There are many methods to cultivate activated sludge, but different methods require different culture time, manpower and material resources. The culture method should be selected according to the wastewater quality, climate and actual permitted conditions. 1. Preparation before culture (1) All structures were built, and the construction waste was removed by pool cleaning. The static pressure test proved that there was no leakage and no subsidence displacement, and finally it was accepted according to relevant regulations. (2) Electrical appliances, machinery, pipelines and other equipment have been built and have been tested by single machine and linkage. Finally, according to the relevant regulations (instructions) acceptance. (3) According to the needs of future operation and management, qualified sewage treatment plants (stations) need to carry out the most basic routine laboratory tests, such as pH, water temperature, COD and biological equivalence, to guide the cultivation process and daily operation of activated sludge. (4) Investigate the basic data, including the diurnal variation of sewage flow, water quality (pH, water temperature, COD, nitrogen, phosphorus, toxic substances, etc.) and its variation, and technical parameters of various facilities and equipment. Where conditions permit, it is best to investigate and record the background water quality of the receiving water body (such as rivers that receive sewage) in order to provide a basis for investigating the impact on the receiving water body after several years. (5) Prepare necessary nutrients (carbon source, nitrogen source and phosphorus source) according to the treated water quality, so as to make up for what is lacking. In addition, dry (or concentrated) sludge from other sewage treatment plants (stations) with similar sewage properties should be prepared as strains for microbial culture of activated sludge by inoculation culture method. (6) Operators should be familiar with the pipeline layout and public works of the whole system, and understand the basic process and control requirements of sludge culture. (7) Personnel are in place. After self-cultivation and domestication, the system should generally run continuously, and people should not be taken off. (8) Prepare the original records and statements of necessary tests and operations, as well as the preliminary rules and regulations. From the beginning of culture, we should gradually establish a more standardized organization and management model to ensure the orderly start-up and formal operation. 2. Natural culture Natural culture, also known as direct culture. It is a culture process that uses a small amount of microorganisms in wastewater to gradually reproduce. This culture method can be considered for urban sewage and some industrial wastewater with complete nutrients and low toxicity, such as wastewater from food factories and meat processing factories, but the culture time is relatively long. Natural culture can be divided into intermittent culture and continuous culture. (1) Intermittent culture. Fill the aeration tank with waste water, and carry out closed aeration (that is, only aeration without waste water). After several days, stop aeration, let it stand for 1 h, then discharge about 1/5 of the upper wastewater in the tank and inject the same amount of fresh sewage. The three processes of stuffy exposure, static sedimentation and water inflow are repeated, but the water inflow is increased each time and the stuffy exposure time is shorter than last time. In spring and autumn, sludge can be cultivated in about two or three weeks. When the sludge concentration of the mixed liquor in the aeration tank reaches about 1 g/L, water can be continuously fed and aerated. Due to the low concentration of sludge in the initial stage of culture, less sludge is accumulated in the sedimentation tank, and the return flow is also less. After that, with the increase of sludge quantity, the return sludge quantity will also increase accordingly. When the sludge concentration reaches the concentration required by the process, it can start normal operation and be controlled according to the process requirements. (2) Continuous culture. Fill the aeration tank with wastewater first, then stop the water inflow. After half a day to a day of stuffy exposure, water can be continuously injected. Continuous aeration, the water inflow gradually increases from small to large, and after a period of continuous operation (similar to intermittent method), activated sludge will appear and gradually increase. When the sludge in aeration tank reaches the concentration required by the process, it shall be controlled according to the process requirements. Because the natural culture method is to directly culture activated sludge with wastewater, its culture process is also a process in which microorganisms gradually adapt to the nature of wastewater and get domesticated. 3. Inoculation culture method has a short culture time, which is a commonly used method of active sludge culture and is suitable for most industrial wastewater treatment plants. This method can also be used in urban sewage plants if there is mud nearby to shorten the culture time. Inoculation culture methods are commonly used in the following two ways: (1) Inoculation culture of concentrated sludge. Concentrated sludge from a nearby sewage treatment plant is used as a strain (seed sludge or seed sludge) for cultivation. In the activated sludge culture of urban sewage and industrial wastewater treatment system with complete nutrition and low toxicity, seed sludge can be directly added to the wastewater to be treated for aeration until the sludge turns brown, and the sewage can be continuously fed (the water inflow should be gradually increased). At this time, the sedimentation tank is also put into operation to allow the sludge to circulate in the system. In order to speed up the culture process, unfermented fecal water or other nutrients can be added during the culture process. The culture process is completed when the concentration of activated sludge reaches the required value. Economically speaking, the amount of seed sludge should be as little as possible, and in general, the concentration of mixed liquid sludge should be controlled above 1.5g/L after dilution. When the toxic industrial wastewater is cultured, river water or tap water can be introduced into the aeration tank first (it needs to be aerated for a period of time to remove the residual chlorine in it), and then seed sludge and unfermented fecal water are put in for aeration until the sludge turns brown, and then the aeration is stopped, so that the sludge settles and a part of supernatant is discharged, and a certain amount of fecal water is added to continue aeration, and the wastewater flow rate is gradually increased after the sludge amount is obviously increased. In the later period of cultivating bacteria, microorganisms in sludge can adapt to the quality of industrial wastewater well. (2) Inoculating and culturing bacteria with dry sludge. "Dry sludge" usually refers to the mud cake dehydrated by a dehydrator, and its water content is about 71 ~ 81%. This method is applicable to remote areas and situations where the transportation distance of seed sludge is long. The process of inoculation and culture of dry sludge is basically the same as that of concentrated sludge culture. Inoculate sludge with fresh mud cake that has just been dehydrated, and add a small amount of water and mash it into mud before adding it to the aeration tank. The dosage of dry sludge is generally 2 ~ 5% of the tank volume. Dry sludge may contain a certain concentration of chemical agents (used for sludge conditioning). If the content of chemical agents is too high and toxic, it is not suitable to be used as seed sludge for cultivating bacteria. To identify whether sludge can be used for inoculation, a small amount of mud can be mashed and put into a small container (such as a beaker or a plastic bucket) for aeration. After a period of time, if the mud can turn yellow, it can be used for inoculation.