JP7807469B2 - Industrial wastewater treatment system, use of industrial wastewater treatment system, industrial wastewater treatment method, and wastewater treatment process - Google Patents

Description

The present disclosure relates to an industrial wastewater treatment system, uses of an industrial wastewater treatment system, a method for treating industrial wastewater, and a wastewater treatment process.

There has been related research into the treatment of persistent organic pollutants, which are often found in industrial wastewater. For example, Patent Document 1 discloses a microbubble ozone catalytic oxidation-non-aeration biochemical coupling process system and its use. Patent Document 1 uses microbubble technology to enhance ozone mass transfer, increase ozone utilization, and utilize the microbubble effect to improve oxidation capacity. This improves the removal efficiency of persistent pollutants and significantly improves biodegradability. Moreover, since the concentration of ozone exhaust gas is close to zero, no treatment of the ozone exhaust gas is necessary. Furthermore, the dissolved oxygen generated after the ozone reaction and the remaining oxygen microbubbles enter the biochemical treatment unit along with the liquid phase, providing sufficient dissolved oxygen for biochemical treatment. This eliminates the need for aeration in the biochemical treatment unit, thereby reducing operating costs.

However, while conventional technologies have only removed persistent organic substances, there is a desire to remove even more persistent organic substances.

Chinese Patent Application Publication No. 106007256

The present disclosure provides methods, processes and systems for treating industrial wastewater, and uses thereof, that efficiently and cost-effectively treat organic pollutants through microbubble (catalytic) ozone oxidation and biochemical cascade.

The industrial wastewater treatment system disclosed herein includes an ozone generator, a microbubble generator, an ozone catalytic oxidation reactor, an aeration deoxidation tank, and an aerobic biofilm reactor, all connected in series. In the aeration deoxidation tank, a portion of the dissolved oxygen and remaining dissolved ozone are removed from the wastewater discharged after undergoing ozone microbubble catalytic oxidation treatment in the ozone catalytic oxidation reactor.

Furthermore, the ozone catalytic oxidation reactor includes a catalyst bed layer. The ozone catalytic oxidation reactor may be divided into a catalytic ozone oxidation reaction zone including the catalyst bed layer and an ozone microbubble oxidation reaction zone below the catalyst bed layer.

Furthermore, the catalyst in the catalyst bed layer is a granular catalyst of 5 mm or more, for example, the catalyst may be a coal-based granular activated carbon catalyst or a granular metal oxide catalyst.

Furthermore, the industrial wastewater treatment system may further include an air-water separator installed between the ozone catalytic oxidation reactor and the aeration deoxidation tank. The air-water separator may separate the air-water mixture discharged after undergoing the ozone microbubble catalytic oxidation treatment in the ozone catalytic oxidation reactor. The separated wastewater may enter the aeration deoxidation tank.

Furthermore, the aerobic biofilm reactor includes a biofiller layer, the biofiller layer including a plurality of biofillers, each of which may be a fibrous suspension filler. The spacing between the fibrous suspension fillers is preferably 2 to 10 cm.

Furthermore, the aerobic biofilm reactor may include a submersible agitator located at the bottom of the aerobic biofilm reactor.

Furthermore, the industrial wastewater treatment system may include an ozone generator, a microbubble generator, an ozone catalytic oxidation reactor, an air-water separator, an aeration deoxidation tank, an aerobic biofilm reactor, and a water storage tank connected in series. The ozone catalytic oxidation reactor may include a catalyst bed layer. The ozone catalytic oxidation reactor may be divided into a catalytic ozone oxidation reaction zone including the catalyst bed layer and an ozone microbubble oxidation reaction zone below the catalyst bed layer. The catalyst in the catalyst bed layer may be a granular catalyst of 5 mm or more. The aerobic biofilm reactor includes a biofiller layer, which includes a plurality of biofillers, each of which may be a fibrous suspension filler. The spacing between the fibrous suspension fillers may be 2 to 10 cm.

Ozone generated in the ozone generator may be transported to a microbubble generator to generate ozone microbubbles. In the microbubble generator, the ozone microbubbles may mix with wastewater before entering the ozone microbubble oxidation reaction zone of the ozone catalytic oxidation reactor. The ozone microbubbles, wastewater, and catalyst bed layer may undergo a heterogeneous catalytic ozone oxidation reaction with the ozone microbubbles in the ozone catalytic oxidation reactor. The treated wastewater may flow out of the top of the ozone catalytic oxidation reactor and enter an air-water separator, where the air-water mixture discharged after the ozone microbubble catalytic oxidation treatment in the ozone catalytic oxidation reactor may be separated. The separated wastewater may then enter an aeration deoxidation tank. A portion of the dissolved oxygen and remaining dissolved ozone may be removed by aeration. The deoxidized wastewater may overflow from the top of the aeration deoxidation tank and enter an aerobic biofilm reactor from the bottom. As the wastewater flows upward, it comes into contact with the biofilm on the surface of the biofiller in the aerobic biofilm reactor, and the organic matter is broken down by the aerobic decomposition action of the biofilm. The wastewater overflowing from the top of the aerobic biofilm reactor may then be put into a storage tank.

The use of the treatment system disclosed herein is the use of an industrial wastewater treatment system in the treatment of wastewater.

The method for treating industrial wastewater according to the present disclosure includes:
1) performing ozone microbubble catalytic oxidation treatment on the wastewater to be treated;
2) subjecting the wastewater treated in step 1) to a deoxidation treatment to limit the dissolved oxygen in the wastewater to 2-8 mg/L, preferably 4-5 mg/L;
3) subjecting the wastewater treated in step 2) to aerobic biochemical treatment and discharging the treated wastewater.

