Stainless steel industrial wastewater reclaimed water reuse and concentrated water crystallization device and method

Abstract

The invention discloses a stainless steel industrial wastewater reclaimed water reuse and concentrated water crystallization device and method, and the method comprises the following steps: stainless steel pickling wastewater and oil-containing wastewater are respectively pretreated and then enter a water distribution tank, then sequentially enter a two-stage denitrification reactor, an aerobic tank and a secondary sedimentation tank for treatment, and then enter a reclaimed water reuse system; and after being treated by UF + RO + ROR + MVR, the wastewater enters a reclaimed water recycling pool. According to the invention, wastewater source diversion, segmented treatment and sludge classified recovery processes are adopted, different pretreatment processes and targeted agent addition are respectively designed, the agent dosage and the sludge yield can be synchronously reduced, biochemical treatment and a reclaimed water recycling system are combined, the reclaimed water recycling rate is increased to 95-98%, and meanwhile, the system sludge is classified, collected and dehydrated; various pollutants in the wastewater can be completely and comprehensively removed, the stable treatment effect is guaranteed, the daily operation cost can be greatly reduced due to the high and medium water recycling rate, and resource utilization of the wastewater / sludge is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a device and method for recycling wastewater from stainless steel industry wastewater and crystallizing concentrated water. Background Art

[0002] Stainless steel has good corrosion resistance, durability, high temperature resistance and low temperature resistance, as well as excellent processing performance and impact resistance. It is easy to recycle and the output of stainless steel is rising steadily. It has been widely used in industrial and civil fields such as construction, petrochemicals, and automobiles, and has broad application prospects. However, the disposal of pickling wastewater and oily wastewater generated in the production process of the stainless steel industry is also a major difficulty.

[0003] After various mechanical processes, a thin and dense oxide film will form on the surface of stainless steel. Its main components contain a large amount of chromium oxide (Cr2O3), nickel oxide (NiO), and insoluble iron oxide (FeO·Cr2O3). This oxide film needs to be completely removed by surface treatment such as pickling. Pickling 1 ton of stainless steel will produce 1 to 3 m 3 Stainless steel pickling wastewater, a large amount of stainless steel pickling wastewater is discharged into the water body, and the components in it will cause harm to the environment or human health, and must be harmlessly treated. Stainless steel surface treatment is mainly pickling. Since Cr2O3 is difficult to dissolve in a single acid, pickling usually uses a mixed acid of nitric acid, sulfuric acid and hydrofluoric acid.

[0004] Pickling is divided into pre-pickling and final pickling. Pre-pickling is to remove or partially remove the oxide scale on the surface of stainless steel according to the degree of oxidation, and final pickling is to remove the residual oxide and chromium deposits. Wastewater mainly comes from processes such as stainless steel pickling and post-degreasing rinsing. It contains a large amount of iron ions, chromium ions, nickel ions, fluorides and nitrides, and its composition is very complex. At present, the main bottleneck restricting the upgrading and continuous growth of the stainless steel industry is the wastewater generated in its production process. The wastewater is highly acidic (pH value is 1-2), high in total nitrogen (more than 3000 mg / L), highly toxic (containing toxic pollutants such as nickel, chromium, and fluorine), and has a large output (about 1-3m 3 / t), difficult to handle, etc.

[0005] Stainless steel pickling wastewater contains Cr 6+ Cr 3+ The acidic wastewater contains a lot of COD, TN, petroleum and other pollutants. Therefore, it is of great significance to research and develop a reclaimed water reuse device for wastewater treatment of stainless steel industry wastewater. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a device and method for recycling the middle water and crystallizing the concentrated water of stainless steel industrial wastewater. Pickling wastewater and oily wastewater in the stainless steel industrial wastewater are classified, collected and treated, and a step-by-step sedimentation method is adopted. According to the different precipitation conditions of various metal and other pollutants, the treatment efficiency is improved, the sludge output and the treatment cost are reduced; a two-stage denitrification reactor and an aerobic tank are combined in the biochemical treatment stage to reduce the addition of carbon source, improve the denitrification efficiency and the biochemical treatment efficiency of organic matter; the recycling rate of the middle water recycling system is high, and the crystals and waste residues are small; various pollutants in the wastewater are completely and comprehensively removed with a stable treatment effect, and the high recycling rate of the middle water can greatly reduce the daily operation cost, and realize the resource utilization of wastewater / sludge.

