Effect of Dilution on the Pollutant Monitoring in Decentralised Treatment Facilities Using Electrical Conductivity Sensors: Experimental and Modelling Insights

Electrical conductivity (EC) is a common and cheap water monitoring sensor, and in some way reflects the water body pollution level qualitatively. In this study, the domestic sewage characteristic analysis for decentralised treatment facilities in plain and mountainous rural areas, Eastern China, showed that influent TN/NH3-N/TP concentrations were strongly and linearly correlated with influent EC values. EC source apportionment indicated that although no single ion in rural domestic sewage dominated the EC value, EC was packed with vast amounts of information on pollutant content and colud be precisely predicted by support vector machine (SVM) regression model (R = 0.9520). According to field investigation and dilution simulation analysis, the mechanism of correlations between influent TN/NH3-N/TP concentrations and EC values was confirmed and attributed to dilutions by background water during pipeline transport. Particularly, although the dilution processes in plain and mountainous areas were similar and the dilution coefficients were speculated to both obey a Poisson distribution, the average dilution coefficient in plain area was 0.35 ± 0.16 with λ=4 while that in mountainous area was 0.23± 0.15 with λ=2. Our results demonstrate that the EC sensor provides a cheap, rapid and reliable alternative pollutant monitoring method for decentralised treatment facilities in rural areas with mechanism clear.