Water is the source of life, breeds all things, and is related to human well-being. However, with the rapid development of industrialization and urbanization, water resources are increasingly strained and water pollution is increasingly serious. In order to make good use of every drop of water, sewage treatment technology is particularly important. The current sewage treatment technology is not only a key link to control water pollution and improve water environment, but also an important way to promote the recycling of water resources and achieve sustainable development.
So how should we deal with the sewage produced in our daily life? What is the compliance with discharge regulations?
100 years of sewage treatment technology - activated sludge method
The core purpose of wastewater treatment technology is to remove pollutants in wastewater and make it meet the standards for discharge or reuse. This process involves a variety of physical, chemical and biological methods. According to Ma Zongkai, "At present, most of China's municipal sewage treatment plants use activated sludge to treat sewage."
Data show that this sewage treatment method was born in Europe in 1914, and in the following less than 10 years, activated sludge method has been applied in many small sewage treatment plants. After the Second World War, the construction of sewage treatment plants in the United States reached its peak, and the activated sludge method also developed rapidly and gradually began to occupy a dominant position. Due to the overall cost, operating cost and difficulty of moderate, activated sludge method from birth to the present, experienced a hundred years of practice, has always maintained a strong vitality, has been widely promoted in the world.
Activated sludge process is the continuous mixing culture of sewage and various microbial communities under artificial oxidation conditions to form activated sludge. These sludge particles are about 200 to 1000 μm in size, are alum flower-shaped amorphous flocs, and usually have a large surface area. The aeration tank is brown and slightly acidic, black when oxygen supply is insufficient, and grayish white when oxygen supply is excessive.
Activated sludge treatment technology
Although large pieces of sludge do not look very beautiful, they play a great role in sewage treatment. Engineers use biological aggregation, adsorption and oxidation of activated sludge to break down and remove organic pollutants from sewage. The sludge is then separated from the water, most of the sludge is returned to the aeration tank, and the excess sludge is discharged from the activated sludge system.
In the development of activated sludge process for more than 100 years, derivative oxidation ditch method, AAO method and CASS method and their improved processes have also appeared.
After the treatment of "sewage", what is produced is "sludge"?
The activated sludge process is composed of aeration tank, sedimentation tank, sludge return system and residual sludge removal system. Sewage and recycled activated sludge enter the aeration tank together to form a mixed liquid. The compressed air discharged from the air compressor station enters the sewage in the form of small bubbles through the air diffusion device laid at the bottom of the aeration pool. The purpose is to increase the dissolved oxygen content in the sewage, so that the mixture is in a state of intense agitation, so that the activated sludge is suspended. Dissolved oxygen, activated sludge and sewage mixed with each other, full contact, so that activated sludge reaction can proceed normally.
After the activated sludge is purified, the mixed liquid enters the secondary sedimentation tank, and the activated sludge and other solid substances suspended in the mixed liquid are precipitated and separated in the secondary sedimentation tank, and the clarified sewage is discharged into the system as treatment water. The sediment concentrated sludge is discharged from the bottom of the sedimentation tank and most of it is returned to the aeration tank as inoculated sludge to ensure the concentration of suspended matter and microorganisms in the aeration tank. The proliferating microorganisms are discharged from the bottom sludge and are called "residual sludge". In fact, most of the pollutants are transferred from sewage to these residual sludge.
