CN107381932B - Chromium-containing wastewater treatment method, treatment system and application - Google Patents
Chromium-containing wastewater treatment method, treatment system and application Download PDFInfo
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- CN107381932B CN107381932B CN201710446977.XA CN201710446977A CN107381932B CN 107381932 B CN107381932 B CN 107381932B CN 201710446977 A CN201710446977 A CN 201710446977A CN 107381932 B CN107381932 B CN 107381932B
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- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 title claims abstract description 109
- 239000011651 chromium Substances 0.000 title claims abstract description 107
- 229910052804 chromium Inorganic materials 0.000 title claims abstract description 105
- 238000004065 wastewater treatment Methods 0.000 title claims description 19
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 184
- 239000002351 wastewater Substances 0.000 claims abstract description 147
- 238000000034 method Methods 0.000 claims abstract description 90
- 238000002425 crystallisation Methods 0.000 claims abstract description 38
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- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 26
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 26
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- 229910052782 aluminium Inorganic materials 0.000 description 4
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 4
- 238000007743 anodising Methods 0.000 description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 4
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- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 2
- PXGOKWXKJXAPGV-UHFFFAOYSA-N Fluorine Chemical compound FF PXGOKWXKJXAPGV-UHFFFAOYSA-N 0.000 description 2
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 2
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- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 description 1
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Images
Classifications
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F9/00—Multistage treatment of water, waste water or sewage
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/001—Processes for the treatment of water whereby the filtration technique is of importance
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
- C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
- C02F1/041—Treatment of water, waste water, or sewage by heating by distillation or evaporation by means of vapour compression
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/441—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by reverse osmosis
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/442—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by nanofiltration
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
- C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
- C02F1/54—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using organic material
- C02F1/56—Macromolecular compounds
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/58—Treatment of water, waste water, or sewage by removing specified dissolved compounds
- C02F1/62—Heavy metal compounds
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F2001/007—Processes including a sedimentation step
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/20—Heavy metals or heavy metal compounds
- C02F2101/22—Chromium or chromium compounds, e.g. chromates
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
- C02F2103/16—Nature of the water, waste water, sewage or sludge to be treated from metallurgical processes, i.e. from the production, refining or treatment of metals, e.g. galvanic wastes
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2303/00—Specific treatment goals
- C02F2303/10—Energy recovery
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- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F3/00—Biological treatment of water, waste water, or sewage
- C02F3/02—Aerobic processes
- C02F3/12—Activated sludge processes
- C02F3/1236—Particular type of activated sludge installations
- C02F3/1268—Membrane bioreactor systems
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F3/00—Biological treatment of water, waste water, or sewage
- C02F3/30—Aerobic and anaerobic processes
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F3/00—Biological treatment of water, waste water, or sewage
- C02F3/34—Biological treatment of water, waste water, or sewage characterised by the microorganisms used
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- Organic Chemistry (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
Abstract
The invention provides a method for treating chromium-containing wastewater, which is characterized by sequentially comprising the following steps: (1) pretreating chromium-containing wastewater to obtain pretreated water; (2) performing biochemical treatment on the pretreated water obtained in the step (1) to obtain biochemical treated water; (3) concentrating the biochemical treatment water obtained in the step (2) to obtain concentrated high-salinity concentrated water and reuse water; (4) carrying out evaporation crystallization treatment on the concentrated high-salinity concentrated water obtained in the step (3) to obtain recycled water and crystals; wherein the standard of the recycled water is as follows: the pH value is 6-8, the conductivity is less than or equal to 50, the COD is less than or equal to 30, and the turbidity is less than or equal to 1; the method has the advantages of simple operation, stable operation, low cost and high treatment efficiency, thereby achieving zero discharge or low discharge of the chromium-containing wastewater in the electroplating production and simultaneously realizing high-purity recovery of each metal ion in the wastewater.
Description
Technical Field
The invention relates to a method and a system for treating wastewater, in particular to a method for treating chromium-containing wastewater in the electroplating industry, a system for treating the chromium-containing wastewater in the electroplating industry by using the method, and application of the method or the system in treating the chromium-containing wastewater in the electroplating industry.
Background
The method commonly used in the wastewater treatment process for treating the chromium-containing wastewater comprises a chemical precipitation method, an electrolysis method, a common ion exchange method and the like. The treatment method and the system have certain limitations and can not realize zero discharge of the chromium-containing wastewater. The chemical precipitation method is widely used for treating chromium-containing wastewater, and a large amount of acid and alkali, ferrous sulfate and polyaluminium chloride are required to be added in the production process, so that the salt content of wastewater discharge is increased, and the chromium ions remaining in the wastewater cannot meet the discharge standard easily. Because the content of the controlled substances specified by the wastewater discharge standard is extremely low, excessive chemicals are required to be added when the wastewater discharge standard is met, the cost is high, and the wastewater cannot be recycled as process water. Meanwhile, the chemical precipitation method cannot directly recover chromium ions in the wastewater, and simultaneously generates a large amount of sludge which contains a large amount of chromium ions, so that the sludge needs to be treated again, and secondary pollution is caused; the process for treating the chromium-containing wastewater by the electrolytic method is mature and operates stably, but because the content of controlled substances specified by the wastewater discharge standard is extremely low, the power consumption is large when the chromium-containing wastewater is treated by the electrolytic method, the treatment cost is high, and toxic gas is easily generated, so that the chromium-containing wastewater is difficult to discharge after reaching the standard; the common ion exchange method adopts organic framework ion exchange resin to effectively remove various harmful ions in the chromium-containing wastewater, and the treated wastewater can be recycled, but the consumption of the resin is large in the wastewater treatment process, the treatment of the regenerated liquid is difficult, a large amount of acid and alkali is consumed, and the treatment cost is high. Meanwhile, the organic framework ion exchange resin also causes a great deal of breakage of the resin in the regeneration process, and the economy is not high.
It can be seen that various treatment methods for chromium-containing wastewater have many problems, most or all of the wastewater cannot be recycled even the existing equipment of each electroplating plant is fully utilized, and valuable metals in the wastewater cannot be effectively separated and recovered.
Disclosure of Invention
The invention aims to overcome the problems and defects in the prior art and provide a chromium-containing wastewater treatment method and a corresponding treatment system which are simple to operate, stable to operate, low in cost and high in treatment efficiency, so that zero emission or low emission of chromium-containing wastewater in electroplating production is achieved, high-purity recovery of metal ions in the wastewater is realized, the production water consumption of the electroplating industry is saved, the pollution of the electroplating industry to the environment is remarkably reduced, the use amount of acid and alkali is reduced, resources are effectively saved, the production cost is reduced, the recovery of equipment investment is realized, and the clean production and sustainable development of the electroplating industry are promoted and promoted.
The purpose of the invention is realized by the following technical scheme:
the invention provides a method for treating chromium-containing wastewater, which is characterized by sequentially comprising the following steps:
(1) pretreating chromium-containing wastewater to obtain pretreated water;
(2) performing biochemical treatment on the pretreated water obtained in the step (1) to obtain biochemical treated water;
(3) concentrating the biochemical treatment water obtained in the step (2) to obtain concentrated high-salinity concentrated water and reuse water;
(4) carrying out evaporation crystallization treatment on the concentrated high-salinity concentrated water obtained in the step (3) to obtain recycled water and crystals;
wherein the standard of the recycled water is as follows: pH 6-8, conductivity less than or equal to 50, COD less than or equal to 30 and turbidity less than or equal to 1.
