A treatment system and method for sodium alginate production wastewater

Abstract

The present disclosure relates to the field of wastewater treatment technology, and in particular to a treatment system and method for sodium alginate production wastewater. The present disclosure provides a safe and stable treatment system for recycling sodium alginate production wastewater resources by orderly combining a wastewater collection unit, a pretreatment unit, a biochemical unit, a solid-liquid separation unit, an ultrafiltration membrane unit, a reverse osmosis membrane unit, a reverse osmosis effluent regulating unit, a concentrated water crystallization unit, and a calcium chloride conversion unit. The treatment system can effectively recycle calcium resources and water resources in sodium alginate production wastewater and apply them to the production system, saving more than 75% of the water consumption of the production system and more than 80% of the calcium chloride consumption, while reducing the TDS content of the dispatched wastewater by more than 10%, reducing enterprise costs, alleviating local water supply pressure, and facilitating industrial production and application.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and in particular to a treatment system and method for sodium alginate production wastewater. Background Art

[0002] my country is a major country in seaweed farming and processing, and seaweed chemical industry is one of the pillar industries of coastal cities. At present, my country's annual output of sodium alginate is about 50,000 tons, ranking first in the world. Seaweed chemical industry consumes a huge amount of water. Every ton of sodium alginate (sodium alginate) produced consumes 500-800 tons of fresh water resources, most of which are waste calcium water generated in the production process, which contains a large amount of calcium salts, sodium salts, organic matter, etc. that cannot be directly reused. Production enterprises usually discharge wastewater directly into the sewage network after it is treated to meet the standards. This has caused a large waste of water and salt resources. The high-salt and high-hardness production wastewater discharged has caused a heavy burden on the downstream sewage treatment system. The discharge of pollutants into the water body has seriously polluted the environment. At the same time, it has also caused great pressure on corporate production and local water use, especially water use in water-scarce areas.

[0003] In the production process of sodium alginate, the conventional method needs to add calcium chloride solution to the finely filtered gel solution during the extraction process to convert alginate into water-insoluble calcium alginate and precipitate it, thereby separating it from a large number of soluble impurities such as inorganic salts, pigments and water, so as to facilitate further coagulation and purification of alginate. The extracted calcium alginate also needs to be further decalcified with hydrochloric acid to convert calcium alginate into alginic acid, and alginic acid is further converted into sodium alginate with alkali to obtain the final product. In the production process, a large amount of fresh water resources are required in the digestion and dilution links. A large amount of acid, alkali, calcium chloride, sodium carbonate, etc. are required to be added in the digestion, calcification, decalcification, neutralization and other processes. Finally, all of them enter the waste calcium water during the dehydration process, forming production wastewater with high hardness and alkalinity. This part of production wastewater accounts for 80~90% of the water used in the production of sodium alginate. For this part of production wastewater, most companies currently focus on standard treatment, and the effluent discharge standards meet the standards for sewage and wastewater management. There is no large-scale application case for the technology of resource recycling of this part of production wastewater.

[0004] Since waste calcium water contains a large amount of salts such as calcium, sodium, potassium, chlorine, bicarbonate, and a large amount of organic matter, the difficulty in recycling the water resources lies in the stable operation of the desalination system and the efficient removal of organic matter. In view of these problems, how to develop a set of technologies suitable for the recycling of production wastewater, strengthen the clean production of enterprises, reduce the water burden of enterprises and landowners, improve the environmental benefits of the production process, and reduce the production costs of enterprises has become a technical problem that needs to be solved urgently. Summary of the invention

[0005] In order to solve the above technical problems, the present disclosure provides a treatment system and a treatment method for sodium alginate production wastewater. The treatment system and the treatment method develop a set of processes suitable for resource recycling of sodium alginate production wastewater through the orderly combination of multiple water treatment technologies. The processes can not only efficiently desalinate and remove organic matter to optimize water quality, but also recycle calcium resources in the water body, provide production materials for the production system, reduce enterprise costs, and have good environmental and economic benefits.

