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Lactic acid bacteria (LAB) such as Enterococcus spp. have an advantage over several bacteria because of their ability to easily adapt to extreme conditions which include high temperatures, highly acidic or alkaline conditions and toxic metals. Although many microorganisms have been shown to reduce selenite (SeO32−) to elemental selenium (Se0), not much work has been done on the combined effect of Enterococcus spp. In this study, aerobic batch reduction of different selenite concentrations (1, 3 and 5 mM) was conducted using Enterococcus hermanniensis sp. and Enterococcus gallinarum sp. (3.5 h, 35 ± 2 °C, starting pH > 8.5). Results from the experiments showed that the average reductions rates were 0.608, 1.921 and 3.238 mmol·(L·h)−1, for the 1, 3 and 5 mM SeO32− concentrations respectively. In addition, more selenite was reduced for the 5 mM concentration compared to the 1 and 3 mM concentrations albeit constant biomass being used for all experiments. Other parameters which were monitored were the glucose consumption rate, protein variation, pH and ORP (oxidation reduction potential). TEM analysis was also conducted and it showed the location of electron-dense selenium nanoparticles (SeNPs). From the results obtained in this study, the authors concluded that Enterococcus species’s high adaptability makes it suitable for rapid selenium reduction and biosynthesis of elemental selenium.
Job T. Tendenedzai; Evans M. N. Chirwa; Hendrik G. Brink. Performance Evaluation of Selenite (SeO32−) Reduction by Enterococcus spp. Catalysts 2021, 11, 1024 .
AMA StyleJob T. Tendenedzai, Evans M. N. Chirwa, Hendrik G. Brink. Performance Evaluation of Selenite (SeO32−) Reduction by Enterococcus spp. Catalysts. 2021; 11 (9):1024.
Chicago/Turabian StyleJob T. Tendenedzai; Evans M. N. Chirwa; Hendrik G. Brink. 2021. "Performance Evaluation of Selenite (SeO32−) Reduction by Enterococcus spp." Catalysts 11, no. 9: 1024.
The objective of the study was to gather insight into the metabolism of lead-removing microorganisms, coupled with Pb(II) removal, biomass viability and nitrate concentrations for Pb(II) bioremoval using an industrially obtained microbial consortium. The consortium used for study has proven to be highly effective at removing aqueous Pb(II) from solution. Anaerobic batch experiments were conducted with Luria-Bertani broth as rich growth medium over a period of 33 h, comparing a lower concentration of Pb(II) with a higher concentration at two different nutrient concentrations. Metabolite profiling and quantification were conducted with the aid of both liquid chromatography coupled with tandem mass spectroscopy (UPLC-HDMS) in a “non-targeted” fashion and high-performance liquid chromatography (HPLC) in a “targeted” fashion. Four main compounds were identified, and a metabolic study was conducted on each to establish their possible significance for Pb(II) bioremoval. The study investigates the first metabolic profile to date for Pb(II) bioremoval, which in turn can result in a clarified understanding for development on an industrial and microbial level.
Carla Cilliers; Evans Chirwa; Hendrik Brink. Insight into the Metabolic Profiles of Pb(II) Removing Microorganisms. Molecules 2021, 26, 4008 .
AMA StyleCarla Cilliers, Evans Chirwa, Hendrik Brink. Insight into the Metabolic Profiles of Pb(II) Removing Microorganisms. Molecules. 2021; 26 (13):4008.
Chicago/Turabian StyleCarla Cilliers; Evans Chirwa; Hendrik Brink. 2021. "Insight into the Metabolic Profiles of Pb(II) Removing Microorganisms." Molecules 26, no. 13: 4008.
Microbial fuel cell (MFC) architectural modification is increasingly becoming an important area of research due to the need to improve energy recovery. This study presents a low-cost modification method of the anode that does not require pre-treatment-step involving hazardous chemicals to improve performance. The modification step involves deposition of granular activated carbon (GAC) which is highly conductive and provides a high specific surface area inside a carbon cloth that acts as an anode and as a supporting material. The GAC particle size of 0.6–1.1 mm resulted in an increase in air-cathode MFC performance due to an increase in available surface area of 879.5 m2 g−1 for attachment of cells based on Brunauer, Emmett, and Teller (BET) results, and an increase in the appropriate surface for attachment of cells which was rough based on the scanning electron microscope (SEM) results. On the other hand, although GAC with size of particles of 0.45–0.6 mm had the highest available surface area for attachment of cells, it lacked the appropriate surface for attachment of cells and reduced MFC performance. This means that particle size optimization of GAC is essential since there is a limit to which the particle diameter can be reduced. The utilization of the GAC with the optimized particle size produced an output voltage of 507.5 mV and maximum power output of 1287.7 mW m−3 at current output of 2537.5 mA m−3. This study also showed that there is an economic benefit in modifying carbon cloth using GAC with optimized particle size.
Mpumelelo T. Matsena; Mziwenene Mabuse; Shepherd M. Tichapondwa; Evans M.N. Chirwa. Improved performance and cost efficiency by surface area optimization of granular activated carbon in air-cathode microbial fuel cell. Chemosphere 2021, 281, 130941 .
AMA StyleMpumelelo T. Matsena, Mziwenene Mabuse, Shepherd M. Tichapondwa, Evans M.N. Chirwa. Improved performance and cost efficiency by surface area optimization of granular activated carbon in air-cathode microbial fuel cell. Chemosphere. 2021; 281 ():130941.