Furthermore, the method for treating industrial wastewater may satisfy at least one condition selected from the group consisting of the following conditions A, B, C, and D.
Condition A: In the ozone microbubble catalytic oxidation treatment in step 1), the volume ratio of gas to water is 1:5 to 1:10, and the outlet pressure of the microbubble generator that generates ozone microbubbles is 0.3 MPa or more.
Condition B: In the ozone microbubble catalytic oxidation treatment of step 1), the average diameter of the ozone microbubbles is 30 μm or less.
Condition C: In the ozone microbubble catalytic oxidation treatment in step 1), the ratio of the ozone input amount to the COD amount of the supplied wastewater is limited to 0.2-1.0 mgO ₃ /mgCOD, and preferably the ratio of the ozone input amount to the COD amount of the supplied wastewater is 0.4-0.6 mgO ₃ /mgCOD.
Condition D: The wastewater to be treated is a salt-containing chemically synthesized wastewater or chemically decomposed wastewater containing nitrogen-containing heterocyclic organic compounds or benzene ring organic compounds.

The wastewater treatment process disclosed herein is a wastewater treatment process using an industrial wastewater treatment system. The treatment system includes an ozone generator, a microbubble generator, an ozone catalytic oxidation reactor, an air-water separator, an aeration deoxidation tank, an aerobic biofilm reactor, and a water storage tank, all connected in series. The ozone catalytic oxidation reactor includes a catalyst bed layer, which is divided into a catalytic ozone oxidation reaction zone including the catalyst bed layer and an ozone microbubble oxidation reaction zone below the catalyst bed layer. The wastewater treatment process includes transporting ozone generated in the ozone generator to a microbubble generator to generate ozone microbubbles. The wastewater treatment process includes mixing ozone microbubbles with wastewater in the microbubble generator before entering the ozone microbubble oxidation reaction zone of the ozone catalytic oxidation reactor. The wastewater treatment process includes causing ozone microbubbles, wastewater, and the catalyst bed layer to undergo ozone microbubble oxidation and heterogeneous catalytic ozone oxidation reactions in the ozone catalytic oxidation reactor. The wastewater treatment process includes a step in which the treated wastewater flows out of the top of the ozone catalytic oxidation reactor, enters an air-water separator, and separates the discharged air-water mixture after undergoing ozone microbubble catalytic oxidation treatment in the ozone catalytic oxidation reactor. The wastewater treatment process also includes a step in which the separated wastewater enters an aeration deoxidation tank. The wastewater treatment process includes a step in which a portion of the dissolved oxygen and remaining dissolved ozone are removed by aeration, the deoxidized wastewater overflows from the top of the aeration deoxidation tank, enters the aerobic biofilm reactor from the bottom, and as it flows upward, comes into contact with the biofilm on the surface of the biofilm filler in the aerobic biofilm reactor, where the biofilm aerobic decomposition action decomposes the organic matter. The wastewater overflows from the top of the aerobic biofilm reactor and enters a water storage tank.

FIG. 1 is a schematic diagram of an advanced treatment system for ultra-low discharge of recalcitrant industrial wastewater according to an embodiment of the present disclosure. FIG. 2 is a schematic diagram of a wastewater treatment system according to Comparative Example 1.

The following embodiments are intended to illustrate the present disclosure and are not intended to limit the scope of the present disclosure. Unless specific techniques or conditions are specified in the embodiments, they will conform to techniques or conditions described in the literature in this field or will be carried out in accordance with the product's instructions. Reagents or equipment used without a manufacturer's designation are ordinary products available for purchase from suppliers.

After extensive research, the present inventors have found the following drawbacks in conventional technologies: (1) The particle size of the catalyst particles is not optimized. When small granular catalysts are used, the channel diameter of the catalyst bed layer is small and the porosity is low. As a result, microbubbles aggregate and merge within the channels as they pass through the catalyst bed, generating larger bubbles. This weakens the microbubbles' effect of improving oxidation ability. (2) After ozone catalytic oxidation treatment, the wastewater has a very high dissolved oxygen concentration and traces of residual ozone. If the wastewater is subjected to biochemical treatment as is, this will affect biological activity and reduce the efficiency of the biochemical treatment. (3) The type of filler is not optimized. Because the biochemical reactor is non-aerated, when a granular biofiller bed layer is used, the flow path is prone to short-circuiting, adversely affecting the contact between the wastewater and biofilm, resulting in insufficient biochemical treatment effectiveness. (4) Biochemical treatment lacks an attached mixing means, and the biochemical reactor is non-aerated and has no direct mixing means, resulting in insufficient power generated from the water, making it difficult for the wastewater to come into sufficient contact with the biofilm, which affects the effectiveness of biochemical treatment. (5) There is a lack of countermeasures and related research to meet higher treatment requirements and stricter treatment standards.

The present disclosure aims to solve at least one of the above problems.

As shown in Figure 1, the treatment system is an advanced treatment system for ultra-low discharge of recalcitrant industrial wastewater. The treatment system includes an ozone generator 100, a microbubble generator 200, an ozone catalytic oxidation reactor 300, an aeration deoxidation tank 400, and an aerobic biofilm reactor 500, which are connected in series.

In Figure 1, the arrows indicate the direction of wastewater flow.

In some examples, the aeration deoxidation tank 400 removes excess dissolved oxygen (a portion of the dissolved oxygen) and residual dissolved ozone from wastewater discharged after undergoing ozone microbubble catalytic oxidation treatment in the ozone catalytic oxidation reactor 300.

In some examples, the advanced treatment system for ultra-low discharge of recalcitrant industrial wastewater further includes a water supply line 800 for transporting the wastewater to be treated.

In some examples, the ozone microbubbles generated in the microbubble generator 200 are mixed with wastewater in the water supply line 800 before entering the ozone catalytic oxidation reactor 300. In some examples, the mixed wastewater enters the ozone catalytic oxidation reactor 300 at the bottom.

In some examples, the water supply line 800 and the microbubble generator 200 are each connected to the bottom of the ozone catalytic oxidation reactor 300. At the bottom of the ozone catalytic oxidation reactor 300, the wastewater to be treated transported from the water supply line 800 mixes with the ozone generated in the microbubble generator 200.

In some examples, the treatment system further includes a water supply pump 900 connected to the water supply line 800 for transporting the treated wastewater in the water supply line 800.

