Chromium-containing wastewater treatment system and method

Abstract

The invention discloses a chromium-containing wastewater treatment system which comprises a concentrated chromium waste liquid treatment unit, a dilute chromium wastewater treatment unit and a recovery treatment unit, a concentrated chromium waste liquid outlet of the unit line is communicated with an inlet of the concentrated chromium waste liquid treatment unit, and a liquid outlet of the concentrated chromium waste liquid treatment unit is communicated with a liquid return port of the unit line; a dilute chromium wastewater outlet of the unit line is communicated with an inlet of the dilute chromium wastewater treatment unit, a concentrated water outlet of the dilute chromium wastewater treatment unit is communicated with an inlet of the concentrated chromium waste liquid treatment unit, and a produced water outlet of the dilute chromium wastewater treatment unit is communicated with an inlet of the recovery treatment unit; a concentrated water outlet of the recovery treatment unit is communicated with an inlet of the concentrated chromium waste liquid treatment unit, and a produced water outlet of the recovery treatment unit is communicated with an industrial water pipeline. The invention also discloses a chromium-containing wastewater treatment method. The system has the beneficial effects that the concentrated chromium waste liquid treatment unit, the dilute chromium waste water treatment unit and the recovery treatment unit are designed, concentrated chromium waste liquid and dilute chromium waste water are treated according to the quality, the treatment mode can reduce the dosage of chemicals, improve the utilization rate of the chemicals and reduce the treatment cost, and the system is green and economical.

Description

Technical Field

[0001] The invention relates to wastewater treatment technology, and in particular to a chromium-containing wastewater treatment system and method. Background Art

[0002] Cold rolling is an important part of the steel industry. The sodium sulfate electrolysis process in the cold-rolled stainless steel production process can dissolve the iron oxide scale generated on the surface of the steel plate, mainly removing the chromium oxide in the iron oxide scale. Therefore, the electrolyte has a high salt content and a large amount of Cr is dissolved in it. 6+ Hexavalent chromium compounds can cause great pollution to water bodies. Their toxicity is Cr 3+ 100 times that of Cr 6+ In addition, requirements have been put forward for total chromium emission limits, and many environmentally sensitive areas currently require that chromium-containing wastewater must achieve zero discharge.

[0003] Generally, cold rolling mills produce dilute chromium wastewater with a total chromium concentration of 13-50 mg / L and concentrated chromium wastewater with a total chromium concentration of 150-550 mg / L. Figure 1 As shown in the figure, the dilute chromium wastewater and concentrated chromium wastewater generated by the cold rolling mill are mixed and then enter the regulating tank. The water in the regulating tank enters the primary and secondary reduction tanks to add H 2 SO 4 and NaHSO 3 Cr 6+ Reduction to generate Cr 3+ Then it enters the primary and secondary neutralization tanks to add NaOH for neutralization, and then enters the flocculation sedimentation tank to convert the generated Cr(OH) 3 The chromium-containing wastewater is then removed by precipitation, and then the suspended solids and turbidity are further reduced by a multi-media filter. The salt content of the chromium-containing wastewater is then reduced by ultrafiltration and reverse osmosis, and the produced water is then reused. The salt content of the concentrated water from reverse osmosis is too high to be reused in the unit line or discharged externally. It needs to be further processed by an evaporation and crystallization process. When the COD (chemical oxygen demand) content in the wastewater is high, it will affect the quality of the evaporated crystallized salt. Therefore, the COD of the incoming water must be reduced first. First, the COD in the incoming water is initially reduced by ozone oxidation, and then it enters the aerated biological filter to further reduce the influent COD. Finally, the hardness removal resin removes Ca 2 + Mg 2+ The produced water is then evaporated and crystallized to obtain the impure salt Na 2 SO 4 , the miscellaneous salts are transported out for disposal.

[0004] However, the existing chromium-containing wastewater treatment process does not treat chromium-containing wastewater of different concentrations separately, resulting in large consumption of reagents and high wastewater treatment costs. Summary of the invention

[0005] The purpose of the present invention is to provide a chromium-containing wastewater treatment system and method to reduce the treatment cost in view of the shortcomings of the prior art.

[0006] The technical solution adopted by the present invention is: a chromium-containing wastewater treatment system, including a concentrated chromium waste liquid treatment unit, a dilute chromium wastewater treatment unit and a recovery treatment unit;

[0007] The concentrated chromium waste liquid outlet of the unit line is connected to the inlet of the concentrated chromium waste liquid treatment unit through the concentrated chromium waste liquid pipeline, and the liquid outlet of the concentrated chromium waste liquid treatment unit is connected to the liquid return port of the unit line;

[0008] The dilute chromium wastewater outlet of the unit line is connected to the inlet of the dilute chromium wastewater treatment unit through the dilute chromium wastewater pipeline, the concentrated water outlet of the dilute chromium wastewater treatment unit is connected to the inlet of the concentrated chromium waste liquid treatment unit, and the produced water outlet of the dilute chromium wastewater treatment unit is connected to the inlet of the recovery treatment unit;

[0009] The concentrated water outlet of the recovery and treatment unit is communicated with the inlet of the concentrated chromium waste liquid treatment unit, and the produced water outlet of the recovery and treatment unit is communicated with the industrial water pipeline.

