Sulfur autotrophic denitrification filler for nitrogen wastewater treatment and preparation method thereof

Abstract

The present application relates to the technical field of water pollution treatment, and discloses a kind of sulfur autotrophic denitrification packing for nitrogen wastewater treatment and preparation method thereof, including a kind of gradually degradable composite particle, which is limited by the synergy of chemical composition and microphysical structure: chemically, sulfur substrate is compounded, main alkali source calcium carbonate and sacrificial alkali source magnesium oxide, interface self-renewal mechanism is established by using the difference in reaction rate; physically, it internally constructs the pore structure composed of reaction chamber and throat, to realize endogenous mass transfer channel self-cleaning by using denitrification product nitrogen, the present application solves the problem of interface passivation and pore silt self-locking caused by reaction product of traditional sulfur-based packing by the internal synergy of the above-mentioned chemical and physical mechanism, realizes the ability of packing active self-renewal and long-term stable operation, thereby releasing the application potential of cheap alkali source.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of sulfur autotrophic denitrification fillers for nitrogen wastewater treatment and its preparation method, belong to water pollution treatment technical field. BACKGROUND

[0002] Currently, sulfur autotrophic denitrification process is considered as a cost-advantageous technical path for treating high-concentration nitrate nitrogen wastewater, as it does not require the addition of external organic carbon source. In this process, the common technical practice is to physically mix sulfur particles as electron donors with cheap alkaline substances to neutralize the acid inevitably produced in the denitrification process. Among them, because of its extremely low cost and huge reserves, calcite, i.e. limestone CaCO3, has become a widely used alkali source option.

[0003] However, when this technical strategy goes from the laboratory to long-term large-scale engineering applications, a deep-seated operational paradox inherent in its core reaction mechanism begins to emerge, i.e. there is an irreconcilable contradiction between the long-term stability and economic feasibility of the system. The reason is that the sulfate ions produced by sulfur oxidation and the calcium ions dissolved from calcite will react in situ to form slightly soluble calcium sulfate CaSO4. This product will directly deposit and crystallize on the surface of calcite particles and gradually form a dense physical barrier, a process commonly known as armoring or interfacial passivation. As a result, although the remaining amount of calcite inside the filler is still sufficient, its effective reaction interface has been completely isolated, leading to a continuous decline in its acid neutralization capacity until it is eventually lost, and thus the denitrification function of the entire system collapses due to acid-base imbalance.

[0004] To cope with this dilemma, the skilled person in the art has also made relevant exploration, but these attempts often fall into new technical or economic difficulties, for example, using periodic strong hydraulic flushing or chemical cleaning and other physical intervention means to try to strip the passivation layer, but this undoubtedly increases the system's equipment complexity and operating energy consumption, which violates the original intention of low cost and low maintenance of the technology; Another idea is to completely abandon limestone and instead add liquid alkali and other strong solubility alkali agents, but this makes the core cost advantage of the technology meaningless, and the choice of the technical route itself loses its meaning. Specifically, the existing technology mainly has the following deficiencies: 1. The system has an internal negative feedback self-locking mechanism, that is, the continuous denitrification reaction generates passivation products that destroy its own operating conditions, resulting in a principled upper limit to the effective life and operating stability of the system; 2. The utilization efficiency of the relatively inexpensive alkali source is low, and most of the alkali source has not been used when the system fails due to surface passivation, resulting in waste of resources and cost; 3. The existing technology lacks an internal mechanism that can actively maintain the continuous update of the reaction interface from the inside of the material, resulting in the system having to rely on external high-cost forced intervention means when facing passivation problems. Therefore, how to design a sulfur autotrophic denitrification filler that can avoid the problems of interface passivation and self-locking caused by reaction products without relying on external intervention, and realize the long-term stable release of the full potential of inexpensive alkali sources through the internal synergy of material components, has become a technical problem to be solved by the present application. SUMMARY

[0005] The present application provides a sulfur autotrophic denitrification filler for nitrogen wastewater treatment and a preparation method thereof, which mainly aims to solve the problems of unstable system operation, short service life and low alkali source utilization rate caused by the formation of a passivation layer on the surface of inexpensive alkali sources by reaction products in the existing sulfur-based filler.

[0006] To achieve the above-mentioned purpose, the present application provides a sulfur autotrophic denitrification filler for nitrogen wastewater treatment, which comprises a porous composite particle containing a sulfur substrate as an electron donor, a calcium-based carbonate as a main alkali source, and a magnesium-based oxide as a sacrificial alkali source; the chemical composition and microstructure of the porous composite particle are cooperatively limited as follows:

[0007] At the chemical composition level, in a water solution at 25 degrees Celsius and pH 5.0, the apparent dissolution reaction rate of the magnesium-based oxide is higher than that of the calcium-based carbonate, and the magnesium-based oxide is configured to preferentially react with acid and release magnesium ions at the reaction interface of the calcium-based carbonate;

[0008] At the micro-physical structure level, the porous composite particle has a pore structure composed of a reaction chamber and a throat connecting the reaction chamber with the outside of the particle, and the pore structure is configured to make the nitrogen generated by the denitrification process accumulate pressure in the reaction chamber and then be pulsed out through the throat and impact the mass transfer channel inside the particle.

[0009] Preferably, the calcium-based carbonate is calcite, and the magnesium-based oxide is light-burned magnesium oxide; the content of the magnesium-based oxide is 5 parts by weight to 35 parts by weight, based on the sum of the weights of the calcium-based carbonate and the magnesium-based oxide being 100 parts by weight; and the mass ratio of the sulfur-based substrate to the sum of the weights of the calcium-based carbonate and the magnesium-based oxide is 0.8 to 1.6.

[0010] Preferably, the magnesium-based oxide is hard-burned magnesium oxide, which, when in contact with wastewater, undergoes a hydration exothermic reaction and causes the local temperature of the reaction microzone in the porous composite particle, which is defined by the reaction chamber and the throat, to rise.

