Sewage Treatment Plant Design For Small Towns In Mountain Area

As China's rapid increase in the level of urbanization, sewage treatment and environmental protection in small-towns have become an increasing concern. To accelerate the construction of more sewage treatment plants for these kinds of towns has become an important task.This dissertation describes the investigation of the design of a sewage treatment plant for Langao County of Shaanxi Province, a small town in the Qinling Mountains. Drainage plans have been proposed based on the statistical analysis of water supply and usage. The necessities of a sewage treatment plant are listed, the amounts of water consumption are predicted and the scale of the plant and the construction scheme of the main sewage pipe network have been proposed. With comparisons of reliability and advantages of the processes, the sewage treatment process plans are selected. Other aspects including environmental protection, labor protection, fire safety and energy saving measures are all discussed. The investment of the construction is estimated and economic evaluation is performed. The social, environmental and economic benefits of the sewage treatment plant have been comprehensively analyzed.The dissertation concludes that because of the incomplete sewage disposal and collection system and old sewage treatment facilities used in Langao County, a large amount of untreated sewage that is directly drained into the Lan River has caused river pollution, directly affecting people's health and sustainable economical development of the area. The impact has extended to the downstream areas. Water pollution also results in the decrease of the river water utilization. A good sewage treatment system in Langao County will be necessary for promoting economic development, protecting local people's health, improving the urban environment, preventing pollution and fully using of water resources.Through the comparison on the processes and economic analysis, it is suggested that a two-stage biological treatment process with phosphorus and nitrogen removal capability should be adopted, cyclic SBR technology is selected and the treated water can be discharged into the Lan River. In the dry season, this will supplement the river water and improve the river landscape. In the future, according to the water quality requirements, some back water can be used for industrial production. Sewage sludge can be used as fertilizer after dehydration or treated by sanitary landfill.Meanwhile, this dissertation suggests further improvement on the drainage system of Langao County, the construction of sewage plants and sewage intercepting pipe networks should be performed in the same time to ensure the drainage system has the capability to transport all sewage of the whole town into the treatment plant after the completion of the plant to fully achieve its expected performance. National and local emission standards should be strictly implemented. Monitoring and control of the discharge of industrial wastewater should be strengthen further. Hazardous waste water from industry has to be treated first by the factories themselves to ensure the proper operation of the sewage treatment plant. The flood control facilities (channel slope) inside the sewage treatment plant that locates near the right bank of the Lan River should be built before the completion of the plant to guarantee compliance of the standard of flood defenses after the completion of the plant.