[0010] According to the above scheme, the concentrated chromium waste liquid treatment unit includes a concentrated chromium waste liquid regulating tank, a reduction tank, a neutralization sedimentation tank, a sedimentation tank and a filter press; the inlet of the concentrated chromium waste liquid regulating tank is respectively connected to the concentrated water outlet of the dilute chromium waste water treatment unit, the concentrated water outlet generated by the recovery treatment unit and the concentrated chromium waste liquid pipeline, and the outlet of the concentrated chromium waste liquid regulating tank, the reduction tank, the neutralization sedimentation tank and the sedimentation tank are connected in sequence through pipelines; the sludge outlet of the sedimentation tank is connected to the inlet of the filter press.

[0011] According to the above scheme, the dilute chromium wastewater treatment unit includes a regulating tank, a sedimentation tank, a primary raw water tank and a primary electrochemical concentrator; the inlet of the regulating tank is connected to the dilute chromium wastewater pipeline, the outlet of the regulating tank, the inlet of the sedimentation tank, the liquid outlet of the sedimentation tank, the primary raw water tank and the primary electrochemical concentrator are connected in sequence through pipelines, the concentrated water outlet of the primary electrochemical concentrator is connected to the inlet of the concentrated chromium waste liquid treatment unit; the produced water outlet of the primary electrochemical concentrator is connected to the inlet of the recovery treatment unit.

[0012] According to the above scheme, the dilute chromium wastewater treatment unit also includes a secondary electrochemical concentrator, the inlet of the secondary electrochemical concentrator is connected to the water output outlet of the primary electrochemical concentrator, and the concentrated water outlet of the secondary electrochemical concentrator is connected to the primary raw water tank; the water output outlet of the secondary electrochemical concentrator is connected to the inlet of the recovery treatment unit.

[0013] According to the above scheme, the recovery and processing unit includes a secondary water production tank and a chromium removal resin connected by a pipeline, the water production outlet of the secondary electrochemical concentration device is connected to the inlet of the secondary water production tank, the outlet of the secondary water production tank is connected to the chromium removal resin, the water production outlet of the chromium removal resin is connected to the industrial water pipeline, and the concentrated water outlet of the chromium removal resin is connected to the inlet of the concentrated chromium waste liquid treatment unit.

[0014] According to the above scheme, the liquid outlet of the sedimentation tank is connected to the liquid return port of the unit line.

[0015] According to the above scheme, the liquid outlet of the filter press device is connected to the liquid return port of the unit line.

[0016] According to the above scheme, the dilute chromium wastewater treatment unit also includes a filter arranged between the sedimentation tank and the primary raw water tank, and the liquid outlet of the sedimentation tank, the filter and the primary raw water tank are connected in sequence through pipelines.

[0017] According to the above scheme, the dilute chromium wastewater treatment unit also includes a filter press, the inlet of the filter press is connected to the sludge outlet of the sedimentation tank, the liquid outlet of the filter press is connected to the filter, and the sludge outlet of the filter press is connected to the outside.

[0018] The present invention also provides a method for treating chromium-containing wastewater, which comprises: providing the chromium-containing wastewater treatment system as described above, sending the dilute chromium wastewater discharged from the unit line into the dilute chromium wastewater treatment unit of the chromium-containing wastewater treatment system, subjecting the dilute chromium wastewater to precipitation, filtration and desalination treatment, and producing produced water entering the recovery treatment unit for recycling treatment, and the concentrated water produced by desalination entering the concentrated chromium waste liquid treatment unit; the concentrated water produced by the recovery treatment unit entering the concentrated chromium waste liquid treatment unit; the concentrated chromium waste liquid discharged from the unit line entering the concentrated chromium waste liquid treatment unit of the chromium-containing wastewater treatment system, mixing with the concentrated water produced by the dilute chromium wastewater treatment unit, adding sulfuric acid for pre-conditioning, and adding NaHSO 3 Cr 6+ Reduction to Cr 3+ , after neutralization and precipitation, Cr(OH) 3 The sludge produced by precipitation is discharged and the supernatant is sent to the unit line for reuse.