[0011] Preferably, the ratio of the equivalent diameter of the throat to the equivalent diameter of the reaction chamber is in the range of 0.05 to 0.30; the equivalent diameter of the throat is the diameter at the largest cross-sectional area of the throat, and the equivalent diameter of the reaction chamber is the diameter of a sphere equivalent in volume to the reaction chamber; and the connected porosity of the porous composite particle accounts for 20% to 45% of the total volume of the particle.

[0012] Preferably, the inner wall of the throat carries a bioaffinity hydrogel precursor, which, together with the extracellular polymers secreted by the denitrifying microorganisms, forms a viscoelastic biological valve body in the throat, which undergoes viscoelastic deformation or overall displacement when the gas pressure in the reaction chamber rises.

[0013] Preferably, the bioaffinity hydrogel precursor is an anionic polysaccharide, which is distributed at least at the entrances of the surface layer pores of the porous composite particle and immobilizes toxic substances of a predetermined type in the wastewater through ionic chelation or chemical reaction, so as to reduce the concentration of the toxic substances of the predetermined type in the wastewater entering the throat.

[0014] Preferably, the pore structure composed of the reaction chamber and the throat is formed by removing a pore-forming agent pre-disposed in the mixture during the granulation process, and the calcium-based carbonate surface of the porous composite particle has a calcium sulfate coverage of less than 30% after 48 hours in a standard sulfate deposition test; the conditions of the standard sulfate deposition test are that the porous composite particle is placed in a static solution with a pH value of 5.0 and a sulfate ion concentration of 2500 mg / L at 25 degrees Celsius.

[0015] Preferably, the porous composite particle is bound by an inert binder containing bentonite and is dried and shaped at a temperature below 95 degrees Celsius; the amount of the inert binder accounts for 2% to 8% of the total weight of the porous composite particle.

[0016] Preferably, the anionic polysaccharide is sodium alginate or sodium carboxymethylcellulose; the bioaffinity hydrogel precursor is loaded on the inner wall of the throat and the entrance of the surface layer pores of the porous composite particles by a secondary impregnation coating process.

[0017] A preparation method of a sulfur autotrophic denitrification filler for nitrogen wastewater treatment, comprising the following steps:

[0018] Step a, mixing sulfur substrate as an electron donor, calcium carbonate as a main alkali source, magnesium oxide as a sacrificial alkali source, an inert binder and a pore former to obtain a mixture;

[0019] Step b, kneading the mixture with water and making wet particles;

[0020] Step c, drying the wet particles at a temperature lower than 95 degrees Celsius, and removing the pore former by dissolution or sublimation during the drying process or in a subsequent soaking process to form a pore structure composed of reaction chambers and throats inside the particles, to obtain dry particles;

[0021] Step d, when it is necessary to load a bioaffinity hydrogel precursor, performing secondary impregnation coating on the dry particles to load the bioaffinity hydrogel precursor on the inner wall of the throat and the entrance of the surface layer pores of the particles.

[0022] Compared with the prior art, the beneficial effects of the present application are:

[0023] 1、The filler of the present application is composed of sulfur substrate as an electron donor, calcium carbonate as a main alkali source and magnesium oxide with a higher acid reaction rate than calcium carbonate, establishing a self-regulating mechanism of interface reaction environment; under the condition of denitrification acid production, magnesium oxide reacts preferentially, and the ion environment formed by its product can continuously inhibit the crystallization and adhesion of calcium sulfate hard shell on the surface of calcium carbonate, so that the reaction interface of calcium carbonate as the main alkali source can be exposed and updated for a long time, avoiding the problem of system dynamics attenuation and final failure caused by product passivation of traditional sulfur-based fillers.

[0024] 2、In the above mechanism, by selecting a specific hard-burned magnesium oxide as magnesium-based oxide, the system is introduced with temperature compensation function; the hydration of hard-burned magnesium oxide releases heat when it is in neutralization reaction with wastewater, and this part of heat directly acts on the reaction microzone inside the particle, so as to locally increase the interface temperature of core reactants, and then maintain the reaction rate of magnesium-based oxide and calcium-based carbonate with acid, so that the core interface passivation resistance and overall treatment performance of the filler remain stable under different seasons and temperature fluctuations; and the composite particle of the application is internally preset with a specific pore structure composed of a reaction chamber and a throat connecting the chamber with the surface of the particle, which makes the nitrogen produced in the denitrification process need to overcome the capillary resistance at the throat before escaping from the chamber, thereby forming a short-term pressure accumulation in the chamber and finally releasing in the form of pulse; this continuous distributed internal gas pulse can cause physical disturbance to the loose and attached biological membrane fragments or inorganic particles on the inner wall of the pore, realize long-term self-cleaning of the mass transfer channel inside the filler, and prolong the effective service life of the filler.

[0025] 3、The application further loads a bio-affinity hydrogel precursor in the inner wall of the throat, which, together with the extracellular polymers secreted by microorganisms, forms a viscoelastic biological valve body in the throat, which can dissipate impact energy through its viscoelastic deformation or overall displacement when the system is subjected to high nitrogen shock, thereby protecting the porous skeleton of the filler; at the same time, if the hydrogel precursor, such as anionic polysaccharide, is also distributed at the entrance of the surface layer pores of the particle, it can be preferentially fixed into certain specific toxic substances in the wastewater through ion chelation or chemical reaction, thereby providing a pre-positioned isolated chemical environment for the stability of the internal core functional microbial community and the valve body structure, and finally forming a stable operation system with physical impact resistance and chemical toxicity resistance. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The figure is a schematic diagram of the operation process of the system of the application;

[0027] Figure 2 The figure is a relationship diagram between the pore structure parameters of the filler of the application and the key performance indicators;

[0028] Figure 3 The figure is a block diagram of the internal synergistic mechanism of the filler of the application;

[0029] Figure 4 The figure is a schematic diagram of the interface self-renewal mechanism of the filler of the application and the passivation phenomenon of the interface of the traditional filler. DETAILED DESCRIPTION

[0030] In order to make the technical solutions and advantages of the present application more clear, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0031] The present application provides a kind of sulphur autotrophic denitrification packing for nitrogen wastewater treatment and its preparation method, the packing is a kind of porous composite particles, in the use process, by the continuous reaction and consumption of main alkali source and sacrificial alkali source, realize the gradual release of function and the synchronous degradation of particle, by the synergistic restriction of chemical composition and microstructure, aim at solving the interface passivation and pore siltation problem caused by reaction product in prior art, to realize the self-renewal and long-term stable operation of packing;The chemical composition of the packing includes sulfur substrate as electron donor, calcium carbonate as main alkali source, and magnesium oxide as sacrificial alkali source, and its microstructure is provided with pore network composed of reaction chamber and throat.

