Understanding the chemical constraints to plant growth and their amelioration is critical for ero... more Understanding the chemical constraints to plant growth and their amelioration is critical for erosion control and slope stability on artificial landforms. Limited studies have investigated the effects of chemical amendments on grass growth, and effects on soil physical and chemical characteristics on the slope surface. Digitaria setivalva (Mardi Digit grass) was used as a grass coverage to control erosion on the steep man made slope. The current slope studies (45o-50o) on Bungor soil series to address two objectives; (1) to investigate the effects nitrogen (N)-phosphate (P)-potassium fertilizer (NPK) and Bio Green fertilizer (BG) on above-ground and root growth, and (2) to determine physico-chemical properties and root shear strength after application of treatments. The Bungor series was acidic pH (4.63), moderate soil organic carbon (1.42%), total N (0.12%),available P (12.2 mg kg-1) and potassium (0.44 mg kg-1), indicating low inherent infertility and chemical constraints to plant...
Land disposal of agro-processing wastes containing potentially toxic compounds may lead to advers... more Land disposal of agro-processing wastes containing potentially toxic compounds may lead to adverse ecotoxicological effects. Compared to agrochemicals, limited data are available on the ecotoxicological effects of biowastes such as those from citrus fruit processing. The objectives of the current study were:(1) to determine the effects of varying concentrations of citrus waste extract on adult mortality, fecundity and avoidance behaviour of the earthworm species Lumbricus terrestris under laboratory conditions; and (2) to determine earthworm abundance on contaminated and uncontaminated soils under field conditions. The laboratory experiment was a short-term acute toxicity test and it showed that the concentration of citrus extract had a significant (p < 0.05) negative effect on mortality, fecundity and avoidance behaviour. Exponential relationships (p < 0.001) were observed between citrus extract concentration and earthworm mortality (r 2 = 0.98-0.99) and fecundity (r 2 = 0.98), respectively. Tests showed that citrus waste-induced avoidance behaviour in earthworms changed by 44% to 100% compared to the control. Mean effect concentration (EC 50) showed that earthworm avoidance behaviour (47%) was more sensitive to citrus waste concentrations than for number of cocoons (91%) and live earthworm counts (83%). Soil dumping of citrus waste significantly increased the concentration of mineral N, available N and exchange Ca, Mg and K but significantly reduced pH relative to the uncontaminated control. The shifts in chemical properties were about 1-2 orders of magnitude for P and Ca, double for K and approximately 30-60% for pH, N and Mg. Field data showed that the contaminated site had 80%significantly lower earthworm abundance than the uncontaminated control. Overall, the current study revealed that citrus waste has adverse ecotoxicological effects, which threatens the soil biota. Further studies should focus on elucidating the exact mechanisms and exploring the pesticidal effects of citrus extract solutions, particularly on meso-and macroinvertebrates. Investigations are also required to determine the persistence and mobility of the waste in soil and how to restore contaminated soils.
Metallic iron (Fe0) has been increasingly used to remove toxics from water over the past three de... more Metallic iron (Fe0) has been increasingly used to remove toxics from water over the past three decades. However, the idea that metallic iron (Fe0) is not an environmental reducing agent has been vigorously refuted. Researchers presenting their findings in a scientific journal have to accept the burden of proving that their argument has any validity. This 30-year-lasting discussion within the Fe0 remediation community is alien to electro-chemists, as it is a century-old knowledge. Nevertheless, the peer-reviewed literature on “remediation using Fe0” seems to be dominated by evaluators thinking that Fe0 is a reducing agent. This communication challenges the view that Fe0 donates any electron to any dissolved species. The sole goal is to reconcile a proven efficient technology with its scientific roots and enable the design of better Fe0 remediation systems.
