A water treatment method and system for denitrification and phosphorus removal as a resource

Abstract

The present invention relates to a denitrification and dephosphorization resource water treatment method and a water treatment system, the water treatment method comprising: treating the initial waste liquid by nitric acid-phosphate ion exchange resin, obtaining a regenerated waste liquid with a high nitrogen and phosphorus concentration and a dischargeable water with a low nitrogen and phosphorus concentration, and the dischargeable water is directly discharged; reducing the nitrate in the regenerated waste liquid to nitrogen oxide gas, using alkali solution to absorb the nitrogen oxide gas, and obtaining liquid nitrogen fertilizer; concentrating the liquid phase obtained by reducing the regenerated waste liquid, purifying the phosphate in the concentrated liquid, and obtaining the residual liquid and acid condensate; mixing the residual liquid and the acid condensate with fresh acid liquid to obtain resin regeneration liquid; and regenerating the nitric acid-phosphate ion exchange resin by using the resin regeneration liquid. The water treatment method can convert phosphate and nitrate in wastewater into valuable products, and can also achieve zero pollution discharge.

Description

Technical Field

[0001] The present invention belongs to the field of water treatment technology, and specifically relates to a water treatment method and a water treatment system for denitrification and phosphorus removal. Background Technology

[0002] When too much sewage flows into natural waters and exceeds their self-purification capacity, the water quality will change, and environmental problems such as eutrophication and organic pollution will appear, seriously affecting the effective use of water resources. Eutrophication of water quality is generally manifested in the imbalance of species distribution in the aquatic ecosystem caused by excessive content of nutrients such as nitrogen and phosphorus in the water body. The rampant growth of a single species destroys the flow of matter and energy in the aquatic ecosystem, thus gradually destroying the entire aquatic ecosystem.

[0003] Existing water treatment technologies include physical treatment, chemical treatment and biological treatment. Physical treatment mainly relies on adding polyaluminium oxide (PAC) to lake water to remove phosphorus, which produces a large amount of chemical precipitation; chemical treatment mainly relies on adding sodium hypochlorite and other methods to reduce the total nitrogen content by reducing ammonia nitrogen, which affects the water ecology; biological treatment relies on microbial strains to reduce the total nitrogen and total phosphorus content of lake water, which requires long-term addition and is costly. SUMMARY OF THE INVENTION

[0004] Aiming at the problems existing in the existing water treatment technology, the present invention provides a water treatment method and a water treatment system for denitrification and phosphorus removal.

[0005] The technical solution provided by the present invention is as follows:

[0006] In a first aspect, the present invention provides a method for treating water for denitrification and phosphorus removal, comprising:

[0007] Treat the initial waste liquid by nitric acid-phosphate ion exchange resin to obtain regenerated waste liquid with high nitrogen and phosphorus concentration and dischargeable water with low nitrogen and phosphorus concentration, and the dischargeable water can be discharged directly;

[0008] Reducing nitrate in the regeneration waste liquid into nitrogen oxide gas, using alkaline solution to absorb the nitrogen oxide gas to obtain liquid nitrogen fertilizer;

[0009] Concentrate the liquid phase obtained by reducing the regenerated waste liquid, purify the phosphate in the concentrated liquid, and obtain the residual liquid and acid condensate;

[0010] Mix the residual liquid, acid condensate and fresh acid liquid to obtain resin regeneration liquid;

[0011] Regenerate the nitric acid-phosphate ion exchange resin using resin regeneration solution.

[0012] Based on the above technical solution, reducing nitrate in the regeneration waste liquid into nitrogen oxide gas includes: converting nitrate in the regeneration waste liquid into nitrogen monoxide through an iron-copper primary battery, and converting iron into iron ions and entering the liquid phase.

[0013] Based on the above technical solution, the concentration of the liquid phase obtained by reducing the regeneration waste liquid includes: heating and concentrating the liquid phase obtained by reducing the regeneration waste liquid through a two-stage MVP crystallizer to obtain ferrous phosphate and ferrous chloride solid products respectively.

