Evaluating the impact of Iron Oxide nanoparticles (IO-NPs) and IO-NPs doped granular activated carbon on the anaerobic digestion of food waste at mesophilic and thermophilic temperature

The impact of Iron oxide nanoparticles (IO-NPs) and IO-NPs doped granular activated carbon (GAC) at three concentration levels of 0.16 g/L, 0.32 g/L and 0.48 g/L for IO-NPs and 2 g/L, 4 g/L and 6 g/L for IO-NPs doped GAC on the anaerobic digestion (AD) of food waste (FW) at mesophilic (35 ± 2 oC) and thermophilic (55 ± 2 oC) temperature has been investigated. Results revealed that the % utilization of volatile fatty acids (VFAs) ranged between 83% and 92% in mesophilic reactors (MRs) while it was between 79% and 84% in thermophilic (TRs) indicating elevated temperatures may lead to VFAs accumulation in the long term operation. Results disclosed that the CH4 (%) and yield was 60% and 0.25 L CH4/g VSreduced in MR-Control and 62% and 0.29 L CH4/g VSreduced in TR-Control respectively. Similarly, in the reactors with 0.32 g/L of IO-NPs the maximum CH4 of 72% and 77% with an yield of 0.43 and 0.54 L CH4/g VSreduced was achieved at mesophilic and thermophilic temperature. Likewise using 4 g/L of IO NPs doped GAC, the maximum CH4 of 74% and 78%, with an yield of 0.41 and 0.53 L CH4/g VSreduced was achieved. This could be attributed to the syntrophic balance between the bacterial groups (Firmicutes, Bacteroidetes, Chloroflexi, Thermotogae) and archaeal groups (Methanosarcina, Methanothrix and Methanosaeta) that enhanced the electron transfer between cell to cell resulting in improved performance. [Display omitted] •IO-NPs and IO-NPs doped GAC enhanced CH4 generation potential from food waste.•CH4 improved from 60% to 74% at 35 ± 2 oC & 62–78% at 55 ± 2 oC using IO-NPs doped GAC (4 g/L).•Addition of IO-NPs & IO-NPs doped GAC promote direct interspecies electron transfer.•Firmicutes, Methanosaeta, Methanosarcina and Geobactor were predominant groups.•0.42 & 0.54 L CH4/gVSreduced was obtained using 0.32 & 4 g/L of IO-NPs & IO NPs+GAC.