Method for intensively removing organic matters in terephthalic acid production wastewater tail water

Abstract

The invention discloses a method for intensively removing organic matters in terephthalic acid production wastewater tail water. The method comprises the following steps: (1) adding zero-valent iron in an anaerobic section to strengthen anaerobic reduction; (2) the anaerobic effluent is sequentially pumped into an anoxic tank and an aerobic tank, and the aerobic effluent flows back to the anoxic tank for denitrification; (3) adding powdered activated carbon into the aerobic section, and constructing a PACT process to enhance the degradation of organic matters; and (4) pumping aerobic effluent into a biological aerated filter, and enhancing biodegradation based on adsorption. By adopting the zero-valent iron reduction-anoxic / aerobic internal circulation-PACT-BAF combined process, the effluent quality of PTA wastewater treatment is improved, and the method has a wide application prospect in industrial wastewater treatment.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial wastewater treatment and relates to a method for strengthening the removal of organic matter in tail water of terephthalic acid production wastewater. Background Art

[0002] Purified Terephthalic Acid (PTA), as the world's highest-yielding dicarboxylic acid, is the core raw material of the polyester industry chain and is widely used in textile fibers, PET packaging materials, engineering plastics and film manufacturing. A large amount of PTA wastewater is generated during the production process. The main organic pollutants in PTA wastewater are aromatic organic compounds (including the target product PTA and by-products benzoic acid (BA), para-toluic acid (PT) and para-xylene (PX)). The molecular structure of these compounds contains a benzene ring conjugated system, with a complex structure and low biodegradability. Discharge of PTA wastewater without effective treatment into the environment will cause serious damage to the ecological environment and human health. After the PTA wastewater is treated, most of the easily degradable organic matter (such as acetic acid) in the wastewater is effectively removed, and the COD concentration is greatly reduced. However, there are still aromatic compounds with stable structure and high biological toxicity in the treated PTA tail water that have not been effectively removed. At present, the treatment of PTA wastewater at home and abroad mainly adopts biochemical treatment technology, and the effluent COD mass concentration is generally between 150 and 200 mg / L. However, with increasingly stringent emission standards, it is difficult to achieve further removal of organic matter in wastewater with existing processes alone. Therefore, it has become a key issue that the industry needs to solve urgently to carry out bio-enhanced treatment technology for PTA production wastewater tail water to achieve lower pollutant emissions.

[0003] At present, the treatment methods for PTA wastewater mainly include physical method, chemical method and biological method. Physical and chemical methods can remove organic matter in wastewater to a certain extent, but due to their high energy consumption, high cost, and easy to cause secondary pollution, they are difficult to use on a large scale in practical applications. Biological method has the advantages of high efficiency, low treatment cost, and not easy to cause secondary pollution. It is the main means of treating PTA wastewater. However, the aromatic compounds with stable structure and high biological toxicity in PTA tail water are difficult to be effectively removed by traditional biological treatment. Therefore, strengthening the traditional biological treatment process and enhancing the degradation of difficult-to-degrade organic matter is the key to improving the system's ability to remove organic pollutants.

[0004] Zero-valent iron (ZVI) has strong reducing properties and can act as an electron donor to promote electron transfer. ZVI can also reduce the redox potential (ORP) to create a good reducing environment for microorganisms, which is conducive to the growth of anaerobic microorganisms. In addition, iron, as an essential nutrient element, can participate in a series of key intracellular processes and increase enzyme activity. Fe(Ⅱ) produced by ZVI corrosion can stimulate microbial metabolism, enhance the abundance and diversity of functional microorganisms, enhance the interaction between microorganisms, and is beneficial to the stability of the biological ZVI system. In addition, ZVI has the advantages of low price and easy availability, so zero-valent iron is widely used in anaerobic systems to promote the reduction and degradation of pollutants. Xu et al. verified the feasibility of adding zero-valent iron to the anaerobic removal of refractory organic matter in coking wastewater (CWW). Experimental results showed that the addition of ZVI enhanced the removal of COD, phenols and heterocyclic compounds (NHCs) (Xu W, Zhao H, Cao H, et al. New insights of enhanced anaerobicdegradation of refractory pollutants in coking wastewater: Role of zero-valentiron in metagenomic functions[J]. Bioresource Technology, 2020, 300: 122667.).

