Study on key technologies for improving quality and efficiency of urban drainage system: a case of Ma′anshan City

The low quality and efficiency of drainage systems are ubiquitous in cities in the middle and lower reaches of the Yangtze River, becoming a bottleneck restricting the long-term improvement of the urban water environment. Based on the Yangtze River eco-environmental protection and restoration requirements of Ma′anshan City, four key technologies for improving the water quality of the main inland river, the Cihu River, in the aspects of accurate source control, sewage interception and pollution control on rainy days were studied. The technologies included: 1) Applying the drainage outlets tracing methods based on grid water quantity and quality monitoring, and combining the inverse problem method, the main discharge areas of pollution load along the Cihu River mainstream were determined, thus fulfilling the simple and accurate sewage outlet investigation. 2) A Monte Carlo chemical mass balance model was developed based on the water quality characteristic factors to identify the mixed sewage volume and groundwater infiltration volume of rainwater pipeline in primary drainage areas of Cihu River, and the microbial genetic algorithm (MGA) was further applied to locate mixed connection and damage points. 3) Comprehensively considering the influence of multiple factors such as rainfall characteristics, sunny days in the early stage, pipeline sediments and mixed sewage, the dynamic process lines of water quality and quantity at discharge outlets were established, and the "concentration-volume" optimizing regulation and storage design based on multiple influencing factors was proposed to greatly improve the interception loads. 4) The feasibility of efficient overflow pollution control techniques based on in-situ coagulation-flocculation in the pipeline was proposed and explored. Through the scientific and technological support and the efforts of all parties, the water quality in the Cihu River, Ma′anshan City, had been steadily improved, which provided a reference for further improving the effectiveness of urban water environment comprehensive treatment in the middle and lower reaches of the Yangtze River.