Academic Editors: Pablo R. Salgado, Germán Giácoman-Vallejos and Adolfo Henríquez Received: 3 February 2025 Revised: 13 February 2025 Accepted: 14 February 2025 Published: 16 February 2025 Citation: González Fernández, L.A.; Medellín Castillo, N.A.; Sánchez Polo, M.; Navarro Frómeta, A.E.; Vilasó Cadre, J.E. Algal-Based Carbonaceous Materials for Environmental Remediation: Advances in Wastewater Treatment, Carbon Sequestration, and Biofuel Applications. Processes 2025, 13, 556. https://doi.org/10.3390/ pr13020556 Copyright: © 2025 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/). Review Algal-Based Carbonaceous Materials for Environmental Remediation: Advances in Wastewater Treatment, Carbon Sequestration, and Biofuel Applications Lázaro Adrián González Fernández 1,2, * , Nahum Andrés Medellín Castillo 1,3, * , Manuel Sánchez Polo 2 , Amado Enrique Navarro Frómeta 4 and Javier Ernesto Vilasó Cadre 5 1 Multidisciplinary Postgraduate Program in Environmental Sciences, Av. Manuel Nava 201, 2nd. Floor, University Zone, San Luis Potosí 78000, Mexico 2 Faculty of Sciences, University of Granada, 18071 Granada, Spain; mansanch@ugr.es 3 Center for Research and Postgraduate Studies, Faculty of Engineering, Autonomous University of San Luis Potosi, Dr. Manuel Nava No. 8, West University Zone, San Luis Potosí 78290, Mexico 4 Food and Environmental Technology Department, Technological University of Izucar de Matamoros, De Reforma 168, Campestre La Paz, Izúcar de Matamoros 74420, Mexico; navarro4899@gmail.com 5 Institute of Metallurgy, Autonomous University of San Luis Potosí, Sierra Leona Av. 550, Lomas 2nd Section, San Luis Potosí 78210, Mexico; a321418@alumnos.uaslp.mx * Correspondence: lazaroadrian1995@gmail.com (L.A.G.F.); nahum.medellin@uaslp.mx (N.A.M.C.) Abstract: Water pollution from industrial, municipal, and agricultural sources is a press- ing global concern, necessitating the development of sustainable and efficient treatment solutions. Algal biomass has emerged as a promising feedstock for the production of carbonaceous adsorbents due to its rapid growth, high photosynthetic efficiency, and ability to thrive in wastewater. This review examines the conversion of algal biomass into biochar and hydrochar through pyrolysis and hydrothermal processes, respectively, and evaluates their potential applications in wastewater treatment, carbon sequestration, and biofuel pro- duction. Pyrolyzed algal biochars typically exhibit a moderate to high carbon content and a porous structure but require activation treatments (e.g., KOH or ZnCl 2 ) to enhance their surface area and adsorption capabilities. Hydrothermal carbonization, conducted at lower temperatures (180–260 ◦ C), produces hydrochars rich in oxygenated functional groups with enhanced cation exchange capacities, making them effective for pollutant removal. Algal- derived biochars and hydrochars have been successfully applied for the adsorption of heavy metals, dyes, and pharmaceutical contaminants, with adsorption capacities significantly increasing through post-treatment modifications. Beyond wastewater treatment, algal biochars serve as effective carbon sequestration materials due to their stable structure and high carbon retention. Their application as soil amendments enhances long-term carbon storage and improves soil fertility. Additionally, algal biomass plays a key role in biofuel production, particularly for biodiesel synthesis, where microalgae’s high lipid content facilitates bio-oil generation. Hydrochars, with energy values in the range of 20–26 MJ/kg, are viable solid fuels for combustion and co-firing, supporting renewable energy gener- ation. Furthermore, the integration of these materials into bioenergy systems allows for waste valorization, pollution control, and energy recovery, contributing to a sustainable circular economy. This review provides a comprehensive analysis of algal-derived biochars and hydrochars, emphasizing their physicochemical properties, adsorption performance, and post-treatment modifications. It explores their feasibility for large-scale wastewater remediation, carbon capture, and bioenergy applications, addressing current challenges and future research directions. By advancing the understanding of algal biomass as a multifunctional resource, this study highlights its potential for environmental sustainability and energy innovation. Processes 2025, 13, 556 https://doi.org/10.3390/pr13020556