Scientific collaboration among various geographically scattered research groups on the broad topi... more Scientific collaboration among various geographically scattered research groups on the broad topic of “metallic iron (Fe0) for water remediation” has evolved greatly over the past three decades. This collaboration has involved different kinds of research partners, including researchers from the same organization and domestic researchers from non-academic organizations as well as international partners. The present analysis of recent publications by some leading scientists shows that after a decade of frank collaboration in search of ways to improve the efficiency of Fe0/H2O systems, the research community has divided itself into two schools of thought since about 2007. Since then, progress in knowledge has stagnated. The first school maintains that Fe0 is a reducing agent for some relevant contaminants. The second school argues that Fe0 in-situ generates flocculants (iron hydroxides) for contaminant scavenging and reducing species (e.g., FeII, H2, and Fe3O4), but reductive transform...
An innovative approach to characterize the reactivity of metallic iron (Fe0) for aqueous contamin... more An innovative approach to characterize the reactivity of metallic iron (Fe0) for aqueous contaminant removal has been in use for a decade: The methylene blue method (MB method). The approach considers the differential adsorptive affinity of methylene blue (MB) for sand and iron oxides. The MB method characterizes MB discoloration by sand as it is progressively coated by in-situ generated iron corrosion products (FeCPs) to deduce the extent of iron corrosion. The MB method is a semi-quantitative tool that has successfully clarified some contradicting reports on the Fe0/H2O system. Moreover, it has the potential to serve as a powerful tool for routine tests in the Fe0 remediation industry, including quality assurance and quality control (QA/QC). However, MB is widely used as a 'molecular probe' to characterize the Fe0/H2O system, for instance for wastewater treatment. Thus, there is scope to avoid confusion created by the multiple uses of MB in Fe0/H2O systems. The present communication aims at filling this gap by presenting the science of the MB method, and its application and limitations. It is concluded that the MB method is very suitable for Fe0 material screening and optimization of operational designs. However, the MB method only provides semi-quantitative information, but gives no data on the solid-phase characterization of solid Fe0 and its reaction products. In other words, further comprehensive investigations with microscopic and spectroscopic surface and solid-state analyses are needed to complement results from the MB method.
Leakage is a common phenomenon in dams, and its early detection is critical for dam safety. In th... more Leakage is a common phenomenon in dams, and its early detection is critical for dam safety. In the present study, a new method based on tracer tests is applied to detect and quantify leakage in the Wanyao Dam, Jiangshan City, China. The objective is to detect the leakage zone of a dam wall by combining the natural tracer test and the artificial tracer test. Temperature, electrical well-logging tests with nature tracers, and the artificial tracer test with salt (NaCl) were conducted using 48 and 5 pre-existing boreholes, respectively. Using natural tracer tests, the 48 boreholes are categorized into 4 leakage classes: (1) Class 1, high connectivity within whole borehole; (2) Class 2 high connectivity at lower depths; (3) Class 3, weaken connectivity; and (4) Class 4, safe boreholes with no connectivity. Using the proposed method, specific leakage rates of some boreholes were estimated. The results of the new method are validated by comparison with those from natural tracer tests, sit...
Metallic iron (Fe0) corrosion under immersed conditions (Fe0/H2O system) has been used for water ... more Metallic iron (Fe0) corrosion under immersed conditions (Fe0/H2O system) has been used for water treatment for the past 170 years. Fe0 generates solid iron corrosion products (FeCPs) which are known to in situ coat the surface of aggregates, including granular activated carbon (GAC), gravel, lapillus, manganese oxide (MnO2), pyrite (FeS2), and sand. While admixing Fe0 and reactive aggregates to build hybrid systems (e.g., Fe0/FeS2, Fe0/MnO2, Fe0/sand) for water treatment, it has been largely overlooked that these materials would experience reactivity loss upon coating. This communication clarifies the relationships between aggregate addition and the sustainability of Fe0/H2O filtration systems. It is shown that any enhanced contaminant removal efficiency in Fe0/aggregate/H2O systems relative to the Fe0/H2O system is related to the avoidance/delay of particle cementation by virtue of the non-expansive nature of the aggregates. The argument that aggregate addition sustains any reducti...
