The synthesis of zeolites from fly ash has become an increasingly promising remedy to the crisis ... more The synthesis of zeolites from fly ash has become an increasingly promising remedy to the crisis of coal fly ash production and disposal in South Africa. In recent studies, South African fly ash was proven to be a suitable feedstock for the synthesis of essential industrially used zeolite A. However, the process involves a costly energy intensive step whereby fly ash is fused at high temperatures, which may make the process economically unattractive on a large scale. The aim of this study is to investigate the possibility of replacing high temperature fusion with less energy intensive sonochemical treatment for the synthesis of zeolite A. Sonochemical treatment was first thought possible due to the violent cavitation caused by high intensity sonication. The results of the study showed that fusion can be replaced by 10min of high intensity sonication. The incorporation of sonication also consequently reduced the crystallization temperature of the process making it possible to synthesize a pure phase zeolite A at lower temperatures and reduced times. This study effectively developed a novel process to replace the energy intensive fusion step with a short, easy and inexpensive treatment. Scale up of this synthesis approach may proffer a promising alternative option to the anticipated energy demand of the synthesis of fly ash-based zeolite with fusion method.
There has been considerable interest in the development and production of biodegradable polymer t... more There has been considerable interest in the development and production of biodegradable polymer to solve the current problem of pollution caused by the continuous use of synthetic polymer of petroleum origin. Polyhydroxyalkanoates (PHAs) are known to be accumulated as intracellular inclusion in some bacteria. The materials properties exhibited by PHAs, ranging from stiff, brittle to rubber-like makes it a close substitute for the synthetic plastic. The high cost of PHAs production has restricted its applications. The possibility of producing this polymer commercially and at comparable cost has been the main focus in this area.
The potential of various organisms to catabolize and metabolize organic compounds has been recogn... more The potential of various organisms to catabolize and metabolize organic compounds has been recognized as potentially effective means of disposing of hazardous wastes. Phenolic compounds has long been recognized as one of the most recalcitrant and persistent substance in petroleum refinery effluents. This is a cause of some concern because of the high toxicity and of this compound. Bioremediation of phenolic compounds has been recognized as a potential solution for the disposal of phenolic compounds due to its scale ability, cost effectiveness and simplicity. The two species of Pseudomonas , P. aeruginosa and P. fluorescence were studied for their bioremediation potential on Refinery effluent with respect to phenol biodegradation in a batch reactor. Phenol was degraded completely by the two species. While P. aeruginosa completely mineralize phenol at the 60th hour of cultivation, only 75% (23 mg/l) of phenol was degraded by P. fluorescence; complete degradation was achieved at the 84...
Fly ash (FA) is a coal combustion by-product. South Africa produces 27 MT of FA annually, of whic... more Fly ash (FA) is a coal combustion by-product. South Africa produces 27 MT of FA annually, of which a small amount (5 %) is beneficially utilized while the rest is disposed in landfill, ash dumps or ponds. This waste product has a serious impact on the environment apart from the high costs associated with its storage. Acid mine drainage (AMD) is another environmental hazard and the detrimental effects of AMD on the environment are well researched and documented in the literature. Neutralization of AMD is being achieved in various ways that include chemical and biological techniques. Low cost and effective treatment methods are constantly being sought and FA treatment is one of the promising methods due its low cost and availability in large quantities. FA has been successfully employed to neutralize and remove toxic elements from AMD. Approximately 80-90 % of sulphate was removed when FA was used as an ameliorant while treating low-pH, Fe, Al and sulphate-rich AMD. In South Africa, m...
Bagasse, corncob and sawdust were used as lignocellulosic substrates for the production of cellul... more Bagasse, corncob and sawdust were used as lignocellulosic substrates for the production of cellulase enzyme using Aspergillus flavus after ballmilling and pretreatment with caustic soda. From the fermentation studies, sawdust gave the best result with an enzyme activity value of 0.0743IU/ml while bagasse and corncob gave 0.0573IU/ml and 0.0502IU/ml respectively. The three lignocellulosics gave their maximum enzyme activities at about the twelfth hour of cultivation, suggesting that the 12th hour is the optimum time when the enzyme may be harvested.
