Optimization of anaerobic digestion using microalgal-based iron nanoparticles

The study explores the use of microalgal-based carbon-encapsulated iron nanoparticles to enhance the anaerobic digestion process. These nanoparticles are synthesized through hydrothermal carbonization (225°C, 3h) by combining iron nitrate with algal biomass grown on urban wastewater (Mantovani et al., 2022; Peng et al., 2014). The nanoparticles have been characterized through ICP-OES, TEM, SEM-EDX, and XRD to understand their morphology, properties, presence and abundance of oxides, and crystalline phases. They were integrated into semi-continuous lab-scale reactors fed with municipal sludges, where different concentrations of nanoparticles (100 mg/L and 500 mg/L) were tested. The results indicated that nanoparticles at 100 mg/L significantly increase methane production by 24% to 180 ± 50 NmL/gVS and biogas production by 30% to 248 ± 58 NmL/gVS compared to the control. Additionally, the presence of nanoparticles improved organic matter degradation and volatile fatty acid conversion. These findings suggest that microalgal-based iron nanoparticles enhance microbial metabolic efficiency, leading to improved biogas yields and a reduction in undesired compounds such as hydrogen sulfide by 54%. It is hypothesized that the inclusion of iron nanoparticles will improve microbial metabolism efficiency, leading to increased methane production while concurrently reducing undesired compounds such as hydrogen sulfide, which will be eliminated via precipitation (Feng et al., 2014).