Treatment method of breeding wastewater

Abstract

The invention discloses a treatment method of aquaculture wastewater, which comprises the following steps: under an alkaline condition, introducing aluminum and magnesium elements into lime to form a calcium hydroxide composite system, and pre-aggregating dispersed calcium hydroxide composite system particles into a porous floc by using cationic polyacrylamide in the calcium hydroxide composite system to form improved lime; the method comprises the following steps: performing primary solid-liquid separation and water quality regulation on breeding wastewater, adding improved lime, and uniformly stirring; according to the breeding wastewater treatment method provided by the invention, the improved lime is used for replacing common lime, and the improved lime has a lime composite system with stronger adsorption and flocculation capabilities, has a larger specific surface area, increases the density of active sites, is beneficial to adsorbing positively charged suspended matters by utilizing static electricity, improves the flocculation capability, and improves the adsorption efficiency. PAM is beneficial to adsorption and flocculation of negatively charged suspended solids, calcium aluminosilicate double salt has strong ion exchange capacity, and silicate generated after improved lime is dissolved in water can coat floc, so that the adsorption capacity and flocculation strength of the composite system are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of aquaculture wastewater treatment, and more particularly to a method for treating aquaculture wastewater. Background Art

[0002] For the treatment of aquaculture wastewater, the traditional process mostly adopts the alkali stripping method, which is to add lime or liquid alkali to the wastewater to adjust the pH to alkaline, so that ammonium ions are converted into free ammonia, and then ammonia nitrogen is separated by air stripping or vacuum suction, and then anaerobic fermentation is carried out to complete the treatment of 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 efficiency of hydroxide ion release are limited, resulting in incomplete conversion of ammonia nitrogen. At the same time, the calcium carbonate precipitate generated has loose flocs and a small specific surface area, and has a weak adsorption capacity for suspended matter, colloidal particles and heavy metal ions in the wastewater, making it difficult to achieve deep purification. Summary of the Invention

[0004] In order to improve the treatment effect of lime on aquaculture wastewater, the present invention provides a method for treating aquaculture wastewater, using improved lime instead of ordinary lime, and introducing Al 3+ Mg 2+ 、PAM、SiO3 2- Combined with Ca(OH)2, it forms a lime composite system with stronger adsorption and flocculation capabilities, among which Al 3+ Mg 2+ Combined with Ca(OH)2, it increases the specific surface area of ​​the composite crystal nucleus and the density of active sites, which is beneficial to the use of electrostatic adsorption of positively charged suspended matter and improves the flocculation ability. At the same time, PAM can neutralize the negative charge on the surface of suspended matter, and its long chain structure is beneficial to the adsorption and flocculation of negatively charged suspended matter such as phosphate. Calcium aluminosilicate complex salt has strong ion exchange capacity, and the SiO3 generated after the modified lime is dissolved in water 2- It can coat the flocs and improve the adsorption capacity and flocculation strength of the composite system.

[0005] The technical solution of the present invention is as follows: A method for treating aquaculture wastewater comprises introducing aluminum and magnesium elements into lime under alkaline conditions to form a calcium hydroxide composite system, and using cationic polyacrylamide in the calcium hydroxide composite system to pre-aggregate dispersed calcium hydroxide composite system particles into porous flocs to form improved lime. After the aquaculture wastewater undergoes preliminary solid-liquid separation and water quality adjustment, modified lime is added and stirred evenly to adjust the pH of the aquaculture wastewater so that ammonia nitrogen exists mainly in the form of free ammonia. Equipment is used to separate the free ammonia from the water body, and clean water spraying is used to recover ammonia gas to obtain ammonia water; Introducing carbon dioxide into the deammonified aquaculture wastewater to lower the pH of the aquaculture wastewater and form turbid liquid; After the precipitation reaction is completed, the aquaculture wastewater is separated into solid and liquid.

[0006] The above-mentioned method for treating aquaculture wastewater and the method for preparing improved lime comprise the following steps: Step S1. Weigh quicklime, add deionized water and stir to dissolve it to generate a calcium hydroxide suspension; Step S2. After dissolving aluminum sulfate in warm water, slowly add calcium hydroxide suspension dropwise, adjust the pH of the system, and stir at a constant temperature to generate aluminum hydroxide colloid and calcium aluminate double salt; Step S3. adding magnesium chloride, adjusting the pH to a strong alkaline state and heating to generate magnesium hydroxide, thereby forming a calcium hydroxide-aluminum hydroxide-magnesium hydroxide ternary hydroxide composite system; Step S4. Dissolve the cationic polyacrylamide in deionized water to prepare a solution, add the composite system, heat to and continue stirring to form a calcium hydroxide-aluminum magnesium hydroxide-polyacrylamide three-dimensional network flocculent; Step S5: filtering the reaction product, washing it with deionized water until no residual ions are left, and grinding it into powder after drying.

