A method for treating low-concentration chromium-containing leather wastewater

Abstract

A kind of low concentration chromium-containing leather wastewater treatment method, comprising the following steps: step one, after adjusting leather wastewater, send into membrane separator and obtain concentrated solution and waste liquid;Step two, send waste liquid into resin adsorption tank, and carry out adsorption recovery to chromium ion;Step three, send concentrated solution into hydrolysis fermentation tank and carry out hydrolysis fermentation;Then send into anaerobic tower and carry out further decomposition;Step four, send concentrated solution of step three into multi-medium filter and treat, the supernatant obtained is sent into resin adsorption tank;The waste of backwashing multi-medium filter is transported to adjusting tank and is treated again;Step five, the wastewater treated after resin adsorption tank is treated biochemically;Step six, resin adsorption tank is treated by desorption, then the pH of desorption waste liquid is adjusted, so that chromium ion is precipitated to obtain chromium precipitation recovery;The present application not only recycles chromium ion in leather wastewater, but also can carry out reduction treatment to leather waste in leather wastewater, reduce the pollution to environment.

Description

Technical Field

[0001] This invention belongs to the field of leather wastewater treatment, specifically relating to a method for treating low-concentration chromium-containing leather wastewater. Background Technology

[0002] The leather industry is characterized by high raw material input and low product output, with only about 20-40% of raw hides being converted into leather. During leather processing, colored raw leather waste is generated, some of which ends up in wastewater. Factory wastewater is treated separately, into high-concentration chromium-containing wastewater and low-concentration chromium-containing wastewater. Sludge from high-concentration chromium-containing wastewater is directly treated as hazardous waste. However, with increasingly stringent water environment management requirements, sludge from low-concentration chromium-containing wastewater has also become a key focus. Sludge with chromium content exceeding the concentration specified in sludge standards is classified as hazardous waste, significantly increasing wastewater treatment costs.

[0003] The main component of waste generated during the deep processing of leather is protein. Although it will deform and its biological activity will decrease after treatment, it will still rot and deteriorate after a long period of fermentation, turning into harmful pollutants such as aldehydes, nitrogen, and sulfur. If it enters water bodies directly, it will cause serious pollution to the ecological environment. When using biodegradation of leather waste, the chromium content in the leather is continuously released, which is detrimental to biological treatment. Moreover, the chromium entering the sludge will become a potential source of chromium pollution as the sludge is transported and treated. Further improvements are needed. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for treating low-concentration chromium-containing wastewater.

[0005] The present invention adopts the following technical solution:

[0006] A method for treating low-concentration chromium-containing leather wastewater includes the following steps:

[0007] Step 1: Collect low-concentration chromium-containing leather wastewater and send it to an equalization tank to adjust the pH of the leather wastewater to 10-12. Then send it to a membrane separator for sedimentation and separation to obtain concentrated liquid and waste liquid containing leather waste.

[0008] Step 2: The waste liquid obtained in Step 1 is sent into a resin adsorption tank to adsorb and recover chromium ions in the waste liquid.

[0009] Step 3: The concentrated liquid obtained in Step 1 is sent to a hydrolysis fermentation tank, and the oxygen concentration in the hydrolysis fermentation tank is controlled to be below 0.1 mg / L. The concentrated liquid containing leather waste is hydrolyzed and fermented to hydrolyze the protein in the leather waste. When the concentration of the concentrated liquid is reduced to 7.5-8.5, the concentrated liquid is sent to an anaerobic tower to further decompose the substances produced during the hydrolysis fermentation process.

[0010] Step 4: The concentrated liquid after anaerobic treatment is sent to a multi-media filter for filtration. The supernatant obtained from filtration is sent to a resin adsorption tank to adsorb and recover chromium ions in the supernatant. The waste obtained from backwashing the multi-media filter is sent to an equalization tank for reprocessing.

