Boosting photosynthetic biogas upgrading via carbon-coated zero-valent iron nanoparticle addition: A pilot proof of concept study

The effect of carbon-coated zero-valent iron nanoparticles (NPs) on the upgrading of biogas based on bacterial-algal symbiosis was assessed in an indoor pilot scale algal open pond interconnected to a biogas purification column. The addition of NPs at 70 mg L−1 stimulated photosynthetic activity, resulting in an enhanced concentration of biomass from 1.56 to 3.26 g VSS L−1. The presence of NPs in the culture broth increased CO2 removal from 86% to 92% at low IC concentrations (≤600 mg L−1) and a decrease in the content of O2 and N2 in the upgraded biomethane. This entailed an increase of the CH4 concentration in the upgraded biomethane from 83% to 91%. However, the higher biomass productivity resulted in a gradual depletion of the IC concentration concomitant with a reduction of the buffer capacity which requires a further optimization in the operational conditions to maintain the beneficial effects of NPs. [Display omitted] •Carbon-coated zero-valent iron nanoparticles boosted algal productivity.•Nanoparticles supported CO2 removals from biogas of 92% at low alkalinities.•Nanoparticles reduced O2 and N2 stripping to the upgraded biogas.•CH4 contents over 90% were achieved only via nanoparticle supplementation.