Electrical conductivity in rural domestic sewage: An indication for comprehensive concentrations of influent pollutants and the effectiveness of treatment facilities

In this study, the electrical conductivity (EC) of the influents and effluents of rural domestic sewage treatment facilities from eight counties in Jiaxing City were investigated through correlation with pollutants, such as chemical oxygen demand (COD), total nitrogen (TN), ammonium nitrogen (NH4+ -N), total phosphorus (TP) and suspended solids (SS). EC exhibited good correlations with the concentrations of TN (R-2 = 0.7068, p < 0.01), NH4+ -N (R-2 = 0.6718, p < 0.01) and TP (R-2 = 0.5944, p < 0.01), suggesting that EC could be used to indicate TN, NH4+ -N and TP concentrations in rural domestic sewage, and thus, dynamically adjust the treatment load of rural domestic sewage treatment facilities. A higher level of pollutants in rural domestic sewage resulted in higher correlations between TN/NH4+ -N/TP and EC. Furthermore, a novel evaluation methodology for rural domestic sewage facilities in Jiaxing was established. This method could indicate the effectiveness of facilities when the ratio of effluent EC to influent EC was below 0.8 or beyond 1.0. In particular, this method identified the ineffective facilities, with a recognition rate of 70% and an accuracy rate of 84%. This study not only provides an efficient, fast and low-cost effectiveness assessment method for rural domestic sewage treatment facilities, but also increases the possibility of remotely controlled evaluation based on online conductivity.