[0007] In order to solve the above technical problems, the present invention provides a method for recycling wastewater from stainless steel industry wastewater and crystallizing concentrated water, wherein the stainless steel industry wastewater includes stainless steel pickling wastewater and oily wastewater, and comprises the following steps:

[0008] S1. The stainless steel pickling wastewater is collected in the pickling wastewater regulating tank and then enters the two-stage coagulation and sedimentation pretreatment system to remove organic matter, SS (suspended matter) and heavy metal ions in the wastewater, specifically:

[0009] a1. The stainless steel pickling wastewater enters the primary reaction tank, and firstly, ammonium bisulfite is added to reduce the highly toxic hexavalent chromium to trivalent chromium, and then lime milk is added to make the metal ions including trivalent chromium, trivalent iron and divalent nickel generate hydroxide precipitation, and fluoride generates calcium fluoride precipitation, and finally PAC (polyaluminium chloride) and PAM (polyacrylamide) are added for flocculation;

[0010] a2. The effluent from the primary reaction tank enters the primary sedimentation tank for sedimentation and sludge-water separation;

[0011] a3, the effluent from the primary sedimentation tank enters the secondary reaction tank, and heavy catching agent, lime milk, PAC and PAM are added for further flocculation;

[0012] a4. The effluent from the secondary reaction tank enters the secondary sedimentation tank for further sedimentation and mud-water separation;

[0013] The oily wastewater is collected in the oily wastewater regulating tank and then enters the coagulation sedimentation + flotation pretreatment system to remove grease and SS in the wastewater. Specifically:

[0014] b1. The oily wastewater enters the pretreatment reaction tank I, and lime milk, demulsifier, PAC and PAM are added to flocculate organic matter, colloidal matter and suspended matter;

[0015] b2. The effluent from the pretreatment reaction tank I enters the pretreatment sedimentation tank I for sedimentation and sludge-water separation;

[0016] b3, the effluent from the pretreatment sedimentation tank I enters the pretreatment reaction tank II, and PAC and PAM are added for further flocculation;

[0017] b4. The effluent from the pretreatment reaction pool II enters the flotation pool. Air is introduced into the wastewater and precipitated from the water in the form of tiny bubbles to become carriers, so that pollutants such as emulsified oil and tiny suspended particles in the wastewater adhere to the bubbles and float to the water surface with the bubbles to form foam (a three-phase mixture of air, water, and particles (oil)). The purpose of separating impurities and purifying wastewater is achieved by collecting foam or scum, and the concentration of emulsified oil and suspended matter is further reduced;

[0018] S2. The effluent from the secondary sedimentation tank and the flotation tank is mixed in the water distribution tank and then enters the biochemical treatment stage, specifically:

[0019] S21, the effluent from the water distribution tank enters a two-stage denitrification reactor, and utilizes the hydrolysis, acidification, and denitrification of anaerobic microorganisms to decompose the refractory organic matter into easily degradable organic matter, decompose the macromolecular organic matter into small molecular organic matter, increase the BOD (biochemical oxygen demand) / COD (chemical oxygen demand) ratio, and reduce nitrate into nitrogen gas at the same time;

[0020] S22, the effluent from the two-stage denitrification reactor enters the aerobic tank to remove NH3-N and BOD5 (biochemical oxygen demand in five days) in the wastewater;

[0021] S23, the effluent from the aerobic pool enters the secondary sedimentation tank for mud-water separation and then enters the biochemical effluent pool;

[0022] S3, the effluent from the biochemical effluent pool enters the reclaimed water reuse system, specifically:

[0023] The effluent from the biochemical effluent pool passes through a filtration device, an ultrafiltration (UF) device, and a reverse osmosis device in sequence, and after intercepting inorganic ions, colloid substances, and macromolecular solutes in the water, the effluent enters a reclaimed water reuse pool.

