A Low-Cost IoT-Enabled Buoy System for Real-Time Detection and Ultrasonication-Based Mitigation of Harmful Algal Blooms in Sri Lankan Freshwater Bodies

Abstract

Harmful algal blooms (HABs) are an increasing threat to drinking-water supply, fisheries and aquatic ecosystems in Sri Lankan reservoirs and urban lakes, yet detection in the country still relies almost entirely on manual sampling and laboratory analysis. This paper presents the design, implementation and

experimental evaluation of a low-cost, solar- powered buoy platform that combines real-time

water-quality sensing with a non-chemical mitigation mechanism. The buoy integrates pH,

turbidity and temperature sensors with a custom- built chlorophyll-a fluorometer built around a 470

nm excitation LED and an OPT101 photodiode, all interfaced to an ATmega328P microcontroller. Sensor data are relayed over a 433 MHz LoRa link to a gateway and displayed on a cloud dashboard, while an ultrasonic transducer array driven by an IR2110/IRF640N H-bridge provides physical algae suppression. Laboratory trials using Beira Lake water showed that algae-contaminated samples produced pH values of 7.20–7.99 against 6.63–6.69 for clear water, and fluorometer readings of 70–78 ADC counts against 58–65 ADC counts for clear water. A three-day ultrasonication trial produced only a modest reduction in turbidity, pH and fluorescence, and LoRa communication remained stable over a 1 km outdoor test link. The results confirm that an affordable sensor–communication– mitigation platform of this kind is technically feasible for early-warning HAB monitoring in resource-limited settings, while also identifying the fluorometer sensitivity and ultrasonic power density as the main areas requiring further development before field deployment.