A method for treating aquaculture wastewater

Abstract

The application discloses a kind of aquaculture wastewater treatment methods, under alkaline condition, introduce aluminum, magnesium element to lime, form calcium hydroxide composite system, use cationic polyacrylamide in calcium hydroxide composite system and pre-aggregation into porous flocculation dispersed calcium hydroxide composite system particle, form improved lime;After preliminary solid-liquid separation and water quality regulation, improved lime is put into aquaculture wastewater and is stirred evenly.The application provides a kind of aquaculture wastewater treatment method, uses improved lime instead of ordinary lime, improved lime has stronger adsorption, flocculation capacity lime composite system, with greater specific surface area, increase active site density, it is favorable to utilize electrostatic adsorption positive suspended solids, improve flocculation capacity, PAM is favorable to the adsorption, flocculation of negative suspended solids, calcium aluminate has strong ion exchange capacity, and the silicate generated after improved lime is dissolved in water can be coated flocculation, improve the adsorption and flocculation strength of composite system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aquaculture wastewater treatment, and more particularly to an aquaculture wastewater treatment method. BACKGROUND

[0002] In the traditional process, the aquaculture wastewater is treated by adding alkali to blow off, i.e., lime or liquid alkali is added to adjust the pH to alkaline, so that the ammonium ion is converted into free ammonia, and then the ammonia nitrogen is separated by air blowing or vacuum pumping, and then anaerobic fermentation is performed to complete the treatment of the aquaculture wastewater.

[0003] However, this method has significant defects: the reaction activity of single lime treatment is low, the dissolution rate of calcium hydroxide and the release efficiency of hydroxyl ion are limited, which leads to incomplete conversion of ammonia nitrogen, and the calcium carbonate precipitate floc generated is loose, has small specific surface area, and has weak adsorption capacity for suspended solids, colloidal particles and heavy metal ions in the wastewater, so it is difficult to achieve deep purification. SUMMARY

[0004] In order to improve the treatment effect of lime on aquaculture wastewater, the present application provides an aquaculture wastewater treatment method, which uses modified lime instead of ordinary lime. 3+ , Mg 2+ , PAM, SiO3 2- and Ca(OH)2to form a lime composite system with stronger adsorption and flocculation capacity. 3+ , Mg 2+ and Ca(OH)2to increase the specific surface area of the composite crystal nucleus and increase the active site density, which is beneficial to the use of electrostatic adsorption of positively charged suspended solids and improves the flocculation capacity. 2- , PAM can neutralize the negative charge on the surface of suspended solids, and its long chain structure is beneficial to the adsorption and flocculation of negatively charged suspended solids such as phosphate, and the calcium aluminosilicate complex salt has strong ion exchange capacity, and SiO3 2- generated by the dissolution of modified lime in water can coat the floc to improve the adsorption capacity and flocculation strength of the composite system.

[0005] The technical scheme of the present application is as follows:

[0006] An aquaculture wastewater treatment method, under alkaline conditions, aluminum and magnesium elements are introduced into lime to form a calcium hydroxide composite system, and cationic polyacrylamide is used in the calcium hydroxide composite system to pre-agglomerate the dispersed calcium hydroxide composite system particles into porous flocs to form modified lime;

[0007] The aquaculture wastewater is subjected to preliminary solid-liquid separation and water quality adjustment, and then modified lime is added and stirred uniformly to adjust the pH of the aquaculture wastewater so that ammonia nitrogen mainly exists in the form of free ammonia, and the free ammonia is separated from the water body by using a device, and the ammonia gas is recovered by spraying clean water to obtain ammonia water;

[0008] Carbon dioxide is introduced into the aquaculture wastewater after ammonia removal to reduce the pH of the aquaculture wastewater to form a turbid liquid.

[0009] After waiting for the completion of the precipitation reaction, the aquaculture wastewater is subjected to solid-liquid separation.

[0010] The above aquaculture wastewater treatment method, the preparation method of the modified lime comprises the following steps:

[0011] Step S1. Weigh the quicklime, add deionized water and stir to digest, to generate a calcium hydroxide suspension;

[0012] Step S2. After dissolving aluminum sulfate in warm water, slowly drop it into the calcium hydroxide suspension to adjust the pH of the system, and constant temperature stirring to generate aluminum hydroxide colloid and calcium aluminate complex salt;

[0013] Step S3. Add magnesium chloride, adjust the pH to strong alkaline and heat to generate magnesium hydroxide, forming a calcium hydroxide-aluminum magnesium hydroxide-magnesium hydroxide ternary hydroxide complex system;

[0014] Step S4. Dissolve cationic polyacrylamide in deionized water to prepare a solution, add the complex system, heat to and continue stirring to form a calcium hydroxide-aluminum magnesium hydroxide-polyacrylamide three-dimensional network flocculation;

[0015] Step S5. Filter the reaction product, wash it with deionized water until there is no residual ion, dry and grind into powder.