[0007] Furthermore, after step 4, sodium silicate solution is added to the system to form a hydroxide-silicate composite gel structure.

[0008] In the above-mentioned method for treating aquaculture wastewater, the raw material mass ratio of the improved lime is: Aluminum sulfate: polyacrylamide: magnesium chloride: lime = (10-15): (8-12): (5-8): (65-77).

[0009] Furthermore, 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).

[0010] The above-mentioned method for treating aquaculture wastewater adds silicate to the porous floc system formed by cationic polyacrylamide, so that the modified lime contains calcium aluminosilicate complex salt. When the modified lime is added into the aquaculture wastewater, the modified lime releases silicate to coat the flocs.

[0011] The above-mentioned method for treating aquaculture wastewater includes the following steps: The aquaculture wastewater flows through the screen, and the multi-stage screen is used to remove larger floating objects and smaller suspended impurities; and / or The aquaculture wastewater enters the sedimentation tank, and the principle of gravity sedimentation is used to settle the particles in the aquaculture wastewater.

[0012] In the above-mentioned method for treating aquaculture wastewater, the clear liquid after solid-liquid separation enters the short-range nitrification reactor. The specific microbial community in the short-range nitrification reactor converts the residual ammonia nitrogen into nitrite, and inhibits the oxidation of nitrite to nitrate by controlling the dissolved oxygen content; after the clear liquid completes the short-range nitrification, it enters the anaerobic ammonia oxidation reaction device. In an oxygen-deficient environment, anaerobic ammonia-oxidizing bacteria use ammonia nitrogen and nitrite as direct raw materials and convert them into nitrogen gas through biocatalysis.

[0013] Furthermore, the effluent after anaerobic ammonia oxidation treatment enters the aerobic activated sludge reaction device, and the aerobic activated sludge reaction device is oxygenated by a blower. After the clear liquid completes the aerobic microbial treatment, it enters the MBR membrane bioreactor, and the gas is pressed into the MBR membrane bioreactor by the blower. The clear liquid passing through the MBR membrane bioreactor is reused after adsorption, and the sludge intercepted by the MBR membrane bioreactor participates in the deammonification treatment of aquaculture wastewater by improved lime.

[0014] In the above-mentioned method for treating aquaculture wastewater, the solid after solid-liquid separation is subjected to composting and fermentation treatment or calcined to obtain lime and carbon dioxide for recycling.

[0015] In the above-mentioned method for treating aquaculture wastewater, the pH range of the aquaculture wastewater during deammonification is 11-11.5, and the pH range of the aquaculture wastewater after the introduction of carbon dioxide is 7-7.5.

[0016] The present invention according to the above scheme has the following beneficial effects: 1. The aluminum hydroxide, magnesium hydroxide and aluminosilicate complex salts in the improved lime can simultaneously remove suspended matter, colloidal organic matter, phosphorus and heavy metal ions through adsorption, complexation and other effects, and can improve the treatment effect of calcium hydroxide in the original lime on ammonia nitrogen, realizing the coordinated treatment of multiple pollutants, and is more suitable for aquaculture wastewater with complex components.

[0017] 2. No acidic substances are introduced to avoid affecting subsequent anaerobic treatment.

[0018] 3. The multiple particles connected by PAM increase the floc particle size and pore size, which increases the sedimentation rate and ammonia nitrogen overflow rate, and improves the flocculation and filtration effects.

[0019] 4. The composite system of aluminum-magnesium-calcium hydroxide has a larger specific surface area and more active points than single calcium hydroxide, which can better react with ammonium ions and has a better deamination effect.

[0020] 5. The calcium aluminosilicate complex salt of the improved lime has strong ion exchange capacity, which improves the adsorption capacity of lime for ammonium and phosphate. The hydrolyzed silicate can coat the flocs, enhance the floc strength, and thus accelerate the precipitation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 This is a flow chart for the treatment of aquaculture wastewater according to the present invention. DETAILED DESCRIPTION

[0023] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0024] A method for treating aquaculture wastewater comprises the following steps: introducing aluminum and magnesium elements into lime under alkaline conditions to form a calcium hydroxide composite system; using cationic polyacrylamide in the calcium hydroxide composite system to pre-aggregate dispersed calcium hydroxide composite system particles into porous flocs to form modified lime; subjecting the aquaculture wastewater to preliminary solid-liquid separation and water quality adjustment, adding the modified lime and stirring evenly to adjust the pH of the aquaculture wastewater so that ammonia nitrogen exists mainly in the form of free ammonia; using equipment to separate the free ammonia from the water body, and using clean water spraying to recover ammonia gas to obtain ammonia water; introducing carbon dioxide into the deammonified aquaculture wastewater to lower the pH of the aquaculture wastewater and form a turbid liquid; and after waiting for the precipitation reaction to be completed, subjecting the aquaculture wastewater to solid-liquid separation.