[0011] Step 5: Adjust the pH of the wastewater treated by the resin adsorption tank to 7.5-8.5, then send it to the hydrolysis tank to degrade the compounds in the wastewater, then send it to the aerobic tank to remove organic matter from the wastewater, and then carry out sedimentation treatment to obtain wastewater that can be discharged.

[0012] Step 6: Desorb the resin adsorption tank after the adsorption treatment is completed and collect the desorption waste liquid. Then adjust the pH of the desorption waste liquid to 4-5 to precipitate the chromium ions in the desorption liquid to obtain chromium precipitate recovery.

[0013] Furthermore, the resin adsorption tank uses a mixed bed resin, which is prepared by mixing a sulfonic acid functional group gel-type ion exchange resin and an ammonium functional group strong base anion exchange resin in a mass ratio of 4-5:1.

[0014] Furthermore, the desorption solution used in the resin adsorption tank includes a hydrochloric acid solution with a concentration of 3-4% and a sodium hydroxide solution with a concentration of 4-5%.

[0015] Furthermore, in step three, the reaction time of the concentrate in the anaerobic tower is 5-10 days.

[0016] Furthermore, the reflux ratio of the anaerobic tower is 200-400%.

[0017] Furthermore, the anaerobic tower is an EGSB anaerobic tower or an IC anaerobic tower.

[0018] Furthermore, in step one, sodium hydroxide is used in the equalization tank to adjust the pH of the leather wastewater.

[0019] Furthermore, the membrane separator uses a ceramic membrane with a pore size of 150-250 micrometers and a concentration factor of 10-20 times.

[0020] Furthermore, the chromium concentration in the low-concentration chromium-containing leather wastewater is 10-60 mg / L.

[0021] As can be seen from the above description of the present invention, compared with the prior art, the beneficial effects of the present invention are as follows: This application, by defining a treatment method for low-concentration chromium-containing leather wastewater, not only recovers chromium ions from the leather wastewater but also reduces the volume of leather waste in the leather wastewater, thereby further recovering chromium ions from the leather waste and minimizing the potential pollution caused by the discharge of chromium metal; wherein, adjusting the concentration of the leather wastewater entering the membrane separator allows the concentrate entering the hydrolysis fermentation tank to be treated under strongly alkaline and anaerobic conditions, hydrolyzing the proteins in the leather waste and effectively reducing the volume of flocculent matter in the concentrate; combined with subsequent treatment in an anaerobic tower, the reduction of leather waste in the leather wastewater is achieved;

[0022] The wastewater treated by the resin adsorption tank is first pH adjusted, and then biochemically treated in conjunction with the hydrolysis tank and the aerobic tank to reduce the concentration of organic matter in the wastewater. The hydrolysis tank uses microorganisms to break down the structure of organic compounds, converting macromolecules into small molecules, thereby improving the biodegradability of the wastewater and facilitating the aerobic action of microorganisms in the aerobic tank, so as to effectively reduce the COD concentration of the wastewater and obtain wastewater that meets the discharge requirements. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the structure of the present invention;

[0024] In the diagram, 1-Equalization tank, 2-Membrane separator, 3-Leather waste treatment unit, 4-Resin adsorption tank, 5-Biochemical treatment unit, 6-Chromium recovery unit, 31-Hydrolysis fermentation tank, 32-Anaerobic tower, 33-Multi-media filter, 34-First conveying pipe, 35-Second conveying pipe, 51-Hydrolysis tank, 52-Aerobic tank, 53-Second sedimentation tank, 54-Transition tank, 61-First storage tank, 62-Second storage tank, 63-First sedimentation tank. Detailed Implementation

[0025] The present invention will be further described below through specific embodiments.

[0026] Reference Figure 1 As shown, a treatment device for low-concentration chromium-containing leather wastewater includes an equalization tank 1, a membrane separator 2, a leather waste treatment unit 3, a resin adsorption tank 4, a biochemical treatment unit 5, and a chromium recovery unit 6; specifically, the chromium concentration in the low-concentration chromium-containing leather wastewater is 10-60 mg / L.