[0014] Based on the above technical solution, the nitrate concentration in the liquid phase obtained by reducing the regenerated waste liquid is ≤100mg / L.

[0015] Based on the above technical solution, the use of alkaline solution to absorb nitrogen oxide gas includes: providing a gas absorption tower with alkaline solution sprayed on the top; introducing nitrogen oxide gas from the bottom of the gas absorption tower to obtain a nitrate solution.

[0016] Based on the above technical solution, before treating the initial waste liquid with nitric acid-phosphate ion exchange resin, the method further includes: filtering and removing particles with a particle size greater than 0.1 mm in the initial waste liquid.

[0017] In a second aspect, the present invention provides a water treatment system for denitrification and phosphorus removal, comprising:

[0018] Anion resin tank, wherein a nitric acid-phosphate ion exchange resin is arranged in the anion resin tank, and is used to separate the initial waste liquid into regeneration waste liquid with high nitrogen and phosphorus concentration and dischargeable water with low nitrogen and phosphorus concentration;

[0019] A waste liquid reduction reaction device, wherein the waste liquid reduction reaction device is provided with an iron-copper primary battery, and the iron-copper primary battery is used to reduce nitrate in the regenerated waste liquid into nitrogen oxide gas;

[0020] Gas phase resource recovery equipment, wherein the gas phase resource recovery equipment is provided with alkaline solution, and the alkaline solution is used to absorb nitrogen oxide gas to obtain nitrogen-containing products;

[0021] The concentration and purification device is used to concentrate and crystallize the water treated by the waste liquid reduction reaction device to obtain ferrous phosphate solid product, residual liquid and acid condensate;

[0022] The resin regeneration liquid storage tank is used to mix the residual liquid, acid condensate and fresh acid liquid into resin regeneration liquid. After the nitric acid-phosphate ion exchange resin is saturated, the resin regeneration liquid storage tank releases the resin regeneration liquid to regenerate the nitric acid-phosphate ion exchange resin.

[0023] Based on the above technical solution, the concentration and purification device includes two-stage MVP crystallizers, which are used to obtain ferrous phosphate solid and ferrous chloride solid in sequence.

[0024] On the basis of the above technical solution, the denitrification and phosphorus removal resource-based water treatment system further includes a filtering unit, which is used to filter particulate matters with a particle size greater than 0.1 mm in the initial waste liquid.

[0025] On the basis of the above technical solution, the gas resource-based equipment is a gas absorption tower.

[0026] The technical solution of the present invention has the following advantages and beneficial effects:

[0027] 1. The denitrification and phosphorus removal resource-based water treatment method provided by the present invention resourceizes phosphate and nitrate pollutants in water bodies, turning pollutants that originally needed to be treated at cost into resources that can generate profits. After nitrate is reduced to nitrogen oxide gas, it is refined or prepared into other nitrogen-containing high-value-added products such as liquid nitrogen fertilizer, and phosphate is concentrated into ferrous phosphate products after being concentrated.

[0028] 2. The denitrification and phosphorus removal resource-based water treatment method provided by the present invention mixes the residual liquid, acid condensate and fresh acid liquid and uses them for the regeneration of nitric acid-phosphate ion exchange resin, which can achieve zero wastewater discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0030] Figure 1 Shows a schematic diagram of the denitrification and phosphorus removal resource-based water treatment system provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0032] As Figure 1 shown, the denitrification and phosphorus removal resource-based water treatment system provided by the present invention includes:

[0033] A filtering and treatment unit, which is used to filter and remove particulate matters with a particle size greater than 0.1 mm in the initial waste liquid;

