AbstractThe addition of iron oxides in anaerobic digestion can increase conversion efficiency. In this study, we investigated the effects of the addition of Fe2O3, Fe2O3 nanoparticles, Fe3O4, and Fe3O4 nanoparticles with different concentrations (0.5%–1.5%) on the anaerobic codigestion of a Pennisetum hybrid and kitchen waste in a batch-mode mesophilic experiment. The results indicated that the additives with different valence states and particle sizes had different effects on the anaerobic codigestion of the Pennisetum hybrid and kitchen waste. The addition of 0.5% Fe2O3 [with a biogas production of 286.0±61.8 mL/g volatile solid (VS)] and 0.5% Fe3O4 (with a biogas production of 309.1±22.3 mL/g VS) improved the cumulative biogas yield by 23.5% and 37.9%, respectively, compared with that of the control group (with a biogas production of 237.2±30.1 mL/g VS). Further correlation analysis showed that pH and total ammonia nitrogen were positively correlated with cumulative biogas yield, whereas bicarbonate alkalinity concentration/volatile alkalinity concentration and volatile fatty acids were negatively correlated with cumulative biogas yield. This study provided insights on anaerobic codigestion of the Pennisetum hybrid and kitchen waste in the presence of iron oxides, which will be beneficial for further studies in the field of renewable energy production.