[0027] The pH of the low-concentration chromium-containing leather wastewater entering the tank is adjusted by adding sodium hydroxide to adjust the pH of the chromium-containing leather wastewater to 10-12, providing an alkaline environment for the subsequent hydrolysis and fermentation of leather waste.

[0028] Membrane separator 2, connected to equalization tank 1, performs membrane concentration and sedimentation separation on the incoming low-concentration chromium-containing leather wastewater to obtain concentrated liquid and waste liquid containing leather waste. Specifically, membrane separator 2 uses a ceramic membrane with a pore size of 150-250 micrometers and a concentration factor of 10-20 times. Furthermore, membrane separator 2 is a commonly used device in the field of wastewater treatment, and its specific structure and working principle will not be described in detail here.

[0029] The resin adsorption tank 4, connected to the membrane separator 2, adsorbs and recovers chromium ions from the incoming wastewater. Specifically, the resin adsorption tank 4 uses a mixed-bed resin, which is made by mixing sulfonic acid functional group gel-type ion exchange resin and ammonium functional group strong base anion exchange resin in a mass ratio of 4-5:1. The sulfonic acid functional group gel-type ion exchange resin adsorbs and recovers trivalent chromium ions, while the ammonium functional group strong base anion exchange resin adsorbs and recovers hexavalent chromium ions. The resin adsorption tank 4 is a commonly used device in the field of wastewater treatment, and its specific structure and working principle will not be further elaborated here.

[0030] The leather waste treatment unit 3, connected to the membrane separator 2, receives concentrated liquid containing leather waste and performs volume reduction treatment on the leather waste. It includes a hydrolysis fermentation tank 31 connected to the membrane separator 2 for hydrolysis fermentation of the concentrated liquid containing leather waste; an anaerobic tower 32 connected to the hydrolysis fermentation tank 31 for further decomposition of the substances produced in the hydrolysis fermentation tank; a multi-media filter 33 connected to the anaerobic tower 32 for filtering the concentrated liquid exiting the anaerobic tower 32; a first conveying pipe 34 connected at one end to the multi-media filter 33 and at the other end to the resin adsorption tank 4; and a second conveying pipe 35 connected at one end to the multi-media filter 33 and at the other end to the equalization tank 1. Specifically... The oxygen concentration in the hydrolysis fermentation tank 31 is less than 0.1 mg / L. During the treatment of leather waste, the proteins in the leather waste are first hydrolyzed by microorganisms in the hydrolysis fermentation tank 31, effectively reducing the volume of flocculent matter in the concentrate. Then, the waste enters the anaerobic tower 32 to further decompose the substances produced in the hydrolysis fermentation tank 31, and then sends them to the multi-media filter 33 for filtration. The supernatant and waste obtained from the treatment are sent to the resin adsorption tank 4 through the first conveying pipe 34 to adsorb and recover chromium ions in the supernatant. The waste is sent to the equalization tank 1 through the second conveying pipe 35 for reprocessing. Furthermore, the anaerobic tower 32 is an EGSB anaerobic tower or an IC anaerobic tower.

[0031] The chromium recovery unit 6, connected to the resin adsorption tank 4, includes a desorption liquid storage tank for desorption treatment of the resin adsorption tank 4 and a first sedimentation tank 63 connected to the resin adsorption tank 4 for collecting and settling the desorption waste liquid. Specifically, the desorption liquid storage tank includes a first storage tank 61 for storing a 3-4% hydrochloric acid solution and a second storage tank 62 for storing a 4-5% sodium hydroxide solution. During resin desorption treatment, trivalent chromium ions in the resin adsorption tank 4 are desorbed by hydrochloric acid solution, and hexavalent chromium ions in the resin adsorption tank are desorbed by sodium hydroxide solution. The desorption waste liquid after desorption treatment is mixed in the first sedimentation tank 63, and then the pH of the desorption waste liquid is adjusted to 4-5 by sodium hydroxide or hydrochloric acid to precipitate the chromium ions in the desorption liquid to obtain chromium precipitate recovery.