[0024] Furthermore, the reverse osmosis device includes RO (reverse osmosis module) and ROR (concentrated water reverse osmosis module). RO produces 50%-60% fresh water which enters the reclaimed water reuse pool, the concentrated water produced enters the ROR for further concentration treatment, and the fresh water produced by the ROR enters the reclaimed water reuse pool to increase the reuse rate of water.

[0025] Furthermore, in a1, the primary reaction tank comprises a first cell, a second cell, a third cell and a fourth cell connected in sequence, the first cell is added with alkali to adjust the pH to 4.3-5.6, and 0.2 kg / m 3 ~0.28kg / m 3 ammonium bisulfite, the second compartment adds lime milk to a pH of 7.2-9.0, and the third compartment adds 0.15kg / m 3~0.2kg / m 3 PAC, the fourth grid is added with 0.005kg / m 3 ~0.008kg / m 3 For PAM, the stirring intensity from the first to the third grid is 68r / min, and the stirring intensity of the fourth grid is 40r / min.

[0026] Wherein, the chemical reaction formula of the first cell of the primary reaction tank is:

[0027] Cr2O7 2- +3HSO3 - +5H +→ 2Cr 3+ +3SO4 2- +4H2O;

[0028] The chemical reaction formula of the second cell of the primary reaction tank includes:

[0029] Ca 2+ +2F - =CaF2↓;

[0030] Ni 2+ +2OH - =Ni(OH)2↓;

[0031] Fe 3+ +3OH - =Fe(OH)3↓;

[0032] Cr 3+ +3OH - =Cr(OH)3↓;

[0033] Mn + +nOH - =Mn(OH)n↓.

[0034] Further, in a3, the secondary reaction tank comprises a first cell, a second cell, a third cell and a fourth cell connected in sequence, and the first cell is dosed with 0.1 kg / m 3 ~0.15kg / m 3 The second compartment adds lime milk to a pH of 6.5 to 8.0, and the third compartment adds 0.1 kg / m 3 ~0.15kg / m 3 PAC, the fourth grid is added with 0.002kg / m 3 ~0.005kg / m 3 For PAM, the stirring intensity from the first to the third grid is 68r / min, and the stirring intensity of the fourth grid is 40r / min.

[0035] Furthermore, the surface load of the primary sedimentation tank and the secondary sedimentation tank is 0.7 to 1.0 m 3 / ㎡·h, the sludge from the primary sedimentation tank and the secondary sedimentation tank enters the physicochemical sludge tank, is filtered by the plate and frame filter press, and then transported out for disposal, and the filtrate is returned to the water distribution tank.

[0036] Furthermore, in b1, the pretreatment reaction tank I includes a first cell, a second cell, a third cell and a fourth cell connected in sequence, the first cell is added with lime milk to adjust the pH to 10-11, the second cell is added with 0.2 kg / m 3 ~0.3kg / m 3 The third grid is dosing 0.15kg / m 3 ~0.2kg / m 3 PAC, the fourth grid is added with 0.005kg / m 3 ~0.008kg / m 3 PAM.

[0037] Further, in b3, the pretreatment reaction tank II includes a first grid and a second grid connected in sequence, and the first grid is dosed with 0.1 kg / m 3 ~0.15kg / m 3 PAC, the second grid is added with 0.002kg / m 3 ~0.005kg / m 3 PAM.

[0038] Furthermore, the sludge from the pre-treatment sedimentation tank I and the flotation tank enters the oily sludge tank, is dehydrated by the screw press dehydrator and then transported out for treatment, and the filtrate is returned to the water distribution tank.

[0039] Furthermore, corresponding accident pools are set up for the pickling wastewater and oily wastewater. When encountering abnormal situations, the wastewater enters the accident pool for buffering and is then pumped into the normal treatment process for treatment.