Water pollution due to dyes and pathogens is problematic worldwide, and the disease burden is hig... more Water pollution due to dyes and pathogens is problematic worldwide, and the disease burden is higher in low-income countries where water treatment facilities are usually inadequate. Thus the development of low-cost techniques for the removal of dyes and pathogens in aquatic systems is critical for safeguarding human and ecological health. In this work, we report the fabrication and use of a photocatalyst derived from waste from coal combustion in removing dyes and pathogens from wastewater. Higher TiO2 loading of the photocatalyst increased the removal efficiency for methyl orange (95.5%), and fluorine-doping improved the disinfection efficacy from 76% to 95% relative to unmodified material. Overall, the work effectively converted hazardous waste into a value-added product that has potential in point-of-use water treatment. Future research should focus on upscaling the technique, investigating the fate of the potential of the photocatalysts for multiple reuse, and the recovery of Ti...
The suitability of remediation systems using metallic iron (Fe0) has been extensively discussed d... more The suitability of remediation systems using metallic iron (Fe0) has been extensively discussed during the past 3 decades. It has been established that aqueous Fe0 oxidative dissolution is not caused by the presence of any contaminant. Instead, the reductive transformation of contaminants is a consequence of Fe0 oxidation. Yet researchers are still maintaining that electrons from the metal body are involved in the process of contaminant reduction. According to the electron efficiency concept, electrons from Fe0 should be redistributed to: i) contaminants of concern (COCs), ii) natural reducing agents (e.g., H2O, O2), and/or iii) reducible co-contaminants (e.g. NO3-). The electron efficiency is defined as the fraction of electrons from Fe0 oxidation which is utilized for the reductive transformations of COCs. This concept is in frontal contradiction with the view that Fe0 is not directly involved in the process of contaminant reduction. This communication recalls the universality of ...
Since January 2020 Elsevier has created a COVID-19 resource centre with free information in Engli... more Since January 2020 Elsevier has created a COVID-19 resource centre with free information in English and Mandarin on the novel coronavirus COVID-19. The COVID-19 resource centre is hosted on Elsevier Connect, the company's public news and information website. Elsevier hereby grants permission to make all its COVID-19-related research that is available on the COVID-19 resource centre -including this research content -immediately available in PubMed Central and other publicly funded repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for free by Elsevier for as long as the COVID-19 resource centre remains active. Review Wastewater, waste, and water-based epidemiology (WWW-BE): A novel hypothesis and decision-support tool to unravel COVID-19 in low-income settings?
Inadequate access to safe drinking water is one of the most pervasive problems currently afflicti... more Inadequate access to safe drinking water is one of the most pervasive problems currently afflicting the developing world. Scientists and engineers are called to present affordable but efficient solutions, particularly applicable to small communities. Filtration systems based on metallic iron (Fe0) are discussed in the literature as one such viable solution, whether as a stand-alone system or as a complement to slow sand filters (SSFs). Fe0 filters can also be improved by incorporating biochar to form Fe0-biochar filtration systems with potentially higher contaminant removal efficiencies than those based on Fe0 or biochar alone. These three low-cost and chemical-free systems (Fe0, biochar, SSFs) have the potential to provide universal access to safe drinking water. However, a well-structured systematic research is needed to design robust and efficient water treatment systems based on these affordable filter materials. This communication highlights the technology being developed to us...
Efficient but affordable water treatment technologies are currently sought to solve the prevalent... more Efficient but affordable water treatment technologies are currently sought to solve the prevalent shortage of safe drinking water. Adsorption-based technologies are in the front-line of these efforts. Upon proper design, universally applied materials (e.g., activated carbons, bone chars, metal oxides) are able to quantitatively remove inorganic and organic pollutants as well as pathogens from water. Each water filter has a defined removal capacity and must be replaced when this capacity is exhausted. Operational experience has shown that it may be difficult to convince some low-skilled users to buy new filters after a predicted service life. This communication describes the quest to develop a filter-clock to encourage all users to change their filters after the designed service life. A brief discussion on such a filter-clock based on rusting of metallic iron (Fe 0 ) is presented. Integrating such filter-clocks in the design of water filters is regarded as essential for safeguarding public health.
