http://www.press.ierek.com ISSN (Print: 2537-0731, online: 2537-074X) Proceedings of Science and Technology pg. 1 Research Paper Received:30 July 2023, Accepted: 25 September 2023, Published online: 30 September 2023 DOI: 10.21625/resourceedings. v3i2.979 Chemical Oxygen Demand Sensor Based on Microbial Fuel Cell Using Low-Cost Electrodes Fabricated from Waste Rice Husks Soichiro Hirose 1 , Trang Nakamoto 2 , Kozo Taguchi 3 1 Department of Electrical and Electronic Engineering, Ritsumeikan University, Kusatsu, Japan. 2 Assistant Professor, Department of Electrical and Electronic Engineering, Ritsumeikan University, Kusatsu, Japan 3 Professor, Department of Electrical and Electronic Engineering, Ritsumeikan University, Kusatsu, Japan taguchi@se.ritsumei.ac.jp Abstract Environmental pollution is one of the problems that humankind must solve for a sustainable future. Monitoring of Chemical Oxygen Demand (COD) is an important indicator for monitoring the status of organic pollution in water. However, conventional methods for monitoring COD face high costs and complicated design issues. In this study, the use of microbial fuel cells (MFC) composed of low-cost and easy-to-fabricate electrodes using smoked charcoal from rice husks and Japanese ink was investigated for use in COD sensors. Rice husks are an industrial waste product. Therefore, they can be used at a low cost, and using them can help solve the waste problem, which is one of the causes of environmental pollution. With these materials, the electrodes were fabricated for the cost of $0.022/cm 3 . In addition, floating MFC was used for the sake of sensing COD in rivers, waterways, and lakes. The high physical stability of the block-shaped electrode used in this study allowed a biofilm to form on the anode surface by inserting the anode into the soil. The block-shaped electrodes were physically stable in solution. The results showed that there was a correlation between COD concentration (30~150 mg/L) and MFC voltage for more than eight months. Block- shaped electrodes fabricated with rice husk smoked charcoal and Japanese ink would be a promising electrode for MFC to monitor COD in solution in real-time. © 2023 The Authors. Published by IEREK Press. This is an open-access article under the CC BY license (https://creativecommons.org/licenses/by/4.0/). Keywords Microbial fuel cell; COD; Sensor; Rice husk 1. Introduction Environmental pollution is one of the problems that humanity must solve for a sustainable future. Among them, water pollution is a major threat to ecosystems and human health around the world (Boelee et al., 2019). Water pollution can be chronic, caused by heavy metals and organic compounds, or sudden, caused by artificial accidents or illegal incidents (Zamora-Ledezma et al., 2021, David & Niculescu, 2021, Liang et al., 2022, Wang et al., 2021). Sudden water pollution seriously threatens the safety of industrial and domestic water supplies and can cause social panic (Long et al., 2019). In recent years, sudden water pollution has become more frequent (Li et al., 2019). To reduce the damage caused by sudden water pollution, it is important to detect the occurrence of water pollution and identify its source (Wu et al., 2020). This requires frequent measurement of water quality at many points.