Ozone oxidation coupled deep denitrification treatment method for degradation-resistant wastewater

Abstract

The invention discloses an ozone oxidation coupled deep denitrification treatment method for degradation-resistant wastewater, which comprises first-stage denitrification, second-stage denitrification, first-stage ozone oxidation, second-stage ozone oxidation, first-stage nitrification and second-stage nitrification treatment, the first-stage ozone oxidation adopts an ozone contact process, the second-stage ozone oxidation adopts an ozone / H2O2 process, and the first-stage nitrification treatment adopts an ozone contact process. The first-stage ozone oxidation effluent flows back to the first-stage denitrification inlet water, the second-stage nitrification effluent flows back to the first-stage denitrification inlet water, and the first-stage nitrification effluent flows back to the second-stage ozone oxidation inlet water. According to the invention, two-stage ozone oxidation is arranged between two-stage denitrification and two-stage nitrification treatment, so that segmented denitrification, segmented oxidation and segmented nitrification treatment of refractory wastewater can be realized, the adverse effect of ozone oxidation effluent on denitrification can be reduced, the dosage of ozone and a carbon source can be reduced, and the treatment cost is reduced. And the deep denitrification treatment project investment and land occupation are reduced.

Description

Technical Field

[0001] The present invention relates to a deep denitrification method for treating refractory wastewater. Specifically, the present invention relates to a deep treatment method for refractory wastewater combining ozone oxidation with a biological denitrification process. The method is particularly suitable for treating refractory wastewater such as RO brine or industrial wastewater biochemical tail water, and belongs to the field of water treatment technology. Background Art

[0002] Denitrification-nitrification is the most widely used biological denitrification treatment technology in wastewater denitrification treatment. Its basic principle is to convert ammonia nitrogen into nitrates through nitrifying bacteria, and then reduce nitrates to nitrogen gas for discharge through denitrifying bacteria. The advantage of this method is that the treatment cost is low and the organic matter in the wastewater is used as a carbon source for denitrification as much as possible. However, its disadvantage is that it is affected and limited by reaction temperature, pH value, oxygen concentration, ozone concentration, salt concentration, toxic organic matter, organic nitrogen, etc.

[0003] For the deep treatment of refractory wastewater, due to the presence of refractory COD, refractory organic nitrogen, insufficient carbon source, biological toxicity and other problems in the wastewater, it is often difficult to achieve the desired effect using the denitrification-nitrification method alone. Therefore, it is necessary to combine ozone oxidation with biological denitrification technology to degrade and reduce refractory COD, organic nitrogen, biological toxicity, etc., while supplementing the carbon source or electron donor required for denitrification. At present, the coupling of ozone oxidation and nitrification-denitrification deep process has been widely used in the deep treatment or upgrading of biochemical tailwater, but there are some problems with the existing technology.

[0004] Although the treatment method for low C / N slightly polluted river water disclosed in Chinese patent document 200910259612.1 combines denitrification, ozone oxidation and biological activated carbon filter, it is difficult to utilize the refractory COD in river water for denitrification and requires frequent replacement of activated carbon.

[0005] In the method for treating RO concentrate containing PTA wastewater disclosed in Chinese patent document 201910231741.3, biological denitrification is preceded by an ozone oxidation unit, which may cause the biological toxicity of RO concentrate to inhibit denitrification-nitrification, and denitrification denitrification requires the addition of a large amount of carbon source.

[0006] The catalytic ozone oxidation-nitrification-denitrification combined treatment process disclosed in Chinese patent document 202410108676.6, although effectively reducing COD while deeply removing nitrogen, may have problems with treatment efficiency and cost.

[0007] In addition, there are some challenges in the combination order of ozone oxidation and denitrification-nitrification process. If ozone oxidation is placed before the denitrification-nitrification process, the residual ozone and supersaturated dissolved oxygen in the ozone oxidation effluent may inhibit the subsequent denitrification and nitrification process, requiring the addition of a degassing tank and prolonged reaction time, thereby increasing investment costs. If ozone oxidation is placed after the denitrification-nitrification process, the amount of ozone required to meet the COD standard is large, and the organic nitrogen and biotoxic organic matter in the wastewater need to be further treated to meet the standard.