[0006] In a first aspect, the present disclosure provides a system for treating sodium alginate production wastewater, the treatment system comprising:

[0007] Wastewater collection unit, used to collect and store sodium alginate production wastewater;

[0008] The pretreatment unit is provided with a grid for separating and recovering the calcium alginate flocs and inorganic particles in the sodium alginate production wastewater; and is also provided with a dissolved air flotation device for separating and recovering the calcium alginate flocs in the water body, while blowing off part of the residual chlorine and settling the impurities;

[0009] The biochemical unit degrades part of the organic matter, ammonia nitrogen and phosphorus in the water from the pretreatment unit through aeration hydraulic action and microbial reaction, and absorbs the remaining residual chlorine;

[0010] a solid-liquid separation unit for settling part of the suspended solids in the water from the biochemical unit;

[0011] An ultrafiltration membrane unit, used for filtering part of the suspended solids, colloids and part of the organic matter in the water from the solid-liquid separation unit;

[0012] A reverse osmosis membrane unit is used to deeply purify the water from the ultrafiltration membrane unit to achieve water desalination and obtain new water and concentrated brine respectively;

[0013] A reverse osmosis effluent regulating unit, used to regulate the pH of the new water from the reverse osmosis membrane unit, and to transport the regulated water to the sodium alginate production system for production;

[0014] A concentrated water crystallization unit is used to crystallize concentrated brine from the reverse osmosis membrane unit to obtain calcium bicarbonate crystals;

[0015] And, a calcium chloride conversion unit is used to convert the calcium bicarbonate crystals from the concentrated water crystallization unit into a calcium chloride solution, and transport the obtained calcium chloride solution to the sodium alginate production system for production.

[0016] In the present disclosure, the biochemical unit utilizes the aeration hydraulic action and the biodegradation and bioflocculation of microorganisms to effectively degrade organic matter in waste calcium water, adsorb flocs such as calcium alginate and sodium alginate in the waste water, and prevent alginate from entering the subsequent units to contaminate the ultrafiltration membrane and reverse osmosis membrane; in addition, the macromolecular structure of alginate plays a good supporting role in the growth and reproduction process of microorganisms, and can effectively improve the structural stability and sedimentation performance of sludge flocs. Further, through the solid-liquid separation unit, it is ensured that most of the suspended solids are settled to less than 50 mg / L before the wastewater enters the ultrafiltration membrane unit, and the residual chlorine in the wastewater is completely consumed.

[0017] The ultrafiltration membrane unit and reverse osmosis membrane unit gradually purify the water quality, provide the production system with high-quality reclaimed water that can be recycled, reduce production water, and provide concentrated brine for the recycling of calcium chloride.

[0018] The recovery rate of wastewater after treatment by the reverse osmosis membrane unit can reach more than 75%, and the quality is better than the tap water quality standard. Using it in the production system can better ensure the improvement of product quality. In addition, through the recycling of wastewater, the tap water replenishment volume of the production system can be reduced to 25% of the original water consumption, saving the company more than 75% of production water and the corresponding sewage treatment costs, providing stable and high-quality water supply guarantees for the company's safe and stable production, and reducing water supply pressure for local areas.

[0019] The concentrated brine crystallization unit and the calcium chloride conversion unit gradually convert concentrated brine into the calcium chloride solution required for production, realizing the resource utilization of wastewater. Under the same production conditions (i.e. compared with all the added calcium chloride solution), it can save more than 80% of the calcium chloride consumption, with good economic benefits.

[0020] The combination of the above processes is indispensable, otherwise the stable operation of the entire system and efficient resource recycling cannot be achieved. In addition, the entire system can be equipped with intelligent monitoring according to the specific usage to monitor the entire operation process.

[0021] The following are preferred technical solutions of the present disclosure, but are not intended to be limitations of the technical solutions provided by the present disclosure. Through the following technical solutions, the technical objectives and beneficial effects of the present disclosure can be better achieved and realized.

[0022] As a preferred technical solution of the present invention, in the pretreatment unit, the spacing of the grid is 5~10mm, for example 5mm, 6mm, 7mm, 8mm, 9mm or 10mm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0023] As a preferred technical solution of the present disclosure, the biochemical unit includes a microbial treatment module.

[0024] And / or, an aeration device is provided in the microbial treatment module.

[0025] As a preferred technical solution of the present disclosure, the biochemical unit also includes an internal reflow module for realizing internal circulation of water in the microbial treatment module; and a sludge reflow module for returning sludge from the solid-liquid separation unit to the microbial treatment module.

[0026] It should be noted that the internal reflow module of the biochemical unit does not affect the treated water output of the biochemical unit, and the wastewater still flows into the next unit at the initial treated volume.

[0027] As a preferred technical solution of the present disclosure, the solid-liquid separation unit includes a sedimentation tank;

[0028] The sedimentation tank is provided with energy dissipation equipment inside to eliminate the kinetic energy of the incoming water flow and avoid disturbing the settled solids.

