PTA wastewater ozone-biochemical coupling deep treatment method for inhibiting bromine oxidation

Abstract

The invention discloses a PTA wastewater ozone-biochemical coupling deep treatment method for inhibiting bromine oxidation. The method comprises pretreatment, pre-ozone oxidation-biological membrane coupling treatment, secondary coagulating sedimentation, post-ozone-BAC filter coupling treatment and an online monitoring control system. According to the process, ozone oxidation is limited in a direct oxidation stage by controlling the ozone dosage and optimizing the reflux ratio, so that oxidation of bromide ions is reduced to the greatest extent while the biodegradability of the wastewater is improved. The front ozonation unit and the rear ozonation unit both adopt high reflux ratio design, so that the direct contact concentration of ozone and raw water is reduced. The online monitoring control system adjusts the ozone adding amount and the reflux ratio in real time, so that the treatment effect is ensured, and meanwhile, generation of bromate is inhibited. The process can effectively remove refractory organic matters and ammonia nitrogen in the PTA wastewater, meanwhile, the bromate content is controlled at a lower level, and the process has a good treatment effect, economical efficiency and environmental friendliness.

Description

Technical Field

[0001] The present invention belongs to the field of water treatment technology, and specifically relates to a method for treating wastewater from the production of paraphthalic acid (PTA). More specifically, the present invention relates to a method combining ozone oxidation and biological treatment for treating biochemical tail water of PTA production wastewater containing high concentration of bromide ions. Background Art

[0002] 1. Overview of PTA production process

[0003] Terephthalic acid (PTA) is an important organic chemical raw material, widely used in the production of polyester fibers, plastics, films and other products. The PTA production process uses paraxylene (PX) as raw material, cobalt, manganese and bromine as ternary catalysts, acetic acid as solvent, and a series of processes under specific temperature and pressure to finally produce PTA powder. At present, the world's mainstream PTA production process technologies include BP of the United Kingdom, Mitsui of Japan, INVISTA of the United States, Lurgi-Eastman of Germany, Kunlun of China and Yisheng Hitachi. Among them, INVISTA's low-temperature oxidation process is the most widely used, accounting for more than 80% of the global market share and a production capacity of more than 60 million tons / year.

[0004] 2. Characteristics of PTA wastewater

[0005] The continuous innovation of PTA production process has led to significant changes in wastewater characteristics. Taking INVISTA's P8 process as an example, compared with P7 and other processes: COD increased from 8000mg / L to 20000mg / L, TDS increased from 2000mg / L to 10000mg / L, bromide ion concentration increased from 80-150mg / L to 300-800mg / L, and alkalinity increased from 1000-2000mg / L to 4000-8000mg / L. yes, Most of the newly added PTA production facilities in China after 2020 mainly use the INVISTA P8 process, with an additional capacity of more than 20 million tons. Although the P8 process has a reduced wastewater discharge coefficient, the difficulty of wastewater treatment has increased significantly.

[0006] 3. Existing processing technologies and their limitations

[0007] PTA wastewater treatment usually includes pretreatment, anaerobic treatment, aerobic treatment and deep treatment. High concentration of Br ions and high alkalinity pose many challenges to deep wastewater treatment:

[0008] High bromide ions interfere with the determination of COD.

[0009] High alkalinity causes the wastewater pH to exceed 8.5, and it is difficult to adjust the pH.

[0010] High bromide ions compete with refractory organic matter for hydroxyl radicals, reducing the effect of the advanced oxidation process; and bromide ions are oxidized to generate hypobromous acid and bromate, which affect the effluent quality.

[0011] High alkalinity acts as a hydroxyl radical quencher, affecting the effect of the advanced oxidation process.

[0012] Existing technologies, such as the ozone oxidation + biofilm process disclosed in China's public patent document 202011022795.8, are mainly used for wastewater with a Br ion concentration of no more than 150 mg / L. For wastewater with a high bromide ion concentration (300-800 mg / L) produced by the INVISTA P8 process, the process has problems such as unstable treatment effect, difficulty in controlling bromate, and high operating costs.