During start-up of heap bioleaching, low grade ores may be treated with acid for agglomeration an... more During start-up of heap bioleaching, low grade ores may be treated with acid for agglomeration and to combat the acid neutralising capacity of the gangue minerals. This may stress the bioleaching inocula, particularly upon inoculation during ore agglomeration. Acid addition for agglomeration varies across operations, ore types and their neutralising capacity, with limited information published on recommended concentrations. The initial pH in the agglomeration mix is typically below pH 1.0 and may be as low as pH 0.5. This paper investigates the effect of acid stress in terms of initial acid concentration and duration of exposure in submerged culture on mesophilic micro-organisms typically implicated in mineral sulphide bioleaching and critical for heap colonisation at start-up. Following acid stress, cultures were returned to standard operating conditions in batch stirred slurry reactors and their performance assessed in terms of mineral leach rates, ferrous oxidation and the rate of microbial growth. Increasing acid stress resulted in an increase in the lag period before onset of microbial growth and iron oxidation due to decreased viable cell numbers, specific metabolic activity or both. Following adaptation, typical growth and ferrous iron oxidation rates were observed under low stress conditions while reduction in the rate and extent of microbial growth and ferrous iron oxidation persisted at extreme conditions. A reduction in yield (microbial cells produced per kg iron oxidised) was observed with increased acid concentration over comparative times. Microbial speciation analysis indicated a substantial decrease in the diversity of the microbial species surviving.
ABSTRACT The application of agrowaste as a substrate in cyanide biodegradation systems is particu... more ABSTRACT The application of agrowaste as a substrate in cyanide biodegradation systems is particularly promising, as reported by Santos et al. [62]. Having a readily accessible waste material, microorganisms will be able to produce enzymes suitable for bioremediating contaminants in wastewater [59]. Besides their application as effective biosorbents, agrowaste can serve as a sole substrate for bioremediation purposes, on condition that it is compatible to the microbial community to be used [67, 45, 17, 16]. In South Africa, approximately 10 million tons of agrowaste is generated per annum [53], of which 96% is classified as pre-consumer waste (Figure 1). This is a large quantity of waste for a developing economy and should be put into profitable use to safe our environment.
The general understanding in bioleaching of sulphide minerals is to keep pH low. A number of publ... more The general understanding in bioleaching of sulphide minerals is to keep pH low. A number of published articles have reported the effect of pH on biooxidation rates of ferrous-iron and/or sulphur by bioleaching microbes, although most of these studies were conducted at optimum or near optimum temperature for microbial performance. Consequently, a series of experiments were conducted in this study to investigate the effect of pH on biooxidation of ferrous-iron at low temperature condition (22°C) by a culture that was predominantly Leptospirillum ferriphilum. The maximum specific microbial activity (2.13 x10 -3 h -1 ) obtained at pH 1.37 was more than 10 times lower than the corresponding activity at optimum temperature. The specific rates decreased as pH increased from 1.37 to 1.88. However, the jarosite precipitation under these conditions was not significant to deplete the available iron. The result of this study, if extended to other microbes would have implications on strain selection and management of heap bioleach processes operating in cold conditions.
This study investigated production of biodiesel from oil seeds of Jatropha curcas, obtained in Ni... more This study investigated production of biodiesel from oil seeds of Jatropha curcas, obtained in Nigeria, with a view to encouraging the cultivation of Jatropha plant in Nigeria and to providing a motivation for the development of biodiesel production from this feedstock. Also effect of oil-to-alcohol molar ratio on the biodiesel production from Nigerian Jatropha curcas seeds oil was investigated with a view to confirming established base case. A maximum yield of fatty acid methyl esters (FAME) of 87% was obtained at 333 Kelvin, oil-to-alcohol molar ratio of 1:6 and at 1wt% NaOH catalyst concentration. The physical properties of the BD obtained from Nigerian Jatropha oil met the ASTM standard of D-6751. Consequently, this study reveals that Jatropha curcas, an economically invaluable plant in Nigeria, could be a good feedstock for biodiesel production in Nigeria.