[0040] Furthermore, in S2, the temperature of the two-stage denitrification reactor is 35±2°C, and the residence time is 2 to 2.5 days; a biological composite filler is configured inside the two-stage denitrification reactor to fix the microorganisms, thereby increasing the solid residence time and making the reaction more thorough;

[0041] And / or, the two-stage denitrification reactor is provided with a circulation pump to return the wastewater from the upper part of the reactor to the bottom of the reactor, thereby reducing the shock load of the inlet water, making the water quality and quantity uniform, and increasing the contact time between the wastewater and the sludge.

[0042] Further, in S2, the solvent load of the aerobic tank is 0.3-0.5 kgCOD / m 3 d. The nitrified liquid in the aerobic pool is refluxed to the secondary denitrification reactor, and the reflux rate is 0.5-1.0 times of the influent rate;

[0043] And / or, the surface load of the secondary sedimentation tank is 0.6-0.7m 3 / ㎡·h, the residence time is 2 to 3 hours, which should not be too long to avoid nitrification and affect the effluent quality. Part of the sludge settled in the secondary sedimentation tank is returned to the secondary denitrification reactor and the aerobic tank, and part of it enters the biochemical sludge tank. After being treated by the plate and frame filter press, it is transported out for treatment, and the filtrate is returned to the water distribution tank.

[0044] The two-stage denitrification reactor uses the nitrite and nitrate carried by the wastewater itself and the nitrification liquid refluxed from the aerobic pool. In an anaerobic environment (DO<0.5mg / L), denitrification reduces nitrate to nitrogen gas and decomposes macromolecular organic matter into small molecular substances, thereby improving the subsequent aerobic removal efficiency. This process is completed by denitrifying bacteria. The reaction formula includes:

[0045] NO3 - →NO2 - →NO→N2O→N2;

[0046] NO3 - +5[H](organic electron donor)→1 / 2N2+2H2O+0H;

[0047] NO2 - +3[H](organic electron donor)→1 / 2N2+H2O+0H;

[0048] [H] is a substance that can provide electrons and reduce NOx-N to nitrogen, including organic matter, sulfide, etc. The bacteria that carry out this type of reaction mainly include facultative bacteria such as Proteus, Micrococcus, Pseudomonas, Bacillus, Alcaligenes, and Flavobacterium, which are widely present in nature. When molecular oxygen is present, O2 acts as the final electron acceptor to oxidize organic matter and perform respiration; when molecular oxygen is not present, NOx-N is used for respiration. This conversion between molecular oxygen and NOx-N is easy to carry out, and even frequent exchange will not inhibit the progress of denitrification. The nitrogen element in the wastewater is mainly brought in by nitric acid in the stainless steel pickling liquid, which is nitrate nitrogen. Therefore, the denitrification reaction can be directly carried out in the form of an external carbon source.

[0049] Furthermore, in S3, the ROR module of the reverse osmosis device further concentrates to produce 30%-40% concentrated water which enters the MVR device for evaporation, and the generated condensed water enters the reclaimed water reuse pool. The MVR device adopts a central tube circulation MVR evaporator device to directly solidify the generated concentrated liquid, avoiding the system load caused by the mother liquor reflux. The MVR evaporator is equipped with CIP automatic cleaning as standard, which can prevent scaling in a timely and effective manner, and the scraper dryer continuously self-cleans the inner surface of the cylinder due to the action of the spring scraper, so it will never scale.

[0050] The RO module, ROR module and MVR device of the method of the present invention output fresh water to the reclaimed water reuse pool, and the reclaimed water utilization rate is increased from the traditional 60-70% to 95-98%.

