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.