[0029] As a preferred technical solution of the present disclosure, the treatment system further includes a sludge dehydration unit for dehydrating the sludge from the pretreatment unit and the solid-liquid separation unit.

[0030] And / or, the treatment system further comprises an ultrafiltration raw water tank, which is arranged between the solid-liquid separation unit and the ultrafiltration membrane unit, and is used to store treated water from the solid-liquid separation unit.

[0031] And / or, the treatment system further comprises a reverse osmosis water inlet regulating unit, which is arranged between the ultrafiltration membrane unit and the reverse osmosis membrane unit and is used to adjust the pH value of the effluent from the ultrafiltration membrane unit.

[0032] The reverse osmosis water inlet adjustment unit can be set according to the actual water quality. If the outlet pH of the ultrafiltration membrane unit reaches the required standard, there is no need to set it.

[0033] As a preferred technical solution of the present disclosure, the ultrafiltration membrane unit includes a water inlet module, an ultrafiltration membrane unit, a backwash module and a chemical cleaning module.

[0034] In addition, the ultrafiltration membrane unit is provided with a pressure gauge for monitoring the operating pressure difference of the membrane system.

[0035] As a preferred technical solution of the present invention, the reverse osmosis membrane unit includes a pressurizing module consisting of an inlet pump, a high-pressure pump, and an inter-stage booster pump, a reverse osmosis membrane, a produced water reuse pipeline, and a concentrated water delivery pipeline, and is provided with a variety of instruments, including but not limited to a pH meter, an ORP meter, a conductivity meter, a pressure gauge, and a flow meter, etc., for monitoring various data.

[0036] As a preferred technical solution of the present disclosure, the concentrated water crystallization unit includes a crystallization reactor and a dosing module. The crystallization reactor is used to crystallize concentrated brine, and the dosing module is used to add calcium hydroxide into the crystallization reactor.

[0037] In a second aspect, the present disclosure provides a method for treating sodium alginate production wastewater, which is carried out using the treatment system as described in the first aspect, and the treatment method comprises:

[0038] The sodium alginate production wastewater from the wastewater collection unit is sequentially treated by a pretreatment unit, a biochemical unit, a solid-liquid separation unit, an ultrafiltration membrane unit and a reverse osmosis membrane unit to obtain new water and concentrated brine respectively;

[0039] The resulting regenerated water enters the reverse osmosis effluent adjustment unit for pH adjustment;

[0040] The obtained concentrated brine enters the concentrated water crystallization unit, and calcium bicarbonate crystals are obtained after crystallization treatment. The obtained calcium bicarbonate crystals enter the calcium chloride conversion unit and react with hydrochloric acid to generate calcium chloride solution.

[0041] As a preferred technical solution of the present disclosure, the treatment form of the biochemical unit includes any one of an anaerobic-aerobic combined process, an MBBR process or a BAF biofilm process.

[0042] And / or, the hydraulic retention time of the water in the biochemical unit is 8 to 12 hours, such as 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0043] As a preferred technical solution of the present disclosure, the treatment method also includes: enabling the water in the biochemical unit to achieve internal circulation, and the reflux ratio of the internal circulation is 100~300%, for example, 100%, 150%, 200%, 250% or 300%, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0044] In the present disclosure, a certain reflux rate is refluxed to the anaerobic / anoxic section through an internal reflux module, and the reflux liquid contains nitrate. The nitrate enters the anaerobic / anoxic section and undergoes denitrification, which has a denitrification effect and can remove nitrogen-containing organic pollutants in the raw water.

[0045] And / or, the treatment method further includes: returning the sludge obtained after treatment by the solid-liquid separation unit to the biochemical unit, and the reflux ratio is 50~200%, for example, 50%, 100%, 150% or 200%, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0046] In the present disclosure, the reflux ratio refers to the ratio of the reflux flow rate to the wastewater flow rate passing from the wastewater collection unit into the pretreatment unit.

[0047] In the biochemical unit, the concentration of sludge is 2-4 g / L, such as 2 g / L, 3 g / L or 4 g / L, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0048] And / or, the membrane flux of the ultrafiltration membrane unit is 40~100LMH, for example, 40LMH, 60LMH, 80LMH or 100LMH, etc.; the operation cycle is 30~60min, for example, 30min, 40min, 50min or 60min, etc., but is not limited to the listed values, and other unlisted values ​​within the above range are also applicable.