In some examples, the ozone catalytic oxidation reactor 300 further includes a catalyst bed layer 301 located above the middle (center) of the ozone catalytic oxidation reactor 300. The catalyst bed layer 301 divides the ozone catalytic oxidation reactor 300 into an upper catalytic ozone oxidation reaction region 302, which includes the catalyst bed layer 301, and an ozone microbubble oxidation reaction region 303, which is located below the catalyst bed layer 301. In the catalytic ozone oxidation reaction region 302, an oxidation reaction in which hydroxyl radicals are generated primarily by the ozone catalyst occurs, contributing approximately 25% to the oxidative decomposition of persistent organic substances. In the ozone microbubble oxidation reaction region 303, an oxidation reaction in which hydroxyl radicals are generated primarily by the contraction and bursting of ozone microbubbles occurs, contributing approximately 75% to the oxidative decomposition of persistent organic substances.

The catalyst in the catalyst bed layer 301 is preferably a granular catalyst of 5 mm or larger, such as a coal-based granular activated carbon catalyst or a granular metal oxide catalyst. Research has shown that larger diameter granular catalysts accumulate without restriction to form a bed layer, and the bed layer has large pore channels, which reduces aggregation and merging of microbubbles as they pass through the bed layer. In some examples, the catalyst particle size is 5-8 mm.

In some examples, the ozone catalytic oxidation reactor 300 further includes a pressure gauge 304 for measuring pressure.

In some examples, the ozone catalytic oxidation reactor 300 is a sealed pressure vessel and the operating pressure is 0.05 to 0.1 MPa or less.

In some examples, the advanced treatment system for ultra-low discharge of refractory industrial wastewater further includes an air-water separator 401 installed between the ozone catalytic oxidation reactor 300 and the aeration deoxidation tank 400. In some examples, the air-water separator 401 separates the air-water mixture discharged after undergoing the ozone microbubble catalytic oxidation treatment in the ozone catalytic oxidation reactor 300. The separated wastewater enters the aeration deoxidation tank 400.

In some examples, the aeration/deoxidation tank 400 includes an air or nitrogen aeration device 402. The aeration/deoxidation tank 400 removes excess dissolved oxygen and residual dissolved ozone. The aeration rate of the aeration device 402 can be adjusted automatically or manually based on dissolved oxygen requirements.

In conventional wastewater treatment methods, the ozone microbubble catalytic oxidation process and biochemical treatment are performed consecutively, with no intervening process between them, which impacts the effectiveness of the biochemical treatment. In particular, the dissolved oxygen concentration is not adjusted after the ozone microbubble catalytic oxidation process, resulting in a very high dissolved oxygen concentration (typically about 20-30 mg/L), making it difficult to achieve stable results in the subsequent biochemical treatment. The present disclosure provides an aeration deoxidation tank 400 between the ozone catalytic oxidation reactor 300 and the aerobic biofilm reactor 500. This serves various purposes, such as slowing down the process, adjusting the dissolved oxygen concentration, and eliminating the effects of residual ozone, thereby further improving the treatment efficiency of persistent organic pollutants. In some preferred examples, the dissolved oxygen concentration of the wastewater treated in the aeration deoxidation tank 400 is limited to a range of 2-8 mg/L. The dissolved oxygen concentration of the wastewater may be 4 mg/L or more, 5 mg/L or more, or 6 mg/L or more. The dissolved oxygen in the wastewater may be 7 mg/L or even 5 mg/L or less, and research has shown that under these conditions, the treatment efficiency of persistent organic pollutants is higher.

In some examples, the aerobic biofilm reactor 500 includes a biofiller layer 501, which includes a plurality of biofillers, each of which is a fibrous suspension filler.

In some examples, the fiber-knit suspension filler may be a commercially available product, for example, purchased from Hebei Yisheng Environmental Protection Technology Co., Ltd.

In conventional wastewater treatment methods, activated carbon or ceramsite fillers are used in aerobic biofilm reactors (500) for biochemical treatment. The resulting filler bed layer is prone to short-circuiting of the flow path under non-aerated conditions. In particular, when the aerobic biofilm reactor (500) is enlarged, the impact of the filler bed layer on the flow in the aerobic biofilm reactor (500) becomes more pronounced. The problem of uneven flow velocity distribution also becomes more severe, affecting the treatment efficiency of persistent organic pollutants. In the present disclosure, a woven fiber suspension filler is used to achieve good flow and flow velocity distribution in the aerobic biofilm reactor (500) under non-aerated conditions, improving mass transfer and reaction conditions in the aerobic biofilm reactor (500) and enhancing treatment efficiency. Another advantage of the suspension chain-type fixed filler is that it ensures biofilm growth and facilitates good flow within the aerobic biofilm reactor (500) under non-aerated conditions. In some examples, the spacing between the woven fiber suspension fillers is 2 to 10 cm. The fiber-knit suspension filler may include, for example, a plurality of filler bodies on which a biofilm is formed and a connecting member connecting the plurality of filler bodies. The connecting member may be, for example, a thread, a string, a chain, or a rope. The filler body may include a mold-shaped fiber filler and a ball shell that houses the fiber filler. The ball shell may be formed by combining two semicircular shells, each having a plurality of openings, and may be configured so that wastewater comes into contact with the fiber filler through the openings.

In some examples, the aerobic biofilm reactor 500 further includes a submersible agitator 502 located at the bottom of the aerobic biofilm reactor 500. The submersible agitator 502 serves as an additional mixing means, improving the dynamics of the water within the aerobic biofilm reactor 500, promoting mixing, and facilitating contact between the wastewater and the biofilm and mass transfer of contaminants, thereby improving the effectiveness of the biochemical treatment.

In some examples, the aerobic biofilm reactor 500 does not include an aeration device.

In some instances, wastewater enters the aerobic biofilm reactor 500 at the bottom and overflows at the top, creating upward flow treatment conditions that facilitate sufficient contact between the wastewater and the biofilm.

