Nitrogen-containing photovoltaic wastewater resourceful treatment method

Abstract

The invention relates to a nitrogen-containing photovoltaic wastewater resourceful treatment method. The method comprises the following steps: S1, feeding nitrogen-containing photovoltaic wastewater into an adjusting tank; s2, lifting the wastewater of the adjusting tank to a first-stage sedimentation tank, a second-stage sedimentation tank and a third-stage sedimentation tank through a pump, respectively adding limestone, sodium carbonate, PAC and PAM into the tanks, and removing F <->, SS, silicon powder and part of COD; s3, the generated sludge enters a sludge dewatering system; s4, adjusting the water quality of effluent of the third-stage sedimentation tank, and pumping the effluent into a sand filtration system to further reduce SS of the effluent; s5, discharging water from the sand filtration system to a resin softener, and removing calcium ions in the wastewater; s6, lifting effluent of the resin softener to a two-stage reverse osmosis system through a pump, and concentrating; s7, the first-stage reverse osmosis concentrated water enters a steam stripping rectifying tower to be converted into concentrated ammonia water; the process adopted by the invention breaks through the limitation of a traditional biochemical treatment process, ammonia nitrogen is recycled, the operation stability of the system is improved, the cost and the occupied area are reduced, the scaling risk of the reverse osmosis system is also reduced, and the service life is prolonged.

Description

Technical Field

[0001] The present invention relates to the field of resource treatment of nitrogen-containing photovoltaic wastewater, and in particular to a resource treatment method of nitrogen-containing photovoltaic wastewater. Background Art

[0002] Currently, a variety of physical, chemical and biological treatment technologies are used for nitrogen-containing photovoltaic wastewater to meet national or local emission standards. The mainstream treatment processes include coagulation and sedimentation, adsorption, hydrolysis and acidification, micro-electrolysis, Fenton oxidation, biological contact oxidation, hydrolysis and acidification, MBR, reverse osmosis, etc. Due to the complex composition of water quality, a single treatment process cannot meet the treatment requirements of photovoltaic nitrogen-containing wastewater. In engineering, according to the actual water quality, the physical and chemical + biochemical treatment method is adopted to combine the above processes to achieve wastewater discharge in compliance with standards, but all of them have certain disadvantages.

[0003] The micro-electrolysis and Fenton oxidation processes are difficult to operate and manage, and the cost of reagents is high; the hydrolysis acidification, biological contact oxidation and MBR processes require a large area, have high investment costs, and are difficult to debug the biochemical system. In addition, the biochemical process only decomposes the ammonia nitrogen pollutants into small molecules and does not utilize them as resources, resulting in a waste of ammonia nitrogen resources.

[0004] Prior art 201810108295.2 discloses a method and system for treating photovoltaic wastewater containing high ammonia nitrogen, arsenic and fluorine, including: 1. The wastewater is homogenized and filtered before pH adjustment; 2. The ammonia nitrogen precipitated by steam stripping is converted into ammonia water with a mass fraction of 16%-19% through an ammonia absorption tower by steam stripping and distillation deammoniation technology; 3. The pH value of the wastewater is adjusted to 9; d. NaClO is added to oxidize and decompose COD, trivalent As and residual ammonia nitrogen in the wastewater; e. A certain concentration of Fe3+ and Ca2+ is added to react by two-stage coagulation and precipitation. The remaining F and As in the water should be removed; F. The effluent enters the primary RO system to concentrate the wastewater and remove organic matter, salt, etc. in the wastewater. The fresh water is recycled as pure water with zero discharge, and the concentrated water is further concentrated in the secondary DTRO system to reduce the evaporation amount of the subsequent evaporation system; g. The fresh water is recycled as pure water with zero discharge, and the concentrated water enters the deep treatment system to remove arsenic in the wastewater by adding heavy metal adsorbents; h. The effluent enters the MVR evaporation system to evaporate and crystallize the salt. The crystals are transported out as general solid waste and the effluent is recycled.