[0008] Therefore, it is of great significance to develop a process that can effectively combine ozone oxidation and biological denitrification and overcome the defects of the existing technology to treat difficult-to-degrade wastewater in deep denitrification. Summary of the invention

[0009] The purpose of the present invention is to provide a balanced and flexible method for deep denitrification of refractory wastewater coupled with ozone oxidation in order to solve the problems existing in the prior art of deep denitrification of refractory wastewater by ozone oxidation coupled with denitrification-nitrification.

[0010] The present invention aims to solve the following technical problems: ozone oxidation effluent inhibits denitrification and nitrification, inhibits biofilter biofilm formation, large denitrification carbon source dosage, large ozone dosage, high operating costs and unstable operation.

[0011] To achieve the above object, the present invention adopts the following technical solutions:

[0012] The method comprises denitrification treatment, ozone oxidation treatment and nitrification treatment connected in series;

[0013] The denitrification treatment comprises a primary denitrification and a secondary denitrification connected in series, wherein the primary denitrification is a denitrification biofilm process and the secondary denitrification is a denitrification biofilm process;

[0014] The ozone oxidation treatment comprises a primary ozone oxidation and a secondary ozone oxidation which are connected in series in sequence, wherein the primary ozone oxidation is an ozone contact process, and the secondary ozone oxidation is an ozone / H2O2 process;

[0015] The nitrification treatment includes a primary nitrification treatment and a secondary nitrification treatment connected in series, both of which are nitrification biofilm processes;

[0016] Moreover, the primary ozone oxidation effluent is returned to the primary denitrification inlet, and the secondary nitrification effluent is returned to the primary denitrification inlet.

[0017] The preferred embodiment of the present invention also includes:

[0018] (1) The effluent from the primary nitrification is refluxed to the secondary ozone oxidation and used in the ozone jet dosing system, and the reflux ratio is (0.2-2):1.

[0019] (2) Bio-rope fillers or suspended fillers are installed in the primary denitrification tank and the primary nitrification tank, and the filling ratio is 30% to 60%; expanded clay, zeolite, volcanic rock or quartz filter materials are installed in the secondary denitrification tank and the secondary denitrification tank, and the filter bed thickness is 0.5 to 1.5 m.

[0020] (3) The reflux ratio from the primary ozone oxidation effluent to the primary denitrification membrane tank is (1-2):1, and the reflux ratio from the secondary nitrification membrane tank to the primary denitrification membrane tank is (0.5-3):1.

[0021] (4) The residence times of primary denitrification, secondary denitrification, primary ozone oxidation, secondary ozone oxidation, primary nitrification, and secondary nitrification are 1-3 h, 0.5-1 h, 0.2-0.5 h, 0.5-1 h, 0.5-1 h, and 1-3 h, respectively.

[0022] (5) The ozone dosage ratio of primary ozone oxidation and secondary ozone oxidation is 1:(2~4).

[0023] A further preferred embodiment of the present invention also includes:

[0024] (1) The residence times of primary denitrification, secondary denitrification, primary ozone oxidation, secondary ozone oxidation, primary nitrification, and secondary nitrification are 1 h, 1 h, 0.5 h, 0.5 h, 1 h, and 1 h, respectively. The addition ratio of primary ozone to secondary ozone is 1:3, the reflux ratio from primary ozone to primary denitrification is 1:1, the reflux ratio from primary nitrification to secondary ozone is 1:1, and the reflux ratio from secondary nitrification to primary denitrification is 1:1.

[0025] (2) When the difficult-to-degrade wastewater in the present invention refers to wastewater with COD≤150mg / L, NH3-N≤15mg / L, TN≤50mg / L, and B / C<0.1, it especially refers to RO concentrated brine; the corresponding residence times of primary denitrification, secondary denitrification, primary ozone oxidation, secondary ozone oxidation, primary nitrification, and secondary nitrification are 2h, 1h, 0.5h, 0.5h, 1h, and 2h, respectively, and the addition ratio of primary ozone to secondary ozone is 1:3, the reflux ratio of primary ozone to primary denitrification is 1:1, the reflux ratio of primary nitrification to secondary ozone is 2:1, and the reflux ratio of secondary nitrification to primary denitrification is 1:1.

