Citation: Kim, H.S.; Kim, M.; Park, W.-K.;Yang, W.-G.; Nayak, M.; Shin, H.H.; Cho, K.; Kim, D.; Oda, T. Microalgae as an Effective Recovery Agent for Vanadium in Aquatic Environment. Energies 2022, 15, 4467. https://doi.org/10.3390/en15124467 Academic Editor: José Carlos Magalhães Pires Received: 22 May 2022 Accepted: 17 June 2022 Published: 19 June 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Article Microalgae as an Effective Recovery Agent for Vanadium in Aquatic Environment Hee Su Kim 1 , Minsik Kim 2 , Won-Kun Park 3 , Won-Geun Yang 1 , Manoranjan Nayak 4 , Hyeon Ho Shin 5, *, Kichul Cho 6 , Daekyung Kim 1, * and Tatsuya Oda 7 1 Daegu Center, Korea Basic Science Institute (KBSI), 80 Daehak-ro, Daegu 41566, Korea; heesuinny@gmail.com (H.S.K.); wgyang1@kbsi.re.kr (W.-G.Y.) 2 Cell Factory Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), 125 Gwahak-ro, Daejeon 34141, Korea; minsik.kim@mgh.harvard.edu 3 Department of Chemistry and Energy Engineering, Sangmyung University, 20 Hongimun 2-gil, Jongno-gu, Seoul 03016, Korea; wkpark@smu.ac.kr 4 Biorefinery and Bioenergy Research Laboratory, Amity Institute of Biotechnology, Amity University Uttar Pradesh, Noida 201313, India; nayakimmt@gmail.com 5 Library of Marine Samples, Korea Institute of Ocean Science & Technology, Geoje 53201, Korea 6 Department of Applied Marine Bioresource Science, National Marine Biodiversity Institute of Korea (MABIK), Seocheon-gun 33662, Korea; kichul.cho@mabik.re.kr 7 School of Fisheries Science & Environmental Studies, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan; t-oda@nagasaki-u.ac.jp * Correspondence: shh961121@kiost.ac.kr (H.H.S.); dkim@kbsi.re.kr (D.K.) Abstract: Given that vanadium is a valuable material, the implementation of vanadium recycling processes is thus necessary to enhance the element’s value chain as well as minimize its undesirable environmental consequences. Among various remediation methods available, a biological method based on microalgal adsorption is known to be eco-friendly and calls for further investigations. Herein, we evaluated V 2 O 5 adsorption efficiencies of four different microalgal strains: Nannochloropsis oculata, Heterocapsa circularisquama, Chattonella marina, and Chattonella antiqua. Inductively coupled plasma mass spectrometry (ICP-MS) data indicated that vanadium concentration in the culture medium of Nannochloropsis oculata was reduced from 4.61 ± 0.11 mg L −1 to 1.85 ± 0.21 mg L −1 after being exposed to V 2 O 5 solution for 24 h, whereas the supernatants of the other three strains displayed no change in vanadium ion concentration. Therefore, our results indicated a strong potential of Nannochloropsis oculata for recycling vanadium with approximately 59.9% of vanadium ion removal efficiency. Furthermore, morphological observation of Nannochloropsis oculata using scanning electron microscopy (SEM) indicated that the cells were able to maintain their intact morphology even under the presence of high concentrations of heavy metals. Due to the high adsorption efficiency and robustness of Nannochloropsis oculata, the results collectively support it as a potential strain for V 2 O 5 recovery. Keywords: Nannochloropsis oculata; vanadium oxide; adsorption; ICP-MS; SEM 1. Introduction Scientists across the world are studying various issues associated with heavy metal recycling because of: (1) environmental pollution and (2) high commercial values of some of the rare elements [1–5]. Among various heavy metals, vanadium (V) is directly used in real- life applications as catalysts in the steel and semiconductor industries [6], and vanadium- based batteries are considered a promising energy storage device [7–10]. Vanadium ore is mined only in a few countries, including China, the United States, and South Africa, therefore it is an industrially valuable commodity [11]. However, vanadium is often discarded in various industrial wastewaters [12,13], even though its different forms have been acknowledged to be toxic [6]. Thus, recycling vanadium ions present in aquatic Energies 2022, 15, 4467. https://doi.org/10.3390/en15124467 https://www.mdpi.com/journal/energies