe degrees at different pH and aeration rates was investigated using quantitative measurement of reactants and products. Under acidic anaerobic conditions, selenate was reduced directly by Fe degrees. Limited aeration increased removal rates by up to four times due to formation of reactive Fe(II)-bearing solid intermediates on the iron surface. Further increase in aeration rate decreased removal rates but also decreased iron release and acid consumption. Under basic conditions, selenate by Fe degrees was negligible under anaerobic conditions and low under limited aeration. Selenate removal rates were shown to be dependent on Se concentration, on available reducing solid surface and on competition with oxygen over electrons. (c) 2013 Elsevier B.V. All rights reserved.
Supercapacitors are energy storage devices that have the ability to be charged and discharged muc... more Supercapacitors are energy storage devices that have the ability to be charged and discharged much faster than batteries but suffer from low energy density. In researching the influence of pore dimensions of activated carbon to increase energy storage, we reported earlier that there can be a significant fraction of charge held in activated carbon that has a very long redistribution time constant, at least for the carbon source with which we were working. This implies that the energy density could be increased if we can understand the reasons for charge redistribution. In this paper, the research has been extended to include other commercial carbon sources and similar charge redistribution phenomenon has been found. The effect of temperature has been studied to understand the phenomenon of charge redistribution in activated carbon supercapacitors.
In the near future, the discharge of nitrate from recirculating aquaculture systems (RAS) to rece... more In the near future, the discharge of nitrate from recirculating aquaculture systems (RAS) to receiving water bodies is expected to be constrained by environmental regulations. Following wastewater treatment terminology, nitrate removal that makes use of the organic solid wastes generated within the RAS as the energy source for denitrification, may be termed 'single-sludge denitrification'. In this approach, the costs associated with the addition of an external carbon source, the treatment of solid-wastes generated in the RAS, and the supplementation of alkalinity are reduced. The simple and economical operation of such a process can be realized by adopting the conventional activated sludge (AS) methodology. Organic solid-wastes taken from the solids-filter of a RAS growing gilthead seabream were characterized for their chemical and biodegradation properties. The results were used to generate a conceptual model to predict the performance of single-sludge denitrification in RAS. The model was run under typical operational conditions, employing the mean solids retention time (SRT) as the key operational parameter. Results indicated that in order to attain high denitrification rates, the ratio of the flux of organic solids (as COD) supplied to the denitrification reactor to the flux of NO 3 -reduced should be between 4.0 and 6.0 g COD (g NO 3 -N) -1 and the SRT values should be lower than 10 d. At these conditions, sludge production was estimated to be between 40% and 60% of the solids feed mass (in terms of COD), and NH 3 -N production as a result of ammonification was estimated to be less than 10% of the NO 3 --N removed. Empirical verification of the model is presented elsewhere. The model can be used as a design tool and for predicting the performance of the process at any operational conditions.
Grey mullet fingerlings were grown in different acclimation solutions for three consecutive years... more Grey mullet fingerlings were grown in different acclimation solutions for three consecutive years, with the aim of developing a procedure for their adjustment to commercial growth in very low salinity (EC = 0.37 dS/m) and Cl -/Na + -deficient inland water (Dan River water, Northern Israel). Tested acclimation conditions composed of simulative solutions of varying ionic compositions (EC range 1.0-1.1 dS/m) and a solution made up by dissolving quarry dolomite beads into the target (Dan River) water by H 2 SO 4 without and with a small NaCl addition (1.5 mM). The latter alternative was favored because of its low production costs and minimal environmental impact (minute addition of extrinsic Na + and Cl -ions to the environment). The results obtained in the three experimental sets showed that stocking the fingerlings in a ∼1 dS/m acclimation solution for 1 week, followed by 20% daily dilution by the target water, was appropriate for attaining survival rates higher than 70% in all acclimation solutions tested (growth periods varied in the range 43-77 d). Survival rate in brackish water control experiments was 85-95%. In the absence of an acclimation period the fish survival rate was ∼35%. No significant difference was observed in fish growth rates between treatments conducted in a given year, suggesting that fish that survived the acclimation period would grow in the low salinity water at a rate similar to fish grown in brackish water. The minor differences in survival and growth results between the different acclimation solutions seemed to indicate that the role of specific ionic constituents in the water was inconsequential and that the most significant parameter is the overall water salinity. However, histological analyses revealed that applying the acclimation period with very low Cl -and Na + concentrations (<∼75 mg/L and ∼45 mg/L, respectively) caused non-reversible adverse effects on the fish, whereas in all of the other treatments recorded adverse effects were of a reversible nature. Considering all the results, the best acclimation solution was defined as dissolution of dolomite by H 2 SO 4 into the target low-salinity water plus addition of 1.5 mM of NaCl. The cost of producing the acclimation solution was shown to amount to only ∼0.03% of the overall culture cost.