[0051] The second aspect of the present invention provides a device for recycling water and crystallizing concentrated water from stainless steel industrial wastewater, which is used to implement the method described in the first aspect, comprising: a pickling wastewater regulating tank and an oily wastewater regulating tank, wherein the pickling wastewater regulating tank is connected to a two-stage coagulation and sedimentation pretreatment system, and the oily wastewater regulating tank is connected to a coagulation and sedimentation + flotation pretreatment system, and both the two-stage coagulation and sedimentation pretreatment system and the coagulation and sedimentation + flotation pretreatment system are connected to a water distribution tank;

[0052] The outlet direction of the water distribution tank also includes a two-stage denitrification reactor, an aerobic tank, a secondary sedimentation tank, a filtration device, an ultrafiltration device, a reverse osmosis device and a reclaimed water reuse tank connected in sequence;

[0053] The concentrated water outlet of the reverse osmosis device is connected to the MVR device, and the condensed water outlet of the MVR device is connected to the reclaimed water reuse pool.

[0054] Furthermore, the filtering device comprises a sand filter tank, an activated carbon filter tank and a resin softening tank which are connected in sequence.

[0055] Beneficial effects of the present invention:

[0056] In view of the different types and amounts of pollutants in the pickling wastewater and oily wastewater of the stainless steel industry, the present invention adopts wastewater source diversion, segmented treatment and sludge classification and recovery processes, designs different pretreatment processes respectively, and adds chemicals in a targeted manner. The pretreatment is designed as a multi-stage process, which can achieve a simultaneous reduction in the amount of chemicals and the sludge output.

[0057] The biochemical treatment process of the present invention adopts a two-stage denitrification reactor with combined fillers combined with an aerobic tank to reduce the addition of carbon sources, improve denitrification efficiency and aerobic biochemical treatment efficiency of organic matter, and reduce biochemical sludge production.

[0058] The present invention combines the UF+RO+ROR+MVR processes in the reclaimed water reuse system, greatly improving the reclaimed water reuse rate to 95%-98%, compensating for the daily operation costs of the wastewater station, and reducing the cost of transporting and disposing of crystals / waste residues.

[0059] This patented device and method can not only completely and comprehensively remove various pollutants in wastewater and ensure its stable treatment effect, but also the high and medium water reuse rate can greatly reduce daily operating costs and realize the resource utilization of wastewater / sludge. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0061] Figure 1 The invention relates to a device and method for recycling wastewater from stainless steel industry and crystallizing concentrated water. DETAILED DESCRIPTION

[0062] The technical solution of the present invention will be described clearly and completely below in conjunction with the specific embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0063] Reference Figure 1 As shown, this embodiment relates to a method for recycling wastewater from stainless steel industry and crystallizing concentrated water. The process flow chart is as follows Figure 1 As shown, the specific processing process is:

[0064] (1) The stainless steel pickling wastewater is collected in the pickling wastewater regulating tank and then enters the two-stage coagulation and sedimentation pretreatment system to remove organic matter, SS (suspended solids) and heavy metal ions in the wastewater, specifically:

[0065] a1. The stainless steel pickling wastewater enters the primary reaction tank, which includes the first cell, the second cell, the third cell and the fourth cell connected in sequence. The first cell is added with alkali to adjust the pH to 5, and 0.25 kg / m 3 ammonium bisulfite, the second compartment adds lime milk to a pH of 8, and the third compartment adds 0.15 kg / m 3 PAC, the fourth grid is added with 0.008kg / m 3 For PAM, the stirring intensity from the first to the third grid is 68r / min, and the stirring intensity of the fourth grid is 40r / min;

[0066] a2. The effluent from the primary reaction tank enters the primary sedimentation tank for sedimentation and sludge-water separation;

[0067] a3. The effluent from the primary sedimentation tank enters the secondary reaction tank, which includes the first grid, the second grid, the third grid and the fourth grid connected in sequence. The first grid is dosed with 0.12 kg / m 3 The second compartment adds lime milk to a pH of 7.0, and the third compartment adds 0.12 kg / m 3PAC, the fourth grid is added with 0.003kg / m 3 For PAM, the stirring intensity from the first to the third grid is 68r / min, and the stirring intensity of the fourth grid is 40r / min;

[0068] a4. The effluent from the secondary reaction tank enters the secondary sedimentation tank for further sedimentation and mud-water separation;

[0069] The oily wastewater is collected in the oily wastewater regulating tank and then enters the coagulation sedimentation + flotation pretreatment system to remove grease and SS in the wastewater. Specifically:

[0070] b1. The oily wastewater enters the pretreatment reaction tank I, which includes the first cell, the second cell, the third cell and the fourth cell connected in sequence. Lime milk is added to the first cell to adjust the pH to 10.5, and 0.25 kg / m 3 The third grid is dosing 0.18kg / m 3 PAC, the fourth grid is added with 0.008kg / m 3 PAM;

[0071] b2. The effluent from the pretreatment reaction tank I enters the pretreatment sedimentation tank I for sedimentation and sludge-water separation;

[0072] b3, the effluent from the pretreatment sedimentation tank I enters the pretreatment reaction tank II, and 0.12kg / m 3 PAC and 0.003kg / m 3 PAM further flocculates;

[0073] b4. The effluent from the pretreatment reaction pool II enters the flotation pool. Air is introduced into the wastewater and precipitated from the water in the form of tiny bubbles to become carriers, so that pollutants such as emulsified oil and tiny suspended particles in the wastewater adhere to the bubbles and float to the water surface with the bubbles to form foam (a three-phase mixture of air, water, and particles (oil)). The purpose of separating impurities and purifying wastewater is achieved by collecting foam or scum, and the concentration of emulsified oil and suspended matter is further reduced;

[0074] (2) The effluent from the secondary sedimentation tank and the flotation tank is mixed in the water distribution tank and then enters the biochemical treatment stage, specifically:

[0075] c1. The effluent from the water distribution tank enters a two-stage denitrification reactor, and uses the hydrolysis, acidification and denitrification of anaerobic microorganisms to decompose the difficult-to-degrade organic matter into easily degradable organic matter, decompose the macromolecular organic matter into small molecular organic matter, increase the BOD (biochemical oxygen demand) / COD (chemical oxygen demand) ratio, and reduce nitrate to nitrogen gas at the same time, wherein the temperature of the two-stage denitrification reactor is 35°C and the residence time is 2 days;

[0076] c2. The effluent from the two-stage denitrification reactor enters an aerobic tank to remove NH3-N and BOD5 from the wastewater;

[0077] c3, the effluent from the aerobic pool enters the secondary sedimentation tank for mud-water separation and then enters the biochemical effluent pool;

[0078] (3) The effluent from the biochemical effluent pool enters the reclaimed water reuse system, specifically: the effluent from the biochemical effluent pool passes through a sand filter tank, an activated carbon filter tank, a resin softening tank, an ultrafiltration device, and an RO in sequence, and the generated fresh water enters the reclaimed water reuse pool; the concentrated water generated by the RO enters the ROR for further concentration treatment, the fresh water generated by the ROR enters the reclaimed water reuse pool, the concentrated water enters the MVR device for further concentration, and the condensed water enters the reclaimed water reuse pool.

[0079] During the process, the sludge from the primary sedimentation tank and the secondary sedimentation tank enters the physicochemical sludge tank, is filtered by the plate and frame filter press and then transported out for treatment, and the filtrate flows back to the water distribution tank; the sludge from the pretreatment sedimentation tank I and the flotation tank enters the oily sludge tank, is dehydrated by the screw press dehydrator and then transported out for treatment, and the filtrate flows back to the water distribution tank; part of the sedimentation sludge from the secondary sedimentation tank flows back to the secondary denitrification reactor and the aerobic tank, and part of it enters the biochemical sludge tank, is treated by the plate and frame filter press and then transported out for treatment, and the filtrate flows back to the water distribution tank. Among them, a high-pressure diaphragm filter press is set up for the physicochemical sludge to dehydrate the sludge to a moisture content of about 60%, and a high-pressure diaphragm filter press is set up for the biochemical sludge to dehydrate the sludge to a moisture content of about 80%.