Chicago/Turabian StyleMpumelelo T. Matsena; Mziwenene Mabuse; Shepherd M. Tichapondwa; Evans M.N. Chirwa. 2021. "Improved performance and cost efficiency by surface area optimization of granular activated carbon in air-cathode microbial fuel cell." Chemosphere 281, no. : 130941.
The main objective of this study was to achieve the continuous biorecovery and bioreduction of Pb(II) using an industrially obtained consortia as a biocatalyst. An upflow anaerobic sludge blanket reactor was used in the treatment process. The bioremediation technique that was applied made use of a yeast extract as the microbial substrate and Pb(NO3)2 as the source of Pb(II). The UASB reactor exhibited removal efficiencies of between 90 and 100% for the inlet Pb concentrations from 80 to 2000 ppm and a maximum removal rate of 1948.4 mg/(L·d) was measured. XRD and XPS analyses of the precipitate revealed the presence of Pb0, PbO, PbS and PbSO4. Supporting experimental work carried out included growth measurements, pH, oxidation–reduction potentials and nitrate levels.
Jeremiah Chimhundi; Carla Hörstmann; Evans Chirwa; Hendrik Brink. Microbial Removal of Pb(II) Using an Upflow Anaerobic Sludge Blanket (UASB) Reactor. Catalysts 2021, 11, 512 .
AMA StyleJeremiah Chimhundi, Carla Hörstmann, Evans Chirwa, Hendrik Brink. Microbial Removal of Pb(II) Using an Upflow Anaerobic Sludge Blanket (UASB) Reactor. Catalysts. 2021; 11 (4):512.
Chicago/Turabian StyleJeremiah Chimhundi; Carla Hörstmann; Evans Chirwa; Hendrik Brink. 2021. "Microbial Removal of Pb(II) Using an Upflow Anaerobic Sludge Blanket (UASB) Reactor." Catalysts 11, no. 4: 512.
Hexavalent chromium (Cr(VI)) is discharged from several anthropogenic activities that make use or produce Cr(VI) leading to environmental pollution. In this study, we explore an environmentally friendly process for the treatment of Cr(VI) with a codeposition of zero-valent palladium on the anode electrode of a microbial fuel cell (MFC). The MFC featured a granular activated carbon (GAC) anode modified with biogenic palladium nanoparticles (Bio-PdNPs). Temperature, pH, and initial Cr(VI) concentration were first optimized to 38 °C, pH 4, and 100 mg L−1 Cr(VI), respectively. Thereafter, the GAC average particle size was successfully optimized to 0.6–1.1 mm which was shown to promote the highest cell attachment. GAC below this size range had minimal cell attachment. The results from the study also showed that the GAC can be successfully modified using Bio-PdNPs to improve the performance of Cr(VI)-reducing MFC with Bio-PdNPs loading of 6 mg Bio-PdNPs g−1 GAC resulting in peak output potential difference of 393.1 mV, maximum power density of 1965.4 mW m−3, and complete removal of 100 mg L−1 Cr(VI) in 25 h.
Mpumelelo T. Matsena; Shepherd M. Tichapondwa; Evans M.N. Chirwa. Improved chromium (VI) reduction performance by bacteria in a biogenic palladium nanoparticle enhanced microbial fuel cell. Electrochimica Acta 2020, 368, 137640 .
AMA StyleMpumelelo T. Matsena, Shepherd M. Tichapondwa, Evans M.N. Chirwa. Improved chromium (VI) reduction performance by bacteria in a biogenic palladium nanoparticle enhanced microbial fuel cell. Electrochimica Acta. 2020; 368 ():137640.
Chicago/Turabian StyleMpumelelo T. Matsena; Shepherd M. Tichapondwa; Evans M.N. Chirwa. 2020. "Improved chromium (VI) reduction performance by bacteria in a biogenic palladium nanoparticle enhanced microbial fuel cell." Electrochimica Acta 368, no. : 137640.
Biomineralisation of polycyclic aromatic hydrocarbons (PAHs) and other toxic organic pollutants to CO2 and H2O is one of the most environmentally friendly and economically efficient options for treatment of deleterious organic pollutants in water and soil. Although most intermediate and high molecular weight (I-, HMW) PAHs are biodegradable, the degradability of these PAHs is limited by their low solubility. Experiments were conducted in batch reactors, and later, in continuous flow fixed-film bioreactor systems to take advantage of mass-transport resistance to reduce toxicity exposure within the biofilm. The results from this study showed a tenfold performance improvement in cumulative removal of PAHs in the biofilm reactor system. The active microbial agents were predominated by Pseudomonas aeruginosa MS-1 and Acinetobacter species. 98%, 88%, and 63% degradation of fluoranthene, pyrene and chrysene was achieved in the biofilm process, respectively, at steady doses of 45 kg/d fluoranthene, 12 kg/d pyrene and 7.5 kg/d chrysene, respectively. Product purification was further evaluated in a continuous flow fed-batch and plug-flow reactor system in which a high quality oil product was separated from oily sludge.
Evans M. Nkhalambayausi Chirwa; Tshilidzi B. Lutsinge-Nembudani; Oluwademilade M. Fayemiwo; Fisseha A. Bezza. Biosurfactant assisted degradation of High Molecular Weight Polycyclic Aromatic Hydrocarbons by mixed cultures from a car service oil dump from Pretoria Central Business District (South Africa). Journal of Cleaner Production 2020, 290, 125183 .
