Amirkabir University of Technology Amirkabir Journal of Civil Engineering 2588-297X 56 2 2024 04 20 Use of response surface method for modeling and optimization of harvesting of Chlorella sorokiniana pa.91 with Fe3O4/PACl from municipal wastewater Use of response surface method for modeling and optimization of harvesting of Chlorella sorokiniana pa.91 with Fe3O4/PACl from municipal wastewater 181 202 5323 10.22060/ceej.2023.22600.8002 FA Sara Akbari Babol Noshirvani University of Technology Farhad Qaderi Babol noshirvani university of technology 0000-0002-9164-4922 Hasan Amini Rad Doctor of Philosophy, Department of Environmental Engineering, Faculty of Civil Engineering, Babol Noshirvani University of Technology, 47148-7313 Babol, Iran. Journal Article 2023 08 07 Microalgae have the potential to produce valuable substances for pharmaceutical purposes as well as serve as a food source, providing bioactive compounds and ingredients for cosmetics. However, harvesting microalgae is a crucial step in the mass production of various high-value products derived from microalgae. This process often becomes a major bottleneck in downstream processing. It is essential to find effective and cost-effective harvesting methods for industrial applications. Among several harvesting methods, magnetic flocculation offers the benefits of modest operation, energy savings, and quick separation. This study investigates the harvesting process of <em>Chlorella sorokiniana pa.91</em> microalgae using a novel flocculation process involving nano-Fe₃O₄ coated with PACl. In this research, we have used the chemical co-precipitation method to prepare nanoparticles. Using the response surface method to optimize the most important parameters of the magnetic flocculation harvesting process to check the microalgae removal efficiency, three variables of time, concentration of nanomaterials, and pH in the culture medium obtained from municipal wastewater have been investigated. The results demonstrated that the highest harvesting efficiency, nearly 90%, was achieved under the conditions of 3.5 g/L Fe₃O₄, a constant concentration of 0.075 g/L PACl, a harvesting duration of 40 minutes, and a pH level of 4. On the other hand, the lowest microalgae harvesting efficiency was observed under specific conditions: a composite nanoparticle concentration of 0.5 g/L per liter, a harvesting time of 27.5 minutes, and a pH of 6.5 resulting in a mere 22% efficiency. The rate of microalgal removal increased from 53% in the most alkaline condition to 75% in the most acidic environment. The highest harvesting efficiency, reaching 80%, was achieved under neutral pH conditions with a settling time of 53 minutes. Furthermore, the investigated combined method investigated enhances the flocculation effectiveness of microalgae. Based on the findings, it can be inferred that the efficiency of microalgae harvesting rises with longer duration, higher nanoparticle concentrations, and lower pH levels Microalgae have the potential to produce valuable substances for pharmaceutical purposes as well as serve as a food source, providing bioactive compounds and ingredients for cosmetics. However, harvesting microalgae is a crucial step in the mass production of various high-value products derived from microalgae. This process often becomes a major bottleneck in downstream processing. It is essential to find effective and cost-effective harvesting methods for industrial applications. Among several harvesting methods, magnetic flocculation offers the benefits of modest operation, energy savings, and quick separation. This study investigates the harvesting process of <em>Chlorella sorokiniana pa.91</em> microalgae using a novel flocculation process involving nano-Fe₃O₄ coated with PACl. In this research, we have used the chemical co-precipitation method to prepare nanoparticles. Using the response surface method to optimize the most important parameters of the magnetic flocculation harvesting process to check the microalgae removal efficiency, three variables of time, concentration of nanomaterials, and pH in the culture medium obtained from municipal wastewater have been investigated. The results demonstrated that the highest harvesting efficiency, nearly 90%, was achieved under the conditions of 3.5 g/L Fe₃O₄, a constant concentration of 0.075 g/L PACl, a harvesting duration of 40 minutes, and a pH level of 4. On the other hand, the lowest microalgae harvesting efficiency was observed under specific conditions: a composite nanoparticle concentration of 0.5 g/L per liter, a harvesting time of 27.5 minutes, and a pH of 6.5 resulting in a mere 22% efficiency. The rate of microalgal removal increased from 53% in the most alkaline condition to 75% in the most acidic environment. The highest harvesting efficiency, reaching 80%, was achieved under neutral pH conditions with a settling time of 53 minutes. Furthermore, the investigated combined method investigated enhances the flocculation effectiveness of microalgae. Based on the findings, it can be inferred that the efficiency of microalgae harvesting rises with longer duration, higher nanoparticle concentrations, and lower pH levels https://ceej.aut.ac.ir/article_5323_db90f689b1567600818428ca3dfc88a3.pdf