[0026] (3) When the difficult-to-degrade wastewater in the present invention refers to the tail water of industrial wastewater with COD≤80mg / L, NH3-N≤5mg / L, TN≤20mg / L, and B / C≤0.1 after pretreatment + biochemical treatment; the corresponding residence times of primary denitrification, secondary denitrification, primary ozone oxidation, secondary ozone oxidation, primary nitrification, and secondary nitrification are 1h, 1h, 0.5h, 0.5h, 0.5h, and 1h, respectively, and the addition ratio of primary ozone to secondary ozone is 1:3, the reflux ratio from primary ozone to primary denitrification is 1:1, the reflux ratio from primary nitrification to secondary ozone is 1:1, and the reflux ratio from secondary nitrification to primary denitrification is 1:1.

[0027] In the present invention, the important feature of the deep denitrification treatment method for refractory wastewater coupled with ozone oxidation is to achieve efficient removal of ammonia nitrogen, nitrate nitrogen, organic nitrogen and refractory COD in sewage through the combination of ozone oxidation and biofilm pool technology, and further optimize the treatment process through multiple reflux. The structure of this method mainly consists of the following parts:

[0028] First and second stage denitrification biofilm tanks;

[0029] One and two ozone oxidation tanks;

[0030] One and two stages of nitrification biofilm tanks;

[0031] Multiple reflow systems: including the reflow from the first stage ozone oxidation tank to the first stage denitrification biofilm tank (reflow of degradable COD after ozone modification), the reflow from the second stage nitrification biofilm tank to the first stage denitrification biofilm tank (reflow of nitrification liquid), and the reflow from the first stage nitrification biofilm tank to the second stage ozone oxidation tank.

[0032] The key innovations of the technical solution of the present invention and its preferred technical solution are:

[0033] 1. Combination of ozone oxidation and denitrification process. As a strong oxidant, ozone oxidation has a strong ability to oxidize and decompose difficult-to-degrade organic matter, organic nitrogen and ammonia nitrogen. In this method, the denitrification membrane tank, ozone oxidation and nitrification membrane tank are used in combination to form a series treatment system, and the ozone oxidation tank is placed between the denitrification membrane tank and the nitrification membrane tank. This coupling method utilizes the selective oxidation effect of ozone, reduces the adverse effects of ozone oxidation effluent on denitrification and nitrification, helps to improve the denitrification effect, reduce the amount of carbon source added, and reduce the amount of ozone added to the wastewater.

[0034] 2. Two-stage classification of denitrification membrane pool and nitrification membrane pool. By dividing the denitrification membrane pool and nitrification membrane pool into one and two sections and combining them with a reflux system, the organic nitrogen, ammonia nitrogen and nitric nitrogen in the difficult-to-degrade wastewater can be more thoroughly treated at different reaction stages. This segmented design has higher flexibility and helps to dynamically adjust according to different water quality conditions, further improving the nitrogen removal rate.

[0035] 3. Two-stage ozone addition in the ozone oxidation tank. In the existing ozone oxidation technology, uniform addition or single-stage ozone oxidation is usually adopted. The ozone addition method commonly used in existing ozone oxidation tanks may be uniform addition or dynamic adjustment of the dosage according to the water quality, but rarely a fixed ratio is clearly used to divide the ozone dosage into the first and second stages. The segmented and differentiated ozone addition design of the present invention makes the ozone oxidation process more hierarchical and flexible in gradient control, and can be precisely controlled according to the needs of different stages, thereby improving the denitrification effect of the overall system and reducing the excessive use of ozone. The present invention divides the ozone oxidation tank into one-stage ozone oxidation and two-stage ozone oxidation, and the ratio of the ozone dosage between the first-stage ozone oxidation tank and the second-stage ozone oxidation tank is set to 1:3. This design is different from the segmented ozone addition method commonly used in ozone oxidation tanks in the prior art.

[0036] (1) Innovation in the proportion of ozone segmentation and dosage: The main function of the first stage ozone oxidation pool may be to perform preliminary oxidation treatment on pollutants that are more easily reactive in water (such as ammonia nitrogen and organic nitrogen), while the second stage ozone oxidation pool undertakes a higher intensity oxidation task and may need to further oxidize and transform the intermediate products (such as nitrogen nitrite or organic oxidation products) after the first stage ozone oxidation. By setting the ratio to 1:3, more precise control of the oxidation process is achieved, making the use of ozone in each stage more targeted, and avoiding the problems of excessive ozone addition or incomplete reaction that may occur in the prior art.

