CN114538615A - Advanced denitrification process and system for caprolactam production wastewater - Google Patents

Abstract

The invention provides a process and a system for deeply denitrifying caprolactam production wastewater, which mainly comprises the following process flows: the caprolactam production wastewater is pretreated by oil removal, steam stripping and the like, then mixed and uniformly mixed, hydrolyzed and acidified, and then sequentially enters a primary anoxic tank, a primary aerobic tank, a secondary anoxic tank and a secondary aerobic tank, a certain amount of organic carbon source is added into the secondary anoxic tank, a part of the effluent of the secondary aerobic tank flows back to the primary anoxic tank, and a part of the effluent enters a reclaimed water recycling treatment process after being precipitated. After the secondary A/O series process is combined with the addition of a carbon source for treatment, the TN of the outlet water can be reduced to below 15mg/L from 200-400mg/L of the inlet water. The method is suitable for upgrading and modifying the denitrification of the caprolactam production wastewater by taking an A/O biochemical treatment process as a core, and can realize the deep denitrification of the caprolactam wastewater on the premise of not increasing the retention time of biochemical treatment.

Description

A kind of deep denitrification process and system of caprolactam production wastewater

technical field

The invention relates to the technical field of sewage treatment, in particular to a deep denitrification process and system for caprolactam production wastewater.

Background technique

Caprolactam is an important organic chemical raw material. The polyamide obtained after polymerization can be processed into nylon fibers, engineering plastics and film materials, which are widely used in textile, electrical, mechanical and other fields. In 2019, the world's annual production capacity of caprolactam was 8.119 million tons, and my country accounted for more than 50%, reaching 4.19 million tons. The production process of caprolactam can be divided into toluene method, phenol method and benzene method according to the raw materials used, and the benzene method is dominant. According to the different production methods of cyclohexanone, benzene method can be divided into cyclohexane oxidation method and cyclohexene hydration method according to the different preparation methods of intermediate cyclohexanone. The cyclohexanone produced by the two methods is subjected to the hydroxylamine phosphate method (HPO) or the amidoximation method (HAO) to obtain cyclohexanone oxime, and finally, the cyclohexanone oxime is subjected to Beckmann rearrangement and refining to obtain the product caprolactam.

Wastewater containing cyclohexanone, cyclohexane, benzene, cyclohexanone oxime, ammonium sulfate and other pollutants will be generated during the production of caprolactam. Due to the high COD of the wastewater (up to 5000mg/L or more in some sections), high NH ₃ -N (up to 400mg/L or more), complex components and poor biodegradability (B/C<0.1 in some sections), its effective treatment It is one of the hot spots of chemical wastewater research. At present, the methods for the treatment of caprolactam production wastewater include biochemical method, electrochemical degradation method, chemical purification method, wet oxidation method, membrane separation method, etc. The current practical application of the treatment process is mainly based on the biochemical method of activated sludge and its deformation process, which has good applicability and economy. In order to enhance the biodegradability of caprolactam production wastewater, pretreatment methods such as iron-carbon micro-electrolysis, Fenton or Fenton-like are used. The treated effluent COD can be reduced to below 100mg/L, NH ₃ -N is less than 1mg/L, but TN generally exceeds 100mg/L.