[0005] The degradation of refractory pollutants is often limited by the availability of electron acceptors (EA). Nitrate is an important nutrient and electron acceptor in microbial growth. It can be reduced by a variety of microorganisms, promote microbial growth, metabolism and proliferation, and participate in the oxidation of organic matter and other reducing substrates. It plays a key role in nitrogen (N) cycle and electron transfer. Studies have shown that nitrate as an electron acceptor can promote the removal of refractory pollutants, while achieving the removal of nitrate and realizing cometabolism (Cheng H, Li Y, Guo G, et al. Advanced methanogenic performance and fouling mechanism investigation of a high-solid anaerobic membrane bioreactor (AnMBR) for the codigestion of food waste and sewage sludge [J]. Water Research, 2020, 187: 116436.). Wang et al. developed an anoxic denitrification system to remove N, N-dimethylformamide (DMF). By analyzing DMF concentration, microbial community structure, and enzyme activity, it was found that denitrification improved the biodegradation ability of specific functional microorganisms and promoted the degradation of DMF (Wang J, Liu X, Jiang X, et al. Facilitated bio-mineralization of N, N-dimethylformamide in anoxic denitrification system: Long-term performance and biological mechanism [J]. Water Research, 2020, 186: 116306.). This result further proves the important role of nitrate as an electron acceptor in promoting the removal of difficult-to-degrade pollutants in anoxic environments.

[0006] Powdered activated carbon-activated sludge method (PAC-AS), also known as powdered activated carbon process (PACT), combines powdered activated carbon (PAC) with traditional activated sludge process to allow adsorption and biodegradation to occur simultaneously, which has been proven to improve biological treatment efficiency. The addition of PAC in the PACT process enhances biological stability, can effectively intercept microorganisms and organic matter, has the advantages of high impact resistance, high process stability, and can improve the removal of difficult-to-biodegrade organic matter. In addition, activated carbon has good conductivity, which can promote direct interspecies electron transfer (DIET) between acidogenic bacteria and methanogens. Hu et al. operated a powdered activated carbon-activated sludge (PAC-AS) system, a traditional activated sludge (AS) system, and a PAC system to study the effect of PAC addition on organisms. The results showed that the COD removal efficiency of biodegradation in the PAC-AS system was significantly higher than that in the AS system. Further analysis showed that the addition of PAC enhanced the biodegradation of AS in the PAC-AS system by increasing biomass, improving metabolic activity, and enhancing sludge settling properties (Hu QY, Li M, Wang C, et al. Influence of powdered activated carbon addition on water quality, sludge properties, and microbial characteristics in the biological treatment of commingled industrial wastewater[J]. Journal of Hazardous Materials, 2015, 295: 1-8.).

[0007] Aerated biological filter (BAF) is a membrane treatment process that integrates adsorption, oxidation and filtration. The filler (such as activated carbon, ceramsite, quartz sand, etc.) in the reactor is used as a carrier. Aeration is carried out at the bottom of the reactor to provide oxygen for microorganisms, so that they adhere to the surface of the carrier to form a biofilm. When the wastewater flows through the filler from bottom to top, the organic compounds in the water are adsorbed, intercepted and degraded. When treating organic compounds in wastewater, the aerated biological filter takes the biofilm on the surface of the filler as the core, and completes the water purification process through physical interception, physical adsorption, biological metabolism and biological predation. In addition, aerobic, anoxic and anaerobic areas can be formed on the surface and inside of the biofilm, and nitrification and denitrification are carried out simultaneously to improve the removal capacity of organic matter. Compared with traditional wastewater treatment processes, it has the advantages of small footprint, large treatment capacity, strong shock load resistance and high efficiency, and is widely used to treat various wastewaters. Chen et al. found that the BAF system can effectively remove antibiotics such as sulfamethoxazole, norfloxacin, and oxytetracycline from aquaculture wastewater, with a total antibiotic removal rate of up to 90% (Chen J, Liu YS, Zhang JN, et al. Removal of antibiotics from piggery wastewater by biological aerated filter system: Treatment efficiency and biodegradation kinetics [J]. Bioresource Technology, 2017, 238: 70-77.). Summary of the invention

