The effect of initial pH on the kinetics of ferrous-iron biooxidation at low temperature

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.Keywords: Bioleaching, ferrous-iron biooxidation, Leptospirillum ferriphilum, low temperature

Production of Polyhydroxyalkanoates, a bacterial biodegradable polymers

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. Key Words: Polyhydroxyalkanoates, biodegradable polymer, bioplastic, poly(3-hydroxybutyrate), biosynthesis. African Journal of Biotechnology Vol.3(1) 2004: 18-2

Evaluation of microbial systems for bioremediation of petroleum refinery effluents in Nigeria

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 84th hour of fermentation. There was highly positive correlation between phenol biodegradation and the microbial growth. (r = +0.994 and r = +0.980 at

Production of biodiesel from crude neem oil feedstock and its emissions from internal combustion engines

This study investigates biodiesel production using crude neem oil having high acid value, as a feedstock. The effects of some operating variables were ascertained and its combustion performance was assessed in an internal combustion engine. Due to its high acid value, the neem oil was processed via two step acid – base transesterification process. The first step reduced the acid level to <2 mgKOH/g while the second step involved direct conversion to fatty acid methyl ester using 1% NaOH as catalyst. The lowest viscosity value was used as a proxy measure to determine the extent of the reaction. The results reveal the optimum conditions for biodiesel production to be ratio 1:6 of oil to methanol and 1.5 h reaction time. The viscosity at this condition was 5.53 cSt. The same procedure was repeated for NaOCH3 catalyst concentrations of 0.5, 0.75, 1 and 1.25%. The lowest viscosity of 6.79 cSt was recorded at both 1 and 1.25% catalyst concentrations. The fuel properties of the biodiesel compared favorably with the recommendation by the American Standard Testing Method. The emissions of different blends showed that neem biodiesel has lower emissions of CO and NO than petrol diesel but higher NOX. Thus, neem oil as non-edible oil can be a good renewable raw material for biodiesel production.Key words: Neem, biodiesel, internal combustion, transesterification, free fatty acid

The transport of atmospheric NOx and HNO3 over Cape Town

Cape Town, the most popular tourist city in Africa, usually experiences air pollution with unpleasant odour in winter. Previous studies have associated the pollution with local emission of pollutants within the city. The present study examines the transport of atmospheric pollutants (NOx and HNO3) over South Africa and shows how the transport of pollutants from the Mpumalanga Highveld, a major South African industrial area, may contribute to the pollution in Cape Town. The study analysed observation data (2001–2008) from the Cape Town air-quality network and simulation data (2001–2004) from a regional climate model (RegCM) over southern Africa. The simulation accounts for the influence of complex topography, atmospheric conditions, and atmospheric chemistry on emission and transport of pollutants over southern Africa. Flux budget analysis was used to examine whether Cape Town is a source or sink for NOx and HNO3 during the extreme pollution events. The results show that extreme pollution events in Cape Town are associated with the lower level (surface – 850 hPa) transport of NOx from the Mpumalanga Highveld to Cape Town, and with a tongue of high concentration of HNO3 that extends from the Mpumalanga Highveld to Cape Town along the south coast of South Africa. The prevailing atmospheric conditions during the extreme pollution events feature an upper-level (700 hPa) anticyclone over South Africa and a lower-level col over Cape Town. The anticyclone induces a strong subsidence motion, which prevents vertical mixing of the pollutants and caps high concentration of pollutants close to the surface as they are transported from the Mpumalanga Highveld toward Cape Town. The col accumulates the pollutants over the city. This study shows that Cape Town can be a sink for the NOx and HNO3 during extreme pollution events and suggests that the accumulation of pollutants transported from other areas (e.g. the Mpumalanga Highveld) may contribute to the air pollution in Cape Town.The project was supported with grants from the National Research Foundation (NRF, South Africa) and the Applied Centre for Climate and Earth Sciences (ACCESS). The third author was supported with grants from the African Centre for Cities (ACC)

Investigation of ferrous-iron biooxidation kinetics by Leptospirillum ferriphilum in a novel packed-column bioreactor: Effects of temperature and jarosite accumulation

