Citation: Gururani, P.; Bhatnagar,P.; Kumar, V.; Vlaskin, M.S.; Grigorenko, A.V. Algal Consortiums: A Novel and Integrated Approach for Wastewater Treatment. Water 2022, 14, 3784. https://doi.org/10.3390/ w14223784 Academic Editor: Alexandre T. Paulino Received: 23 September 2022 Accepted: 17 November 2022 Published: 21 November 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/). water Review Algal Consortiums: A Novel and Integrated Approach for Wastewater Treatment Prateek Gururani 1 , Pooja Bhatnagar 2 , Vinod Kumar 2,3, * , Mikhail S. Vlaskin 4 and Anatoly V. Grigorenko 4 1 Department of Biotechnology, Graphic Era (Deemed to be University), Dehradun 248002, Uttarakhand, India 2 Algal Research and Bioenergy Lab, Department of Life Sciences, Graphic Era (Deemed to be University), Dehradun 248002, Uttarakhand, India 3 Peoples’ Friendship University of Russia (RUDN University), Moscow 117198, Russia 4 Joint Institute for High Temperatures of the Russian Academy of Sciences, 13/2 Izhorskaya St., Moscow 125412, Russia * Correspondence: kumarvinod.ls@geu.ac.in Abstract: Urbanization, industrialization and other human-related activities discharge various inor- ganic and organic toxic compounds into the environment. Many physical, chemical and biological methods have been practiced, to treat contaminated wastewater: among these, the biological method of wastewater treatment by utilizing algae has been reviewed widely. However, the removal effi- cacy of algae monoculture is low, as compared to the algae consortium systems. The presence of microorganisms such as fungi or bacteria in wastewater can establish various relationships, such as mutualism or symbiosis with algae, which help in the removal of various organic and inorganic compounds from wastewater, thus acting as a wastewater treatment system. Heterotrophic microor- ganisms can segregate natural organic matter, which is released by algae in the form of dissolved organic carbon, and releases carbon dioxide, which is utilized by algae for photosynthesis. In ac- cordance with existing studies, microalgal consortiums with bacteria or fungi occurring naturally or crafted artificially can be utilized for wastewater treatment; therefore, the present review pro- vides an outline of the symbiotic relationships between algae and other microorganisms, and their applications in wastewater treatment. Various mechanisms—such as mutualism, commensalism and parasitism—for the removal of different pollutants from wastewater by consortium systems have been elucidated in this review; moreover, this review addresses the challenges that are re- stricting large-scale implementation of these consortiums, thus demanding more research to enable enhanced commercialization. Keywords: wastewater treatment; algae; algae–bacteria consortium; algae–fungi consortium 1. Introduction Water, along with air, is the most precious and liberal resource for human survival [1]; however, in recent decades, the constant development of societies, and their increased dependence on fresh water sources, have led to the extensive generation of wastewater from different non-pointed and pointed sources, such as food wastewater, industrial wastewater, domestic wastewater and many more [2]. Wastewater constitutes various contaminants and pollutants, involving nutrients such as phosphorus and nitrogen, and heavy metals such as lead and zinc, which are of emerging concern; furthermore, it has been reported that in 2020, emissions of total phosphorus and total nitrogen reached 336,700 tons and 3,223,400 tons, respectively. In addition, emissions of chemical oxygen demand (COD) were five times greater in 2020 than in 2019, extending to 25.6476 MT, and the overall discharge of heavy metals reached around 26,680 kg [3]. If the wastewaters are directly released into the environment without any effective treatment, such toxic pollutants will not only harm aquatic life, but will also risk human health [4]. It is estimated that by 2030 the world will be faced with a 40% water shortage in existing water resources such as rivers, lakes and Water 2022, 14, 3784. https://doi.org/10.3390/w14223784 https://www.mdpi.com/journal/water