[0025] like Figure 1 The specific processing process is as follows.

[0026] The aquaculture wastewater is transported to the regulating pond to adjust the water quality and quantity, making the subsequent treatment process more stable. At the same time, sedimentation, filtration, and blocking methods can be used to initially precipitate large particles of impurities, reducing the burden on subsequent treatment units.

[0027] Specifically, aquaculture wastewater first flows through a screen, where multi-stage screens (i.e., screens with varying bar spacing, such as 10-50 mm for a coarse screen and 1-10 mm for a fine screen) remove larger floating debris and smaller suspended impurities. The wastewater then enters a sedimentation tank, where gravity sedimentation is used to settle inorganic particles such as sand and gravel, such as in advection or cyclone sedimentation tanks. Screen blocking or sedimentation in a sedimentation tank can be used separately or sequentially, with screen blocking followed by sedimentation in the sedimentation tank.

[0028] Since the discharge of aquaculture wastewater is intermittent and unstable, the water quality and water quantity fluctuate greatly, so it needs to enter the regulating tank. The regulating tank plays the role of homogenizing the water quality and water quantity, making the subsequent treatment process more stable. The residence time of the regulating tank is generally determined according to the scale of aquaculture and the pattern of aquaculture wastewater discharge, usually 8-24 hours. In the regulating tank, a stirring device, such as a mechanical stirrer or an air stirring system, can be installed to fully mix the aquaculture wastewater and avoid the precipitation of suspended matter. At the same time, the pH value, ammonia nitrogen parameters, phosphorus parameters, COD and other indicators of the aquaculture wastewater in the regulating tank are monitored to provide data basis for subsequent treatment.

[0029] The aquaculture wastewater is introduced into the pH adjustment device, modified lime is added, and stirred evenly to adjust the pH of the aquaculture wastewater to 11-11.5, so that the ammonia nitrogen in the aquaculture wastewater exists mainly in the form of free ammonia (NH3). In this process, the calcium hydroxide of the modified lime dissolves and ionizes into hydroxide ions (OH - ), increase the pH value of aquaculture wastewater. Under strong alkaline conditions, hydroxide ions (OH - ) and ammonium ions (NH4 + ) reaction, hydroxide ions (OH - ) and ammonium ions (NH4 + ) reaction, which moves the equilibrium toward the formation of free ammonia, i.e., NH4 + +OH − NH3 + H2O. During this process, aluminum hydroxide, magnesium hydroxide, and other materials form composite crystal nuclei with calcium hydroxide, resulting in a larger specific surface area and more active sites, increasing the reaction rate between calcium hydroxide and ammonium ions. Simultaneously, the Al(OH)3 and Mg(OH)2 particles and polyacrylamide (PAM) in the modified lime act as flocculation agents. The positively charged PAM molecules adsorb negatively charged suspended matter in the wastewater (such as fecal particles and organic colloids), forming flocs through charge neutralization and bridging. Calcium silicate (CaSiO3) and silicate coating precipitate the flocs, strengthening the flocs and accelerating the settling of suspended matter.

[0030] At this point, the ammonia nitrogen in the aquaculture wastewater will precipitate as free ammonia. The free ammonia is removed from the water through vacuum extraction, air stripping, or mechanical agitation (vacuum extraction uses a vacuum pump to create a negative pressure environment within the deammonification unit, allowing free ammonia to escape more easily from the water; air stripping involves introducing large amounts of air into the wastewater to remove the free ammonia; mechanical agitation uses a high-speed agitator to increase the contact area and time between the wastewater and air, accelerating the volatilization of free ammonia). This process causes ammonia gas to escape from the water and be discharged from the air outlet at the top of the deammonification unit into an absorption tower, where it is recovered by spraying with clean water to produce ammonia water.

