Insight into anaerobic digestion mechanisms by fine-tuning structural properties of nanomaterial supplements

Using biochemical methane potential (BMP) assays, this study aims to elucidate the underlying mechanisms by which nanomaterials enhance municipal sludge anaerobic digestion (AD). To this end, four distinct nanomaterials-graphene oxide (GO), magnetite, magnetic GO (MGO), and magnetic reduced GO (MrGO)- were synthesized and supplemented into BMP assays. Results highlighted the critical role of surface functionality in nanomaterials, evidenced by a 300% impedance reduction when transitioning from MGO to MrGO. Methane production kinetics also revealed high sensitivity to the surface functionality, with MrGO-amended BMPs exhibiting a 100% increase in hydrolysis rate constant compared to MGO-amended BMPs. The obtained results propose surface functionality as the dominant mechanism inducing oxidative stress on microorganisms, specifically fermentative bacteria. Further analyses revealed the primary role of direct interspecies electron transfer (DIET), augmented soluble iron concentrations, and zeta potential in the AD system performance.