Microbial ecology of methanogenic sludge granulation and its application in the reduction of selenate and selenite
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This thesis attempts to address some of the knowledge gaps in the literature around methanogenic granulation. Much existing research focuses on granulation of flocculent biomass up to the point at which satisfactory granular biomass is obtained. However, granulation is a dynamic process, where continual granule formation, disintegration and reformation occurs throughout the period of bioreactor operation. In addition, much of the well cited literature on methanogenic granulation was published in the 1980s. While these articles provided a solid foundation for the area of granulation research much of the work was carried out prior to the advent of many culture independent techniques for microbial community analysis. Therefore, specifically designed bioreactor trials are required to capture data on actively, forming, growing and disintegrating granules, at different stages of development and microbial community analysis could provide significant advancements in the field of granulation research. This is precisely what this thesis attempts to achieve, through a novel lab-scale bioreactor trial outlined in Chapters 3 and 4. In addition, this thesis attempted to increase our understanding of selenate and selenite reducing communities in methanogenic granular sludge and obtain selenate and selenite reducing isolates from methanogenic granular sludge. Specifically, it was investigated whether the selenite reducing community constituted a sub-population of the selenate reducing community, since selenate reduction is generally believed to be a two-step mechanism where selenate is first reduced to selenite by anaerobic respiration and selenite is then reduced to elemental selenium.