[0005] Although the above method can treat photovoltaic wastewater and recover ammonia water, it is a treatment process for photovoltaic wastewater with high ammonia nitrogen, arsenic and fluorine content, and cannot be applied to the treatment of photovoltaic wastewater with low concentration of ammonia nitrogen. Summary of the invention

[0006] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for resource-based treatment of nitrogen-containing photovoltaic wastewater.

[0007] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a method for resource treatment of nitrogen-containing photovoltaic wastewater, comprising the following steps:

[0008] S1. The nitrogen-containing photovoltaic wastewater enters the regulating tank to homogenize the water quality and water volume;

[0009] S2. The wastewater from the regulating tank is pumped to a multi-stage sedimentation tank. Limestone is added to the first-stage sedimentation tank to remove fluoride ions and fluorosilicic acid, forming calcium fluoride and calcium silicate precipitation. Sodium carbonate is added to the second-stage sedimentation tank to remove excess calcium ions in the first-stage effluent and form calcium carbonate precipitation. PAC and PAM are added to the third-stage sedimentation tank to further remove Fˉ, SS, silica powder and part of COD.

[0010] S3, the generated sludge enters the sludge dewatering system, and is returned to the primary reaction sedimentation tank at night, and the mud cake is transported out;

[0011] S4, the effluent from the tertiary sedimentation tank is regulated and pumped into the sand filtration system to further reduce the effluent SS;

[0012] S5, the effluent from the sand filtration system is sent to the resin softener, which removes calcium ions from the wastewater through adsorption of exchange resin;

[0013] S6. The effluent from the resin softener is pumped to a two-stage reverse osmosis system. The first-stage reverse osmosis product water enters the second-stage reverse osmosis, and the second-stage reverse osmosis concentrate returns to the first-stage reverse osmosis inlet water. The second-stage reverse osmosis product water is reused, and the first-stage reverse osmosis concentrate enters the stripping ammonia distillation system.

[0014] S7. After the primary reverse osmosis concentrated water is adjusted in water quality, it enters the stripping distillation tower and is converted into concentrated ammonia water.

[0015] Preferably, in step S1, the nitrogen-containing photovoltaic wastewater in the regulating tank needs to stay for 8-12 hours.

[0016] Preferably, in step S2, the wastewater in the tertiary sedimentation tank needs to stay for 15 minutes; the amounts of PAC and PAM added to the tertiary sedimentation tank are 50-100 mg / L and 5-10 mg / L respectively; the water quality of the wastewater effluent from the tertiary sedimentation tank is pH 8-9, and the mass concentration of fluoride ions in the water is 10 mg / L-15 mg / L.

[0017] Preferably, in step S4, the water quality of the effluent from the tertiary sedimentation tank is adjusted to pH 6-8.

[0018] Preferably, in step S5, the resin softener is regenerated regularly, and the regenerated wastewater is returned to the regulating tank for circulation treatment.

[0019] Preferably, the resin softener uses sodium-type strongly acidic ion exchange resin.

[0020] Preferably, in step S7, the concentrated water from the primary reverse osmosis is adjusted to a pH of 10-13 by using liquid alkali.

[0021] Preferably, in step S7, the ammonia-containing wastewater in the stripping section of the stripping distillation tower moves from top to bottom and countercurrently contacts with direct steam from the bottom of the tower, and the ammonia therein is removed. A deammoniation wastewater discharge system with an ammonia content of less than 15 mg / L is obtained at the bottom of the tower kettle; ammonia gas and water vapor in the stripping distillation tower countercurrently contact with concentrated ammonia water refluxed from the top of the tower, and the ammonia concentration is further increased, and the water content is further reduced, and enters the top ammonia condenser from the top of the tower; the ammonia and water vapor in the top ammonia condenser of the stripping distillation tower are condensed into ammonia water by circulating water, and all of them are refluxed from the top of the tower, which can be recycled and utilized as resources.