The ferrite process is an established method for treating wastewaters containing dissolved toxic ... more The ferrite process is an established method for treating wastewaters containing dissolved toxic metals, using precipitation at temperatures above 65 • C. Various ambient-temperature operation methodologies have also been proposed, but the effects of temperature reduction on product stability, and on the extent of isomorphous substitution (in terms of x in Me x Fe 3-x O 4 , Me representing a non-iron metal), have not been adequately quantified. At ambient temperature precipitation, maximal x of Zn 2+ , Co 2+ , Ni 2+ and Cd 2+ was found in the current study to be approximately 0.73, 0.67, 0.39 and 0.17, respectively. These values are 73% to 50% of the corresponding values attained by precipitation at 90 • C. The chemical stability of the ferrites produced under ambient temperatures was found to deteriorate upon high Me 2+ incorporation levels, in stark contrast with the trend observed in ferrites precipitated at 90 • C. Both observations were ascribed to the increased importance of Fe 2+ -Fe 3+ interaction under ambient conditions in driving spinel ordering. In the presence of high Me to Fe ratio in the initial solution, this interaction is weaker, resulting in impeded dehydration.
Removal of heavy metals (HM) from industrial wastewater is of primary environmental importance. T... more Removal of heavy metals (HM) from industrial wastewater is of primary environmental importance. The seeded ambient temperature ferrite process, in which heavy metals are removed from solution by their incorporation into a magnetite structure, is an attractive alternative for both complete metals separation and generation of stable magnetic sludge. Despite its potential, the effects of various operational parameters on the composition and stability of the final product are not fully understood to-date. The current paper addresses the combined effect of selected operational parameters on Co 2+ incorporation efficiency. Co 2+ , which is used in many industries (e.g., plating, alloys manufacturing, catalytic converters, and paint pigments) and hence may pose a significant environment risk, was shown previously to be incorporated successfully into ferrite structures. Co 2+ -bearing ferrites were synthesized from Fe(II) solutions at ambient temperature (20 and 30°C), applying slow oxidation, pH 10.5, 20 g (as Fe) l -1 ferrite seed, and different Fe 2+ to Co 2+ influent ratios. Pure magnetite was used as an initial seed, which was gradually exchanged, as the reaction proceeded, by the Co 2+ -bearing ferrite generated within the reactor (until full exchange at steady state). Under all conditions investigated >99% of the Co 2+ was removed from solution (yielding Co 2+ levels below 20 μg/l in the effluent) while the generated precipitates were composed predominately of magnetite/ferrite (based on XRD analysis). Favorable results in terms of Co 2+ incorporation efficiency and sludge stability were obtained when the following operational conditions were applied: 1:10 Co 2+ :Fe 2+ molar influent ratio, 30°C, 1,500 mgFe 2+ l -1 metal intermediate concentration, and 16 h aging period (pH 10.5).
