Citation: Sibiya, N.P.; Amo-Duodu, G.; Tetteh, E.K.; Rathilal, S. Effect of Magnetized Coagulants on Wastewater Treatment: Rice Starch and Chitosan Ratios Evaluation. Polymers 2022, 14, 4342. https:// doi.org/10.3390/polym14204342 Academic Editors: Alexandre Vetcher and Alexey Iordanskii Received: 18 August 2022 Accepted: 10 October 2022 Published: 15 October 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/). polymers Article Effect of Magnetized Coagulants on Wastewater Treatment: Rice Starch and Chitosan Ratios Evaluation Nomthandazo Precious Sibiya * , Gloria Amo-Duodu * , Emmanuel Kweinor Tetteh and Sudesh Rathilal Green Engineering Research Group, Department of Chemical Engineering, Faculty of Engineering and The Built Environment, Durban University of Technology, Durban 4001, South Africa * Correspondence: nomtha.presh@gmail.com (N.P.S.); gamoduodu04@gmail.com (G.A.-D.); Tel.: +27-63205-5378 (N.P.S.); +27-84-9992841 (G.A.-D.) Abstract: Coagulation with synthetic chemicals has been used to treat a wide range of industrial effluents. Herein, the unique characteristics of industrial effluents being detrimental to the environ- ment warrants urgent resource-efficient and eco-friendly solutions. Therefore, the study investigated the use of two magnetized coagulants (chitosan magnetite (CF) and rice starch magnetite (RF)), prepared via co-precipitation in three different ratios (1:2, 1:1 and 2:1) of natural coagulants (chitosan or rice starch) and magnetite nanoparticles (F) as alternative coagulants to alum for the treatment of wastewater. A Brunauer–Emmett–Teller (BET) analyzer, an X-ray diffraction (XRD) analyzer, and energy-dispersive X-ray (EDX) spectroscopy were used to characterize the surface area, crystal structure, and elemental composition of the coagulants. The influences of settling time (10–60 min) on the reduction of turbidity, color, phosphate, and absorbance were studied. This was carried out with a jar test coupled with six beakers operated under coagulation conditions of rapid stirring (150 rpm) and gentle stirring (30 rpm). Wastewater with an initial concentration of 45.6 NTU turbidity, 315 Pt. Co color, 1.18 mg/L phosphate, 352 mg/L chemical oxygen demand (COD), and 73.4% absorbance was used. The RF with a ratio of 1:1 was found to be the best magnetized coagulant with over 80% contaminant removal and 90% absorbance. The treatability performance of RF (1:1) has clearly demonstrated that it is feasible for wastewater treatment. Keywords: coagulation; chitosan; rice starch; magnetite; wastewater treatment; magnetized coagulants 1. Introduction The demand on freshwater resource supply is deteriorating as industrial and agricul- tural activities are upsurging and population growth shows a constant increase. Conse- quentially, wastewater treatment becomes inevitable due to the detrimental effects it has on human health and the environment [1]. Water scarcity affects approximately 2 billion people [2]. Wastewater treatment plants (WWTPs) are a substantial source of pollutants discharged into water bodies [3,4] due to the fact that they do not meet the Environmental Protection Agency’s strict criteria for controlling effluent plant quality [5,6]. Therefore, it is critical for WWTPs to release clean effluent into water bodies since they serve as potable water and are utilized for agriculture purposes and other recreational activities. Various processes and technologies have been explored to enhance the quality of water in order to meet the water demand at a low cost [7]. These technologies are divided into three categories: physical (settling, filtration and membrane technology), chemical (coagulation, ion exchange, disinfection, oxidation, catalytic reduction and softening processes) and biological (microbial biodegradation, bioreactor processes, etc.) treatment techniques [8,9]. Coagulation/flocculation is frequently used in water and wastewater treatment to effi- ciently reduce the organic load prior to subsequent treatment processes [10]. Furthermore, it has sparked widespread attention in the industrial sector due to easy usability, high efficiency, and low cost. In coagulation, tiny particles are aggregated into bigger aggregates Polymers 2022, 14, 4342. https://doi.org/10.3390/polym14204342 https://www.mdpi.com/journal/polymers