[0031] The mixed liquid after deammoniation enters the precipitation device, into which carbon dioxide is introduced. Carbon dioxide reacts with calcium ions in the mixed liquid to form calcium carbonate precipitation (Ca 2+ +CO2+H2O⇌CaCO3↓+2H + ), while simultaneously lowering the pH of the mixed liquid to 7-7.5 (under weakly alkaline conditions, the Al(OH)3 and Mg(OH)2 precipitates remain stable and have low solubility, acting as a flocculent framework to envelop the CaCO3 particles, forming a dense precipitate), resulting in a turbid solution. During this process, the magnesium hydroxide, aluminum hydroxide, and polyacrylamide in the modified lime continue to enhance flocculation and sedimentation, making it easier for impurities and pollutants to settle.

[0032] The initial clear solution is strongly alkaline. As CO2 is continuously introduced, the residual hydroxide ions (OH - ) reacts with dissolved CO2 to form bicarbonate ions (HCO3 - ), carbonate ions in the system (CO3 2- ) is also gradually converted into bicarbonate ions (HCO3 - ), establish bicarbonate-carbonic acid buffer pair, which will gradually reduce the pH value to the weak alkaline range, providing chemical stability for subsequent treatment. 2+ ) and bicarbonate ions (HCO3 - ) combined, nano-scale calcium carbonate (CaCO3) crystals are precipitated through heterogeneous nucleation. The new crystals have high specific surface area and surface active sites, which capture residual phosphate (PO4 3- ), promoting its conversion into hydroxyapatite precipitation, while adsorbing trace heavy metal ions and organic colloids to achieve deep purification. When the modified lime contains sodium silicate, silicate (SiO3 2- ) dehydrates and condenses under weakly alkaline conditions, forming an amorphous silica gel network. This network encapsulates the calcium carbonate crystals, forming a core-shell composite structure that enhances the mechanical strength of the flocs and improves solid-liquid separation efficiency. Residual magnesium hydroxide (Mg(OH)2) maintains a stable solid phase in the weakly alkaline environment, serving as a template for calcium carbonate crystallization. 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, enhancing pollutant retention.

[0033] After the precipitation reaction is complete, the turbid liquid is transferred to a separation device. Before separation, the liquid is allowed to stand for 20-40 minutes to allow the flocs to fully settle. Filtration is typically used for solid-liquid separation, using equipment such as plate and frame filter presses, belt filter presses, or bag filters. Plate and frame filter presses use strong pressure to squeeze water from the filter cloth, producing a filter cake with a low moisture content. Belt filter presses separate solids and liquids through squeezing and filtering between two filter belts. Bag filters utilize the filtering action of the filter bags to remove fine particles from the wastewater. After solid-liquid separation, a clear liquid and a precipitate are obtained. The precipitate is primarily calcium carbonate and also contains some flocs that have absorbed pollutants. The precipitate is transferred to a calcining unit for storage, while the clear liquid enters subsequent treatment. During this process, the flocs formed by the modified lime, due to the PAM (also the effect of silicates), have a larger particle size (50-100 μm), a settling rate 30% faster than that of CaCO₃ alone, and reduced filtration resistance.

[0034] Through the proton transfer of CO2, mild acidification of alkaline wastewater is achieved, the pH adjustment process is completed, and ion contamination introduced by strong acids is avoided. 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 a calcination device and is reused in a precipitation device). Ultimately, the water turbidity is reduced to zero, the alkalinity buffer capacity is increased, and an environment in which microorganisms can survive is created.

[0035] The clear liquid after solid-liquid separation enters the short-range nitrification reactor, which nitrifies or short-range nitrifies a portion of the aquaculture wastewater containing ammonia nitrogen to produce nitrite or nitrate. In the short-range nitrification reactor, the remaining ammonia nitrogen (NH4 + ) is oxidized to nitrite (NO2 - ), while inhibiting the further oxidation of nitrite to nitrate (NO3 - ), so that the aquaculture wastewater contains a certain amount of nitrite (NO2 - ) as the electron acceptor in the anaerobic ammonium oxidation reaction.

[0036] The effluent from the short-cut nitrification reactor enters the anaerobic ammonium oxidation reactor, which operates under strictly controlled anoxic conditions. In the anaerobic ammonium oxidation reactor, anaerobic ammonium oxidizing bacteria (AnAOB) use the autotrophic denitrification pathway to efficiently remove nitrogen, and the residual ammonia nitrogen (NH4 + ) and nitrite (NO2 - It is usually produced by part of the nitrification process or needs to be provided by a short-range nitrification unit before the anaerobic ammonium oxidation reaction) as a substrate, which is directly converted into harmless nitrogen (N2) and releases a small amount of nitrate (NO3 - ), its core reaction formula is: NH4++NO2 --→N2 + 2H2O. Compared to traditional anaerobic fermentation, the anaerobic ammonium oxidation process requires no organic carbon source (saving costs), produces very low sludge (reducing the burden of sludge treatment), has high denitrification efficiency, and consumes relatively low energy. The gases (primarily N2) produced by the anaerobic ammonium oxidation reaction can be directly discharged or collected and treated. The ammonia nitrogen concentration in the treated effluent is further reduced, creating favorable conditions for subsequent aerobic treatment.