[0032] In the long-term operation of sulphur autotrophic denitrification process, the sulfate ions generated by sulfur oxidation process will react with the calcium ions dissolved out of calcium carbonate as alkali source, generate slightly soluble calcium sulfate and deposit on the surface of calcium carbonate particles, form a dense physical barrier, i.e. interface passivation phenomenon, this layer of barrier will isolate the contact between calcium carbonate and acidic wastewater, which can cause the imbalance of acid-base balance of the system and reduce the denitrification function;To solve this problem, the porous composite particles of the present application are specifically synergistically configured in the aspect of chemical composition, which contains a sacrificial alkali source magnesium oxide, the apparent dissolution reaction rate of the magnesium oxide in the aqueous solution at 25 degrees Celsius and pH value of 5.0 is higher than that of the main alkali source calcium carbonate, when the denitrification process starts to produce acid, H + + in the pore microenvironment of the particle will preferentially react with magnesium oxide, this preferential reaction releases high concentration of magnesium ions Mg 2+ According to the principle of crystallization kinetics, high concentration of coexisting cations increases the nucleation energy barrier of calcium sulfate and interferes with the regular growth of its crystal lattice, at the same time, since the solubility of magnesium sulfate is much higher than that of calcium sulfate, the system will preferentially maintain the magnesium sulfate in liquid phase, thereby inhibiting the attachment and crystallization of solid calcium sulfate hard shell layer on the surface of calcium carbonate, so that the effective reaction interface of calcium carbonate can be exposed and renewed for a long time, and its effect is verified by standard sulfate deposition test, i.e. after placing the porous composite particles in static solution with pH value of 5.0 and sulfate ion concentration of 2500 mg / L at 25 degrees Celsius for 48 hours, the coverage of calcium carbonate surface by calcium sulfate is less than 30%.

[0033] To realize the above-mentioned interface self-renewal mechanism, the types and proportions of each component are limited, wherein the calcium carbonate is calcite, and the magnesium oxide is light burned magnesium oxide; the content of the magnesium oxide is calibrated based on the total weight of the calcium carbonate and the magnesium oxide being 100 parts by weight, and the results show that when the content of the magnesium oxide is less than 5 parts by weight, the concentration of the released magnesium ions is not enough to form an effective crystallization inhibition environment at the interface of the calcium carbonate, and the passivation phenomenon still occurs, and when the content of the magnesium oxide is higher than 35 parts by weight, the excessive consumption of the magnesium oxide will cause the alkalinity of the particles to be released too quickly in the early stage, and does not bring further performance improvement, but increases the material cost, therefore, the content of the magnesium oxide is determined to be in the range of 5 parts by weight to 35 parts by weight; accordingly, the mass ratio of the sulfur substrate as an electron donor to the total weight of the calcium carbonate and the magnesium oxide also has a suitable working range, when the mass ratio is less than 0.8, the sulfur substrate as an electron donor is insufficient, which limits the denitrification rate of the system, and when the mass ratio is higher than 1.6, excessive sulfur substrate will produce acid that exceeds the neutralization capacity of the alkali source, shortening the effective service life of the filler, therefore, the mass ratio is determined to be 0.8 to 1.6; to further verify and calibrate the boundary effect of the mass ratio of the sulfur substrate as an electron donor to the total alkali source (the total weight of the calcium carbonate and the magnesium oxide) on the long-term performance of the system, the verification test is specially performed, two test groups are set in this experiment, the sulfur-alkali mass ratio of test group A is 0.8, and the sulfur-alkali mass ratio of test group B is 1.6, after 90 days of continuous operation, it is observed that: the system water pH value of test group A (sulfur-alkali ratio 0.8) is stably above 7.3 throughout the whole process, showing excellent acid-base buffering capacity, but its average nitrate nitrogen removal rate is stably in the range of 88% ± 3% in the later stage of operation, and the analysis considers that the reason is that the sulfur substrate as an electron donor becomes the limiting substrate of the denitrification reaction, test group B (sulfur-alkali ratio 1.6) maintains a nitrate nitrogen removal rate higher than 97% throughout the whole operation period, but its water pH value starts to show a slow downward trend from the 55th day, and is stably at 6.7 ± 0.1 at the end of the test, after the test, it is found that the consumption degree of the magnesium oxide in the filler is significantly higher than that in the intermediate ratio group.

[0034] After the interface passivation problem at the chemical level is solved, the system also faces the gradual pore clogging problem at the physical level in long-period operation, that is, the aged biofilm and inorganic particles that fall off are slowly deposited in the mass transfer channels inside the filler, resulting in blocked mass transfer and invalidation of the filler; in view of this, the porous composite particle of the application is functionally designed at the micro-physical structure level, and has a pore structure composed of a reaction chamber and a throat connecting the reaction chamber and the outside of the particle, which is formed by removing the pore-forming agent pre-positioned in the mixture during the granulation process, and the operation mechanism is that the nitrogen produced in the denitrification process first nucleates and accumulates in the relatively large reaction chamber, and due to the surface tension, the gas needs to overcome the capillary resistance at the narrow throat when escaping, thereby forming pressure accumulation in the chamber, when the gas pressure in the chamber accumulates enough to overcome the capillary resistance at the throat, the accumulated gas will be pulsed out through the throat, and this continuous and distributed internal gas pulse can produce physical disturbance and scouring to the loose biofilm residues or inorganic particles attached to the inner wall of the pore, thereby realizing self-cleaning of the mass transfer channel inside the filler; at the same time, in order to ensure the effective realization of the internal gas pulse self-cleaning function, the key geometric parameters of the pore structure are calibrated, that is, the ratio of the equivalent diameter of the throat to the equivalent diameter of the reaction chamber, wherein the equivalent diameter of the throat is the diameter at the maximum cross-sectional area of the throat, and the equivalent diameter of the reaction chamber is the diameter of the volume-equivalent sphere of the reaction chamber; it is found through experimental calibration that when the ratio is less than 0.05, the throat is too narrow, the gas escape resistance is too large, and the internal structure of the particle may be damaged due to excessive pressure accumulation, and when the ratio is higher than 0.30, the throat is relatively wide, the capillary resistance is insufficient, the gas cannot form effective pressure accumulation and directly escapes, and the pulse intensity is insufficient to achieve the dredging effect, therefore, the ratio is determined to be in the range of 0.05 to 0.30; in order to ensure sufficient reaction interface and mass transfer channel, the connected porosity of the porous composite particle is set to 20% to 45% of the total volume of the particle.

