Underwater IoT System for Water Quality Monitoring at the Marine Outfall

Monitoring ocean salinity and temperature is vital for understanding ecosystem health and mitigating marine pollution from untreated municipal sewage. This paper explores the use of IoT systems for continuous underwater monitoring of marine outfalls from wastewater treatment plants, providing early warnings of contamination. The system is composed of multiple sensors, highlighting the temperature and salinity sensors in this paper. We have used a commercial temperature sensor, the DS18B20 and a tailored salinity sensor. Those sensors are connected to the sensor node, an ESP32. The node collects the data and sends it to a database. The temperature and salinity sensors are calibrated and validated with generated samples. The samples have a variation of salinity from 0 to $40 \mathrm{~g} / \mathrm{L}$, and the variation in temperature goes from 40 to $10^{\circ} \mathrm{C}$. The results indicated that the commercial temperature sensor has a bias, and we proposed an equation to correct it. The salinity sensor is calibrated, obtaining an equation with an R2 of 99.5%. The network traffic analysis indicates an increase in traffic when errors in TPC packets appear.