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 cor-responding 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 ID/IG ratio from 0.74 to 1.01, con-firming the reduction of GO due to anaerobic respiration. The anaerobic removal of model antibiotics sulfa-methoxazole 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).

Automated summary

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. The results show that GO can be reduced in anaerobic conditions, and the formation of bioRGO inhibits the formation of transformation products of certain organic contaminants. However, the GO addition does not affect the removal of model antibiotics, and the presence of high levels of GO inhibits methane production.