[0019] The beneficial effects of the present invention are:

[0020] 1. The present invention designs a concentrated chromium waste liquid treatment unit, a dilute chromium waste water treatment unit and a recovery treatment unit. The dilute chromium waste water treatment unit pre-treats the dilute chromium waste water of the unit, and the concentrated water produced by the treatment enters the concentrated chromium waste liquid treatment unit together with the concentrated chromium waste liquid from the unit line for treatment. Compared with the prior art, the method of the present invention for treating the concentrated chromium waste liquid and the dilute chromium waste water separately can reduce the addition of reagents, improve the utilization rate of reagents, reduce the treatment cost, and be green and economical; the produced water of the dilute chromium waste water treatment unit enters the recovery treatment unit for treatment, and high-quality industrial water can be obtained for reuse. Compared with the prior art, the utilization rate of produced water is improved.

[0021] 2. The filtrate and supernatant (containing sodium sulfate) in the concentrated chromium wastewater treatment unit and the dilute chromium wastewater treatment unit of the present invention are reused. Compared with the prior art, the utilization rate of the reagents is improved, the consumption of the reagents is greatly reduced, the treatment cost is reduced, and the reuse of the salts is realized.

[0022] 3. In the present invention, no new polluting ions are introduced, the near-zero discharge of chromium-containing wastewater is achieved, no external wastewater is generated, and environmental pollution is effectively prevented.

[0023] 4. The present invention utilizes a two-stage electrochemical concentration device to concentrate and reduce the chromium-containing wastewater, and has the advantages of good concentration effect and high precipitation efficiency, which is of great significance to the resource utilization of chromium-containing wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the flow chart of existing chromium-containing wastewater treatment technology.

[0025] Figure 2 It is a simplified flow chart of the present invention.

[0026] Figure 3 It is a flow chart of the present invention.

[0027] Figure 2 The figures are marked as follows: 1. unit line; 2. concentrated chromium waste liquid pipeline; 3. concentrated chromium waste liquid regulating tank; 4. reduction tank; 5. neutralization sedimentation tank; 6. sedimentation tank; 7. filter press; 8. dilute chromium waste water pipeline; 9. regulating tank; 10. sedimentation tank; 11. filter; 12. primary raw water tank; 13. primary electrochemical concentration device; 14. secondary electrochemical concentration device; 15. secondary water production tank; 16. chromium removal resin; 17. filter press. DETAILED DESCRIPTION

[0028] In order to better understand the present invention, the present invention is further described in detail below in conjunction with the schematic diagram.

[0029] like Figure 2 and Figure 3A chromium-containing wastewater treatment system shown is specifically a chromium-containing wastewater treatment system for a cold rolling mill line, comprising a concentrated chromium wastewater treatment unit, a dilute chromium wastewater treatment unit and a recovery treatment unit;

[0030] The concentrated chromium waste liquid outlet of the unit line 1 is connected to the inlet of the concentrated chromium waste liquid treatment unit through the concentrated chromium waste liquid pipeline 2, and the liquid outlet of the concentrated chromium waste liquid treatment unit is connected to the liquid return port of the unit line 1 through a pipeline;

[0031] The dilute chromium wastewater outlet of the unit line 1 is connected to the inlet of the dilute chromium wastewater treatment unit through the dilute chromium wastewater pipeline 8, the concentrated water outlet of the dilute chromium wastewater treatment unit is connected to the inlet of the concentrated chromium waste liquid treatment unit through a pipeline, and the produced water outlet of the dilute chromium wastewater treatment unit is connected to the inlet of the recovery treatment unit through a pipeline;

[0032] The concentrated water outlet of the recovery and processing unit is communicated with the inlet of the concentrated chromium waste liquid processing unit, and the produced water outlet of the recovery and processing unit is communicated with the industrial water pipeline.

[0033] In the present invention, the total chromium concentration in the dilute chromium wastewater produced by the cold rolling mill line 1 is 13-50 mg / L, and the total chromium concentration in the concentrated chromium waste liquid produced is 150-550 mg / L. The dilute chromium wastewater generated by unit line 1 first enters the dilute chromium wastewater treatment unit through the dilute chromium wastewater pipeline 8 for treatment. The chromium-containing concentrated water (total chromium concentration of 50-200 mg / L) generated by the dilute chromium wastewater treatment unit is collected in the concentrated chromium waste liquid treatment unit and mixed with the concentrated chromium waste liquid from unit line 1. The solution generated after treatment by the concentrated chromium waste liquid treatment unit (total chromium concentration in the solution is 0.1-0.5 mg / L) enters the unit line 1 again for reuse; the produced water (total chromium concentration of ≤5 mg / L) of the dilute chromium wastewater treatment unit enters the recovery treatment unit for treatment, and the produced water (total chromium concentration of ≤0.05 mg / L) of the recovery treatment unit enters the industrial water pipeline for reuse as industrial water, and the concentrated water (total chromium concentration of 13-50 mg / L) generated by the recovery treatment unit enters the concentrated chromium waste liquid treatment unit for treatment.