Preferably, in the step (1), the chromium-containing wastewater has a pH value of 4-6 and contains pollutants such as hexavalent chromium, trivalent chromium, sulfuric acid, nitric acid, oxide, COD and the like;
preferably, the step of pre-treating is:
(1-1) introducing the chromium-containing wastewater into a chromium breaking tank, adding sulfuric acid into the chromium breaking tank until the pH value is 2-3, and then adding sodium sulfite into the chromium breaking tank until the ORP value is 230-270mv to carry out chromium breaking reaction;
(1-2) introducing the wastewater treated in the step (1-1) into a pH adjusting tank, and adding sodium hydroxide until the pH is 8-9;
(1-3) introducing the wastewater treated in the step (1-2) into a chemical reaction tank, adding a coagulant, then adding a flocculant, and stirring for 20-30 min;
(1-4) introducing the wastewater treated in the step (1-3) into a precise control efficient precipitation system;
preferably, in the step (1-1), a 10% sulfuric acid solution is added to adjust the pH; preferably, sodium sulfite solution with the concentration of 10 percent is added to adjust the ORP value;
preferably, the chromium breaking reaction time of the step (1-1) is 20-30 min;
preferably, in the step (1-2), a sodium hydroxide solution with the concentration of 10% is added to adjust the pH;
preferably, in the step (1-3), the coagulant is an inorganic coagulant, more preferably PAC; preferably, the flocculant is an organic flocculant, more preferably PAM; preferably, the time interval between the addition of the coagulant and the flocculant is 20-40 min;
preferably, the pH of the wastewater treated by the step (1-3) is 8-9;
preferably, the ORP value of the wastewater treated by the steps (1-3) is 230-270 mv;
preferably, in the step (1-4), the precise control efficient sedimentation system is formed by sequentially connecting a water distribution system, a sedimentation treatment tank, an inclined pipe, a water outlet weir and a sludge hopper; preferably, the wastewater treated in the step (1-3) is sequentially introduced into the water distribution system, the sedimentation treatment tank and the inclined pipe; the supernatant after the treatment enters an effluent weir to obtain pretreated water, and the obtained sludge is deposited in a sludge hopper; preferably, the pressure of the sedimentation treatment tank is 2-3 Mpa.
Preferably, in the step (2), the biochemical treatment step is: sequentially feeding the pretreated water obtained in the step (1) into an anaerobic tank, an aerobic tank and a membrane bioreactor;
preferably, the anaerobic pool comprises anaerobic bacteria; preferably, the anaerobic bacteria are selected from one or more of yeast, nitrate bacteria, clostridium or bacteroides;
preferably, the yeast, nitrate, clostridia or bacteroides are acclimatized to be salt-tolerant;
preferably, the aerobic tank contains aerobic microorganisms;
preferably, the aerobic microorganism is selected from one or more of bacillus, rhizobium, nitrobacteria or mould;
preferably, the bacillus, rhizobium, nitrifier or mould is acclimated to be salt tolerant;
preferably, the membrane bioreactor consists of a hollow fiber membrane component and a membrane pool; preferably, the hollow fiber membrane module is located in the membrane tank;
preferably, the pore diameter of the hollow fiber membrane is 0.01-0.1 μm;
preferably, the pH after the biochemical treatment is 6 to 8.
Preferably, in the step (3), the concentration treatment step is: sequentially passing the biochemical treatment water obtained in the step (2) through a primary nanofiltration system, a primary reverse osmosis system and a secondary reverse osmosis system;
preferably, the primary nanofiltration system is formed by sequentially connecting a precision filter and a primary nanofiltration membrane;
preferably, the filter element of the precision filter is melt-blown PP cotton;
preferably, the filter element pore size of the precise microporous filter is 5 μm;
preferably, the primary nanofiltration membrane is an industrial grade high-desalination-rate nanofiltration membrane;
preferably, the aperture of the primary nanofiltration membrane is 1-2 nm;
preferably, the rejection rate of the primary nanofiltration membrane to sodium ions is 50-70%; preferably, the rejection rate of the primary nanofiltration membrane on heavy metal ions and salts is more than 97%;
preferably, the membrane feeding pressure of the primary nanofiltration system is 1.0-1.5 Mpa;
preferably, the relative molecular mass cut-off range of the primary nanofiltration system is 150-300 daltons;
preferably, the pH of the water entering the primary nanofiltration system is 6-8;
preferably, the permeate of the primary nanofiltration system can be used as reuse water;
preferably, the concentrated solution of the primary nanofiltration system enters a primary reverse osmosis system.
Preferably, in the step (3), the first-stage reverse osmosis system is formed by sequentially connecting a precision filter and a first-stage reverse osmosis membrane;
preferably, the filter element of the precision filter is melt-blown PP cotton;
preferably, the filter element pore size of the precise microporous filter is 5 μm;
preferably, the first-stage reverse osmosis membrane is a brackish water reverse osmosis membrane;
preferably, the rejection rate of the first-stage reverse osmosis membrane on heavy metal ions and salts is more than 98 percent;
preferably, the aperture of the primary reverse osmosis membrane is 0.1-1 nm;
preferably, the membrane inlet pressure of the primary reverse osmosis system is 1.8 Mpa;
preferably, the pH of the water entering the primary reverse osmosis system is 5-6;
preferably, the primary reverse osmosis system is adjusted in pH by adding hydrochloric acid;
preferably, hydrochloric acid with the concentration of 0.2-0.5% is added to adjust the pH;
preferably, the permeate of the primary reverse osmosis system returns to the primary nanofiltration system;
preferably, the concentrate of the primary reverse osmosis system enters a secondary reverse osmosis system.
Preferably, in the step (3), the secondary reverse osmosis system is formed by sequentially connecting a precision filter and a secondary reverse osmosis membrane;
preferably, the filter element of the precision filter is melt-blown PP cotton;
preferably, the filter element pore size of the precise microporous filter is 5 μm;
preferably, the secondary reverse osmosis membrane is a seawater reverse osmosis membrane;
preferably, the rejection rate of the secondary reverse osmosis membrane on heavy metal ions and salts is more than 99.5%;
preferably, the aperture of the secondary reverse osmosis membrane is 0.1-1 nm;
preferably, the membrane inlet pressure of the secondary reverse osmosis system is 4-5 Mpa;
preferably, the pH of the water entering the secondary reverse osmosis system is 6 to 8;
preferably, the secondary reverse osmosis system is adjusted in pH by adding hydrochloric acid;
preferably, the concentration of the hydrochloric acid is 0.2-0.5%;
preferably, the permeate of the secondary reverse osmosis system returns to the primary nanofiltration system;
preferably, the concentrate of the secondary reverse osmosis system is the high salinity concentrate.
Preferably, in the step (4), the evaporative crystallization treatment step is: sequentially passing the high-salinity concentrated water obtained in the step (3) through a heat exchanger, a concentration evaporator and an evaporation crystallizer;
preferably, the operating temperature of the heat exchanger is 80-100 ℃;
preferably, the operating pressure of the heat exchanger is 0.05-0.1 MPa;
preferably, the concentration evaporator is formed by sequentially connecting a heating chamber, a separation chamber, a circulating chamber, a liquid distributor and a demister;
preferably, the evaporative crystallizer is formed by sequentially connecting a separation chamber, a salt leg, a thickener and a crystallization kettle;
preferably, the condensed water of the high-salinity concentrated water after passing through the concentration evaporator returns to the secondary reverse osmosis system;
preferably, the concentrated high-salt water passes through a concentration evaporator to obtain concentrated high-salt water;
preferably, the concentrated high-salinity concentrated water has the salinity of 30-35%;
preferably, the concentrated high-salinity concentrated water passes through an evaporative crystallizer to obtain a crystal substance and condensed water; preferably, the crystal is sodium sulfate and/or sodium chloride; preferably, the condensed water is used as reuse water.
The invention also provides a treatment system of the chromium-containing wastewater treatment method, and the system comprises a pretreatment unit, a biochemical treatment unit, a concentration treatment unit and an evaporation crystallization treatment unit which are sequentially communicated.
Preferably, the pretreatment unit comprises a chromium breaking tank, a pH adjusting tank, a chemical reaction tank and a precise control efficient precipitation system which are sequentially communicated; preferably, the precise control efficient sedimentation system is formed by sequentially connecting a water distribution system, a sedimentation treatment tank, an inclined pipe, a water outlet weir and a sludge hopper.
Preferably, the biochemical treatment unit comprises an anaerobic tank, an aerobic tank and a membrane bioreactor which are communicated in sequence;
preferably, the membrane bioreactor consists of a hollow fiber membrane component and a membrane pool;
preferably, the hollow fiber membrane module is located in the membrane tank;
preferably, the pore diameter of the hollow fiber membrane is 0.01-0.1 μm.
Preferably, the concentration treatment unit comprises a primary nanofiltration system, a primary reverse osmosis system and a secondary reverse osmosis system which are communicated in sequence.