[0034] Anion resin tank. Inside the anion resin tank, there is a nitric acid - phosphate ion exchange resin. The selective adsorption order of the nitric acid - phosphate ion exchange resin for various anions is: NO 3 - ≥PO 4 3- >>SO 4 2- >CL - > other anions, which can separate the initial waste liquid into a regenerated waste liquid with a high nitrogen and phosphorus concentration and a drainable water with a low nitrogen and phosphorus concentration;

[0035] Waste liquid reduction reaction device. Inside the waste liquid reduction reaction device, there is an iron - copper primary battery, which is used to reduce nitrate in the regenerated waste liquid into nitrogen oxide gas, thereby reducing the total nitrogen content in the liquid phase;

[0036] Gas - phase resource utilization equipment. Inside the gas - phase resource utilization equipment, there is an alkali solution, which is used to absorb nitrogen oxide gas to obtain a nitrogen - containing product (liquid nitrogen fertilizer);

[0037] Concentration and purification device, which is used to concentrate and crystallize the water treated by the waste liquid reduction reaction device to obtain solid products of ferrous phosphate, solid products of ferrous chloride, a residual liquid mainly composed of iron salts, an acid condensate mainly composed of hydrochloric acid, and a later condensate with less impurities;

[0038] Resin regeneration liquid storage tank, which is used to mix the residual liquid, acid condensate, and fresh acid liquid into a resin regeneration liquid. After the nitric acid - phosphate ion exchange resin is saturated in operation, the resin regeneration liquid storage tank discharges the resin regeneration liquid to regenerate the nitric acid - phosphate ion exchange resin.

[0039] The filtration treatment unit of the present invention may include a filter tank, graded filter media (such as quartz sand, anthracite, ceramsite, etc.), backwashing facilities, and can treat solid suspended matter in the water body to be less than or equal to 10 mg / L and remove particulate matter with a particle size greater than 0.1 mm.

[0040] The denitrification and dephosphorization resource - based water treatment method provided by the present invention includes the following steps:

[0041] Treat the initial waste liquid with a nitric acid - phosphate ion exchange resin to obtain a regenerated waste liquid with a high nitrogen and phosphorus concentration and a drainable water with a low nitrogen and phosphorus concentration. The drainable water is directly discharged into lakes or rivers;

[0042] Reduce nitrate in the regenerated waste liquid into nitrogen oxide gas, and use an alkali solution to absorb the nitrogen oxide gas to obtain liquid nitrogen fertilizer;

[0043] Concentrate the liquid phase obtained by reducing the regenerated waste liquid, purify the phosphate in the concentrated liquid, and obtain a residual liquid mainly composed of iron salts, an acid condensate mainly composed of hydrochloric acid, and a later condensate with less impurities;

[0044] The residual liquid, acid condensate and fresh acid are mixed to obtain resin regeneration liquid; the later condensate can be directly discharged into lakes or rivers, or discharged after being treated with nitric acid-phosphate ion exchange resin;

[0045] Regenerate the nitric acid-phosphate ion exchange resin using resin regeneration solution.

[0046] Based on the above technical solution, reducing nitrate in the regeneration waste liquid into nitrogen oxide gas includes: converting nitrate in the regeneration waste liquid into nitric oxide through an iron-copper primary battery, and in this process, the iron element is converted into ferrous ions and enters the water.

[0047] Based on the above technical solution, most of the nitrate in the liquid phase after reduction is reduced to nitrogen oxide gas for recovery, and only a small amount of nitrate remains in the liquid phase. Preferably, the nitrate concentration in the liquid phase obtained by reducing the regenerated waste liquid is ≤100mg / L.

[0048] Based on the above technical solution, the use of alkaline solution to absorb nitrogen oxide gas includes: providing a gas absorption tower with alkaline solution sprayed on the top; introducing nitrogen oxide gas from the bottom of the gas absorption tower to obtain a nitrate solution.