[0049] And / or, the membrane flux of the reverse osmosis membrane unit is 15~20LMH, for example, 15LMH, 17LMH, 19LMH or 20LMH, etc.; the operation cycle is 10~24h, for example, 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h, etc., but is not limited to the listed values, and other unlisted values ​​within the above range are also applicable.

[0050] And / or, the water body treated by the ultrafiltration membrane unit is adjusted to pH 6.5-7.0 using hydrochloric acid, for example, 6.5, 6.6, 6.7, 6.8, 6.9 or 7.0, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable, and then passed into the reverse osmosis membrane unit.

[0051] And / or, during the treatment process, the reverse osmosis membrane unit is also added with an antiscalant, and the dosage of the antiscalant is 3~5 mg / L, for example, 3 mg / L, 4 mg / L or 5 mg / L, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0052] And / or, the water treated by the reverse osmosis effluent regulating unit is transported to the sodium alginate production system for production.

[0053] And / or, the concentrated water crystallization unit uses calcium hydroxide to adjust the pH value of the system to 8.3-9.0 during the treatment process, such as 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9 or 9.0, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0054] And / or, the processing time of the concentrated water crystallization unit is 15 to 30 minutes, for example, 15 minutes, 20 minutes, 25 minutes or 30 minutes, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0055] And / or, the calcium chloride solution obtained after being treated by the calcium chloride conversion unit is transported to the sodium alginate production system for production.

[0056] As a preferred technical solution of the present disclosure, the concentrated water crystallization unit

[0057] And / or, in the concentrated water crystallization unit, the dosage of calcium hydroxide satisfies Formula I:

[0058] Formula I

[0059] in, ——Calcium hydroxide addition flow rate, m 3 / d;

[0060] ——Brine flow rate, m 3 / d;

[0061] α ——The proportion of bicarbonate in the brine, ,in, k 1=10 -6.35 , k 2=10 -10.33 , pH is the pH value of the inlet water of the concentrated water crystallization unit;

[0062] ——Concentration of bicarbonate in brine, mg / L;

[0063] K 1——Empirical response coefficient, 0.5-1.0;

[0064] ——density of calcium hydroxide solution, g / ml;

[0065] r 1——Mass percentage of calcium hydroxide;

[0066] The relative molecular mass of calcium hydroxide is 74; the relative molecular mass of bicarbonate is 61;

[0067] And / or, in the calcium chloride conversion unit, the dosage of hydrochloric acid satisfies Formula II:

[0068] Formula II

[0069] in, M HCl ——The amount of hydrochloric acid required for the preparation of calcium chloride, m 3 / d;

[0070] M 1——the output of calcium bicarbonate crystals of the concentrated water crystallization unit, kg / d;

[0071] K 2——Reaction coefficient, take 1.0~1.2, and obtain it according to actual conditions;

[0072] r 2——mass percentage of hydrochloric acid, preferably 30~37%;

[0073] The relative molecular mass of calcium bicarbonate is 162.

[0074] In the prior art, the production system of sodium alginate consumes a large amount of water resources and calcium chloride. In the present disclosure, by calculating the output of calcium bicarbonate crystals, the amount of calcium chloride that can be recycled is obtained, and then according to the subsequent production needs, the lack of calcium chloride is supplemented in the production system. Under the same production conditions, more than 80% of the calcium chloride can be saved, and the TDS content of the discharged wastewater can be reduced by more than 10%, realizing the resource treatment of concentrated water.

[0075] The yield of calcium bicarbonate crystals can be calculated by formula III:

[0076] Formula III

[0077] in, M 1——yield of calcium bicarbonate crystals, kg / d;

[0078] K 3——Productivity coefficient, based on experience, it is 1.10~1.50;

[0079] C inf ——Average hardness concentration of influent to the concentrate crystallization unit (measured in CaCO3), mg / L;

[0080] C eff ——Average hardness concentration of the concentrated water crystallization unit (calculated as CaCO3), mg / L;

[0081] ——Brine flow rate, m 3 / d;

[0082] The relative molecular mass of calcium bicarbonate is 162; the relative molecular mass of calcium carbonate is 100. Further, based on the amount of calcium chloride recycled by the treatment system of the present disclosure, the amount of calcium chloride to be supplemented by the production system satisfies Formula IV:

[0083] Formula IV

[0084] in,C 0——Concentration of calcium chloride solution required to be added to the production system, mg / L;

[0085] Q 0——Production water flow rate to be supplemented, m 3 / d;

[0086] M 1——The amount of calcium bicarbonate crystals produced by the concentrated water crystallization unit, kg / d;

[0087] r 3——Mass percentage of calcium chloride solution, generally 10% according to actual production needs;

[0088] ——density of calcium chloride solution, g / ml;

[0089] The relative molecular mass of calcium bicarbonate is 162; the relative molecular mass of calcium chloride is 111;

[0090] when M When 2≤0, it means that the production system does not need additional calcium chloride.