[0034] Preferably, the concentrated chromium waste liquid treatment unit comprises a concentrated chromium waste liquid regulating tank 3, a reduction tank 4, a neutralization sedimentation tank 5 and a sedimentation tank; the inlet of the concentrated chromium waste liquid regulating tank 3 is respectively connected with the concentrated water outlet of the dilute chromium waste water treatment unit (that is, the concentrated water outlet of the primary electrochemical concentration device 13 described later), the concentrated water outlet of the recovery treatment unit (that is, the concentrated water outlet of the chromium removal resin 16 described later) and the concentrated chromium waste liquid pipeline 2, and the concentrated chromium waste liquid regulating tank 3, the reduction tank 4, the neutralization sedimentation tank 5 and the sedimentation tank 6 are connected in sequence through pipelines; the liquid outlet of the sedimentation tank 6 is connected with the return liquid port of the unit line 1 through a pipeline.

[0035] Preferably, the concentrated chromium waste liquid treatment unit also includes a filter press 7, the sludge outlet of the sedimentation tank 6 is connected to the inlet of the filter press 7, the liquid outlet of the filter press 7 is connected to the liquid return port of the unit line 1 through a pipeline, and the mud cake produced by the filter press 7 is transported out.

[0036] Preferably, an aeration and stirring device is provided in the reduction pool 4, and the aeration and stirring device is used to aerate the reduction pool 4 to improve the reduction efficiency.

[0037] In the present invention, sulfuric acid is added to the concentrated chromium waste liquid regulating tank 3, and the concentrated chromium waste liquid entering the concentrated chromium waste liquid regulating tank 3 is adjusted to a pH of 2.0-3.0 by sulfuric acid, and then enters the reduction tank 4, and the reducing agent NaHSO is added to the reduction tank 4. 3 solution, the Cr in the waste liquid 6+ Reduction to Cr 3+ , the produced water enters the neutralization sedimentation tank 5 (specifically the NaOH neutralization sedimentation tank), Cr 3+ Cr(OH) is generated in the neutralization sedimentation tank 5 3 , and then enters the precipitation tank 6 for precipitation. After precipitation, the supernatant of the precipitation tank 6 (including various salts such as sodium sulfate) enters the unit line 1 for reuse through the liquid outlet; the sludge produced by the precipitation tank 6 enters the filter press device 7 through the sludge outlet for filter press treatment, and the filtered liquid produced by the filter press device 7 (including salts such as sodium sulfate, etc.) is cleaned by the electrolytic sodium sulfate on the surface of the steel plate, thereby stripping a large amount of Cr from the surface of the steel plate. 6+ ) is recycled to unit line 1 after adjusting the concentration by adding sodium sulfate, and the generated mud cake is transported out for the next treatment.

[0038] Preferably, the dilute chromium wastewater treatment unit comprises a regulating tank 9, a sedimentation tank 10, a primary raw water tank 12 and a primary electrochemical concentrator 13; the inlet of the regulating tank 9 is connected to the dilute chromium wastewater pipeline 8, the regulating tank 9, the inlet of the sedimentation tank 10, the liquid outlet of the sedimentation tank 10, the primary raw water tank 12 and the primary electrochemical concentrator 13 are connected in sequence through pipelines, the concentrated water outlet of the primary electrochemical concentrator 13 is connected to the inlet of the concentrated chromium waste liquid treatment unit (specifically connected to the inlet of the concentrated chromium waste liquid regulating tank 3), and the produced water outlet of the primary electrochemical concentrator 13 is connected to the inlet of the recovery treatment unit.

[0039] Preferably, the dilute chromium wastewater treatment unit further comprises a filter 11 disposed between the sedimentation tank 10 and the primary raw water tank 12, and the liquid outlet of the sedimentation tank 10, the filter 11 and the primary raw water tank 12 are sequentially connected through pipelines. The filter 11 comprises a quartz sand filter and a security filter arranged in series.

[0040] Preferably, the dilute chromium wastewater treatment unit further comprises a filter press 17, the inlet of the filter press 17 is connected to the sludge outlet of the sedimentation tank 10, the liquid outlet of the filter press 17 is connected to the filter 11, and the sludge outlet of the filter press 17 is connected to the outside.

[0041] Preferably, the dilute chromium wastewater treatment unit also includes a secondary electrochemical concentrator 14; the inlet of the secondary electrochemical concentrator 14 is connected to the water output outlet of the primary electrochemical concentrator 13, and the concentrated water outlet of the secondary electrochemical concentrator 14 is connected to the primary raw water tank 12; the water output outlet of the secondary electrochemical concentrator 14 is connected to the inlet of the recovery treatment unit.