[0037] The amount of ozone added is closely related to the reactivity and reaction time of pollutants in the water. By placing a higher amount of ozone in the second-stage oxidation tank, the reaction can be ensured to be complete, while avoiding excessive ozone addition in the first-stage ozone oxidation tank, which will cause residual ozone and oxygen in the effluent to enter the denitrification membrane tank. This helps to reduce the amount of ozone added and reduce the carbon source consumption of the denitrification membrane tank. In the prior art, ozone is often added evenly or concentratedly in a certain stage, which may lead to incomplete or excessive reaction, thereby increasing energy consumption and costs.

[0038] (2) Gradient control of the ozone oxidation process: The effect of ozone oxidation is affected by many factors, such as the oxidation reaction time, ozone concentration, type and concentration of pollutants in water, etc. By dividing the ozone dosage into segments and setting a 1:3 ratio, this gradient control design allows the reaction environment at different stages to be optimized:

[0039] One-stage ozone oxidation pool: In the first stage, lower ozone dosage can ensure mild preliminary treatment of pollutants. Ozone is mainly used to improve biodegradability. The ozone consumption in this stage is usually less than 20% of the total ozone demand. In addition, the B / C of the wastewater modified by ozone oxidation is improved and returned to the denitrification membrane pool for denitrification, so that the difficult-to-degrade organic matter in the wastewater can be used as the carbon source for denitrification after ozone oxidation.

[0040] Second stage ozone oxidation pool: In the second stage, a higher ozone dosage can deeply oxidize the difficult-to-biodegrade and difficult-to-modify organic matter left after the first stage treatment.

[0041] 4. Design of multi-stage biofilm pool, ozone oxidation pool and reflow system: By dividing the denitrification biofilm pool, ozone oxidation pool and nitrification biofilm pool into one and two sections, the segmented treatment method is adopted, which not only improves the flexibility and adaptability of the system, but also can adjust the reaction intensity of each stage according to different water quality, and optimize the removal efficiency of difficult-to-degrade COD, ammonia nitrogen, total nitrogen and organic nitrogen. The reflow system ensures the effective material exchange between the pool areas and improves the overall treatment capacity of the system.

[0042] Compared with the prior art, the beneficial technical effects of the present invention are:

[0043] (1) By placing ozone oxidation between denitrification and nitrification, the effect of ozone oxidation on improving biodegradability is fully utilized, reducing the adverse effects on denitrification, while improving the nitrification of ammonia nitrogen and the removal of total nitrogen.

[0044] (2) The use of graded treatment and reflow system design improves the flexibility and adaptability of the system, and can be dynamically adjusted according to different water quality conditions, further improving the COD, ammonia nitrogen and total nitrogen removal rates.

[0045] (3) Through the hierarchical design and differentiated addition of ozone oxidation, more precise control of the oxidation process is achieved, which not only ensures the treatment effect but also reduces the amount of ozone added and the consumption of denitrification carbon source.

[0046] (4) The use of biofilm technology and multi-stage treatment structure improves the overall treatment capacity and stability of the system, and is particularly suitable for treating difficult-to-degrade wastewater such as RO brine or industrial wastewater biochemical tail water. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The present invention is further described below in conjunction with the accompanying drawings and embodiments:

[0048] Figure 1 This is a process flow chart for deep denitrification of refractory wastewater by coupling the method of the present invention with ozone oxidation. DETAILED DESCRIPTION

[0049] The specific technical solutions of the present invention are further described below with reference to the accompanying drawings, so that those skilled in the art can further understand the present invention without limiting the rights thereof.

[0050] In order to fully explain the technical features and innovations of the present invention, the following embodiments are arranged from basic to in-depth, from single variable to multi-variable logic, and are divided into seven parts:

[0051] Example 1: Basic process flow verification

[0052] Test conditions: The COD of biochemical tailwater in a petrochemical park is 60mg / L, B / C=0.05, NH3-N is 5.0mg / L, and TN is 20mg / L. The wastewater temperature is 25±2℃, and the PH is 7.0~7.5

[0053] 1. Process parameters:

[0054] (1) Primary denitrification: carbon source dosage: C / N = 2:1, residence time 2 hours;

[0055] (2) Secondary denitrification: carbon source dosage C / N = 1:1, residence time 1.5 hours;

[0056] (3) Primary ozone oxidation: ozone dosage 0.6 mgO3 / mgCOD, contact time 15 minutes;

[0057] (4) Secondary ozone oxidation: ozone dosage 1.8 mgO3 / mgCOD, contact time 10 minutes;

[0058] (5) Primary nitrification: dissolved oxygen 2-3 mg / L, residence time 4 hours;

[0059] (6) Secondary nitrification: dissolved oxygen 2-3 mg / L, residence time 3 hours;

[0060] (7) Reflux ratio: primary ozone to primary denitrification 100%, secondary nitrification to primary denitrification 200%, primary nitrification to secondary ozone 100%.