A lab-scale activated-sludge type reactor was used to induce denitrification by using the organic... more A lab-scale activated-sludge type reactor was used to induce denitrification by using the organic solid waste of a typical Recirculating Aquaculture System (RAS) as the electron donor ('Single-sludge denitrification'). The results were compared with the predictions of a stoichiometry-based model. As predicted by the model, reactor's performance was found to be strongly related to the mean solids retention time (SRT) employed. Measured denitrification rates conformed very well to model predictions. High nitrate removal rates of up to 590 mg N (L reactor d d) -1 were recorded at a relatively low SRT of 4 d. Oxygen, that entered the reactor via both atmospheric diffusion and with the stream used to simulate the influent from a fish tank, reduced the amount of organic matter available for denitrification, resulting in lower denitrification rates. This interference was more significant when the system was operated at the longer SRTs. Most of the excess ammonia released to the aqueous phase through ammonification was oxidized (presumably by anammox bacteria) under the prevailing anoxic conditions, resulting in very low effluent TAN concentrations. Phosphate release to the aqueous phase was significantly lower than predicted, suggesting above-typical microbial P assimilation. Reaction kinetics was found to be zero order with respect to nitrate at concentrations of above 1.5 to 2.0 mg N L -1 . Taken together the findings indicate that intensive single-sludge denitrification for treating RAS effluents is technically feasible, and that the process appears to be a cost-effective solution to reducing both the nutrient and the organic loads generated by intensive fish farms. The main advantages of the method include minimal formation of undesired by-products, small reactor volume and simple control and operation. Furthermore, the process is well described by a conceptual mathematical model, allowing its application as a part of any RAS design.
h i g h l i g h t s g r a p h i c a l a b s t r a c t Kinetics of seeded aeration softening in re... more h i g h l i g h t s g r a p h i c a l a b s t r a c t Kinetics of seeded aeration softening in real desalination concentrate was assessed. Reaction followed zero,1st, or 2nd order kinetics, depending on aeration rate. Aeration rate and seed concentration increased mass transfer constant linearly. Up to 73% of calcium was removed as calcite at up to 1.05 g-CaCO 3 L À1 h À1 . Calcite may be recovered to reduce operational costs.
Separation and Purification Technology, Sep 1, 2013
ABSTRACT Selenate (SeO42-) is a toxic soluble compound and its presence in the environment should... more ABSTRACT Selenate (SeO42-) is a toxic soluble compound and its presence in the environment should be minimized. Reduction of selenate ions by elemental iron is a promising approach for treating contaminated waters. However, uncertainty exists regarding both the favorable conditions required and the associated mechanisms. In this study, the kinetics and mechanisms of selenate removal using Fe degrees at different pH and aeration rates was investigated using quantitative measurement of reactants and products. Under acidic anaerobic conditions, selenate was reduced directly by Fe degrees. Limited aeration increased removal rates by up to four times due to formation of reactive Fe(II)-bearing solid intermediates on the iron surface. Further increase in aeration rate decreased removal rates but also decreased iron release and acid consumption. Under basic conditions, selenate by Fe degrees was negligible under anaerobic conditions and low under limited aeration. Selenate removal rates were shown to be dependent on Se concentration, on available reducing solid surface and on competition with oxygen over electrons. (c) 2013 Elsevier B.V. All rights reserved.
Supercapacitors are energy storage devices that have the ability to be charged and discharged muc... more Supercapacitors are energy storage devices that have the ability to be charged and discharged much faster than batteries but suffer from low energy density. In researching the influence of pore dimensions of activated carbon to increase energy storage, we reported earlier that there can be a significant fraction of charge held in activated carbon that has a very long redistribution time constant, at least for the carbon source with which we were working. This implies that the energy density could be increased if we can understand the reasons for charge redistribution. In this paper, the research has been extended to include other commercial carbon sources and similar charge redistribution phenomenon has been found. The effect of temperature has been studied to understand the phenomenon of charge redistribution in activated carbon supercapacitors.