AMA StyleEvans M. Nkhalambayausi Chirwa, Tshilidzi B. Lutsinge-Nembudani, Oluwademilade M. Fayemiwo, Fisseha A. Bezza. Biosurfactant assisted degradation of High Molecular Weight Polycyclic Aromatic Hydrocarbons by mixed cultures from a car service oil dump from Pretoria Central Business District (South Africa). Journal of Cleaner Production. 2020; 290 ():125183.
Chicago/Turabian StyleEvans M. Nkhalambayausi Chirwa; Tshilidzi B. Lutsinge-Nembudani; Oluwademilade M. Fayemiwo; Fisseha A. Bezza. 2020. "Biosurfactant assisted degradation of High Molecular Weight Polycyclic Aromatic Hydrocarbons by mixed cultures from a car service oil dump from Pretoria Central Business District (South Africa)." Journal of Cleaner Production 290, no. : 125183.
Cuprous oxide nanoparticles (Cu2O NPs) were fabricated in reverse micellar templates by using lipopeptidal biosurfactant as a stabilizing agent. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive x-ray spectrum (EDX) and UV–Vis analysis were carried out to investigate the morphology, size, composition and stability of the nanoparticles synthesized. The antibacterial activity of the as-synthesized Cu2O NPs was evaluated against Gram-positive B. subtilis CN2 and Gram-negative P. aeruginosa CB1 strains, based on cell viability, zone of inhibition and minimal inhibitory concentration (MIC) indices. The lipopeptide stabilized Cu2O NPs with an ultra-small size of 30 ± 2 nm diameter exhibited potent antimicrobial activity against both Gram-positive and Gram-negative bacteria with a minimum inhibitory concentration of 62.5 µg/mL at pH5. MTT cell viability assay displayed a median inhibition concentration (IC50) of 21.21 μg/L and 18.65 μg/mL for P. aeruginosa and B. subtilis strains respectively. Flow cytometric quantification of intracellular reactive oxygen species (ROS) using 2,7-dichlorodihydrofluorescein diacetate staining revealed a significant ROS generation up to 2.6 to 3.2-fold increase in the cells treated with 62.5 µg/mL Cu2O NPs compared to the untreated controls, demonstrating robust antibacterial activity. The results suggest that lipopeptide biosurfactant stabilized Cu2O NPs could have promising potential for biocompatible bactericidal and therapeutic applications.
Fisseha A. Bezza; Shepherd M. Tichapondwa; Evans M. N. Chirwa. Fabrication of monodispersed copper oxide nanoparticles with potential application as antimicrobial agents. Scientific Reports 2020, 10, 1 -18.
AMA StyleFisseha A. Bezza, Shepherd M. Tichapondwa, Evans M. N. Chirwa. Fabrication of monodispersed copper oxide nanoparticles with potential application as antimicrobial agents. Scientific Reports. 2020; 10 (1):1-18.
Chicago/Turabian StyleFisseha A. Bezza; Shepherd M. Tichapondwa; Evans M. N. Chirwa. 2020. "Fabrication of monodispersed copper oxide nanoparticles with potential application as antimicrobial agents." Scientific Reports 10, no. 1: 1-18.
Biological sulphate reduction (BSR) has been identified as a promising alternative for treating acid mine drainage. In this study, the effect of pH, temperature, and hydraulic retention time (HRT) on BSR was investigated. The Box–Behnken design was used to matrix independent variables, namely pH (4–6), temperature (10–30 °C), and HRT (2–7 days) with the sulphate reduction efficiency and sulphate reduction rate as response variables. Experiments were conducted in packed bed reactors operating in a downflow mode. Response surface methodology was used to statistically analyse the data and to develop statistical models that can be used to fully understand the individual effects and the interactions between the independent variables. The analysis of variance results showed that the data fitted the quadratic models well as confirmed by a non-significant lack of fit. The temperature and HRT effect were significant (p < 0.0001), and these two variables had a strong interaction. However, the influence of pH was insignificant (p > 0.05).
Mukhethwa Judy Mukwevho; Dheepak Maharajh; Evans M. Nkhalambayausi Chirwa. Evaluating the Effect of pH, Temperature, and Hydraulic Retention Time on Biological Sulphate Reduction Using Response Surface Methodology. Water 2020, 12, 2662 .
AMA StyleMukhethwa Judy Mukwevho, Dheepak Maharajh, Evans M. Nkhalambayausi Chirwa. Evaluating the Effect of pH, Temperature, and Hydraulic Retention Time on Biological Sulphate Reduction Using Response Surface Methodology. Water. 2020; 12 (10):2662.
Chicago/Turabian StyleMukhethwa Judy Mukwevho; Dheepak Maharajh; Evans M. Nkhalambayausi Chirwa. 2020. "Evaluating the Effect of pH, Temperature, and Hydraulic Retention Time on Biological Sulphate Reduction Using Response Surface Methodology." Water 12, no. 10: 2662.
