The role of iron nanoparticles on anaerobic digestion: mechanisms, limitations, and perspectives.

Anaerobic digestion (AD) is the most widely used technology for organic matter treatment. However, multiple types of research have reported on improving the process because different operation inhibition factors and limitations affect the performance of AD process. Owing to the increasing use of iron-nanoparticles (Fe-NP) on AD, this review addresses the knowledge gaps and summarizes the finding from academic articles based on (i) the AD upgrading operations: limitations and upgrade techniques, (ii) Fe-NPs mechanisms on AD, (iii) Fe-NP effect on microbial communities associated to AD systems, and (iv) perspectives. The selected topics give the Fe-NP positive effects on the AD methane-production process in terms of gas production, effluent quality, and process optimization. The main results of this work indicate that (i) Fe-NP addition can be adapted among different feedstocks and complement other pretreatments, (ii) Fe-NP physicochemical characteristics enhance biogas production via direct interspecies electron transfer (DIET) mechanisms, and Fe-ion release due to their structure and their conductivity capability, and (iii) syntrophic bacteria and acetoclastic methanogens have been reported as the communities that better uptake Fe-NPs on their metabolisms. Finally, our research perspectives and gaps will be discussed to contribute to our knowledge of using Fe-NPs on AD systems.