[0042] In the present invention, the dilute chromium wastewater produced by the unit line 1 is in large quantity, which is collected and transported to the regulating tank 9, the wastewater is homogenized in the regulating tank 9, and then transported to the sedimentation tank 10, a flocculant is added in the sedimentation tank 10 to remove suspended matter in the dilute chromium wastewater, the sludge precipitated in the sedimentation tank 10 is sent to the filter press 17, the mud cake produced by the filter press 17 is transported out, and the filtered liquid (containing sodium sulfate) of the filter press 17 is sent to the filter 11 again; the supernatant (containing sodium sulfate) after precipitation in the sedimentation tank 10 is further removed from the suspended matter by the filter 11, and then enters the primary raw water tank 12 for storage and homogenization treatment, and the water in the primary raw water tank 12 is capacitively desalted by the primary electrochemical concentration device 13 to remove 70% of the ions (Cr 6+ Cr 3+ 、Na + 、SO 4 2— ), the concentrated water (i.e., the salt-containing concentrated water, with a total chromium concentration of 50-200 mg / L) enters the concentrated chromium waste liquid regulating tank 3, the produced water (i.e., the solution after deionization) enters the secondary electrochemical concentration device 14 for further desalination treatment, and the concentrated water (i.e., the concentrated water containing impure salts, with a total chromium concentration of 13-50 mg / L) produced by the secondary electrochemical concentration device 14 enters the primary raw water tank 12 for treatment; the produced water (with a total chromium concentration of ≤5 mg / L) obtained by the secondary electrochemical concentration device 14 enters the recovery and treatment unit.

[0043] Preferably, the recovery and processing unit includes a secondary water production pool 15 and a chromium removal resin 16 connected by a pipeline, the water production outlet of the secondary electrochemical concentration device 14 is connected to the inlet of the secondary water production pool 15, the outlet of the secondary water production pool 15 is connected to the chromium removal resin 16, the water production outlet of the chromium removal resin 16 is connected to the industrial water pipeline, and the concentrated water outlet of the chromium removal resin 16 is connected to the inlet of the concentrated chromium waste liquid treatment unit (specifically connected to the inlet of the concentrated chromium waste liquid regulating pool 3).

[0044] In the present invention, the produced water (with a total chromium concentration of ≤5 mg / L) obtained by the secondary electrochemical concentration device 14 enters the secondary water production pool 15, and then enters the chromium removal resin 16 to treat the residual Cr 6+ The produced water (total chromium concentration is ≤ 0.05 mg / L) is used as industrial water for reuse (high-quality industrial water), and the concentrated water (total chromium concentration is 13-50 mg / L) produced by the chromium removal resin 16 enters the concentrated chromium waste liquid regulating tank 3 for treatment.

[0045] In the present invention, the devices are connected via pipelines.

[0046] A method for treating chromium-containing wastewater, the method comprising: providing the above-mentioned chromium-containing wastewater treatment system, wherein the dilute chromium wastewater discharged from unit line 1 is sent to the dilute chromium wastewater treatment unit of the chromium-containing wastewater treatment system, the dilute chromium wastewater is subjected to precipitation, filtration and desalination treatment, the produced water is sent to the recovery treatment unit for recycling treatment, the concentrated water produced by desalination is sent to the concentrated chromium waste liquid treatment unit; the concentrated water produced by the recovery treatment unit is sent to the concentrated chromium waste liquid treatment unit; the concentrated chromium waste liquid discharged from unit line 1 is sent to the concentrated chromium waste liquid treatment unit of the chromium-containing wastewater treatment system, mixed with the concentrated water produced by the dilute chromium wastewater treatment unit, sulfuric acid is added for pre-conditioning, and NaHSO is added 3 Cr 6+ Reduction to Cr 3+ , after neutralization and precipitation, Cr(OH) 3 The sludge produced by precipitation is discharged, and the supernatant is sent to unit line 1 for reuse. The specific method is:

[0047] After being collected, the dilute chromium wastewater enters the dilute chromium wastewater treatment unit, and is homogenized in the regulating tank 9. The effluent from the regulating tank 9 enters the sedimentation tank 10, where flocculants are added to remove large particles of sediment in the incoming water. The effluent after sedimentation enters the filter 11 for filtration (firstly, the suspended matter and turbidity in the incoming water are removed by the quartz sand filter, and the effluent from the quartz sand filter is further filtered by the security filter) and then enters the primary raw water tank 12. The water in the primary raw water tank 12 is treated by the primary electrochemical concentration device 13 to remove 70% of the ions (Cr 6+ Cr 3+ 、Na + 、SO 4 2— ), the effluent from the primary electrochemical concentration device 13 is further processed in the recovery unit; the effluent from the primary electrochemical concentration device 13 is further processed in the secondary electrochemical concentration device 14 for capacitive desalination treatment, and then the effluent enters the secondary water production pool 15. The effluent from the secondary water production pool 15 is further adsorbed by the chromium removal resin 16, and the total chromium concentration is ≤0.05 mg / L, thereby obtaining high-quality industrial water.