Chinese invention patent CN201110119504.1 discloses a membrane treatment process for caprolactam wastewater, and CN201410286565.0 discloses a method and device for treating caprolactam wastewater using membrane technology. Although a better wastewater treatment effect can be obtained, the membrane technology The operation and maintenance costs are high, and it is not suitable for the direct treatment of large amounts of wastewater. Invention patent ZL201110232634.6 discloses a treatment method for caprolactam-containing wastewater and its treatment device. Through pre-aeration, coagulation sedimentation, anaerobic, aerobic, secondary coagulation sedimentation, ultrasonic disinfection and other treatments, the method embodiment Among them, the removal rate of NH ₃ -N is only 91.8%, and it is difficult to reduce TN to below 30 mg/L. Invention patent ZL201410811338.5 discloses a method for treating caprolactam wastewater by salting-out method. Part of the organic matter in the wastewater is precipitated by salting-out and flocculation, and then the reacted wastewater and precipitate are biochemically treated and incinerated respectively. This method The investment and operation costs are high, and it is difficult to implement for large amounts of wastewater. Invention patent CN201510868816.0 discloses a process and device for advanced treatment of caprolactam wastewater. The method treats biochemically treated wastewater through acid adjustment, Fenton-like oxidation, pH adjustment, and coagulation sedimentation, in order to further reduce COD, color, and color. and total phosphorus, the removal effect of TN is limited. Invention patent CN201610927362.4 discloses a method for treating caprolactam wastewater. After pretreatment of oximation plant wastewater and hydrogen peroxide purification wastewater, oil separation, pH adjustment, iron-carbon pre-oxidation, Fenton oxidation, precipitation, etc., it is combined with other processes in the plant area. Section wastewater, domestic sewage and device flushing water are mixed, and after air flotation and hydrolysis, they enter the A/O biochemical system for treatment. This method can increase the B/C of the influent biochemically treated wastewater to 0.4. In the embodiment, NH ₃ -N can be reduced to below 10 mg/L, but TN is still difficult to reduce to 30 mg/L. Patent CN201910865981.9 discloses a caprolactam wastewater treatment device and treatment method and application. The method combines ammonia oximation wastewater and hydrogen peroxide wastewater through acid conditioning tank, micro-electrolysis tower, intermediate water tank, Fenton oxidation tank, neutralization tank, flocculation tank After pretreatment in pond and sedimentation tank, it is mixed with process wastewater such as cyclohexanol wastewater, cyclohexanone wastewater, ammonium sulfate condensate wastewater, and domestic sewage treated by oil separation, and then passed through air flotation tank, UBF tank, anoxic tank, etc. Aerobic tank, sedimentation tank, pH adjustment tank, secondary Fenton oxidation tank, neutralization reaction tank, coagulation reaction tank, flocculation reaction tank, coagulation sedimentation tank, secondary aerobic reaction tank, MBR membrane biochemical system and clean water out of the pool. The process of this method is complicated. Although the effluent NH ₃ -N can be reduced to 2 mg/L, it is still difficult to reduce TN to a lower level. Patent CN202011136843.6 discloses a method for concentrating and recovering caprolactam wastewater, which mainly concentrates caprolactam in wastewater by a combination of three-stage filtration methods such as microfiltration, bag filtration, and reverse osmosis filtration, and is mainly used for the recovery of caprolactam in wastewater. Not suitable for process wastewater treatment.

To sum up, the existing caprolactam wastewater treatment technologies are mainly the pretreatment of high-concentration and difficult biochemical degradation section wastewater such as oximation and hydrogen peroxide, the concentration and recovery of caprolactam, and the advanced treatment after A/O for reuse. These technologies mainly solve the problem of effluent. The problem of high NH ₃ -N and COD cannot effectively reduce TN. In fact, after the primary A/O treatment, the TN in the wastewater mainly occurs in the form of nitrate nitrogen. Even if the NH ₃ -N in the effluent is reduced to 1 mg/L, the TN in the wastewater generally exceeds 100 mg/L. With the gradual implementation of the TN emission index, the control of TN in caprolactam wastewater has become a top priority, and the steady reduction of TN to below 30 mg/L has become the goal of wastewater treatment technology research.

SUMMARY OF THE INVENTION

In order to solve the deficiencies in the prior art, the present invention provides a process and system for deep denitrification of caprolactam production wastewater, which utilizes a secondary A/O series process and the addition of a carbon source for deep denitrification; at the same time, the technical scheme It is economical and feasible, and the operating cost is low. For the caprolactam sewage treatment facility that has been built using the AO process, it does not need to be completely demolished and rebuilt. It is only necessary to add relevant structures and pipelines to implement the process of this technical solution and achieve the effect of deep denitrification. , effectively control the cost of upgrading and transformation, the specific technical solutions are as follows:

The invention first provides a deep denitrification process for caprolactam production wastewater, which comprises the following steps:

Step 1: pretreatment of caprolactam production wastewater, mixing and mixing, and then hydrolysis and acidification;

Step 2: The acidified wastewater enters the first-level anoxic tank and the first-level aerobic tank in turn. The first-level aerobic tank is added with alkali to adjust the pH. A part of the effluent from the first-level aerobic tank is returned to the first-level anoxic tank, and a part enters the second-level anoxic tank. Grade anoxic pool;

Step 3: Add organic carbon source to the secondary anoxic tank, and the effluent enters the secondary aerobic tank;

Step 4: After sedimentation of the effluent from the secondary aerobic tank, the sludge is returned, and the supernatant is discharged.