[0035] Further, in the face of winter low-temperature wastewater working conditions, the decline of chemical reaction kinetics may weaken the reliability of the aforementioned interface passivation resistance mechanism; to deal with this situation, the application provides an implementation with temperature compensation function, which selects hard-burned magnesia instead of light-burned magnesia as a sacrificial alkali source, and when the hard-burned magnesia contacts with wastewater, it will not only undergo neutralization reaction, but also hydration exothermic reaction, that is, MgO+H2O→Mg(OH)2+Heat, this part of heat is directly released in the reaction microzone inside the particle defined by the reaction chamber and the throat, which can locally improve the temperature of the core reaction interface when the external water temperature is low, thereby compensating for the decrease in reaction rate caused by low temperature, so that the interface passivation resistance function and overall treatment performance of the filler can remain stable under different working temperature fluctuations.

[0036] In addition, when the system encounters high load nitrogen shock or intermittent toxic substance shock caused by upstream accidental discharge, the conventional filler structure is tested; therefore, the application provides an embodiment with multiple impact resistance, which carries biological affinity hydrogel precursors, such as sodium alginate or sodium carboxymethyl cellulose in anionic polysaccharides, on the inner wall of the throat and the entrance of the surface layer pores of the porous composite particles through a secondary impregnation coating process; the biological affinity hydrogel precursor and the extracellular polymer secreted by the denitrifying microorganism together form a viscoelastic biological valve body in the throat, which can enhance the gas pressure accumulation effect under normal working conditions, and when the internal gas pressure rises due to high load nitrogen shock, the valve body can dissipate impact energy through its viscoelastic deformation or overall displacement, thereby buffering and protecting the porous framework of the filler; at the same time, the anionic polysaccharide coating distributed at the entrance of the surface layer pores of the particles can use the functional groups on the molecular chains to preferentially fix specific types of toxic substances in the wastewater, such as heavy metal cations or residual oxidants, through ion chelation or chemical reaction, thereby reducing the concentration of the type of toxic substances in the wastewater entering the throat, providing a pre-chemical environment guarantee for the stability of the internal core functional microbial community and the valve body structure, and finally forming an operation system with physical impact resistance and chemical toxicity resistance.

[0037] The preparation method of the sulfur autotrophic denitrification filler for nitrogen wastewater treatment provided by the application comprises the following steps: first, mixing sulfur substrate as an electron donor, calcium carbonate as a main alkali source, magnesium oxide as a sacrificial alkali source, inert binder containing bentonite, and pore-forming agent to obtain a mixture, wherein the amount of the inert binder accounts for 2-8% of the total weight of the porous composite particles; then, kneading the mixture with water and making wet particles; then, drying the wet particles at a temperature lower than 95 DEG C, and removing the pore-forming agent by dissolution or sublimation during the drying process or in a subsequent soaking process to form a pore structure composed of reaction chambers and throats in the particles, to obtain dry particles; finally, when it is necessary to carry biological affinity hydrogel precursors, the dry particles are subjected to secondary impregnation coating to carry biological affinity hydrogel precursors on the inner wall of the throat and the entrance of the surface layer pores of the particles.

[0038] Embodiment 1: This embodiment is a specific application of the technical solution described in the foregoing detailed description in a specific industrial wastewater treatment scenario, in a chemical production facility treating high-concentration nitrogen-containing wastewater, the effluent wastewater of which has a nitrate nitrogen concentration higher than 400 mg / L, a high sulfate concentration, and a carbon-nitrogen ratio lower than 1.5, after the wastewater treatment system of the facility enters winter working conditions, the influent temperature decreases to below 10°C, and after the autotrophic denitrification reactor using conventional sulfur-scalcite mixed fillers has been operated for 90 days, the effluent pH continuously decreases to below 5.5, the denitrification efficiency decreases from more than 95% at the initial stage to less than 30%, and finally the system functionally fails, and upon inspection of the fillers, it is found that the surface of the scalcite particles is covered with a dense white calcium sulfate crystalline layer, and there is a phenomenon of caking in the filler bed.

[0039] To restore the function of the treatment system, the failed mixed fillers are replaced with the porous composite particles of the present application, which are prepared according to the method of the detailed description, wherein the sacrificial alkali source is hard-burned magnesium oxide, and the particles are loaded with sodium alginate through a secondary impregnation coating process; after the system is restarted, under normal temperature working conditions, the chemical composition and synergistic mechanism inside the particles begin to operate, the acid produced by denitrification preferentially reacts with the hard-burned magnesium oxide, which has a higher reaction rate, the magnesium ion microenvironment formed around the scalcite reaction interface inhibits the crystallization and adhesion of calcium sulfate, and the surface of the scalcite as the main alkali source is continuously exposed, thereby maintaining a stable pH environment and denitrification rate; when winter working conditions arrive and the influent temperature decreases to 10°C, the hard-burned magnesium oxide undergoes a hydration exothermic reaction, which produces a local temperature rise in the microzone defined by the reaction chamber and the throat of the particle, and this process compensates for the negative effects of low temperature on chemical reaction kinetics and microbial activity, so that the interface anti-passivation mechanism remains effective at low temperatures, avoiding the functional failure of the system caused by low temperature as before.

