Development and application of hydrostatically produced photogranules for non-aerated wastewater treatment

Date

2026-8-28

Author

Gökdağ, Bumin

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This thesis study investigated the microalgal-bacterial granular sludge (MBGS), i.e. photogranules from a microalgal-bacterial consortium under hydrostatic conditions, and their subsequent application in photo-sequencing batch reactors (PSBRs) for externally non-aerated wastewater treatment. Initially, the MBGS were cultivated from suspended sludge under hydrostatic batch conditions. The effects of seed sludge type and initial nitrogen type (NH4 or NO3) on hydrostatic batch photogranulation were investigated. Seed sludge type was found to strongly affect the rate and success of photogranulation. Membrane bioreactor sludge (MBS) led to 100% photogranulation success within one week, whereas conventional activated sludge (CAS) exhibited substantially lower (25%) photogranulation success. The initial nitrogen type (NH4 or NO3) was principally found to influence granular morphology. Nitrate feed led to formation of spherical photogranules mostly, while ammonium promoted the formation of disk-shaped and microbial mat-type photogranules. The hydrostatically produced photogranules were subsequently used to rapidly initiate non-aerated MBGS process in PSBRs. Initial disintegration of large seed granules under hydrodynamic conditions (100 rpm) quickly produced smaller offspring photogranules within one week. The effects of photoperiod and influent COD/N ratio on non-aerated MBGS process were also investigated. Photoperiod experiments comparing 12 h dark/12 h light, 8 h dark/16 h light, and 4 h dark/20 h light regimes demonstrated that the 12 h dark/12 h light regime achieved the highest sCOD, TN and PO4-P removal, stable bacterial and microalgal growth, and consistently good granular settleability, while extending illumination beyond 12 h provided no clear process-level advantage. Influent COD/N ratios of 5 to 13 significantly affected pollutant removal and microbial growth. As the COD/N ratio increased, cyclic sCOD, TN, and PO4-P removal efficiencies increased significantly, being attributed to the promoted biomass growth and cellular nutrient assimilation. Granular stability and settleability were not significantly affected by the COD/N range tested. Under optimum operational conditions (12-h dark/12-h light and COD/N of 13), average cyclic removal efficiencies of 59±16% sCOD, complete TAN, 70±3% TN, and 25±7% PO4-P were achieved without any aeration need. This study revealed that MBGS can be cultivated under non-aerated hydrostatic batch conditions with different seed sludges and initial N sources, while enrichment of filamentous cyanobacteria is seen as a prerequisite for this process. Hydrostatically produced photogranules can provide an effective inoculation strategy for rapidly initiating a non-aerated MBGS process in PSBRs at varied photoperiods and COD/N ratios. MBGS process is promising for achieving effective harvesting and treatment performance without any aeration need.

Subject Keywords

Microalgal-bacterial consortium, Hydrostatic, Photogranulation, Non-aerated, Wastewater treatment

URI

https://hdl.handle.net/11511/121024

Collections

Graduate School of Natural and Applied Sciences, Thesis