1. Activated sludge process In recent years, the activated sludge process has become a very mature treatment process, and has been widely used in urban sewage environmental treatment in my country and the world. The main advantages of the activated sludge method are high pollution purification, good and stable effluent quality, etc. The activated sludge system is mainly composed of four parts: aeration tank, sedimentation tank, sludge return, and excess sludge discharge system. First of all, send urban sewage and activated sludge into the aeration tank for full mixing, and at the same time fill it with oxygen to react with the mixture to have an aerobic metabolic reaction, try to stir the mixture evenly, and promote the organic matter, oxygen and microorganisms in the sewage to be better. contact reaction. Secondly, the mixture is sent to the sedimentation tank to promote the effective separation of solid and liquid to ensure the quality of the effluent of the sedimentation tank. The sedimentation tank contains a large amount of sludge, part of which is returned to the aeration tank through the sludge return system, mainly to ensure that the concentration of microorganisms in the aeration tank can meet the requirements of sewage treatment. However, the biochemical reaction in the aeration tank will promote the reproduction of microorganisms, and these microorganisms will be discharged from the sedimentation tank, thereby ensuring the efficient operation of the activated sludge system. Activated sludge can not only oxidize and decompose organic substances, but also has efficient coagulation and sedimentation functions, which is convenient for solid-liquid separation in sedimentation tanks. However, the application of this method requires a large investment of cost and occupies a large area, which is not in line with the concept of intensive development. For the application of sewage treatment, more attention is paid to energy saving, high efficiency, convenience and economy in order to achieve higher investment and resource benefits. For this reason, people should think about urban sewage environmental governance from a higher level, and take into account sustainable and high-quality development while ensuring effective sewage treatment. 2. Biofilm method The biofilm method and the activated sludge method have the same effect. As a sewage aerobic biological treatment technology, it is also widely used in the current urban sewage environment treatment. It mainly removes soluble and colloidal organic substances in sewage, and plays a vital role in the biological treatment of urban sewage. The biofilm method is mainly to attach microorganisms to the surface of solid media to treat organic pollutants in urban sewage. The bacteria attached to the biofilm include: aerobic bacteria, anaerobic bacteria, facultative bacteria, fungi, etc., which together with protozoa, algae and other organisms constitute the ecosystem on the biofilm. The filter part can be divided into four levels: anaerobic layer, aerobic layer, attached water layer, and moving water layer. There is a large amount of organic matter in urban sewage, and biofilm can adsorb it on the membrane body, and then decompose it by the aerobic bacteria attached to it, and then decompose it by the anaerobic bacteria attached to the anaerobic layer, while the movement The water layer is mainly to wash away the membrane that has lost its function, to ensure that the biofilm maintains sufficient activity and rapid regeneration, so that the sewage can be continuously purified. However, this method is costly and inefficient, so it is only suitable for large sewage treatment plants. 3. Oxidation method At present, people have begun to study and apply oxidation method in urban sewage treatment, which is mainly for pretreatment of urban domestic sewage, and it is a method with the most development potential at this stage. Oxidation methods are mainly divided into five types according to the type of oxidant and the type of generating device: chemical oxidation method, catalytic oxidation method, wet oxidation method, photocatalytic oxidation method, supercritical oxidation method, etc. Among them, the chemical oxidation method is easy to operate and has obvious effects, but due to the high input cost, it is not widely used in urban domestic sewage treatment; the photocatalytic method has the advantages of simple process equipment, low operation requirements, and strong oxidation capacity. , better treatment effect and other advantages, which are more in line with the development trend of urban sewage treatment; photocatalytic reactions mainly carry out chemical reactions through light, when molecules in sewage absorb electromagnetic radiation of a specific wavelength, molecular excited states will be generated, and then chemical reactions will occur. New substances in which the activation energy of the photocatalytic reaction mainly comes from the energy of photons.