[0040] After the system ran steadily for six months, a process fluctuation of an upstream production unit caused the nitrate nitrogen concentration in the wastewater entering the denitrification reactor to increase to 650 mg / L within 4 hours, accompanied by the infiltration of trace amounts of organic toxic substances. The sodium alginate coating carried on the surface pores of the particles preferentially fixed most of the toxic substances entering the particles through ion chelation, providing a chemical environment guarantee for the internal microorganisms. Under the impact of high-concentration nitrate nitrogen, the activity of the protected microorganisms inside the particles increased, causing the nitrogen production rate to rise sharply, and the gas pressure formed in the reaction chamber to be higher than normal. At this time, the viscoelastic biological valve formed by sodium alginate and extracellular polymeric substances in the throat dissipated the impact energy of the rapid gas pulse through its own viscoelastic deformation and partial displacement, playing a buffering protection and safety pressure relief role, avoiding the rupture of the particle structure due to internal high pressure. At the same time, the nitrogen gas continuously produced by the denitrification process was released in a pulse through the throat, periodically physically disturbing the slowly accumulated biofilm residues and inorganic particles in the mass transfer channel of the particles, maintaining the unobstructedness of the pores. This physical self-cleaning effect and chemical interface self-renewal effect formed a synergy, with the former guaranteeing the effective transfer of reactants and products, and the latter guaranteeing the continuous chemical reaction. After one year of continuous operation, including a complete winter low-temperature period and several unplanned load shock events, the nitrate nitrogen concentration in the effluent of the sulfur autotrophic denitrification system using the invented packing material remained below the discharge standard, and the system pH value could be automatically maintained in the range of 6.8 to 7.5 without external addition of alkali. Part of the packing particles were taken out for detection, and no obvious calcium sulfate hard shell layer was found on the internal calcite surface, and the pore structure remained complete and unobstructed. The system achieved a stable operation period of more than one year.

[0041] Example 2: To quantitatively verify the stability and anti-passivation performance of the invented packing material during long-term operation, an accelerated comparative test was set up. The test aimed to investigate the differential performance of the invented packing material and conventional sulfur-based packing material in key performance indicators by simulating high-load conditions that are prone to cause calcium sulfate crystallization and precipitation. The test platform consisted of two sets of upflow anaerobic packed bed reactors with the same specifications running in parallel, each with an effective volume of 2.0 L. The reaction temperature was constantly controlled at 25.0 degrees Celsius by an external water bath jacket, with a temperature control accuracy of ±0.5 degrees Celsius. The influent was supplied at a constant speed by a peristaltic pump, with a flow rate set accuracy of ±2%.

[0042] The test sets up a control group and a test group, wherein the control group is filled with a conventional filler physically mixed by sulfur powder and calcite particles in the reactor, and the test group is filled with the porous composite particles of the application prepared according to the specific embodiments in the reactor, the particle size of the two fillers ranges from 3.0 to 5.0 mm, and the weight ratio of sulfur matrix to total alkali source is kept consistent; the test uses artificially configured simulated wastewater, and the water quality parameters are set to continuously stress the alkali source stability of the fillers, specifically containing nitrate nitrogen concentration 400 mg / L, sulfate concentration 1500 mg / L, supplemented with trace elements such as phosphate necessary for microbial activity; the hydraulic retention time HRT of the system is determined to be 6.0 h, and the setting of this parameter aims to balance the nitrate load and reaction sufficiency to ensure that the biological denitrification process is not limited by hydraulic conditions in the steady period, so that the chemical stability of the fillers themselves becomes the main variable affecting the long-term performance of the system.

[0043] After the two sets of reactors are inoculated with activated sludge and undergo a 15-day start-up and commissioning period, they enter a 120-day continuous operation and monitoring phase. In the initial 30 days of operation, the performance of the two systems is similar, with effluent pH values maintained above 7.3 and nitrate nitrogen removal rates higher than 97%; since the 45th day, the performance of the control group has begun to deteriorate, with effluent pH dropping to 6.82, while the test group has stabilized at 7.35; by the 60th day, the difference has further expanded, with the effluent pH of the control group having dropped to 6.41, and the corresponding nitrate nitrogen removal rate has also declined to 75.6%, while the nitrate nitrogen removal rate of the test group remains at the level of 97.5%; on the 90th day of the test, the effluent pH of the control group has dropped to 5.88, and the nitrate nitrogen removal rate is only 31.4%, indicating that its acid neutralization capacity and denitrification function have seriously deteriorated, while the effluent pH of the test group is still 7.25, and the nitrate nitrogen removal rate is as high as 96.8%; by the end of the test on the 120th day, the pH of the control group has further dropped to 5.65, and the nitrate nitrogen removal rate is only 24.1%, while the effluent pH and nitrate nitrogen removal rate of the test group are stable at 7.23 and 96.6% respectively, showing sustained operational stability.

[0044] The differentiation trend of the above test data verifies the difference of the internal action mechanism of the two fillers. The performance degradation of the control group is caused by the calcium sulfate armoring phenomenon on the surface of calcite, resulting in the gradual loss of its acid neutralization capacity. The test group can maintain long-term stable pH and denitrification performance because the sacrificial alkali source of magnesium oxide inside the particle preferentially reacts with the acid, forming an ion microenvironment at the interface of the main alkali source calcite that inhibits the crystallization of calcium sulfate, thereby ensuring the long-acting of the main alkali source. After the test, the two fillers are dissected and analyzed, and it is also observed that there is a dense white covering layer on the surface of the calcite particles in the control group, while the surface of the calcite inside the test group particles remains clean. This comparison test proves that the porous composite particles of the present application can use calcium carbonate as the main alkali source while avoiding the interface passivation problem caused by the reaction product through the synergistic effect of the internal chemical components, thereby realizing the long-term stable operation of the sulfur autotrophic denitrification system under the condition of treating high-concentration nitrogen-containing and sulfate-containing wastewater.