[0016] Further, after step 4, sodium silicate solution is added to the system to form a hydroxide-silicate composite gel structure.

[0017] The above aquaculture wastewater treatment method, the raw material mass ratio of the modified lime is:

[0018] Aluminum sulfate: polyacrylamide: magnesium chloride: lime = (10-15): (8-12): (5-8): (65-77).

[0019] Further, the raw material mass ratio of the modified lime is:

[0020] Aluminum sulfate: polyacrylamide: magnesium chloride: lime: sodium silicate = (10-15): (8-12): (5-8): (65-77): (2-5).

[0021] The method for treating aquaculture wastewater comprises the following steps: adding the silicate into the porous flocculation system formed by the cationic polyacrylamide, so that the modified lime contains calcium aluminum silicate double salt; and releasing the silicate to coat the flocculation when the modified lime is put into the aquaculture wastewater.

[0022] The method for treating aquaculture wastewater comprises the following steps: adding the silicate into the porous flocculation system formed by the cationic polyacrylamide, so that the modified lime contains calcium aluminum silicate double salt; and releasing the silicate to coat the flocculation when the modified lime is put into the aquaculture wastewater.

[0023] The aquaculture wastewater flows through the grid, and the multi-stage grid is used to remove the larger floating objects and smaller suspended impurities.

[0024] And / or

[0025] The aquaculture wastewater enters the sedimentation tank, and the gravity sedimentation principle is used to make the particles in the aquaculture wastewater precipitate.

[0026] The method for treating aquaculture wastewater comprises the following steps: adding the silicate into the porous flocculation system formed by the cationic polyacrylamide, so that the modified lime contains calcium aluminum silicate double salt; and releasing the silicate to coat the flocculation when the modified lime is put into the aquaculture wastewater.

[0027] Further, the effluent after the anaerobic ammonia oxidation treatment enters the aerobic activated sludge reaction device, the aerobic activated sludge reaction device realizes oxygenation through the air blower, the clear liquid after the aerobic microbial treatment enters the MBR membrane bioreactor, the air blower realizes gas ramming to the MBR membrane bioreactor, the clear liquid passing through the MBR membrane bioreactor is reused after adsorption, and the sludge cut off by the MBR membrane bioreactor participates in the ammonia removal treatment of the modified lime on the aquaculture wastewater.

[0028] The method for treating aquaculture wastewater comprises the following steps: adding the silicate into the porous flocculation system formed by the cationic polyacrylamide, so that the modified lime contains calcium aluminum silicate double salt; and releasing the silicate to coat the flocculation when the modified lime is put into the aquaculture wastewater.

[0029] The method for treating aquaculture wastewater comprises the following steps: adding the silicate into the porous flocculation system formed by the cationic polyacrylamide, so that the modified lime contains calcium aluminum silicate double salt; and releasing the silicate to coat the flocculation when the modified lime is put into the aquaculture wastewater.

[0030] The method for treating aquaculture wastewater comprises the following steps: adding the silicate into the porous flocculation system formed by the cationic polyacrylamide, so that the modified lime contains calcium aluminum silicate double salt; and releasing the silicate to coat the flocculation when the modified lime is put into the aquaculture wastewater.

[0031] 1. The aluminum hydroxide, magnesium hydroxide and silicate double salt in the modified lime can simultaneously remove suspended solids, colloidal organic matter, phosphorus and heavy metal ions through adsorption, complexation and other effects, can improve the treatment effect of calcium hydroxide in the original lime on ammonia nitrogen, realizes the collaborative treatment of multiple pollutants, and is more suitable for complex aquaculture wastewater.

[0032] 2. Without introducing acidic substances, the influence on subsequent anaerobic treatment is avoided.

[0033] 3. The multiple particles connected by PAM increase the size of the floc and the porosity, which improves the settling rate, the ammonia nitrogen overflow rate, and the flocculation and filtration effects.

[0034] 4. The composite system of aluminum-magnesium-calcium hydroxide has a larger specific surface area than single calcium hydroxide, more active sites, and better reaction with ammonium, thus having better deamination effect.

