This study evaluated long-term performance of graphene oxide (GO) and magnetic GO (MGO) nanosheets in semi-continuous-flow anaerobic digestion (AD) of municipal sludge over 230 days. At organic loading rates (OLRs) of 2.6 and 3.4 g chemical oxygen demand (COD)fed/L/day, 20 and 200 mg/L of GO and MGO did not affect AD performance. However, at an OLR of 5.2 g CODfed/L/day, where control digesters failed, 20 and 200 mg/L of GO and MGO sustained biogas yields at 190 mL/g CODfed/day, similar to yields at lower OLRs (2.6 and 3.4 g CODfed/L/day). This performance persisted after thedaily nanosheet replenishment stopped. Improvements were due to enhanced conductivity and microbial syntropy. The results showed a strong correlation with previous biochemical methane potential (BMP) assays, positioning BMPs as a predictive tool for continuous-flow AD performance. Overall, this study demonstrated potential of GO/MGO nanosheets to improve the stability and efficiency of AD systems under stress.
Read full abstract