Coking wastewater treatment system

Coking wastewater treatment system

Coking wastewater mainly comes from the initial cooling of coke oven gas, production water during coking production, and steam condensation wastewater. The main characteristics are: high concentration of pollutants, difficult to degrade, and due to the presence of nitrogen in coking wastewater, there is an excess of nitrogen sources required for biological purification, which poses significant difficulties in meeting treatment standards; The amount of wastewater discharged is large, with a water consumption of more than 2.5 tons per ton of coke. The harm of wastewater is significant, as polycyclic aromatic hydrocarbons in coking wastewater are not only difficult to degrade, but also often strong carcinogens, causing serious pollution to the environment and directly threatening human health.

工艺流程

(1) The production wastewater and domestic sewage from each workshop are uniformly discharged into the regulating tank. The main function of the regulating tank is to balance the water quality and quantity of the wastewater, ensuring the stability of the subsequent operation of the biochemical treatment facilities. Due to the extremely low phosphorus content in wastewater, phosphorus nutrients are added to the regulating tank to provide the nutrients needed by microorganisms.

(2) The wastewater from the regulating tank is pumped to the treatment system. In the biochemical treatment system, the degradation process of the wastewater is as follows:

a. Coking wastewater first enters the anaerobic acidification section. In this section, phenol, xylenol, and heterocyclic compounds such as quinoline, isoquinoline, indole, pyridine, etc. in the wastewater have been significantly converted or removed. The establishment of the anaerobic acidification section is very advantageous for the conversion and removal of complex organic compounds. Therefore, after the anaerobic acidification stage, the water quality of the wastewater has been greatly improved, and the biodegradability of the wastewater has been enhanced compared to the raw water, providing a more effective carbon source for the subsequent denitrification stage.

b. The main process carried out in the anoxic section is denitrification reaction. The wastewater from the acidification section enters the anoxic section, while the effluent treated in the aerobic section also partially flows back to the anoxic section, providing nitrate nitrogen for the anoxic section. In addition, due to the insufficient denitrification carbon source in coking wastewater, methanol needs to be added to the anoxic tank as a supplementary carbon source. After treatment in the anoxic stage, nitrate nitrogen is converted into nitrogen gas to achieve denitrification. At the same time, most of the organic matter in the wastewater has been removed, allowing the wastewater to enter the aerobic stage with lower COD, which is very beneficial for the nitrification reaction in the aerobic stage.

c. After being treated in the anoxic stage, the wastewater enters the aerobic stage. In the aerobic stage, due to the high content of ammonia nitrogen and low COD in the wastewater. Therefore, the main process carried out here is nitrification reaction, and in the aerobic stage, pure alkali solution needs to be added to provide the alkalinity required for nitrification reaction. After the wastewater is treated in the aerobic stage, almost all of the ammonia nitrogen can be converted into nitrate nitrogen (nitrate nitrogen is effectively denitrified by refluxing to the anoxic stage, where it is finally converted into nitrogen). At the same time, organic matter is further degraded to ensure that the final effluent COD meets the standard.

(3) After being treated by a biochemical system, the wastewater is separated into sludge and water in a coagulation sedimentation tank. Polyiron is added to the coagulation section to increase the sedimentation performance of the sludge and further reduce the COD of the effluent.

(4) The remaining sludge discharged from the secondary sedimentation tank is regularly discharged to the sludge concentration tank for concentration and stabilization treatment. The clear liquid on the concentration tank flows back to the regulating tank for further treatment. The sludge from the concentration tank is discharged into the sludge storage tank and is regularly dehydrated by the sludge dewatering machine. PAM needs to be added to the sludge for flocculation reaction before dewatering to improve the efficiency of sludge dewatering.