Influence of carbon-coated zero-valent iron-based nanoparticle concentration on continuous photosynthetic biogas upgrading

Abstract

This study assessed the influence of carbon-coated zero-valent nanoparticle concentration (70, 140 and 280 mg L−1) on the performance of photosynthetic biogas upgrading in an indoor pilot scale plant composed of an algal-bacterial photobioreactor interconnected to an external biogas absorption column. In addition, the influence of nanoparticle concentration on the abiotic CO2 gas-liquid mass transfer in the biogas absorption column was also evaluated. Microalgae productivity was enhanced by > 100 % when nanoparticles were added to the cultivation broth, which also boosted nitrogen and phosphorus assimilation from centrate. The biomethane produced complied with most international standards only when nanoparticles were supplemented, achieving CO2 concentrations < 1 % (CO2 removal efficiencies > 98 %) and CH4 concentrations > 94 % in the treated biogas. Finally, this research consistently demonstrated that the improvement of biogas upgrading performance by the addition of nanoparticles was based on a photosynthesis enhancement or stimulation (which significantly increased the pH in the algal cultivation broth) rather than on an improved nanoparticle-mediated CO2 capture in the biogas absorption column.