In some examples, the advanced treatment system for ultra-low discharge of recalcitrant industrial wastewater further includes a reservoir 600 connected to the aerobic biofilm reactor 500 for collecting wastewater treated in the aerobic biofilm reactor 500.

In some examples, the advanced treatment system for ultra-low discharge of persistent industrial wastewater further includes a return pump 700 connected to the water tank 600 for discharging the wastewater in the water tank 600. In some examples, the wastewater in the water tank 600 is transported to a wastewater tank to be treated by the return pump 700. Alternatively, the wastewater in the water tank 600 is transported directly to the water supply line 800, mixed with the feedwater, and then subjected to two cascade circulation treatments. Alternatively, the wastewater in the water tank 600 is treated in the next stage of the cascade treatment device. This further removes persistent organic substances. By adjusting the execution mode of multiple circulations or multi-stage treatments, or a combination thereof, different COD removal rates can be achieved to achieve the requirements for removal of persistent organic substances and the goal of ultra-low discharge. In some examples, the wastewater in the water tank 600 is discharged by the return pump 700 once it meets the discharge standards, thereby realizing safe discharge.

In some examples, the ozone generator 100 and the water supply line 800 are each connected to the microbubble generator 200. In some examples, the microbubble generator 200 is connected to the bottom of the ozone catalytic oxidation reactor 300. In some examples, the top of the ozone catalytic oxidation reactor 300 is connected to the bottom or a position lower than the center of the aeration deoxidation tank 400. In some examples, the top of the aeration deoxidation tank 400 is connected to the bottom of the aerobic biofilm reactor 500.

In some examples, ozone gas is generated in the ozone generator 100 using pure oxygen as a gas source. In some examples, ozone gas enters the microbubble generator 200 to generate ozone microbubbles. In some examples, the ozone microbubbles are mixed with feedwater (wastewater) before entering the ozone catalytic oxidation reactor 300 from the bottom. The ozone microbubbles, wastewater, and catalyst bed layer 301 undergo a heterogeneous catalytic ozone oxidation reaction with the ozone microbubbles in the ozone catalytic oxidation reactor 300. Hydroxyl radicals are then generated through the contraction and collapse of the ozone microbubbles and the catalytic ozonolysis. This decomposes persistent organic pollutants, producing easily degradable small-molecule organic compounds and improving the biodegradability of the wastewater. After the ozone catalytic oxidation reaction, the air-water mixture is pressurized and flows out of the top of the ozone catalytic oxidation reactor 300. The air-water mixture enters the aeration and deoxidation tank 400 from the bottom or a lower position than the center without the need for powered transportation. Excess dissolved oxygen and remaining dissolved ozone are removed by aeration. The deoxidized wastewater overflows from the top of the aeration and deoxidation tank 400 and enters the aerobic biofilm reactor 500 from the bottom. As the deoxidized wastewater flows upward, it comes into contact with the biofilm on the surface of the biofiller in the aerobic biofilm reactor 500. The aerobic decomposition action of the biofilm removes (decomposes) more easily decomposable small-molecule organic matter from the wastewater, and the wastewater overflows from the top of the biochemical reactor (aerobic biofilm reactor 500). The wastewater overflowing from the aerobic biofilm reactor 500 enters the water storage tank 600.

Embodiments of the present disclosure further provide for the use of advanced treatment systems for ultra-low discharge of recalcitrant industrial wastewater in the treatment of wastewater.

In an embodiment of the present disclosure, further
1) performing ozone microbubble catalytic oxidation treatment on the wastewater to be treated;
2) subjecting the wastewater treated in step 1) to a deoxidation treatment to limit the dissolved oxygen in the wastewater to 2-8 mg/L;
and 3) subjecting the wastewater treated in step 2) to aerobic biochemical treatment, and discharging treated wastewater that meets the standard.

Preferably, in the deoxygenation treatment in step 2), the dissolved oxygen in the wastewater after treatment in step 1) is limited to 4 to 5 mg/L.

In some cases, if the wastewater after treatment in step 3) does not meet the discharge standards, it is returned to step 1) for cascade circulation treatment and continues to be treated until it meets the standards.

In some cases, persistent organic substances remain in the wastewater after one cascade treatment. Therefore, a certain proportion of the wastewater in the water storage tank 600 is transported by the circulation pump 700 to the water supply line 800, where it is mixed with the feedwater before a second treatment is carried out. Alternatively, the wastewater in the water storage tank 600 is treated in the next stage of the cascade treatment device. This further removes persistent organic substances. By adjusting the execution method of multiple circulations or multi-stage treatment, or a combination thereof, different COD removal rates can be achieved to achieve the requirements for persistent organic substance removal and ultra-low discharge targets.

In some examples, the volume ratio of gas to water within the microbubble generator 200 is limited to 1:5 to 1:10. That is, in some examples, the volume ratio of gas to water in the ozone microbubble catalytic oxidation process is 1:5 to 1:10. Also, in some examples, the pressure before the tube is 0.3 MPa or higher. For example, the outlet pressure of the microbubble generator 200 is 0.3 MPa or higher. In some examples, the microbubble generator 200 stably generates microbubbles with an average diameter of 30 μm or less. Such microbubbles generate hydroxyl radicals upon contraction and bursting, which is highly effective in improving oxidizing ability. The average diameter of the microbubbles is, for example, the number-average diameter of the circle-equivalent diameter of approximately 100 bubbles obtained by image analysis.

In some examples, in the ozone microbubble catalytic oxidation treatment described in step 1), the ratio of the ozone input rate to the COD content of the feed wastewater is limited to 0.2-1.0 _mgO3 /mgCOD. Preferably, the ratio of the ozone input rate to the COD content of the feed wastewater is 0.4-0.6 _mgO3 /mgCOD. This ensures that the ozone input rate and the ozone oxidation consumption rate are approximately balanced, ensuring not only a fast rate of oxidizing and removing pollutants, but also sufficient utilization of ozone and a high ozone utilization rate.