[0013] 4. Latest research progress

[0014] In recent years, researchers have tried a variety of new treatment technologies, such as membrane bioreactor (MBR) combined with advanced oxidation process, electrochemical oxidation, etc. However, these technologies still face challenges such as low efficiency and high cost when treating PTA wastewater with high bromide ion content.

[0015] In summary, given the limitations of existing technologies in treating PTA wastewater with high bromide ion content (300-800 mg / L), it is urgent to develop a new and efficient deep treatment technology. This technology should be able to effectively degrade organic matter, control bromate generation, achieve stable emission standards and reduce operating costs. Summary of the invention

[0016] The purpose of the present invention is to address the deficiencies of the prior art and provide a deep treatment method suitable for treating high-bromine ion wastewater generated by modern PTA production processes (such as INVISTA P8 process), which can effectively control bromate generation, improve ozone utilization efficiency, reduce ozone oxidation costs, and stably ensure that the effluent COD is ≤40mg / L.

[0017] The technical problem to be solved by the present invention is that when the ozone oxidation process is used to treat PTA wastewater with a high bromide ion content (300-800 mg / L), ozone is mainly used to oxidize bromide ions to generate bromate, resulting in limited effect of ozone oxidation on COD degradation in the wastewater, large ozone dosage and high operating cost.

[0018] In order to solve the above technical problems, the present invention provides a PTA wastewater deep treatment method for inhibiting the generation of bromate, which is suitable for treating the biochemical tail water after the PTA production wastewater is treated by anaerobic + aerobic process, wherein the wastewater Br - The content exceeds 300 mg / L and the COD is 120-450 mg / L. The method comprises the following steps:

[0019] (1) Pretreatment: The PTA biochemical tail water is pretreated by coagulation and sedimentation. The coagulant used is polyferric sulfate (PFS) with a dosage of 20-50 mg / L. The SS of the treated wastewater is required to be ≤10 mg / L.

[0020] (2) Pre-ozone-biofilm coupling treatment: The ozone contact oxidation process is adopted. Ozone is produced by an oxygen source ozone generator. The ozone concentration is 120-150 mg / L. The ozone dosage does not exceed 60 mg / L. The residence time in the ozone oxidation tank does not exceed 60 min. The biofilm reactor uses MBBR filler or bio-rope filler with a filling ratio of not less than 40%. The effluent from the biofilm tank is returned to the pre-ozone oxidation tank at a ratio of 200-400%.

[0021] (3) Intermediate treatment: The water treated in step (2) is subjected to secondary coagulation and sedimentation; a high-efficiency sedimentation tank process is used. At the same time, powdered activated carbon is added at a dosage of 50-100 mg / L.

[0022] (4) Post-ozone-BAC filter coupling treatment: adopt ozone / H2O2 process; ozone is generated by an oxygen source ozone generator with a concentration of 120-150 mg / L, and the ozone dosage does not exceed 40 mg / L; the residence time of the ozone oxidation tank is 10-30 min; the BAC filter uses a downflow fixed bed filled with granular activated carbon, the iodine value ratio is not less than 800 mg / g, the volume proportion of the granular carbon bed is not less than 30%, the filtration speed is 5-10 m / h, and the backwash cycle is 24-48 h. The effluent from the BAC filter is returned to the post-ozone oxidation tank at a ratio of 200-400%, and the effluent from the BAC filter is returned to the post-ozone oxidation tank at a ratio of 200-400%;

[0023] Among them: online ORP and bromate concentration monitoring and control systems are set in both the pre-ozone and post-ozone treatment units. ORP control range: 500-700mV in the pre-ozone section, 600-800mV in the post-ozone section. Bromate concentration control threshold: no more than 6000μg / L in the pre-ozone section, no more than 8000μg / L in the post-ozone section.