[0008] The purpose of the present invention is to provide a method for enhancing the removal of organic matter in the tail water of terephthalic acid production wastewater. The method uses a zero-valent iron reduction-anoxic / aerobic internal circulation-PACT-BAF combined process to treat the tail water of PTA production wastewater, combines zero-valent iron to enhance anaerobic degradation, promotes microbial metabolism by providing electrons, and enhances the removal efficiency of difficult-to-degrade organic matter; constructs anoxic-aerobic denitrification process to enhance denitrification and promote the co-metabolic degradation of organic matter; and introduces activated carbon enhancement technology to improve the removal rate of difficult-to-degrade organic matter through the synergistic effect of adsorption and biodegradation.

[0009] The technical solution for achieving the purpose of the present invention is as follows:

[0010] The method for enhancing the removal of organic matter in the tail water of terephthalic acid production wastewater includes adding zero-valent iron in the anaerobic section to provide an electron donor, create a good reducing environment, and improve the activity of microorganisms; constructing anoxic-aerobic internal circulation to enhance denitrification; adding PAC to the aerobic section to allow physical adsorption and biodegradation to occur simultaneously through the PACT process to enhance the removal of organic matter; building an aerated biological filter to form a biofilm on the surface of the filler to enrich microorganisms, thereby enhancing the degradation of refractory organic matter. The method specifically includes the following steps:

[0011] (1) The tail water of PTA production wastewater is passed into an anaerobic tank with zero-valent iron added for treatment to enhance anaerobic reduction;

[0012] (2) The effluent from the anaerobic tank is pumped into the anoxic tank and the aerobic tank in sequence through a peristaltic pump, and the effluent from the aerobic tank flows into the sedimentation tank. The supernatant in the sedimentation tank is returned to the anoxic tank for denitrification treatment, and the treatment effect is enhanced through the anoxic-aerobic internal cycle;

[0013] (3) The effluent from the anoxic pool after internal circulation is passed into an aerobic pool with powdered activated carbon added to construct a powdered activated carbon process to effectively retain microorganisms and enhance the removal of organic matter;

[0014] (4) The effluent from the aerobic pool treated by the powdered activated carbon process flows into the sedimentation tank, and the supernatant in the sedimentation tank is passed into the aerated biological filter. Activated carbon particles are used as fillers to enrich microorganisms and form a biofilm to deeply treat the PTA wastewater.

[0015] Furthermore, in step (1), the COD concentration of the PTA production wastewater tail water is 150 to 200 mg / L.

[0016] Furthermore, in step (1), the zero-valent iron is iron shavings.

[0017] Furthermore, in step (2), the anaerobic / aerobic reflux ratio is 100% to 200%, preferably 200%.

[0018] Furthermore, in step (3), the PAC concentration in the aerobic tank is above 0.3 mg / L, preferably 1 mg / L.

[0019] Furthermore, in step (4), the wastewater flows through the packing layer from bottom to top to ensure uniform distribution of the water flow.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] (1) Iron shavings are cheap and easy to obtain, with low cost, and are not likely to cause sludge compaction, thus ensuring the treatment effect of wastewater. In addition, ZVI can act as an electron donor to reduce the redox potential in the anaerobic system, create a good reducing environment for microorganisms, and improve microbial activity, thereby promoting the removal of difficult-to-degrade organic matter;

[0022] (2) Anoxic / aerobic denitrification systems can synergistically remove organic matter through cometabolism;

[0023] (3) The PACT process can enhance the sedimentation of sludge, allowing a large number of microorganisms to adhere to the surface of sludge particles, thereby enhancing the efficiency of the biodegradation process and improving the removal capacity of organic matter;

[0024] (4) The BAF process enhances the removal of organic matter from PTA wastewater by combining microbial degradation and adsorption of granular activated carbon;

[0025] (5) The present invention utilizes zero-valent iron to couple anaerobic process, anoxic denitrification process, powdered activated carbon process and BAF process for combined treatment. Zero-valent iron can act as an electron donor and create a good reducing environment. Under anaerobic conditions, its reducing effect can destroy the structure of aromatic pollutants and convert them into more easily degradable intermediates, thereby improving their bioavailability and reducing the organic load of subsequent treatment. The anoxic denitrification system can utilize co-metabolism to improve the removal effect of organic matter. The PACT process can effectively retain microorganisms, and the biofilter can enrich microorganisms to form a biofilm, thereby improving the removal effect of organic matter. The total TOC removal rate of PTA wastewater tail water reached 80.29%, which improved the effluent quality of PTA wastewater treatment and has broad application prospects in industrial wastewater treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a flow chart of the method for enhanced removal of organic matter in the tail water of PTA production wastewater.