[0022] Preferably, the stripping distillation tower produces concentrated ammonia water with a concentration of ≥18% from the top ammonia condenser.

[0023] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0024] 1. The present invention adopts the process of "regulating tank + three-stage reaction precipitation + sand filtration + softening + two-stage reverse osmosis + stripping ammonia distillation", breaking the limitations of traditional biochemical treatment processes, and utilizing ammonia nitrogen in photovoltaic wastewater as a resource, which not only improves the system operation stability, but also reduces investment costs and floor space;

[0025] 2. The pretreatment of the present invention adopts "three-stage precipitation + sand filtration + resin softening" to reduce the scaling risk of the reverse osmosis system, increase the service life of the membrane, and reduce the cleaning frequency;

[0026] 3. The two-stage reverse osmosis system of the present invention ensures that the produced water meets the standards for reuse while concentrating the wastewater and entering the stripping and ammonia distillation system to achieve resource utilization of ammonia nitrogen. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The technical solution of the present invention is further described below in conjunction with the accompanying drawings:

[0028] Attached Figure 1 It is a schematic diagram of the process flow of the method for resource treatment of nitrogen-containing photovoltaic wastewater according to the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0030] Attached Figure 1 The method for resource treatment of nitrogen-containing photovoltaic wastewater according to the present invention comprises the following steps:

[0031] S1. The nitrogen-containing photovoltaic wastewater enters the regulating tank to homogenize the water quality and water volume;

[0032] S2. The wastewater from the regulating tank is pumped to a multi-stage sedimentation tank. Limestone is added to the first-stage sedimentation tank to remove fluoride ions and fluorosilicic acid, forming calcium fluoride and calcium silicate precipitation. Sodium carbonate is added to the second-stage sedimentation tank to remove excess calcium ions in the first-stage effluent and form calcium carbonate precipitation. PAC and PAM are added to the third-stage sedimentation tank to further remove Fˉ, SS, silica powder and part of COD.

[0033] S3, the generated sludge enters the sludge dewatering system, and is returned to the primary reaction sedimentation tank at night, and the mud cake is transported out;

[0034] S4, the effluent from the tertiary sedimentation tank is regulated and pumped into the sand filtration system to further reduce the effluent SS;

[0035] S5, the effluent from the sand filtration system is sent to the resin softener, which removes calcium ions from the wastewater through adsorption of exchange resin;

[0036] S6. The effluent from the resin softener is pumped to a two-stage reverse osmosis system. The first-stage reverse osmosis product water enters the second-stage reverse osmosis, and the second-stage reverse osmosis concentrate returns to the first-stage reverse osmosis inlet water. The second-stage reverse osmosis product water is reused, and the first-stage reverse osmosis concentrate enters the stripping ammonia distillation system.

[0037] S7, the concentrated water from the first-stage reverse osmosis is adjusted and then enters the steam stripping distillation tower to be converted into concentrated ammonia water;

[0038] The nitrogen-containing photovoltaic wastewater in the regulating tank needs to stay for 8-12 hours; the wastewater in the tertiary sedimentation tank needs to stay for 15 minutes; the amounts of PAC and PAM added to the tertiary sedimentation tank are 50-100 mg / L and 5-10 mg / L respectively; the wastewater quality of the effluent from the tertiary sedimentation tank is pH8-9, and the mass concentration of fluoride ions in the water is 10 mg / L-15 mg / L; the water quality of the effluent from the tertiary sedimentation tank is adjusted to pH6-8; the resin softener is regenerated regularly, and the regenerated wastewater is returned to the regulating tank for cyclic treatment; the concentrated water from the first-level reverse osmosis is adjusted to pH10-13 with liquid alkali; the ammonia-containing wastewater in the stripping section of the stripping distillation tower moves from top to bottom, and contacts with the direct steam from the bottom of the tower in countercurrent, and the ammonia therein is removed. A deammoniation wastewater discharge system with an ammonia content of less than 15 mg / L is obtained at the bottom of the tower kettle; ammonia gas and water vapor are in countercurrent contact with concentrated ammonia water refluxed from the top of the tower in the distillation section of the stripping distillation tower, and the ammonia concentration is further increased, and the water content is further reduced, and enters the top ammonia condenser from the top of the tower; ammonia and water vapor in the top ammonia condenser of the stripping distillation tower are condensed into ammonia water by circulating water, and all of them are refluxed from the top of the tower, which can be recycled and utilized as resources; the stripping distillation tower produces concentrated ammonia water with a concentration of ≥18% from the top ammonia condenser.