In some examples, the wastewater to be treated undergoes ozone microbubble catalytic oxidation, deoxidation, and aerobic biochemical treatment, in that order. In ozone microbubble catalytic oxidation, hydroxyl radicals oxidize persistent organic substances, removing 30-40% of the persistent organic substances and generating some easily decomposable small-molecule organic substances. In deoxidation, excess dissolved oxygen and remaining dissolved ozone remaining after microbubble (catalytic) ozone oxidation are removed. In aerobic biochemical treatment, the easily decomposable small-molecule organic substances generated are biochemically removed, with an organic matter removal efficiency reaching 30%.

In some cases, in cascade circulation or multi-stage treatment, the wastewater after one cascade treatment enters the water storage tank 600. Then, for persistent organic substances that have not been removed, a predetermined proportion of the wastewater is circulated back to the water supply line 800 using a circulation pump 700, where it is mixed with the feedwater and then subjected to cascade circulation treatment again. Alternatively, the wastewater enters the next stage of cascade treatment equipment and is treated there, and by performing multi-stage cascade treatment, the persistent organic substances in the wastewater are further reduced.

In some cases, a single cascade recycle treatment can achieve a COD removal rate of 55-70% for persistent organic substances, while a double cascade recycle treatment or a two-stage cascade treatment can achieve a COD removal rate of 70-80%. The proportion of recycled water and the number of cascade recycles or treatment stages are determined based on the requirements for removing persistent organic substances. Different COD removal rates and wastewater COD concentrations can be achieved by adjusting the implementation method of multiple recycles or multi-stage treatments, or a combination thereof.

An embodiment of the present disclosure further provides a wastewater treatment process using an advanced treatment system for ultra-low discharge of refractory industrial wastewater. The wastewater treatment process includes transporting ozone generated in an ozone generator (100) to a microbubble generator (200) to generate ozone microbubbles. The wastewater treatment process includes mixing the ozone microbubbles with wastewater in the microbubble generator (200) and then entering the ozone microbubble oxidation reaction zone (303) at the bottom of an ozone catalytic oxidation reactor (300). The wastewater treatment process includes carrying out ozone microbubble oxidation and heterogeneous catalytic ozone oxidation reactions in the ozone catalytic oxidation reactor (300) with the ozone microbubbles, wastewater, and catalyst bed layer (301). The wastewater treatment process also includes separating the treated wastewater from the top of the ozone catalytic oxidation reactor (300) and entering an air-water separator (401), which separates the discharged air-water mixture after the ozone microbubble catalytic oxidation treatment in the ozone catalytic oxidation reactor (300). The wastewater treatment process includes a step in which the separated wastewater enters the aeration and deoxidation tank 400. The wastewater treatment process involves removing excess dissolved oxygen and remaining dissolved ozone through aeration, and the deoxidized wastewater overflows from the top of the aeration and deoxidation tank 400 and enters the aerobic biofilm reactor 500 from the bottom. As it flows upward, it comes into contact with the biofilm on the surface of the biofiller in the aerobic biofilm reactor 500, where the aerobic decomposition action of the biofilm removes (decomposes) a further layer of easily decomposable small-molecule organic matter. The wastewater overflowing from the top of the biochemical reactor (aerobic biofilm reactor 500) enters the water storage tank 600.

Wastewater to be treated

Related experiments have demonstrated that the treatment system and method described herein are particularly suitable for treating high-salt, refractory chemical synthesis wastewater or chemical decomposition wastewater containing large amounts of nitrogen-containing heterocyclic organic compounds or complex benzene ring organic compounds. In the case of chemical decomposition wastewater, for example, coal-based chemical wastewater, which contains large amounts of nitrogen-containing heterocyclic organic compounds, conventional catalytic ozone oxidation and aerobic biochemical treatment achieve an overall COD removal rate of less than 30% under the same conditions. However, using the treatment system and method described herein, the COD removal rate reaches more than 40% with microbubble catalytic ozone oxidation alone, reaching an overall COD removal rate of approximately 60% in a single treatment. Furthermore, in the case of chemical synthesis wastewater, for example, wastewater generated from the manufacture of p-phenylbenzonitrile-based products, conventional catalytic ozone oxidation and aerobic biochemical treatment achieve almost zero overall COD removal under the same conditions. However, using the treatment system and method of the present disclosure, the COD removal rate can reach 40-50% through microbubble catalyzed ozone oxidation alone, and the overall COD removal rate can reach approximately 65% in a single treatment.

A treatment method according to an embodiment of the present disclosure is an efficient, low-cost treatment method for ultra-low emissions of persistent organic pollutants using microbubble (catalytic) ozone oxidation and biochemical cascade circulation or multi-stage treatment. This treatment method utilizes microbubble technology in microbubble (catalytic) ozone oxidation and biochemical cascade treatment to enhance ozone mass transfer and increase ozone utilization. By utilizing the microbubble effect to improve oxidation capacity, the decomposition efficiency of persistent pollutants and the production efficiency of easily degradable small-molecule organic substances are improved, resulting in significant improvements in biodegradability. Furthermore, by removing excess dissolved oxygen and remaining dissolved ozone generated after the ozone reaction through deoxidation, this prevents adverse effects on subsequent biochemical treatment and provides an optimal supply of dissolved oxygen for subsequent aerobic biochemical treatment. Furthermore, by removing easily degradable small-molecule organic substances generated through aerobic biochemical treatment, operational costs are reduced. Furthermore, by limiting the recirculation ratio to a predetermined value and performing cascade circulation or multi-stage treatment, persistent organic substances can be sustainably reduced. By adjusting the implementation method of multiple circulation or multi-stage treatment or a combination thereof, different COD removal rates and wastewater COD concentrations can be limited, and ultimately the removal requirements of persistent organic substances and the goal of ultra-low discharge can be achieved.

