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Goodarzi, Milad

University of British Columbia

This study explored the integration of graphene oxide (GO) and magnetite-decorated graphene oxide (MGO) into the anaerobic digestion (AD) of municipal sludge. In recent years, conductive nanosheets, including GO and MGO, have emerged as promising supplements for enhancing AD. To investigate their potential, GO and MGO were synthesized. By controlling MGO's surface functionality, another type of nanosheet, magnetic reduced GO (MrGO), was also synthesized, demonstrating 300% lower charge transfer impedance (higher conductivity) than MGO. This was to assess the importance of surface functionality on the enhancement of AD of municipal sludge. Biochemical methane potential (BMP) assays were subsequently conducted to evaluate the impact of nanosheets and their interaction mechanisms within batch AD utilizing municipal sludge. Results revealed that all tested nanosheets improved methane production kinetics, ranging from 1% to 61%, with MrGO outperforming the others. Furthermore, a 100% increase in the hydrolysis rate was achieved after transitioning from MGO to MrGO, highlighting the significant role of surface functionality. The results also underscored the importance of operational factors, such as digester pH, in the observed performance. For instance, as pH shifted from neutral (7.5) to ≈ 9, the impact of MrGO on methane production kinetics changed from +56% to -14%, demonstrating the strong dependence of its behavior on AD operational factors. The study also examined the impact of AD on the structural properties of GO and MGO, tracing their fate at the end of utilization in AD. The nanosheets were primarily found to partition with biosolids, land-applied as fertilizer, as indicated by a significant reduction in the surface functionality of GO/MGO, evidenced by a shift in the Raman G-band from 1606 cm⁻¹ to 1565 cm⁻¹. After batch AD experiments, the focus shifted to semi-continuous flow digesters to assess the long-term effects of nanosheets on full-scale operations. The results demonstrated that nanosheet enhancements were discernible only at high organic loadings when control (non-amended) AD struggled. 20 mg/L of GO/MGO nanosheets successfully rescued failing digesters at 5.2 g chemical oxygen demandfed/L/day. These findings are crucial for developing an understanding of the utilization and end-of-life trajectory of nanosheets for AD enhancement.

Text

2025-01-07

Attribution-NoDerivatives 4.0 International

http://hdl.handle.net/2429/90071

Civil Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nd/4.0/