[0032] The biochemical treatment unit 5, connected to the resin adsorption tank 4, performs biochemical treatment on the wastewater after resin adsorption to remove organic matter. It includes a hydrolysis tank 51, an aerobic tank 52, a second sedimentation tank 53, and a transition tank 54. The hydrolysis tank 51, connected to the resin adsorption tank 4, contains microorganisms that degrade compounds in the wastewater. The aerobic tank 52, connected to the hydrolysis tank 51, removes organic matter from the wastewater treated in the hydrolysis tank 51. The second sedimentation tank 53, connected to the aerobic tank 52, further settles the wastewater treated in the aerobic tank 52 to obtain dischargeable wastewater. The transition tank 54, located between the hydrolysis tank 51 and the resin adsorption tank 4, adjusts the pH of the wastewater entering the hydrolysis tank 51 to 7.5-8.5 to ensure the normal operation of the subsequent biochemical treatment.

[0033] The method for treating low-concentration chromium-containing leather wastewater based on the above-mentioned treatment device specifically includes the following steps:

[0034] Step 1: Collect low-concentration chromium-containing leather wastewater and send it to equalization tank 1 to adjust the pH of the leather wastewater to 10-12. Then send it to membrane separator 2 for sedimentation and separation to obtain concentrated liquid and waste liquid containing leather waste.

[0035] Step 2: The waste liquid obtained in Step 1 is sent into the resin adsorption tank 4 to adsorb and recover chromium ions in the waste liquid.

[0036] Step 3: The concentrated liquid obtained in Step 1 is sent to the hydrolysis fermentation tank 31, and the oxygen concentration in the hydrolysis fermentation tank 31 is controlled to be lower than 0.1 mg / L. The concentrated liquid containing leather waste is subjected to hydrolysis fermentation to hydrolyze the protein in the leather waste. When the concentration of the concentrated liquid is reduced to 7.5-8.5, the concentrated liquid is sent to the anaerobic tower 32 for further decomposition of the substances produced during the hydrolysis fermentation process.

[0037] Step 4: The concentrated liquid after treatment by anaerobic tower 32 is sent to multi-media filter 33 for filtration. The supernatant obtained by filtration is sent to resin adsorption tank 4 to adsorb and recover chromium ions in the supernatant. The waste obtained by backwashing multi-media filter 33 is sent to equalization tank 1 for reprocessing.

[0038] Step 5: Adjust the pH of the wastewater treated by the resin adsorption tank 4 to 7.5-8.5, and then send it to the hydrolysis tank 51 to degrade the compounds in the wastewater. Then send it to the aerobic tank 52 to remove organic matter from the wastewater, and then carry out sedimentation treatment to obtain wastewater that can be discharged.

[0039] Step 6: Desorb the resin adsorption tank 4 after the adsorption treatment is completed and collect the desorption waste liquid. Then adjust the pH of the desorption waste liquid to 4-5 to precipitate the chromium ions in the desorption liquid to obtain chromium precipitate recovery.

[0040] This application describes a treatment device and method for treating low-concentration chromium-containing leather wastewater. This method not only recovers chromium ions from the wastewater but also reduces the volume of leather waste within it. This one-step recovery of chromium ions from the wastewater minimizes potential pollution from chromium discharge. Specifically, the concentration of the leather wastewater entering the membrane separator 2 is adjusted so that the concentrate entering the hydrolysis fermentation tank 31 is treated under strongly alkaline and anaerobic conditions. This hydrolyzes the proteins in the leather waste, effectively reducing the volume of flocculent matter in the concentrate. Combined with subsequent treatment in the anaerobic tower 32, this achieves the reduction of leather waste in the wastewater.