Palladium (Pd) is a cheap and effective electrocatalyst that is capable of replacing platinum (Pt) in various applications. However, the problem in using chemically synthesized Pd nanoparticles (PdNPs) is that they are mostly fabricated using toxic chemicals under severe conditions. In this study, we present a more environmentally-friendly process in fabricating biogenic Pd nanoparticles (Bio-PdNPs) using Citrobacter sp. isolated from wastewater sludge. Successful fabrication of Bio-PdNPs was achieved under anaerobic conditions at pH six and a temperature of 30 °C using sodium formate (HCOONa) as an electron donor. Citrobacter sp. showed biosorption capabilities with no enzymatic contribution to Pd(II) uptake during absence of HCOONa in both live and dead cells. Citrobacter sp. live cells also displayed high enzymatic contribution to the removal of Pd(II) by biological reduction. This was confirmed by Scanning Electron Microscope (SEM), Electron Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD) characterization, which revealed the presence Bio-PdNPs deposited on the bacterial cells. The bio-PdNPs successfully enhanced the anode performance of the Microbial Fuel Cell (MFC). The MFC with the highest Bio-PdNPs loading (4 mg Bio-PdNP/cm2) achieved a maximum power density of 539.3 mW/m3 (4.01 mW/m2) and peak voltage of 328.4 mV.
Mpumelelo Thomas Matsena; Shepherd Masimba Tichapondwa; Evans Martin Nkhalambayausi Chirwa. Synthesis of Biogenic Palladium Nanoparticles Using Citrobacter sp. for Application as Anode Electrocatalyst in a Microbial Fuel Cell. Catalysts 2020, 10, 838 .
AMA StyleMpumelelo Thomas Matsena, Shepherd Masimba Tichapondwa, Evans Martin Nkhalambayausi Chirwa. Synthesis of Biogenic Palladium Nanoparticles Using Citrobacter sp. for Application as Anode Electrocatalyst in a Microbial Fuel Cell. Catalysts. 2020; 10 (8):838.
Chicago/Turabian StyleMpumelelo Thomas Matsena; Shepherd Masimba Tichapondwa; Evans Martin Nkhalambayausi Chirwa. 2020. "Synthesis of Biogenic Palladium Nanoparticles Using Citrobacter sp. for Application as Anode Electrocatalyst in a Microbial Fuel Cell." Catalysts 10, no. 8: 838.
The remediation of soil contaminated with petrochemicals using conventional methods is very difficult because of the complex emulsions formed by solids, oil, and water. Electrokinetic remediation has of recent shown promising potential in the removal of organics from contaminated media as calls for further improvement of the technology are still made. This work investigated the performance of electrokinetic remediation of soil contaminated with petrochemicals by applying fixed electrode configurations and continuous approaching electrode configurations. This was done in combination with bioremediation by inoculating hydrocarbon degrading bacteria and biosurfactants with the aim of obtaining an improved method of remediation. The results obtained show that the biosurfactant produced by the hydrocarbon degrading bacteria Pseudomonas aeruginosa was able to enhance oil extraction to 74.72 ± 2.87%, 57.375 ± 3.75%, and 46.2 ± 4.39% for 185 mm fixed electrodes, 335-260-185 mm continuous approaching electrodes, and 335 mm fixed electrode configurations, respectively. By maintaining high current flow, the 335-260-185 mm continuous approaching electrodes configuration enhanced electroosmotic flow (EOF) on every event of electrodes movement. The fixed electrode configuration of 185 mm provided amiable pH conditions for bacterial growth by allowing quick neutrality of the pH due to high EOF as compared to the 335 mm fixed electrodes configuration. After 240 h, the carbon content in the soil was reduced from 0.428 ± 0.11 mg of carbon/mg of the soil to 0.103 ± 0.005, 0.11355 ± 0.0006, and 0.1309 ± 0.004 for 185 mm, 335-260-185 mm, and 335 mm, respectively. The application of biosurfactants and continuous approaching electrodes reduced the energy expenditure of electrokinetic remediation by enhancing the decontamination process with respect to time.
Brian Gidudu; Evans M. Nkhalambayausi Chirwa. Application of Biosurfactants and Pulsating Electrode Configurations as Potential Enhancers for Electrokinetic Remediation of Petrochemical Contaminated Soil. Sustainability 2020, 12, 5613 .
AMA StyleBrian Gidudu, Evans M. Nkhalambayausi Chirwa. Application of Biosurfactants and Pulsating Electrode Configurations as Potential Enhancers for Electrokinetic Remediation of Petrochemical Contaminated Soil. Sustainability. 2020; 12 (14):5613.
Chicago/Turabian StyleBrian Gidudu; Evans M. Nkhalambayausi Chirwa. 2020. "Application of Biosurfactants and Pulsating Electrode Configurations as Potential Enhancers for Electrokinetic Remediation of Petrochemical Contaminated Soil." Sustainability 12, no. 14: 5613.
Forerunner investigators of photocatalysis utilized TiO2 as the photocatalyst of choice. It has major drawbacks of which the most important one is that it is only activated under ultraviolet (UV) light irradiation. This high energy consumption made the process practically unfeasible. Solar energy (natural light and heat from sun) has great prospects with regards to acting as a substitute for UV light since it is a renewable and cheaper energy source. In this work, the development of a heterogeneous silver/ silver chloride/ bismuth oxychloride (Ag/AgCl/BiOCl) photocatalyst that is able to utilize natural light through visible light activation was investigated. This will successfully serve as a green alternative in the use of renewable energy for pollution reduction while saving energy. The synthesized photocatalysts were characterized using various techniques. The purity and crystallinity of the synthesized photocatalysts were determined using x-ray diffraction (XRD) while x-ray photoelectron spectroscopy (XPS) was used to determine the elemental composition and chemical states present in the synthesized catalysts as well as confirm the presence of elemental Ag. Fourier-transform infrared spectroscopy (FTIR) specified the functional groups present while the morphology and chemical composition were determined using a scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The surface area and pore size were measured on a Brunauer-Emmett-Teller (BET) and thermogravimetric analysis (TGA) was done to determine the thermal degradation of synthesized particles. Ultraviolet-visible spectroscopy (UV–vis) was done to determine the photoabsorption range and bandgap of the particles as efficiency of photocatalysis is dependent on these properties together with the morphology of the semiconductor material. Ag/AgCl/BiOCl photocatalyst showed good photocatalytic activity of 52 % under a low-wattage simulated visible light irradiation in 4 h. This work therefore shows great prospect for pollution control through energy reduction thereby protecting the environment.