[0061] 2. Test results

[0062] parameter COD(mg / L) <![CDATA[NH3-N(mg / L)]]> TN(mg / L) Water Intake 65 5.0 20 Water 29 0.2 12 Removal rate 55.4％ 96％ 40％

[0063] 3. Conclusion

[0064] (1) The process flow proposed by the present invention can effectively remove COD, ammonia nitrogen and total nitrogen in water.

[0065] (2) The COD removal rate reached 60%, the ammonia nitrogen removal rate was as high as 96%, and the total nitrogen removal rate was 45%, all of which achieved good treatment effects.

[0066] (3) The process achieves the synergistic removal of organic matter and nitrogen through a combination of multi-stage ozone oxidation, denitrification and nitrification processes.

[0067] (4) The application of the reflux strategy effectively improved the removal efficiency of total nitrogen.

[0068] Example 2 Optimization of ozone dosage

[0069] 1. Test conditions: The COD of biochemical tail water in a petrochemical park is 66 mg / L, B / C=0.05, NH3-N is 5.0 mg / L, and TN is 20 mg / L. The wastewater temperature is 25±2°C, and the pH is 7.0-7.5. The other process parameters are the same as those in Example 1, but the ozone dosage is adjusted according to the following scheme:

[0070]

[0071] 2. Test results

[0072]

[0073] 3. Conclusion

[0074] (1) When the dosage ratio of primary ozone to secondary ozone was kept at 1:3, the removal rates of COD and TN increased with the increase of total ozone dosage.

[0075] (2) From Scheme A to Scheme B, the ozone dosage increased by 20%, and the COD and TN removal rates increased by 4.7 and 4 percentage points, respectively, with a significant improvement in effect. From Scheme B to Scheme C, the ozone dosage increased by another 16.7%, and the COD and TN removal rates increased by 3 and 4 percentage points, respectively, with a significant improvement in effect. From Scheme C to Scheme D, the ozone dosage increased by 14.3%, but the COD and TN removal rates only increased by 1.6 and 2 percentage points, respectively, and the marginal benefit began to decline.

[0076] (3) Considering the treatment effect, ozone utilization efficiency and economy, Scheme B (0.6 mg O3 / mg COD for primary and 1.8 mg O3 / mg COD for secondary) is recommended as the optimal ozone dosage. Scheme B can achieve a good treatment effect at a lower ozone dosage, and the effect improvement brought by further increasing the ozone dosage is not significant enough.

[0077] Example 3 Optimization of carbon source dosage

[0078] 1. Experimental conditions: The COD of biochemical tail water in a petrochemical park is 65 mg / L, B / C=0.05, NH3-N is 5.0 mg / L, and TN is 20 mg / L. The wastewater temperature is 25±2°C, and the pH is 7.0-7.5. The other process parameters are the same as those in Example 1, but the carbon source dosage (C:N) is adjusted according to the following scheme:

[0079] plan Primary denitrification Secondary denitrification A 1.5:1 0.5:1 B 2.0:1 1.0:1 C 2.5:1 1.5:1 0.8 3.0:1 2.0:1

[0080] 2. Test results

[0081]

[0082]

[0083] 3. Conclusion

[0084] (1) With the increase of C / N ratio, the removal rate of TN gradually increases.

[0085] (2) Scheme A (primary stage 1.5:1, secondary stage 0.5:1) effluent TN has reached the expected target.

[0086] (3) Considering the treatment effect and the cost of carbon source addition, Scheme A is the best carbon source addition scheme.

[0087] In this scheme, the biodegradable COD contained in the effluent from the first-stage ozone oxidation is used as a carbon source to ensure that the TN of the effluent meets the standard and play a role in reducing carbon source consumption.

[0088] (4) To further reduce the outlet TN, Schemes B to D can be considered.