[0027] Figure 2 This is a graph showing the change in TOC concentration after adding ZVI to the anaerobic system.

[0028] Figure 3 This is a graph showing the effect of adding ZVI on ORP (a) and pH (b) in an anaerobic system.

[0029] Figure 4 The effect of adding ZVI in the anaerobic system on INT-ETS (a) and the change of cyclic voltammetry (CV) curve (b).

[0030] Figure 5 is the TOC concentration under different reflux ratios (a); NO3 - -N concentration (b) changes.

[0031] Figure 6 These are the confocal laser scanning microscopy (CLSM) images of sludge at reflux ratios of 0% and 150%: superposition of live and dead cells in the system when the reflux ratio is 150% (a); live cells (b); dead cells (c); superposition of live and dead cells in the system when the reflux ratio is 0% (d); live cells (e); dead cells (f); percentage of dead / live cell area (g).

[0032] Figure 7 This is a graph showing the effect of different PAC concentrations on sludge SVI.

[0033] Figure 8 These are SEM images of activated sludge without (a) and with (b) PAC addition.

[0034] Fig. 9 This is a graph showing the change in TOC concentration after adding powdered activated carbon (PAC).

[0035] Fig.10 This is the comparison of the surface morphology of granular activated carbon before and after biofilm formation (a) granular activated carbon before biofilm formation (b) granular activated carbon after biofilm formation.

[0036] Fig.11 This is a diagram showing the degradation effect of BAF process on TOC.

[0037] Fig.12 This is a graph showing the change in TOC concentration in effluent from different processes.

[0038] Fig.13 Concentration changes of PTA (a); benzoic acid (BA) (b); p-xylene (PX) (c) and p-toluic acid (PT) (d) in PTA wastewater after combined process treatment. DETAILED DESCRIPTION

[0039] The present invention is further described below in conjunction with specific embodiments and drawings.

[0040] The wastewater targeted by the present invention is PTA production wastewater tail water, and the organic matter in the wastewater is mainly aromatic pollutants, the benzene ring structure is relatively stable, the biodegradability is low, and it is difficult to be degraded by microorganisms. Therefore, it is necessary to perform bio-enhanced treatment on the PTA production tail water to improve the removal effect of organic matter.

[0041] The processing technology of the present invention is as follows Figure 1As shown: The tail water of PTA wastewater production is first pumped into an anaerobic reactor with zero-valent iron added for anaerobic reduction. Then the wastewater treated by the ZVI coupled anaerobic system is passed into the anoxic reactor and the aerobic reactor, and the aerobic effluent flows into the sedimentation tank. A peristaltic pump is set between the anoxic reactor and the sedimentation tank to return the supernatant in the sedimentation tank to the anoxic reactor for anoxic denitrification. Powdered activated carbon is added to the aerobic reactor to construct the PACT process for enhanced degradation of organic matter. In addition to returning the supernatant in the sedimentation tank to the anoxic reactor for denitrification, it is also pumped into the aerated biological filter for deep treatment of PTA wastewater.

[0042] Example 1

[0043] In this embodiment, the tail water of PTA wastewater production is passed into an anaerobic reactor to which zero-valent iron is added for anaerobic reduction. This study explores the feasibility of enhancing anaerobic degradation with zero-valent iron by comparing the difference in TOC removal effect under the conditions of adding zero-valent iron and not adding zero-valent iron. The experiment used two groups of reactors, both of which had an effective volume of 2.0L and a hydraulic retention time (HRT) of 24h. 250g of iron shavings were added to the experimental group, and no iron shavings were added to the other group, which served as the control group. The experimental water was taken from a sewage treatment plant. During the experiment, the TOC, ORP and pH of the two reactors were measured, and the ETS and cyclic voltammetry (CV) curves in the two groups of sludge were measured.