ABSTRACT This work reports on the exploitation of Beta vulgaris for biosurfactant production by B... more ABSTRACT This work reports on the exploitation of Beta vulgaris for biosurfactant production by Bacillus licheniformis STK 01 and its optimization using statistical modeling of response surface methodology (RSM). Three variables were investigated: agro-waste concentration, pH, and temperature. The response and contour plots of the RSM showed perfect interaction among the variables, with the highest surface tension reduction of the culture medium to 30 mN/m observed at 42 °C, a pH of 8, and a substrate concentration of 4% (w/v). The biosurfactant produced demonstrated a high tendency for hydrocarbon emulsification. Furthermore, by numerical optimization techniques, the optimum conditions were found to be as follows: a pH of 6.72, an agro-waste concentration of 4% (w/v), and a temperature of 44.5 °C. The experiment conducted to validate the optimum conditions obtained showed a biosurfactant with remarkable surface activity, lowering the surface tension of the broth to 30 mN/m, when the organism was grown on B. vulgaris, and to 23.5 mN/m, when grown in glucose medium – the later representing one of the highest surface tension reductions ever reported for a biosurfactant. This study revealed, among others, that the exclusive utilization of cheap solid agro-waste without supplementation with a refined nutrient source is feasible and could ensure the economic sustainability of biosurfactant production.
ABSTRACT This study reports on the isolation of novel biosurfactant-producing strains from hydroc... more ABSTRACT This study reports on the isolation of novel biosurfactant-producing strains from hydrocarbon-contaminated environments that exclusively utilize agro-waste as their primary carbon source for the expression of biosurfactants, quantified using various standardized methods. Among the agro-waste screened, Beta vulgaris (Beetroot) proved to be the most suitable substrate, for which the biosurfactants produced by three bacterial isolates–B. licheniformis STK01, B. subtilis STK02, and P. aeruginosa STK03–lowered the surface tension of the culture media to 30.0, 32.98, and 30.37 mN/m, respectively. The biosurfactants produced achieved considerable emulsification activity, particularly for heavy hydrocarbons, with the highest emulsification indices being 65.5% and 95% for anthracene and lubricant oil, respectively. The emulsion formed with lubricant oil was thermally stable even up to 50 °C for 21 days. The results obtained in this study exemplify the proficiency of the novel bacterial isolates used, as well as the suitability of solid agro-waste for biosurfactant production, thus suggesting that exclusive utilization of solid agro-waste is a promising option for use in biosurfactant production for environmental remediation. The outstanding emulsification activity and thermal stability demonstrated by the biosurfactants produced showed their potential applications in enhancing bioavailability and bioremediation of recalcitrant and hydrophobic environmental contaminants.
South African fly ash has been shown to be a useful feedstock for the synthesis of some zeolites.... more South African fly ash has been shown to be a useful feedstock for the synthesis of some zeolites. The present study focuses on the effect of impeller design and agitation rates on the synthesis of zeolite Na-P1 which are critical to the commercialization of this product. The effects of three impeller designs (4-flat blade, Anchor and Archimedes screw impellers) and three agitation speeds (150, 200 and 300 rpm) were investigated using a modified previously reported synthesis conditions; 48 hours of ageing at 47 °C and static hydrothermal treatment at 140 °C for 48 hours. The experimental results demonstrated that the phase purity of zeolite Na-P1 was strongly affected by the agitation rate and the type of impeller used during the ageing step of the synthesis process. Although zeolite Na-P1 was synthesized with a space time yield (STY) of 15 ± 0.4 kg d −1 m −3 and a product yield of 0.98±0.05 g zeolites/g fly ash for each impeller at different agitation speeds, zeolite formation was assessed to be fairly unsuccessful in some cases due the occurrence of undissolved mullite and/or the formation of impurities such as hydroxysodalite with the zeolitic product. This study also showed that a high crystalline zeolite Na-P1 can be synthesized from South African coal fly ash using a 4-flat blade impeller at an agitation rate of 200 rpm during the ageing step at 47 °C for 48 hours followed by static hydrothermal treatment at 140 °C for 48 hours.