[0049] Based on the above technical solution, the liquid phase obtained by reducing the regenerated waste liquid is concentrated, including: heating and concentrating the liquid phase obtained by reducing the regenerated waste liquid through a two-stage MVP crystallizer to obtain solid products of ferrous phosphate and ferrous chloride, respectively. The liquid phase produced by the waste liquid reduction reaction device is mainly ferrous salt, and enters the concentration and purification device to obtain a product mainly composed of ferrous salt (if sulfuric acid is selected as the fresh acid liquid, it is mainly ferrous sulfate, and if hydrochloric acid is selected as the acid liquid, it is mainly ferrous chloride) and contains some ferrous phosphate crystals.

[0050] Based on the above technical solution, before treating the initial waste liquid with nitric acid-phosphate ion exchange resin, the method further includes: filtering and removing particles with a particle size greater than 0.1 mm in the initial waste liquid.

[0051] The technical solution of the present invention is described in detail below through specific embodiments:

[0052] Example 1

[0053] If Figure 1 As shown, the denitrification and phosphorus removal resource water treatment system provided in this embodiment includes:

[0054] Filtration treatment unit, used to filter out solid impurities in the water;

[0055] Anion resin tank, the anion resin tank is equipped with nitric acid-phosphate ion exchange resin, the nitric acid-phosphate ion exchange resin selects the order of adsorption of each anion as follows: NO3 - ≥PO 4 3- >>SO 4 2- >CL - > other anions;

[0056] Waste liquid reduction reaction device. There is an iron - copper primary battery in the waste liquid reduction reaction device, and the iron - copper primary battery can reduce nitrate in water body to nitrogen oxide gas, thereby reducing the total nitrogen content in the water body;

[0057] Gas - phase resource utilization equipment. The gas - phase resource utilization equipment is a gas absorption tower filled with alkali solution, and nitrogen oxide gas is absorbed by the alkali solution to obtain nitrogen - containing products (liquid nitrogen fertilizer);

[0058] Concentration and purification device, including two - stage MVP crystallizers, which concentrate and crystallize the water body treated by the waste liquid reduction reaction device to obtain solid products of ferrous phosphate and ferrous chloride respectively;

[0059] Resin regeneration liquid storage tank, which is used to mix the residual liquid, acid condensate and fresh acid liquid to obtain resin regeneration liquid; and temporarily store the resin regeneration liquid. After the nitric acid - phosphate ion exchange resin is saturated in operation, the resin regeneration liquid storage tank discharges part of the resin regeneration liquid to regenerate the nitric acid - phosphate ion exchange resin.

[0060] The denitrification and dephosphorization resource - based water treatment method provided in this embodiment includes the following steps:

[0061] (1) Filter the poor - quality lake - river water body with a total nitrogen content of 4 mg / L and a total phosphorus content of 2 mg / L at a rate of 10000 t / d;

[0062] (2) The filtered water body (with a total nitrogen content of 4 mg / L and a total phosphorus content of 2 mg / L) flows through an anion resin tank equipped with nitric acid - phosphate ion exchange resin. Anions are adsorbed by the nitric acid - phosphate ion exchange resin to obtain drainable water with low nitrogen and phosphorus concentrations (total nitrogen content of 0.2 mg / L, total phosphorus content of 0.01 mg / L, 1003 t / d) and regeneration waste liquid with high nitrogen and phosphorus concentrations (total nitrogen content of 1950 mg / L, total phosphorus content of 1045 mg / L, 20 t / d). The drainable water meets the requirements of Class I lakes and reservoirs (total nitrogen less than 1.0 mg / L and total phosphorus less than 0.05 mg / L) and is directly discharged into lakes or rivers;

[0063] (3) The regeneration waste liquid generated in step (2) enters a waste liquid reduction device equipped with an iron-copper primary battery (built-in iron-copper primary battery, reaction principle: in an acidic environment, copper and nitrate react to generate nitric oxide, water and ions; then iron reduces copper ions to copper element), and the iron-copper primary battery reduces nitrate in the regeneration waste liquid to nitric oxide gas, obtaining a liquid phase with a reduced nitrogen content (total nitrogen content of 60 mg / L, total phosphorus content of 1045 mg / L, 20 t / d) and a gas phase;