[0091] Compared with the prior art, the technical solution provided by the embodiments of the present disclosure has the following advantages:

[0092] The present invention provides a safe and stable treatment system for recycling wastewater resources from sodium alginate production by orderly combining a wastewater collection unit, a pretreatment unit, a biochemical unit, a solid-liquid separation unit, an ultrafiltration membrane unit, a reverse osmosis membrane unit, a reverse osmosis effluent adjustment unit, a concentrated water crystallization unit, and a calcium chloride conversion unit. The treatment system can effectively recycle calcium resources and water resources in sodium alginate production wastewater and apply them to the production system, saving more than 75% of the water consumption of the production system and more than 80% of the calcium chloride consumption, while reducing the TDS content of the dispatched wastewater by more than 10%, reducing enterprise costs, alleviating local water supply pressure, and facilitating industrial production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0094] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0095] Figure 1It is a structural schematic diagram of a system for treating sodium alginate production wastewater according to a specific embodiment of the present disclosure;

[0096] Figure 2 This is a graph showing the change in calcium hardness and hardness removal rate of water in and out of the crystallization reactor during operation of the concentrated water crystallization unit in Example 1 of the present disclosure;

[0097] Figure 3 This is a particle size distribution diagram of the calcium bicarbonate crystals obtained from the concentrated water crystallization unit in Example 1 of the present disclosure.

[0098] Among them, 1. Production system; 1-1. Tap water feeding unit; 1-2. Calcium chloride feeding unit; 2. Wastewater collection unit; 3. Pretreatment unit; 4. Biochemical unit; 4-1 Internal reflux pump; 4-2. Sludge reflux pump; 5. Solid-liquid separation unit; 6. Ultrafiltration raw water tank; 7. Ultrafiltration membrane unit; 8. Reverse osmosis inlet regulating unit; 9. Reverse osmosis membrane unit; 10. Reverse osmosis effluent regulating unit; 11. Concentrated water crystallization unit; 12. Calcium chloride conversion unit; 13. Sludge dehydration unit.

[0099] It should be noted that 100%Q, 75%Q and 25%Q in the figure only represent exemplary flow distribution of wastewater. DETAILED DESCRIPTION

[0100] In order to more clearly understand the above-mentioned objectives, features and advantages of the present disclosure, the scheme of the present disclosure will be further described below. It should be noted that the embodiments of the present disclosure and the features in the embodiments can be combined with each other without conflict.

[0101] In the following description, many specific details are set forth to facilitate a full understanding of the present disclosure, but the present disclosure may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present disclosure, rather than all of the embodiments.

[0102] It should be noted that in order to fully explain the operation of the entire processing system, this disclosure incorporates the production system into the system structure;

[0103] The production system 1, including a tap water feeding unit 1-1 and a calcium chloride feeding unit 1-2, is used for producing sodium alginate and generating sodium alginate production wastewater.

[0104] The present invention provides a system for treating sodium alginate production wastewater, the structural schematic diagram of which is shown in FIG. Figure 1 As shown,

[0105] The processing system comprises:

[0106] A wastewater collection unit 2, used for collecting and storing sodium alginate production wastewater from the production system 1;

[0107] The pretreatment unit 3 is provided with a grid with a spacing of 5 to 10 mm, which is used to separate and recover the calcium alginate flocs and inorganic particles in the water body; it is also provided with a dissolved air flotation device, which is used to separate and recover the calcium alginate flocs in the water body, blow off part of the residual chlorine, and settle the impurities;

[0108] The biochemical unit 4 degrades part of the organic matter, ammonia nitrogen and phosphorus in the water from the pretreatment unit 3 through aeration hydraulic action and microbial reaction, and absorbs the remaining residual chlorine;

[0109] A solid-liquid separation unit 5, used to settle part of the suspended solids in the water from the biochemical unit 4;

[0110] An ultrafiltration raw water tank 6, used for storing the treated water from the solid-liquid separation unit 5;