[0089] Example 4 Reflux Ratio Optimization

[0090] 1. Test conditions: COD of biochemical tail water in a petrochemical park is 65 mg / L, B / C=0.05, NH3-N is 5.0 mg / L, and TN is 20 mg / L. Wastewater temperature is 25±2°C, and PH is 7.0-7.5. Other process parameters are the same as in Example 1, but the reflux scheme is adjusted:

[0091]

[0092]

[0093] 2. Test results

[0094]

[0095] 3. Conclusion

[0096] (1) Under the condition of no reflux (Scheme A), the removal effect of COD and TN was the worst, which fully demonstrated the importance of reflux in improving treatment efficiency.

[0097] (2) With the increase of reflow ratio, COD removal rate increased significantly. Compared with the case without reflow, the COD removal rate of the optimal reflow scheme (I) increased by 33.8 percentage points, which fully demonstrated the significant effect of reflow on COD removal.

[0098] (3) The return of secondary nitrification effluent to primary denitrification has a significant effect on COD and TN removal. This return allows the wastewater to undergo multiple ozone oxidation-biochemical treatment cycles, greatly improving the removal efficiency of difficult-to-degrade organic matter.

[0099] (4) The return of primary ozone effluent also has a positive effect on COD and TN removal, but the degree of influence is relatively small. This is because the biodegradable carbon source in the primary ozone effluent promotes the denitrification process.

[0100] (5) Scheme I (200% / 200%) achieved the best treatment effect, with a COD removal rate of 64.6% and a TN removal rate of 45%. However, a high recirculation ratio may increase energy consumption. Scheme F (100% / 200%) achieved a good balance between treatment effect and energy consumption, with a COD removal rate of 60%, a TN removal rate of 43%, and good effluent quality. Comparing Scheme C (0% / 200%) and Scheme F (100% / 200%), it can be seen that increasing the recirculation of the first-stage ozone effluent can further improve the COD and TN removal rates, indicating that the partial oxidation products in the first-stage ozone effluent have a promoting effect on subsequent biochemical treatment.

[0101] The experimental results fully demonstrate the importance of the reflow strategy to improve the removal efficiency of COD and TN, especially by strengthening the coupling effect of ozone oxidation and biochemical treatment, achieving efficient removal of refractory organic matter. In practical applications, according to the fluctuation of influent water quality and treatment requirements, adjustments can be made between Scheme E and Scheme F to balance the treatment effect and operating cost. It should be noted that the energy consumption of the reflow pump should be considered in actual operation, and the appropriate reflow ratio should be selected to optimize energy utilization while ensuring the treatment effect.

[0102] Example 5 Hydraulic Retention Time (HRT) Optimization

[0103] 1. Test conditions: COD of biochemical tail water in a petrochemical park is 65 mg / L, B / C=0.05, NH3-N is 5.0 mg / L, and TN is 20 mg / L. Wastewater temperature is 25±2°C, PH is 7.0-7.5. The ozone dosage adopts the best solution of Example 2, the carbon source dosage adopts the best solution of Example 3, and the reflux ratio adopts the best solution of Example 4. The hydraulic retention time HRT scheme is as follows:

[0104]

[0105] 2. Test results

[0106]

[0107]

[0108] 3. Conclusion

[0109] (1) The effluent quality of all schemes met the discharge standard of deep denitrification treatment of biochemical tailwater (COD < 50 mg / L, NH3-N < 5 mg / L, TN < 15 mg / L), indicating that the process of the present invention can effectively treat sewage under different HRT conditions.

[0110] (2) Although Scheme A (total HRT 3.5h) has the shortest treatment time, the effluent quality has reached the standard. The COD and TN removal rates are relatively low, but considering its short treatment time and possible low energy consumption, it can be considered when the influent quality is good or the treatment requirements are not high.

[0111] (3) Scheme B (total HRT 5.5 h) achieved better treatment results, with significant reductions in effluent COD and TN. Considering the balance between treatment effect and HRT, this may be the most economical solution.

[0112] (4) Scheme C (total HRT 7.5 h) and Scheme D (total HRT 9.5 h) further improved the treatment effect, but considering that all schemes have met the standards, these two schemes may not be as economical as Scheme B.

[0113] (5) Taking into account the efficiency and economy of meeting the standards, Scheme B is recommended as the optimal HRT configuration scheme. This scheme provides a higher pollutant removal efficiency while ensuring that the standards are met, and the HRT is relatively short, which may have better economy.

[0114] (6) In practical applications, it is possible to adjust between Scheme A and Scheme B according to the fluctuation of influent water quality and specific treatment requirements. When the influent water quality is good, it is possible to consider adopting an HRT configuration closer to Scheme A to reduce energy consumption and operating costs.