[0024] The following is a preferred technical solution of the method of the present invention:

[0025] In step (2), the biochemical process adopts a hydrolysis acidification + A / O process, the hydrolysis acidification residence time is 6 to 8 hours, and the A / O residence time is 6 to 12 hours.

[0026] In step (2), the ozone dosage does not exceed 30 mg / L, and the biochemical effluent is returned to the pre-ozone oxidation tank at a ratio of 300%. More preferably, the ozone dosage does not exceed 20 mg / L.

[0027] The pH of the ozone oxidation treatment before step (2) is controlled at 7.0-8.0.

[0028] Step (3) The surface load of the high-efficiency sedimentation tank is 0.5 to 2.0 m 3 / (m 2 h), the sludge from the high-efficiency sedimentation tank is returned to the A pool of the A / O pool, and the powdered carbon concentration in the A / O pool is maintained at 5000-20000 mg / L.

[0029] In step (4), the amount of ozone added does not exceed 20 mg / L, the effluent from the BAC filter is returned to the post-ozone oxidation tank at a ratio of 200%, and the molar ratio of H2O2 to ozone is controlled at 0.3-0.5.

[0030] Compared with the prior art, the beneficial technical effects of the present invention include:

[0031] (1) The treatment effect is significantly improved: the effluent quality after treatment meets the direct emission limit requirements in Table 1 of the Petrochemical Industry Pollutant Emission Standard (GB31571-2015), and the effluent COD can be stably reduced to below 40 mg / L.

[0032] (2) Bromate generation is effectively controlled: Through graded ozone oxidation and precise control strategy, bromate generation is reduced by more than 50% compared with existing technologies.

[0033] (3) Greatly improved ozone utilization efficiency: Multi-stage ozone oxidation and high-ratio reflux design reduce ozone consumption by more than 40% compared with existing technologies.

[0034] (4) System stability is significantly enhanced: Multi-stage treatment and reflux design improve the system's ability to resist shock loads, and the fluctuation of effluent water quality is reduced by more than 30%.

[0035] (5) Improved automation level: The use of online ORP and bromate monitoring systems enables real-time and precise control of ozone, and the system operation stability is improved by more than 20%. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The present invention is a flow chart of the ozone oxidation-biochemical coupling treatment method for PTA wastewater for inhibiting the generation of bromate. DETAILED DESCRIPTION

[0037] 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.

[0038] Example 1 Basic treatment plan

[0039] A PTA production enterprise uses the INVISTA P8 process to treat 6,000 tons of PTA wastewater per day. The biochemical tail water quality after the wastewater is treated by anaerobic + aerobic process is as follows: COD 250mg / L, NH3-N 15mg / L, TN 25mg / L, Br - 600mg / L, TDS10000mg / L, pH 8.7, SS 70mg / L.

[0040] The method of the present invention is used to process:

[0041] (1) Pretreatment: The biochemical tail water was transported to the coagulation sedimentation tank, and polyferric sulfate (PFS) was added as a coagulant at a dosage of 40 mg / L; the fast mixing time was 2 minutes, the slow mixing time was 15 minutes, and the sedimentation time was 30 minutes; the effluent SS was reduced to 10 mg / L and the COD was reduced to 230 mg / L;

[0042] (2) Pre-ozone oxidation-biofilm coupling treatment:

[0043] Pre-ozone oxidation: Two ozone contact tanks are connected in series, each with a volume of 75m 3 , the total ozone dosage is 20 mg / L evenly distributed in two grids, the ozone contact time is 30 minutes, the ozone generator output is 12.5 kg / h, and the ozone concentration is 150 mg / L;

[0044] Biofilm reactor: MBBR process, filler ratio 45%, reactor volume 1800m 3 , residence time 7.2 hours, dissolved oxygen concentration 3-4 mg / L;