Dorcas O. Adenuga; Shepherd M. Tichapondwa; Evans M.N. Chirwa. Facile synthesis of a Ag/AgCl/BiOCl composite photocatalyst for visible – light – driven pollutant removal. Journal of Photochemistry and Photobiology A: Chemistry 2020, 401, 112747 .
AMA StyleDorcas O. Adenuga, Shepherd M. Tichapondwa, Evans M.N. Chirwa. Facile synthesis of a Ag/AgCl/BiOCl composite photocatalyst for visible – light – driven pollutant removal. Journal of Photochemistry and Photobiology A: Chemistry. 2020; 401 ():112747.
Chicago/Turabian StyleDorcas O. Adenuga; Shepherd M. Tichapondwa; Evans M.N. Chirwa. 2020. "Facile synthesis of a Ag/AgCl/BiOCl composite photocatalyst for visible – light – driven pollutant removal." Journal of Photochemistry and Photobiology A: Chemistry 401, no. : 112747.
The present study aims at developing an efficient bacterial consortium to biodegrade butyric acid, one of the odor-causing compounds that contribute significantly to pit latrine malodors. Six bacterial strains isolated from pit latrine fecal sludge were selected for the study. Nineteen bacterial consortia of different combinations were artificially constructed. The individual bacterial strains and bacterial consortia were compared by culturing in mineral salt medium supplemented with 1000 mg/L butyric acid as a sole carbon and energy source at pH 7, 30 °C, and 110 rpm under aerobic growth conditions. A co-culture of Serratia marcescens and Bacillus cereus was an effective bacterial consortium compared to individual component bacterial strains and other bacterial consortia, in which 1000 mg/L butyric acid was completely degraded within 16 h of incubation. A temperature of 30 °C and pH 7 were found to be optimum for the maximum degradation for both S. marcescens and B. cereus. The inoculation sizes of 2.0 and 2.5 were optimal for the maximum degradation for B. cereus and S. marcescens, respectively. The study provides insights that will be of substantial help in the development of effective biological treatment technologies for pit latrine odor to change the pit latrine user community’s and would be users’ perception of pit latrines.
John Njalam’Mano; Evans Chirwa; Refilwe Seabi. In Vitro Study of Butyric Acid Deodorization Potential by Indigenously Constructed Bacterial Consortia and Pure Cultures from Pit Latrine Fecal Sludge. Sustainability 2020, 12, 5156 .
AMA StyleJohn Njalam’Mano, Evans Chirwa, Refilwe Seabi. In Vitro Study of Butyric Acid Deodorization Potential by Indigenously Constructed Bacterial Consortia and Pure Cultures from Pit Latrine Fecal Sludge. Sustainability. 2020; 12 (12):5156.
Chicago/Turabian StyleJohn Njalam’Mano; Evans Chirwa; Refilwe Seabi. 2020. "In Vitro Study of Butyric Acid Deodorization Potential by Indigenously Constructed Bacterial Consortia and Pure Cultures from Pit Latrine Fecal Sludge." Sustainability 12, no. 12: 5156.
The presence of priority and emerging aromatic-based pollutants in water sources is of growing concern as they are not bioavailable and are present in reuse plant feed streams. These pollutants have known mutagenic and carcinogenic effects and must therefore be removed. Adsorption has been widely accepted as a suitable remediation technology due to its simplicity. Clay-based adsorbents have attracted significant attention due to their low cost, environmentally benign properties and regeneration potential. The present work focused on the thermal modification of a commercial Layered Double Hydroxide (LDH) clay and its subsequent effectiveness as an adsorbent in the removal of phenol from wastewater. Calcination of the neat clay resulted in the formation of metal oxides with varying phases and crystallinity depending on the treatment temperature. The BET surface area increased by 233% upon calcination at 500 °C. The highest phenol removal (85%) was observed in the clay calcined at 500 °C compared to 10% for the neat clay. Optimization studies revealed a maximum adsorption capacity of 12 mg/g at an adsorbent loading of 10 g/L at pH 7. Phenol adsorption was postulated to occur via a two-stage intercalation and surface adsorption mechanism. The equilibrium data were best fitted on the Freundlich isotherm model which describes heterogeneous adsorption. The adsorption kinetics followed a pseudo-second-order kinetic model with rate constants of 4.4 x 10−3 g/mg.h for the first 12h and 6.1 x 10−3 g/mg.h thereafter.
Lehlogonolo Tabana; Shepherd Tichapondwa; Frederick Labuschagne; Evans Chirwa. Adsorption of Phenol from Wastewater Using Calcined Magnesium-Zinc-Aluminium Layered Double Hydroxide Clay. Sustainability 2020, 12, 4273 .
AMA StyleLehlogonolo Tabana, Shepherd Tichapondwa, Frederick Labuschagne, Evans Chirwa. Adsorption of Phenol from Wastewater Using Calcined Magnesium-Zinc-Aluminium Layered Double Hydroxide Clay. Sustainability. 2020; 12 (10):4273.