[0048] The concentrated water from the primary electrochemical concentration device 13 enters the concentrated chromium waste liquid regulating tank 3 and is treated simultaneously with the concentrated chromium waste liquid generated by the unit line 1. At this time, the waste sulfuric acid from the unit line 1 is added for acid pre-conditioning and pumped into the reduction tank 4 (the reduction tank 4 is equipped with a multi-stage reduction tank, and the number of stages can be adjusted according to the reduction requirements and the on-site water quality). NaHSO is added in an environment with a pH of 2.0-3.0. 3 Cr 6+ Reduction to Cr 3+ After that, the wastewater enters the neutralization sedimentation tank 5, where NaOH is added to adjust the pH to 7.0-9.0, so that the wastewater reaches the optimal pH value required for metal ion co-precipitation; the wastewater coming out of the neutralization sedimentation tank 5 already contains metal hydroxide Cr(OH) 3 After precipitation, the wastewater enters the sedimentation tank 6 for sedimentation. If the site space is sufficient, in order to increase the sedimentation efficiency, a coagulation and flocculation tank can be added to add flocculants to improve its sedimentation effect; the supernatant after precipitation is recycled to the unit line 1, and the sludge produced by the precipitation is sent to the filter press 7, and the filtered liquid is recycled to the unit line 1, and the produced mud cake is transported out for treatment.

[0049] Example

[0050] The amount of dilute chromium wastewater produced by each unit line 1 of a steel plant is 30m 3 / h, the water volume of concentrated chromium waste liquid is 5m 3 / h, the inlet water quality indicators of the two are shown in Table 1.

[0051] Table 1 Influent water quality of dilute chromium wastewater and concentrated chromium wastewater

[0052] Test items unit Detection value of dilute chromium wastewater Concentrated chromium waste liquid detection value PH 7～8 7～8 Conductivity μs / cm 1500-8000 20000～120000 Turbidity NTU 500～700 7500～9000 Suspended matter mg / L 200～500 3000～5500 Total hardness mg / L 100～500 1200～5500 <![CDATA[Cl - ]]> mg / L 1000～5000 10000～50000 Total Iron mg / L 0.5～10 5～100 Hexavalent Chromium mg / L 12～50 150～480 Total Chromium mg / L 13～50 150～550 Chemical oxygen demand (COD) mg / L 30～100 300～1300 Total salt mg / 750～5000 10000～60000

[0053] The above-mentioned dilute chromium wastewater and concentrated chromium waste liquid are treated by the above-mentioned method. During the treatment process: the conductivity of the concentrated water of the first-level electrochemical concentration device 13 is about 40000-50000us / cm, and the water volume is about 6m 3 / h (adjustable), the total chromium concentration is 50-200mg / L; the effluent conductivity of the first-stage electrochemical concentration device 13 is about 2000-3000us / cm, and the total chromium concentration is ≤

[0054] 15mg / L; the effluent conductivity after secondary desalination treatment is ≤1000us / cm, and the total chromium concentration is ≤5mg / L; after adsorption by chromium removal resin 16, the total chromium concentration in the water is ≤0.05mg / L, and high-quality industrial water is obtained.

[0055] In the present invention, the specific functions of each device are as follows:

[0056] a. Regulating tank 9: homogenize the water from unit line 1;

[0057] b. Sedimentation tank 10: used to remove suspended matter in the water body;

[0058] c. Filter 11: reduce the turbidity of the incoming water to meet the water quality requirements of the electrochemical concentration device;

[0059] d. The first-stage electrochemical concentration device 13 and the second-stage electrochemical concentration device 14: Both are capacitive desalination devices based on capacitive desalination technology. The basic principle is to apply an external voltage to the electrosorption water treatment module to form a double electron layer at the electrode solution interface. Raw water flows into the electrosorption water treatment module from one end and flows out from the other end. When a positive voltage is applied to the module, the anions and cations in the raw water move to the anode and cathode respectively and are adsorbed on the porous carbon materials on the surfaces of the positive and negative electrodes, so that the salts in the solution (such as Cr in this embodiment) 6+ Cr 3+ 、Na + 、SO 4 2— ), the concentration of charged colloidal particles and other charged substances is reduced, organic matter is decomposed, etc., thereby achieving water desalination and purification; when adsorption saturation is reached, the ions adsorbed on the electrode plate are released into the regenerated solution by applying a reverse external voltage or reversing the power supply, and the electrode plate can be reused after complete desorption. The core electrode material of the electrosorption desalination technology is an inert carbon material, which is resistant to strong acids and alkalis; the desalination device adopts a channel structure (channel width is millimeter level) and is not easy to clog. In the present invention, the first-stage electrochemical concentration device 13 and the second-stage electrochemical concentration device 14 are both mature equipment in the industry, and the structure and function are all existing, so they will not be repeated here;