The synthesis of zeolites from fly ash has become an increasingly promising remedy to the crisis ... more The synthesis of zeolites from fly ash has become an increasingly promising remedy to the crisis of coal fly ash production and disposal in South Africa. In recent studies, South African fly ash was proven to be a suitable feedstock for the synthesis of essential industrially used zeolite A. However, the process involves a costly energy intensive step whereby fly ash is fused at high temperatures, which may make the process economically unattractive on a large scale. The aim of this study is to investigate the possibility of replacing high temperature fusion with less energy intensive sonochemical treatment for the synthesis of zeolite A. Sonochemical treatment was first thought possible due to the violent cavitation caused by high intensity sonication. The results of the study showed that fusion can be replaced by 10min of high intensity sonication. The incorporation of sonication also consequently reduced the crystallization temperature of the process making it possible to synthesize a pure phase zeolite A at lower temperatures and reduced times. This study effectively developed a novel process to replace the energy intensive fusion step with a short, easy and inexpensive treatment. Scale up of this synthesis approach may proffer a promising alternative option to the anticipated energy demand of the synthesis of fly ash-based zeolite with fusion method.
There has been considerable interest in the development and production of biodegradable polymer t... more There has been considerable interest in the development and production of biodegradable polymer to solve the current problem of pollution caused by the continuous use of synthetic polymer of petroleum origin. Polyhydroxyalkanoates (PHAs) are known to be accumulated as intracellular inclusion in some bacteria. The materials properties exhibited by PHAs, ranging from stiff, brittle to rubber-like makes it a close substitute for the synthetic plastic. The high cost of PHAs production has restricted its applications. The possibility of producing this polymer commercially and at comparable cost has been the main focus in this area.
The potential of various organisms to catabolize and metabolize organic compounds has been recogn... more The potential of various organisms to catabolize and metabolize organic compounds has been recognized as potentially effective means of disposing of hazardous wastes. Phenolic compounds has long been recognized as one of the most recalcitrant and persistent substance in petroleum refinery effluents. This is a cause of some concern because of the high toxicity and of this compound. Bioremediation of phenolic compounds has been recognized as a potential solution for the disposal of phenolic compounds due to its scale ability, cost effectiveness and simplicity. The two species of Pseudomonas , P. aeruginosa and P. fluorescence were studied for their bioremediation potential on Refinery effluent with respect to phenol biodegradation in a batch reactor. Phenol was degraded completely by the two species. While P. aeruginosa completely mineralize phenol at the 60th hour of cultivation, only 75% (23 mg/l) of phenol was degraded by P. fluorescence; complete degradation was achieved at the 84...
Fly ash (FA) is a coal combustion by-product. South Africa produces 27 MT of FA annually, of whic... more Fly ash (FA) is a coal combustion by-product. South Africa produces 27 MT of FA annually, of which a small amount (5 %) is beneficially utilized while the rest is disposed in landfill, ash dumps or ponds. This waste product has a serious impact on the environment apart from the high costs associated with its storage. Acid mine drainage (AMD) is another environmental hazard and the detrimental effects of AMD on the environment are well researched and documented in the literature. Neutralization of AMD is being achieved in various ways that include chemical and biological techniques. Low cost and effective treatment methods are constantly being sought and FA treatment is one of the promising methods due its low cost and availability in large quantities. FA has been successfully employed to neutralize and remove toxic elements from AMD. Approximately 80-90 % of sulphate was removed when FA was used as an ameliorant while treating low-pH, Fe, Al and sulphate-rich AMD. In South Africa, m...
Bagasse, corncob and sawdust were used as lignocellulosic substrates for the production of cellul... more Bagasse, corncob and sawdust were used as lignocellulosic substrates for the production of cellulase enzyme using Aspergillus flavus after ballmilling and pretreatment with caustic soda. From the fermentation studies, sawdust gave the best result with an enzyme activity value of 0.0743IU/ml while bagasse and corncob gave 0.0573IU/ml and 0.0502IU/ml respectively. The three lignocellulosics gave their maximum enzyme activities at about the twelfth hour of cultivation, suggesting that the 12th hour is the optimum time when the enzyme may be harvested.