[0064] (4) The gas phase (nitric oxide gas) produced in step (3) enters the gas phase resource recovery equipment filled with alkali solution, and the nitrogen oxide gas is absorbed by the alkali solution to obtain a nitrogen-containing product (liquid nitrogen fertilizer, nitrogen content 37.8kg / d); the liquid phase produced in step (3) enters the concentration and purification device to obtain a phosphorus-containing product (the main component is ferrous phosphate, the total nitrogen content is 0.2kg / d, the total phosphorus content is 19kg / d), and the residual liquid (total nitrogen content is 4532mg / L, total phosphorus content is 4515mg / L) / L, 0.2t / d), acid condensate (total nitrogen content of 10mg / L, total phosphorus content of 10mg / L, hydrogen chloride content of 11%, 17t / d), and late condensate (total nitrogen content <5mg / L, total phosphorus content <5mg / L, 3t / d); phosphorus-containing products and nitrogen-containing products are collected and refined or sold directly. The late condensate is basically clear water and can be directly discharged into lakes or rivers. It is safer to discharge it into lakes or rivers after adsorption by nitric acid-phosphate ion exchange resin;

[0065] (5) The residual liquid and acid condensate produced in step (4) enter the resin regeneration liquid storage tank, and fresh acid solution (35% hydrochloric acid, 3t / d) is added to obtain resin regeneration liquid (total nitrogen content of 50mg / L, total phosphorus content of 50mg / L, hydrogen chloride content of 14.6%, 20t / d).

[0066] (6) After the nitric acid-phosphate ion exchange resin is saturated, the resin regeneration liquid in the resin regeneration liquid storage tank and the late condensate produced in step (4) enter the anion resin tank for regeneration of the nitric acid-phosphate ion exchange resin.

[0067] According to the denitrification and phosphorus removal resource water treatment system and water treatment method provided in Example 1, the lake and river water bodies (initial wastewater) that need emergency treatment are filtered and then enter the anion resin tank, which is filled with nitrate ion exchange resin. After the reaction is completed, the dischargeable water is obtained, and its total nitrogen can be stably less than 0.2mg / L, and its total phosphorus can be stably less than 0.01mg / L. Both indicators can meet the requirements of Class I lakes and reservoirs (generally: total nitrogen is less than 1.0mg / L, and its total phosphorus is less than 0.05mg / L. It can be discharged if it meets the Class 3 water body standards), and can be directly discharged into natural rivers.

[0068] ​In the experiments of the present invention, it is found that the resin regeneration liquid prepared by adding 0.5 parts by weight of residual liquid, 0.5 parts by weight of acid liquid and 9 parts by weight of water can meet the regeneration requirements of the nitric acid-phosphate ion exchange resin. Compared with the regeneration liquid prepared entirely from acid liquid, the acid consumption is reduced by about 50% or more.

[0069] The above are only specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for treating water for nitrogen and phosphorus removal and resource utilization, characterized in that: include: Treating the initial waste liquid with nitric acid-phosphate ion exchange resin to obtain regenerated waste liquid with high nitrogen and phosphorus concentration and dischargeable water with low nitrogen and phosphorus concentration, and the dischargeable water is directly discharged; The nitrate in the regeneration waste liquid is reduced to nitrogen oxide gas, and the nitrogen oxide gas is absorbed by alkaline solution to obtain liquid nitrogen fertilizer; Concentrating the liquid phase obtained by reducing the regeneration waste liquid, purifying the phosphate in the concentrated liquid, and obtaining the residual liquid and the acid condensate; The residual liquid, the acid condensate and the fresh acid solution are mixed to obtain the resin regeneration solution; Regenerating the nitric acid-phosphate ion exchange resin using a resin regeneration solution; The reducing of nitrate in the regeneration waste liquid into nitrogen oxide gas comprises: The nitrate in the regenerated waste liquid is converted into nitric oxide through the iron-copper primary battery, and the iron element is converted into iron ions and enters the liquid phase; The concentration of the liquid phase obtained by reducing the regenerated waste liquid comprises: The liquid phase obtained by reducing the regenerated waste liquid is heated, concentrated and crystallized in a two-stage MVP crystallizer to obtain solid products of ferrous phosphate and ferrous chloride respectively; The method of converting nitrate in the regenerated waste liquid into nitric oxide through the iron-copper primary battery and converting the iron element into iron ions that enter the liquid phase specifically includes: in an acidic environment, copper and nitrate react to generate nitric oxide, water and copper ions; then iron reduces the copper ions to obtain copper element and iron ions.

