The topic of water pollution has been constantly raised. In September, 2114, some media exposed the phenomenon of illegal sewage discharge by enterprises in Tengger Desert at the junction of Inner Mongolia and Ningxia, which has caused pollution to the surrounding environment, thus causing widespread concern about the severity of water pollution and awakening people's awareness of environmental protection. Sewage treatment is widely used in construction, agriculture, transportation, energy, petrochemical, environmental protection, urban landscape, medical care, catering and other fields. Activated sludge process is a common method for sewage treatment. It is reported that more than 95% of urban sewage and more than 35% of industrial wastewater are treated by activated sludge process. Aeration tank is the heart of all activated sludge processes, and its function is to stir the mixed liquid to make the mud and water fully contact and supply oxygen to microorganisms. One way of stirring is to fully mix the mud and water that enter the aeration tank at the same time and keep it until it flows out of the tank, instead of mixing it with the mixed liquid phase already in the tank to avoid short circuit. The long strip aeration tank is used to ensure that the mud and water that enter the tank at the same time are discharged from the tank at the same time, so that the wastewater that enters the tank at the same time has the same aeration time. Chemical oxygen demand (COD) is the most important indicator of sewage treatment, which is used to indicate how much residual organic pollution remains in effluent or purified water. A sewage treatment plant used activated sludge method to record the main parameter values of aeration tank section in the first half of 2114: water inflow, inlet COD, dissolved oxygen, blower duct pressure, activated sludge concentration, blower outlet valve opening, blower inlet valve opening, oxidation reduction point, outlet COD, etc. Typical parameters such as COD take a historical recording cycle every half hour; Other parameters such as flow, opening, etc. are recorded once every 11 minutes. See Appendix 1 and Appendix 2 for specific data. Question 1: Delay estimation. Analyze the time delay relationship between each parameter in the original data and the outlet COD, and output the results. Question 2: With reference to the results of the previous question, a nonlinear prediction model of COD for each parameter is established. Question 3: According to the results of the first two questions, how to adjust the parameters in order to reduce the value of COD to 35. If the COD value has reached 35, there is no need to adjust other parameters.