Impact of magnetite nanoparticles supplementation on the anaerobic digestion of food wastes: Batch and continuous-flow investigations

Anaerobic digestion is one of the most attractive technologies for the treatment of industrial, civil and agricultural organic waste because of its capacity to reduce the biodegradable matter while recovering renewable energy in the form of methane. However, this bioprocess sometime suffers of problems in the interspecies electron transfer between acetogenic bacteria and methanogenic archaea with consequent yields reduction or failure. Recently, direct interspecies electron transfer between species via solid conductive materials like nanoparticles has been observed. This study, in particular, examined the effect of magnetite nanoparticles supplementation on the methanogic conversion of organic substrates both in batch trials using pure compounds (i.e., propionate and butyrate) and continuous trials using real food waste as substrate. Batch experiments demonstrated once again the validity of the proposed approach, whereby the conductive particles likely promoted the occurrence of direct interspecies electron transfer processes between acetogens and methanogens. Notably, continuous experiments confirmed the significance of this mechanism also for the treatment of real substrates, although the relative magnitude of the stimulatory effect was slightly lower.