[0044] Depend on Figure 2 It can be seen that the addition of zero-valent iron (250g iron shavings) in the anaerobic reactor can promote the anaerobic reduction of organic matter in PTA wastewater. The TOC concentration of the water used in the PTA experiment was tested to be 20-22mg / L. After treatment in the anaerobic reactor, the TOC concentration dropped to 18mg / L. In the ZVI coupled anaerobic biodegradation system, the TOC concentration was further reduced to 15mg / L, indicating that the addition of zero-valent iron can effectively improve the degradation capacity of organic matter in the anaerobic system. Oxidation-reduction potential (ORP) can be used to characterize the redox capacity of the entire system. When the entire system exhibits oxidizing properties, the ORP value is higher, and vice versa. Figure 3a It can be seen that the ORP value in the control group is -200±50mV, and the ORP value in the ZVI coupled anaerobic biodegradation system is -450±25mV, which is significantly lower than that in the control group, indicating that the ZVI coupled anaerobic biodegradation system creates a good reducing environment for microorganisms, which is conducive to the growth of anaerobic microorganisms and improves the removal capacity of organic matter. The pH value affects the degradation rate of pollutants and the progress of various reactions in the system. In the ZVI coupled anaerobic biodegradation system, changes in pH value will not only affect the corrosion process of ZVI, but also affect the activity and degradation effect of microorganisms. In addition, during the degradation of pollutants, ZVI will corrode and produce OH - It may increase the pH, adjust the pH in the system, and provide a good growth environment for the growth of methanogens. Figure 3 As shown in b, the pH value in the anaerobic biodegradation control group was 7.15±0.05, and the pH value in the ZVI coupled anaerobic biodegradation system was 7.30±0.05. This may be due to the generation of OH after ZVI corrosion. - , which increases the pH of the ZVI-coupled anaerobic biodegradation system.

[0045] ETS is closely related to its respiratory activity, indicating the electron transfer rate in the respiratory chain of microorganisms in the system. The higher the ETS activity, the stronger the ability of microorganisms in the system to degrade organic matter. Figure 4 a It can be seen that the ETS activity in the control group was only 4.68TFg -1 min -1 , the ETS activity in the experimental group was 43.22TFg -1 min -1 , which was significantly higher than that in the control group. This difference indicates that the addition of ZVI significantly promoted the activity of microbial electron transfer in anaerobic sludge, enhanced microbial respiration and promoted electron transfer in microbial metabolism. In the field of sludge treatment, cyclic voltammetry can be used to evaluate the electrochemical response of sludge, thereby indirectly reflecting the activity of electron transfer between microbial communities. The redox characteristics of the sludge-water mixture in the control group and the experimental group were studied by CV scanning. The results are as follows: Figure 4 As shown in Figure b, it can be seen from the figure that the reduction peak current in the control group is only -1.14 mA, while it is significantly increased to -1.60 mA in the experimental group. This shows that appropriate conductive materials can increase the redox activity of sludge. This may be because ZVI can not only act as an electron donor in sludge, but also produce Fe through electrochemical corrosion. 2+ , promoting the occurrence of redox reactions. These effects together enhance the electrochemical response of sludge and promote the occurrence of extracellular electron transfer processes. The experimental results show that the addition of ZVI significantly improves the electrochemical activity of sludge.

[0046] The above results show that ZVI-coupled anaerobic system creates a good reducing environment for microorganisms by degrading ORP in the system. ZVI acts as an electron donor to increase the electron transfer rate and improve microbial activity, thereby improving the TOC removal effect.

[0047] Example 2

[0048] The wastewater treated by the ZVI coupled anaerobic system in Example 1 is passed into an anoxic reactor and then into an aerobic reactor for treatment. After the effluent from the aerobic reactor enters a sedimentation tank, the supernatant is returned to the anoxic reactor through a peristaltic pump, and the treatment effect of PTA wastewater is enhanced through anoxic-aerobic internal circulation.

[0049] Nitrate can act as an electron acceptor to increase the activity of denitrifying bacteria and metabolize with pollutants, thereby promoting the removal of pollutants. In this embodiment, the effective volume of the anoxic reactor is 1.9L, and the effective volume of the aerobic reactor is 1.0L.