Preferably, the primary nanofiltration system is formed by sequentially connecting a precision filter and a primary nanofiltration membrane;
preferably, the filter element of the precision filter is melt-blown PP cotton;
preferably, the filter element pore size of the precision filter is 5 μm;
the primary nanofiltration membrane is an industrial grade high-desalination-rate nanofiltration membrane;
preferably, the aperture of the primary nanofiltration membrane is 1-2 nm;
preferably, the rejection rate of the primary nanofiltration membrane to sodium ions is 50-70%; preferably, the rejection rate of the primary nanofiltration membrane on heavy metal ions and salts is more than 97%;
preferably, the membrane feeding pressure of the primary nanofiltration system is 1.0-1.5 Mpa;
preferably, the relative molecular mass cut-off range of the primary nanofiltration system is 150-300 daltons;
preferably, the pH of the water entering the primary nanofiltration system is 6-8.
Preferably, the first-stage reverse osmosis system is formed by sequentially connecting a precision filter and a first-stage reverse osmosis membrane;
preferably, the filter element of the precision filter is melt-blown PP cotton;
preferably, the filter element pore size of the precision filter is 5 μm;
preferably, the first-stage reverse osmosis membrane is a brackish water reverse osmosis membrane;
preferably, the rejection rate of the first-stage reverse osmosis membrane on heavy metal ions and salts is more than 98 percent;
preferably, the aperture of the primary reverse osmosis membrane is 0.1-1 nm;
preferably, the membrane inlet pressure of the primary reverse osmosis system is 1.8 Mpa;
preferably, the pH of the water entering the primary reverse osmosis system is 5-6;
preferably, the primary reverse osmosis system is adjusted in pH by adding hydrochloric acid;
preferably, the concentration of the hydrochloric acid is 0.2-0.5%.
Preferably, the secondary reverse osmosis system is formed by sequentially connecting a precision filter and a secondary reverse osmosis membrane;
preferably, the filter element of the precision filter is melt-blown PP cotton;
preferably, the filter element pore size of the precision filter is 5 μm;
preferably, the secondary reverse osmosis membrane is a seawater reverse osmosis membrane;
preferably, the rejection rate of the secondary reverse osmosis membrane on heavy metal ions and salts is more than 99.5%;
preferably, the aperture of the secondary reverse osmosis membrane is 0.1-1 nm;
preferably, the membrane inlet pressure of the secondary reverse osmosis system is 4-5 Mpa;
preferably, the pH of the water entering the secondary reverse osmosis system is 6 to 8;
preferably, the secondary reverse osmosis system is adjusted in pH by adding hydrochloric acid;
preferably, the concentration of the hydrochloric acid is 0.2-0.5%.
Preferably, the evaporative crystallization unit comprises a heat exchanger, a concentration evaporator and an evaporative crystallizer which are communicated in sequence;
preferably, the operating temperature of the heat exchanger is 80-100 ℃;
preferably, the operating pressure of the heat exchanger is 0.05-0.1 MPa;
preferably, the concentration evaporator is formed by sequentially connecting a heating chamber, a separation chamber, a circulating chamber, a liquid distributor and a demister;
preferably, the evaporative crystallizer consists of a separation chamber, a salt leg, a thickener and a crystallization kettle which are connected in sequence.
The chromium-containing wastewater treatment method or the chromium-containing wastewater treatment system provided by the invention is applied to treatment of chromium-containing wastewater.
The invention provides a novel method for treating chromium-containing wastewater, which overcomes the defects in the prior art, and comprises the following steps:
the invention discloses a method for analyzing the source of chromium-containing wastewater pollutants, which comprises the following steps: the chromium-containing wastewater is mainly wastewater generated in the working procedures of cleaning a plated part, cleaning a polar plate, passivating zinc and other plated parts, electrolytic polishing of stainless steel, anodizing of aluminum, treating the plated part and the like after a chromium plating process, has a pH of 2-4, and mainly contains pollutants such as hexavalent chromium, trivalent chromium, sulfuric acid, nitric acid, oxides, COD and the like.
According to the chromium-containing wastewater treatment method and the treatment system, the chromium-containing wastewater after being treated is completely recycled for production through a technical route of wastewater diversion, classification treatment, wastewater recycling and resource recovery, and a heavy metal high-precision removal technology, a high-salinity wastewater biochemical technology, a special membrane concentration technology and a mechanical negative pressure evaporation crystallization technology, so that zero discharge of wastewater is realized, the wastewater recycling rate is improved to 99.67%, the cyclic utilization of water resources is realized to the maximum extent, pollutants in the wastewater are converted into solids for recycling, and the zero discharge of the wastewater is completely realized.
The invention discloses a pretreatment process of chromium-containing wastewater, which comprises the following steps: 1. introducing the chromium-containing wastewater into a chromium breaking tank, adding sulfuric acid into the chromium breaking tank until the pH value is 2-3, and then adding sodium sulfite until the ORP value is 230-270mv, so that hexavalent chromium is reduced into trivalent chromium, wherein the reaction time is preferably controlled to be 20-30 min; then introducing the wastewater into a pH adjusting tank, adding sodium hydroxide until the pH is 8-9 to ensure that trivalent chromium forms chromium hydroxide precipitate, and removing harmful metal impurities in the wastewater by utilizing the principle that chromium metal ions form hydroxide precipitate under an alkaline condition; 2. introducing the wastewater into a chemical reaction tank, adding a coagulant and then adding a flocculant for stirring for 20-30min to form larger alum flocs (0.6-1.0mm) in order to accelerate coagulation reaction, thereby accelerating precipitation, realizing that the coagulant and the flocculant are added at different time intervals in the flocculation process to ensure that the coagulant and the flocculant are in the best reaction time, adopting mechanical stirring in a flocculation reaction system, having high reaction speed, good effect and less dosage, and having higher removal effect on phosphorus, fluorine and COD while removing heavy metals; 3. then introducing a precise control efficient precipitation system; preferably, the precise control efficient sedimentation system is formed by sequentially connecting a water distribution system, a sedimentation treatment tank, an inclined pipe, a water outlet weir and a sludge hopper; introducing the treated wastewater into the water distribution system, the sedimentation tank treatment tank and the inclined pipe in sequence; the supernatant after the treatment enters an effluent weir to obtain pretreated water, and sludge is deposited in a sludge hopper; in order to increase the precipitation area, shorten the precipitation time and improve the precipitation efficiency, the precise control efficient precipitation system efficiently precipitates flocs and SS under the action of hydraulic water distribution, efficient precipitation and the like, the inclined pipe is arranged in the tank at the same time, so that the precipitated particles are not interfered by steady flow, and the rapid precipitation effect is achieved, the processing capacity of the precise control efficient precipitation system is 3-7 times greater than that of a common precipitation tank, the sludge at the bottom of the tank is discharged into a sludge tank through a static pressure sludge discharge device for further concentration, and then is pumped into a sludge filter press for filter pressing, and sludge cakes are reprocessed according to properties, so that about 80% of suspended matters and 40-70% of oils can be removed, the turbidity of the effluent is less than 30NTU, the COD is reduced by 40-60%, and the like; among these, the reactions that mainly occur are as follows:
4CrO7 2-+3S2O3 2-+26H+→8Cr3++6SO4 2-+13H2O
or Cr2O7 2-+3HSO3 2-+5H+→2Cr3++3SO4 2-+4H2O
Cr3++3OH-＝Cr(OH)3
The invention relates to a biochemical treatment process of chromium-containing wastewater, which comprises the following steps: the pretreated water sequentially enters an anaerobic tank, an aerobic tank and a membrane bioreactor; removing most of COD, ammonia nitrogen, SS and other substances in the wastewater through biodegradation of the A/O/MBR; the anaerobic process of the invention utilizes the function of anaerobic bacteria under the condition of no dissolved oxygen or under the condition of oxygen deficiency to hydrolyze and acidify organic matters, remove the organic matters in the wastewater, improve the biodegradability of the sewage and be beneficial to the subsequent aerobic treatment process; the aerobic process of the invention is that under aerobic condition, organic matter is oxidized and decomposed under the action of aerobic microorganisms, the concentration of the organic matter is reduced, the amount of the microorganisms is increased, the organic matter in the sewage is firstly adsorbed on the surfaces of activated sludge and biological membranes and is contacted with the surfaces of microbial cells, micromolecular organic matter can directly permeate cell walls to enter the microbial bodies, and macromolecular organic matterThe substance must be hydrolyzed into small molecules by the action of extracellular enzyme-hydrolase and then taken into the cell body by the microorganism. The organic matter is finally decomposed into CO2And H2O; the membrane bioreactor consists of a hollow fiber membrane component and a membrane pool; preferably, the hollow fiber membrane module is located in the membrane tank; the membrane component is placed in the membrane pool, aeration is carried out in the pool, and as the aperture of the hollow fiber membrane is smaller than 0.1 micron, zoogloea and free bacteria can be completely retained in the membrane pool, so that mud-water separation is achieved, various suspended particles, bacteria, algae, turbidity and organic matters are effectively removed, and excellent effluent quality with the effluent suspended matters close to zero is ensured. The efficient interception function of the membrane bioreactor can effectively intercept nitrifying bacteria, so that the nitrification reaction is smoothly carried out, and ammonia nitrogen is effectively removed; meanwhile, macromolecular organic matters which are difficult to degrade can be intercepted, and the retention time of the macromolecular organic matters in the biochemical reaction tank is prolonged, so that the macromolecular organic matters are decomposed to the maximum extent.