During start-up of heap bioleaching, low grade ores may be treated with acid for agglomeration an... more During start-up of heap bioleaching, low grade ores may be treated with acid for agglomeration and to combat the acid neutralising capacity of the gangue minerals. This may stress the bioleaching inocula, particularly upon inoculation during ore agglomeration. Acid addition for agglomeration varies across operations, ore types and their neutralising capacity, with limited information published on recommended concentrations. The initial pH in the agglomeration mix is typically below pH 1.0 and may be as low as pH 0.5. This paper investigates the effect of acid stress in terms of initial acid concentration and duration of exposure in submerged culture on mesophilic micro-organisms typically implicated in mineral sulphide bioleaching and critical for heap colonisation at start-up. Following acid stress, cultures were returned to standard operating conditions in batch stirred slurry reactors and their performance assessed in terms of mineral leach rates, ferrous oxidation and the rate of microbial growth. Increasing acid stress resulted in an increase in the lag period before onset of microbial growth and iron oxidation due to decreased viable cell numbers, specific metabolic activity or both. Following adaptation, typical growth and ferrous iron oxidation rates were observed under low stress conditions while reduction in the rate and extent of microbial growth and ferrous iron oxidation persisted at extreme conditions. A reduction in yield (microbial cells produced per kg iron oxidised) was observed with increased acid concentration over comparative times. Microbial speciation analysis indicated a substantial decrease in the diversity of the microbial species surviving.
ABSTRACT The application of agrowaste as a substrate in cyanide biodegradation systems is particu... more ABSTRACT The application of agrowaste as a substrate in cyanide biodegradation systems is particularly promising, as reported by Santos et al. [62]. Having a readily accessible waste material, microorganisms will be able to produce enzymes suitable for bioremediating contaminants in wastewater [59]. Besides their application as effective biosorbents, agrowaste can serve as a sole substrate for bioremediation purposes, on condition that it is compatible to the microbial community to be used [67, 45, 17, 16]. In South Africa, approximately 10 million tons of agrowaste is generated per annum [53], of which 96% is classified as pre-consumer waste (Figure 1). This is a large quantity of waste for a developing economy and should be put into profitable use to safe our environment.
The general understanding in bioleaching of sulphide minerals is to keep pH low. A number of publ... more The general understanding in bioleaching of sulphide minerals is to keep pH low. A number of published articles have reported the effect of pH on biooxidation rates of ferrous-iron and/or sulphur by bioleaching microbes, although most of these studies were conducted at optimum or near optimum temperature for microbial performance. Consequently, a series of experiments were conducted in this study to investigate the effect of pH on biooxidation of ferrous-iron at low temperature condition (22°C) by a culture that was predominantly Leptospirillum ferriphilum. The maximum specific microbial activity (2.13 x10 -3 h -1 ) obtained at pH 1.37 was more than 10 times lower than the corresponding activity at optimum temperature. The specific rates decreased as pH increased from 1.37 to 1.88. However, the jarosite precipitation under these conditions was not significant to deplete the available iron. The result of this study, if extended to other microbes would have implications on strain selection and management of heap bioleach processes operating in cold conditions.
This study investigated production of biodiesel from oil seeds of Jatropha curcas, obtained in Ni... more This study investigated production of biodiesel from oil seeds of Jatropha curcas, obtained in Nigeria, with a view to encouraging the cultivation of Jatropha plant in Nigeria and to providing a motivation for the development of biodiesel production from this feedstock. Also effect of oil-to-alcohol molar ratio on the biodiesel production from Nigerian Jatropha curcas seeds oil was investigated with a view to confirming established base case. A maximum yield of fatty acid methyl esters (FAME) of 87% was obtained at 333 Kelvin, oil-to-alcohol molar ratio of 1:6 and at 1wt% NaOH catalyst concentration. The physical properties of the BD obtained from Nigerian Jatropha oil met the ASTM standard of D-6751. Consequently, this study reveals that Jatropha curcas, an economically invaluable plant in Nigeria, could be a good feedstock for biodiesel production in Nigeria.