In some specific embodiments of the present invention, the pretreatment method in step 1 includes one or more of oil separation treatment, stripping treatment or Fenton treatment;

The hydrolysis and acidification includes adjusting the pH to 8.5-9.0 by adding sulfuric acid, and then staying in the hydrolysis and acidification tank for 16-24 hours.

In some specific embodiments of the present invention, the residence time of the first-level anoxic tank in step 2 is 20-24h, and the dissolved oxygen is 0.1-0.3 mg/L; the residence time of the first-level aerobic tank is 36-72h, and the dissolved oxygen Oxygen is 3.5-4.5mg/L; sodium carbonate or caprolactam production process waste alkali can be used to add alkali to the first-level aerobic tank, and the pH can be adjusted to 7.5-8.5.

In some specific embodiments of the present invention, the reflux ratio in step 2 is 300%-400%.

In some specific embodiments of the present invention, the organic carbon source in step 3 is one or more of methanol, sodium acetate, sugar or biomass carbon source.

In some specific embodiments of the present invention, the organic carbon source in step 3 is methanol, and the dosage of methanol is 2.5-3 times of [NO ₃ ^- ].

In some specific embodiments of the present invention, the residence time of the secondary anoxic tank in step 3 is 15-20h, the dissolved oxygen is 0.1-0.3mg/L; the residence time of the secondary aerobic tank is 12-24h, the dissolved oxygen is 12-24h It is 3.5-4.5mg/L.

In some specific embodiments of the present invention, the return ratio of the sludge return in step 4 is 80%-100%.

In some specific embodiments of the present invention, the supernatant liquid described in step 4 can be further connected to the reclaimed water reuse treatment process after being discharged.

The present invention also provides a system utilizing the aforementioned deep denitrification process for caprolactam production wastewater, including a regulating tank, a hydrolysis acidification tank, a first-level anoxic tank, a first-level aerobic tank, and a second-level anoxic tank connected in sequence through pipes , a secondary aerobic tank and a sedimentation tank, the outlet end of the primary aerobic tank is connected with the inlet end of the primary anoxic tank through a pipeline, and the sedimentation tank is connected with the inlet end of the primary anoxic tank through a pipeline.

In some specific embodiments of the present invention, the secondary anoxic tank is provided with a carbon source dosing device.

In some specific embodiments of the present invention, the primary aerobic tank is provided with alkali dosing equipment.

The technical scheme of the present invention is semi-open, and non-biochemical reaction steps can be added to the process flow, and a physicochemical tank (such as a Fenton pond, a micro-electrolysis cell, etc.) can be placed in front, or a physicochemical pond (air flotation pond) can be placed after , oxidation tank, flocculation tank, etc.).

Compared with the existing caprolactam wastewater treatment technology, the method provided by the invention has the following beneficial effects:

1. High total nitrogen removal rate and high treatment efficiency

The traditional one-level A/O process is changed to a two-level A/O series process. At present, the mainstream one-level A/O process requires more than 96 hours of residence time, while the two-level A/O series process does not increase the total residence time, only the one-level A/O process. The residence time of the secondary aerobic tank is reduced to about 40h, and the total residence time of the secondary anoxic tank and the aerobic tank does not exceed 32h, that is, the secondary A/O series process does not increase the biochemical treatment time, which ensures the treatment efficiency, but combined with the secondary A/O process After the carbon source is added to the anoxic tank, the biochemical treatment effect of the system is remarkable, especially the TN removal rate can be greatly improved.

2. The cost of upgrading and transformation is low, and it is easy to transform the existing process

For the already built caprolactam wastewater treatment facility using the AO process, it is only necessary to add structures and pipelines in the primary aerobic tank, which can achieve the purpose of deep denitrification without completely tearing down and rebuilding the existing wastewater treatment facility, and the cost of upgrading is low. .

3. Operational economy, which is conducive to commercial operation

It avoids the physicochemical deep denitrification technology, only needs to add conventional carbon sources, and the operation is economical, which is conducive to commercial operation.