The invention relates to a concentration treatment process of chromium-containing wastewater, which comprises the following steps: the biochemical treatment water sequentially passes through a primary nanofiltration system, a primary reverse osmosis system and a secondary reverse osmosis system; in order to realize zero emission of the chromium-containing wastewater, the rear end of the biochemical treatment system is provided with a concentration treatment system for treating strong brine generated by the biochemical treatment system; the concentration treatment system is a process combining multi-stage concentration and nanofiltration/reverse osmosis concentration, and gradually reduces the water amount of the high-salt-content wastewater (the salt content of the obtained high-salt concentrated water is 40-60g/L) through the step-by-step concentration of the membrane, so that the investment and the operating cost of a subsequent evaporative crystallization system are reduced; the concentration treatment process reduces the concentrated brine to be treated in a subsequent evaporation crystallization system by 80 percent compared with a conventional concentration treatment system, reduces the investment cost of the whole wastewater treatment system by 20 to 30 percent, reduces the running cost of wastewater treatment by 30 to 40 percent, and improves the automation degree of the system.
The invention relates to a chromium-containing wastewater evaporation crystallization treatment process which comprises the following steps: the high-salinity concentrated water obtained by concentration treatment sequentially passes through a heat exchanger, a concentration evaporator and an evaporation crystallizer; the invention treats the wastewater to the evaporation crystallization stage and then recycles the wastewater to obtain the chromium-containing wastewaterZero emission; the waste water firstly enters a heat exchanger in the evaporative crystallization system, and the O in the waste water is removed through heat exchange2And CO2And (3) gas and waste water after heat exchange enter a concentration evaporator for evaporation concentration, when the salt concentration of the waste water is 30-35%, namely before sodium sulfate and sodium chloride are crystallized, the waste water is sent to an evaporation crystallizer to obtain crystals and condensed water, and the condensed water is used as reuse water. The evaporative crystallization system utilizes mechanical temperature increasing equipment to cause negative pressure of the waste water evaporation part, so that energy can be saved, compressed waste water steam is heated and pressurized to enter the outside of a concentration evaporator, latent heat is transferred to a pipe, the pipe is condensed into condensed water, and meanwhile, salt-containing waste water in the pipe is evaporated. The evaporative crystallization system has the characteristics of small volume, small occupied area, low energy consumption and high thermal efficiency, the power consumption of one ton of waste water is 16-20kwh, the thermal efficiency is 27 times that of a single-effect flash evaporation system and 7 times that of a four-effect flash evaporation system, the evaporative crystallization system is the most advanced evaporative concentration system at present, the generated crystals can be treated or sent to related departments for purification and utilization, and the main components of the evaporative crystallization system are sodium sulfate and sodium chloride.
The advantages of the evaporative crystallization system are as follows: (1) the system adopts mixed process water supply to reduce the ton water power consumption of the same water making tonnage device by 40-50% compared with the foreign technology; (2) because the mixed process of the system supplies water, the high-salinity concentrated water passing through the concentration treatment system sequentially enters the low-temperature effect from the high-temperature effect of the evaporative crystallization system, the concentration is gradually increased, and the temperature is gradually reduced. The increase of the concentration of the high-temperature effect feed water caused by circulating feed water from low-temperature effect to high-temperature effect in foreign technologies is avoided, and the scaling and corrosion conditions of high-temperature effect are effectively reduced; (3) the high-salinity concentrated water passing through the concentration treatment system is uniformly distributed on the concentration evaporator, so that the defect that the spray head type water supply in the existing evaporative crystallization system is not uniform and is easy to block is avoided; (4) the vacuum system adopts a differential pressure air extractor, and the designed differential pressure is accurately formed among the effects, so that the system is stable and reliable in operation.
The treatment system of the chromium-containing wastewater treatment method adopts the programmable logic controller, simultaneously realizes the automatic control and monitoring of electric appliances and instruments, and adopts the industrial personal computer to monitor the operation process state and the operation parameters of the system. In addition, a membrane system in the system is periodically flushed by using a permeate liquid to flush pollutants and protect a membrane; and an on-line chemical cleaning system is established, so that long-term, stable and efficient operation of the system can be ensured.
At present, the conventional treatment technology of chromium-containing wastewater in the prior art comprises a chemical precipitation technology, a biological treatment technology and a membrane separation technology, the conventional technology is mainly designed according to a route of standard discharge, and compared with the invention, the invention has the following defects:
(1) the system waste water reuse rate of the conventional technology is 60%, wherein water resources are not fully recycled, and the waste water is discharged after being treated, so that the load of the surrounding environment is increased;
(2) the tolerance of the microorganism to salt in the conventional biochemical treatment technology is poor, the sludge concentration is generally 3000mg/L, and the sludge concentration of the biochemical system in the technology of the invention is 7000-8000 mg/L.
(3) Heavy metal ions are not removed 100%, and environmental pollution still exists;
(4) concentrated water generated by the membrane concentration system needs to be treated again, otherwise, two layers of pollution can be caused;
(5) the conductivity of the reuse water in the conventional technology is 200-300 mu S/cm, and the conductivity of the reuse water in the technology is less than or equal to 50 mu S/cm.
The chromium-containing wastewater treatment method and the treatment system have the beneficial effects that:
(1) according to different reaction conditions of various heavy metal ions, the pretreatment process of the chromium-containing wastewater adopts online monitoring instruments such as pH, ORP and the like, automatically controls a metering pump to quantitatively feed chemicals, adds the chemicals to fully react with the wastewater, and carries out solid-liquid separation treatment by a precisely controlled high-efficiency precipitation system, so that the removal rate of the heavy metal ions can reach 99.99%.
(2) The biochemical process of the chromium-containing wastewater adopts an A/O/MBR process, the system consists of a biochemical tank, a membrane component and a membrane tank, and the activated sludge can be completely retained in the membrane tank, so that various suspended particles, bacteria, organic matters and other pollutants can stay for a long time, the pollutants are fully removed, the quality of effluent is ensured to be excellent, and SS is almost zero. The process has high volume load and strong adaptability to water quality and water quantity, and adopts the domesticated special microorganism with salt tolerance to remove the wastewater with high salt content and hard-to-degrade COD with high efficiency and good denitrification effect.
(3) The concentration process of the chromium-containing wastewater adopts a special membrane concentration technology to concentrate the salt in the wastewater by more than 30 times according to the technology of combining desalination concentration and fine desalination concentration, and the produced water of an advanced treatment system can be directly reused for production. The special membrane concentration technology has the characteristics of high efficiency desalination rate under high flow rate, higher mechanical strength, longer service life, capability of playing a function under lower operation pressure, good chemical stability and high cost performance.
(4) The chromium-containing wastewater evaporative crystallization adopts a German special vapor compression technology, and consists of a distilled water heat exchanger, a concentration evaporator, a crystallizer, a centrifuge and the like, when the evaporator is used for treating wastewater, heat energy required by the wastewater evaporation is provided by vapor condensation and heat energy released when condensed water is cooled, and no latent heat is lost in the operation process, so that the wastewater is evaporated at low temperature and under negative pressure. When the compressor compresses, the pressure and the temperature are increased, and the high enthalpy steam is used as a heat source again to fully recover the heat of the distilled water and the concentrated solution, thereby saving the energy consumption. During evaporation, the evaporation outside the pipe is adopted, so that the efficiency is high and the scale in the pipe is never accumulated.
