Citation: Chandrasekhar, T.; Varaprasad, D.; Gnaneswari, P.; Swapna, B.; Riazunnisa, K.; Anu Prasanna,V.; Korivi, M.; Wee, Y.-J.; Lebaka, V.R. Algae: The Reservoir of Bioethanol. Fermentation 2023, 9, 712. https://doi.org/10.3390/ fermentation9080712 Academic Editor: Zhihua Liu Received: 27 June 2023 Revised: 20 July 2023 Accepted: 22 July 2023 Published: 27 July 2023 Copyright: © 2023 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/). fermentation Review Algae: The Reservoir of Bioethanol Thummala Chandrasekhar 1, * ,† , Duddela Varaprasad 1,† , Poreddy Gnaneswari 1,† , Battana Swapna 2 , Khateef Riazunnisa 3 , Vankara Anu Prasanna 4 , Mallikarjuna Korivi 5 , Young-Jung Wee 6 and Veeranjaneya Reddy Lebaka 7, * 1 Department of Environmental Science, Yogi Vemana University, Kadapa 516005, A.P, India; varaprasad.toxic@gmail.com (D.V.); gnaniporeddy1997@gmail.com(P.G.) 2 Department of Botany, Vikrama Simhapuri University College, Kavali 524201, A.P, India; swapnaivsr@gmail.com 3 Department of Biotechnology & Bioinformatics, Yogi Vemana University, Kadapa 516005, A.P, India; khateefriaz@gmail.com 4 Department of Zoology, Yogi Vemana University, Kadapa 516005, A.P, India; annuprasanna@gmail.com 5 Institute of Human Movement and Sports Engineering, College of Physical Education and Health Sciences, Zhejiang Normal University, Jinhua 321004, China; mallik.k5@gmail.com 6 Department of Food Science and Technology, Yeungnam University, TGyeongsan 712749, Gyeongbuk, Republic of Korea; yjwew@ynu.ac.kr 7 Departmentof Microbiology, Yogi Vemana University, Kadapa 516005,A.P, India * Correspondence: tcsbiotech@gmail.com or tcs@yogivemanauniversity.ac.in (T.C.); lvereddy@gmail.com (V.R.L.); Tel.: +91-918-263-3585 (T.C.) † These authors contributed equally to this work. Abstract: Overuse of non-renewable fossil fuels due to the population explosion urges us to focus on renewable fuels such as bioethanol. It is a well-known fact that ethanol is useful as a blending product with common fuels such as petrol and diesel. This reduces the cost besides bringing down environmental pollution. Apart from chemical methods, bioethanol is generated from photosynthetic plants including algae, plant-based products, microbial organisms and their waste. Specifically, the production of ethanol from microalgal sources has been an attractive method in recent days. The reason behind using microalgal species is their simple structure with photosynthetic ability. In contrast, certain algal species often go disused in some regions. Hence, the production of ethanol from algal sources is one of the best waste management practices. Moreover, it is easy to improve the biomass in microalgal species by altering the physicochemical conditions such as light, pH, temperature, external supply of nutrients, vitamins, nano-sized particles, gene alterations etc., which will enhance ethanol production. In this review, the methods used for ethanol production are discussed. In addition, the factors involved in algal growth and ethanol production are emphasized. Overall, this review focuses on ethanol production from various algal species. This information will be useful for industrial-level production of ethanol and future renewable energy research. Keywords: algae; photosynthesis; biomass; fermentation; bioethanol; enhancement 1. Introduction Current lifestyles undoubtedly make us dependent on a continuous supply of energy. In addition, the population explosion and their necessities have been progressing toward a conflict with energy obligations in recent times [1]. In contrast, regular consumption of fossil fuels depletes a major portion of non-renewable energy sources. According to the world energy outlook 2015, fossil fuels such as coal, petrol products and natural gas are being used predominantly for energy requirements in various sectors, providing more than 80% of the world’s energy between 2013 and 2035 [2]. Specifically, energy demands across the industrial and transport sectors are high compared to other sectors [3,4]. The gap between demand and supply of fossil fuels is increasing continuously, thereby raising Fermentation 2023, 9, 712. https://doi.org/10.3390/fermentation9080712 https://www.mdpi.com/journal/fermentation