[0037] The trace aluminum (Al 3+ ), magnesium (Mg 2+ ) plasma serves as essential trace elements or enzyme cofactors for microorganisms. Magnesium is an activator of key enzymes in nitrifying bacteria and anaerobic ammonium-oxidizing bacteria. Aluminum also participates in specific enzymatic reactions, collectively enhancing microbial activity and metabolic efficiency. The improved lime's powerful chemical phosphorus removal capabilities (generating Ca-P, Al-P, and Mg-P precipitates) significantly reduce the phosphorus load entering the biological unit. Otherwise, excessive phosphate would combine with key elements like magnesium to form precipitates, leading to microbial trace element deficiencies. The efficient phosphorus removal achieved in the previous treatment process ensures the bioavailability of elements like magnesium to microorganisms in the biological stage.

[0038] The effluent after anaerobic ammonia oxidation treatment enters an aerobic activated sludge reactor (such as a plug-flow aeration tank, a completely mixed aeration tank, or a sequencing batch reactor (SBR)). Aerobic microorganisms (including bacteria, protozoa, and metazoa) use sufficient dissolved oxygen (DO) to oxidize and decompose organic matter and perform nitrification. The aeration system of the aerobic activated sludge reactor injects air or pure oxygen into the aerobic activated sludge reactor through the blower. The functions of aeration are: (1) to provide dissolved oxygen required for microbial metabolism; (2) to vigorously stir the mixed liquid to maintain the activated sludge in a suspended state, ensuring that the microorganisms and pollutants are fully in contact; (3) to blow off some volatile organic matter. Under aerobic conditions, heterotrophic bacteria (aerobic microorganisms) metabolize the soluble, colloidal, and particulate organic matter (COD, BOD) remaining in the wastewater as a carbon source and energy, oxidizing and decomposing them into carbon dioxide (CO2), water (H2O), and new cellular substances (sludge growth), thereby stabilizing and removing organic pollutants. At the same time, ammonia oxidizing bacteria (mainly ammonia oxidizing bacteria AOB and nitrite oxidizing bacteria NOB) convert ammonia nitrogen (NH4 + ) is oxidized to nitrite (NO2 - ), nitrite oxidizing bacteria then convert nitrite (NO2 - ) is oxidized to nitrate (NO3 - ), that is, nitrification process: NH4 + →NO2 - →NO3 - The nitrification process consumes alkalinity (HCO3 -) and a large amount of oxygen to continue to remove the remaining ammonia nitrogen. The remaining trace heavy metal ions are also adsorbed or precipitated by the activated sludge at this stage. Part of the sludge can be returned to the front end of the aeration tank through the return system to maintain a sufficient biomass concentration in the reactor. Aerobic activated sludge treatment uses aerobic heterotrophic bacteria to completely oxidize and decompose the remaining soluble organic pollutants in the wastewater, deeply treat the remaining trace ammonia nitrogen, The mixed liquor after aerobic activated sludge treatment (i.e., a mixture of aerobic effluent and activated sludge) enters the membrane bioreactor (MBR). In the MBR, a blower introduces air beneath the membrane modules or into the membrane tank, creating gas pressure (often referred to as "membrane scrubbing aeration"). This provides the oxygen required for the biological reaction and creates intense shear forces and turbulence on the membrane filaments, scouring the membrane surface and preventing the accumulation of sludge flocs and contaminants on the membrane surface and clogging the membrane pores. This effectively controls membrane fouling and maintains stable membrane flux. The sludge treated in the MBR is returned to the pH adjustment device. This sludge is rich in microbial flocs. Microbial extracellular polymeric substances (EPS) strengthen and modify the inorganic floc structure formed by lime, improving its ability to adsorb and capture colloidal organic matter and fine particles. The organic nitrogen in the sludge can be partially converted to ammonia nitrogen and blown off under subsequent strong alkaline deamination conditions. Microbial metabolites also help maintain the alkalinity balance of the system.

[0039] The preparation process of modified lime is as follows.