[0045] Embodiment 3: This embodiment combines Figures 1 to 4 to realize and illustrate a kind of sulfur autotrophic denitrification filler for nitrogen wastewater treatment and its preparation method. As Figure 1 shown, high-nitrogen wastewater enters the reactor attached with denitrification microorganisms, and the composite filler starts the denitrification process as an electron donor. The acidic substances produced in this process activate the interface self-renewal and self-cleaning mechanisms. The former activates the interface protection and maintains the alkalinity balance by preferential reaction of magnesium oxide, and the latter uses the generated nitrogen gas for gas pulse cleaning to keep the mass transfer channel unobstructed. The synergistic effect of the two ensures the long-term stable operation of the system and produces stable and qualified effluent. The effluent quality after treatment is monitored by the system monitoring part for pH and denitrification rate to feedback the operating status and provide data support for continuous optimization.

[0046] As Figure 2 shown, the horizontal coordinate is the ratio of the throat to the equivalent diameter of the reaction chamber, with a value range of 0.05 to 0.30, and the vertical coordinate is the performance index. The three curves in the figure represent the relationship between gas pulse intensity (relative value), structure stability score and comprehensive performance index with the ratio. As the ratio increases from 0.05 to 0.30, the gas pulse intensity continuously weakens, while the structure stability score correspondingly strengthens. The comprehensive performance index, as a balance of the two, provides quantitative basis for optimizing the pore structure parameters within the ratio range defined in the present application.

[0047] As Figure 3 shown, the porous composite particle is the core of the system, achieving self-renewal and stable operation through chemical synergy and physical synergy. In the chemical synergy interface self-renewal mechanism, sulfur substrate acts as an electron donor to participate in denitrification to produce acid (H +), the sacrificial base source magnesium-based oxide preferentially reacts and releases Mg 2+ ions, thereby inhibiting the crystallization of CaSO4 on the surface of the main base source calcium-based carbonate, avoiding interface passivation; in the physical synergistic mass transfer channel self-cleaning mechanism, the pre-set pore structure composed of the reaction chamber and the throat makes the denitrification product nitrogen (N2) accumulate and then pulse out after pressurization, thereby self-cleaning the mass transfer channel.

[0048] As shown in Figure 4 the left side of the figure shows the interface passivation phenomenon of the conventional filler, in which the reaction interface between the sulfur substrate (S) and the calcium-based carbonate (CaCO3) is covered by a dense CaSO4 passivation layer, thereby blocking the continuation of the reaction; the right side of the figure shows the interface self-renewal mechanism of the filler of the present application, in which the presence of the sacrificial base source magnesium-based oxide (MgO) forms an Mg 2+ ion cloud in the reaction microenvironment, which prevents the deposition of CaSO4 on the surface of the calcium-based carbonate through crystallization inhibition, thereby ensuring the continuous renewal of the active reaction interface.

[0049] Example 4: In a specific engineering application scenario, a new industrial facility needs to be designed with a sulfur autotrophic denitrification system, and the concentration of nitrate nitrogen in the wastewater to be treated is stable, but the concentration of sulfate will fluctuate in the range of 1500 mg / L to 3000 mg / L due to different upstream production batches; in order to ensure that the system can run stably in the entire fluctuation range for a long time, a standardized engineering calibration procedure needs to be established to determine the applicable process parameters and chemical ratio of the porous composite particles of the present application, and the core lies in solving two technical problems, one is how to obtain particles with a pre-determined pore structure through process control, and the other is how to determine the appropriate content of the sacrificial base source to cope with high-concentration sulfate environment based on this structure.

[0050] To solve the first technical problem, i.e. to realize the directional construction of the pore structure composed of the reaction chamber and the throat, soluble porogen sodium chloride is used as the pore-forming material, and the final pore geometry parameters are regulated by controlling the particle size of the porogen and the material ratio in the granulation process. Specifically, two groups of test samples are prepared. The sample group one uses sodium chloride microcrystals with a particle size distribution of 100 to 150 microns as the porogen, and the sample group two uses sodium chloride particles with a particle size distribution of 400 to 500 microns as the porogen. The types and proportions of the sulfur matrix, calcium-based carbonate, magnesium-based oxide and inert binder of the two groups of samples are consistent. In the water addition and kneading granulation step, the density of the wet granules is adjusted by controlling the water addition amount and the kneading shear force, and then the sodium chloride porogen is removed by drying at a temperature below 95 degrees Celsius and elution. The mercury intrusion method is used to characterize the pore structure of the two groups of dried granules. The results show that the sample group one forms a pore structure with a throat equivalent diameter to reaction chamber equivalent diameter ratio of about 0.25, and the sample group two forms a pore structure with a ratio of about 0.08, which confirms that the porogen particle size mainly determines the size of the reaction chamber, and the granulation process parameters affect the formation of the throat. Through the synergistic regulation of the two, the pore structure parameters can be stabilized in the target range of 0.05 to 0.30.

[0051] To solve the second technical problem, i.e. to determine the appropriate content of the sacrificial alkali source, the sample group two particles prepared in the previous step, which have a more significant throat restriction effect, are selected as the physical structure base, and on this basis, four batches of test fillers with different formulations are prepared, numbered one to four. The four batches of fillers have the same physical structure, and the mass ratio of the sulfur matrix to the total weight of the calcium-based carbonate and magnesium-based oxide is also fixed at 1.2. The only variable is the content of the light burned magnesium oxide as the sacrificial alkali source in the total alkali source, i.e. the sum of the weights of the calcium-based carbonate and the magnesium-based oxide, which is 5 parts by weight, 15 parts by weight, 25 parts by weight and 35 parts by weight, respectively. The four batches of fillers are placed in independent reactors, and an accelerated aging test is carried out using simulated wastewater at 25 degrees Celsius. The pH value of the simulated wastewater is constant at 5.0, and the sulfate ion concentration is set at 2500 milligrams per liter. The anti-passivation ability of each batch of filler is continuously monitored, and the judgment basis for the functional failure of the filler is that the effluent pH value is stably lower than 6.0.