[0045] Return system: The effluent from the biofilm pool is returned to the front ozone oxidation pool at a ratio of 200%, and the return pump flow rate is 750m 3 / h;

[0046] After this stage of treatment, the effluent COD dropped to 65 mg / L;

[0047] (3) Secondary coagulation and sedimentation:

[0048] Adopt high-efficiency sedimentation tank with surface load of 1.2m 3 / (m 2 h); add 30mg / L polyaluminium chloride PAC and 75mg / L powdered activated carbon; fast mixing time 1.5 minutes, slow mixing time 10 minutes, sedimentation time 25 minutes, effluent SS dropped to 10mg / L, COD dropped to 60mg / L; high-efficiency sedimentation tank sludge returned to pool A of the A / O pool, maintaining the A / O pool powder carbon concentration at 8000mg / L;

[0049] (4) Post-ozone-BAC filter coupling treatment:

[0050] Post-ozone / H2O2 oxidation: Two ozone contact tanks are connected in series, each with a volume of 50m 3 ; Total ozone dosage: 10 mg / L, evenly distributed in two cells; H2O2 dosage: 4 mg / L (O3 / H2O2 molar ratio is 0.4), ozone contact time: 30 min, ozone generator output: 7.5 kg / h;

[0051] BAC filter: Downflow fixed bed, filled with coal-made activated carbon; activated carbon iodine value 1000mg / g, granular carbon bed volume accounts for 35%; filter area 60m 2 , filter bed height 3m;

[0052] Return system: The effluent from the biofilm pool is returned to the front ozone oxidation pool at a ratio of 200%, and the return pump flow rate is 750m 3 / h;

[0053] Online monitoring and control system:

[0054] Online redox potential (ORP) and bromate concentration monitoring and control systems are installed in both the pre-ozone and post-ozone treatment units:

[0055] Front ozone stage redox potential ORP control range: 550-650mV;

[0056] Post-ozone stage redox potential ORP control range: 650-750mV;

[0057] Bromate concentration control threshold: 2000μg / L

[0058] After the above treatment, the effluent quality is: COD 35-45 mg / L, NH3-N 2 mg / L, TN 8 mg / L, chromaticity 25 times, bromate 1000 μg / L.

[0059] in conclusion:

[0060] (1) A two-stage ozone-biofilm coupling process is adopted, and the amount of ozone extracted is added to the two-stage ozone units respectively, which reduces the single-stage ozone addition concentration, thereby reducing the consumption of ozone by Br- and improving the utilization efficiency of ozone in the two-stage ozone unit.

[0061] (2) The COD removal rate of the secondary coagulation sedimentation tank is improved by adding activated carbon. At the same time, the sludge / activated carbon in the sedimentation tank is returned to the front-end biochemical unit, so that the unsaturated activated carbon continues to be adsorbed and removed in the biochemical system, thereby improving the overall removal effect of the biochemical unit.

[0062] (3) By installing online redox potential (ORP) and bromate monitoring systems in both the pre-ozone and post-ozone treatment units, the changes in redox potential (ORP) and bromate concentration in the wastewater can be monitored in real time, and the ozone dosage can be adjusted in time to ensure that the ozone utilization efficiency is ≥90%.

[0063] (4) The method of the present invention is used to treat PTA wastewater, and the effluent COD can be less than 50 mg / L and SS can be less than 10 mg / L. When the influent COD fluctuates by ±25%, the effluent COD fluctuation is controlled within ±6%; the system can operate stably for more than 180 days.

[0064] Example 2, Treatment of low concentration fluctuating influent

[0065] When the production load of a PTA production enterprise fluctuates greatly, the wastewater quality changes greatly: COD150mg / L, NH3-N 8mg / L, TN 18mg / L, Br - 450mg / L, TDS10000mg / L, pH 8.8, SS 60mg / L.

[0066] Based on Example 1, the following adjustments and optimizations are made:

[0067] (1) Pretreatment: The PFS dosage was reduced to 35 mg / L, and other parameters remained unchanged.