[0060] e. Chromium removal resin 16: It is an existing technology used to reduce the concentration of chromium in the produced water to obtain high-quality industrial water;

[0061] f. Concentrated chromium waste liquid regulating tank 3: Use the waste sulfuric acid generated in the plant to adjust the pH of the wastewater, saving costs;

[0062] g. Reduction tank 4: adding NaHSO 3 Cr 6+ Reduction to Cr 3+ , an aeration and stirring device may also be provided in the reduction tank 4;

[0063] h. Neutralization sedimentation tank 5: Add NaOH and Cr 3+ The reaction generates Cr(OH) 3 of precipitation;

[0064] i. Sedimentation tank 6: Add polyacrylamide and other flocculants to enhance the sedimentation effect;

[0065] j. Filter press device 7: The mud cake produced by the filter press 17 is transported out for disposal, and the filtered liquid is returned to unit line 1.

[0066] After conducting a cost analysis on the different chromium-containing wastewater treatment processes of this steel plant, as mentioned above, the dilute chromium wastewater 30m 3 / h, concentrated chromium waste liquid 5m 3 / h, the traditional process is to mix the two, a total of 35m 3 / h, the investment cost per ton of water is 800,000 yuan, the total investment cost is 28 million yuan, and the operating cost is 20-30 yuan / ton; while the total investment cost of the treatment using the technical solution of the present invention is 12 million yuan, and the operating cost is 10-15 yuan / ton. Comparing the investment cost and the operating cost, for the same treatment scale, the investment cost of the present invention saves 16 million yuan, and the operating cost saves 10-20 yuan / ton. Compared with the traditional process, the present invention has great advantages in both investment cost and operating cost.

[0067] In the present invention, the concentrated chromium waste liquid and the diluted chromium waste water generated by the unit line 1 are treated by the process flow, and the sodium sulfate, the filtered liquid, the supernatant, etc. are recycled to the unit, forming a whole process recycling, achieving near-zero discharge of chromium-containing waste water, and no external waste water is generated; the system does not generate impurities, and NaHSO 3 Reduced Cr 6+ Sodium sulfate and Cr generated in the process 3+ , for subsequent Cr 3+ The precipitation creates conditions, and the sodium sulfate generated in the reaction process can also be introduced into the unit line 1 for reuse, so that the sodium sulfate in the wastewater is recycled, reducing the use of reagents; the dilute chromium wastewater is recycled and treated by the chromium removal resin 16 to obtain high-quality industrial water for reuse, so as to realize the resource utilization of chromium-containing wastewater; the concentrated water after the dilute chromium wastewater is treated by the primary electrochemical concentration device 13 is mixed with the concentrated chromium waste liquid of the unit line 1, and the produced water after the dilute chromium wastewater is treated by the primary electrochemical concentration device 13 is further treated by the secondary electrochemical concentration device 14, and the concentrated water and the dilute water (i.e., the produced water) are treated by quality separation, which is green and economical; the highly toxic Cr 6+ By NaHSO 3 Reduction to Cr 3+ , and then enters the neutralization sedimentation tank 5, without the introduction of new polluting ions, reducing environmental pollution; the chromium-containing wastewater is concentrated and reduced by two-stage electrochemical concentration treatment; the system has the advantages of low investment cost and operating cost, green economy, no introduction of polluting ions, recycling of sodium sulfate in the wastewater, good concentration effect, high precipitation efficiency, etc., which is of great significance to the resource utilization of chromium-containing wastewater.

[0068] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

[0069] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to replace some of the technical features therein with equivalents. However, any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A chromium-containing wastewater treatment system, characterized in that: It includes concentrated chromium waste liquid treatment unit, diluted chromium waste water treatment unit and recovery treatment unit; The concentrated chromium waste liquid outlet of the unit line is connected to the inlet of the concentrated chromium waste liquid treatment unit through the concentrated chromium waste liquid pipeline, and the liquid outlet of the concentrated chromium waste liquid treatment unit is connected to the liquid return port of the unit line; The dilute chromium wastewater outlet of the unit line is connected to the inlet of the dilute chromium wastewater treatment unit through the dilute chromium wastewater pipeline, the concentrated water outlet of the dilute chromium wastewater treatment unit is connected to the inlet of the concentrated chromium waste liquid treatment unit, and the produced water outlet of the dilute chromium wastewater treatment unit is connected to the inlet of the recovery treatment unit; The concentrated water outlet of the recovery and treatment unit is communicated with the inlet of the concentrated chromium waste liquid treatment unit, and the produced water outlet of the recovery and treatment unit is communicated with the industrial water pipeline.