Understanding the chemical constraints to plant growth and their amelioration is critical for ero... more Understanding the chemical constraints to plant growth and their amelioration is critical for erosion control and slope stability on artificial landforms. Limited studies have investigated the effects of chemical amendments on grass growth, and effects on soil physical and chemical characteristics on the slope surface. Digitaria setivalva (Mardi Digit grass) was used as a grass coverage to control erosion on the steep man made slope. The current slope studies (45o-50o) on Bungor soil series to address two objectives; (1) to investigate the effects nitrogen (N)-phosphate (P)-potassium fertilizer (NPK) and Bio Green fertilizer (BG) on above-ground and root growth, and (2) to determine physico-chemical properties and root shear strength after application of treatments. The Bungor series was acidic pH (4.63), moderate soil organic carbon (1.42%), total N (0.12%),available P (12.2 mg kg-1) and potassium (0.44 mg kg-1), indicating low inherent infertility and chemical constraints to plant...
Land disposal of agro-processing wastes containing potentially toxic compounds may lead to advers... more Land disposal of agro-processing wastes containing potentially toxic compounds may lead to adverse ecotoxicological effects. Compared to agrochemicals, limited data are available on the ecotoxicological effects of biowastes such as those from citrus fruit processing. The objectives of the current study were:(1) to determine the effects of varying concentrations of citrus waste extract on adult mortality, fecundity and avoidance behaviour of the earthworm species Lumbricus terrestris under laboratory conditions; and (2) to determine earthworm abundance on contaminated and uncontaminated soils under field conditions. The laboratory experiment was a short-term acute toxicity test and it showed that the concentration of citrus extract had a significant (p < 0.05) negative effect on mortality, fecundity and avoidance behaviour. Exponential relationships (p < 0.001) were observed between citrus extract concentration and earthworm mortality (r 2 = 0.98-0.99) and fecundity (r 2 = 0.98), respectively. Tests showed that citrus waste-induced avoidance behaviour in earthworms changed by 44% to 100% compared to the control. Mean effect concentration (EC 50) showed that earthworm avoidance behaviour (47%) was more sensitive to citrus waste concentrations than for number of cocoons (91%) and live earthworm counts (83%). Soil dumping of citrus waste significantly increased the concentration of mineral N, available N and exchange Ca, Mg and K but significantly reduced pH relative to the uncontaminated control. The shifts in chemical properties were about 1-2 orders of magnitude for P and Ca, double for K and approximately 30-60% for pH, N and Mg. Field data showed that the contaminated site had 80%significantly lower earthworm abundance than the uncontaminated control. Overall, the current study revealed that citrus waste has adverse ecotoxicological effects, which threatens the soil biota. Further studies should focus on elucidating the exact mechanisms and exploring the pesticidal effects of citrus extract solutions, particularly on meso-and macroinvertebrates. Investigations are also required to determine the persistence and mobility of the waste in soil and how to restore contaminated soils.
Metallic iron (Fe0) has been increasingly used to remove toxics from water over the past three de... more Metallic iron (Fe0) has been increasingly used to remove toxics from water over the past three decades. However, the idea that metallic iron (Fe0) is not an environmental reducing agent has been vigorously refuted. Researchers presenting their findings in a scientific journal have to accept the burden of proving that their argument has any validity. This 30-year-lasting discussion within the Fe0 remediation community is alien to electro-chemists, as it is a century-old knowledge. Nevertheless, the peer-reviewed literature on “remediation using Fe0” seems to be dominated by evaluators thinking that Fe0 is a reducing agent. This communication challenges the view that Fe0 donates any electron to any dissolved species. The sole goal is to reconcile a proven efficient technology with its scientific roots and enable the design of better Fe0 remediation systems.