[0068] (2) Pre-ozone-biofilm coupling treatment:

[0069] The dosage is 25 mg / L and the residence time in the ozone oxidation pool is 30 min.

[0070] ●The filling rate of the biofilm reactor MBBR is increased to 50%.

[0071] ●The flow rate ratio of biofilm effluent back to the pre-ozone oxidation is 350%.

[0072] (3) The dosage of powdered activated carbon in secondary coagulation and sedimentation was increased to 80 mg / L.

[0073] (4) Post-ozone-BAC filter coupling treatment:

[0074] ● Post ozone dosage 15mg / L

[0075] ● The volume proportion of the granular carbon bed exceeds 40%, the superficial velocity is reduced to 6m / h, and the residence time is extended to 60 minutes;

[0076] ●Backflow: The reflux ratio of the BAC filter effluent back to the post-ozone oxidation unit is 200%.

[0077] (5) Online monitoring system redox potential (ORP) control: 500-600 mV in the front ozone oxidation section and 600-700 mV in the rear ozone oxidation section.

[0078] After the above adjustments, the effluent water quality indicators are as follows;

[0079] COD 38mg / L, NH3-N 1.6mg / L, TN 7.2mg / L, SS 6mg / L, chromaticity 10 times, bromate 500μg / L.

[0080] in conclusion:

[0081] (1) Compared with Example 1, when the water quality of the incoming water fluctuates (decreases) greatly, by adjusting (reducing) the amount of flocculant added to the coagulation sedimentation tank and the amount of ozone added to the ozone oxidation unit, the fluctuation of the water quality can be effectively dealt with while reducing the operating cost.

[0082] (2) Compared with Example 1, this example improves the filling rate of the biofilm reactor and the reflux ratio of the biochemical effluent, thereby increasing the total amount of microorganisms in the biochemical system, improving the treatment efficiency of the biochemical system, and making the removal of pollutants in the wastewater more complete.

[0083] (3) This embodiment further improves the adsorption effect of the unit on COD and the interception efficiency of SS by increasing the activated carbon filling amount in the BAC filter and extending the residence time. The effluent quality is better and can provide good water quality conditions for the sewage reuse system.

[0084] Example 3, Optimization of biological fillers

[0085] The method of the present invention is used to treat the PTA biochemical tail water in Example 1. Based on Example 1, the following adjustments and optimizations are made:

[0086] (1) PFS was used as a coagulant in the pretreatment, with a dosage of 40 mg / L. The SS in the effluent was reduced to 10 mg / L and the COD was reduced to 226 mg / L.

[0087] (2) Pre-ozone oxidation-biofilm:

[0088] The initial ozone dosage is 18 mg / L.

[0089] ●The biofilm reactor adopts the bio-rope filling process, the filling ratio is 55%, and the dissolved oxygen is controlled at 4-5mg / L.

[0090] ●Return system: The effluent from the biofilm pool is returned to the pre-ozone oxidation pool at a ratio of 200%. After the "pre-ozone oxidation-biofilm coupling" treatment, the effluent COD is reduced to 62mg / L.

[0091] (3) Secondary coagulation tank: PFS was added as a coagulant at a dosage of 40 mg / L, and powdered activated carbon was added at a dosage of 85 mg / L. The effluent SS dropped to 13 mg / L and COD dropped to 55 mg / L.

[0092] (4) Post-ozone-BAC filter coupling treatment:

[0093] ● The ozone dosage is 12mg / L, and the H2O2 dosage is 6mg / L (the molar ratio of O3 / H2O2 is 0.5.

[0094] ●BAC filter uses an upflow fixed bed, and the volume proportion of the granular carbon bed is increased to 38%.

[0095] ●The reflux ratio of BAC filter effluent to post-ozone is 200%.

[0096] After the above treatment, the effluent water quality indicators are: COD36mg / L, NH3-N 1.2mg / L, TN 6.5mg / L, SS6mg / L.

