Coking wastewater is a typical toxic and refractory organic wastewater.

The coking wastewater mainly comes from the production water and steam condensation wastewater in the primary cooling of coke oven gas and coking production.

Features: The concentration of pollutants in coking wastewater is high and difficult to degrade. Due to the presence of nitrogen in coking wastewater, the nitrogen source required for biological purification is excessive, which brings great difficulties to the treatment standard;

The amount of wastewater discharge is large, and the water consumption per ton of coke is greater than 2.5t ;

Wastewater is very harmful. Polycyclic aromatic hydrocarbons in coking wastewater are not only difficult to degrade, but are usually strong carcinogens, causing serious pollution to the environment and directly threatening human health.

Wastewater source:

The coking plant mainly produces chemical products such as coke, commercial gas, ammonium sulfate and light benzene. The tar recovery system of the plant adopts the ammonium sulfate process, and the tar processing adopts two-tower continuous distillation in a tubular furnace, and the industrial naphthalene production process is a double-furnace two-tower continuous distillation, washing and refining. During coke oven gas cooling, washing, crude benzene processing and tar processing, industrial wastewater containing phenol, cyanide, oil, ammonia and a large amount of organic matter is produced.

Processing technology:

process flow

The expansion project includes two parts: original system renovation and new construction. According to the results of coking wastewater treatment, combined with the original wastewater treatment process, the new expansion project adopts A1 - A2 - O biofilm process.

Try not to change the function and structure of the existing wastewater treatment facilities, make full use of the treatment capacity of the existing wastewater treatment structures, transform the old system, and add an anaerobic acidification tank on the basis of the 　　original A/O system, that is, change it to A1 - A2 - O biochemical system. A new set of A1 - A2 - O biochemical system will be built , each of which will handle half of the treated water.

Flow Description

( 1 ) The production wastewater and domestic sewage coming out of each workshop will enter into the adjustment pool. The main function of the adjustment pool is to balance the water quality and quantity of the wastewater and ensure the stability of the subsequent biochemical treatment facilities. Since the phosphorus content of wastewater is very small, phosphorus nutrient salts are added to the regulating tank to provide the nutrients needed by microorganisms.

( 2 ) The wastewater from the regulating tank is raised by two pumps to the old and new A1 - A2 - O biochemical systems respectively. In the biochemical treatment system, the degradation process of wastewater is as follows:

a. Coking wastewater first enters the anaerobic acidification section. In this section, phenol, xylenol, quinoline, isoquinoline, indole, pyridine and other heterocyclic compounds in the wastewater have been greatly converted or removed. is very beneficial. Therefore, the water quality of wastewater has been greatly improved after the anaerobic acidification stage, and the biodegradability of the wastewater has been improved compared with the raw water, which provides a more effective carbon source for the subsequent denitrification stage.

b. The denitrification reaction is mainly carried out in the anoxic section. The wastewater from the acidification section enters the anoxic section, and at the same time, part of the effluent treated in the aerobic section returns to the anoxic section to provide nitrate nitrogen for the anoxic section. In addition, because the denitrification carbon source contained in the coking wastewater is insufficient, it is necessary to add methanol as a supplementary carbon source in the anoxic tank. After the treatment in the anoxic section, the nitrate nitrogen is converted into nitrogen gas to achieve the purpose of denitrification. At the same time, most of the organic matter in the wastewater is removed, so that the wastewater enters the aerobic section with a lower COD , which is very beneficial to the nitrification reaction in the aerobic section.

c. Wastewater enters the aerobic section after being treated in the anoxic section. In the aerobic section, the COD is lower due to the higher ammonia nitrogen contained in the wastewater. Therefore, the nitrification reaction is mainly carried out here, and soda ash solution needs to be added in the aerobic section to provide the alkalinity required for the nitrification reaction. After the wastewater is treated in the aerobic section, the ammonia nitrogen can basically be completely converted into nitrate nitrogen (the nitrate nitrogen is returned to the anoxic section, and finally converted into nitrogen in the anoxic section to obtain effective denitrification), and at the same time, the organic matter is further denitrified Degradation, so that the effluent COD reaches the standard.

( 3 ) After the wastewater is treated by the biochemical system, it is separated from the mud and water through the coagulation sedimentation tank, and polyferric iron is added to the coagulation part to increase the sedimentation performance of the sludge in the sedimentation part and further reduce the COD of the effluent .

( 4 ) The remaining sludge discharged from the secondary sedimentation tank is regularly discharged to the sludge thickening tank for concentrated and stable treatment, the supernatant of the concentrated tank is returned to the regulating tank for further treatment, and the sludge from the concentrated tank is discharged into the sludge storage tank, and is regularly Sludge dewatering machine for dehydration. Before dehydration, PAM needs to be added to carry out flocculation reaction with sludge to improve sludge dehydration efficiency.

Process conditions

( 1 ) Control the quality and quantity of influent water

According to the original statistical data of the water quality and quantity of the main source of coking wastewater and the design scheme, the quality and quantity of wastewater entering the sewage treatment system must meet the design requirements

( 2 ) Wastewater pretreatment

In order to reduce the load of subsequent biochemical treatment, reduce the impact load of toxic substances, and to stabilize the effect of subsequent biochemical treatment and facilitate operation and management, wastewater needs to be pretreated before entering the system.

a. Control the COD content of the incoming water If the COD of the incoming water fluctuates too much, it will have a great impact on the operation of the system. Therefore, according to the design requirements, the influent COD should be strictly controlled within the scope of the design requirements.

b. Control the inlet water temperature

The final cooling wastewater, ammonia distillation wastewater and 5# and 6# coke oven ammonia distillation wastewater 　　　　from the old factory area have high water temperature, so they need to be cooled to below 38 ℃ by plate condenser and atomization cooler before being discharged into the regulating tank.

c. Control the oil content in the influent

Gas condensate waste water and turbid water separated from turbidity are treated by gravity oil separation and air flotation to remove oil (oil content is less than 30mg/L ), so that the oil content is lower than the concentration that affects the normal growth of microorganisms, and then discharged into the adjustment tank.

c. Reduce ammonia nitrogen

Part of the ammonia distillation wastewater first passes through the fixed ammonia decomposition device to reduce the ammonia nitrogen concentration from 800 mg/L to 250 mg/L , and then discharges into the regulating tank.

d. Reduce ash content

follow the principle

1. The technology is mature and reliable, and it has a good pertinence to the water inflow of this wastewater treatment plant. The treatment effect is stable, ensuring long-term continuous operation, and the effluent water quality is stable and up to standard.

2. The infrastructure investment is reasonable, the operation cost is low, the operation mode is flexible, and the maximum possible return can be obtained with the smallest possible investment.

3. The operation and management are convenient, and the operation mode and parameters can be adjusted according to the fluctuation of the influent water quality, so as to maximize the processing capacity of the treatment structure.

4. It is convenient to realize the automatic control of the process, improve the management level, and reduce the labor intensity and labor cost.

5. The selected equipment is advanced, reliable, highly localized and well-equipped.