Description of drawings

In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

Fig. 1 is a schematic diagram of the deep denitrification process flow diagram of caprolactam production wastewater provided by the present invention;

Fig. 2 is a graph showing the changes in the content of TN, NO ₃ -N, NO ₂ -N and NH ₃ -N in a simulated two-stage A/O series process (without carbon source);

Fig. 3 is a graph showing the changes in the content of TN, NO ₃ -N, NO ₂ -N and NH ₃ -N in a simulated two-stage A/O series process (adding carbon source);

Fig. 4 is a graph showing the variation of TN in and out of the pilot-scale experiment of the secondary A/O series process (adding carbon source);

Fig. 5 is a graph showing the variation of NH ₃ -N in the influent and effluent of the pilot-scale experiment of the secondary A/O series process (adding carbon source);

Figure 6 is a data diagram of the treatment effect of the pilot-scale experiment of the secondary A/O series process (adding carbon source).

Detailed ways

The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention and should not be used to limit the present invention. protected range. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

The above technical solutions are elaborated and explained below, and other related technical details are explained and explained in detail:

A process for deep denitrification of caprolactam production wastewater comprises the following steps, which are executed in sequence according to a certain operation cycle:

The process before entering the biochemical treatment is mainly to pretreat the wastewater in some special sections to ensure that the wastewater entering the biochemical section has good biodegradability, mainly including oil-containing water oil separation treatment, cyclohexanone, oxime water stripping treatment, Fenton treatment of hydrogen peroxide wastewater, these are all conventional treatment methods. The treated wastewater is mixed and thoroughly mixed, so the pH of the solution is still high. The pH of the solution can be adjusted to 8.5-9.0 by adding sulfuric acid, and the effluent enters the conventional hydrolysis and acidification tank. About 16-24h, pH of effluent is 7.8-8.5, COD 1500-2500mg/L, NH ₃ -N<400mg/L, B/C>0.3.

The effluent from the hydrolysis and acidification tank enters the first-level anoxic tank, the first-level aerobic tank, the second-level anoxic tank, and the second-level aerobic tank. Among them, the residence time of the first-level anoxic tank is 20-24h, the residence time of the first-level aerobic tank is 36-72h, the residence time of the second-level anoxic tank is 15-20h, and the residence time of the second-level aerobic tank is 12-24h; Alkali is added to the primary aerobic tank to maintain a certain alkalinity. The alkali can be used as waste alkali from the caprolactam production process. The main component is sodium carbonate, and the pH should be 7.5-8.5; the dissolved oxygen in the primary and secondary anoxic tanks is 0.1-0.3 mg/L, the dissolved oxygen in the primary and secondary aerobic tanks is 3.5-4.5 mg/L; a part of the effluent from the primary aerobic tank is returned to the primary anoxic tank, and the reflux ratio of the mixed solution is 300%-400%; _A certain amount of organic carbon source is added to the oxygen tank to supplement carbon source for denitrification and denitrification. ^- ] 2.5-3 times); after the effluent of the secondary aerobic tank is precipitated, the sludge is returned, and the return ratio is 80%-100%, and the supernatant enters the reclaimed water reuse treatment process.

Through the deep denitrification process of the caprolactam production waste water and the caprolactam production waste water after the system treatment of the present invention, the TN of the effluent can be stably reduced to below 15mg/L, so that it can still satisfy no more than 30mg/L after being concentrated by RO.

The process flow chart is shown in Figure 1.

The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

Example 1: Intermittent Demonstration Experiment

The experiment is divided into two groups, A and B, which are carried out in 2L beakers respectively. The wastewater to be treated is the effluent of the aerobic tank of the first-level A/O treatment process of a caprolactam production enterprise. The COD is about 110mg/L, and the TN is about 90mg. /L. The sludge is the acclimated return sludge of the middle settling tank, and the sludge concentration is 3.78g/L. Group A was directly sealed with plastic wrap at the mouth of the beaker, and the mixture in the beaker was magnetically stirred to simulate denitrification in the secondary hypoxia tank; in group B, methanol (247 mg/L) was added, and then the beaker was sealed with plastic wrap, and the mixed solution in the beaker was added. By magnetic stirring, denitrification in a secondary anoxic tank was simulated. The changes of TN, NO ₃ -N, NO ₂ -N and NH ₃ -N of the two groups of mixed solutions were detected at the 12th, 18th and 24th hours respectively. The data of group A are shown in Figure 2, and the data of group B are shown in Figure 3.