2. The method for treating water for denitrification and phosphorus removal as resource according to claim 1, characterized in that: The nitrate concentration in the liquid phase obtained by reducing the regenerated waste liquid is ≤100 mg / L.

3. The method for treating water for denitrification and phosphorus removal as resource according to claim 1, characterized in that: The method of using alkaline solution to absorb nitrogen oxide gas comprises: Provide a gas absorption tower with top spray of alkali solution; The nitrogen oxide gas is introduced from the bottom of the gas absorption tower to obtain a nitrate solution.

4. The method for treating water for denitrification and dephosphorization as resource according to claim 1, characterized in that: Before the initial waste liquid is treated by the nitric acid-phosphate ion exchange resin, the method further includes filtering and removing particles with a particle size greater than 0.1 mm in the initial waste liquid.

5. A water treatment system for denitrification and phosphorus removal, characterized in that: include: An anion resin tank, wherein a nitric acid-phosphate ion exchange resin is arranged in the anion resin tank, and is used to separate the initial waste liquid into a regeneration waste liquid with a high nitrogen and phosphorus concentration and a dischargeable water with a low nitrogen and phosphorus concentration; A waste liquid reduction reaction device, wherein the waste liquid reduction reaction device is provided with an iron-copper primary battery, and the iron-copper primary battery is used to reduce nitrate in the regenerated waste liquid into nitrogen oxide gas; The reducing of nitrate in the regeneration waste liquid into nitrogen oxide gas comprises: The nitrate in the regenerated waste liquid is converted into nitric oxide through the iron-copper primary battery, and the iron element is converted into iron ions and enters the liquid phase; Gas phase resource recovery equipment, wherein the gas phase resource recovery equipment is provided with alkaline solution, and the alkaline solution is used to absorb nitrogen oxide gas to obtain nitrogen-containing products; A concentration and purification device is used to concentrate and crystallize the water treated by the waste liquid reduction reaction device to obtain a solid ferrous phosphate product, residual liquid and acid condensate; The resin regeneration liquid storage tank is used to mix the residual liquid, the acid condensate and the fresh acid liquid into the resin regeneration liquid. After the nitric acid-phosphate ion exchange resin is saturated, the resin regeneration liquid storage tank releases the resin regeneration liquid to regenerate the nitric acid-phosphate ion exchange resin; The concentration and purification device includes a two-stage MVP crystallizer for obtaining different ferrous salt solids, ferrous phosphate solids and ferrous chloride solids; The method of converting nitrate in the regenerated waste liquid into nitric oxide through the iron-copper primary battery and converting the iron element into iron ions that enter the liquid phase specifically includes: in an acidic environment, copper and nitrate react to generate nitric oxide, water and copper ions; then iron reduces the copper ions to obtain copper element and iron ions.

6. The denitrification and phosphorus removal resource water treatment system according to claim 5 is characterized in that: The denitrification and phosphorus removal resource water treatment system also includes a filtering unit, which is used to filter particles with a particle size greater than 0.1 mm in the initial waste liquid.

7. The denitrification and phosphorus removal resource water treatment system according to claim 5 is characterized by: The gas phase resource recovery equipment is a gas absorption tower.

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