[0035] 5. The modified lime calcium aluminum silicate double salt has strong ion exchange capacity, improves the adsorption capacity of lime for ammonium and phosphate, and the hydrolyzed silicate can coat the floc to enhance the floc strength, thus accelerating the precipitation effect. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0037] Figure 1 The process flow chart for the present application of aquaculture wastewater treatment. DETAILED DESCRIPTION

[0038] In order to make the technical problems, technical solutions and beneficial effects of the present application more clear, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0039] A method for treating aquaculture wastewater, under alkaline conditions, aluminum and magnesium elements are introduced into lime to form a calcium hydroxide composite system, and cationic polyacrylamide is used in the calcium hydroxide composite system to pre-agglomerate the dispersed calcium hydroxide composite system particles into porous flocs to form modified lime; after the aquaculture wastewater is subjected to preliminary solid-liquid separation and water quality adjustment, the modified lime is added and stirred uniformly, the pH of the aquaculture wastewater is adjusted so that the ammonia nitrogen mainly exists in the form of free ammonia, the free ammonia is separated from the water body using equipment, and ammonia gas is recovered by spraying water to obtain ammonia water; carbon dioxide is introduced into the deaminated aquaculture wastewater to reduce the pH of the aquaculture wastewater to form a turbid liquid; after waiting for the precipitation reaction to complete, the aquaculture wastewater is subjected to solid-liquid separation.

[0040] As shown in Figure 1 , the specific treatment process is as follows.

[0041] The aquaculture wastewater is transported to the adjusting tank to adjust the water quality and quantity, so that the subsequent treatment process is more stable. Meanwhile, the preliminary sedimentation of large-particle impurities can be realized by using sedimentation, filtration, blocking and other methods, so as to reduce the burden of the subsequent treatment unit.

[0042] Specifically, the aquaculture wastewater first flows through the grid to remove larger floating objects and smaller suspended impurities by using multi-stage grids (i.e. grids with different grid bar spacings, for example, the grid bar spacing of a coarse grid is 10-50 mm, and the grid bar spacing of a fine grid is 1-10 mm). The aquaculture wastewater enters the sedimentation tank to make the inorganic particles such as sand and stones in the aquaculture wastewater precipitate by using the principle of gravity sedimentation, such as a horizontal flow sedimentation tank or a cyclone sedimentation tank. The grid blocking or the sedimentation in the sedimentation tank can be used alone or in sequence, i.e. the grid blocking is first used and then the sedimentation in the sedimentation tank is used.

[0043] Since the discharge of aquaculture wastewater is intermittent and unstable, the water quality and quantity fluctuate greatly, so it is necessary to enter the adjusting tank. The adjusting tank plays a role in homogenizing the water quality and quantity, so that the subsequent treatment process is more stable. The residence time of the adjusting tank is generally determined according to the aquaculture scale and the discharge law of the aquaculture wastewater, and is usually 8-24 hours. In the adjusting tank, a stirring device such as a mechanical stirrer or an air stirring system can be provided to make the aquaculture wastewater fully mixed and avoid the precipitation of suspended solids. At the same time, the pH value, ammonia nitrogen parameter, phosphorus parameter, COD and other indicators of the aquaculture wastewater in the adjusting tank are monitored to provide data basis for the subsequent treatment.

[0044] The aquaculture wastewater is introduced into the pH adjusting device, and modified lime is added and uniformly stirred to adjust the pH of the aquaculture wastewater to 11-11.5, so that the ammonia nitrogen in the aquaculture wastewater mainly exists in the form of free ammonia (NH3). In this process, the calcium hydroxide of the modified lime dissolves and ionizes into hydroxyl ions (OH - ) in water, thereby increasing the pH value of the aquaculture wastewater. Under strong alkaline conditions, the hydroxyl ions (OH - ) react with the ammonium ions (NH4 + ) in the aquaculture wastewater, and the hydroxyl ions (OH - ) react with the ammonium ions (NH4), which promotes the balance to move in the direction of generating free ammonia, i.e. NH4 + +OH −NH3+H2O. In this process, the composite crystal nucleus formed by aluminum hydroxide, magnesium hydroxide and calcium hydroxide has larger specific surface area and more active points, which improves the reaction rate of calcium hydroxide and ammonium ion. At the same time, the Al(OH)3, Mg(OH)2 particles in the modified lime and polyacrylamide (PAM) play a flocculation effect, and the positively charged PAM molecules adsorb the negatively charged suspended solids (such as fecal particles and organic colloids) in the wastewater, forming a flocculation body through charge neutralization and bridging effect, and then forming a dense precipitate covered by calcium silicate (CaSiO3) and silicate, which enhances the strength of the flocculation body and accelerates the settlement of suspended solids.

[0045] At this time, the ammonia nitrogen in the aquaculture wastewater is precipitated in the form of free ammonia. The free ammonia is separated from the water body by vacuum suction, air stripping or mechanical stirring (vacuum suction uses a vacuum pump to create a negative pressure environment in the ammonia removal device, so that the free ammonia is more easily released from the water body; air stripping is to blow a large amount of air into the wastewater to strip the free ammonia; mechanical stirring increases the contact area and contact time of the wastewater and air through the high-speed rotation of the stirrer, and accelerates the volatilization of free ammonia), and then is discharged from the gas outlet at the top of the ammonia removal device and enters the absorption tower, where the ammonia gas is recovered by spraying water, and ammonia water is obtained.