Scientific collaboration among various geographically scattered research groups on the broad topi... more Scientific collaboration among various geographically scattered research groups on the broad topic of “metallic iron (Fe0) for water remediation” has evolved greatly over the past three decades. This collaboration has involved different kinds of research partners, including researchers from the same organization and domestic researchers from non-academic organizations as well as international partners. The present analysis of recent publications by some leading scientists shows that after a decade of frank collaboration in search of ways to improve the efficiency of Fe0/H2O systems, the research community has divided itself into two schools of thought since about 2007. Since then, progress in knowledge has stagnated. The first school maintains that Fe0 is a reducing agent for some relevant contaminants. The second school argues that Fe0 in-situ generates flocculants (iron hydroxides) for contaminant scavenging and reducing species (e.g., FeII, H2, and Fe3O4), but reductive transform...
An innovative approach to characterize the reactivity of metallic iron (Fe0) for aqueous contamin... more An innovative approach to characterize the reactivity of metallic iron (Fe0) for aqueous contaminant removal has been in use for a decade: The methylene blue method (MB method). The approach considers the differential adsorptive affinity of methylene blue (MB) for sand and iron oxides. The MB method characterizes MB discoloration by sand as it is progressively coated by in-situ generated iron corrosion products (FeCPs) to deduce the extent of iron corrosion. The MB method is a semi-quantitative tool that has successfully clarified some contradicting reports on the Fe0/H2O system. Moreover, it has the potential to serve as a powerful tool for routine tests in the Fe0 remediation industry, including quality assurance and quality control (QA/QC). However, MB is widely used as a 'molecular probe' to characterize the Fe0/H2O system, for instance for wastewater treatment. Thus, there is scope to avoid confusion created by the multiple uses of MB in Fe0/H2O systems. The present communication aims at filling this gap by presenting the science of the MB method, and its application and limitations. It is concluded that the MB method is very suitable for Fe0 material screening and optimization of operational designs. However, the MB method only provides semi-quantitative information, but gives no data on the solid-phase characterization of solid Fe0 and its reaction products. In other words, further comprehensive investigations with microscopic and spectroscopic surface and solid-state analyses are needed to complement results from the MB method.
Leakage is a common phenomenon in dams, and its early detection is critical for dam safety. In th... more Leakage is a common phenomenon in dams, and its early detection is critical for dam safety. In the present study, a new method based on tracer tests is applied to detect and quantify leakage in the Wanyao Dam, Jiangshan City, China. The objective is to detect the leakage zone of a dam wall by combining the natural tracer test and the artificial tracer test. Temperature, electrical well-logging tests with nature tracers, and the artificial tracer test with salt (NaCl) were conducted using 48 and 5 pre-existing boreholes, respectively. Using natural tracer tests, the 48 boreholes are categorized into 4 leakage classes: (1) Class 1, high connectivity within whole borehole; (2) Class 2 high connectivity at lower depths; (3) Class 3, weaken connectivity; and (4) Class 4, safe boreholes with no connectivity. Using the proposed method, specific leakage rates of some boreholes were estimated. The results of the new method are validated by comparison with those from natural tracer tests, sit...
Metallic iron (Fe0) corrosion under immersed conditions (Fe0/H2O system) has been used for water ... more Metallic iron (Fe0) corrosion under immersed conditions (Fe0/H2O system) has been used for water treatment for the past 170 years. Fe0 generates solid iron corrosion products (FeCPs) which are known to in situ coat the surface of aggregates, including granular activated carbon (GAC), gravel, lapillus, manganese oxide (MnO2), pyrite (FeS2), and sand. While admixing Fe0 and reactive aggregates to build hybrid systems (e.g., Fe0/FeS2, Fe0/MnO2, Fe0/sand) for water treatment, it has been largely overlooked that these materials would experience reactivity loss upon coating. This communication clarifies the relationships between aggregate addition and the sustainability of Fe0/H2O filtration systems. It is shown that any enhanced contaminant removal efficiency in Fe0/aggregate/H2O systems relative to the Fe0/H2O system is related to the avoidance/delay of particle cementation by virtue of the non-expansive nature of the aggregates. The argument that aggregate addition sustains any reducti...