In the near future, the discharge of nitrate from recirculating aquaculture systems (RAS) to rece... more In the near future, the discharge of nitrate from recirculating aquaculture systems (RAS) to receiving water bodies is expected to be constrained by environmental regulations. Following wastewater treatment terminology, nitrate removal that makes use of the organic solid wastes generated within the RAS as the energy source for denitrification, may be termed 'single-sludge denitrification'. In this approach, the costs associated with the addition of an external carbon source, the treatment of solid-wastes generated in the RAS, and the supplementation of alkalinity are reduced. The simple and economical operation of such a process can be realized by adopting the conventional activated sludge (AS) methodology. Organic solid-wastes taken from the solids-filter of a RAS growing gilthead seabream were characterized for their chemical and biodegradation properties. The results were used to generate a conceptual model to predict the performance of single-sludge denitrification in RAS. The model was run under typical operational conditions, employing the mean solids retention time (SRT) as the key operational parameter. Results indicated that in order to attain high denitrification rates, the ratio of the flux of organic solids (as COD) supplied to the denitrification reactor to the flux of NO 3 -reduced should be between 4.0 and 6.0 g COD (g NO 3 -N) -1 and the SRT values should be lower than 10 d. At these conditions, sludge production was estimated to be between 40% and 60% of the solids feed mass (in terms of COD), and NH 3 -N production as a result of ammonification was estimated to be less than 10% of the NO 3 --N removed. Empirical verification of the model is presented elsewhere. The model can be used as a design tool and for predicting the performance of the process at any operational conditions.
The ferrite process is an established method for treating wastewaters containing dissolved toxic ... more The ferrite process is an established method for treating wastewaters containing dissolved toxic metals, using precipitation at temperatures above 65 • C. Various ambient-temperature operation methodologies have also been proposed, but the effects of temperature reduction on product stability, and on the extent of isomorphous substitution (in terms of x in Me x Fe 3-x O 4 , Me representing a non-iron metal), have not been adequately quantified. At ambient temperature precipitation, maximal x of Zn 2+ , Co 2+ , Ni 2+ and Cd 2+ was found in the current study to be approximately 0.73, 0.67, 0.39 and 0.17, respectively. These values are 73% to 50% of the corresponding values attained by precipitation at 90 • C. The chemical stability of the ferrites produced under ambient temperatures was found to deteriorate upon high Me 2+ incorporation levels, in stark contrast with the trend observed in ferrites precipitated at 90 • C. Both observations were ascribed to the increased importance of Fe 2+ -Fe 3+ interaction under ambient conditions in driving spinel ordering. In the presence of high Me to Fe ratio in the initial solution, this interaction is weaker, resulting in impeded dehydration.
Journal of Technology and Science Education, Jul 29, 2021
Technology-enriched lessons can contribute to improving student engagement and learning in engine... more Technology-enriched lessons can contribute to improving student engagement and learning in engineering courses. In this study we systematically incorporated Kahoot!, a game-based response system, in two mandatory content-intensive undergraduate engineering courses. In both courses, short quizzes were incorporated regularly at the beginning of the lesson. The questions were mostly about concepts, and students earned bonus points. At the end of the course, the students filled in an anonymous survey regarding their perceptions of the Kahoot! part of the lessons. In addition, the students' grades in the final test were compared to their gains in the Kahoot! quizzes. We found that student satisfaction with the systematic incorporation of the Kahoot! quizzes was high in both courses. Most students were motivated to review the course content before class and about half were motivated to attend class. Most students perceived Kahoot! quizzes as contributing to their understanding of the course content. We also found a positive association between student success in the quizzes and their performance in the final exam in both courses. The frequent Kahoot! quizzes supplied continuous feedback to the students and lecturers, and the students became more engaged in the course content. Our findings indicate that technologyenriched strategies, specifically gamification techniques, contribute to increased student engagement, motivation, and performance in content-intensive engineering courses.
Removal of heavy metals (HM) from industrial wastewater is of primary environmental importance. T... more Removal of heavy metals (HM) from industrial wastewater is of primary environmental importance. The seeded ambient temperature ferrite process, in which heavy metals are removed from solution by their incorporation into a magnetite structure, is an attractive alternative for both complete metals separation and generation of stable magnetic sludge. Despite its potential, the effects of various operational parameters on the composition and stability of the final product are not fully understood to-date. The current paper addresses the combined effect of selected operational parameters on Co 2+ incorporation efficiency. Co 2+ , which is used in many industries (e.g., plating, alloys manufacturing, catalytic converters, and paint pigments) and hence may pose a significant environment risk, was shown previously to be incorporated successfully into ferrite structures. Co 2+ -bearing ferrites were synthesized from Fe(II) solutions at ambient temperature (20 and 30°C), applying slow oxidation, pH 10.5, 20 g (as Fe) l -1 ferrite seed, and different Fe 2+ to Co 2+ influent ratios. Pure magnetite was used as an initial seed, which was gradually exchanged, as the reaction proceeded, by the Co 2+ -bearing ferrite generated within the reactor (until full exchange at steady state). Under all conditions investigated >99% of the Co 2+ was removed from solution (yielding Co 2+ levels below 20 μg/l in the effluent) while the generated precipitates were composed predominately of magnetite/ferrite (based on XRD analysis). Favorable results in terms of Co 2+ incorporation efficiency and sludge stability were obtained when the following operational conditions were applied: 1:10 Co 2+ :Fe 2+ molar influent ratio, 30°C, 1,500 mgFe 2+ l -1 metal intermediate concentration, and 16 h aging period (pH 10.5).