[0046] After the ammonia is removed, the mixed liquid enters the precipitation device, and carbon dioxide is introduced into the mixed liquid, and the carbon dioxide reacts with the calcium ions in the mixed liquid to form calcium carbonate precipitate (Ca 2+ +CO2+H2O⇌CaCO3↓+2H + ), and at the same time, the pH of the mixed liquid is reduced to 7-7.5 (under weak alkaline conditions, Al(OH)3, Mg(OH)2 precipitate remains stable and has low solubility, which acts as a flocculation skeleton to wrap CaCO3 particles to form a dense precipitate), forming a turbid liquid. In this process, the magnesium hydroxide, aluminum hydroxide and polyacrylamide in the modified lime continue to enhance the flocculation and precipitation effect, so that the impurities and pollutants are more easily settled.

[0047] The initial clear liquid is strongly alkaline, and as CO2 continues to be introduced, the residual hydroxide ions (OH - ) react with dissolved CO2 to form bicarbonate ions (HCO3 - ), and the carbonate ions (CO3 2- ) in the system are also gradually converted to bicarbonate ions (HCO3 - ), establishing a bicarbonate-carbonate weak acid buffer pair, which will gradually reduce the PH value to the weak alkaline range, providing chemical stability for subsequent treatment. The residual calcium ions (Ca 2+ ) in the clear liquid react with the bicarbonate ions (HCO3 -) and surface active sites, capturing residual phosphate (PO4 3- ) and transforming it into hydroxyapatite precipitates, while also adsorbing trace heavy metal ions and organic colloids, achieving deep purification. When the modified lime contains sodium silicate, the silicate (SiO3 2- ) undergoes dehydration and polycondensation under weak alkaline conditions, forming an amorphous silica gel network that encapsulates the calcium carbonate crystals, creating a core-shell composite structure that enhances the mechanical strength of the flocs and improves the efficiency of solid-liquid separation. The residual magnesium hydroxide (Mg(OH)2) remains stable in a solid phase in the weak alkaline environment, serving as a template for calcium carbonate crystallization. The trace amounts of aluminum hydroxide (Al(OH)3) partially dissolve and reprecipitate, embedding into the silica gel framework to form a zeolite-like adsorption structure, further strengthening the immobilization of pollutants.

[0048] After the precipitation reaction is complete, the turbid liquid is transported to a separation device. Before separation, a standing period of 20-40 minutes is usually required to allow the flocs to fully settle. Solid-liquid separation is typically achieved through filtration, which can be performed using a plate-and-frame filter press, a belt filter press, or a bag filter. The plate-and-frame filter press uses strong pressure to squeeze water out of the filter cloth, resulting in a filter cake with low water content. The belt filter press achieves solid-liquid separation through the squeezing and filtering action of two filter belts. The bag filter removes fine particles from the wastewater using the filtering action of the filter bag. After solid-liquid separation, clear liquid and precipitate are obtained. The precipitate is mainly calcium carbonate and also contains some flocs that have adsorbed pollutants. The precipitate is transported to a calcination device for later use, and the clear liquid is sent to subsequent treatment stages. In this process, the flocs generated by the modified lime have larger particle sizes (50-100 μm) due to the presence of PAM (and also the effect of silicates), and their settling speed is 30% faster than that of single CaCO3, resulting in reduced filtration resistance.

[0049] The mild acidification of the alkaline wastewater is achieved through the proton transfer of CO2, completing the PH adjustment process and avoiding ion pollution caused by strong acids. At the same time, residual pollutants are converted into recyclable functional materials (such as high-purity calcium carbonate, which produces carbon dioxide after calcination in the calcination device and is recycled to the precipitation device). Ultimately, the water quality turbidity is zero, the alkalinity buffer capacity is improved, and a microorganism-sustainable environment is created.

[0050] The clear liquid after solid-liquid separation is sent to a short-cut nitrification reactor, where a portion of the residual ammonia-containing aquaculture wastewater is nitrified or short-cut nitrified to produce nitrite or nitrate. In the short-cut nitrification reactor, part of the residual ammonia (NH4 + ) in the aquaculture wastewater is oxidized to nitrite (NO2 - ), and the amount of dissolved oxygen is controlled to inhibit the further oxidation of nitrite to nitrate (NO3 -), so that the aquaculture wastewater contains a certain amount of nitrite (NO2 - ) as the electron acceptor of anaerobic ammonia oxidation reaction.