[0039] Furthermore, the resin softener adopts sodium-type strongly acidic ion exchange resin to improve the softening effect.

[0040] During use: nitrogen-containing photovoltaic wastewater enters the regulating tank and stays for 8-12 hours to homogenize the water quality and water volume. Then the wastewater in the regulating tank is pumped to three sedimentation tanks for sedimentation for 15 minutes. Limestone is added to the primary sedimentation tank to remove fluoride ions and fluorosilicic acid to form calcium fluoride and calcium silicate precipitation. Sodium carbonate is added to the secondary sedimentation tank to remove excess calcium ions in the primary effluent to generate calcium carbonate precipitation. PAC and PAM are added to the tertiary sedimentation tank to further remove Fˉ, SS, silicon powder and part of COD. The effluent quality is pH8-9, and the mass concentration of fluoride ions in the treated water is 10mg / L-15mg / L. The sludge generated then enters the sludge dewatering system, returns to the primary reaction sedimentation tank at night, and the mud cake is transported out. Then the precipitated water is adjusted to pH6-8, and then the adjusted water is pumped into the sand filtration system for filtration to further reduce SS in the water and ensure the safe and stable operation of subsequent reverse osmosis. Then the water filtered by the sand filtration system enters the resin softener, which removes calcium ions in the wastewater through exchange resin adsorption and softens. The water after the treatment is pumped to a two-stage reverse osmosis system. The first-stage reverse osmosis product water enters the second-stage reverse osmosis, and the second-stage reverse osmosis concentrated water returns to the first-stage reverse osmosis inlet water, thereby increasing the concentration of ammonia nitrogen in the concentrated water. The second-stage reverse osmosis product water is reused, and then the first-stage reverse osmosis concentrated water is adjusted to pH 10-13 with liquid caustic soda before entering the stripping ammonia distillation system. In the stripping section of the stripping distillation tower, the ammonia-containing wastewater moves from top to bottom and contacts with the direct steam from the bottom of the tower in countercurrent, and the ammonia in it is removed, and the ammonia content is less than 15mg / L at the bottom of the tower kettle. The deammoniation wastewater is then discharged from the system. In the distillation section of the stripping distillation tower, ammonia gas and water vapor are countercurrently contacted with concentrated ammonia water refluxed from the top of the tower, and the ammonia concentration is further increased, and the water content is further reduced. It enters the top ammonia condenser from the top of the tower, where ammonia and water vapor are condensed into ammonia water by circulating water and all refluxed from the top of the tower. Concentrated ammonia water with a concentration of about ≥18% is extracted from the top ammonia condenser, which can be recycled and utilized as a resource. The kettle wastewater is preheated to the raw material after passing through the preheater, and then cooled to about 50°C after passing through the cooler.

[0041] The above are only specific application examples of the present invention and do not constitute any limitation on the protection scope of the present invention. Any technical solution formed by equivalent transformation or equivalent replacement shall fall within the protection scope of the present invention.