A lab-scale activated-sludge type reactor was used to induce denitrification by using the organic... more A lab-scale activated-sludge type reactor was used to induce denitrification by using the organic solid waste of a typical Recirculating Aquaculture System (RAS) as the electron donor ('Single-sludge denitrification'). The results were compared with the predictions of a stoichiometry-based model. As predicted by the model, reactor's performance was found to be strongly related to the mean solids retention time (SRT) employed. Measured denitrification rates conformed very well to model predictions. High nitrate removal rates of up to 590 mg N (L reactor d d) -1 were recorded at a relatively low SRT of 4 d. Oxygen, that entered the reactor via both atmospheric diffusion and with the stream used to simulate the influent from a fish tank, reduced the amount of organic matter available for denitrification, resulting in lower denitrification rates. This interference was more significant when the system was operated at the longer SRTs. Most of the excess ammonia released to the aqueous phase through ammonification was oxidized (presumably by anammox bacteria) under the prevailing anoxic conditions, resulting in very low effluent TAN concentrations. Phosphate release to the aqueous phase was significantly lower than predicted, suggesting above-typical microbial P assimilation. Reaction kinetics was found to be zero order with respect to nitrate at concentrations of above 1.5 to 2.0 mg N L -1 . Taken together the findings indicate that intensive single-sludge denitrification for treating RAS effluents is technically feasible, and that the process appears to be a cost-effective solution to reducing both the nutrient and the organic loads generated by intensive fish farms. The main advantages of the method include minimal formation of undesired by-products, small reactor volume and simple control and operation. Furthermore, the process is well described by a conceptual mathematical model, allowing its application as a part of any RAS design.
h i g h l i g h t s g r a p h i c a l a b s t r a c t Kinetics of seeded aeration softening in re... more h i g h l i g h t s g r a p h i c a l a b s t r a c t Kinetics of seeded aeration softening in real desalination concentrate was assessed. Reaction followed zero,1st, or 2nd order kinetics, depending on aeration rate. Aeration rate and seed concentration increased mass transfer constant linearly. Up to 73% of calcium was removed as calcite at up to 1.05 g-CaCO 3 L À1 h À1 . Calcite may be recovered to reduce operational costs.
Separation and Purification Technology, Sep 1, 2013
ABSTRACT Selenate (SeO42-) is a toxic soluble compound and its presence in the environment should... more ABSTRACT Selenate (SeO42-) is a toxic soluble compound and its presence in the environment should be minimized. Reduction of selenate ions by elemental iron is a promising approach for treating contaminated waters. However, uncertainty exists regarding both the favorable conditions required and the associated mechanisms. In this study, the kinetics and mechanisms of selenate removal using Fe degrees at different pH and aeration rates was investigated using quantitative measurement of reactants and products. Under acidic anaerobic conditions, selenate was reduced directly by Fe degrees. Limited aeration increased removal rates by up to four times due to formation of reactive Fe(II)-bearing solid intermediates on the iron surface. Further increase in aeration rate decreased removal rates but also decreased iron release and acid consumption. Under basic conditions, selenate by Fe degrees was negligible under anaerobic conditions and low under limited aeration. Selenate removal rates were shown to be dependent on Se concentration, on available reducing solid surface and on competition with oxygen over electrons. (c) 2013 Elsevier B.V. All rights reserved.