Example 1
As shown in FIG. 1 , this embodiment provides an advanced treatment system for ultra-low discharge of refractory industrial wastewater. The treatment system includes a serially connected ozone generator 100, a microbubble generator 200, an ozone catalytic oxidation reactor 300, an air-water separator 401, an aeration deoxidation tank 400, and an aerobic biofilm reactor 500. The ozone catalytic oxidation reactor 300 includes a catalyst bed layer 301 disposed above the middle of the reactor. The catalyst bed layer 301 divides the reactor 300 into an upper catalytic ozone oxidation reaction zone 302 and a lower ozone microbubble oxidation reaction zone 303. The catalyst in the catalyst bed layer 301 is a granular catalyst of 5 mm or larger (e.g., a coal-based granular activated carbon catalyst or a granular metal oxide catalyst). The aerobic biofilm reactor 500 includes a biofiller layer 501, which is a woven fiber suspension filler. The spacing between the knitted fiber suspension fillers is 2 to 10 cm.

The ozone generated in the ozone generator 100 is transported to the microbubble generator 200, where ozone microbubbles (average diameter less than 30 μm) are generated. In the microbubble generator 200, the ozone microbubbles mix with wastewater before entering the ozone microbubble oxidation reaction region 303 at the bottom of the ozone catalytic oxidation reactor 300. The ozone microbubbles, wastewater, and catalyst bed layer 301 undergo ozone microbubble oxidation and heterogeneous catalytic ozone oxidation reactions within the ozone catalytic oxidation reactor 300. The treated wastewater flows out the top of the ozone catalytic oxidation reactor 300 and enters the air-water separator 401, where it is separated into an air-water mixture that is discharged after undergoing the ozone microbubble catalytic oxidation treatment in the ozone catalytic oxidation reactor 300. The separated wastewater enters the aeration and deoxidation tank 400. Excess dissolved oxygen and remaining dissolved ozone are removed by aeration, and the deoxidized wastewater overflows from the top of the aeration and deoxidation tank 400 and enters the aerobic biofilm reactor 500 from the bottom. As the wastewater flows upward, it comes into contact with the biofilm on the surface of the biofiller in the aerobic biofilm reactor 500, and the aerobic decomposition action of the biofilm removes even more easily decomposable small-molecule organic matter. The wastewater overflowing from the top of the biochemical reactor (aerobic biofilm reactor 500) enters the water storage tank 600.

A pharmaceutical company's wastewater, with a COD concentration of approximately 400 mg/L from conventional biochemical treatment, was treated using the advanced treatment system and process for ultra-low discharge of persistent industrial wastewater described in Example 1. Ozone microbubble catalytic oxidation was performed using a 5-8 mm diameter coal-based cylindrical granular activated carbon catalyst bed. After treatment, the COD removal rate reached 130 mg/L, with a removal rate of 32.4%. After air deoxidation of the ozone catalytically oxidized wastewater, the dissolved oxygen concentration was limited to approximately 8 mg/L. The wastewater then flowed into an aerobic biochemical reactor (aerobic biofilm reactor 500). The aerobic biochemical reactor was a non-aerated fiber-woven suspension fixed-filler biofilm reactor. After aerobic biochemical treatment, the COD removal rate reached 120 mg/L, with a removal rate of 44.6%. Finally, the COD concentration of the wastewater was stable at about 150 mg/L, and the overall COD removal amount of the cascade treatment reached 250 mg/L (about 62.5%).

Example 2
A conventional biochemical treatment wastewater with a COD concentration of approximately 200 mg/L from a coal-fired chemical company was subjected to advanced treatment using the advanced treatment system for ultra-low discharge of refractory industrial wastewater described in Example 1. In one cascade treatment, a 5-8 mm diameter coal-based cylindrical granular activated carbon catalyst bed was used for ozone microbubble catalytic oxidation. When the ratio of ozone input to COD content of the feed wastewater was limited to 0.4 mg _O3 /mg COD, the COD removal rate of the treated wastewater reached 35.0%. After air deoxidation, the ozone catalytically oxidized wastewater was limited to a dissolved oxygen concentration of 8 mg/L and then flowed into an aerobic biochemical reactor. The aerobic biochemical reactor was a non-aerated suspension chain fiber filler biofilm reactor. After aerobic biochemical treatment, the COD removal rate reached 30.1%. A second circulating cascade treatment was then performed. The ratio of recycled wastewater to untreated water was 1:1, and the ratio of ozone input to COD content of the feed wastewater during the ozone microbubble catalytic oxidation treatment was limited to 0.3 _mgO3 /mgCOD. The COD removal rate of the treated wastewater reached 21.2%. After air deoxidation, the dissolved oxygen concentration of the ozone catalytic oxidation wastewater was limited to 5 mg/L. After aerobic biochemical treatment, the COD removal rate reached 18.6%. After two cascade circulation processes, the final COD concentration of the wastewater was reduced to 40 mg/L, and the overall COD removal rate was close to 80%, meeting the COD requirements for ultra-low wastewater discharge.

Example 3
The COD concentration of conventional biochemical wastewater from a pharmaceutical intermediate manufacturing company was approximately 1030 mg/L, and the wastewater contained a large amount of complex benzene ring organic compounds.

Advanced treatment was performed using the advanced treatment system for ultra-low discharge of persistent industrial wastewater in Example 1. Ozone microbubble catalytic oxidation used a 5-8 mm diameter coal-based cylindrical granular activated carbon catalyst bed. After treatment, the COD removal rate reached 460 mg/L, with a removal rate of 44.7%. After air deoxidation, the ozone catalytically oxidized wastewater was limited to a dissolved oxygen concentration of approximately 6-7 mg/L and then flowed into an aerobic biochemical reactor. The aerobic biochemical reactor was a non-aerated fiber-woven suspension fixed-filler biofilm reactor. After aerobic biochemical treatment, the COD removal rate reached 220 mg/L, with a removal rate of 38.6%. Finally, the wastewater COD concentration stabilized at approximately 350 mg/L, and the overall COD removal rate of the cascade process reached 66.0%.

