Development of rapid biochemical oxygen demand (BOD) biosensor using suspended microorganism system

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ABSTRACT

Biochemical Oxygen Demand (BOD) is a critical indicator of water and wastewater quality; however, the conventional five-day incubation period of the BOD5 method limits its usefulness for real-time monitoring and process control. This study reports the development and validation of a rapid bioreactor-type BOD biosensor (BODr) employing a suspended microorganism system with oxidation–reduction potential (ORP) monitoring as an alternative to the standard BOD5 method. The fabricated biosensor uses a 100-mL closed glass bioreactor operated at 30 °C in a temperature-controlled water bath, enabling accelerated microbial respiration and redox responses. Changes in ORP associated with microbial electron transfer during organic matter oxidation were continuously monitored, allowing BOD determination within a 15-minute reaction period. Method validation demonstrated a strong linear relationship (r = 0.998) between BOD concentration and biosensor response over an operational range of 25–800 mg L?¹, indicating its potential for accurate quantification. A paired t-test showed no significant difference between BODr and BOD5 measurements in standard solutions, confirming comparable accuracy. The limit of detection (LOD = 9.26 mg L^-1) and limit of quantitation (LOQ = 29.5 mg L^-1) indicated that the biosensor could detect and quantify BOD below the regulatory limit for Class C receiving water bodies (50 mg L^-1). Application of the biosensor to actual water and wastewater samples representing low-, medium-, and high-strength BOD conditions showed no significant differences between BOD values obtained with the BODr biosensor (field and laboratory tests) and those obtained with the conventional BOD5 method, as confirmed by analysis of variance (ANOVA). These results confirmed that the developed BODr biosensor offers a viable and rapid alternative to the traditional BOD5 test for accurate and timely water quality assessment. Further studies are recommended to evaluate its long-term performance and suitability for routine and in-line water quality monitoring.

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