Advanced treatment of chemical wastewater by catalytic ozone oxidation +BAF technology
Advanced treatment of chemical wastewater by catalytic ozone oxidation +BAF technology
The types of chemical enterprises are complex and the products are diverse, which makes the wastewater received by the sewage treatment plant in the chemical industry park have the characteristics of complex pollutant composition, large fluctuation of water quality and quantity, toxic and difficult to degrade, etc. As a result, it is difficult to discharge according to the standard through traditional biological process treatment, and in-depth treatment is required.
This paper takes the upgrading project of wastewater treatment plant in a chemical industry park as the research object, carries on the process design and discusses the treatment effect, in order to provide reference for the treatment of wastewater in chemical industry park.
1. Project overview
In order to meet the development needs of the park, a chemical park upgraded the sewage treatment facility of an enterprise in the park into a sewage treatment plant in the park. The industrial park mainly develops pyridine base industrial chain, pesticides, biomedicine and new chemical materials projects. The wastewater of the industrial park is mainly agrochemical and pharmaceutical wastewater and other comprehensive chemical wastewater, and the wastewater production volume is about 6500~8500m3/d.
1.1 Status of sewage treatment plants
The treatment sewage is the diluted pyridine base, organophosphorus and fungicide production wastewater, the design scale is 30000m3/d, using hydrolysis acidification +CASS process, the effluent is subject to the "Comprehensive sewage Discharge Standard" level 1 standard. Through on-site analysis and accounting, it is difficult for the existing process effluent to meet GB18918-2002 Grade A standard, so it needs to be upgraded.
1.2 Design scale and quality of incoming and outgoing water
Design scale 10000m3/d.
Due to the complex types of enterprises in the chemical industry park, the different production products, the different concentrations of pollutants in the discharged wastewater, the different types of characteristic pollutants, the unified direct collection and treatment is extremely difficult. Therefore, after each enterprise's own pretreatment reaches the sewage plant's management standard, it is connected to the sewage plant. The design inlet and outlet water quality is shown in Table 1.
2. Process design
2.1 Upgrading plan
Through on-site analysis and accounting, the hydrolytic acidification +CASS process can be considered to be fully utilized and transformed into a strengthened biochemical treatment section to reduce investment. The existing hydrolytic acidification pool is pulsed hydrolytic acidification, and the treatment effect is general. The water distribution mode is reformed, and the hydrolytic acidification effect is improved by sludge reflux. The existing CASS tank has a good treatment effect on organic matter, ammonia nitrogen, total nitrogen, total phosphorus and other pollutants in sewage, so it can continue to be used. However, some pipes are seriously corroded, the aeration effect is very poor, and the equipment has aging problems. According to the design processing scale, only 8 of them need to be transformed. The pre-reaction area of CASS tank was transformed into a pre-anoxic tank for denitrification, reducing the competition between phosphorus accumulating bacteria and denitrifying bacteria in CASS tank, and strengthening the effect of nitrogen and phosphorus removal.
After intensive biochemical treatment, most of the organic pollutants were degraded, but the refractory organic matter remaining in the water affected the standard discharge of sewage. Obviously, the efficiency of pure biochemical treatment of such sewage is extremely low. Ozone catalytic oxidation technology is a new advanced oxidation technology developed on the basis of traditional ozone oxidation, with faster oxidation rate and higher ozone utilization rate, which can carry out in-depth treatment of such sewage.
Due to the high SS of the effluent from CASS process, about 50~60mg/L, it will directly affect the normal operation of ozone catalytic oxidation, increase the amount of ozone dosage, and increase the operating cost. Therefore, before ozone catalytic oxidation, a high-efficiency sedimentation tank with small footprint, low engineering cost and impact load resistance will be added.
After ozone catalytic oxidation treatment, the biodegradability of wastewater is enhanced, and it can be further biochemical treatment. Compared with the traditional activated sludge method, the biological aerated filter (BAF) technology has the advantages of high treatment efficiency, small footprint, low infrastructure and operating costs, convenient management and good effluent quality, and is often used in the advanced treatment of wastewater. Studies have shown that the combination of ozone catalytic oxidation and BAF for chemical wastewater treatment can not only play the advantages of physicochemical and biochemical treatment, but also improve the efficiency of wastewater treatment and reduce the cost of treatment.
In summary, the advanced treatment stage adopts the combined process of ozone catalytic oxidation and BAF.
2.2 Process Flow
As shown in Figure 1.
2.3 Main structures and design parameters
See Table 2.
3. Debug the operation effect
The upgrading project started in June 2018, and the water quality commissioning and acceptance work was completed in August 2019. The water quality of CODCr, ammonia nitrogen and TP during commissioning is shown in Table 3.
As can be seen from Table 3, the influent CODCr, ammonia nitrogen and TP concentrations fluctuated greatly during commissioning, and the average value exceeded the designed influent index. After treatment, the average concentrations of CODCr, ammonia nitrogen and TP in the effluent were 23mg/L, 1.14mg/L and 0.27mg/L, respectively, and the average removal rates were 97.81%, 98.99% and 93.08%, which reached the standard. It can be seen that the process has a strong ability to resist impact load.
The removal of CODCr and ammonia nitrogen mainly occurred in CASS pond, and the average removal amounts accounted for 68.73% and 85.95% of the total amount, respectively (considering the increase of ammonia nitrogen in hydrolytic acidification pond). However, it is far from the design water requirements, which requires in-depth treatment. In the advanced treatment stage, the average removal rate of CODCr in ozone catalytic oxidation tank was 24.24%. The removal rate of CODCr in BAF pool ranged from 50% to 75%, with an average removal rate of 69.33%. The effluent CODCr was basically stable at 25mg/L at the end of commissioning. High efficiency sedimentation tank and ozone catalytic oxidation tank had no effect on ammonia nitrogen removal. The average removal rate of ammonia nitrogen in BAF tank was 91.86%, and the optimal effluent quality was 0.69mg/L. It can be seen that the ozone catalytic oxidation +BAF process has good effect on the advanced treatment of CODCr and ammonia nitrogen.
In the case that the influent TP concentration exceeds the design value, real-time monitoring of the influent TP concentration changes, timely adjustment of the dosage and sludge discharge of the high-efficiency sedimentation tank, and strengthening the effect of chemical phosphorus removal. The average concentration of TP in the high-efficiency sedimentation tank is 0.48mg/L, basically meeting the design effluent index. The subsequent BAF tank also has partial biological phosphorus removal function, which can again improve the effluent quality, reduce the TP concentration, and stabilize the effluent below 0.3mg/L, reaching the surface Class IV water standard.
4. Conclusion
(1) It is feasible to use the process of "hydrolytic acidification +CASS+ high-efficiency sedimentation tank + ozone catalytic oxidation +BAF" to treat the wastewater of the chemical park, which not only makes full use of the old structures and equipment, but also greatly saves the investment cost, and the process has A strong impact load resistance, and the treatment effect has reached the GB18918-2002 Grade A standard.
(2) As an advanced treatment process, the combined process of "ozone catalytic oxidation +BAF" can effectively increase the biodegradability of wastewater, strengthen the treatment effect of refractory wastewater, and ensure the standard discharge. The average removal rate of CODCr in the ozone catalytic oxidation tank is 24.24%. The average removal rates of CODCr and ammonia nitrogen in BAF were 69.33% and 91.86%, respectively.