[0051] The effluent of the short-cut nitrification reactor enters the anaerobic ammonia oxidation reaction device, which operates under strictly controlled anoxic conditions. In the anaerobic ammonia oxidation reaction device, anaerobic ammonia oxidation bacteria (AnAOB) utilize the autotrophic denitrification pathway for efficient denitrification, and the residual ammonia nitrogen (NH4 + ) and nitrite (NO2 - ) generated in the reactor are used as substrates under the action of anaerobic ammonia oxidation bacteria, and are directly converted into harmless nitrogen gas (N2) and release a small amount of nitrate (NO3 - ). The core reaction is: NH4++ NO2 - -→ N2+ 2H2O. Compared with traditional anaerobic fermentation, the anaerobic ammonia oxidation process does not require organic carbon source (saving cost), has very low sludge production (reducing sludge treatment burden), high denitrification efficiency, and relatively low energy consumption. The gas produced by anaerobic ammonia oxidation reaction (mainly N2) can be directly discharged or collected and treated, and the ammonia nitrogen concentration of the treated effluent is further greatly reduced, creating favorable conditions for subsequent aerobic treatment.

[0052] And the trace amounts of aluminum (Al 3+ ) and magnesium (Mg 2+ ) remaining in the improved lime act as trace elements or enzyme cofactors necessary for microorganisms. Magnesium is an activator of key enzymes of nitrifying bacteria and anaerobic ammonia oxidation bacteria, and aluminum can also participate in certain enzyme reactions, together improving microbial activity and metabolic efficiency. The strong chemical phosphorus removal capacity of improved lime (generating Ca-P, Al-P, Mg-P precipitates) greatly reduces the phosphorus load entering the biological unit. Otherwise, excessive phosphate will combine with key elements such as magnesium to form precipitates, leading to a lack of trace elements for microorganisms. The high-efficiency phosphorus removal of the previous treatment process ensures the biological availability of magnesium and other elements for microorganisms in the biological section.

[0053] The effluent after anaerobic ammonia oxidation treatment enters an aerobic activated sludge reaction device (such as a plug flow aeration tank, a complete mixing aeration tank or a sequencing batch reactor SBR), and the organic matter is oxidized and decomposed by aerobic microorganisms (including bacteria, protozoa and metazoans, etc.) under sufficient dissolved oxygen (DO) conditions, and nitrification is carried out. The aerobic activated sludge reaction device injects air or pure oxygen into the aerobic activated sludge reaction device through the aeration system of the air blower, and the aeration function is: (1) providing dissolved oxygen required for microbial metabolism; (2) making the mixed liquid agitated violently to maintain the activated sludge in a suspended state, ensuring that the microorganisms and pollutants are in sufficient contact; (3) stripping part of the volatile organic matter. Under aerobic conditions, heterotrophic bacteria (aerobic microorganisms) will oxidize and decompose the residual dissolved, colloidal and part of the particulate organic matter (COD, BOD) in the wastewater as carbon source and energy, into carbon dioxide (CO2), water (H2O) and new cell material (sludge growth), realizing the stabilization and removal of organic pollutants. At the same time, the ammonia-oxidizing bacteria of the nitrifying bacteria group (mainly ammonia-oxidizing bacteria AOB and nitrite-oxidizing bacteria NOB) oxidize ammonia nitrogen (NH4 + ) to nitrite (NO2 - ), and the nitrite-oxidizing bacteria oxidize the nitrite (NO2 - ) to nitrate (NO3 - ), that is, the nitrification process: NH4 + → NO2 - → NO3 - . The nitrification process consumes alkalinity (HCO3 - ) and a large amount of oxygen, continues to remove residual ammonia nitrogen, and residual trace heavy metal ions are also adsorbed by activated sludge or precipitated at this stage. Part of the sludge can return to the front end of the aeration tank through the reflux system to maintain sufficient biomass concentration in the reactor. The aerobic activated sludge treatment utilizes aerobic heterotrophic bacteria to completely oxidize and decompose the residual dissolved organic pollutants in the wastewater, and deeply treats the residual trace ammonia nitrogen,

[0054] The mixed liquor after aerobic activated sludge treatment (i.e. the mixture of aerobic effluent and activated sludge) enters a membrane bioreactor (MBR). In the membrane bioreactor, an air blower blows air into the lower part of the membrane assembly or the membrane tank to achieve gas ramming (commonly known as "membrane scrubbing aeration"), which on the one hand provides oxygen required for biological reaction and on the other hand generates strong shear force and turbulence on the surface of the membrane wire, which washes the membrane surface to prevent sludge flocs and pollutants from accumulating on the membrane surface and blocking the membrane holes, thereby effectively controlling membrane fouling and maintaining stable membrane flux. The sludge treated by the membrane bioreactor is returned to the pH adjusting device, and the sludge is rich in microbial zooglea, and microbial extracellular polymeric substances (EPS) can strengthen the structure of inorganic flocs formed by improved lime, improve the ability to adsorb and capture colloidal organic matter and fine particles, and the organic nitrogen in the sludge can be partially converted into ammonia nitrogen under the subsequent strong alkali deamination condition and blown off, and the microbial metabolites also help to maintain the alkalinity balance of the system.