[0111] The ultrafiltration membrane unit 7 is used to filter part of the suspended solids, colloids and part of the organic matter in the water from the ultrafiltration raw water pool 6;

[0112] Optionally, a reverse osmosis water inlet regulating unit 8 is used to adjust the pH value of the outlet water of the ultrafiltration membrane unit 7;

[0113] The reverse osmosis membrane unit 9 is used to deeply purify the water from the reverse osmosis water inlet regulating unit 8 to achieve water desalination, and obtain new water and concentrated brine respectively;

[0114] The reverse osmosis effluent regulating unit 10 is used to adjust the pH of the new water from the reverse osmosis membrane unit 9 and transport the adjusted water to the production system 1 for production;

[0115] A concentrated water crystallization unit 11 is used to crystallize the concentrated brine from the reverse osmosis membrane unit 9 to obtain calcium bicarbonate crystals;

[0116] A calcium chloride conversion unit 12 is used to convert the calcium bicarbonate crystals from the concentrated water crystallization unit 11 into a calcium chloride solution, and to transport the obtained calcium chloride solution to the production system 1 for production;

[0117] And, the sludge dehydration unit 13 is used to collect the sludge from the pretreatment unit 3 and the solid-liquid separation unit 5 and dehydrate it.

[0118] Further, the biochemical unit 4 includes a microbial processing module;

[0119] Furthermore, the biochemical unit 4 further comprises an internal reflow module, the internal reflow module is provided with an internal reflow pump 4-1 for realizing the internal circulation of the water in the microbial treatment module; and a sludge reflow module, the sludge reflow module is provided with a sludge reflow pump 4-2 for returning the sludge from the solid-liquid separation unit to the microbial treatment module;

[0120] Furthermore, the solid-liquid separation unit 5 comprises a sedimentation tank; an energy dissipation device is arranged inside the sedimentation tank to eliminate the kinetic energy of the influent water flow to avoid disturbing the settled solids;

[0121] Furthermore, the concentrated brine crystallization unit 11 includes a crystallization reactor and a dosing module. The crystallization reactor is used to crystallize concentrated brine, and the dosing module is used to add calcium hydroxide into the crystallization reactor.

[0122] Example 1

[0123] This embodiment provides a treatment system and method for sodium alginate production wastewater. The treatment system refers to the treatment system in the specific implementation, wherein:

[0124] The grid spacing is 5 mm.

[0125] The processing method comprises:

[0126] Wastewater collection unit 2 collects sodium alginate production wastewater from a seaweed chemical enterprise. The wastewater contains COD 400~600mg / L, ammonia nitrogen 10~40mg / L, suspended solids 100~300mg / L, and total phosphorus 1~4mg / L.

[0127] The sodium alginate production wastewater from the wastewater collection unit 2 is passed into the pretreatment unit 3 for treatment, wherein the operating parameters of the dissolved air flotation equipment are: reflux ratio 15-30%, dissolved air ratio 0.04-0.06;

[0128] The water body treated by the pretreatment unit 3 is passed into the biochemical unit 4, and the biochemical unit 4 adopts an anaerobic-aerobic combined process for treatment, and the hydraulic retention time is controlled to be 4h (anaerobic section) + 6h (aerobic section), wherein the concentration of dissolved oxygen in the aerobic section is controlled to be not less than 2mg / L; at the same time, the effluent of the aerobic section in the biochemical unit 4 is controlled to flow back to the anaerobic section of the biochemical unit 4 at a reflux ratio of 300%, forming an internal circulation of the biochemical unit 4; after treatment by the biochemical unit 4, the effluent COD is <80mg / L, the suspended solids are <15mg / L, the ammonia nitrogen is <1mg / L, and the TOC is <20mg / L;

[0129] The water treated by the biochemical unit 4 is passed into the solid-liquid separation unit 5, and sludge and treated water are obtained after solid-liquid separation. A part of the obtained sludge is returned to the biochemical unit 4 at a return ratio of 50%, so that the sludge concentration in the biochemical unit 4 is 2-4 g / L; the other part enters the sludge dehydration unit 13 for dehydration;

[0130] The treated water obtained from the solid-liquid separation unit 5 enters the ultrafiltration membrane unit 6 for ultrafiltration treatment, wherein the ultrafiltration membrane flux is 60LMH and the operation cycle is 40-60min;