[0041] Specifically, the structure of the biochemical treatment unit 5 is defined. The wastewater treated by the resin adsorption tank 4 is first pH adjusted, and then biochemically treated in conjunction with the hydrolysis tank 51 and the aerobic tank 52 to remove organic matter from the wastewater. The hydrolysis tank 51 uses microorganisms to break down the structure of organic compounds, converting macromolecules into small molecules, thereby improving the biodegradability of the wastewater and facilitating the aerobic action of microorganisms in the aerobic tank 52, so as to effectively reduce the COD concentration of the wastewater and obtain wastewater that meets the discharge requirements.

[0042] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent application and the contents of the specification of the present invention should still fall within the scope of the patent of the present invention.

Claims

1. A method for treating low concentration chromium-containing leather wastewater, characterized by: The method comprises the following steps: Step one, collect low concentration chromium-containing leather wastewater, send it into the adjusting tank to adjust the pH of the leather wastewater to 10-12, and then send it into the membrane separator for sedimentation separation to obtain concentrated liquid containing leather waste and waste liquid; Step two, send the waste liquid obtained in step one into the resin adsorption tank to adsorb and recover chromium ions in the waste liquid; Step three, send the concentrated liquid obtained in step one into the hydrolysis and fermentation tank, and control the oxygen concentration in the hydrolysis and fermentation tank to be lower than 0.1 mg / L, to hydrolyze and ferment the concentrated liquid containing leather waste to hydrolyze the protein in the leather waste; when the concentration of the concentrated liquid is reduced to 7.5-8.5, send the concentrated liquid into the anaerobic tower to further decompose the substances produced in the hydrolysis and fermentation process; Step four, send the concentrated liquid treated by the anaerobic tower into the multi-medium filter for filtration treatment, send the supernatant obtained by filtration into the resin adsorption tank to adsorb and recover chromium ions in the supernatant; send the waste obtained by backwashing the multi-medium filter to the adjusting tank for reprocessing; Step five, adjust the pH of the wastewater treated by the resin adsorption tank to 7.5-8.5, and then send it into the hydrolysis tank to degrade the compounds in the wastewater, and then send it into the aerobic tank to remove organic matter in the wastewater, and then perform sedimentation treatment to obtain dischargeable wastewater; Step six, perform desorption treatment on the resin adsorption tank after adsorption treatment and collect the desorption waste liquid, then adjust the pH of the desorption waste liquid to 4-5, and perform precipitation on the chromium ions in the desorption liquid to obtain chromium precipitation recovery; The chromium concentration in the low concentration chromium-containing leather wastewater is 10-60 mg / L.

2. A method for treating low concentration chromium-containing leather wastewater according to claim 1, characterized in that: The resin adsorption tank adopts mixed bed resin, and the mixed bed resin is prepared by mixing sulfonic acid functional group gel type ion exchange resin and ammonium functional group strong base type anion exchange resin at a mass ratio of 4-5:

1.

3. A method for treating low concentration chromium-containing leather wastewater according to claim 2, characterized in that: The desorption liquid used in the resin adsorption tank comprises 3-4% hydrochloric acid solution and 4-5% sodium hydroxide solution.

4. The method for treating low concentration chromium-containing leather wastewater according to claim 1, characterized in that: In step three, the reaction time of the concentrated liquid in the anaerobic tower is 5-10 days.

5. The method for treating low concentration chromium-containing leather wastewater according to claim 1, characterized in that: The reflux ratio of the anaerobic tower is 200-400%.

6. The method for treating low concentration chromium-containing leather wastewater according to claim 1, characterized in that: The anaerobic tower is an EGSB anaerobic tower or an IC anaerobic tower.

7. The method for treating low concentration chromium-containing leather wastewater according to claim 1, characterized in that: In step one, the adjusting tank adjusts the pH of the leather wastewater by using sodium hydroxide.

8. The method for treating low concentration chromium-containing leather wastewater according to claim 1, characterized in that: The membrane separator adopts ceramic membrane, and the pore size of the ceramic membrane is 150-250 microns, and the concentration multiple is 10-20 times.

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