Claims

1. A method for resource treatment of nitrogen-containing photovoltaic wastewater, characterized in that: The following steps are included: S1. The nitrogen-containing photovoltaic wastewater enters the regulating tank to homogenize the water quality and water volume; S2. The wastewater from the regulating tank is pumped to a multi-stage sedimentation tank. Limestone is added to the first-stage sedimentation tank to remove fluoride ions and fluorosilicic acid, forming calcium fluoride and calcium silicate precipitation. Sodium carbonate is added to the second-stage sedimentation tank to remove excess calcium ions in the first-stage effluent and form calcium carbonate precipitation. PAC and PAM are added to the third-stage sedimentation tank to further remove Fˉ, SS, silica powder and part of COD. S3, the generated sludge enters the sludge dewatering system, and is returned to the primary reaction sedimentation tank at night, and the mud cake is transported out; S4, the effluent from the tertiary sedimentation tank is pumped into the sand filtration system after the water quality is adjusted to further reduce the effluent SS; S5, the effluent from the sand filtration system is sent to the resin softener, which removes calcium ions from the wastewater through adsorption of exchange resin; S6. The effluent from the resin softener is pumped to a two-stage reverse osmosis system. The first-stage reverse osmosis product water enters the second-stage reverse osmosis, and the second-stage reverse osmosis concentrate returns to the first-stage reverse osmosis inlet water. The second-stage reverse osmosis product water is reused, and the first-stage reverse osmosis concentrate enters the stripping ammonia distillation system. S7. After the primary reverse osmosis concentrated water is adjusted in water quality, it enters the stripping distillation tower and is converted into concentrated ammonia water.

2. The method for resource treatment of nitrogen-containing photovoltaic wastewater according to claim 1, characterized in that: In step S1, the nitrogen-containing photovoltaic wastewater in the regulating tank needs to stay for 8-12 hours.

3. The method for resource treatment of nitrogen-containing photovoltaic wastewater according to claim 1, characterized in that: In step S2, the wastewater in the tertiary sedimentation tank needs to stay for 15 minutes; the amounts of PAC and PAM added to the tertiary sedimentation tank are 50-100 mg / L and 5-10 mg / L respectively; the water quality of the wastewater effluent from the tertiary sedimentation tank is pH 8-9, and the mass concentration of fluoride ions in the water is 10 mg / L-15 mg / L.

4. The method for resource treatment of nitrogen-containing photovoltaic wastewater according to claim 1, characterized in that: In step S4, the water quality of the effluent from the tertiary sedimentation tank is adjusted to pH 6-8.

5. The method for resource treatment of nitrogen-containing photovoltaic wastewater according to claim 1, characterized in that: In step S5, the resin softener is regenerated regularly, and the regenerated wastewater is returned to the regulating tank for circulation treatment.

6. The method for resource treatment of nitrogen-containing photovoltaic wastewater according to claim 1, characterized in that: The resin softener adopts sodium type strong acid ion exchange resin.

7. The method for resource treatment of nitrogen-containing photovoltaic wastewater according to claim 1, characterized in that: In step S7, the concentrated water from the first-stage reverse osmosis is adjusted to a pH of 10-13 by using liquid alkali.

8. The method for resource treatment of nitrogen-containing photovoltaic wastewater according to claim 1, characterized in that: In step S7, the ammonia wastewater in the stripping section of the stripping distillation tower moves from top to bottom and countercurrently contacts with the direct steam from the bottom of the tower, and the ammonia therein is removed. A deammoniation wastewater discharge system with an ammonia content of less than 15 mg / L is obtained at the bottom of the tower kettle; ammonia gas and water vapor in the stripping distillation tower countercurrently contact with the concentrated ammonia water refluxed from the top of the tower, the ammonia concentration is further increased, the water content is further reduced, and enters the top ammonia condenser from the top of the tower; the ammonia and water vapor in the top ammonia condenser of the stripping distillation tower are condensed into ammonia water by circulating water, and all of them are refluxed from the top of the tower, which can be recycled and utilized as resources.

9. The method for resource treatment of nitrogen-containing photovoltaic wastewater according to claim 8, characterized in that: The stripping distillation tower produces concentrated ammonia water with a concentration of ≥18% from the tower top ammonia condenser.

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