[0080] The removal of various substances by each processing unit in this embodiment is shown in Table 1:

[0081] Table 1 Removal of various substances by each treatment unit

[0082]

[0083]

[0084] In summary, the present invention aims at the different types and water amounts of pollutants in the pickling wastewater and oily wastewater of the stainless steel industry, adopts wastewater source diversion, segmented treatment and sludge classification and recovery processes, designs different pretreatment processes respectively, and adds chemicals in a targeted manner. The pretreatment is designed as a multi-stage segment, which can achieve the simultaneous reduction of the amount of chemicals and the sludge output. Various indicators of the effluent meet the standards of the reclaimed water reuse system, and after passing through the reclaimed water reuse system, the effluent meets the reuse standards, and the reuse rate reaches 98%.

[0085] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

Claims

1. A method for recycling wastewater from stainless steel industry and crystallizing concentrated water, wherein the stainless steel industry wastewater includes stainless steel pickling wastewater and oily wastewater, characterized in that: The steps include: S1. The stainless steel pickling wastewater is collected in the pickling wastewater regulating tank and then enters the two-stage coagulation and sedimentation pretreatment system, specifically: a1. The stainless steel pickling wastewater enters the primary reaction tank, and firstly, ammonium bisulfite is added to reduce the highly toxic hexavalent chromium to trivalent chromium, and then lime milk is added to make trivalent chromium, trivalent iron and divalent nickel generate hydroxide precipitation, and fluoride generates calcium fluoride precipitation, and finally PAC and PAM are added for flocculation; a2. The effluent from the primary reaction tank enters the primary sedimentation tank for sedimentation and sludge-water separation; a3, the effluent from the primary sedimentation tank enters the secondary reaction tank, and heavy catching agent, lime milk, PAC and PAM are added for further flocculation; a4. The effluent from the secondary reaction tank enters the secondary sedimentation tank for further sedimentation and mud-water separation; The oily wastewater is collected in the oily wastewater regulating tank and then enters the coagulation sedimentation + flotation pretreatment system, specifically: b1. The oily wastewater enters the pretreatment reaction tank I, and lime milk, demulsifier, PAC and PAM are added to flocculate organic matter, colloidal matter and suspended matter; b2. The effluent from the pretreatment reaction tank I enters the pretreatment sedimentation tank I for sedimentation and sludge-water separation; b3, the effluent from the pretreatment sedimentation tank I enters the pretreatment reaction tank II, and PAC and PAM are added for further flocculation; b4. The effluent from the pretreatment reaction tank II enters the flotation tank to further reduce the concentration of emulsified oil and suspended solids; S2. The effluent from the secondary sedimentation tank and the flotation tank is mixed in the water distribution tank and then enters the biochemical treatment stage, specifically: S21, the effluent from the water distribution tank enters the two-stage denitrification reactor, and utilizes the hydrolysis, acidification and denitrification of anaerobic microorganisms to decompose the refractory organic matter into easily degradable organic matter, decompose the macromolecular organic matter into small molecular organic matter, and reduce nitrate into nitrogen gas at the same time; S22, the effluent from the two-stage denitrification reactor enters an aerobic tank to remove NH3-N and BOD5 from the wastewater; S23, the effluent from the aerobic pool enters the secondary sedimentation tank for mud-water separation and then enters the biochemical effluent pool; S3, the effluent from the biochemical effluent pool enters the reclaimed water reuse system, specifically: The effluent from the biochemical effluent pool passes through a filtration device, an ultrafiltration device, and a reverse osmosis device in sequence, intercepting inorganic ions, colloid substances, and macromolecular solutes in the water, and then enters a reclaimed water reuse pool.

2. The method for recycling wastewater from stainless steel industry and crystallizing concentrated water according to claim 1, characterized in that: In a1, the primary reaction tank includes the first cell, the second cell, the third cell and the fourth cell connected in sequence. The first cell is added with alkali to adjust the pH to 4.3-5.6, and 0.2 kg / m 3 ~0.28kg / m 3 ammonium bisulfite, the second compartment adds lime milk to a pH of 7.2-9.0, and the third compartment adds 0.15kg / m 3 ~0.2kg / m 3 PAC, the fourth grid is added with 0.005kg / m 3 ~0.008kg / m 3 For PAM, the stirring intensity from the first to the third grid is 68r / min, and the stirring intensity of the fourth grid is 40r / min.