[0040] Weigh some quicklime (CaO), add deionized water and stir to dissolve, generating calcium hydroxide suspension. CaO dissolves to generate Ca(OH)2, which provides a strong alkaline environment for the preparation of improved lime and Al 3+ Mg 2+ Conversion to hydroxide precipitation lays the foundation.

[0041] After aluminum sulfate (Al2(SO4)3) is dissolved in warm water (40℃-60℃), it is slowly dripped into the calcium hydroxide suspension, and the pH of the system is adjusted to strong alkalinity (pH>12) (excess calcium hydroxide is added dynamically), and stirred at a constant temperature for a certain period of time to promote the reaction of aluminum ions with hydroxide to form aluminum hydroxide colloid, so as to achieve the introduction of Al 3+ And converted into Al(OH)3. In addition, the excess OH - Promoting Al(OH)3 to further react to form aluminate ions (AlO2 - ), and Ca 2+ Combine to form calcium aluminate double salt:

[0042] Calcium aluminate double salt has a porous structure, a large specific surface area and a strong adsorption capacity.

[0043] Add magnesium chloride (MgCl2) to the system, adjust the pH to strong alkalinity and raise the temperature (80℃-90℃) (excess alkaline system substances and dynamic replenishment) to promote the reaction of magnesium ions with hydroxide to form magnesium hydroxide, and introduce Mg 2+ It is converted into Mg(OH)2, forming a ternary hydroxide composite system with Al(OH)3 and Ca(OH)2, enhancing the adsorption capacity and floc strength of the precipitate.

[0044] Dissolve cationic polyacrylamide (PAM) in deionized water to prepare a solution, add the above composite precipitation system, heat up (60℃-70℃) and continue stirring for a few minutes. The amino groups (-NH3 + ) dissociates in water, giving PAM a positive charge and forming a water-soluble polymer solution. The positively charged PAM molecules adsorb onto the negatively charged surfaces of hydroxide precipitate particles (such as Al(OH)3 and Mg(OH)2, which are negatively charged due to their high pH), neutralizing the electrostatic repulsion between the particles. Simultaneously, the long PAM chains simultaneously adsorb onto multiple particles (including Ca(OH)2, calcium aluminate, and Mg(OH)2), forming a "particle-PAM-particle" network structure. This promotes the aggregation of tiny particles into large flocs and pre-aggregates dispersed hydroxide and calcium aluminate particles into porous flocs. Increasing the temperature increases the molecular motion rate, accelerating the expansion of the PAM molecular chains, enhancing their adsorption efficiency onto the particles, and forming tighter flocs.

[0045] Optionally, sodium silicate solution (Na2SiO3) is added to the system. 2- AlO2 on the surface of calcium aluminate - , Ca 2+ Lattice doping or surface adsorption occurs to form calcium aluminosilicate double salt: .

[0046] The porosity and adsorption capacity of the precipitate are enhanced by aluminosilicate formation (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, forming multi-component composite particles, and providing efficient pH adjustment, flocculation, and impurity adsorption functions for subsequent wastewater treatment. + Group can adsorb SiO3 2- (negative charge), forming "PAM-silicate" ion pairs, enhancing the charge neutralization effect inside the flocs, and promoting the agglomeration of calcium aluminosilicate and Mg(OH)2.

[0047] The reaction product is filtered, washed with deionized water several times to remove residual ions, and then dried and ground to obtain improved lime powder.

[0048] 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).

[0049] Calcium hydroxide (Ca(OH)2) and calcium aluminate complex salts dissolve in water to release OH - , adjust the pH of the aquaculture wastewater to 10-13), so that the ammonium ion (NH4 + ) is converted into free ammonia (NH3), which is discharged from the aquaculture wastewater through stirring or stripping to achieve the purpose of removing nitrogen from the aquaculture wastewater. At the same time, aluminum hydroxide (Al(OH)3) and magnesium hydroxide (Mg(OH)2) also enhance the removal of NH4 + Aluminum hydroxide (Al(OH)3) and magnesium hydroxide (Mg(OH)2) serve as the core of the flocs to neutralize the negatively charged particles in the aquaculture wastewater, reduce the zeta potential (electric potential), promote the coagulation of suspended solids (SS), and adsorb suspended solids, colloidal particles and some heavy metal ions in the wastewater.

[0050] On this basis, cationic PAM accelerates the formation of large-sized flocs and promotes solid-liquid separation through charge neutralization (neutralizing the negative charge on the particle surface) and the bridging effect formed by the long chain structure (connecting multiple particles).

