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Author ORCID Identifier
Open Access Dissertation
Doctor of Philosophy (PhD)
Civil and Environmental Engineering
Year Degree Awarded
Month Degree Awarded
John E. Tobiason
Civil Engineering | Environmental Engineering
Photogranular biomass has yet to be utilized at large scale for wastewater treatment despite their potential to lower energy demand due to self-aerating capacity in addition to better process control compared to conventional technologies. An evaluation of critical driving factors affecting scaling up has yet to be undertaken. The current generation of oxygenic photogranules under hydrostatic conditions (a deviation from orthodox conditions creating other granules) limit seeding of larger reactors in time and scale. In addition, evaluating the photosynthetic productivity of granules which exist as closely commingled consortia with tightly coupled production and consumption processes, has yet to be undertaken.
We experimentally evaluate the alternative generation of oxygenic photogranules under hydrodynamic conditions. The photochemical capacity of oxygenic photogranules under variable light conditions was also determined. Concomitantly, we evaluate the effects of light intensity on the performance of reactors of varying scales and the light demand therewith. Finally, granular physical attributes that impact hydrodynamic behaviour and interaction with the bulk fluid due to agitation were assessed.
Oxygenic photogranules were formed only under some combinations of different pressures in 8 days, suggesting a ‘goldilocks zone’ of selection pressure interaction fostering granulation. Rapid generation of multiple granules would ease seeding of reactors higher volume reactors.
OPGs phototrophic capacity was also found to increase with light intensity to a curvilinear maximum beyond which photoinhibition ensues. This implies the existence of light-limited operating conditions below maximal sunlight intensities. Photoelasticity was also observed for granules treated under different light stress with apparent adaptability to abiotic stresses. Moreover, the light dependency is influenced by reactor design and operation, allowing for recovery of the photosynthetic mechanism and selecting for different microbial dominance. This, in turn, affects different treatment metrics in rectors at a different scale. No linear relationship was observed between reactor performance and increasing light intensity while density, porosity and permeability were found to be in the range of other granular biomass.
No spontaneous granulation has been recorded in conventional wastewater basins. We surmise that this could be due to a mismatch of conditions suppressing potential granulation. Altering the magnitudes of these o could potentially result in the formation of granular aggregates.
Gitau, Joseph G., "SCALING UP THE OXYGENIC PHOTOGRANULE (OPG) WASTEWATER TREATMENT PROCESS" (2020). Doctoral Dissertations. 1918.