[0097] Conclusion: Compared with the embodiment, this embodiment mainly changes the MBBR filler in the biofilm reactor into a bio-rope filler process. The bio-rope filler has a better specific surface area and biofilm efficiency. At the same time, the filler filling ratio is increased, which significantly increases the total amount of microorganisms in the reactor, so that the biochemical system can more fully remove COD, NH3-N and TN indicators.

[0098] Example 4, using hydrolysis acidification + A / O process

[0099] The method of the present invention is used to treat the PTA biochemical tail water in Example 1. Based on Example 1, the following adjustments and optimizations are made:

[0100] (1) Pretreatment: PFS was used as a coagulant with a dosage of 50 mg / L. The effluent SS was reduced to 8 mg / L and the COD was reduced to 225 mg / L.

[0101] (2) Pre-ozone oxidation-biofilm coupling:

[0102] ●The initial ozone dosage is 22mg / L.

[0103] ●The biofilm reactor adopts the bio-rope filling technology, with a filling ratio of 60%. The retention time of the hydrolysis acidification tank is 8 hours, the dissolved oxygen is controlled at 0.5-0.8 mg / L, the A / O retention time is 10 hours, and the dissolved oxygen is controlled at 4-5 mg / L. Powdered activated carbon is added to the A / O tank, and the addition concentration is 60 mg / L.

[0104] ●The reflux ratio of A / O effluent back to the front ozone oxidation unit is 200%;

[0105] After "pre-ozone oxidation-biofilm coupling" treatment, the effluent COD dropped to 58 mg / L.

[0106] (3) Secondary coagulation tank: Add PFS 40mg / L, return the sedimentation tank sludge to the A / O tank, and maintain the A / O tank powder carbon concentration at 15000mg / L. The effluent SS dropped to 13mg / L and COD dropped to 53mg / L.

[0107] (4) Post-ozone-BAC filter:

[0108] The ozone dosage in the post-ozone oxidation tank is 15 mg / L, and the H2O2 dosage is 7.5 mg / L (the O3 / H2O2 molar ratio is 0.5).

[0109] After the above treatment, the effluent water quality indicators are: COD 34mg / L, NH3-N 1mg / L, TN 6.3mg / L, SS 7mg / L.

[0110] Conclusion: Compared with Example 1, the biofilm reactor in this example adopts the hydrolysis acidification + A / O process and adopts biological rope filler, which adds a hydrolysis acidification unit, prolongs the residence time of the biochemical system, and improves the COD removal effect of the reactor; the method in this example increases the civil engineering investment to a certain extent, but reduces the dosage of ozone and activated carbon during operation, which can greatly save the operating cost of wastewater treatment and further reduce the effluent water quality indicators.

[0111] Example 5, Treatment of high concentration influent

[0112] Under the condition of high production load, the wastewater quality of a PTA production enterprise increased significantly: COD 380mg / L, NH3-N 28mg / L, TN 38mg / L, Br - 950mg / L, TDS12000mg / L, pH 8.9, SS 90mg / L. The daily processing capacity is still 6000 tons.

[0113] Based on Example 1, the optimization is adjusted as follows:

[0114] (1) Pretreatment:

[0115] ●Use PFS as coagulant and increase the dosage to 60mg / L

[0116] ●Add PAM as coagulant, dosage 1mg / L

[0117] ● Outlet SS dropped to 15mg / L, COD dropped to 350mg / L

[0118] (2) Pre-ozone oxidation-biofilm coupling treatment:

[0119] ● The ozone dosage was adjusted to 30mg / L

[0120] ●The biofilm reactor adopts MBBR technology, and the filler filling ratio is increased to 55%

[0121] ●Increase the amount of carbon source, such as sodium acetate, and control the C / N ratio at 5:1