Comparative Example 1
As shown in Figure 2, a wastewater treatment system was provided in this comparative example, and the only difference from Example 1 was that it did not include the aeration deoxidation tank 400 and the water-air separator 401. The wastewater treatment process was the same as Example 1, except that it was not subjected to deoxidation treatment by the water-air separator 401 and the aeration deoxidation tank 400. In Figure 2, the arrows indicate the flow direction of the wastewater.

A pharmaceutical company's conventional biochemically treated wastewater (same as in Example 1) with a COD concentration of approximately 400 mg/L was treated using the wastewater treatment system of Comparative Example 1. Ozone microbubble catalytic oxidation was performed using a 5-8 mm diameter coal-based cylindrical granular activated carbon catalyst bed. After treatment, the COD removal rate reached 124 mg/L, with a removal rate of 31.0%. The ozone catalytically oxidized wastewater did not undergo deoxygenation treatment and had a dissolved oxygen concentration of approximately 28 mg/L. It flowed directly into the aerobic biochemical reactor, which was a non-aerated fiber-woven suspension fixed-filler biofilm reactor. After aerobic biochemical treatment, the COD removal rate gradually decreased to 93 mg/L, with a removal rate of 33.7%. The final COD concentration of the wastewater stabilized at approximately 183 mg/L. The overall COD removal rate of the cascade process reached 217 mg/L (approximately 54.3%). In the aerobic biochemical reactor, biofilm shedding was evident due to the hyperoxidative conditions.

Example 4
In this example, a wastewater treatment system was provided, and the only difference from Example 1 was that the aerobic biochemical reactor was a ceramsite bed biofilm reactor rather than a woven fiber suspension filler biofilm reactor. Example 4 had a similar effective biomass to the aerobic biofilm reactor 500 of Example 1, at approximately 6-7 g/L (calculated by measuring the suspended solids (SS) in the wash solution after washing away the biofilm from a given filler).

A pharmaceutical company's conventional biochemically treated wastewater (same as in Example 1) with a COD concentration of approximately 400 mg/L was treated using the wastewater treatment system of Example 4. Ozone microbubble catalytic oxidation was performed using a 5-8 mm diameter coal-based cylindrical granular activated carbon catalyst bed. After treatment, the COD removal rate was approximately 133 mg/L, with a removal rate of 33.2%. The ozone catalytically oxidized wastewater was subjected to air deoxidation, with the dissolved oxygen concentration limited to approximately 8 mg/L, before flowing into an aerobic biochemical reactor. The aerobic biochemical reactor was a non-aerated ceramsite bed biofilm reactor. After aerobic biochemical treatment, the COD removal rate reached 95 mg/L, with a removal rate of 35.6%. The final effluent COD concentration stabilized at approximately 172 mg/L, and the overall COD removal rate of the cascade process reached 228 mg/L (approximately 57%).

Comparative Example 2
As shown in Figure 2, a wastewater treatment system was provided in this comparative example. The difference from Example 1 was that the aeration deoxidation tank 400 and the air-water separator 401 were not included, and the microbubble generator 200 was replaced with a normal bubble generator (the average diameter of the bubbles was more than 1000 μm).

In conventional biochemical treatment wastewater (same as in Example 3) from a pharmaceutical intermediate manufacturer, the COD concentration was approximately 1030 mg/L, and the wastewater contained a large amount of complex benzene ring organic compounds. When the wastewater was treated using the wastewater treatment system and process of Comparative Example 2, the COD removal efficiency was less than 10%.

This example fully utilizes the strong oxidation capabilities and high reaction efficiency of microbubble (catalytic) ozone oxidation, as well as low-cost aerobic biochemical treatment. In this example, when used for advanced treatment of persistent industrial wastewater, the ozone utilization rate reached over 90%. A single cascade treatment achieved a COD removal rate of 55-70% for persistent organic substances. Two cascade circulation treatments or two-stage cascade treatments achieved a COD removal rate of 70-80% for persistent organic substances. In Example 2, the COD concentration of the wastewater after treatment was reduced to below 50 mg/L. This meets stricter emission standards.

The entire contents of Chinese Patent Application No. 202210080512.8 (filing date: January 24, 2022) are incorporated herein by reference.

Although the present disclosure has been described in detail above through a general description and specific embodiments, modifications or improvements that are obvious to those skilled in the art can be made within the scope of the present disclosure. Therefore, any modifications or improvements made without departing from the spirit of the present disclosure are included in the scope of protection of the present disclosure.

100 Ozone generator 200 Microbubble generator 300 Ozone catalytic oxidation reactor 301 Catalyst bed layer 302 Catalytic ozone oxidation reaction zone 303 Ozone microbubble oxidation reaction zone 400 Aeration deoxidation tank 401 Air-water separator 500 Aerobic biofilm reactor 501 Biofiller layer 502 Submerged agitator 600 Water tank

Claims (10)