[0115] (7) Although extending the HRT can improve the treatment effect, it will also increase the volume of the treatment facility and the operating cost. Therefore, in the actual design, the most economical HRT configuration should be selected under the premise of meeting the standards. It is recommended that in actual applications, a more detailed economic analysis should be conducted in combination with factors such as local electricity prices and land costs to determine the optimal HRT configuration plan.

[0116] Example 6 Study on adaptability to influent water quality fluctuations

[0117] 1. Test conditions:

[0118] Temperature 25±2℃, PH 7.0~7.5

[0119] ·Process flow: primary denitrification, secondary denitrification, primary ozone oxidation, secondary ozone oxidation, primary nitrification, secondary nitrification

[0120] Ozone dosage: primary ozone 0.6mg O3 / mg COD, secondary ozone 1.8mg O3 / mg COD

[0121] Carbon source dosage: primary denitrification C / N=2:1, secondary denitrification C / N=1:1

[0122] ● Reflux ratio: 100% of the first-stage ozone effluent is refluxed, 200% of the second-stage nitrification effluent is refluxed

[0123] HRT: Use regimen B of Example 5 (total HRT 5.5 h)

[0124] The inlet water quality plan is as follows:

[0125]

[0126] 2. Test results

[0127]

[0128] 2. Test conclusion

[0129] (1) The process of the present invention shows good treatment effect under different influent water quality conditions, and in most cases can meet the discharge standards (COD < 50 mg / L, NH3-N < 5 mg / L, TN < 15 mg / L).

[0130] (2) Under Scheme B, although the concentration of influent pollutants increased significantly, the effluent COD and NH3-N still met the standards, and TN only slightly exceeded the standards. Under highly polluted conditions (Scheme C), the effluent COD and NH3-N still met the standards, but TN exceeded the standards. This shows that in the face of more difficult-to-degrade chemical wastewater biochemical tail water and petrochemical RO concentrated water, it is necessary to adjust the process parameters (such as increasing the ozone dosage, increasing the reflux ratio, and increasing the carbon source dosage) to ensure that the discharge meets the standards.

[0131] Example 7 Engineering Application Example

[0132] 1. Project Overview:

[0133] ●Location: A sewage treatment plant in a chemical park

[0134] ●Processing scale: 10000m 3 / d

[0135] ●Operation time: 12 months of continuous operation

[0136] ●Water source: comprehensive wastewater discharged by chemical companies in the park

[0137] 2. Process parameters:

[0138] ●Process flow: primary denitrification, secondary denitrification, primary ozone oxidation, secondary ozone oxidation, primary nitrification, secondary nitrification

[0139] Ozone dosage: primary ozone 0.6mg O3 / mg COD, secondary ozone 1.8mg O3 / mg COD

[0140] Carbon source addition: primary denitrification C / N=2:1, secondary denitrification C / N=1:1

[0141] ● Reflux ratio: 100% of the first-stage ozone effluent is refluxed, 200% of the second-stage nitrification effluent is refluxed

[0142] Total HRT: 6 hours

[0143] 3. Operation results: The following data are the average and standard deviation during the 12-month operation period.

[0144] parameter COD(mg / L) <![CDATA[NH3-N(mg / L)]]> TN(mg / L) Water Intake 120±30 10±3 35±8 Water 38±5 0.5±0.2 10.5±2.2 Removal rate % 68.3±4.2 95.0±2.0 61.4±3.5

[0145] 4. Analysis of compliance rate:

[0146] ●COD compliance rate (<50mg / L): 100%

[0147] ●NH3-N compliance rate (<5mg / L): 100%

[0148] TN compliance rate (<15 mg / L): 100%

[0149] The above embodiments are merely descriptions of preferred implementation modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for deep denitrification of refractory wastewater coupled with ozone oxidation, characterized in that: The method comprises denitrification treatment, ozone oxidation treatment and nitrification treatment connected in series; The denitrification treatment comprises a primary denitrification and a secondary denitrification connected in series, wherein the primary denitrification is a denitrification biofilm process and the secondary denitrification is a denitrification biofilm process; The ozone oxidation treatment comprises a primary ozone oxidation and a secondary ozone oxidation which are sequentially connected in series, wherein the primary ozone oxidation is an ozone contact process, and the secondary ozone oxidation is an ozone / H2O2 process; The nitrification treatment includes a primary nitrification treatment and a secondary nitrification treatment connected in series, both of which are nitrification biofilm processes; Moreover, the primary ozone oxidation effluent is returned to the primary denitrification inlet, and the secondary nitrification effluent is returned to the primary denitrification inlet.

