Design and development of an optical setup to study light attenuation by suspended sediments in water

Suspended sediment concentration (SSC) and turbidity are two essential measurements used to evaluate water quality, as they reflect their impact on aquatic ecosystems. The conventional method requires manual intervention and is unable to promptly sense any environmental changes due to urban development, surface run-off, erosion, or climatic effects. Herein, an optical sensor is developed using light-dependent resistors (LDRs), which are non-linear devices used to measure light attenuation through turbidity in the liquid medium. It aims to create affordable sensors that can be expanded to monitor SSC levels using specific measurement techniques that require specialized equipment for precise calibration across different turbidity levels. LDRs were tested for resistance response at different path lengths (50-500 cm), SSC levels (0-7500 mg/L), and laser light wavelengths (532 and 650 nm). The study conducted baseline tests in air and water to measure light attenuation by assessing LDR performance at the center, top, and bottom locations. Four calibration models were developed and evaluated for their accuracy based on metrics such as R², RMSE, NRMSE, MAE, and the agreement index. Of these four models, the BiDoseResp model was found to be the best fitting, with R² and RMSE values of 0.98 and 150.05 mg/L, respectively. The system measures LDR data through its controlled calibration process. The testing of ionic compounds and matrices through dose-response curves establishes the verification of sensor performance. The study develops real-time SSC monitoring systems that enable sustainable water management and environmental protection in aquatic ecosystems.