Thesis supervisor: Botond Ráduly
Location of studies (in Hungarian): Csíkszereda Abbreviation of location of studies: Csík
Description of the research topic:
The aerobic granular technology is a novel and promising wastewater treatment technology. Aerobic granules are compact and relatively large bioaggregates, with several advantages over the traditional activated sludge flocks, such as better settling characteristics and better resistance to environmental factors. As compared to the activated sludge technology, the use of aerobic granular sludge (AGS) allows for higher biomass concentration, reduced excess sludge production, small biomass loss and reduced reactor volumes. Due to such advantages the AGS technology can handle wastewaters with high organic load, and one of its target application area is the treatment of food processing wastewaters.
The main challenges of the AGS technology are the slow granule formation and the stability of the mature granules. Granule formation depends on a series of factors such as reactor geometry, hydrodynamics, type of volatile fatty acids or presence of nuclei; the mechanism of granulation is not completely elucidated, but the production of extracellular polymeric substances and intermolecular interactions are known to be the key factors. It cannot be predicted exactly how long the formed granules will remain stable, because the reasons and the mechanism of granule disintegration are not well understood.
The effect of disinfectants frequently used in the food industry (e.g. sodium hypochlorite, quaternary ammonium compounds, chlorine dioxid) on the formation, structure and stability of AGS is not documented yet. Throughout the PhD research these aspects will be investigated in laboratory scale airlift reactors, under controlled conditions (using synthetic wastewater, fixed disinfectant concentration, etc.). The structural and functional changes of the granules and of the microbial population within the granules will be monitored in parallel with the process parameters, using in-situ fluorescent microscopy and molecular biology methods. The expected results of the research will allow a better understanding of the granule formation and disintegration under chemical stress conditions. The determination of the tolerance thresholds for the different disinfectants will be of practical use with regard to the industrial applicability of the AGS technology.
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