Green integrative large scale treatment of tannery effluent, CO2 sequestration, and biofuel production using oleaginous green microalga Nannochloropsis oculata TSD05: An ecotechnological approach

In this present investigation, the freshwater microalga Nannochloropsis oculata TSD05 was used to demonstrate multiforius environmental applications viz., bioremediation of tannery effluent, carbon sequestration, and green renewable biodiesel production from treated microalgal biomass. The microalga Nannochloropsis oculata TSD05 was exhibited unique heavy metal reduction capabilities and reduced significant amount of heavy metals viz., 96.62% of copper (Cu²⁺), 99.9% of chromium (Cr³⁺), 98.36% of zinc (Zn²⁺), 98.71% of cadmium (Cd²⁺), 97.96% of lead (Pb²⁺), 98.88% of Cobalt (Co²⁺), and 98.76% of nickel (Ni²⁺). The biosorption capacity rate (q_max) of heavy metals reduction and highest R² of 97.84% exhibited at 12 days of effluent treatment by Langmuir and Freundlich isotherm models. The phytotoxicity analysis was tested againt treated tannery effluent using Vigna radiate, Sapindus muukorossi seeds and 98.45%, 99.05% seeds were germinated. The Nannochloropsis oculata TSD05 microalga was utilized 98.45% of CO₂ by biofixation kinetics, 372 mg g⁻¹ of lipid, 3.65 mg mL⁻¹ of biomass and 4.64 mLg⁻¹ of biodiesel were produced. The produced biodiesel was confirmed and identification of 18 fatty acid methyl ester (biodiesel) compounds using GCMS. The recognition of 17 functional groups was identified using FTIR analysis and the microalga Nannochloropsis oculata TSD05 potential for sustainable and renewable green energy production. The potential future application of Nannochloropsis oculata TSD05 is to increase lipid production and biodiesel yield. Scaling up the bioremediation process can also validate these microalga's feasibility for use in wastewater treament. Enhancing heavy metal biosorption and carbon sequestration efficiency through genetic engineering could also maximize environmental benefits.