The results showed that the TN of the mixed solution did not change significantly even after 24 hours in the group A without adding carbon source, indicating that only the two-stage A/O series process could not further reduce the TN of the effluent; After 24 h of methanol, TN decreased from 90.8 mg/L to 16.4 mg/L, indicating that the secondary A/O series combined with the carbon source addition process can significantly reduce effluent TN.

Example 3: Pilot test of secondary A/O series process (adding carbon source)

The pilot plant has a designed flow rate of 1m ³ /h, and consists of one hydrolysis and acidification tank, two anoxic tanks, two aerobic tanks, one sedimentation tank and corresponding equipment such as aeration, stirring, and online dissolved oxygen meter. The body is made of Q235A anti-corrosion material. Sludge backflow is controlled by time relay, and the fan enters aeration volume through frequency conversion control to control dissolved oxygen within a certain range. The dosing of carbon source and lye is realized by two diaphragm pumps with a flow rate of 0-25L/h. The pump head of the diaphragm pump for dosing methanol is made of PP material, and the suction pipe is made of stainless steel to prevent methanol corrosion. The inlet water and nitrification liquid return pipes are equipped with rotameters to adjust the inlet water flow.

The influent water comes from a homogenization tank for wastewater treatment in a caprolactam production enterprise. During the experiment, the pH of the influent water was 8.0-8.5, the COD was 1000-1600 mg/L, and the NH ₃ -N and TN were 130-220 mg/L and 150-260 mg/L, respectively. .

Adopt the deep denitrification process of caprolactam production wastewater according to the technical scheme of the present invention, carry out deep denitrification treatment to the above-mentioned influent, and the specific operations are as follows:

First, oil separation treatment, stripping treatment, and Fenton treatment of hydrogen peroxide wastewater are carried out on the influent water. The treated wastewater is mixed and thoroughly mixed, and the pH is adjusted to 8.5-9.0 by adding sulfuric acid. pH is 7.8-8.5, COD 1500-2500mg/L, _NH3 -N<400mg/L, B/C>0.3.

The effluent from the hydrolysis and acidification tank enters the first-level anoxic tank, the first-level aerobic tank, the second-level anoxic tank, and the second-level aerobic tank. Among them, the residence time of the first-level anoxic tank is 24h, the first-level aerobic tank is divided into three grids, the residence time is 72h, the residence time of the second-level anoxic tank is 15h, and the residence time of the second-level aerobic tank is 22.5h; Sodium carbonate is added to the aerobic tank, the pH is kept at about 8.0, and the fluctuation range is limited to 7.5-8.5; the dissolved oxygen in the first and second anoxic tanks is about 0.1 mg/L, and the dissolved oxygen in the first and second aerobic tanks is 4.0 mg About /L; the sludge concentration of the primary and secondary anoxic tanks and aerobic tanks are both 3.2-4.5g/L; a part of the effluent of the primary aerobic tank is returned to the primary anoxic tank, and the return ratio of the mixed solution is 300%; A certain amount of methanol (0.6-1g/L/h) is added to the secondary anoxic tank; after the effluent from the secondary aerobic tank is precipitated, the sludge is refluxed, and the reflux ratio is 100%, and the supernatant enters the reclaimed water for reuse Process flow.

Through the deep denitrification process of the caprolactam production waste water and the caprolactam production waste water after the system treatment of the present invention, the TN of the effluent can be stably reduced to below 15mg/L, so that it can still satisfy no more than 30mg/L after being concentrated by RO.

The inlet and outlet water TN and NH ₃ -N in the test process were monitored respectively, and the monitoring data were shown in Figure 4 (I stage methanol dosage was: 1kg/m ³ h; II stage methanol dosage was: 0.6kg/ m ³ ·h) and Figure 5.

The results show that when methanol is added at 0.6-1 g/L/h, the effluent TN can be stabilized at about 10 mg/L, and the effluent NH ₃ -N can be stabilized below 1 mg/L.

