Recently, the Environmental Protection Department of Jiangsu Province released the environmental credit rating of key state-owned enterprises. Among the worst rated red and black polluting enterprises, more than half are sewage treatment plants. The two pollution enterprises rated as red in Nanjing are all sewage treatment plants. In the online monitoring data of key national controlled enterprises regularly released by the environmental protection department, sewage treatment plants accounted for the majority of the list of enterprises with excessive pollutant emissions, and some sewage treatment plants even made the list every month.
Where is the pollution? Excessive discharge and difficulty in sludge disposal
According to the red and black polluting enterprises released by the Provincial Environmental Protection Department, the main reason for poor credit rating is excessive pollution emissions. In our province, all key state-owned enterprises, including sewage treatment plants, steel, thermal power, chemical industry, etc., have achieved online monitoring of pollution emissions. For the sewage treatment plant, the online monitoring mainly includes the total phosphorus, total nitrogen, ammonia nitrogen, Chemical oxygen demand and other indicators in the sewage.
According to personnel from relevant departments of the Nanjing Environmental Protection Bureau, the excessive pollution discharge from sewage treatment plants is the main reason for their pollution. In monitoring, it can be found that many sewage treatment plants have indicators such as total phosphorus, total nitrogen, ammonia nitrogen, and solid suspended solids that exceed the standard, with some exceeding the standard by four times. This means that sewage is discharged without complete treatment.
In addition to excessive sewage discharge, there is also a prominent environmental pollution in sewage treatment plants, which is sludge pollution. The main treatment process of Nanjing sewage treatment plant is sludge disposal, which generates a large amount of sludge during the production process. If the sludge is buried, it will cause secondary pollution, and incineration will produce harmful substances such as dioxins. At present, the disposal of sludge from sewage treatment plants is an industry challenge in China.
Is the standard too low? The treated water is classified as inferior in five categories
In addition to reasons such as excessive emissions, the regulatory authorities also revealed in the interview that even if the sewage treatment plant meets the discharge standards, the treated water discharged is still sewage.
According to China's standards for wastewater treatment in sewage treatment plants, the Chemical oxygen demand is lower than 50 mg/L and the PH value is 6-9 in the highest level of Class A standards, while the standard for the worst surface water, which is inferior to Class 5 water, is the same as Class A standards. This also means that the wastewater treated by sewage treatment plants, even if it reaches the highest standard, will be discharged as inferior to Class 5 water, "said a person from the Municipal Environmental Protection Bureau. Moreover, most sewage treatment plants have exceeded discharge standards, and some rural sewage treatment plants have discharge standards of Class 2 or even Class 3. This creates a terrifying phenomenon, where some sewage treatment plants treat water that is even dirtier than Class 5 water, and this water is directly discharged into rivers and the Yangtze River, causing pollution that can be imagined.
Expert suggestion: wastewater treatment plant tail water should be standardized
It is reported that sewage treatment fees are included in the tap water fees paid by residents, but most sewage treatment plants operate at a loss. In addition to bearing daily production costs, enterprises also have to bear the expenses incurred in sludge disposal and other aspects. Urban sewage treatment plants are relatively better, while almost all rural sewage treatment plants suffer from serious losses, which is the fundamental reason for the excessive discharge of sewage treatment plants.
Industry insiders believe that the water and environmental protection departments have regulatory responsibilities for sewage treatment plants. If a sewage treatment plant experiences excessive emissions, it cannot be punished by just one enterprise. The government should also bear the responsibility. "Losing profits and bearing penalties will make the sewage treatment enterprise bear even more heavy burden, and in the long run, it will form a vicious cycle. The investment of enterprises in the treatment process is limited, and the exceeding of sewage emissions will be even more serious
Experts believe that standards should be raised for the treated tail water of sewage treatment plants, such as upgrading from the current inferior five categories to four categories. Experts say that raising standards mainly refers to lower concentrations of total nitrogen and total phosphorus in the tail water, especially in urban sewage treatment plants. If the concentration of pollutants in the tail water is high, it will cause greater pollution to the city.
