Improving photosynthetic biogas purification via process aeration and nanoparticle supplementation

This study evaluated the influence of nanoparticles in both suspension and solid format on the performance of a microalgal process devoted to photosynthetic biogas purification. The experimental system consisted of an enclosed tubular photobioreactor coupled to a biogas absorption column through a mixing chamber. The high NH₄⁺ concentration in the inlet mineral medium (530 mg N-NH₄⁺ L^-1) and the punctual addition of 115 mL of nanoparticle suspension to the system caused inhibition of the microalgal-bacterial cultivation. Conversely, cultivation broth aeration (0.5 L min^-1 air flowrate) allowed the biomethane production fulfilling the EN 16723 (CH₄ > 90 %, CO₂ < 2 %). The nanoparticle suspension performance was superior to that of their solid counterparts in terms of CO₂ removal efficiency at equivalent nanoparticle dose (77 % vs. 49 %). However, parameters such as the nanoparticle suspension dosage and biomass concentration in the photobioreactor should be optimized to further improve biomethane quality before its industrial application.