[0050] In the anoxic-aerobic (A / O) internal circulation process, the reflow ratio (i.e., the ratio of the return sewage to the influent) has a crucial impact on the wastewater treatment effect. If the reflow ratio is too low, difficult-to-degrade pollutants may remain in the wastewater, resulting in a decrease in the system treatment efficiency; while a high reflow ratio may destroy the anoxic environment of the anoxic section, which is not conducive to the growth of denitrifying bacteria and thus inhibits the denitrification effect. Figure 5 The effect of the reflow ratio on the effluent TOC concentration is shown. It can be seen that when the reflow ratio increases from 0% to 100%, the effluent TOC concentration does not change significantly, and the average value is stable at 14.5±0.5mg / L, indicating that within this reflow ratio range, the system's treatment capacity has not changed significantly. When the reflow ratio continues to increase to 150%, the effluent TOC concentration is the lowest (13±0.5mg / L), indicating that under this reflow ratio condition, the system has achieved the best organic matter removal effect. However, when the reflow ratio continues to increase to 200%, the effluent TOC concentration in the aerobic section does not decrease further, but instead shows an increasing trend. The possible reason is that the excessively high reflow ratio leads to an increase in the dissolved oxygen concentration in the anoxic section, destroying the anoxic environment, inhibiting the activity of denitrifying bacteria, and reducing the denitrification efficiency. Therefore, when the reflow ratio is around 150%, it can effectively promote the denitrification process and maintain a good treatment effect.

[0051] The sludge samples were taken when the nitrification liquid reflux ratio was 0% and the TOC degradation effect was the best (150%) for CLSM scanning analysis. Figure 6 It can be seen that when the reflux ratio of the nitrifying solution is 150%, the proportion of green living cells in the sample is significantly higher than that when the reflux ratio is 0% (increased from 85.51% to 88.94%), indicating that the activity of the microorganisms is stronger and the metabolic function is more active at this time.

[0052] The above analysis shows that when the reflux ratio is 0%, the electron acceptor supply in the system is insufficient, which inhibits the activity of denitrifying microorganisms and leads to a decrease in the proportion of live cells. When the reflux ratio of nitrification liquid is 150%, the refluxed nitrification liquid can effectively supplement nitrate nitrogen, provide stable electron acceptors for denitrifying microorganisms, improve the activity of microbial communities, and thus promote the degradation of difficult-to-degrade organic matter.

[0053] Example 3

[0054] The PTA wastewater after anoxic denitrification treatment in Example 2 is passed into an aerobic reactor, and activated carbon is added to the aerobic reactor to construct a PACT process for enhanced treatment of wastewater. In this embodiment, different concentrations of PAC are added to the aerobic section to systematically study the effect of the dosage of PAC on the wastewater treatment performance. By monitoring the changes in TOC concentration in the wastewater, the effect of PAC on the organic matter removal efficiency is evaluated. At the same time, after each addition of PAC, the sludge volume index (SVI) is determined to analyze the effect of PAC on sludge properties (such as sedimentation performance and floc structure) to further reveal its effect on the sludge system. In addition, the effect of PAC on activated sludge microorganisms is explored in combination with SEM.

[0055] SVI is an important parameter to characterize the settling performance of activated sludge. The smaller the value, the better the settling performance. Figure 7 As shown in the figure, when PAC was not added, the SVI value of the sludge was 48.4 mL / g. As the amount of powdered activated carbon added increased, the SVI value gradually decreased, and the sludge settling property was significantly improved. After a cumulative addition of 3 g / L of powdered activated carbon, the SVI dropped to 13.5 mL / g. This may be because powdered activated carbon has a large specific surface area and a certain surface charge, which can promote flocculation between sludge particles. The activated carbon particles combine with the sludge flocs to form larger composite particles, which accelerate the settling rate and improve the sludge settling property.

