Sewage treatment plant becomes a big polluter due to sludge treatment
Recently, the environmental protection department of Jiangsu Province released the environmental protection credit rating of key state-controlled enterprises in 2020. Among the worst red and black polluting enterprises, more than half are sewage treatment plants. The two polluting enterprises rated red in Nanjing are all sewage treatment plants. In the online monitoring data of key state-controlled enterprises regularly released by the environmental protection department, sewage treatment plants account for the majority in the list of enterprises with excessive pollutant emissions, and some sewage treatment plants even appear on the list every month.
Query the red and black polluting enterprises released by the provincial environmental protection department. The main reason for the poor credit rating is that the pollution emission exceeds the standard. In our province, all key state-controlled enterprises, including sewage treatment plants, iron and steel, thermal power and chemical industry, have realized on-line monitoring of pollution discharge. For sewage treatment plants, online monitoring mainly includes several indicators such as total phosphorus, total nitrogen, ammonia nitrogen and chemical oxygen demand in sewage.
According to the relevant departments of Nanjing Environmental Protection Bureau, the excessive pollution discharge of sewage treatment plant is the main cause of pollution. "In the monitoring, it can be found that the total phosphorus, total nitrogen, ammonia nitrogen, solid suspended solids and other indicators of many sewage treatment plants will exceed the standard, and some single exceeding the standard can reach four times." This means that the sewage is discharged without complete treatment.
In addition to excessive sewage discharge, there is also a prominent environmental pollution in the sewage treatment plant, that is, sludge pollution. The treatment process of Nanjing sewage treatment plant is mainly sludge disposal method, which will produce a large amount of sludge in the production process. If the sludge is buried, it will cause secondary pollution, and incineration will produce dioxin and other harmful substances. At present, the disposal of sludge from sewage treatment plants is an industry problem in China.
Is the standard too low? The treated water is classified into five inferior categories
In addition to excessive discharge and other reasons, in the interview, the regulatory authorities also revealed a message that even if the sewage treatment plant meets the discharge standard, the treated water discharged by it is also sewage.
According to China's standards for the treatment of wastewater by sewage treatment plants, in the highest level of class a standard, the chemical oxygen demand is less than 50 mg / L and the pH value is 6-9. Compared with the worst class 5 water standard of surface water, it is the same as class a standard. "This means that even if the wastewater treated by the sewage treatment plant reaches the highest standard, it is inferior to class V water." A person from the Municipal Environmental Protection Bureau said that what's more, most sewage treatment plants have discharge exceeding the standard, and some village and town sewage treatment plants have discharge standards of secondary standards or even tertiary standards. This has caused a terrible phenomenon. The water treated by some sewage treatment plants is even dirtier than the inferior five kinds of water, and these water is discharged directly to the river and the Yangtze River, resulting in pollution.
It is reported that the tap water fee paid by residents includes the cost of sewage treatment, but most sewage treatment plants are operating at a loss. Enterprises should not only bear the daily production cost, but also bear the cost of sludge disposal and other links. Urban sewage treatment plants are relatively better, and almost all rural sewage treatment plants have serious losses, which is the fundamental reason for the excessive discharge of sewage treatment plants.
Some people in the industry believe that the water affairs department and the environmental protection department have the regulatory responsibility for the sewage treatment plant. If the sewage treatment plant exceeds the standard discharge, we can't punish only one enterprise, and the government department should also bear the responsibility. "The loss operation plus the punishment, the sewage treatment enterprise will bear a heavier burden. In the long run, a vicious circle will be formed. The enterprise's investment in the treatment process is limited, and the sewage discharge exceeding the standard will be more serious."