Drawings
Embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein:
FIG. 1 is a schematic view of a chromium-containing wastewater treatment system according to the present invention.
Detailed Description
The invention is illustrated below with reference to specific examples. It will be understood by those skilled in the art that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention in any way.
The experimental procedures in the following examples are conventional unless otherwise specified. The raw materials and reagent materials used in the following examples are all commercially available products unless otherwise specified.
Firstly, the source analysis of the chromium-containing wastewater pollutants of the invention is as follows: the chromium-containing wastewater is mainly wastewater generated in the working procedures of cleaning a plated part, cleaning a polar plate, passivating zinc and other plated parts, electrolytic polishing of stainless steel, anodizing of aluminum, treating the plated part and the like after a chromium plating process, has a pH of 2-4, and mainly contains pollutants such as hexavalent chromium, trivalent chromium, sulfuric acid, nitric acid, oxides, COD and the like;
secondly, the pretreatment process of the chromium-containing wastewater comprises the following steps: 1. introducing the chromium-containing wastewater into a chromium breaking tank, adding a sulfuric acid solution with the concentration of 10% into the chromium breaking tank to adjust the pH value to 2-3, then adding a 10% sodium sulfite solution until the ORP value is 230-270mv, so that hexavalent chromium is reduced into trivalent chromium, and the reaction time is preferably controlled to be 20-30 min; then introducing the wastewater into a pH adjusting tank, adding sodium hydroxide until the pH is 8-9 to ensure that trivalent chromium forms chromium hydroxide precipitate, and removing harmful metal impurities in the wastewater by utilizing the principle that chromium metal ions form hydroxide precipitate under an alkaline condition; 2. introducing the wastewater into a chemical reaction tank, adding PAC (polyaluminium chloride), adding PAM (polyacrylamide), and stirring for 20-30min to form larger alum floc (0.6-1.0mm) in order to accelerate coagulation reaction, so that precipitation is accelerated, PAC and PAM are added at different time intervals in the flocculation process, the PAC and PAM are in the best reaction time, a flocculation reaction system adopts mechanical stirring, the reaction speed is high, the effect is good, the dosage is small, and the heavy metal removal effect on phosphorus, fluorine and COD (chemical oxygen demand) is high; 3. then introducing a precise control efficient precipitation system; the precise control efficient sedimentation system is formed by sequentially connecting a water distribution system, a sedimentation treatment tank, an inclined pipe, a water outlet weir and a sludge hopper; introducing the treated wastewater into the water distribution system, the sedimentation treatment tank and the inclined pipe in sequence; the supernatant after the treatment enters an effluent weir to obtain pretreated water, and sludge is deposited in a sludge hopper; the precise control efficient precipitation system can increase the precipitation area, shorten the precipitation time and improve the precipitation efficiency.
In order to increase the precipitation area, shorten the precipitation time and improve the precipitation efficiency, the precise precipitation system efficiently precipitates flocs and SS by the functions of hydraulic water distribution, efficient precipitation and the like of the precise control efficient precipitation system, and meanwhile, a steady flow interference device is arranged in the tank to prevent the precipitated particles from being interfered by the steady flow so as to achieve the rapid precipitation effect, the processing capacity of the precise control efficient precipitation system is 3-7 times greater than that of a common precipitation tank, the sludge at the bottom of the tank is discharged into a sludge tank through a static pressure sludge discharge device to be further concentrated and then is pumped into a sludge filter press to be filter-pressed, and sludge cakes are reprocessed according to the properties, about 80 percent of suspended matters and 40-70 percent of oil can be removed, the turbidity of the effluent is less than 30NTU, the COD is reduced by 40-60 percent and;
thirdly, the biochemical treatment process of the chromium-containing wastewater comprises the following steps: the pretreated water sequentially enters an anaerobic tank, an aerobic tank and a membrane bioreactor; removing most of COD, ammonia nitrogen, SS and other substances in the wastewater through biodegradation of the A/O/MBR; the anaerobic process of the invention utilizes the function of anaerobic bacteria under the condition of no dissolved oxygen or under the condition of oxygen deficiency to hydrolyze and acidify organic matters, remove the organic matters in the wastewater, improve the biodegradability of the sewage and be beneficial to the subsequent aerobic treatment process; the aerobic process is that under aerobic condition, organic matter is oxidized and decomposed under the action of aerobic microbe, the concentration of organic matter is reduced, the amount of microbe is increased, the organic matter in sewage is adsorbed on the surface of active sludge and biomembrane and contacts with the surface of microbe cell, small molecular organic matter can enter microbe body through cell wall directly, and large molecular organic matter must be hydrolyzed into small molecular under the action of extracellular enzyme-hydrolase and then taken into cell body by microbe. The organic matter is finally decomposed into CO2And H2O; the membrane bioreactor comprises a hollow fiber membrane component and a membrane pool, wherein the membrane component is placed in the membrane pool, aeration is carried out in the membrane pool, and as the pore diameter of the hollow fiber membrane is smaller than 0.1 micron, zoogloea and free bacteria can be completely retained in the membrane pool, so that mud-water separation is achieved, various suspended particles, bacteria, algae, turbidity and organic matters are effectively removed, and the excellent effluent quality with the effluent suspended matters close to zero is ensured. The efficient interception function of the membrane bioreactor can effectively intercept nitrifying bacteria, so that the nitrification reaction is smoothly carried out, and ammonia nitrogen is effectively removed; meanwhile, macromolecular organic matters which are difficult to degrade can be intercepted, and the retention time of the macromolecular organic matters in the biochemical reaction tank is prolonged, so that the macromolecular organic matters are decomposed to the maximum extent.
Fourthly, the concentration treatment process of the chromium-containing wastewater of the invention comprises the following steps: the biochemical treatment water sequentially passes through a primary nanofiltration system, a primary reverse osmosis system and a secondary reverse osmosis system; in order to realize zero emission of the chromium-containing wastewater, the rear end of the biochemical treatment system is provided with a concentration treatment system for treating strong brine generated by the biochemical treatment system; the concentration treatment system is a process combining multi-stage concentration and nanofiltration/reverse osmosis concentration, and gradually reduces the water amount of the high-salt-content wastewater (the salt content of the obtained high-salt concentrated water is 40-60g/L) through the step-by-step concentration of the membrane, so that the investment and the operating cost of a subsequent evaporative crystallization system are reduced; the concentration treatment process reduces the concentrated brine to be treated in a subsequent evaporation crystallization system by 80 percent compared with a conventional concentration treatment system, reduces the investment cost of the whole wastewater treatment system by 20 to 30 percent, reduces the running cost of wastewater treatment by 30 to 40 percent, and improves the automation degree of the system.
The concentration treatment process of the chromium-containing wastewater is characterized in that the chromium-containing wastewater is pre-concentrated by a primary nanofiltration system, the permeate of the primary nanofiltration system can be used as reuse water after ion exchange, and the concentrated solution of the primary nanofiltration system enters a primary reverse osmosis system; the permeate of the primary reverse osmosis system returns to the primary nanofiltration system, and the concentrated solution of the primary reverse osmosis system enters the secondary reverse osmosis system; and the permeate of the secondary reverse osmosis system returns to the primary nanofiltration system, and the concentrated solution of the secondary reverse osmosis system is the high-salinity concentrated water.
Fifthly, the chromium-containing wastewater evaporation crystallization treatment process comprises the following steps: the high-salinity concentrated water obtained by the concentration treatment process sequentially passes through a heat exchanger, a concentration evaporator and an evaporation crystallizer, wherein the concentration evaporator is formed by sequentially connecting a heating chamber, a separation chamber, a circulating chamber, a liquid distributor and a demister, and the evaporation crystallizer is formed by sequentially connecting a separation chamber, a salt leg, a thickener and a crystallization kettle; and (3) the concentrated high-salt concentrated water passes through an evaporative crystallizer to obtain a crystal substance and condensed water, wherein the crystal substance is sodium sulfate and/or sodium chloride, and the condensed water is used as reuse water.