[0055] The preparation process of the improved lime is as follows.

[0056] A certain amount of quicklime (CaO) is weighed, added to deionized water and stirred to digest, generating a calcium hydroxide suspension. CaO digestion generates Ca(OH)2, which provides strong alkaline environmental conditions for the preparation of improved lime, and provides a basis for the conversion of Al 3+ , Mg 2+ to hydroxide precipitate.

[0057] After dissolving aluminum sulfate (Al2(SO4)3) in warm water (40-60°C), slowly drop it into the calcium hydroxide suspension, adjust the pH of the system to strong alkaline (pH>12) (excess calcium hydroxide and dynamic supplement), constant temperature stirring for a period of time, promote the reaction of aluminum ions and hydroxide to generate aluminum hydroxide colloid, achieve the result of introducing Al 3+ and converting it to Al(OH)3. In addition, excess OH - promotes Al(OH)3 to further react to form aluminate ions (AlO2 - ), and combine with Ca 2+ to form calcium aluminate complex salt:

[0058]

[0059] The calcium aluminate complex salt has a porous structure, a large specific surface area, and a strong adsorption capacity.

[0060] Add magnesium chloride (MgCl2) to the system, adjust the pH to strong alkaline and increase the temperature (80-90°C) (excess alkaline system material and dynamic supplement), promote the reaction of magnesium ions and hydroxide to generate magnesium hydroxide, introduce Mg 2+ and convert it to Mg(OH)2, form a ternary hydroxide complex system with Al(OH)3 and Ca(OH)2, and enhance the adsorption capacity and floc strength of the precipitate.

[0061] Cationic PAM is dissolved in deionized water to form a solution, and the above composite precipitation system is added. The solution is heated (60-70°C) and continuously stirred for a certain period of time. The amino groups (-NH3 + ) on the molecular chain of cationic PAM dissociate in water, making the PAM positively charged and forming a water-soluble polymer solution. The positively charged PAM molecules adsorb on the surface of negatively charged hydroxide precipitate particles (such as Al(OH)3, Mg(OH)2, which are negatively charged due to high pH), neutralizing the electrostatic repulsion between particles. At the same time, the long-chain molecules of PAM adsorb multiple particles (including Ca(OH)2, calcium aluminate, Mg(OH)2, etc.), forming a "particle-PAM-particle" network structure, promoting the aggregation of micro-particles into large flocs, and pre-aggregating the dispersed hydroxide particles and calcium aluminate particles into porous flocs. The increase in temperature increases the molecular motion rate, accelerates the unfolding of PAM molecular chains, enhances their adsorption efficiency on particles, and forms more compact flocs.

[0062] Optionally, sodium silicate solution (Na2SiO3) is added to the system. SiO3 2- in sodium silicate undergoes lattice doping or surface adsorption with AlO2 - and Ca 2+ on the surface of calcium aluminate, forming calcium aluminosilicate complex:

[0063]

[0064] Through silicate aluminization, the porosity and adsorption capacity of the precipitate are enhanced (similar to the precursor of zeolite structure), forming a "hydroxide-silicate" composite gel structure, further strengthening the adsorption capacity and mechanical strength of the flocs, fixing calcium, magnesium, aluminum, and silicon elements in the flocs, and forming a multi-component composite particle, providing efficient pH adjustment, flocculation, and impurity adsorption functions for subsequent wastewater treatment. The -NH3 + group of cationic PAM can adsorb SiO3 2- (negative charge), forming a "PAM-silicate" ion pair, enhancing the charge neutralization effect inside the flocs and promoting the agglomeration of silicate calcium aluminate and Mg(OH)2.

[0065] After filtering the reaction product, washing it several times with deionized water to remove residual ions, drying and grinding, the improved lime powder is obtained.

[0066] The mass ratio of the four is: aluminum sulfate: polyacrylamide: magnesium chloride: lime = (10-15): (8-12): (5-8): (65-77). Preferably, the mass ratio of the four is: aluminum sulfate: polyacrylamide: magnesium chloride: lime = 12:10:6.5:71.5. After adding sodium silicate, the mass ratio is: aluminum sulfate: polyacrylamide: magnesium chloride: lime: sodium silicate = (10-15): (8-12): (5-8): (65-77): (2-5).

[0067] Calcium hydroxide (Ca(OH)2), calcium aluminate complex salt dissolved in water to release OH - , ammonium ions (NH4 + ) in aquaculture wastewater are converted into free ammonia (NH3), which is discharged from the aquaculture wastewater by stirring or stripping to achieve the purpose of deamination nitrogen. At the same time, aluminum hydroxide (Al(OH)3) and magnesium hydroxide (Mg(OH)2) also enhance the adsorption capacity of NH4 + . And aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2) as the core of the floc, neutralize the negative charge particles in the aquaculture wastewater, reduce the zeta potential (electrokinetic potential), promote the coagulation of suspended solids (SS), and adsorb suspended solids, colloidal particles and part of heavy metal ions in the wastewater.