2. The method for deep denitrification of refractory wastewater coupled with ozone oxidation according to claim 1 is characterized by: The effluent from the primary nitrification is returned to the secondary ozone oxidation and used in the ozone jet dosing system.

3. The method for deep denitrification of refractory wastewater coupled with ozone oxidation according to claim 2, characterized in that: The reflux ratio from the primary nitrification effluent to the secondary ozone oxidation is (0.2-2):

1.

4. The method for deep denitrification of refractory wastewater coupled with ozone oxidation according to any one of claims 1 to 3, characterized in that: The primary denitrification tank and the primary nitrification tank are installed with biological rope fillers or suspended fillers, and the filling ratio is 30% to 60%; and the secondary denitrification tank and the secondary denitrification tank are installed with ceramsite, zeolite, volcanic rock or quartz filter material, and the filter bed thickness is 0.5 to 1.5 m.

5. The method for deep denitrification of refractory wastewater coupled with ozone oxidation according to any one of claims 1 to 4, characterized in that: The reflux ratio of the primary ozone oxidation effluent to the primary denitrification membrane pool is (1-2):1, and the reflux ratio of the secondary nitrification membrane pool to the primary denitrification membrane pool is (0.5-3):

1.

6. The method for deep denitrification of refractory wastewater coupled with ozone oxidation according to any one of claims 1 to 5, characterized in that: The residence times of the primary denitrification, secondary denitrification, primary ozone oxidation, secondary ozone oxidation, primary nitrification and secondary nitrification are 1-3h, 0.5-1h, 0.2-0.5h, 0.5-1h, 0.5-1h and 1-3h respectively.

7. According to any one of claims 1 to 6, it is characterized in that: The ozone dosage of the primary ozone oxidation and the secondary ozone oxidation is 1:(2~4).

8. The method for deep denitrification of refractory wastewater coupled with ozone oxidation according to any one of claims 4 to 6, characterized in that: The residence times of the primary denitrification, secondary denitrification, primary ozone oxidation, secondary ozone oxidation, primary nitrification, and secondary nitrification are 1h, 1h, 0.5h, 0.5h, 1h, and 1h, respectively, and the addition ratio of primary ozone to secondary ozone is 1:3, the reflux ratio from primary ozone to primary denitrification is 1:1, the reflux ratio from primary nitrification to secondary ozone is 1:1, and the reflux ratio from secondary nitrification to primary denitrification is 1:

1.

9. The method for deep denitrification of refractory wastewater coupled with ozone oxidation according to claim 1, characterized in that: The difficult-to-degrade wastewater is RO concentrated brine or industrial wastewater biochemical tail water.

10. The method for deep denitrification of refractory wastewater coupled with ozone oxidation according to claim 1, characterized in that: The refractory wastewater is wastewater with COD≤150mg / L, NH3-N≤15mg / L, TN≤50mg / L, and B / C<0.1, especially RO concentrated brine, and the corresponding residence times of primary denitrification, secondary denitrification, primary ozone oxidation, secondary ozone oxidation, primary nitrification, and secondary nitrification are 2h, 1h, 0.5h, 0.5h, 1h, and 2h, respectively, and the addition ratio of primary ozone to secondary ozone is 1:3, the reflux ratio of primary ozone to primary denitrification is 1:1, the reflux ratio of primary nitrification to secondary ozone is 2:1, and the reflux ratio of secondary nitrification to primary denitrification is 1:1; Alternatively, the difficult-to-degrade wastewater refers to the tail water of industrial wastewater with COD≤80mg / L, NH3-N≤5mg / L, TN≤20mg / L, and B / C≤0.1 after pretreatment + biochemical treatment, and the corresponding residence times of primary denitrification, secondary denitrification, primary ozone oxidation, secondary ozone oxidation, primary nitrification, and secondary nitrification are 1h, 1h, 0.5h, 0.5h, 0.5h, and 1h, respectively, and the addition ratio of primary ozone to secondary ozone is 1:3, the reflux ratio of primary ozone to primary denitrification is 1:1, the reflux ratio of primary nitrification to secondary ozone is 1:1, and the reflux ratio of secondary nitrification to primary denitrification is 1:1.

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