Example 4: Pilot test of secondary A/O series process (adding carbon source)

The pilot plant has a designed flow rate of 1m ³ /h, and consists of one hydrolysis and acidification tank, two anoxic tanks, two aerobic tanks, one sedimentation tank and corresponding equipment such as aeration, stirring, and online dissolved oxygen meter. The body is made of Q235A anti-corrosion material. Sludge backflow is controlled by time relay, and the fan enters aeration volume through frequency conversion control to control dissolved oxygen within a certain range. The dosing of carbon source and lye is realized by two diaphragm pumps with a flow rate of 0-25L/h. The pump head of the diaphragm pump for dosing methanol is made of PP material, and the suction pipe is made of stainless steel to prevent methanol corrosion. The inlet water and nitrification liquid return pipes are equipped with rotameters to adjust the inlet water flow.

The influent water comes from the existing homogenization tank for wastewater treatment in the factory area. During the experiment, the pH of the influent water was 8.0-8.5, and the COD, TN, and NH ₃ -N of the influent water were 1068 mg/L, 239 mg/L, and 212 mg/L, respectively.

Adopt the deep denitrification process of caprolactam production wastewater according to the technical scheme of the present invention, carry out deep denitrification treatment to the above-mentioned influent, and the specific operations are as follows:

First, oil separation treatment, stripping treatment, and Fenton treatment of hydrogen peroxide wastewater are carried out on the influent water. The treated wastewater is mixed and thoroughly mixed, and the pH is adjusted to 8.5-9.0 by adding sulfuric acid. pH is 7.8-8.5, COD 1500-2500mg/L, _NH3 -N<400mg/L, B/C>0.3.

The effluent from the hydrolysis and acidification tank enters the first-level anoxic tank, the first-level aerobic tank, the second-level anoxic tank, and the second-level aerobic tank. Among them, the residence time of the first-level anoxic tank is 24h, the first-level aerobic tank is divided into three grids, the residence time is 72h, the residence time of the second-level anoxic tank is 15h, and the residence time of the second-level aerobic tank is 22.5h; Sodium carbonate is added to the aerobic tank, the pH is kept at about 8.0, and the fluctuation range is limited to 7.5-8.5; the dissolved oxygen in the first and second anoxic tanks is about 0.1 mg/L, and the dissolved oxygen in the first and second aerobic tanks is 4.0 mg About /L; the sludge concentration of the primary and secondary anoxic tanks and aerobic tanks are both 3.2-4.5g/L; a part of the effluent of the primary aerobic tank is returned to the primary anoxic tank, and the return ratio of the mixed solution is 300%; A certain amount of methanol (0.4g/L/h) is added to the secondary anoxic tank; after the effluent from the secondary aerobic tank is precipitated, the sludge is refluxed, and the reflux ratio is 100%, and the supernatant enters the reclaimed water for reuse. process.

The effluent COD, TN, and NH ₃ -N were detected during the test, and the detection data are shown in Figure 6.

The results showed that when the influent COD, TN, and NH ₃ -N were 1068 mg/L, 239 mg/L and 212 mg/L, respectively, the secondary A/O in series combined with the addition of methanol (0.4 g/L/h), the effluent COD , TN and NH ₃ -N were 85 mg/L, 9.1 mg/L and 0.3 mg/L, respectively.

Embodiment 5: Application test of deep denitrification process of caprolactam production wastewater

Existing caprolactam production enterprises, the current wastewater treatment process with primary A/O as the core, the waste water volume per hour is about 600m ³ , the residence time of the primary anoxic tank and the aerobic tank are 24h and 72h respectively, and the effluent COD of the aerobic tank 100-150mg/L, NH ₃ -N<1mg/L, TN 90-150mg/L, due to the need for reuse of reclaimed water, there are new requirements for TN discharge standards, the goal is to reduce TN in aerobic pool effluent to 15mg/L Below L, and due to the limited space available in the factory area, it can only be retrofitted in the original treatment facility.

By adopting the technical scheme of the present invention, the existing first-level aerobic tank is transformed, the space of the original first-level aerobic tank is reserved for about 40h, and the remaining part is subjected to the second-level anoxic tank (retention time-16h) and the second-level aerobic tank (retention time-16h) Time-12h) transformation, while adding carbon source dosing equipment in the secondary anoxic pool.

Adopt the deep denitrification process of caprolactam production wastewater according to the technical scheme of the present invention, carry out deep denitrification treatment to the above-mentioned influent, and the specific operations are as follows:

First, oil separation treatment, stripping treatment, and Fenton treatment of hydrogen peroxide wastewater are carried out on the influent water. The treated wastewater is mixed and thoroughly mixed, and the pH is adjusted to 8.5-9.0 by adding sulfuric acid. pH is 7.8-8.5, COD 1500-2500mg/L, _NH3 -N<400mg/L, B/C>0.3.