[0131] The water treated by the ultrafiltration membrane unit 6 flows into the reverse osmosis water inlet regulating unit 8 through the ultrafiltration raw water pool 7, and the pH of the water is adjusted to 6.5-7.0 with hydrochloric acid; then the water is passed into the reverse osmosis membrane unit 9 for reverse osmosis treatment to obtain new water and concentrated brine respectively; wherein, the reverse osmosis membrane flux is 16-18LMH, the operation cycle is 600-700min, and the scale inhibitor dosage is 3-5mg / L;

[0132] The new water obtained by the reverse osmosis membrane unit 9 enters the reverse osmosis effluent regulating unit 10, and sodium hydroxide is added to adjust the pH to 6.5, and then it is transported to the production system 1 for production;

[0133] The concentrated brine (calcium hardness reaches 5000 mg / L) obtained from the reverse osmosis membrane unit 9 enters the concentrated water crystallization unit 11, and calcium hydroxide is added to control the system pH to 8.3~8.5 (the amount of calcium hydroxide added is calculated according to formula I, where the empirical reaction coefficient K 1 is taken as 0.52), and after crystallization treatment, calcium bicarbonate crystals with a purity of more than 95% are obtained (the yield is calculated according to formula III, where the yield coefficient K 3 takes 1.24~1.47); after being treated by the concentrated water crystallization unit 11, the removal rate of public calcium hardness in the water body reaches 80~85%, the effluent COD<300mg / L, TOC<100mg / L, ammonia nitrogen<4mg / L, TP<5mg / L, and TDS reaches 16000~20000mg / L, meeting the water quality requirements of the downstream treatment unit;

[0134] Further, Figure 2 The calcium hardness and hardness removal rate of the inlet and outlet water of the crystallization reactor during the operation of the concentrated water crystallization unit 11 are shown. Figure 2 It can be seen that when the inlet water hardness of the crystallization reactor is kept stable at 5000 mg / L, the outlet water hardness is basically stable at 600~1000 mg / L, and the hardness removal rate is kept stable at 80~85%;

[0135] Figure 3The particle size distribution diagram of the calcium bicarbonate crystals obtained by the concentrated water crystallization unit 11; Table 1 The particle size distribution results of the calcium bicarbonate crystals obtained by the concentrated water crystallization unit 11, Figure 3 As shown in Table 1, the calcium bicarbonate crystals grow well, and the crystal size is mainly distributed in the range of 20-200 μm, which greatly improves the sedimentation performance of the crystals and facilitates the crystals to be discharged from the system after solid-liquid separation in the crystallization reactor;

[0136] Table 1

[0137]

[0138] The calcium bicarbonate crystals obtained in the concentrated water crystallization unit 11 enter the calcium chloride conversion unit 12 and react with hydrochloric acid (the amount of hydrochloric acid added is calculated by formula II, where the reaction coefficient K 2 takes 1.05) and generates calcium chloride solution after reaction, which is transported to production system 1 for production.

[0139] Furthermore, the tap water feeding unit 1-1 and the calcium chloride feeding unit 1-2 in the production system 1 are additionally supplemented according to the amount of new water and calcium chloride recovered in the treatment system. The amount of calcium chloride supplemented by the calcium chloride feeding unit is calculated according to Formula IV.

[0140] It should be noted that, based on the fluctuations in the operating conditions of the production system, the water quality of the obtained sodium alginate production wastewater fluctuates within a certain range. Therefore, the treatment method described in this embodiment is based on the experience of the operator within the above operating range to ensure the stable operation of the entire system.

[0141] Under the stable operation of this embodiment, the water consumption of the production system can be saved by more than 75%, and the calcium chloride consumption can be saved by more than 80%.

[0142] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0143] The above description is only a specific embodiment of the present disclosure, so that those skilled in the art can understand or implement the present disclosure. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure will not be limited to the embodiments described herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A treatment device for sodium alginate production wastewater, characterized in that: The processing device comprises: Wastewater collection unit, used to collect and store sodium alginate production wastewater; The pretreatment unit is provided with a grid for separating and recovering the calcium alginate flocs and inorganic particles in the sodium alginate production wastewater; and is also provided with a dissolved air flotation device for separating and recovering the calcium alginate flocs in the water body, while blowing off part of the residual chlorine and settling the impurities; The biochemical unit degrades part of the organic matter, ammonia nitrogen and phosphorus in the water from the pretreatment unit through aeration hydraulic action and microbial reaction, and absorbs the remaining residual chlorine; The biochemical unit includes a microbial processing module; The biochemical unit further comprises an internal reflow module for realizing internal circulation of water in the microbial treatment module, and a sludge reflow module for reflowing sludge from the solid-liquid separation unit to the microbial treatment module; a solid-liquid separation unit for settling part of the suspended solids in the water from the biochemical unit; An ultrafiltration membrane unit, used for filtering part of the suspended solids, colloids and part of the organic matter in the water from the solid-liquid separation unit; A reverse osmosis membrane unit is used to deeply purify the water from the ultrafiltration membrane unit to achieve water desalination and obtain new water and concentrated brine respectively; A reverse osmosis effluent regulating unit, used for regulating the pH of the new water from the reverse osmosis membrane unit; A concentrated water crystallization unit is used to crystallize concentrated brine from the reverse osmosis membrane unit to obtain calcium bicarbonate crystals; and a calcium chloride conversion unit for converting the calcium bicarbonate crystals from the concentrated water crystallization unit into a calcium chloride solution.