2. The chromium-containing wastewater treatment system according to claim 1, characterized in that: The concentrated chromium waste liquid treatment unit comprises a concentrated chromium waste liquid regulating tank, a reduction tank, a neutralization sedimentation tank, a sedimentation tank and a filter press; the inlet of the concentrated chromium waste liquid regulating tank is respectively connected with the concentrated water outlet of the dilute chromium waste water treatment unit, the concentrated water outlet generated by the recovery treatment unit and the concentrated chromium waste liquid pipeline, and the outlet of the concentrated chromium waste liquid regulating tank, the reduction tank, the neutralization sedimentation tank and the sedimentation tank are connected in sequence through pipelines; the sludge outlet of the sedimentation tank is connected with the inlet of the filter press.

3. The chromium-containing wastewater treatment system according to claim 2, characterized in that: The diluted chromium wastewater treatment unit comprises a regulating tank, a sedimentation tank, a primary raw water tank and a primary electrochemical concentration device; the inlet of the regulating tank is connected to the diluted chromium wastewater pipeline, the outlet of the regulating tank, the inlet of the sedimentation tank, the liquid outlet of the sedimentation tank, the primary raw water tank and the primary electrochemical concentration device are connected in sequence through pipelines, the concentrated water outlet of the primary electrochemical concentration device is connected to the inlet of the concentrated chromium waste liquid treatment unit; the produced water outlet of the primary electrochemical concentration device is connected to the inlet of the recovery treatment unit.

4. The chromium-containing wastewater treatment system according to claim 3, characterized in that: The dilute chromium wastewater treatment unit also includes a secondary electrochemical concentrator, the inlet of the secondary electrochemical concentrator is connected to the water output outlet of the primary electrochemical concentrator, the concentrated water outlet of the secondary electrochemical concentrator is connected to the primary raw water tank; the water output outlet of the secondary electrochemical concentrator is connected to the inlet of the recovery treatment unit.

5. The chromium-containing wastewater treatment system according to claim 4, characterized in that: The recovery and processing unit includes a secondary water production pool and a chromium removal resin connected by a pipeline, the water production outlet of the secondary electrochemical concentration device is connected to the inlet of the secondary water production pool, the outlet of the secondary water production pool is connected to the chromium removal resin, the water production outlet of the chromium removal resin is connected to an industrial water pipeline, and the concentrated water outlet of the chromium removal resin is connected to the inlet of the concentrated chromium waste liquid treatment unit.

6. The chromium-containing wastewater treatment system according to claim 5, characterized in that: The liquid outlet of the sedimentation tank is connected to the liquid return port of the unit line.

7. The chromium-containing wastewater treatment system according to claim 6, characterized in that: The liquid outlet of the filter press device is connected to the liquid return port of the unit line.

8. The chromium-containing wastewater treatment system according to claim 7, characterized in that: The dilute chromium wastewater treatment unit further comprises a filter arranged between the sedimentation tank and the primary raw water tank, and the liquid outlet of the sedimentation tank, the filter and the primary raw water tank are connected in sequence through pipelines.

9. The chromium-containing wastewater treatment system according to claim 8, characterized in that: The dilute chromium wastewater treatment unit further comprises a filter press, the inlet of the filter press is connected to the sludge outlet of the sedimentation tank, the liquid outlet of the filter press is connected to the filter, and the sludge outlet of the filter press is connected to the outside.

10. A method for treating chromium-containing wastewater, characterized in that: The method comprises the following steps: providing the chromium-containing wastewater treatment system according to claim 5, wherein the dilute chromium wastewater discharged from the unit line is sent to the dilute chromium wastewater treatment unit of the chromium-containing wastewater treatment system, the dilute chromium wastewater is subjected to precipitation, filtration and desalination treatment, the produced water is sent to the recovery treatment unit for recycling treatment, the concentrated water produced by desalination is sent to the concentrated chromium waste liquid treatment unit; the concentrated water produced by the recovery treatment unit is sent to the concentrated chromium waste liquid treatment unit; the concentrated chromium waste liquid discharged from the unit line is sent to the concentrated chromium waste liquid treatment unit of the chromium-containing wastewater treatment system, mixed with the concentrated water produced by the dilute chromium wastewater treatment unit, sulfuric acid is added for pre-adjustment, and NaHSO3 is added to Cr 6+ Reduction to Cr 3+ After neutralization and precipitation, Cr(OH)3 is precipitated, the sludge produced by precipitation is discharged, and the supernatant is sent to the unit line for reuse.

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