[0051] Furthermore, the calcium aluminosilicate complex salt generated by adding modified lime with sodium silicate has a stronger ion exchange capacity (such as for NH4 + PO4 3- Silicate can also be used as a binder to coat flocs, enhancing their mechanical strength and reducing floc breakage during filtration.

[0052] For phosphorus removal, the Al content in the improved lime 3+ Mg 2+ , Ca 2+ Under strong alkaline conditions, they can react with phosphate to form precipitation, and Al 3+ Mg 2+ The solubility product of the precipitate generated by the reaction with phosphate is lower than that of calcium phosphate, resulting in better phosphorus removal. While the flocs formed by phosphorus-containing precipitates alone are easily broken, the phosphorus-containing precipitate formed with modified lime is stronger and less prone to breakage due to the binding effect of PAM (which can be further reinforced with silicate).

[0053] Aluminum hydroxide, calcium aluminate, magnesium hydroxide, and PAM of modified lime form composite crystal nuclei with calcium hydroxide. Compared with calcium hydroxide alone, they have a larger specific surface area and more active sites, and can more efficiently adsorb NH4 in wastewater. + PO4 3- If aluminum hydroxide and magnesium hydroxide are added directly, their crystal structure is dense, their reaction activity is low, and their contact area with lime is small, so it takes longer to dissolve and release Al. 3+ Mg 2+ , resulting in decreased pH adjustment and precipitation efficiency. During the preparation of modified lime, PAM is added after the precipitate forms. Through charge neutralization and bridging, it evenly coats the composite precipitate particles, forming a three-dimensional network structure of "calcium hydroxide-aluminum magnesium hydroxide-PAM." This pre-aggregates the tiny hydroxide particles into larger, porous flocs, providing more channels for the escape of free ammonia. This also increases the contact area between the wastewater and air, improving vacuum extraction / stripping efficiency and significantly increasing the settling rate of the flocs. Furthermore, by pre-forming the modified lime system, after the modified lime is added to the aquaculture wastewater, PAM is able to maintain its aggregated state while releasing calcium hydroxide, aluminum hydroxide, and magnesium hydroxide. However, if PAM is added directly to the aquaculture wastewater without pre-forming the lime system, it will mostly or partially preferentially adsorb other ions or impurities in the water, failing to effectively anchor the precipitation cores, such as calcium hydroxide. This results in a dispersed and reduced flocculation effect.

[0054] Prepare improved lime first instead of directly adding aluminum hydroxide, magnesium hydroxide, calcium hydroxide and other substances to the aquaculture wastewater. In addition to controlling the introduction of impurity ions (such as sulfate, chloride ions, etc.) (avoiding the input of inorganic acid), it can also increase the reaction rate (aluminum hydroxide, magnesium hydroxide, etc. need time to contact with calcium hydroxide, and the dissolution of these hydroxides themselves also takes time. In addition, the composite crystal nuclei formed by aluminum hydroxide, magnesium hydroxide, etc. and calcium hydroxide are more efficient in purifying aquaculture wastewater than hydroxides alone).

[0055] The test process and data are shown below.

[0056] Experimental group one was modified lime (including sodium silicate), experimental group two was lime, experimental group three was blank, and experimental group four was modified lime (excluding sodium silicate).

[0057] Prepare four sets of reaction vessels of the same specifications, labeled A (for experimental group 1), B (for experimental group 2), C (for experimental group 3), and D (for experimental group 4). Collect sufficient amounts of piggery wastewater from the same pig farm, mix them evenly, and then add equal volumes of wastewater samples to each of the four reaction vessels.

[0058] Add an appropriate amount of modified lime to container A (sodium silicate is added during the preparation process) to adjust the pH value of the wastewater to 11; add lime to container B and also adjust the pH value of the wastewater to 11; do not add anything to container C; add an appropriate amount of modified lime to container D (sodium silicate is not added during the preparation process).

[0059] The wastewater in each of the four containers was stirred at a consistent stirring speed and time. After 30 minutes of stirring, ammonia was removed by air stripping for 60 minutes. Carbon dioxide was introduced into containers A, B, and D to adjust the pH of the mixed solution to 7.5. An equal amount of carbon dioxide (the average of the carbon dioxide introduced into containers A, B, and D) was introduced into container C. The solutions in the four containers were then allowed to stand for 30 minutes before being filtered to separate the clear solution and the precipitate.

[0060] The ammonia nitrogen content in the wastewater before and after treatment was determined by Nessler's reagent spectrophotometry; the total phosphorus concentration was determined by ammonium molybdate spectrophotometry; and the chemical oxygen demand (COD) was determined by potassium dichromate method.