ABSTRACT This work reports on the exploitation of Beta vulgaris for biosurfactant production by B... more ABSTRACT This work reports on the exploitation of Beta vulgaris for biosurfactant production by Bacillus licheniformis STK 01 and its optimization using statistical modeling of response surface methodology (RSM). Three variables were investigated: agro-waste concentration, pH, and temperature. The response and contour plots of the RSM showed perfect interaction among the variables, with the highest surface tension reduction of the culture medium to 30 mN/m observed at 42 °C, a pH of 8, and a substrate concentration of 4% (w/v). The biosurfactant produced demonstrated a high tendency for hydrocarbon emulsification. Furthermore, by numerical optimization techniques, the optimum conditions were found to be as follows: a pH of 6.72, an agro-waste concentration of 4% (w/v), and a temperature of 44.5 °C. The experiment conducted to validate the optimum conditions obtained showed a biosurfactant with remarkable surface activity, lowering the surface tension of the broth to 30 mN/m, when the organism was grown on B. vulgaris, and to 23.5 mN/m, when grown in glucose medium – the later representing one of the highest surface tension reductions ever reported for a biosurfactant. This study revealed, among others, that the exclusive utilization of cheap solid agro-waste without supplementation with a refined nutrient source is feasible and could ensure the economic sustainability of biosurfactant production.
ABSTRACT This study reports on the isolation of novel biosurfactant-producing strains from hydroc... more ABSTRACT This study reports on the isolation of novel biosurfactant-producing strains from hydrocarbon-contaminated environments that exclusively utilize agro-waste as their primary carbon source for the expression of biosurfactants, quantified using various standardized methods. Among the agro-waste screened, Beta vulgaris (Beetroot) proved to be the most suitable substrate, for which the biosurfactants produced by three bacterial isolates–B. licheniformis STK01, B. subtilis STK02, and P. aeruginosa STK03–lowered the surface tension of the culture media to 30.0, 32.98, and 30.37 mN/m, respectively. The biosurfactants produced achieved considerable emulsification activity, particularly for heavy hydrocarbons, with the highest emulsification indices being 65.5% and 95% for anthracene and lubricant oil, respectively. The emulsion formed with lubricant oil was thermally stable even up to 50 °C for 21 days. The results obtained in this study exemplify the proficiency of the novel bacterial isolates used, as well as the suitability of solid agro-waste for biosurfactant production, thus suggesting that exclusive utilization of solid agro-waste is a promising option for use in biosurfactant production for environmental remediation. The outstanding emulsification activity and thermal stability demonstrated by the biosurfactants produced showed their potential applications in enhancing bioavailability and bioremediation of recalcitrant and hydrophobic environmental contaminants.
South African fly ash has been shown to be a useful feedstock for the synthesis of some zeolites.... more South African fly ash has been shown to be a useful feedstock for the synthesis of some zeolites. The present study focuses on the effect of impeller design and agitation rates on the synthesis of zeolite Na-P1 which are critical to the commercialization of this product. The effects of three impeller designs (4-flat blade, Anchor and Archimedes screw impellers) and three agitation speeds (150, 200 and 300 rpm) were investigated using a modified previously reported synthesis conditions; 48 hours of ageing at 47 °C and static hydrothermal treatment at 140 °C for 48 hours. The experimental results demonstrated that the phase purity of zeolite Na-P1 was strongly affected by the agitation rate and the type of impeller used during the ageing step of the synthesis process. Although zeolite Na-P1 was synthesized with a space time yield (STY) of 15 ± 0.4 kg d −1 m −3 and a product yield of 0.98±0.05 g zeolites/g fly ash for each impeller at different agitation speeds, zeolite formation was assessed to be fairly unsuccessful in some cases due the occurrence of undissolved mullite and/or the formation of impurities such as hydroxysodalite with the zeolitic product. This study also showed that a high crystalline zeolite Na-P1 can be synthesized from South African coal fly ash using a 4-flat blade impeller at an agitation rate of 200 rpm during the ageing step at 47 °C for 48 hours followed by static hydrothermal treatment at 140 °C for 48 hours.
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