[0052] The test results show that the first batch of fillers, i.e. the sample with 5 parts by weight of magnesium-based oxide, the effluent pH value began to decrease continuously and eventually failed after about 30 days of operation, indicating that under this high sulfate stress, the lower content of sacrificial alkali source is not enough to provide long-term interface protection; the second and third batches of fillers, i.e. the samples with 15 and 25 parts by weight of magnesium-based oxide, the effluent pH value remained stable during the continuous operation period of more than 90 days, and no functional failure occurred; and the fourth batch of fillers, i.e. the sample with 35 parts by weight of magnesium-based oxide, also showed long-period stability, but after the test, the particles were analyzed, and it was found that the residual amount of magnesium-based oxide inside was higher than that of the second and third batches, indicating that under the premise of meeting the anti-passivation performance, excessive addition caused a certain material redundancy; the calibration procedure confirms that for wastewater with a maximum sulfate concentration of 2500 mg / L, the content of sacrificial alkali source magnesium-based oxide is set in the interval of 15 to 25 parts by weight, which can balance the anti-passivation performance and material utilization.

[0053] In a specific application, in order to enable the porous composite particles to cope with high-load nitrogen shock and intermittent toxic substances, they need to be coated with a secondary functionalization, and this process follows a standardized impregnation and quality control procedure; first, the prepared dry particles, i.e. particles without bio-affinity hydrogel precursors, are immersed in a 1.5% by weight sodium alginate aqueous solution for 60 seconds, the setting of this immersion time aims to make the hydrogel precursor solution with a certain viscosity preferentially wet and adhere to the outer surface and surface pore entrance of the particles, rather than completely penetrating deep into the particles, after immersion, the particles are taken out and drained of excess liquid, then low-temperature drying is carried out at 60°C until constant weight, thereby loading the bio-affinity hydrogel precursor on the inner wall of the throat and the entrance of the surface pores of the particles.

[0054] In order to verify the functional consistency of the particles after each batch of coating, a pre-delivery quality control procedure needs to be performed, which is realized by measuring the wet gas permeation back pressure of the particles; to perform this measurement, the coated particles after sampling are completely wetted in water and packed in a test column with a gas distribution plate at the bottom, then nitrogen is introduced from the bottom of the test column at a constant low flow rate of 0.2 times the reactor bed volume per minute, and a micro-pressure gauge with an accuracy of 0.01 kPa is used to monitor the pressure change at the bottom of the test column, recording the maximum pressure value corresponding to the first breakthrough of the gas through the filler layer and escaping in pulse form, which is the gas pulse back pressure; for a qualified batch of products, the measured gas pulse back pressure value should fall within the predetermined interval of 1.05 to 1.25 kPa, below this interval indicates insufficient coating or uneven distribution, which cannot form an effective viscoelastic biological valve body, while above this interval may cause excessive pressure accumulation, affecting the normal operation of the system.

[0055] Example 6: To apply the filler of the present application to different characteristics of wastewater treatment, an off-line optimization parameter selection procedure is established to determine the appropriate pore structure parameters for specific objective functions, i.e. for wastewater with high solid content and low gas production rate, the objective is to maximize the anti-physical clogging ability, while for wastewater with high gas production rate, the objective is to maximize the long-term structural stability of the particles; where the anti-physical clogging ability is quantified by the change in hydraulic pressure difference of the reactor bed, and the long-term structural stability is evaluated by the microstructure integrity of the particles after operation; according to the process parameter regulation method of the present application, two batches of porous composite particles with the same indicators except for pore structure parameters are prepared, the ratio of throat diameter to reaction chamber equivalent diameter of batch one particles is controlled at about 0.08, and the ratio of batch two particles is controlled at about 0.25; for the above two types of applications, parallel comparison tests are set up, i.e. for each type of application, two sets of identical packed bed reactors are set up, one set is packed with batch one particles, and the other set is packed with batch two particles, and the simulated wastewater matched with the target application water quality is used for continuous operation for 90 days; during this process, the clogging situation is monitored by regularly measuring the pressure difference between the two ends of the bed at a constant inlet water flow rate.

[0056] In the test for the first type of application, i.e. wastewater with high solid content and low gas production rate, the reactor filled with batch two particles, i.e. the ratio of 0.25, its bed pressure difference started to rise slowly from the 40th day, and by the 90th day, it was 1.8 times the initial value, indicating that the gas pulse intensity was not sufficient to effectively remove the continuously entering inorganic particles; while the reactor filled with batch one particles, i.e. the ratio of 0.08, its bed pressure difference remained stable throughout the operation period, achieving the objective of maximizing the anti-physical clogging ability; in the test for the second type of application, i.e. wastewater with high gas production rate, the bed pressure differences of the two sets of reactors did not change significantly, but when the particles were detected for microstructure after the test, it was found that the internal pore wall of batch one particles had micro-cracks, while the structure of batch two particles remained intact, achieving the objective of maximizing the long-term structural stability of the particles; the test results of this off-line optimization parameter selection procedure established a selection criterion for pore structure parameters, i.e. for wastewater with low gas production rate but high risk of physical clogging, the ratio of throat diameter to reaction chamber equivalent diameter should be selected close to the 0.05 interval to optimize its physical self-cleaning effect; while for wastewater with high gas production rate, the ratio should be selected close to the 0.30 interval to optimize its long-term structural stability.

[0057] Example 7: This example aims to verify the specific influence of the end-point parameter of the mass ratio of sulfur substrate to total alkali source (0.8 to 1.6) on the system performance; the test setup adopts three sets of up-flow anaerobic packed bed reactors (R1, R2, R3) operating in parallel, the device specifications and operating conditions (temperature 25.0℃, HRT 6.0h, simulated wastewater quality) are consistent with those of Example 2, the three sets of reactors are all filled with the porous composite particles prepared by the present application, the pore structure parameters, particle size and internal proportion of alkali source (20 parts by weight of magnesium-based oxide in the total alkali source) of the particles are all the same, the only variable is the mass ratio of sulfur substrate to total alkali source (the sum of the weight of calcium-based carbonate and magnesium-based oxide), wherein the ratio of the R1 reactor (control group) is 1.2, the R2 reactor (low ratio group) is 0.8, and the R3 reactor (high ratio group) is 1.6; the test results are that after a 15-day start-up period, the three sets of systems are continuously monitored for 100 days.