The effluent from the hydrolysis and acidification tank enters the first-level anoxic tank, the first-level aerobic tank, the second-level anoxic tank, and the second-level aerobic tank. Among them, the residence time of the first-level anoxic tank is 24h, the first-level aerobic tank is divided into three grids, the residence time is 40h, the residence time of the second-level anoxic tank is 16h, and the residence time of the second-level aerobic tank is 12h; Sodium carbonate is added to the oxygen tank, the pH is kept at about 8.0, and the fluctuation range is limited to 7.5-8.5; the dissolved oxygen in the first and second anoxic tanks is about 0.1 mg/L, and the dissolved oxygen in the first and second aerobic tanks is 4.0 mg/L. About L; the sludge concentration of the primary and secondary anoxic tanks and aerobic tanks are both 3.2-4.5g/L; part of the effluent of the primary aerobic tank is returned to the primary anoxic tank, and the return ratio of the mixed solution is 300%; A certain amount of methanol (0.4g/L/h) is added to the secondary anoxic tank; after the effluent from the secondary aerobic tank is precipitated, the sludge is refluxed, and the reflux ratio is 100%, and the supernatant enters the reclaimed water reuse treatment process .

Monitor the effluent TN and NH ₃ -N.

By adopting the deep denitrification process of caprolactam production wastewater of the present invention, in terms of pure methanol, the secondary anoxic tank is added at 0.4g/L/h, the TN of the effluent can be stabilized at about 10mg/L, and the cost per ton of water treatment can be realized. An increase of about 0.5-0.7 yuan.

The original one-stage A/O caprolactam wastewater treatment system is transformed by using the technical scheme of the invention, the scheme is simple and easy to implement, and the cost is low. Moreover, since caprolactam production enterprises generally use methanol as a material for the hydrogen peroxide refining process, low-quality circulating methanol can be used as a carbon source at the same time, which is cheap and easy to obtain, which can further reduce operating costs and effectively improve wastewater denitrification efficiency.

Embodiment 6: the experiment of applying the technical scheme of the present invention to the production wastewater of other chemical enterprises

Existing chemical enterprise wastewater, NH ₃ -N>300mg/L, COD 1500-3000mg/L, currently adopts A/O-based biochemical treatment process, but effluent TN exceeds 100mg/L.

By adopting the technical scheme of the present invention, the existing first-level aerobic tank is transformed, the space of the original first-level aerobic tank is reserved for about 40h, and the remaining part is subjected to the second-level anoxic tank (retention time-16h) and the second-level aerobic tank (retention time-16h) Time-12h) transformation, while adding carbon source dosing equipment in the secondary anoxic pool.

Adopt the deep denitrification process of caprolactam production wastewater according to the technical scheme of the present invention, carry out deep denitrification treatment to the above-mentioned influent, and the specific operations are as follows:

First, oil separation treatment, stripping treatment, and Fenton treatment of hydrogen peroxide wastewater are carried out on the influent water. The treated wastewater is mixed and thoroughly mixed, and the pH is adjusted to 8.5-9.0 by adding sulfuric acid. pH is 7.8-8.5, COD 1500-2500mg/L, _NH3 -N<400mg/L, B/C>0.3.

The effluent from the hydrolysis and acidification tank enters the first-level anoxic tank, the first-level aerobic tank, the second-level anoxic tank, and the second-level aerobic tank. Among them, the residence time of the first-level anoxic tank is 24h, the first-level aerobic tank is divided into three grids, the residence time is 40h, the residence time of the second-level anoxic tank is 16h, and the residence time of the second-level aerobic tank is 12h; Add sodium carbonate to the oxygen tank, and the pH should be 7.5-8.5; the dissolved oxygen in the first and second anoxic tanks is about 0.1 mg/L, and the dissolved oxygen in the first and second aerobic tanks is about 4.0 mg/L; The sludge concentration of the anoxic tank and the aerobic tank are both 3.2-4.5g/L; part of the effluent of the first-level aerobic tank is returned to the first-level anoxic tank, and the return ratio of the mixed solution is 300%; A certain amount of methanol (addition at 0.25-0.3g/L/h); after sedimentation of the effluent from the secondary aerobic tank, the sludge is refluxed with a reflux ratio of 100%, and the supernatant enters the reclaimed water reuse treatment process.

