The COD concentration of the inlet water of the sewage treatment plant refers to the COD concentration of the water inlet of the sewage treatment plant. It is an indicator of the amount of reducing substances in the water at the water inlet. If sewage with low COD content enters the sewage plant for treatment, it will not only increase the operational burden of the sewage plant, but also destory the sludge activity and affect the operating efficiency of the sewage biological treatment system. These phenomena should be paid full attection to and effective measures should be taken for rectification and management. There is no upper limit for sewage inflow, but there is a lower limit. Those below 100mg/L do not need to be treated. There are two ways to detect COD at the water inlet, the traditional laboratory measurement method is simple and technically mature, but the disadvantage is that the detection time is long, at least a few hours. Therefore, if you want to continuously monitor the COD value in real time, online COD sensors are now commonly used. The online sensor COD351 developed and produced by Daruifuno is a digital sensor that uses ultraviolet absorption method to measure the COD value in water. The measurement range has low range and high range options. This chemical oxygen demand sensor requires no reagents, is pollution-free, and can continously monitor the COD value of water quality. Automatically compensates for turbidity interface, with self-cleaning wiper and long maintenance cycle.