Journal of Water and Soil https://jsw.um.ac.ir Research Article Vol. 38, No. 5, Dec.-Jan. 2024, p. 541-554 Investigation of Nitrate Adsorption Isotherms by Iron (III) and Zinc-coated Biochars Using Ultrasonic M.R. Alashti 1 , M. Khoshravesh 2 *, F. Sadegh-Zadeh 3 , H.M. Azamathulla 4 1 and 2- Ph.D. Student of Irrigation and Drainage and Associate Professor, Water Engineering Department, Faculty of Agricultural Engineering, Sari Agricultural Sciences and Natural Resources University, Sari, Iran, respectively. (*- Corresponding Author Email: m.khoshravesh@sanru.ac.ir) 3- Associate Professor, Department of Soil Science, Faculty of Crop Sciences, Sari Agricultural Sciences and Natural Resources University, Sari, Iran 4- Professor, Department of Civil and Environmental Engineering, Faculty of Engineering, The University of the West Indies, St. Augustine Campus, St Augustine, Trinidad and Tobago Received: 01-02-2024 1 Revised: 13-09-2024 Accepted: 19-09-2024 Available Online: 19-09-2024 How to cite this article: Alashti, M.R., Khoshravesh, M., Sadegh-Zadeh, F., & Azamathulla, H.M. (2024). Investigation of nitrate adsorption isotherms by iron(III) and zinc-coated biochars using ultrasonic assistance. Journal of Water and Soil, 38(5), 541-554. (In Persian with English abstract). https://doi.org/10.22067/jsw.2024.86650.1379 Introduction The rapid growth and development of urban communities, coupled with the increased industrial and economic activities in recent years, have led to the production and release of various pollutants into the environment. These pollutants have adverse effects on human health, living organisms, and the overall environment. With limitations in water resources, insufficient rainfall, the looming risk of water crises in many countries, and the escalating pollution of surface and underground water, there is a pressing need for environmental solutions to mitigate these issues. It is important to acknowledge that wastewater often contains pollutants that may render it unsuitable for certain applications. The utilization of biochar derived from cost-effective materials and innovative technologies such as ultrasonics is one avenue that warrants exploration for enhancing water quality. In this approach, a nitrate solution is exposed to both an adsorbent and ultrasonic waves. This dual treatment induces changes in the physical and chemical properties of water, thereby offering potential improvements in water quality. Materials and Methods This study aimed to explore the impact of utilizing biochar derived from rice straw, which was coated with iron(III) and zinc cations, and subjected to ultrasonication, on the nitrate adsorption process from aqueous solutions. In order to produce biochar, cheap materials of rice straw were used. The chopped straw was placed in the electric furnace and heated for one hour to reach the desired temperature. Then it was kept at that temperature for 2 hours. After that, the obtained biochar was washed three times with distilled water at a ratio of 1:20 and dried in an oven at 70°C for 24 hours. In this study, two temperature levels, 350 °C and 650 °C, were used for biochar production. Based on the results from pre-tests, it was found that biochars produced at 650 °C exhibited higher nitrate removal efficiency. These biochars were then used for the continuation of the experiments. To optimize the adsorbent dose, pre-tests were conducted using doses of 0.1, 0.3, 0.5, 0.8, and 1 gram of the adsorbent with 40 ml of nitrate solution. The concentrations of nitrate solution tested were 20, 45, 80, 100, 150, and 200 mg L -1 . The research involved conducting experiments to determine the optimal parameters for each treatment, with three repetitions conducted in the water quality laboratory of Sari agricultural sciences and Natural Resources University during the years 2021 and 2022. The treatments comprised biochar (B), biochar and ultrasonic (BU), biochar with iron(III) coating (BF), biochar ©2024 The author(s). This is an open access article distributed under Creative Commons Attribution 4.0 International License (CC BY 4.0) . https://doi.org/10.22067/jsw.2024.86650.1379