Ecological ditch system for nutrient removal of rural domestic sewage in the hilly area of the central Sichuan Basin, China

Abstract

Domestic sewage is a key source of surface water pollution in rural areas of developing countries, especially in China, where a large amount of highly concentrated nutrients is directly discharged into the receiving waters. Therefore, in this study, a set of ecological ditch systems was designed to remove nutrients from rural domestic sewage in the hilly area of the central Sichuan Basin, China. The results show that the total nitrogen (TN) removal efficiencies range from 14.87% to 84.24%, with an average of 47.97%, and the total phosphorus (TP) removal efficiencies range from 13.93% to 86.22% with an average of 49.79%. The highest daily TN and TP removal rates are 13.06 and 1.30 g m−2 d−1, respectively, and the average removal rates are 3.19 g m−2 d−1 for TN and 0.28 g m−2 d−1 for TP. Our results indicate that the ecological ditch system to treat rural domestic sewage with high nutrient concentrations can be used in the study area or areas with similar topography. Furthermore, we found that the nutrient removal efficiencies exhibit considerable seasonal variations and are sensitive to the hydraulic flow rates. The nutrient removal capacity of the ecological ditch system is therefore somewhat limited. Based on our findings, the use of winter-hardy wetland plants and increase of the size of the filter unit are recommended to make the ecological ditch system more efficient and maintain high nutrient removal rates year-round. Furthermore, we suggest that regular mowing of plants and the removal of accumulated sediment are necessary to manage the ecological ditch system.