Evaluation of carbon-coated zero-valent iron nanoparticle suspensions supplementation on the performance of high-rate algal pond treating biogas and wastewater

This study assessed the effect of carbon-coated zero-valent iron nanoparticle (ZVI-NPs) suspension on enhancing photosynthetic biogas upgrading. A continuous photobioreactor system co-cultivating microalgae and bacteria was operated using synthetic biogas and real digestate to evaluate microalgal growth, photosynthetic performance, and CO 2 removal with ZVI-NPs suspension. The addition of ZVI-NPs suspension notably increased biomass concentration (up to 3.1 g L −1 ) and photosynthetic efficiency (up to 0.64). These enhancements raised the pH of the cultivation broth to 9.3 and improved CO 2 mass transfer, resulting in a CO 2 removal efficiency of 95.0% and an average CH 4 content of 91.9% in the upgraded biogas, meeting grid-injection standards. Although bicarbonate supplementation was required to avoid inorganic carbon limitation, the ZVI-NPs significantly reduced the overall inorganic carbon demand by boosting photosynthesis. Overall, these findings demonstrate that ZVI-NPs suspensions can effectively enhance microalgal performance and CO 2 capture, supporting their application as sustainable and cost-effective strategy for biogas upgrading.