New insights on improved growth and biogas production potential of Chlorella pyrenoidosa through intermittent iron oxide nanoparticle supplementation

In the present work, the effect of α-Fe 2 O 3 -nanoparticles (IONPs) supplementation at varying doses (0, 10, 20 and, 30 mg L −1 ) at the intermittent stage (after 12th day of growth period) was studied on the growth and biogas production potential of Chlorella pyrenoidosa . Significant enhancements in microalgae growth were observed with all the tested IONPs doses, the highest (2.94 ± 0.01 g L −1 ) being at 20 mg L −1 . Consequently, the composition of the biomass was also improved. Based on the precedent determinations, theoretical chemical oxygen demand (COD th ) as well as theoretical and stoichiometric methane potential (TMP, and SMP) were also estimated. The COD th , TMP, SMP values indicated IONPs efficacy for improving biogas productivity. Further, the biochemical methane potential (BMP) test was done for IONPs supplemented biomass. The BMP test revealed up to a 25.14% rise in biogas yield (605 mL g –1 VS fed ) with 22.4% enhanced methane content for 30 mg L −1 IONPs supplemented biomass over control. Overall, at 30 mg L −1 IONPs supplementation, the cumulative enhancements in biomass, biogas, and methane content proffered a net rise of 98.63% in biomethane potential (≈ 2.86 × 10 4 m 3 ha −1 year −1 ) compared to control. These findings reveal the potential of IONPs in improving microalgal biogas production.