The release of effluents containing cadmium ions into aquatic ecosystems is hazardous to humans and marine organisms. In the current investigation, biosorption of Cd²⁺ ions from aqueous solutions by freely suspended and immobilized Turbinaria ornata biomasses was studied. Compared to free cells (94.34%), the maximum Cd²⁺ removal efficiency reached 98.65% for immobilized cells obtained via Box–Behnken design under optimized conditions comprising algal doses of 5.04 g L⁻¹ and 4.96 g L⁻¹, pH values of 5.06 and 6.84, and initial cadmium concentrations of 25.2 mg L⁻¹ and 26.19 mg L⁻¹, respectively. Langmuir, Freundlich, and Temkin isotherm models were suitably applied, providing the best suit of data for free and immobilized cells, but the Dubinin–Radushkevich model only matched the immobilized algal biomass. The maximum biosorption capacity of Cd²⁺ ions increased with the immobilized cells (29.6 mg g⁻¹) compared to free cells (23.9 mg g⁻¹). The Cd²⁺ biosorption data obtained for both biomasses followed pseudo-second-order and Elovich kinetic models. In addition, the biosorption process is controlled by film diffusion followed by intra-particle diffusion. Cd²⁺ biosorption onto the free and immobilized biomasses was spontaneous, feasible, and endothermic in nature, according to the determined thermodynamic parameters. The algal biomass was further examined via SEM/EDX and FTIR before and after Cd²⁺ biosorption. SEM/EDX analysis revealed Cd²⁺ ion binding onto the algal surface. Additionally, FTIR analysis confirmed the presence of numerous functional groups (hydroxyl, carboxyl, amine, phosphate, etc.) participating in Cd²⁺ biosorption. This study verified that immobilized algal biomasses constitute a cost-effective and favorable biosorbent material for heavy metal removal from ecosystems.

Background: The production of microbial lipids from oleaginous fungi is a promising method to support sustainable biofuels, but maximizing biomass and lipid accumulation requires carefully optimizing growth conditions using effective statistical approaches. The aim of this study was to enhance the biomass and lipid accumulation of a newly indigenous strain of the oleaginous fungus Fusarium solani OQ275245 by assessing the correlation between experimental results and independent design variables. The optimization process used a Box–Behnken experimental design with a response surface methodology, selecting starch, peptone, and inoculum size as independent parameters. The impacts of the parameters on the dependent responses (biomass yield, lipid yield, and lipid content) were investigated using response surfaces and contour plots, and the data was analyzed using ANOVA. Results: The optimal culture conditions were starch, peptone, and inoculum size at levels of 38.43 g/L, 0.53 g/L, and 1.0%, respectively. After validation of quadratic models, it was found that the optimized medium increased biomass yield by 1.06-fold, from 20.80 ± 1.90 g/L to 22.04 ± 2.51 g/L; lipid yield increased by 4.03-fold, from 1.31 ± 0.38 g/L to 5.28 ± 0.55 g/L; and the lipid content increased 3.81-fold, from 6.29 ± 1.36% to 23.96 ± 0.99% compared to the non-optimized medium. Hence, the use of RSM contributed to determining the concentrations of the studied variables to enhance biomass and lipid production in the fungal strain. Furthermore, fungal lipids analyzed by GC/MS were found to contain a high amount of long-chain saturated fatty acids, including myristic acid, palmitic acid, and stearic acid. This indicated that the Fusarium strain had a good fatty acid composition that can be effectively applied for production of biodiesel. Ultimately, we evaluated the characteristics of biodiesel generated by the F. solani strain, and the results met established criteria. Conclusions: These results suggest that Fusarium solani OQ275245 represents a sustainable and promising resource for the production of microbial lipids suitable for biofuel applications, and that the use of surface response methodology is an effective approach for improving the production of biomass and high-quality lipids.