Rapid biological reduction of graphene oxide: Impact on methane production and micropollutant transformation

This study investigates the impact of graphene oxide (GO) addition to anaerobic sludge and the formation of biologically reduced GO (bioRGO) on both the anaerobic transformation of organic contaminants and the corresponding biogas production. A hydrogel-like material of anaerobic digestate and bioRGO was formed on the first day after GO addition. Raman spectroscopy showed an increase in the I_D/I_Gratio from 0.74 to 1.01, confirming the reduction of GO due to anaerobic respiration. The anaerobic removal of model antibiotics sulfamethoxazole and trimethoprim was unaffected by the GO addition. Yet formation of bioRGO inhibited the formation of the identified transformation products (TPs) of sulfamethoxazole, TP253 and TP257. Furthermore, the formation of TP253 and TP257 biotransformation products of sulfamethoxazole in sterilized sludge confirmed that their removal was likely achieved via intracellular enzymes that had enough thermal stability to remain active after the sterilization. For trimethoprim, no transformation products could be detected using the employed analytical method. The production of methane was generally inhibited up to 18% due to the presence of high GO levels (>100 mg/L) (288 vs. 353 mL CH₄/g VS).