Water pollution due to dyes and pathogens is problematic worldwide, and the disease burden is hig... more Water pollution due to dyes and pathogens is problematic worldwide, and the disease burden is higher in low-income countries where water treatment facilities are usually inadequate. Thus the development of low-cost techniques for the removal of dyes and pathogens in aquatic systems is critical for safeguarding human and ecological health. In this work, we report the fabrication and use of a photocatalyst derived from waste from coal combustion in removing dyes and pathogens from wastewater. Higher TiO2 loading of the photocatalyst increased the removal efficiency for methyl orange (95.5%), and fluorine-doping improved the disinfection efficacy from 76% to 95% relative to unmodified material. Overall, the work effectively converted hazardous waste into a value-added product that has potential in point-of-use water treatment. Future research should focus on upscaling the technique, investigating the fate of the potential of the photocatalysts for multiple reuse, and the recovery of Ti...
The suitability of remediation systems using metallic iron (Fe0) has been extensively discussed d... more The suitability of remediation systems using metallic iron (Fe0) has been extensively discussed during the past 3 decades. It has been established that aqueous Fe0 oxidative dissolution is not caused by the presence of any contaminant. Instead, the reductive transformation of contaminants is a consequence of Fe0 oxidation. Yet researchers are still maintaining that electrons from the metal body are involved in the process of contaminant reduction. According to the electron efficiency concept, electrons from Fe0 should be redistributed to: i) contaminants of concern (COCs), ii) natural reducing agents (e.g., H2O, O2), and/or iii) reducible co-contaminants (e.g. NO3-). The electron efficiency is defined as the fraction of electrons from Fe0 oxidation which is utilized for the reductive transformations of COCs. This concept is in frontal contradiction with the view that Fe0 is not directly involved in the process of contaminant reduction. This communication recalls the universality of ...
Since January 2020 Elsevier has created a COVID-19 resource centre with free information in Engli... more Since January 2020 Elsevier has created a COVID-19 resource centre with free information in English and Mandarin on the novel coronavirus COVID-19. The COVID-19 resource centre is hosted on Elsevier Connect, the company's public news and information website. Elsevier hereby grants permission to make all its COVID-19-related research that is available on the COVID-19 resource centre -including this research content -immediately available in PubMed Central and other publicly funded repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for free by Elsevier for as long as the COVID-19 resource centre remains active. Review Wastewater, waste, and water-based epidemiology (WWW-BE): A novel hypothesis and decision-support tool to unravel COVID-19 in low-income settings?
Inadequate access to safe drinking water is one of the most pervasive problems currently afflicti... more Inadequate access to safe drinking water is one of the most pervasive problems currently afflicting the developing world. Scientists and engineers are called to present affordable but efficient solutions, particularly applicable to small communities. Filtration systems based on metallic iron (Fe0) are discussed in the literature as one such viable solution, whether as a stand-alone system or as a complement to slow sand filters (SSFs). Fe0 filters can also be improved by incorporating biochar to form Fe0-biochar filtration systems with potentially higher contaminant removal efficiencies than those based on Fe0 or biochar alone. These three low-cost and chemical-free systems (Fe0, biochar, SSFs) have the potential to provide universal access to safe drinking water. However, a well-structured systematic research is needed to design robust and efficient water treatment systems based on these affordable filter materials. This communication highlights the technology being developed to us...
Efficient but affordable water treatment technologies are currently sought to solve the prevalent... more Efficient but affordable water treatment technologies are currently sought to solve the prevalent shortage of safe drinking water. Adsorption-based technologies are in the front-line of these efforts. Upon proper design, universally applied materials (e.g., activated carbons, bone chars, metal oxides) are able to quantitatively remove inorganic and organic pollutants as well as pathogens from water. Each water filter has a defined removal capacity and must be replaced when this capacity is exhausted. Operational experience has shown that it may be difficult to convince some low-skilled users to buy new filters after a predicted service life. This communication describes the quest to develop a filter-clock to encourage all users to change their filters after the designed service life. A brief discussion on such a filter-clock based on rusting of metallic iron (Fe 0 ) is presented. Integrating such filter-clocks in the design of water filters is regarded as essential for safeguarding public health.
Uploads
Papers by Willis Gwenzi