Impact of Metal Oxide Nanoparticles (NiO, CoO and Fe3O4) on the Anaerobic Digestion of Sewage Sludge

This study intends to examine the effects of NiO, CoO and Fe 3 O 4 nanoparticles (NPs) (experiment A) and their combinations (experiment B) on the anaerobic digestion (AD) of mixture of primary sludge and waste activated sludge of municipal wastewater treatment plant. The effects of NPs addition, each at three different concentrations (1, 10 and 100 mg/l) and their combinations were evaluated by running laboratory-scale batch reactors and measuring biogas production, methane and hydrogen sulfide (H 2 S) content of biogas and organic matter reduction. The results indicated that the efficiency of anaerobic digesters exposed to the NPs was dosage-dependent. In experiment A, Addition of 1 mg/l NiO, 1 mg/l CoO, 10 and 100 mg/l Fe 3 O 4 NPs increased biogas yield by 26.94%, 21.12%, 23.41% and 14.29% and methane yield by 39.04%, 30.37%, 35.59% and 22.65% in comparison with the control respectively. While 100 mg/l NiO and CoO NPs decreased biogas and methane yield significantly compared to the control. Furthermore 10 mg/l NiO and CoO and 1 mg/l Fe 3 O 4 NPs didn’t affect AD process significantly. In experiment B all the combinations led to enhancement of biogas and methane production except combination of 100 mg/l of the three NPs and the highest increase including 43.90% for biogas and 62.85% for methane belonged to the combination of the optimum dosages of NPs in experiment A. H 2 S concentration in biogas was not affected by low dosages of NPs (1 and 10 mg/l), while high dosages (100 mg/l) could reduce it 13.36–52.57% compared to the control. Graphical Abstract