2. The processing device according to claim 1, characterized in that The solid-liquid separation unit includes a sedimentation tank; The sedimentation tank is provided with energy dissipation equipment inside to eliminate the kinetic energy of the incoming water flow and avoid disturbing the settled solids.

3. The processing device according to claim 1, characterized in that The concentrated water crystallization unit comprises a crystallization reactor and a dosing module. The crystallization reactor is used to crystallize concentrated brine, and the dosing module is used to add calcium hydroxide into the crystallization reactor.

4. The processing device according to claim 1, characterized in that The treatment device further comprises a sludge dehydration unit for dehydrating the sludge from the pretreatment unit and the solid-liquid separation unit; And / or, the treatment device further comprises an ultrafiltration raw water tank, which is arranged between the solid-liquid separation unit and the ultrafiltration membrane unit, and is used to store the treated water from the solid-liquid separation unit; And / or, the treatment device further includes a reverse osmosis water inlet regulating unit, which is arranged between the ultrafiltration membrane unit and the reverse osmosis membrane unit and is used to adjust the pH value of the effluent from the ultrafiltration membrane unit.

5. A method for treating sodium alginate production wastewater, characterized in that: The processing method is carried out using the processing device according to any one of claims 1 to 3, wherein the processing method comprises: The sodium alginate production wastewater from the wastewater collection unit is sequentially treated by a pretreatment unit, a biochemical unit, a solid-liquid separation unit, an ultrafiltration membrane unit and a reverse osmosis membrane unit to obtain new water and concentrated brine respectively; The resulting regenerated water enters the reverse osmosis effluent adjustment unit for pH adjustment; The obtained concentrated brine enters the concentrated water crystallization unit, and calcium bicarbonate crystals are obtained after crystallization treatment. The obtained calcium bicarbonate crystals enter the calcium chloride conversion unit and react with hydrochloric acid to generate calcium chloride solution.

6. The processing method according to claim 5, characterized in that: The treatment form of the biochemical unit includes any one of an anaerobic-aerobic combined process, an MBBR process or a BAF biofilm process; And / or, the hydraulic retention time of the water in the biochemical unit is 8 to 12 hours.

7. The processing method according to claim 6, characterized in that: The treatment method further comprises: enabling the water in the biochemical unit to achieve internal circulation, wherein the reflux ratio of the internal circulation is 100-300%; And / or, the treatment method further comprises: returning the sludge obtained after treatment by the solid-liquid separation unit to the biochemical unit, with a return ratio of 50-200%; In the biochemical unit, the concentration of sludge is 2-4 g / L; And / or, the membrane flux of the ultrafiltration membrane unit is 40-100LMH, and the operation cycle is 30-60min; And / or, the membrane flux of the reverse osmosis membrane unit is 15-20LMH, and the operation cycle is 10-24h; And / or, the water treated by the ultrafiltration membrane unit is adjusted to pH 6.5-7.0 using hydrochloric acid, and then passed into the reverse osmosis membrane unit; And / or, during the treatment process, the reverse osmosis membrane unit further adds an antiscalant, wherein the dosage of the antiscalant is 3-5 mg / L; and / or, the water treated by the reverse osmosis effluent regulating unit is transported to a sodium alginate production system for production; And / or, the concentrated water crystallization unit uses calcium hydroxide to adjust the pH value of the system to 8.3-9.0 during the treatment process; And / or, the treatment time of the concentrated water crystallization unit is 15 to 30 minutes; And / or, the calcium chloride solution obtained after being treated by the calcium chloride conversion unit is transported to the sodium alginate production system for production.

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