[0061] Table 1 - Improved lime test table

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for treating aquaculture wastewater, characterized in that: Under alkaline conditions, aluminum and magnesium elements are introduced into lime to form a calcium hydroxide composite system. Cationic polyacrylamide is used in the calcium hydroxide composite system to pre-aggregate the dispersed calcium hydroxide composite system particles into porous flocs to form improved lime. After the aquaculture wastewater undergoes preliminary solid-liquid separation and water quality adjustment, modified lime is added and stirred evenly to adjust the pH of the aquaculture wastewater so that ammonia nitrogen exists mainly in the form of free ammonia. Equipment is used to separate the free ammonia from the water body, and clean water spraying is used to recover ammonia gas to obtain ammonia water; Introducing carbon dioxide into the deammonified aquaculture wastewater to lower the pH of the aquaculture wastewater and form turbid liquid; After the precipitation reaction is completed, the aquaculture wastewater is separated into solid and liquid.

2. The method for treating aquaculture wastewater according to claim 1, wherein: The method for preparing improved lime comprises the following steps: Step S1. Weigh quicklime, add deionized water and stir to dissolve it to generate a calcium hydroxide suspension; Step S2. After dissolving aluminum sulfate in warm water, slowly add calcium hydroxide suspension dropwise, adjust the pH of the system, and stir at a constant temperature to generate aluminum hydroxide colloid and calcium aluminate double salt; Step S3. adding magnesium chloride, adjusting the pH to a strong alkaline state and heating to generate magnesium hydroxide, thereby forming a calcium hydroxide-aluminum hydroxide-magnesium hydroxide ternary hydroxide composite system; Step S4. Dissolve the cationic polyacrylamide in deionized water to prepare a solution, add the composite system, heat to and continue stirring to form a calcium hydroxide-aluminum magnesium hydroxide-polyacrylamide three-dimensional network flocculent; Step S5: filtering the reaction product, washing it with deionized water until no residual ions are left, and grinding it into powder after drying.

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

4. The method for treating aquaculture wastewater according to claim 1, wherein: The mass ratio of raw materials of improved lime is: Aluminum sulfate: polyacrylamide: magnesium chloride: lime = (10-15): (8-12): (5-8): (65-77).

5. The method for treating aquaculture wastewater according to claim 4, wherein: The mass ratio of raw materials of improved lime is: Aluminum sulfate: polyacrylamide: magnesium chloride: lime: sodium silicate = (10-15): (8-12): (5-8): (65-77): (2-5).

6. The method for treating aquaculture wastewater according to claim 1, wherein: Silicate is added to the porous floc system formed by cationic polyacrylamide, so that the modified lime contains calcium aluminosilicate complex salt. When the modified lime is added into the aquaculture wastewater, the modified lime releases silicate to coat the floc.

7. The method for treating aquaculture wastewater according to claim 1, wherein: Initial solid-liquid separation process: The aquaculture wastewater flows through the screen, and the multi-stage screen is used to remove larger floating objects and smaller suspended impurities; and / or, The aquaculture wastewater enters the sedimentation tank, and the principle of gravity sedimentation is used to settle the particles in the aquaculture wastewater.

8. The method for treating aquaculture wastewater according to claim 1, wherein: The clear liquid after solid-liquid separation enters the short-range nitrification reactor. The specific microbial community in the short-range nitrification reactor converts the residual ammonia nitrogen into nitrite, and inhibits the oxidation of nitrite to nitrate by controlling the dissolved oxygen content; after the short-range nitrification, the clear liquid enters the anaerobic ammonia oxidation reaction device. In an oxygen-deficient environment, anaerobic ammonia-oxidizing bacteria use ammonia nitrogen and nitrite as direct raw materials and convert them into nitrogen gas through biocatalysis.

9. The method for treating aquaculture wastewater according to claim 8, characterized in that: The effluent after anaerobic ammonia oxidation treatment enters the aerobic activated sludge reaction device, and the aerobic activated sludge reaction device is oxygenated by a blower. After the clear liquid completes the aerobic microbial treatment, it enters the MBR membrane bioreactor, and the gas is pressed into the MBR membrane bioreactor by the blower. The clear liquid passing through the MBR membrane bioreactor is reused after adsorption, and the sludge intercepted by the MBR membrane bioreactor participates in the deammonification treatment of aquaculture wastewater by improved lime.

10. The method for treating aquaculture wastewater according to claim 1, characterized in that: The solids after solid-liquid separation are subjected to composting and fermentation treatment or calcined to obtain lime and carbon dioxide for recycling.

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