The system includes an ozone generator, a microbubble generator, an ozone catalytic oxidation reactor, an aeration deoxidation tank, and an aerobic biofilm reactor, which are connected in series;
In the aeration deoxidation tank, a part of dissolved oxygen and residual dissolved ozone are removed from the wastewater discharged after undergoing the ozone microbubble catalytic oxidation treatment in the ozone catalytic oxidation reactor ,
The deoxidized wastewater from which a portion of the dissolved oxygen and the remaining dissolved ozone have been removed in the aeration deoxidation tank enters the aerobic biofilm reactor,
The aerobic biofilm reactor of the industrial wastewater treatment system includes a submerged agitator that promotes contact between the deoxygenated wastewater and a biofilm . The ozone catalytic oxidation reactor includes a catalyst bed layer, and the ozone catalytic oxidation reactor is divided into a catalytic ozone oxidation reaction zone including the catalyst bed layer and an ozone microbubble oxidation reaction zone below the catalyst bed layer,
2. The industrial wastewater treatment system according to claim 1, wherein the catalyst in the catalyst bed layer is a granular catalyst of 5 mm or more, and the catalyst is a coal-based granular activated carbon catalyst or a granular metal oxide catalyst. The industrial wastewater treatment system of claim 1 or 2 further includes an air-water separator provided between the ozone catalytic oxidation reactor and the aeration deoxidation tank, wherein the air-water separator separates the air-water mixture discharged after undergoing ozone microbubble catalytic oxidation treatment in the ozone catalytic oxidation reactor, and the separated wastewater enters the aeration deoxidation tank. The industrial wastewater treatment system of claim 1 or 2, wherein the aerobic biofilm reactor includes a biofiller layer, the biofiller layer includes a plurality of biofillers, each of the plurality of biofillers being a fibrous suspension filler, and the spacing between the fibrous suspension fillers is 2 to 10 cm. The industrial wastewater treatment system according to claim 1 or 2, wherein the submersible agitator is provided at the bottom of the aerobic biofilm reactor. the ozone catalytic oxidation reactor, the microbubble generator, the ozone catalytic oxidation reactor, the air-water separator, the aeration deoxygenation tank, the aerobic biofilm reactor, and the water storage tank are connected in series, the ozone catalytic oxidation reactor includes a catalyst bed layer, the ozone catalytic oxidation reactor is divided into a catalytic ozone oxidation reaction zone including the catalyst bed layer and an ozone microbubble oxidation reaction zone below the catalyst bed layer, the catalyst in the catalyst bed layer is a granular catalyst of 5 mm or more, the aerobic biofilm reactor includes a biofiller layer, the biofiller layer includes a plurality of biofillers, each of the plurality of biofillers is a fiber suspension filler, and the spacing between the fiber suspension fillers is 2 to 10 cm;
The ozone generated in the ozone generator is transported to the microbubble generator to generate ozone microbubbles. In the microbubble generator, the ozone microbubbles are mixed with wastewater and then enter the ozone microbubble oxidation reaction region of the ozone catalytic oxidation reactor. The ozone microbubbles, the wastewater, and the catalyst bed layer undergo a heterogeneous catalytic ozone oxidation reaction with the ozone microbubbles in the ozone catalytic oxidation reactor. The treated wastewater flows out from the top of the ozone catalytic oxidation reactor and enters the air-water separator. 3. The industrial wastewater treatment system according to claim 1 or 2, wherein the air-water mixture discharged after the catalytic oxidation treatment is separated, the separated wastewater enters the aeration deoxidation tank, a portion of the dissolved oxygen and remaining dissolved ozone are removed by aeration, the deoxidized wastewater overflows from the top of the aeration deoxidation tank and enters the aerobic biofilm reactor from the bottom, and as it flows upward, it comes into contact with the biofilm on the surface of the biofiller in the aerobic biofilm reactor, and organic matter is decomposed by the aerobic decomposition action of the biofilm, and the wastewater overflowing from the top of the aerobic biofilm reactor enters the water tank. Use of the industrial wastewater treatment system described in claim 1 or 2 in treating wastewater. 1) performing ozone microbubble catalytic oxidation treatment on the wastewater to be treated;
2) subjecting the wastewater treated in step 1) to a deoxidation treatment to limit the dissolved oxygen in the wastewater to 2-8 mg/L;
3) performing aerobic biochemical treatment by promoting contact between the wastewater treated in step 2) and the biofilm using a submerged agitator , and discharging the treated wastewater;
A method for treating industrial wastewater, comprising: 9. The method for treating industrial wastewater according to claim 8, wherein at least one condition selected from the group consisting of the following conditions A, B, C, and D is satisfied.
Condition A: In the ozone microbubble catalytic oxidation treatment in step 1), the volume ratio of gas to water is 1:5 to 1:10, and the outlet pressure of the microbubble generator that generates the ozone microbubbles is 0.3 MPa or more.
Condition B: In the ozone microbubble catalytic oxidation treatment in step 1), the average diameter of the ozone microbubbles is 30 μm or less.
Condition C: In the ozone microbubble catalytic oxidation treatment in step 1), the ratio of the amount of ozone input to the amount of COD in the supplied wastewater is 0.2 to 1.0 mgO ₃ /mgCOD.
Condition D: The wastewater to be treated is a salt-containing chemical synthesis wastewater or chemical decomposition wastewater containing nitrogen-containing heterocyclic organic compounds or benzene ring organic compounds. A wastewater treatment process using the industrial wastewater treatment system according to claim 1 or 2,
The treatment system includes the ozone generator, the microbubble generator, the ozone catalytic oxidation reactor, the air-water separator, the aeration deoxidation tank, the aerobic biofilm reactor, and a water tank, which are connected in series;
The ozone catalytic oxidation reactor includes a catalyst bed layer, and the ozone catalytic oxidation reactor is divided into a catalytic ozone oxidation reaction zone including the catalyst bed layer and an ozone microbubble oxidation reaction zone below the catalyst bed layer,
The wastewater treatment process comprises:
transporting the ozone generated in the ozone generator to the microbubble generator to generate ozone microbubbles;
The ozone microbubbles are mixed with wastewater in the microbubble generator before entering the ozone microbubble oxidation reaction zone of the ozone catalytic oxidation reactor;
The ozone microbubbles, the wastewater, and the catalyst bed layer undergo ozone microbubble oxidation and heterogeneous catalytic ozone oxidation reactions in the ozone catalytic oxidation reactor;
The treated wastewater flows out from the top of the ozone catalytic oxidation reactor and enters the water-air separator, and separates the water-air mixture that is discharged after passing through the ozone microbubble catalytic oxidation treatment in the ozone catalytic oxidation reactor;
The separated wastewater enters the aeration and deoxidation tank;
aeration to remove a portion of the dissolved oxygen and remaining dissolved ozone, the deoxidized wastewater overflowing from the top of the aeration and deoxidation tank, entering the aerobic biofilm reactor from the bottom, and while flowing upward, coming into contact with the biofilm on the surface of the biofiller in the aerobic biofilm reactor, where the aerobic decomposition action of the biofilm decomposes organic matter, and the wastewater overflowing from the top of the aerobic biofilm reactor enters the water tank;
wastewater treatment processes, including