The process flow of the following embodiment of the invention comprises the following basic treatment flows: electroplating chromium-containing wastewater → pretreatment process → biochemical treatment process → anaerobic tank → aerobic tank → membrane bioreactor → pressurization → first-stage nanofiltration membrane separation → pressurization → first-stage reverse osmosis membrane separation → pressurization → second-stage reverse osmosis membrane separation, and the separated high-salt concentrated water enters an evaporative crystallization system; in the evaporative crystallization system, condensed water generated by treating high-salinity concentrated water by a concentration evaporator can meet the water quality requirement of workshop reuse water.
Example 1
(1) Pretreating chromium-containing wastewater to obtain pretreated water
Firstly, taking chromium-containing wastewater, wherein the chromium-containing wastewater is mainly wastewater generated in the working procedures of cleaning a plated part, cleaning a polar plate, passivating zinc and other plated parts, electrolytic polishing of stainless steel, anodizing aluminum, treating the plated part and the like after a chromium plating process, has a pH of 2-3 and mainly contains pollutants such as hexavalent chromium, trivalent chromium, sulfuric acid, nitric acid, oxides, COD and the like; pumping the chromium-containing wastewater into a chromium breaking tank, adding 10% sulfuric acid into the chromium breaking tank until the pH value is 2-3, and simultaneously adding 10% sodium sulfite solution until the ORP value is 230-270mv, so that hexavalent chromium ions in the wastewater are reduced into trivalent chromium ions, wherein the reaction time is 20 min; then introducing the wastewater into a pH adjusting tank, adding a 10% sodium hydroxide solution, adjusting the pH to 8-9, and enabling trivalent chromium ions in the wastewater to form chromium hydroxide precipitate; and introducing the wastewater into a chemical reaction tank, adding a coagulant PAC and a flocculant PAM, and stirring for 25 min. And then introducing the wastewater into a precise control efficient precipitation system.
(2) Performing biochemical treatment on the pretreated water to obtain biochemical treated water
The pretreated water sequentially enters an anaerobic tank, an aerobic tank and a membrane bioreactor; wherein, the anaerobic pool contains anaerobic bacteria, and the aerobic pool contains aerobic microorganisms; then enters a membrane bioreactor which consists of a hollow fiber membrane (the aperture of the hollow fiber membrane is 0.01-0.1 mu m) component and a membrane pool; the membrane assembly is placed in a membrane tank, aeration is carried out in the membrane tank, the pH value after biochemical treatment is 6-8, and most of substances such as COD, ammonia nitrogen, SS and the like in the wastewater can be removed; the anaerobic process of the invention utilizes the function of anaerobic bacteria under the condition of no dissolved oxygen or under the condition of oxygen deficiency to hydrolyze organic matters,Acidification is carried out to remove organic matters in the wastewater, so that the biodegradability of the wastewater is improved, and the subsequent aerobic treatment process is facilitated; the aerobic process is that under aerobic condition, organic matter is oxidized and decomposed under the action of aerobic microbe, the concentration of organic matter is reduced, the amount of microbe is increased, the organic matter in sewage is adsorbed on the surface of active sludge and biomembrane and contacts with the surface of microbe cell, small molecular organic matter can enter microbe body through cell wall directly, and large molecular organic matter must be hydrolyzed into small molecular under the action of extracellular enzyme-hydrolase and then taken into cell body by microbe. The organic matter is finally decomposed into CO2And H2O; the membrane bioreactor comprises a hollow fiber membrane component and a membrane pool, wherein the membrane component is placed in the membrane pool, aeration is carried out in the membrane pool, and as the pore diameter of the hollow fiber membrane is smaller than 0.1 micron, zoogloea and free bacteria can be completely retained in the membrane pool, so that mud-water separation is achieved, various suspended particles, bacteria, algae, turbidity and organic matters are effectively removed, and the excellent effluent quality with the effluent suspended matters close to zero is ensured. The efficient interception function of the membrane bioreactor can effectively intercept nitrifying bacteria, so that the nitrification reaction is smoothly carried out, and ammonia nitrogen is effectively removed; meanwhile, macromolecular organic matters which are difficult to degrade can be intercepted, and the retention time of the macromolecular organic matters in the biochemical reaction tank is prolonged, so that the macromolecular organic matters are decomposed to the maximum extent.
(3) Concentrating the biochemical treatment water to obtain high-salinity concentrated water and reuse water
The biochemical treatment water sequentially passes through a primary nanofiltration system, a primary reverse osmosis system and a secondary reverse osmosis system; the primary nanofiltration system is formed by sequentially connecting a precision filter and a primary nanofiltration membrane, wherein a filter element of the precision filter is melt-blown PP cotton, and the aperture of the precision microporous filter is 5 mu m; the aperture of the primary nanofiltration membrane is 1nm, when water to be treated passes through the primary nanofiltration membrane, the rejection rate of sodium ions is 50%, and the rejection rate of heavy metal ions and salt is 98%; then passing through a primary nanofiltration system, wherein the pH is 6-8, and the membrane inlet pressure is 1.5 Mpa; the relative molecular mass interception range of the primary nanofiltration system is 300 daltons; the permeate of the primary nanofiltration system can be used as reuse water for continuous use through ion exchange;
the concentrated solution of the treated water passing through the primary nanofiltration system enters a primary reverse osmosis system, the primary reverse osmosis system is formed by sequentially connecting a precision filter and a primary reverse osmosis membrane (a brackish water reverse osmosis membrane with the aperture of 0.1-1nm), the membrane inlet pressure of the primary reverse osmosis system is 1.8Mpa, the pH is adjusted to 5-6 by 0.2% hydrochloric acid, and the rejection rate of heavy metal ions and salt is 99% by the primary reverse osmosis membrane; the permeate of the treated water passing through the primary reverse osmosis system returns to the primary nanofiltration system, and the concentrated solution enters the secondary reverse osmosis system. The secondary reverse osmosis system is formed by sequentially connecting a precision filter and a secondary reverse osmosis membrane (a seawater reverse osmosis membrane with the aperture of 0.1-1 nm); the membrane inlet pressure of the secondary reverse osmosis system is 5Mpa, the pH value is adjusted to 6-8 by 0.2% hydrochloric acid, and the rejection rate of heavy metal ions and salt is 99.9% by the secondary reverse osmosis membrane; the permeate of the treated water passing through the secondary reverse osmosis system returns to the primary nanofiltration system, the concentrated solution is high-salt concentrated water, the salt content of the high-salt concentrated water is 40g/L, in addition, the secondary reverse osmosis system also comprises a security filter, the aperture is 5 mu m, and a filter element is melt-blown PP cotton.
In order to realize zero emission of the chromium-containing wastewater, the rear end of the biochemical treatment system is provided with a concentration treatment system for treating strong brine generated by the biochemical treatment system; the concentration treatment system is a process combining multi-stage concentration and nanofiltration/reverse osmosis concentration, and gradually reduces the water amount of the high-salt-content wastewater (the salt content of the obtained high-salt concentrated water is 40g/L) through the step-by-step concentration of the membrane, so that the investment and the operating cost of a subsequent evaporative crystallization system are reduced; the concentration treatment process reduces the concentrated brine to be treated in a subsequent evaporation crystallization system by 80 percent compared with a conventional concentration treatment system, reduces the investment cost of the whole wastewater treatment system by 30 percent, reduces the running cost of wastewater treatment by 40 percent, and improves the automation degree of the system. The concentration treatment process of the chromium-containing wastewater is characterized in that the chromium-containing wastewater is pre-concentrated by a precision filter and a primary nanofiltration system, the permeate of the primary nanofiltration system can be used as reuse water after ion exchange, and the concentrated solution of the primary nanofiltration system enters a primary reverse osmosis system; the permeate of the primary reverse osmosis system returns to the primary nanofiltration system, and the concentrated solution of the primary reverse osmosis system enters the secondary reverse osmosis system; and the permeate of the secondary reverse osmosis system returns to the primary nanofiltration system, and the concentrated solution of the secondary reverse osmosis system is the high-salinity concentrated water.