[0058] The R1 reactor (sulfur-alkali ratio 1.2) showed consistently stable high performance, with the effluent pH value stabilizing between 7.2-7.4 and the nitrate nitrogen removal rate consistently higher than 96%, consistent with the results of the test group of Example 2; the effluent pH value of the R2 reactor (sulfur-alkali ratio 0.8) maintained above 7.4 throughout the period, without acid accumulation, and its nitrate nitrogen removal rate could be maintained above 95% within the first 60 days of operation, but after the 60th day, due to the relative shortage of sulfur substrate, the removal rate slowly decreased and eventually stabilized at about 89%, indicating that the system processing capacity was limited by the amount of electron donor supply; the nitrate nitrogen removal rate of the R3 reactor (sulfur-alkali ratio 1.6) remained at an extremely high level of 98% throughout the monitoring period, however, due to the excessive sulfur substrate leading to a high acid production rate, the system's alkali source consumption accelerated, and its effluent pH value slowly decreased from 7.2 since the 50th day, to 6.65 by the 100th day. The comparative data of this example clearly confirms that a mass ratio of 0.8 is the lower limit to ensure the system to achieve high denitrification efficiency, and a mass ratio of 1.6 is the upper limit for the system to not prematurely shorten the effective operation life due to excessive acid production, therefore, the range of 0.8 to 1.6 is the optimized interval for achieving high-efficiency, stable and long-period operation.

[0059] It is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application.

[0060] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limiting, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the present application.

Claims

1. A sulfur autotrophic denitrification packing for nitrogen wastewater treatment, a porous composite particle comprising a sulfur substrate as an electron donor, a calcium-based carbonate as a main alkali source, and a magnesium-based oxide as a sacrificial alkali source; characterized in that, The chemical composition and the micro-physical structure of the porous composite particle are cooperatively defined as: At the chemical composition level, the apparent dissolution reaction rate of the magnesium-based oxide is higher than that of the calcium-based carbonate in a water solution with a temperature of 25 degrees Celsius and a pH value of 5.0, and the magnesium-based oxide is configured to preferentially react with the acid and release magnesium ions at the reaction interface of the calcium-based carbonate; At the micro-physical structure level, the porous composite particle has a pore structure composed of reaction chambers and throat passages connecting the reaction chambers and the outside of the particle, and the pore structure is configured to make the nitrogen gas generated by the denitrification process accumulate pressure in the reaction chamber and then be pulsed out through the throat passage and impact the mass transfer channel inside the particle; The ratio of the equivalent diameter of the throat passage to the equivalent diameter of the reaction chamber is in the range of 0.05 to 0.30; wherein the equivalent diameter of the throat passage is the diameter at the maximum cross-sectional area of the throat passage, and the equivalent diameter of the reaction chamber is the diameter of the volume-equivalent sphere of the reaction chamber; the connected porosity of the porous composite particle accounts for 20% to 45% of the total volume of the particle; The inner wall of the throat passage carries a biocompatible hydrogel precursor, which, together with the exopolymers secreted by the denitrifying microorganisms, forms a viscoelastic biological valve body in the throat passage, which undergoes viscoelastic deformation or overall displacement when the gas pressure in the reaction chamber rises.

2. The sulfur autotrophic denitrification media for nitrogen wastewater treatment according to claim 1, characterized in that, The calcium-based carbonate is calcite, and the magnesium-based oxide is light-burned magnesium oxide; the content of the magnesium-based oxide is 5 parts by weight to 35 parts by weight, based on the sum of the weights of the calcium-based carbonate and the magnesium-based oxide being 100 parts by weight; the mass ratio of the sulfur substrate to the sum of the weights of the calcium-based carbonate and the magnesium-based oxide is 0.8 to 1.

6.

3. The sulfur autotrophic denitrification media for nitrogen wastewater treatment according to claim 1, characterized in that, The magnesium-based oxide is hard-burned magnesium oxide, which undergoes a hydration exothermic reaction when in contact with wastewater, causing the local temperature of the reaction microzone inside the porous composite particle, which is bounded by the reaction chamber and the throat passage, to rise.

4. The sulfur autotrophic denitrification media for nitrogen wastewater treatment according to claim 1, characterized in that, The biocompatible hydrogel precursor is an anionic polysaccharide, which is at least distributed at the entrances of the surface layer pores of the porous composite particle and immobilizes toxic substances of a predetermined type in the wastewater through ionic chelation or chemical reaction.

5. The sulfur autotrophic denitrification media for nitrogen wastewater treatment according to claim 1, characterized in that, The pore structure composed of the reaction chamber and the throat passage is formed by removing the pore-forming agent pre-disposed in the mixture during the granulation process, and the calcium-based carbonate surface of the porous composite particle has a calcium sulfate coverage of less than 30% after 48 hours in a standard sulfate deposition test; the conditions of the standard sulfate deposition test are: placing the porous composite particle in a static solution with a pH value of 5.0 and a sulfate ion concentration of 2500 milligrams per liter at a temperature of 25 degrees Celsius.

6. The sulfur autotrophic denitrification media for nitrogen wastewater treatment according to claim 1, characterized in that, The porous composite particle is bound by an inert binder containing bentonite and is dried and shaped at a temperature below 95 degrees Celsius; the amount of inert binder is 2% to 8% of the total weight of the porous composite particle.

7. The sulfur autotrophic denitrification media for nitrogen wastewater treatment according to claim 4, characterized in that, The anionic polysaccharide is sodium alginate or sodium carboxymethyl cellulose; the biocompatible hydrogel precursor is carried on the inner wall of the throat passage and the entrances of the surface layer pores of the porous composite particle through a secondary impregnation coating process.

8. The method for preparing a sulfur-autotrophic denitrification packing for nitrogen wastewater treatment according to any one of claims 1-7, characterized in that, The method comprises the following steps: Step a, mixing sulfur substrate as electron donor, calcium carbonate as main base source, magnesium oxide as sacrificial base source, inert binder and pore former to obtain a mixture; Step b, kneading the mixture with water and making wet granules; Step c, drying the wet granules at a temperature below 95 degrees Celsius and removing the pore former by dissolution or sublimation during the drying process or in a subsequent soaking process to form a pore structure consisting of reaction chambers and throats inside the granules to obtain dry granules; Step d, secondary dip coating of the dry granules to load the inner walls of the throats and the entrances of the surface layer pores of the granules with a bioaffine hydrogel precursor.

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