Chicago/Turabian StyleLehlogonolo Tabana; Shepherd Tichapondwa; Frederick Labuschagne; Evans Chirwa. 2020. "Adsorption of Phenol from Wastewater Using Calcined Magnesium-Zinc-Aluminium Layered Double Hydroxide Clay." Sustainability 12, no. 10: 4273.
This study presents the effect of aqueous Pb(II) and nutrient concentrations on the Pb(II)-removal, biomass viability, active species identities, and population distribution of an industrial Pb(II) resistant microbial consortium. The studied consortium has previously shown to be highly effective at precipitating Pb(II) from solution. At all conditions tested (80 and 500 ppm Pb(II), and varying nutrients conditions) it was found that circa 50% of Pb(II) was removed within the first 3 h, with the absence of any visual changes, followed by a slower rate of Pb(II) removal accompanied by the formation of a dark precipitate. The Pb(II) removal was found to be independent of microbial growth, while growth was observed dependent on the concentration of Pb(II), nutrients, and nitrates in the system. SEM analysis indicated viable bacilli embedded in precipitate. These findings indicate that precipitation occurs on the surface of the biomass as opposed to an internal excretion mechanism. BLAST (Basic Local Alignment Search Tool) results indicated Klebsiella pneumoniae as the active species responsible for Pb(II) bioprecipitation for both the 80 and 500 ppm isolated colonies, while a diverse population distribution of organisms was observed for the streak plate analyses. A quicker microbial generation rate was observed than what was expected for Klebsiella pneumoniae, indicating that the overall consortial population contributed to the growth rates observed. This study provided insights into the factors affecting Pb(II) bio-removal and bioprecipitation by the investigated industrially obtained consortium, thereby providing invaluable knowledge required for industrial application.
Carla Hörstmann; Hendrik G. Brink; Evans M.N. Chirwa. Pb(II) Bio-Removal, Viability, and Population Distribution of an Industrial Microbial Consortium: The Effect of Pb(II) and Nutrient Concentrations. Sustainability 2020, 12, 2511 .
AMA StyleCarla Hörstmann, Hendrik G. Brink, Evans M.N. Chirwa. Pb(II) Bio-Removal, Viability, and Population Distribution of an Industrial Microbial Consortium: The Effect of Pb(II) and Nutrient Concentrations. Sustainability. 2020; 12 (6):2511.
Chicago/Turabian StyleCarla Hörstmann; Hendrik G. Brink; Evans M.N. Chirwa. 2020. "Pb(II) Bio-Removal, Viability, and Population Distribution of an Industrial Microbial Consortium: The Effect of Pb(II) and Nutrient Concentrations." Sustainability 12, no. 6: 2511.
Uniformly dispersed silver nanoparticles (AgNPs) with remarkable colloidal stability were synthesised using chemical reduction method in lipopeptide biosurfactant reverse micelles. Transmission Electron microscopy (TEM), Scanning electron microscopy (SEM) and UV–vis spectroscopy analysis exhibited monodisperse nanoparticles with spherical morphology of diameter of 21 ± 2. The lipopeptide stabilized AgNPs displayed remarkable antibacterial activity with minimum inhibitory concentration (MIC) value of 15.625 μg/mL against Gram-negative Pseudomonas aeruginosa CB1 and Gram-positive Bacillus subtilis CN2 strains with a significant dose-dependent reduction of cell viability and loss of membrane integrity. Investigation of AgNPs internalization and dissolution assays demonstrated 42-fold higher leaching of the lipopeptide-stabilized AgNPs compared to the bare AgNPs, and concentration dependent increase in cellular uptake with subsequent damage to intracellular organelles. Further ultrastructural observation using TEM revealed internalization and strong binding of considerable amount of AgNPs on the lipopolysaccharide layer of the Gram-negative and peptidoglycans layer of Gram-positive bacteria indiscriminately, demonstrating robust antibacterial activity and potential application to treat multidrug resistant bacteria.
Fisseha A. Bezza; Shepherd M. Tichapondwa; Evans M.N. Chirwa. Synthesis of biosurfactant stabilized silver nanoparticles, characterization and their potential application for bactericidal purposes. Journal of Hazardous Materials 2020, 393, 122319 .
AMA StyleFisseha A. Bezza, Shepherd M. Tichapondwa, Evans M.N. Chirwa. Synthesis of biosurfactant stabilized silver nanoparticles, characterization and their potential application for bactericidal purposes. Journal of Hazardous Materials. 2020; 393 ():122319.
Chicago/Turabian StyleFisseha A. Bezza; Shepherd M. Tichapondwa; Evans M.N. Chirwa. 2020. "Synthesis of biosurfactant stabilized silver nanoparticles, characterization and their potential application for bactericidal purposes." Journal of Hazardous Materials 393, no. : 122319.