The kinetics of microbial ferrous-iron by Leptospirillum ferriphilum was studied at substrate loading rate of 3–90 mmol L−1 h−1 in a novel packed column bioreactor. The study was conducted with a view to providing an understanding of the reaction kinetics in a flow-through system which may be assumed to mimic bioheap solution flow, rather than the more typical batch reactors. The bioreactor was maintained at pH of 1.45 ± 0.05 and constant air flow rate of 15 mL s−1 . The Boon and Hansford, and the Monod models accurately described the experimental data. The effect of temperature on the kinetic parameters was investigated at 25, 30 and 35 °C. The maximum oxidation rate, rmax Fe2þ = 15.10 mmol L−1 h−1 , was highest at 35 °C. The activation energy, Ea = 20.97 kJ mol−1 , of ferrous-iron biooxidation in the novel bioreactor is indicative of a system that is limited by both biochemical and diffusion factors. The result also showed about 38.80% increase in the maximum microbial ferrous-iron oxidation,r max Fe2þ , due to accumulation of jarosite. However, the decreasing values of substrate affinity constant, KFe2þ , and the apparent affinity constant, K′ Fe2þ revealed that the microbial affinity for ferrous biooxidation increases with increase in jarosite formation. This study reveals that jarosite maybe beneficial to bioleach heaps if it is carefully managed.This project was funded by National Research Foundation (NRF) and University Research Fund (URF) of Cape Peninsula University of Technology

Fungi solubilisation of low rank coal: Performances of stirred tank, fluidised bed and packed bed reactors

Coal biosolubilisation was investigated in stirred tank reactor, fluidised bed and fixed bed bioreactors with a view to highlight the advantages and shortcomings of each of these reactor configurations. The stirred aerated bioreactor and fluidised bioreactor represent slurry reactor systems enabling a comparative study. Direct comparison between these and the fixed bed bioreactor could not be carried as the corresponding particle sizes will result to a pressure drop in the fixed bed reactor. Coal solubilisation showed a higher coal weight loss in the stirred tank slurry bioreactor in comparison to the fluidised bed slurry bioreactor at 5% (w/v) coal loading and 600–850 µm coal fractions. Higher aeration is required in the fluidised bed bioreactor than in the stirred tank slurry bioreactor at constant coal loading and particle size because in fluidised bed bioreactor aeration was also used for mixing. Coal biosolubilisation in the packed bed bioreactor was minimal. The low performance was attributed to the large coal particle size fraction (1.5–2 mm) used. Minimal damage to the fungal culture was observed. However, clogging of bed by fungi resulted in channelling or misdistribution that ultimately leads to poor and unpredictable internal mass transport

Kinetic modeling of cell growth, substrate utilization, and biosurfactant production from solid agrowaste (Beta vulgaris) by Bacillus licheniformis STK 01

The kinetics of cell growth, substrate utilization and biosurfactant production by Bacillus licheniformis STK 01 from a solid agrowaste substrate (Beta vulgaris) and a refined substrate (mineral salts, MS) was investigated. Data obtained were fitted to the integrated Monod equation, logistic models, and Leudeking–Piret model using nonlinear regression analyses. The maximum cell growth was observed after 72 h of fermentation for both substrates. The highest biosurfactant production was 5.8 ± 0.5 g/L when the B. vulgaris waste substrate was used, while the production increased up to 9.78 ± 1.02 g/L when MS was used. The biosurfactant produced from B. vulgaris and MS lowered the surface tension of the broth to 30 and 23.5 mN/m respectively. Furthermore, from the kinetic data analyses, cell growth and B. vulgaris utilization were described by the logistic model and modified Monod equation, respectively, with the maximum cell growth rate of 0.026 h−1, cell yield of 0.617, and the Monod saturation constant being 0.418 g/L. Similarly, biosurfactant production was best described by the logistic model while the production rate constant was 0.140 h−1. This study is applicable, among other areas, in the design of biological systems augmented with B. vulgaris waste.Cape Peninsula Universityof Technology through the University Research Fund (URF

Potential applications of zeolite membranes in reaction coupling separation processes

Future production of chemicals (e.g., fine and specialty chemicals) in industry is faced with the challenge of limited material and energy resources. However, process intensification might play a significant role in alleviating this problem. A vision of process intensification through multifunctional reactors has stimulated research on membrane-based reactive separation processes, in which membrane separation and catalytic reaction occur simultaneously in one unit. These processes are rather attractive applications because they are potentially compact, less capital intensive, and have lower processing costs than traditional processes. Therefore this review discusses the progress and potential applications that have occurred in the field of zeolite membrane reactors during the last few years. The aim of this article is to update researchers in the field of process intensification and also provoke their thoughts on further research efforts to explore and exploit the potential applications of zeolite membrane reactors in industry. Further evaluation of this technology for industrial acceptability is essential in this regard. Therefore, studies such as techno-economical feasibility, optimization and scale-up are of the utmost importance