[0068] On this basis, cationic PAM accelerates the formation of large-size flocs through charge neutralization (neutralizing the negative charge on the particle surface) and bridging effect (connecting multiple particles) formed by long-chain structure, and promotes solid-liquid separation.

[0069] Further, the aluminum-silicate calcium complex salt generated by adding sodium silicate to the improved lime has stronger ion exchange capacity (such as adsorption of NH4 + , PO4 3- ), which improves the removal efficiency of ammonia nitrogen and phosphorus in wastewater treatment. In addition, silicate as a cementing agent can coat the flocs, enhance the mechanical strength of the flocs, and reduce the phenomenon of floc breakage during filtration.

[0070] For phosphorus removal, Al 3+ , Mg 2+ , Ca 2+ in the improved lime can all react with phosphate under strong alkaline conditions and generate precipitates, and the solubility product of the precipitates generated by Al 3+ , Mg 2+ reacting with phosphate is lower than that of calcium phosphate, and the phosphorus removal effect is better. The flocs formed by the precipitate containing phosphorus alone are easy to break, while the precipitate containing phosphorus formed by the improved lime has a larger strength due to the binding effect of PAM (further supplemented by silicate), and is not easy to break.

[0071] Aluminum hydroxide, calcium aluminate, magnesium hydroxide, PAM modified lime, these products form complex crystal nucleus with calcium hydroxide, compared with calcium hydroxide alone, the specific surface area is larger, the active site is more, can more efficient adsorption of NH4 + , PO4 3- and heavy metal ions in wastewater. If directly add aluminum hydroxide, magnesium hydroxide, its crystal structure is dense, low reactivity, small contact area with lime, need longer time to dissolve to release Al 3+ , Mg 2+ , leading to the decline of pH adjustment and precipitation efficiency. In the preparation process of modified lime, PAM is added after the formation of precipitation, through charge neutralization and bridging effect, uniform package of composite precipitation particles, form "calcium hydroxide-aluminum magnesium hydroxide-PAM" three-dimensional network structure, pre-aggregation of small hydroxide particles into larger porous flocs, provide more channels for free ammonia escape, at the same time, increase the contact area of wastewater and air, improve the efficiency of vacuum suction / blow-off, also can significantly improve the settling velocity of flocs. In addition, the modified lime system is prepared in advance, after the modified lime is put into aquaculture wastewater, PAM can be released at the same time as calcium hydroxide, aluminum hydroxide, magnesium hydroxide, etc. still maintain the state of polymerizing these hydroxides, while if not preformed lime system, PAM is directly put into aquaculture wastewater, PAM will preferentially adsorb most or part of other ions or impurities in water, unable to effectively anchor the precipitation core of calcium hydroxide, etc., leading to discrete flocculation effect and reduced flocculation effect.

[0072] First prepare modified lime, rather than directly put aluminum hydroxide, magnesium hydroxide, calcium hydroxide and other substances into aquaculture wastewater, in addition to being able to control the introduction of impurity ions (such as sulfate, chloride ions, etc.) (avoiding the input of inorganic acid), also can improve the reaction rate (aluminum hydroxide, magnesium hydroxide, etc. need time to contact with calcium hydroxide, and the dissolution of these hydroxides also needs time, in addition, the complex crystal nucleus formed by aluminum hydroxide, magnesium hydroxide and calcium hydroxide has higher purification efficiency of aquaculture wastewater than single hydroxide).

[0073] The test process and data are shown below.

[0074] Test group one is modified lime (including sodium silicate), test group two is lime, test group three is blank group, test group four is modified lime (not including sodium silicate).

[0075] Prepare four groups of same size reaction vessels, respectively marked as A (representing test group one), B (representing test group two), C (representing test group three), D (representing test group four). Collect enough amount of aquaculture wastewater from the same pig farm, mix uniformly, then respectively take the same volume of wastewater sample into the four reaction vessels.

[0076] In A container, add appropriate amount of modified lime (add sodium silicate during preparation) to adjust the pH value of wastewater to 11; In B container, add lime to adjust the pH value of wastewater to 11; C container does not add anything; In D container, add appropriate amount of modified lime (do not add sodium silicate during preparation).

[0077] Stir the wastewater in the four containers respectively, keep the stirring speed and time consistent, after stirring for 30 minutes, discharge ammonia gas by air stripping method, and the stripping time is 60 minutes. Carbon dioxide is introduced into A, B and D containers to adjust the pH value of the mixed solution to 7.5, and the same amount of carbon dioxide is introduced into C container (the average value of the carbon dioxide introduced into A, B and D containers). Then, the solutions in the four containers are left to stand for 30 minutes, and then filtered to separate the supernatant and the precipitate.