Metals are used in several products essential to humans. However, processes for extraction of the metals generate effluents containing chemical by-products many of which are toxic to living organisms and are disruptive to ecosystems. Processes used in the creation of useful products from the metals leave a legacy of pollution that may take generations to clear. Metals such as mercury, cadmium, lead, chromium, and uranium, and a range of metalloids such as arsenic and selenium, are widely known for their acute toxicity at high doses and carcinogenicity at low doses. Several technologies for treatment of land and water that have been contaminated with toxic heavy metals have been proposed. Other metallic elements, although possessing no significant chemical toxicity to organisms, occur as radioactive isotopes that impart oxidative stress on organisms leading to increased incidence of mutations and carcinomas in animal tissue. The main difficulty in the treatment of metals is that the metals cannot be degraded or mineralized as is the case with organic pollutants. Metallic elements can only be oxidized or reduced to forms that are less mobile and easier to extract from the environment. This chapter is compiled from information from projects in which metals were either oxidized or reduced to less mobile and less toxic states using pure or consortium cultures of bacteria followed by immobilization or extraction using physical or biological media. The uptake of metals for reuse was attempted using bioengineered molecular adsorbents on cell surfaces. The latter process was developed to facilitate selective uptake of different metallic species as a low energy biorefinery.
Evans M. Nkhalambayausi-Chirwa; Pulane Elsie Molokwane; Tshilidzi Bridget Lutsinge; Tony Ebuka Igboamalu; Zainab S. Birungi. Advances in Bioremediation of Toxic Heavy Metals and Radionuclides in Contaminated Soil and Aquatic Systems. Bioremediation of Industrial Waste for Environmental Safety 2019, 21 -52.
AMA StyleEvans M. Nkhalambayausi-Chirwa, Pulane Elsie Molokwane, Tshilidzi Bridget Lutsinge, Tony Ebuka Igboamalu, Zainab S. Birungi. Advances in Bioremediation of Toxic Heavy Metals and Radionuclides in Contaminated Soil and Aquatic Systems. Bioremediation of Industrial Waste for Environmental Safety. 2019; ():21-52.
Chicago/Turabian StyleEvans M. Nkhalambayausi-Chirwa; Pulane Elsie Molokwane; Tshilidzi Bridget Lutsinge; Tony Ebuka Igboamalu; Zainab S. Birungi. 2019. "Advances in Bioremediation of Toxic Heavy Metals and Radionuclides in Contaminated Soil and Aquatic Systems." Bioremediation of Industrial Waste for Environmental Safety , no. : 21-52.
Biological uranium (VI) reduction was investigated using a mixed-culture of U(VI) reducing bacteria isolated from tailing dumps at an abandoned uranium mine in Pharaborwa (Limpopo Province, South Africa). A fixed-film reactor was used in the investigation, whereby the reactor was operated in the up-flow mode under fully submerged conditions at a recirculation ratio of, Qin/QR = 20. The performance of the bioreactor was evaluated over a range of influent U(VI) concentrations [75-100 mg U(VI)/L] and 24 h hydraulic retention time [HRT]. Complete U(VI) removal was observed in phases with 30 to 85 mg/L influent U(VI). When influent U(VI) was increased to 100 mg/L, approximately 60% U(VI) removal was achieved. The oxidation states of reduced uranium species were determined by Scanning and Transmission Electron Microscopy followed by X-ray Diffractometer (SEM/TEM-XRD). Earlier studies in batch systems showed that U(VI) was non-toxic to U(VI) reducing organisms at concentrations up to 400 mg/L. The decrease in U(VI) removal efficiency observed in the fixed-film reactor after 42 days was therefore attributed to the accumulation of U(IV) hydroxide precipitates in the reactor. Genetic identification using the 16S rRNA gene sequence analysis showed that the species Kocuria turfanensis, Arthrobacter creatinolyticus, Bacillus licheniformis, and Microbacterium aerolatum survived from the original cultures. The feasibility of continuous removal of U(VI) in an inoculated indigenous culture system was thus demonstrated.
Phalazane J. Mtimunye; Evans M.N. Chirwa. Uranium (VI) reduction in a fixed-film reactor by a bacterial consortium isolated from uranium mining tailing heaps. Biochemical Engineering Journal 2019, 145, 62 -73.
AMA StylePhalazane J. Mtimunye, Evans M.N. Chirwa. Uranium (VI) reduction in a fixed-film reactor by a bacterial consortium isolated from uranium mining tailing heaps. Biochemical Engineering Journal. 2019; 145 ():62-73.
Chicago/Turabian StylePhalazane J. Mtimunye; Evans M.N. Chirwa. 2019. "Uranium (VI) reduction in a fixed-film reactor by a bacterial consortium isolated from uranium mining tailing heaps." Biochemical Engineering Journal 145, no. : 62-73.
A biosurfactant producing culture of bacteria was isolated from an automobile engine oil dump site which was later used as an inoculum in batch and continuous flow oil recovery from oily sludge. Initially, an emulsion of oily sludge was prepared by mixing 5% m/v solids: 21% v/v bituminous sludge: 77% v/v water. The isolated cultures were added to vessels with stable emulsions to facilitate the separation of oil droplets from the sludge matrix. In batches with live cultures, up to 35% oil recovery was achieved after incubation for 10 days. Further investigations were conducted in a semi-continuous feed, fed-batch plug flow reactor (FB-PFR) system. Up to 99.7% was achieved in the FB-PFR after operation for 10 days, much higher than the recovery achieved in the pure batch systems where only 35% oil was recovered after incubation for 10 days. The improved performance in the FB-PFR was attributed to differential separation of particles under variable velocity along the reactor. The culture in the reactor was predominated by Klebsiellae, Enterobacteriaceae and Bacilli throughout the experiment. A crude biosurfactant produced by the cultures was partially purified and analyzed using the liquid chromatograph coupled to a tandem mass spectrometer (LC-MS/MS) which showed that the molecular structure of the biosurfactant produced closely matched the structure of lipopeptides identified in earlier studies. This process is aimed at recovering useful oil from oily waste sludge with the added advantage of degrading aromatic organic impurities in the oil to produce a cleaner oil product. The further advantage of the FB-PFR system was that, the bacteria discharged together with effluent sludge residue further degraded chemical oxygen demand (COD) in the treated sludge thereby reducing the polluting potential of the final disposed sludge.