[0056] Figure 8 The SEM images of activated sludge and sludge in the powdered activated carbon (PACT) process. Figure 8 aIt can be seen that when powdered activated carbon is not added, the surface of the sludge particles is relatively flat, with fewer pores and cracks, and the structure appears relatively loose. This structure may lead to poor sludge settling performance and affect the sewage treatment effect. After adding powdered activated carbon, the powdered activated carbon particles and sludge flocs form a composite structure. The powdered activated carbon improves the structure of the sludge flocs, making it denser, and the sludge settling performance is improved. Figure 8b After adding powdered activated carbon, more microorganisms appeared on the surface of sludge particles. This phenomenon may be due to the fact that powdered activated carbon can provide a large specific surface area and abundant adsorption sites, providing a carrier for the attachment and growth of microorganisms, thereby enhancing the degradation ability of microorganisms and promoting the removal of pollutants. Therefore, in the PACT process, powdered activated carbon not only improves the sedimentation of sludge, but also enhances the degradation ability of microorganisms by providing a carrier for microbial attachment, which helps to improve the stability and treatment efficiency of the sewage treatment system. Fig. 9 The treatment effect of PACT process on PTA wastewater after adding different concentrations of powdered activated carbon. It can be found from the figure that when powdered activated carbon is not added, the effluent TOC concentration is 14.0 mg / L, and the effluent TOC concentration decreases with the increase of PAC concentration. When the PAC concentration is 1 mg / L, the effluent TOC drops to the minimum, that is, 12.5 mg / L. If the PAC concentration is further increased, the effluent TOC concentration will no longer continue to decrease. The results show that the PACT process can enhance the removal of refractory organic matter in PTA wastewater.

[0057] Therefore, the addition of activated carbon in the PACT process improves the stability of the sludge treatment system by improving the sedimentation of the sludge. In addition, since powdered activated carbon has a strong adsorption capacity, it can effectively remove toxic and harmful substances in wastewater, reduce toxic stress on microorganisms, and provide a better growth environment for microorganisms. Moreover, powdered activated carbon can provide a growth carrier for microorganisms and enhance their resistance to environmental fluctuations and external stress.

[0058] Example 4

[0059] The wastewater that flows into the sedimentation tank after being treated by the PACT process in Example 2 is passed into an aerated biological filter for deep treatment of PTA wastewater. In this embodiment, an aerated biological filter reactor (BAF) is constructed to evaluate its ability to remove residual organic matter. Activated carbon particles (GAC) are selected as fillers in BAF. Activated carbon not only provides a high specific surface area for biofilm attachment, but also has the ability to adsorb organic matter. The design of the wastewater flowing through the filler layer from bottom to top ensures the uniform distribution of water flow. During the study, the changes in TOC of the effluent in the BAF reactor were monitored to analyze its further removal effect on residual pollutants.

[0060] Fig.10 The surface morphology of GAC before and after biofilm formation. Fig.10 aIt can be seen that the surface of GAC granular activated carbon is rough and has gaps before biofilm formation. Its irregular surface structure gives it good adsorption capacity and can provide more sites for microbial attachment, which helps to form a stable biofilm and promote the interaction between microorganisms and pollutants. Moreover, depending on the thickness of the biofilm, anaerobic, anoxic and aerobic reactions can be carried out simultaneously, thereby improving the wastewater treatment efficiency. Fig.10b is an electron microscope scanning image of the granular activated carbon after the reactor had been running for 45 days. It can be seen from the figure that a biofilm is formed on the surface of GAC, and a large number of microorganisms are attached to the surface of GAC. The formation of biofilm can increase the contact between microorganisms and difficult-to-degrade pollutants and improve the efficiency of wastewater treatment.

[0061] Fig.11 The results show that the TOC concentration of the effluent after PACT treatment was 13±0.5 mg / L, and after further treatment with BAF, the TOC concentration was significantly reduced to 3.5±0.5 mg / L. This change shows that the BAF process has a significant effect in improving the removal efficiency of organic matter in PTA wastewater.

[0062] Analyzing the above results, it was found that BAF can maintain a higher concentration of biomass. These microorganisms are enriched on the surface of the filler and form biofilms, which promote the removal of organic matter.