[0078] The content of ammonia nitrogen in the wastewater before and after treatment is determined by Nash reagent spectrophotometry; the total phosphorus concentration is determined by ammonium molybdate spectrophotometry; and the chemical oxygen demand (COD) is determined by potassium dichromate method.

[0079]

[0080] The above only describes the preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for treating aquaculture wastewater, characterized by, Under alkaline conditions, aluminum and magnesium elements are introduced into lime to form a calcium hydroxide composite system, and cationic polyacrylamide is used in the calcium hydroxide composite system to pre-agglomerate the dispersed calcium hydroxide composite system particles into porous flocs to form improved lime; After the aquaculture wastewater is subjected to preliminary solid-liquid separation and water quality adjustment, the improved lime is added and stirred uniformly to adjust the pH of the aquaculture wastewater so that the ammonia nitrogen mainly exists in the form of free ammonia, the free ammonia is separated from the water body using equipment, and ammonia gas is recovered by spraying clean water to obtain ammonia water; Carbon dioxide is introduced into the aquaculture wastewater after ammonia removal to reduce the pH of the aquaculture wastewater to form a turbid liquid; After waiting for the precipitation reaction to complete, the aquaculture wastewater is subjected to solid-liquid separation; The preparation method of the improved lime comprises the following steps: Step S1. Weigh the quicklime, add deionized water and stir to digest to form a calcium hydroxide suspension; Step S2. Dissolve aluminum sulfate in warm water and slowly drop it into the calcium hydroxide suspension to adjust the pH of the system, and constant temperature stirring is performed to generate aluminum hydroxide colloid and calcium aluminate complex salt; Step S3. Add magnesium chloride, adjust the pH to strong alkaline and heat to generate magnesium hydroxide to form a calcium hydroxide-aluminum hydroxide-magnesium hydroxide ternary hydroxide composite system; Step S4. Dissolve cationic polyacrylamide in deionized water to prepare a solution, add the composite system, heat to and continuously stir to form a calcium hydroxide-aluminum magnesium hydroxide-polyacrylamide three-dimensional network floc; Step S5. Filter the reaction product, wash it with deionized water until there is no residual ion, dry it and grind it into powder; The raw material mass ratio of the improved lime is: Aluminum sulfate: polyacrylamide: magnesium chloride: lime = (10-15): (8-12): (5-8): (65-77).

2. The method for treating aquaculture wastewater according to claim 1, characterized in that, After step 4, sodium silicate solution is added to the system to form a hydroxide-silicate composite gel structure.

3. The method of claim 2, wherein The raw material mass ratio of the improved lime is: Aluminum sulfate: polyacrylamide: magnesium chloride: lime: sodium silicate = (10-15): (8-12): (5-8): (65-77): (2-5).

4. The method for treating aquaculture wastewater according to claim 1, characterized in that, Silicon is added to the porous floc system formed by the cationic polyacrylamide to form aluminum calcium silicate complex salt in the improved lime, and when the improved lime is added to the aquaculture wastewater, the improved lime releases silicon to coat the floc.

5. The method for treating aquaculture wastewater according to claim 1, wherein Preliminary solid-liquid separation process: The aquaculture wastewater flows through a grid to remove larger floating objects and smaller suspended impurities using multiple levels of grids; And / or The aquaculture wastewater enters a sedimentation tank to precipitate particles in the aquaculture wastewater using the principle of gravity settling.

6. The method for treating aquaculture wastewater according to claim 1, wherein The clear liquid after solid-liquid separation enters a short-cut nitrification reactor, and a specific microbial community in the short-cut nitrification reactor converts residual ammonia nitrogen into nitrite, and by controlling the dissolved oxygen content, the oxidation of nitrite to nitrate is inhibited; after the completion of short-cut nitrification, the clear liquid enters an anaerobic ammonia oxidation reaction device, and under anoxic conditions, anaerobic ammonia oxidation bacteria directly use ammonia nitrogen and nitrite as raw materials to convert them into nitrogen gas through biological catalysis.

7. The method for treating aquaculture wastewater according to claim 6, characterized in that, The effluent after anaerobic ammonia oxidation treatment enters an aerobic activated sludge reaction device, the aerobic activated sludge reaction device is oxygenated by a blower, and the clear liquid is subjected to aerobic microbial treatment and then enters an MBR membrane bioreactor, the MBR membrane bioreactor is subjected to gas ramming by a blower, the clear liquid passing through the MBR membrane bioreactor is reused after adsorption, and the sludge cut off by the MBR membrane bioreactor participates in the ammonia removal treatment of aquaculture wastewater by improved lime.

8. The method for treating aquaculture wastewater according to claim 1, wherein, The solid after solid-liquid separation is subjected to composting fermentation treatment or calcination to obtain recycled lime and carbon dioxide.

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