Evans M. Nkhalambayausi Chirwa; Chidinyane T. Mampholo; Oluwademilade M. Fayemiwo; Fisseha A. Bezza. Biosurfactant assisted recovery of the C 5 -C 11 hydrocarbon fraction from oily sludge using biosurfactant producing consortium culture of bacteria. Journal of Environmental Management 2017, 196, 261 -269.
AMA StyleEvans M. Nkhalambayausi Chirwa, Chidinyane T. Mampholo, Oluwademilade M. Fayemiwo, Fisseha A. Bezza. Biosurfactant assisted recovery of the C 5 -C 11 hydrocarbon fraction from oily sludge using biosurfactant producing consortium culture of bacteria. Journal of Environmental Management. 2017; 196 ():261-269.
Chicago/Turabian StyleEvans M. Nkhalambayausi Chirwa; Chidinyane T. Mampholo; Oluwademilade M. Fayemiwo; Fisseha A. Bezza. 2017. "Biosurfactant assisted recovery of the C 5 -C 11 hydrocarbon fraction from oily sludge using biosurfactant producing consortium culture of bacteria." Journal of Environmental Management 196, no. : 261-269.
Effect of biosurfactant on biodegradation of pyrene was studied using a microbial consortium predominantly composed of Pseudomonas viridiflava (49.5%) and Pseudomonas nitroreducens (32.5%) in a batch experiment containing lipopeptidic biosurfactant, produced by Paenibacillus dendritiformis CN5 strain, and mineral salt medium. The results showed that the lipopeptide at 600 and 300mgL(-1) enhanced pyrene degradation to 83.5% and 67% respectively in 24days compared to 16% degradation in its absence. However degradation of pyrene was reduced to 57% as the lipopeptide supplementation was raised to 900mgL(-1). This demonstrates that the biodegradation of pyrene was found to increase with an increase in the lipopeptide concentration up to a threshold level. The experimental data were fitted to the logistic kinetic model which provided best fit with a coefficient of determination (R(2)) values≥0.97. Maximum specific growth rate, μmax of 0.97 and 0.69d(-1) were achieved in the 600 and 300mgL(-1) lipopeptide amendments in comparison to 0.54d(-1) in the unamended one. The carrying capacity, Xmax increased 4.4-fold in 600mgL(-1) lipopeptide supplemented samples in comparison to its absence. Generally the lipopeptide showed potential application in improving bioremediation of polycyclic aromatic hydrocarbons contaminated environmental media.
Fisseha Andualem Bezza; Evans M. Nkhalambayausi Chirwa. Pyrene biodegradation enhancement potential of lipopeptide biosurfactant produced by Paenibacillus dendritiformis CN5 strain. Journal of Hazardous Materials 2017, 321, 218 -227.
AMA StyleFisseha Andualem Bezza, Evans M. Nkhalambayausi Chirwa. Pyrene biodegradation enhancement potential of lipopeptide biosurfactant produced by Paenibacillus dendritiformis CN5 strain. Journal of Hazardous Materials. 2017; 321 ():218-227.
Chicago/Turabian StyleFisseha Andualem Bezza; Evans M. Nkhalambayausi Chirwa. 2017. "Pyrene biodegradation enhancement potential of lipopeptide biosurfactant produced by Paenibacillus dendritiformis CN5 strain." Journal of Hazardous Materials 321, no. : 218-227.
A mechanistic isopercentile flocculent sedimentation model was derived from basic fractal behavior of colloidal particles in turbid water. The model showed the fractal nature of growing particles, which was in opposition to the most commonly used semiempirical models that assume growth of particles as compact spheres. The model development was based on particle size distribution (PSD) analysis results from settling batch column experiments. The experimental batches were conducted at initial concentrations ranging from 150 to 350 mg/L and coagulant doses in the range of 10–70 mg/L. From the collected PSD data, a fractal dimension D (L), fractal settling velocity av (LT−1), and model-fit parameters affecting the shape of isopercentile removal trajectories were obtained. The resulting calibrated model performed better than previously proposed semiempirical models. Lower degrees of fitting error, represented by sum of squares error (SSE) = 0.44–0.90, were achieved using the new model, which was much lower than the SSE range of 3.10–9.44 from previous models fitted to the same data set. The improved fitness of the new model was attributed to its ability to capture the fractal growth property of settling particles, which resulted in incipient buoyancy and settling deceleration of the formed flocs–properties that were not represented in previous models.
Nomcebo P. Sithebe; Evans M. Nkhalambayausi Chirwa. Mechanistic Flocculation Model Incorporating the Fractal Properties of Settling Particles. Journal of Environmental Engineering 2016, 142, 04016027 .
AMA StyleNomcebo P. Sithebe, Evans M. Nkhalambayausi Chirwa. Mechanistic Flocculation Model Incorporating the Fractal Properties of Settling Particles. Journal of Environmental Engineering. 2016; 142 (7):04016027.
Chicago/Turabian StyleNomcebo P. Sithebe; Evans M. Nkhalambayausi Chirwa. 2016. "Mechanistic Flocculation Model Incorporating the Fractal Properties of Settling Particles." Journal of Environmental Engineering 142, no. 7: 04016027.