3. The method for recycling wastewater from stainless steel industry and crystallizing concentrated water according to claim 1, characterized in that: In a3, the secondary reaction tank includes a first cell, a second cell, a third cell and a fourth cell connected in sequence, and the first cell is dosed with 0.1 kg / m 3 ~0.15kg / m 3 The second compartment adds lime milk to a pH of 6.5 to 8.0, and the third compartment adds 0.1 kg / m 3 ~0.15kg / m 3 PAC, the fourth grid is added with 0.002kg / m 3 ~0.005kg / m 3 For PAM, the stirring intensity from the first to the third grid is 68r / min, and the stirring intensity of the fourth grid is 40r / min.

4. The method for recycling wastewater from stainless steel industry and crystallizing concentrated water according to claim 1, characterized in that: In b1, the pretreatment reaction tank I includes the first cell, the second cell, the third cell and the fourth cell connected in sequence. The first cell is added with lime milk to adjust the pH to 10-11, and the second cell is added with 0.2 kg / m 3 ~0.3kg / m 3 The third grid is dosing 0.15kg / m 3 ~0.2kg / m 3 PAC, the fourth grid is added with 0.005kg / m 3 ~0.008kg / m 3 PAM.

5. The method for recycling wastewater from stainless steel industry and crystallizing concentrated water according to claim 1, characterized in that: In b3, the pretreatment reaction tank II includes a first grid and a second grid connected in sequence, and the first grid is dosed with 0.1 kg / m 3 ~0.15kg / m 3 PAC, the second grid is added with 0.002kg / m 3 ~0.005kg / m 3 PAM.

6. The method for recycling wastewater from stainless steel industry and crystallizing concentrated water according to claim 1, characterized in that: In S2, the temperature of the two-stage denitrification reactor is 35±2°C, and the residence time is 2 to 2.5 days; And / or, the two-stage denitrification reactor is provided with a circulation pump to reflux the wastewater from the upper part of the reactor to the bottom of the reactor.

7. The method for recycling wastewater from stainless steel industry and crystallizing concentrated water according to claim 1, characterized in that: In S2, the solvent load of the aerobic tank is 0.3-0.5 kgCOD / m 3 d. The nitrified liquid in the aerobic pool is refluxed to the secondary denitrification reactor, and the reflux rate is 0.5-1.0 times of the influent rate; And / or, the surface load of the secondary sedimentation tank is 0.6-0.7m 3 / ㎡·h, stay time 2 to 3h.

8. The method for recycling wastewater from stainless steel industry and crystallizing concentrated water as claimed in claim 1, characterized in that: In S3, the concentrated water produced by the reverse osmosis device enters the MVR device for evaporation and concentration, and the generated condensed water enters the reclaimed water reuse pool.

9. A device for recycling wastewater from stainless steel industry and crystallizing concentrated water, used to implement the method according to any one of claims 1 to 8, characterized in that: include: A pickling wastewater regulating tank and an oily wastewater regulating tank, wherein the pickling wastewater regulating tank is connected to a two-stage coagulation and sedimentation pretreatment system, and the oily wastewater regulating tank is connected to a coagulation and sedimentation + flotation pretreatment system, and both the two-stage coagulation and sedimentation pretreatment system and the coagulation and sedimentation + flotation pretreatment system are connected to a water distribution tank; The outlet direction of the water distribution tank also includes a two-stage denitrification reactor, an aerobic tank, a secondary sedimentation tank, a filtration device, an ultrafiltration device, a reverse osmosis device and a reclaimed water reuse tank connected in sequence; The concentrated water outlet of the reverse osmosis device is connected to the MVR device, and the condensed water outlet of the MVR device is connected to the reclaimed water reuse pool.

10. The device for recycling wastewater from stainless steel industry and crystallizing concentrated water as claimed in claim 9, characterized in that: The filtering device comprises a sand filter tank, an activated carbon filter tank and a resin softening tank which are connected in sequence.

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