Municipal sewage includes industrial sewage and our domestic sewage, that is, our daily excrement and domestic waste. So how are these sewage treated? Read on to learn more about municipal sewage.
Urban domestic sewage is a product of urban development. With the acceleration of urbanization and industrialization, its production volume continues to increase, and its pollution is increasingly serious, which has severely restricted the sustainable development of urban society and economy. With the rapid development of the global economy today, environmental protection issues, especially urban sewage water treatment, have become the focus of research in various countries. The typical urban sewage treatment process mainly includes mechanical treatment, biochemical treatment, sludge treatment and other sections.
The system composed of mechanical treatment and biochemical treatment belongs to the secondary treatment system, and the removal rate of BOD5 and SS can reach 90% to 98%. The treatment effect between primary and secondary treatment is generally called enhanced primary treatment, primary semi-treatment or incomplete secondary treatment. There are mainly two categories of high-load biological treatment and chemical treatment. The BOD5 removal rate reaches 45% to 75%. The secondary treatment system with biological phosphorus and nitrogen removal is usually called advanced secondary treatment. In order to remove specific substances, the treatment system set up after the secondary treatment belongs to the tertiary treatment. The large amount of organic matter contained in urban sewage is discharged into the water body, which will reduce the content of dissolved oxygen in the water body, and even reach an oxygen-deficient state, which will seriously pollute the water body and make the fish unable to survive in the water. The concentration of organic matter in sewage is generally expressed by biochemical oxygen demand, chemical oxygen demand, total oxygen demand and total organic carbon. Nutrients mainly refer to nitrogen and phosphorus, which can cause algae and plankton to multiply and form "blooms" and "red tides". Municipal sewage treatment methods can be divided into physical treatment method, biological treatment method, sludge disposal and chemical treatment method according to the type of water quality, and can also be divided into primary treatment, secondary treatment and tertiary treatment according to the degree of treatment. process.
Urban sewage mainly comes from domestic sewage discharged from households, institutions, commerce, and urban public facilities and a moderate amount of industrial production wastewater. The amount of wastewater is large and has obvious diurnal and seasonal periodic changes. The main pollutants in sewage are animal and vegetable oils, suspended solids, carbohydrates, proteins, surfactants, nitrogen and phosphorus compounds, microorganisms, etc. These organic pollutants are generally easier to biodegrade, and the biodegradable BOD/COD value reaches 0.5~0.6, and contains nutrients such as nitrogen and phosphorus, providing a good growth environment for organisms. For a long time, the secondary biological treatment of urban domestic sewage has mostly adopted the activated sludge method, which is currently the most widely used secondary biological treatment process in the world. It has the advantages of high processing capacity and good effluent quality. However, there are common problems such as high capital construction cost, high operating cost, high energy consumption, complicated management, easy sludge bulking and sludge floating, and inability to remove inorganic nutrients such as nitrogen and phosphorus. Since municipal sewage treatment is a project focusing on environmental and social benefits, it is often limited by funds during construction and actual operation, making treatment technology and financial issues a "bottleneck" for water pollution control.