(4) Carrying out evaporation crystallization treatment on the high-salinity concentrated water to obtain recycled water and crystals
Sequentially passing the high-salinity concentrated water through a heat exchanger, a concentration evaporator and an evaporation crystallizer; the operating temperature of the heat exchanger is 80-100 ℃; the operating pressure of the heat exchanger is 0.05-0.1 MPa; the concentration evaporator is formed by sequentially connecting a heating chamber, a separation chamber, a circulating chamber, a liquid distributor and a demister; the evaporative crystallizer is formed by sequentially connecting a separation chamber, salt legs, a thickener and a crystallization kettle; the condensed water of the high-salinity concentrated water after passing through the concentration evaporator returns to the secondary reverse osmosis system; the concentrated solution obtained after the high-salt concentrated water passes through a concentration evaporator is concentrated high-salt concentrated water, and the salt content is 40-60 g/L; the concentrated high-salinity concentrated water passes through an evaporative crystallizer to obtain a crystal and condensed water; the obtained crystal is sodium sulfate and/or sodium chloride; and the condensed water is returned to the workshop as reuse water for continuous use.
Wherein, the concentration evaporator is composed of a plurality of evaporators connected in series, low-temperature (about 90 ℃) heating steam is introduced into the first effect to heat feed liquid therein, so that the feed liquid generates almost equivalent evaporation with the temperature lower than that of the steam. The steam produced is introduced into the second effect as heating steam, causing the feed liquid of the second effect to evaporate at a lower temperature than the first effect. This process is repeated until the final effect. The first effect condensate water returns to the heat source, other effect condensate water is collected and then output as desalted water, and one part of steam is input and can evaporate multiple times of water to be output. Meanwhile, the feed liquid is sequentially concentrated from the first effect to the last effect, and the feed liquid is supersaturated at the last effect and crystallized and separated out. Thereby realizing the solid-liquid separation of the feed liquid.
The technical parameters of the evaporative crystallization system for treating concentrated water are as follows:
(1) the desalted water has a salt content (TDS) of less than 10ppm
(2) Consumption of steam for desalting per ton is (1/effect number)/90% t/t
(3) The electric power consumption of the desalinated water is 2-4 kwh/t
Compared with the prior art, the method for treating the chromium-containing wastewater improves the reuse rate of the wastewater to 99.67 percent, can greatly reduce the treatment cost, reduce the generation amount of solid waste and the resource of metal ions in the wastewater, and thoroughly realizes the zero discharge of the wastewater.
Comparative example 1
(1) Firstly, taking chromium-containing wastewater, wherein the chromium-containing wastewater is mainly wastewater generated in the working procedures of cleaning a plated part, cleaning a polar plate, passivating zinc and other plated parts, electrolytic polishing of stainless steel, anodizing aluminum, treating the plated part and the like after a chromium plating process, has a pH of 2-3 and mainly contains pollutants such as hexavalent chromium, trivalent chromium, sulfuric acid, nitric acid, oxides, COD and the like; pumping the chromium-containing wastewater into a chromium breaking tank, adding 10% of sulfuric acid and 10% of sodium sulfite into the chromium breaking tank to reduce hexavalent chromium ions in the wastewater into trivalent chromium ions, wherein the reaction time is 20-25 min; and introducing the wastewater into a chemical reaction tank, adding a coagulant PAC and a flocculant PAM, and stirring for 25 min. And introducing the wastewater into a precipitation system for mud-water separation, introducing the sludge into a sludge treatment system, and introducing the supernatant into a biochemical system.
(2) The pretreated water sequentially enters an anaerobic tank, an aerobic tank and a biochemical sedimentation tank; wherein, the anaerobic pool contains anaerobic bacteria, and the aerobic pool contains aerobic microorganisms; then enters a biochemical sedimentation tank, and the biochemical sedimentation tank consists of a water distribution area, a sludge area, a separation area and a water outlet weir; the SS of the effluent of the biochemical sedimentation tank is 30mg/L, the COD is 50mg/L, 40 percent of the effluent of the biochemical sedimentation tank reaches the standard and is discharged, and 60 percent of the effluent enters a membrane concentration system.
(3) The effluent after biochemical treatment sequentially passes through a precision filter and a reverse osmosis membrane device; wherein the filter element of the precise filter is PP cotton, and the aperture of the precise microporous filter is 5 mu m; the membrane inlet pressure of the reverse osmosis system is 1.2-1.6Mpa, the pH value is adjusted to 5-6 by hydrochloric acid, and the rejection rate of heavy metal ions and salt is 99% by the reverse osmosis membrane; the concentrated solution of the reverse osmosis membrane returns to the pretreatment system for treatment, the conductivity of the permeate of the reverse osmosis membrane is 200 and 300 mu S/cm, which accounts for about 60 percent of the total wastewater, and the permeate is recycled to the production line as reuse water.
In conclusion, the above description of the embodiments of the present invention is not intended to limit the present invention, and those skilled in the art can make various changes or modifications according to the present invention without departing from the spirit of the present invention, which falls within the scope of the appended claims.
Claims (20)
1. The method for treating the chromium-containing wastewater is characterized by comprising the following steps in sequence:
(1) pretreating chromium-containing wastewater to obtain pretreated water;
(2) performing biochemical treatment on the pretreated water obtained in the step (1) to obtain biochemical treated water;
(3) concentrating the biochemical treatment water obtained in the step (2) to obtain concentrated high-salinity concentrated water and reuse water;
(4) carrying out evaporation crystallization treatment on the concentrated high-salinity concentrated water obtained in the step (3) to obtain recycled water and crystals;
wherein, in the step (1), the pretreatment step is:
(1-1) introducing the chromium-containing wastewater into a chromium breaking tank, adding 10% sulfuric acid into the chromium breaking tank until the pH value is 2-3, then adding 10% sodium sulfite into the chromium breaking tank until the ORP value is 230-270mv, and carrying out chromium breaking reaction for 20-30 min;
(1-2) introducing the wastewater treated in the step (1-1) into a pH adjusting tank, and adding 10% sodium hydroxide until the pH is 8-9;
(1-3) introducing the wastewater treated in the step (1-2) into a chemical reaction tank, adding PAC, adding PAM after 20-40min, and stirring for 20-30 min;
(1-4) introducing the wastewater treated in the step (1-3) into a precise control efficient precipitation system, wherein the precise control efficient precipitation system is formed by sequentially connecting a water distribution system, a precipitation treatment tank, an inclined pipe, a water outlet weir and a sludge hopper; introducing the wastewater treated in the step (1-3) into the water distribution system, the sedimentation treatment tank and the inclined pipe in sequence; the supernatant after the treatment enters an effluent weir to obtain pretreated water, and the obtained sludge is deposited in a sludge hopper; the pressure of the sedimentation treatment tank is 2-3 Mpa;
in the step (2), the biochemical treatment step is: sequentially feeding the pretreated water obtained in the step (1) into an anaerobic tank, an aerobic tank and a membrane bioreactor;
the membrane bioreactor consists of a hollow fiber membrane component and a membrane pool; the hollow fiber membrane module is positioned in the membrane pool; the aperture of the hollow fiber membrane is 0.01-0.1 μm;
in the step (3), the concentration treatment step is: sequentially passing the biochemical treatment water obtained in the step (2) through a primary nanofiltration system, a primary reverse osmosis system and a secondary reverse osmosis system;
the primary nanofiltration system is formed by sequentially connecting a precision filter and a primary nanofiltration membrane, wherein a filter element of the precision filter is melt-blown PP cotton, and the primary nanofiltration membrane is an industrial-grade high-desalination-rate nanofiltration membrane; the aperture of a filter element of the precise microporous filter is 5 mu m, and the aperture of the primary nanofiltration membrane is 1-2 nm; the membrane inlet pressure of the primary nanofiltration system is 1.0-1.5 Mpa; the permeate of the primary nanofiltration system is used as reuse water, and the concentrated solution of the primary nanofiltration system enters a primary reverse osmosis system;
the first-stage reverse osmosis system is formed by sequentially connecting a precision filter and a first-stage reverse osmosis membrane; the filter element of the precision filter is melt-blown PP cotton; the first-stage reverse osmosis membrane is a brackish water reverse osmosis membrane; the aperture of the filter element of the precise microporous filter is 5 mu m; the aperture of the first-stage reverse osmosis membrane is 0.1-1 nm; the membrane inlet pressure of the primary reverse osmosis system is 1.8 Mpa; the pH value of the water entering the first-stage reverse osmosis system is 5-6; the permeate of the first-stage reverse osmosis system returns to the first-stage nanofiltration system; the concentrated solution of the first-stage reverse osmosis system enters a second-stage reverse osmosis system;
the secondary reverse osmosis system is formed by sequentially connecting a precision filter and a secondary reverse osmosis membrane; the filter element of the precision filter is melt-blown PP cotton; the secondary reverse osmosis membrane is a seawater reverse osmosis membrane; the aperture of the filter element of the precise microporous filter is 5 mu m; the aperture of the secondary reverse osmosis membrane is 0.1-1 nm; the membrane inlet pressure of the secondary reverse osmosis system is 4-5 Mpa; the pH value of the water entering the secondary reverse osmosis system is 6-8; the permeate of the secondary reverse osmosis system returns to the primary nanofiltration system;
in the step (4), the evaporative crystallization treatment step is: sequentially passing the high-salinity concentrated water obtained in the step (3) through a heat exchanger, a concentration evaporator and an evaporation crystallizer; wherein,
the operating temperature of the heat exchanger is 80-100 ℃;
the operating pressure of the heat exchanger is 0.05-0.1 MPa;
the concentration evaporator is formed by sequentially connecting a heating chamber, a separation chamber, a circulating chamber, a liquid distributor and a demister;
the evaporative crystallizer is formed by sequentially connecting a separation chamber, salt legs, a thickener and a crystallization kettle;
the condensed water of the high-salinity concentrated water after passing through the concentration evaporator returns to the secondary reverse osmosis system;
the high-salinity concentrated water passes through a concentration evaporator to obtain concentrated high-salinity concentrated water;
the salt content of the concentrated high-salt concentrated water is 30-35%;
the concentrated high-salinity concentrated water passes through an evaporative crystallizer to obtain a crystal and condensed water; the crystal is sodium sulfate and/or sodium chloride; the condensed water is used as reuse water;
wherein the standard of the recycled water is as follows: pH 6-8, conductivity less than or equal to 50, COD less than or equal to 30 and turbidity less than or equal to 1.