[0122] ●Dissolved oxygen adjusted to 2-3 mg / L

[0123] ●The return rate of biofilm pool effluent increased to 400%

[0124] (3) Secondary coagulation and sedimentation:

[0125] ●PAC dosage increased to 40mg / L

[0126] ●The dosage of powdered activated carbon is increased to 100mg / L

[0127] ● Outlet SS is reduced to 20mg / L, COD is reduced to 80mg / L

[0128] (4) Post-ozone-BAC filter coupling treatment:

[0129] ●The ozone dosage was adjusted to 10mg / L

[0130] ●H2O2 dosage increased to 16mg / L (O3 / H2O2 molar ratio maintained at 0.4)

[0131] ●The thickness of the carbon layer in the BAC filter is increased to 3.5m

[0132] (5) Online monitoring and control system:

[0133] ●The ORP control range of the front ozone section is adjusted to: 600-700mV

[0134] ●The ORP control range of the rear ozone stage is adjusted to: 700-800mV

[0135] The bromate concentration control threshold remains unchanged at 2000 μg / L

[0136] The quality of the treated effluent is: COD 46mg / L, BOD56mg / L, NH3-N 0.5mg / L, TN 9.5mg / L, SS 8mg / L, chromaticity 10 times, bromate 1800μg / L

[0137] in conclusion:

[0138] (1) By increasing the dosage of reagents at each stage and optimizing process parameters, this system can effectively cope with high-concentration influent.

[0139] (2) When the bromide ion concentration increases significantly, bromate can still be controlled at a low level by precisely controlling the ozone dosage and ORP.

[0140] (2) The effluent quality remained stable and met the standards, with COD removal rate reaching 87.9% and ammonia nitrogen removal rate reaching 91.1%.

[0141] Comparative Example 1: Primary ozone oxidation + biological aerated filter (BAF) + biological activated carbon filter (BAC)

[0142] The “primary ozone oxidation + aerated biological filter BAF + biological activated carbon filter BAF” process was used to treat the PTA wastewater biochemical tail water in Example 1. The process parameters of the main process units were:

[0143] (1) Pretreatment: Same as Example 1.

[0144] (2) Ozone oxidation-biochemical treatment:

[0145] Ozone oxidation: Two ozone contact tanks are connected in series, each with a volume of 100m 3 , total ozone dosage 300mg / L evenly distributed in two grids, ozone contact time 40 minutes, ozone generator output 75kg / h, ozone concentration: 150mg / L

[0146] Biochemical system: BAF process, filler ratio 45%, reactor volume 1800m 3 , residence time 7.2 hours, dissolved oxygen concentration 3-4 mg / L.

[0147] Return system: The effluent from the biofilm pool is 100% returned to the ozone oxidation pool.

[0148] (3) BAC filter: same as in Example 1.

[0149] The effluent quality after treatment is: COD50-55mg / L, NH3-N is 4mg / L, TN is 10mg / L, SS<5mg / L, Br- is 380mg / L.

[0150] Conclusion: It can be seen from the comparative example that when the process method of comparative example 1 treats PTA biochemical tail water, when the ozone dosage reaches 300 mg / L, the O / C (ratio of unit ozone dosage to COD removal) exceeds 10, and the operating cost is too high; at the same time, the Br in the wastewater - The decrease from 600 mg / L to 380 mg / L indicates that ozone is replaced by Br during the ozone oxidation process. - The consumption of ozone reduces the utilization efficiency of ozone in the system.

