Scale-up and Optimization of Biogenic Magnetite Production

  • Howbeer Muhamad Ali

Student thesis: Master of Philosophy

Abstract

Interest in biogenic magnetite nanoparticles is increasing as their potential applications are better understood. Magnetite can be produced by anaerobic Fe(III)-reducing and Fe(II)-oxidising bacteria. In this project the dissimilatory Fe(III)-reducing ability of G. sulfurreducens was harnessed for biogenic magnetite production. The main aim of this project was to scale up (from 5L to 50L, and potentially 750L volumes) and optimise the medium and growth conditions to achieve the highest biomass yield in the shortest time, while maintaining the Fe(III)-reduction ability of the grown cells at a high level. The results of this project suggest that, of the conditions tested, a defined "NBAF" medium containing 80 mM fumarate as the electron acceptor and 50 mM acetate as the electron donor, with 50 rpm stirring speed during incubation at 30°C produces the highest biomass yield. Using 20 mM bicarbonate buffer in the growth medium during the incubation period was sufficient to keep the pH between the ranges of 6.8-7.2. To optimise the process further, different concentrations of the electron shuttle (riboflavin) were used to find the optimal concentration to be used to accelerate the rate of Fe(III) reduction and subsequent biogenic magnetite production process. 10µM riboflavin concentration resulted in optimal magnetite production and therefore was considered as standard concentration for the purpose of this study. One of the most interesting observations of this project was the changes occurring in the growth pattern of the cells during the scale-up process. As the volume of the medium was increased, the lag phase of the cultures increased. This illustrates that the performance of microbial systems is not always predictable during scale-up. However, changes that were apparent during biomass preparation did not prevent the efficient production of bionanomagnetite at large-scale, which is an important step in the potential commercial use of these materials.
Date of Award1 Aug 2012
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorJonathan Lloyd (Supervisor)

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