Enhancing anaerobic digestion by simultaneous application of a combined treatment of nano-zero valent iron and magnetite nanoparticles

Abstract

Anaerobic digestion (AD) is one of the most energy-efficient technologies for treating biodegradable waste since biogas can be generated as a by-product. AD is a biochemical process mediated by a consortium of microorganisms without oxygen in four stages: hydrolysis, acidification, acetogenic and methanogenesis. The addition of iron-based nanoparticles (Fe-NPs) aims to boost the AD process to enhance the biogas output by degrading biomass through interspecies electron transfer. In this work, three AD batch experiments were explored to assess the enhancement of methane production yield via the incorporation of conductive nanomaterials, zero-valent iron (nZVI), magnetite nanoparticles (Fe3O4-NPs), and a combination of the two nZVI/Fe3O4-NPs, under two concentrations (200 mgL-1 and 400 mgL-1). Glucose (1.5 gL-1) was used as the main carbon source for biogas production. The granular inoculum was obtained from brew beer waste organic waste treatment. Chemical oxygen demand (COD mgL-1) and methane production (NmL) were determined as the main responses via analytic and gas chromatography methods. After sixteen days, COD removal (%), pH, glucose reduction (%), and methane yield production (NmLmgCOD-1) were determined. Control samples were anaerobic reactors without nanomaterials. Regarding the control, significant differences were observed in COD removal by incorporating 200 mgL-1 nZVI, 400 mgL-1 Fe3O4-NPs, and 200 mgL-1 nZVI/Fe3O4-NPs: 13%, 26%, 30%, respectively. However, cumulative methane volume was not significant after eighteen days. In addition, an inhibitory methane production behavior was observed in the presence of 400 mgL-1 nZVI. Maximum methane yield production was 0.693 NmLmgCOD-1, 0.359 NmLmgCOD- 1, and 0.299 NmLmgCOD-1 in the presence of 200 mgL-1 nZVI, 200 mgL-1 nZVI/Fe3O4- NPs, and 400 mgL-1 Fe3O4-NPs, respectively. Considering the results, 200 mgL-1 nZVI/Fe3O4-NPs showed interesting insights regarding COD remotion and methane yield production. Their combined effect should be deeply studied for medium exposure to methane production. This study is the first report to test combined nZVI/Fe3O4-NPs addition.