Investigating the impact of oxygenic photo granules (OPGs) structure on wastewater treatment and bioenergy generation

This study investigates an innovative and cost-effective wastewater treatment (WWT) method using oxygenic photogranulation (OPG) technology for institutional WWT and bioenergy generation. Two 1.5 L sequencing batch OPG-based bioreactors, R1 with spherical seeds (SS) and R2 with mat seeds (MS), were developed and operated without external aeration under light/dark conditions to evaluate granule formation, wastewater treatment, and bioenergy potential. R2 performed better in terms of WWT with granule size (2.5 0.2 mm), SVI (92 3 %), effluent quality (COD: 34 4 mg/L; nitrate: 11 2 mg/L; phosphates: 11 3 mg/L) compared to R1 with granule size (2.1 0.2 mm), SVI (88 3 %), effluent quality (COD: 37 4 mg/L; nitrate: 12 2 mg/L; phosphates: 12 3 mg/L). Biomass from R2 showed higher bioenergy potential with GCV of 15.5 MJ/kg, increased crystalline structure, thermal decomposition, microbial adhesion, and porosity revealed by XRD, TGA, Raman, FTIR, and SEM analyses, respectively. Furthermore, the Coats-Redfern method revealed the lowest activation energy (Ea) in R1 and R2 in both stages (230-340 ?C: 37.47 kJ/mol and 36.57 kJ/mol, respectively; 340-650 ?C: 17.79 and 16.84 kJ/mol, respectively) and higher decomposition efficiency. This OPG-based, environmentally friendly WWT method plays a vital role in bioenergy generation and efficiency, climate change mitigation, and sustainable development.