Supercapacitors are energy storage devices that have the ability to be charged and discharged muc... more Supercapacitors are energy storage devices that have the ability to be charged and discharged much faster than batteries but suffer from low energy density. In researching the influence of pore dimensions of activated carbon to increase energy storage, we reported earlier that there can be a significant fraction of charge held in activated carbon that has a very long redistribution time constant, at least for the carbon source with which we were working. This implies that the energy density could be increased if we can understand the reasons for charge redistribution. In this paper, the research has been extended to include other commercial carbon sources and similar charge redistribution phenomenon has been found. The effect of temperature has been studied to understand the phenomenon of charge redistribution in activated carbon supercapacitors.
In the near future, the discharge of nitrate from recirculating aquaculture systems (RAS) to rece... more In the near future, the discharge of nitrate from recirculating aquaculture systems (RAS) to receiving water bodies is expected to be constrained by environmental regulations. Following wastewater treatment terminology, nitrate removal that makes use of the organic solid wastes generated within the RAS as the energy source for denitrification, may be termed 'single-sludge denitrification'. In this approach, the costs associated with the addition of an external carbon source, the treatment of solid-wastes generated in the RAS, and the supplementation of alkalinity are reduced. The simple and economical operation of such a process can be realized by adopting the conventional activated sludge (AS) methodology. Organic solid-wastes taken from the solids-filter of a RAS growing gilthead seabream were characterized for their chemical and biodegradation properties. The results were used to generate a conceptual model to predict the performance of single-sludge denitrification in RAS. The model was run under typical operational conditions, employing the mean solids retention time (SRT) as the key operational parameter. Results indicated that in order to attain high denitrification rates, the ratio of the flux of organic solids (as COD) supplied to the denitrification reactor to the flux of NO 3 -reduced should be between 4.0 and 6.0 g COD (g NO 3 -N) -1 and the SRT values should be lower than 10 d. At these conditions, sludge production was estimated to be between 40% and 60% of the solids feed mass (in terms of COD), and NH 3 -N production as a result of ammonification was estimated to be less than 10% of the NO 3 --N removed. Empirical verification of the model is presented elsewhere. The model can be used as a design tool and for predicting the performance of the process at any operational conditions.
Grey mullet fingerlings were grown in different acclimation solutions for three consecutive years... more Grey mullet fingerlings were grown in different acclimation solutions for three consecutive years, with the aim of developing a procedure for their adjustment to commercial growth in very low salinity (EC = 0.37 dS/m) and Cl -/Na + -deficient inland water (Dan River water, Northern Israel). Tested acclimation conditions composed of simulative solutions of varying ionic compositions (EC range 1.0-1.1 dS/m) and a solution made up by dissolving quarry dolomite beads into the target (Dan River) water by H 2 SO 4 without and with a small NaCl addition (1.5 mM). The latter alternative was favored because of its low production costs and minimal environmental impact (minute addition of extrinsic Na + and Cl -ions to the environment). The results obtained in the three experimental sets showed that stocking the fingerlings in a ∼1 dS/m acclimation solution for 1 week, followed by 20% daily dilution by the target water, was appropriate for attaining survival rates higher than 70% in all acclimation solutions tested (growth periods varied in the range 43-77 d). Survival rate in brackish water control experiments was 85-95%. In the absence of an acclimation period the fish survival rate was ∼35%. No significant difference was observed in fish growth rates between treatments conducted in a given year, suggesting that fish that survived the acclimation period would grow in the low salinity water at a rate similar to fish grown in brackish water. The minor differences in survival and growth results between the different acclimation solutions seemed to indicate that the role of specific ionic constituents in the water was inconsequential and that the most significant parameter is the overall water salinity. However, histological analyses revealed that applying the acclimation period with very low Cl -and Na + concentrations (<∼75 mg/L and ∼45 mg/L, respectively) caused non-reversible adverse effects on the fish, whereas in all of the other treatments recorded adverse effects were of a reversible nature. Considering all the results, the best acclimation solution was defined as dissolution of dolomite by H 2 SO 4 into the target low-salinity water plus addition of 1.5 mM of NaCl. The cost of producing the acclimation solution was shown to amount to only ∼0.03% of the overall culture cost.
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Papers by Sivan Klas