Development and Field Evaluation of a Mobile Water-Quality Sensing System for Environmental Monitoring in Tainan, Taiwan

This study presents the design, deployment, and field performance of a city-scale mobile water-quality sensing network developed to complement regulatory inspections and citizen-complaint investigations in Tainan, Taiwan. Six IP68-rated mobile sensor units measuring pH, electrical conductivity (EC), dissolved oxygen (DO), and temperature were deployed at two regulatory inspection sites and four complaint hotspots within the Yanshui River, Liuchong Creek, and Liucuo Drain systems. The network operated from 7 April to 31 August 2025, with temporary retrievals during typhoon events and one theft incident followed by successful recovery and redeployment. High-frequency measurements revealed recurrent pH excursions beyond the effluent standard range (6.0–9.0) at three sites, as well as persistent hypoxia (DO ≤ 1 mg/L on average) across multiple reaches, findings that are consistent with suspected industrial and livestock pollution sources. Overall, the results demonstrate that compact, rapidly deployable, solar-assisted sensing units can effectively capture short-lived water-quality violations and delineate spatiotemporal pollution hotspots that are often missed by conventional low-frequency grab sampling, while also underscoring operational considerations such as antifouling maintenance, security, and storm-response protocols.