2. The treatment method according to claim 1, wherein in the step (1), the chromium-containing wastewater has a pH of 4 to 6 and contains hexavalent chromium, trivalent chromium, sulfuric acid, nitric acid, oxides and COD.
3. The treatment method according to claim 1, wherein the pH of the wastewater treated in the steps (1-3) is 8-9.
4. The treatment method as claimed in claim 1, wherein the ORP value of the wastewater treated by the steps (1-3) is 230-270 mv.
5. The process of claim 1, wherein in step (2), the anaerobic pond contains anaerobic bacteria.
6. The process of claim 5, wherein the anaerobic bacteria are selected from one or more of yeast, nitrate bacteria, clostridia or bacteroides.
7. The process of claim 6, wherein the yeast, nitrate-producing bacteria, clostridia or bacteroides are acclimatized to be salt tolerant.
8. The treatment method as claimed in claim 1, wherein in the step (2), the aerobic tank contains aerobic microorganisms.
9. The process of claim 8, wherein the aerobic microorganisms are selected from one or more of bacillus, rhizobia, nitrobacteria or mold.
10. The method of claim 9, wherein the bacillus, rhizobium, nitrifier or mold is acclimated to provide salt tolerance.
11. The treatment method according to claim 1, wherein the post-biochemical treatment has a pH of 6 to 8.
12. The treatment method as claimed in claim 1, wherein the rejection rate of the primary nanofiltration membrane on sodium ions is 50-70%; the rejection rate of the first-stage nanofiltration membrane on heavy metal ions and salts is more than 97%.
13. The process as claimed in claim 1, wherein the relative molecular mass cut-off of the primary nanofiltration system is in the range of 150-300 daltons.
14. The process of claim 1, wherein the water entering the primary nanofiltration system has a pH of 6 to 8.
15. The process of claim 1 wherein the primary reverse osmosis membrane has a rejection rate of > 98% for heavy metal ions and salts.
16. The process of claim 1 wherein the primary reverse osmosis system is adjusted to pH by the addition of 0.2 to 0.5% hydrochloric acid.
17. The process of claim 1 wherein the secondary reverse osmosis membrane has a rejection rate of > 99.5% for heavy metal ions and salts.
18. The process of claim 1 wherein the pH is adjusted in the secondary reverse osmosis system by adding hydrochloric acid at a concentration of 0.2 to 0.5%.
19. A treatment system for implementing the chromium-containing wastewater treatment method according to any one of claims 1 to 18, wherein the system comprises a pretreatment unit, a biochemical treatment unit, a concentration treatment unit and an evaporative crystallization treatment unit which are communicated in sequence; the pretreatment unit comprises a chromium breaking tank, a pH adjusting tank, a chemical reaction tank and a precise control efficient precipitation system which are sequentially communicated; the precise control efficient sedimentation system is formed by sequentially connecting a water distribution system, a sedimentation treatment tank, an inclined pipe, a water outlet weir and a sludge hopper;
the biochemical treatment unit comprises an anaerobic tank, an aerobic tank and a membrane bioreactor which are communicated in sequence; the membrane bioreactor consists of a hollow fiber membrane component and a membrane pool; the hollow fiber membrane module is positioned in the membrane pool; the aperture of the hollow fiber membrane is 0.01-0.1 μm;
the concentration treatment unit comprises a primary nanofiltration system, a primary reverse osmosis system and a secondary reverse osmosis system which are sequentially communicated; the primary nanofiltration system is formed by sequentially connecting a precision filter and a primary nanofiltration membrane; the filter element of the precision filter is melt-blown PP cotton; the primary nanofiltration membrane is an industrial grade high-desalination-rate nanofiltration membrane; the aperture of the filter element of the precision filter is 5 mu m; the aperture of the primary nanofiltration membrane is 1-2 nm;
the first-stage reverse osmosis system is formed by sequentially connecting a precision filter and a first-stage reverse osmosis membrane; the filter element of the precision filter is melt-blown PP cotton; the first-stage reverse osmosis membrane is a brackish water reverse osmosis membrane; the aperture of the filter element of the precision filter is 5 mu m; the aperture of the first-stage reverse osmosis membrane is 0.1-1 nm;
the secondary reverse osmosis system is formed by sequentially connecting a precision filter and a secondary reverse osmosis membrane; the filter element of the precision filter is melt-blown PP cotton; the secondary reverse osmosis membrane is a seawater reverse osmosis membrane; the aperture of the filter element of the precision filter is 5 mu m; the aperture of the secondary reverse osmosis membrane is 0.1-1 nm;
the evaporative crystallization unit comprises a heat exchanger, a concentration evaporator and an evaporative crystallizer which are sequentially communicated; the concentration evaporator is formed by sequentially connecting a heating chamber, a separation chamber, a circulating chamber, a liquid distributor and a demister; the evaporative crystallizer is formed by sequentially connecting a separation chamber, a salt leg, a thickener and a crystallization kettle.
20. Use of a treatment method according to any one of claims 1 to 18 or a treatment system according to claim 19 in the treatment of chromium-containing wastewater.
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| CN109607908A (en) * | 2018-11-13 | 2019-04-12 | 长沙埃比林环保科技有限公司 | A kind of processing method of chromate waste water |
| CN109574353A (en) * | 2018-12-17 | 2019-04-05 | 佛山市诚德新材料有限公司 | A kind of recovery method of chromium stainless steel waste water |
| CN111115661B (en) * | 2020-01-13 | 2023-02-28 | 中国神华煤制油化工有限公司 | Nitric acid wastewater treatment system and method |
| CN112979059A (en) * | 2021-02-03 | 2021-06-18 | 浙江新寰科环保科技股份有限公司 | Device for reducing COD (chemical oxygen demand) of electroplating wastewater |
| CN113548757A (en) * | 2021-08-24 | 2021-10-26 | 山东建筑大学 | Zero-discharge treatment process for chromium-containing wastewater |
| CN115432890B (en) * | 2022-09-21 | 2024-01-23 | 无锡市道格环保科技有限公司 | Treatment device and method for reducing pollutant emission in chromium-containing metal ion wastewater |
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