A Low-Cost LoRa Optical Fluorometer–Nephelometer for Wireless Monitoring of Water Quality Parameters in Real Time

Real-time monitoring of water quality parameters using optical sensors has become widespread. However, the price of commercial sensors and the ability to integrate them into customized sensing networks can limit their application in research and monitoring programs. This study introduces the design, verification, and validation of an innovative, low-cost, portable, low-power fluorometer-nephelometer device, employing Long-Range Wide Area Network technology. The developed Internet of Things capable device can measure temperature, turbidity, phycocyanin fluorescence (a proxy for cyanobacteria biomass), and chlorophyll- a fluorescence (a proxy for phytoplankton (cyanobacteria plus algae) biomass) in aquatic ecosystems. The fluorometer-nephelometer structure employs one digital thermistor probe, three distinct light-emitting diodes (LEDs) that are amber (590 nm) to excite phycocyanin pigments of cyanobacteria, blue (465 nm) to excite chlorophyll- a pigments of phytoplankton, and near-infrared (870 nm) to measure turbidity through light scattering. Two orthogonal silicon photodiodes are used as detectors set in line with long pass filters of 830 nm for turbidity and 630 nm for phytoplankton. A peristaltic pump circulates water through a polymethylmethacrylate cuvette within a 3D-printed fluorometer assembled in a weatherproof box. The activation by personalization LoRaWAN protocol is utilized for real-time wireless transmission of water quality data while a micro-SD card is employed for storing the data locally. The optical sensor tests are conducted in the laboratory using standard turbidity solutions and pigments. The turbidity, phycocyanin, and chlorophyll-a sensing ranges are 3-200 FTU, 0.025-2.5 mg-PC/L, and 1-50 μg-chl/L, respectively. In repeated laboratory tests, the relative percent difference is consistently less than 10%.