Monitor the effluent TN and NH ₃ -N.

By adopting the deep denitrification process of caprolactam production wastewater of the present invention, since the effluent is directly discharged into a tube and not reused, the effluent TN can be realized by adding 0.25-0.3 g/L/h to the secondary anoxic tank in terms of pure methanol. Stable at about 18mg/L, the cost of water treatment per ton increases by about 0.4-0.5 yuan.

Using the technical scheme of the present invention to transform the original wastewater treatment system of other chemical enterprises, the scheme is simple and easy to implement, and the cost is low.

The above-mentioned specific embodiments are only specific cases of the present invention, and the scope of patent protection of the present invention includes but is not limited to the product forms and styles of the above-mentioned specific embodiments. Appropriate changes or modifications made shall fall within the scope of patent protection of the present invention.

Claims (10)

1. a deep denitrification process for caprolactam production waste water, is characterized in that, comprises following operation: Step 1: pretreatment of caprolactam production wastewater, mixing and mixing, and then hydrolysis and acidification; Step 2: The acidified wastewater enters the first-level anoxic tank and the first-level aerobic tank in turn. The first-level aerobic tank is added with alkali to adjust the pH. A part of the effluent from the first-level aerobic tank is returned to the first-level anoxic tank, and a part enters the second-level anoxic tank. Grade anoxic pool; Step 3: Add organic carbon source to the secondary anoxic tank, and the effluent enters the secondary aerobic tank; Step 4: After sedimentation of the effluent from the secondary aerobic tank, the sludge is returned, and the supernatant is discharged. 2. the deep denitrification process of caprolactam production wastewater as claimed in claim 1, is characterized in that, The pretreatment method described in step 1 includes one or more of oil separation treatment, stripping treatment or Fenton treatment; The hydrolysis and acidification includes adjusting the pH to 8.5-9.0 by adding sulfuric acid, and then staying in the hydrolysis and acidification tank for 16-24 hours. 3. the deep denitrification process of caprolactam production wastewater as claimed in claim 1, is characterized in that, the residence time of the first-level anoxic tank described in step 2 is 20-24h, and dissolved oxygen is 0.1-0.3mg/L; The residence time of the first-level aerobic tank is 36-72h, and the dissolved oxygen is 3.5-4.5mg/L; the sodium carbonate or caprolactam production process waste alkali can be used to add alkali to the first-level aerobic tank, and the pH is adjusted to 7.5-8.5. 4. The deep denitrification process of caprolactam production wastewater according to claim 1, wherein the reflux ratio in step 2 is 300%-400%. 5. The deep denitrification process of caprolactam production wastewater according to claim 1, wherein the organic carbon source in step 3 is one or more of methanol, sodium acetate, sugar or biomass carbon source. 6 . The deep denitrification process for caprolactam production wastewater according to claim 1 , wherein the organic carbon source in step 3 is methanol, and the methanol dosage is 2.5-3 times of [NO ₃ ⁻ ]. 7 . 7. The deep denitrification process of caprolactam production wastewater as claimed in claim 1, wherein the residence time of the secondary anoxic tank in step 3 is 15-20h, and the dissolved oxygen is 0.1-0.3 mg/L; The residence time of the aerobic tank is 12-24h, and the dissolved oxygen is 3.5-4.5mg/L. 8. The deep denitrification process for caprolactam production wastewater according to any one of claims 1 to 7, wherein the reflux ratio of the sludge reflux in step 4 is 80%-100%. 9. a system that is applied to the deep denitrification process of caprolactam production wastewater described in any one of claims 1-8, is characterized in that: It includes a regulating tank, a hydrolysis and acidification tank, a first-level anoxic tank, a first-level aerobic tank, a second-level anoxic tank, a second-level aerobic tank and a sedimentation tank which are connected in sequence through pipelines. The outlet end of the first-level aerobic tank is connected to the The inlet end of the first-level anoxic tank is connected through a pipeline, and the sedimentation tank is connected with the inlet end of the first-level anoxic tank through a pipeline. 10. The system of claim 9, wherein a carbon source dosing device is provided in the secondary anoxic pool.

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