Efficacy of magnetite (Fe3O4) nanoparticles for enhancing solid-state anaerobic co-digestion: Focus on reactor performance and retention time

[Display omitted] •Magnetic nanoparticles (nFe3O4) mitigated acetic acidification.•nFe3O4 fed reactor enriched anaerobes for optimal hemicellulose conversion.•Microbial diversity of bacteria was uniquely modified in 20 mg/L nFe3O4 fed reactor. The influence of magnetite nanoparticle (nFe3O4) concentrations (20, 50, and 75 mg/L) on reactor performance and retention time was investigated for the first time in an initially upset solid-state anaerobic batch (SSAB) reactor. nFe3O4 mitigated acidification threat, enhanced reactor stability, ensured rapid volatile fatty acids bioconversion, and modified microbial community. The impacts reduced retention time by 27 days relative to the control. Of the nFe3O4 concentrations, 20 mg/L had the highest hemicellulose degradation (93%) and methane yield (191.2 L/kg VS) with no threat to anaerobic microbes. Besides, existing kinetic models, novel models equally well-described methane yield with low root mean square errors (RMSE) 98%, therefore could be used for downstream applications. This study provides useful information on the impact of nFe3O4 on reactor stability and reactor performance in an initially upset SSAB reactor.