[0063] Fig.12 The figure shows the change of total organic carbon (TOC) concentration in PTA wastewater by combined process. As can be seen from the figure, the initial TOC concentration of PTA wastewater is 21.04 mg / L. After a series of treatment processes, the TOC concentration gradually decreases, and finally significant removal is achieved. Specifically, the wastewater undergoes four treatment stages: zero-valent iron (ZVI) coupled anaerobic process, anoxic denitrification process, powdered activated carbon process, and BAF process. The effluent TOC is 16.63 mg / L, 14.61 mg / L, 12.51 mg / L, and 4.15 mg / L, respectively. Through the combined treatment of the four stages, the total TOC removal rate reached 80.29%, indicating the significant effect of the combined process in PTA wastewater treatment. Among them, each treatment unit plays a specific role in different stages of organic matter degradation, especially the final BAF process, which greatly reduces the concentration of residual organic matter. Fig.13The figure shows the change of characteristic pollutant concentration after each process treatment. It can be seen from the figure that the concentrations of the four main characteristic pollutants in PTA influent, terephthalic acid, benzoic acid, p-xylene and p-toluic acid, are 15.78 mg / L, 28.97 mg / L, 17.00 mg / L and 23.14 mg / L, respectively. These pollutants are aromatic compounds with high chemical stability and biodegradability. After treatment by different processes, the concentrations of the four characteristic pollutants decreased significantly. The concentrations of the four characteristic pollutants in the final effluent were 5.19 mg / L, 2.30 mg / L, 1.93 mg / L and 3.97 mg / L, respectively, and the corresponding removal rates were 67.11%, 92.06%, 88.65% and 82.84%, respectively, which shows that each treatment process has achieved a high degradation effect on these characteristic pollutants. Among them, the removal efficiency of benzoic acid is the highest, which is 92.06%. This may be because benzoic acid has a strong biodegradability and is easily metabolized and degraded by microorganisms in wastewater treatment. Relatively speaking, the removal rate of terephthalic acid was low, only 67.11%, which is consistent with the results of Kurodad et al. Studies have shown that the biodegradation of terephthalic acid is easily inhibited by other easily degradable organic substances (such as benzoic acid and acetic acid) (MaK, Li X, Bao L. Influence of organic loading rate on purified terephthalic acid wastewater treatment in a temperature staged anaerobic treatment (TSAT) system: Performance and metagenomic characteristics [J]. Chemosphere, 2019, 220: 1091-1099.). Specifically, in the presence of substrates such as benzoic acid and acetic acid, these more easily degradable compounds may be preferentially utilized by microorganisms, thereby competitively inhibiting the degradation of terephthalic acid.

[0064] Therefore, the zero-valent iron reduction-anoxic / aerobic internal circulation-PACT-BAF combined process can effectively reduce the concentration of characteristic pollutants in the secondary effluent after PTA production wastewater treatment, thereby reducing the concentration of organic matter.

Claims

1. A method for enhancing the removal of organic matter from tail water of terephthalic acid production wastewater, characterized in that: The specific steps include: (1) The tail water of PTA production wastewater is passed into an anaerobic tank with zero-valent iron added for treatment to enhance anaerobic reduction; (2) The effluent from the anaerobic tank is pumped into the anoxic tank and the aerobic tank in sequence through a peristaltic pump. The effluent from the aerobic tank flows into the sedimentation tank. The supernatant in the sedimentation tank is returned to the anoxic tank for denitrification treatment. The treatment effect is enhanced through the anoxic-aerobic internal cycle. (3) The effluent from the anoxic pool after internal circulation is passed into the aerobic pool with powdered activated carbon added to construct a powdered activated carbon process to effectively retain microorganisms and enhance the removal of organic matter; (4) The effluent from the aerobic pool treated by the powdered activated carbon process flows into the sedimentation tank, and the supernatant in the sedimentation tank is passed into the aerated biological filter. Activated carbon particles are used as fillers to enrich microorganisms and form biofilms to deeply treat PTA wastewater.

2. The method according to claim 1, characterized in that In step (1), the COD concentration of the PTA production wastewater tail water is 150~200 mg / L.

3. The method according to claim 1, characterized in that In step (1), the zero-valent iron is iron shavings.

4. The method according to claim 1, characterized in that: In step (2), the anoxic / aerobic reflux ratio is 100% to 200%.

5. The method according to claim 1, characterized in that In step (2), the anoxic / aerobic reflux ratio is 200%.

6. The method according to claim 1, characterized in that In step (3), the PAC concentration in the aerobic pool is above 0.3 mg / L.

7. The method according to claim 1, characterized in that In step (3), the PAC concentration in the aerobic tank is 1 mg / L.

8. The method according to claim 1, characterized in that In step (4), the wastewater flows through the packing layer from bottom to top to ensure uniform distribution of the water flow.

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