[0151] 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 treating PTA wastewater by ozone oxidation-biochemical coupling to inhibit the formation of bromate, wherein the wastewater is the biochemical tail water of PTA production wastewater after being treated by anaerobic + aerobic process, and Br in the wastewater - The content exceeds 300 mg / L, COD is 120~450 mg / L, characterized in that: The method comprises the following steps: (1) Pretreatment: The PTA biochemical tail water is pretreated by coagulation and sedimentation. The coagulant is polyferric sulfate PFS with a dosage of 20-50 mg / L; (2) Pre-ozone-biofilm coupling treatment: The wastewater treated in step (1) is subjected to pre-ozone-biofilm coupling treatment, wherein: the pre-ozone adopts an ozone direct contact oxidation process, the ozone is generated by an oxygen source ozone generator and the concentration is 120-150 mg / L, the ozone dosage does not exceed 60 mg / L, the residence time in the ozone oxidation tank does not exceed 60 min, and the biochemical effluent is returned to the pre-ozone oxidation tank at a ratio of 200-400%; (3) Intermediate treatment: The water treated in step (2) is subjected to secondary coagulation and sedimentation, wherein the coagulation and sedimentation process is a high-efficiency sedimentation tank process; (4) Post-ozone-BAC filter coupling treatment: The wastewater treated in step (3) is subjected to post-ozone-BAC filter coupling treatment, wherein: the post-ozone adopts an ozone / H2O2 process, the ozone is generated by an oxygen source ozone generator with a concentration of 120-150 mg / L and the ozone dosage does not exceed 40 mg / L, the residence time in the ozone oxidation tank does not exceed 30 min, and the effluent from the BAC filter is returned to the post-ozone oxidation tank at a ratio of 200-400%; Among them: both the pre-ozone and post-ozone treatment units are equipped with online redox potential ORP and bromate concentration monitoring systems.

2. The method according to claim 1, characterized in that: In step (2), the front ozone oxidation tank is divided into two compartments connected in series, and ozone is evenly added to the two compartments; the biofilm treatment adopts MBBR filler or bio-rope filler and the filling ratio is not less than 40%.

3. The method according to claim 1, characterized in that: In step (4), the ozone oxidation tank is divided into two compartments connected in series, and ozone is evenly added to the two compartments; the BAC filter adopts a downflow fixed bed, filled with granular activated carbon, the iodine value ratio is not less than 800 mg / g and the volume proportion of the granular carbon bed is not less than 30%, the filtration speed is 5-10m / h, and the backwash cycle is 24-48h.

4. The method according to claim 1, characterized in that: The pH of the ozone treatment before step (2) is controlled within the range of 7.0 to 8.0, and the molar ratio of H2O2 to ozone in the post-ozone treatment in step (4) is controlled within the range of 0.3 to 0.

5.

5. The method according to claim 1, characterized in that: The ORP control range is: the front ozone treatment unit is controlled at 500~700mV, and the rear ozone treatment unit is controlled at 600~800mV; the bromate concentration control threshold is: 1000~6000μg / L in the front ozone section, and 2000~8000μg / L in the rear ozone section.

6. The method according to claim 1, characterized in that: Step (3) adds powdered activated carbon, and the powdered carbon addition concentration is 50-100 mg / L.

7. The method according to claim 2, characterized in that: In step (2), the biochemical process is a hydrolysis acidification + A / O process, and the hydrolysis acidification residence time is 6 to 8 hours and the A / O residence time is 6 to 12 hours.

8. The method according to any one of claims 1 to 8, characterized in that: In step (2), the ozone dosage does not exceed 30 mg / L, and the biochemical effluent is returned to the front ozone oxidation tank at a ratio of 300%.

9. The method according to any one of claims 6 to 8, characterized in that: Powdered activated carbon is added to the A / O tank, and the powdered carbon concentration is 50~100 mg / L; the secondary coagulation sedimentation process in step (3) is a high-efficiency sedimentation tank, and the surface load is 0.5~2.0m 3 / (m 2 •h), the sludge from the high-efficiency sedimentation tank is returned to pool A of the A / O tank, and the powdered carbon concentration in the A / O pool is maintained at 5000~20000mg / L.

10. The method according to any one of claims 1 to 9, characterized in that: In step (4), the ozone dosage does not exceed 20 mg / L, and the effluent from the BAC filter is returned to the post-ozone oxidation tank at a ratio of 200%.

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