Water-phase granulation in-situ pore-forming sulfur autotrophic denitrification filter material and preparation method thereof

Abstract

The application discloses a kind of water-phase granulation in-situ pore-forming sulfur autotrophic denitrification filter materials and its preparation method, the method is placed in water-phase granulation environment after mixing sulfur-based electron donor, iron-based electron donor, carbon-based biofilm component, mineral skeleton component and binder, so that it is agglomerated to form wet-state granule soft cake;During water-phase granulation, water droplet template or gas-liquid core is formed in the interior or surface layer of wet-state granule soft cake using the difference in hydrophilicity and hydrophobicity, density, particle size and water absorption performance of each component;Subsequently, the surface layer of the granule is solidified before the interior, and the water droplet template, gas-liquid core and / or local dissolved phase escape outward along the preferential release path, thereby forming dominant flow biofilm pores in-situ on the surface of the filter material granule. When used for low carbon-nitrogen ratio wastewater treatment, the filter material can improve sulfur autotrophic denitrification mass transfer, in-pore biofilm formation, nitrogen release and iron-based synergistic phosphorus removal effect, and is beneficial to retaining part of the in-pore active biofilm after backwashing.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment materials technology, specifically to an aqueous phase granulation in-situ porous sulfur autotrophic denitrification filter material and its preparation method. Background Technology

[0002] With increasingly stringent effluent discharge requirements from wastewater treatment plants, the demand for advanced nitrogen and phosphorus removal in secondary effluent, wastewater treatment plant tailwater, and low C / N ratio wastewater is gradually increasing. For these types of water bodies, available organic carbon sources are typically insufficient. If traditional heterotrophic denitrification processes are used, external organic carbon sources such as methanol, sodium acetate, and glucose are often required. While adding external carbon sources can increase the denitrification rate, it also increases operating costs and may lead to problems such as increased effluent COD, increased difficulty in dosing control, and increased excess sludge.

[0003] Sulfur-autotrophic denitrification technology utilizes elemental sulfur, reduced sulfur, or sulfur-containing minerals as electron donors and nitrates as electron acceptors to convert nitrate nitrogen into nitrogen gas. Compared to heterotrophic denitrification, which relies on external organic carbon sources, sulfur-autotrophic denitrification has advantages such as not relying on external organic carbon sources, relatively low sludge production, and suitability for treating wastewater with low C / N ratios. Therefore, sulfur-based autotrophic denitrification materials and their applications in filters, packed beds, and biofilters have attracted considerable attention.

[0004] Existing sulfur autotrophic denitrification materials mainly include elemental sulfur particles, sulfur-limestone composites, sulfur-iron mineral composites, sulfur-biochar composites, sulfur-based porous fillers, and sulfur-loaded porous supports. Some materials buffer acidification during sulfur autotrophic denitrification by adding limestone, carbonates, or other alkaline components; some materials introduce iron-based components to participate in autotrophic denitrification or to adsorb and precipitate phosphates; and some materials improve microbial attachment conditions by using carriers such as activated carbon, biochar, zeolite, and ceramsite.

[0005] The literature "Application of Sulfur-Based Functional Materials in Advanced Wastewater Denitrification—Research Progress and Development Trends" summarizes the application of sulfur-based functional materials in advanced wastewater denitrification. This research indicates that the composition, morphology, and particle size of sulfur-based functional materials affect denitrification efficiency and filter bed operation. Fixed-bed or biofilter operation may also encounter problems such as bed clogging, biofilm aging and shedding, accumulation of denitrification gas, and backwashing recovery. The above research provides a foundation for the application of sulfur-based functional materials in advanced wastewater denitrification, but its focus is mainly on material systems, reaction mechanisms, and process adaptation. Further improvements are still needed in the technical solution of forming dominant flow biofilm pores in situ during aqueous granulation of filter media particles, and using this pore structure to improve flow guidance, biofilm formation, gas release, and biofilm retention after backwashing.

[0006] Documents CN114772723A / CN114772723B disclose a porous sulfur material for autotrophic denitrification, its preparation method, apparatus, and application. This method involves heating sulfur to form liquid sulfur, then introducing gas into the liquid sulfur to create numerous bubbles. After cooling, a porous sulfur material with a specific porosity and pore size is obtained, thus improving the adhesion conditions for autotrophic denitrifying bacteria. CN114291900A discloses sulfur autotrophic denitrification particles, their preparation method, and application. This method involves mixing sulfur autotrophic denitrifying bacteria solution, bio-sulfur, sodium thiosulfate, activated carbon, and an encapsulating agent, then dripping this mixture into a crosslinking agent solution to crosslink into spheres, obtaining immobilized sulfur autotrophic denitrification particles. CN113044974A discloses a denitrification material based on sulfur autotrophic denitrification, its preparation method and application. The scheme uses sulfur, alkalinity-providing materials, slow-release phosphorus materials and foaming agents as the main components, and improves the performance of sulfur autotrophic denitrification materials through formulation compounding and foaming pore formation.

[0007] The above-mentioned schemes can improve the mass transfer, biofilm formation, or operational performance of sulfur autotrophic denitrification materials from different perspectives, but they still have certain limitations. CN114772723A / CN114772723B mainly belong to gas blowing pore formation in molten sulfur systems, and their pore structure is closer to the foaming pore system. They do not involve using water as both the granulation medium and the pore-forming medium in the aqueous phase granulation process, nor do they disclose the formation of dominant flow biofilm pores on the surface of composite filter media particles through water droplet templates or gas-liquid nuclei. CN114291900A mainly focuses on bacterial liquid immobilization and cross-linking into spheres. It does not utilize the agglomeration, rolling, compaction, and shrinkage in the aqueous phase granulation process to form soft filter media particles, nor does it design functional pore structures that expose sulfur-based, iron-based, carbon-based, and mineral framework components on the pore walls. CN113044974A primarily relies on foaming agents to form a porous structure. It does not disclose that after the particle surface solidifies before the interior, the water droplet template, gas-liquid core, or locally dissolved phase escapes along a preferred path, thereby forming dominant flow biofilm attachment pores in the form of unilaterally open pores, blind pores, shallow concave pores, semi-through pores, or irregular concave pores on at least part of the particle surface. The aforementioned existing solutions also fail to fully utilize the influence of non-uniform particle size, non-uniform pore size, and the structure of a single dominant pore in porous particles on flow guidance, biofilm attachment, gas release, and biofilm retention after backwashing.

[0008] Patent application CN117138738A discloses a method for preparing a rapid biofilm-attached sulfur autotrophic denitrification packing material. Similarly, patent application CN120923025A discloses a novel hexagonal porous sulfur autotrophic denitrification packing material. While both methods can improve the pore structure and biofilm attachment performance of sulfur autotrophic denitrification packing materials to some extent, they still have shortcomings: CN117138738A mainly relies on the heating and melting of sulfur and rotary granulation to form the packing material, resulting in high energy consumption during the preparation process; CN120923025A mainly relies on the release of gas from components such as ammonium bicarbonate and baking soda to form a porous structure, and its pore-forming method is closer to chemical foaming or gas release pore-forming. Therefore, it is difficult to simultaneously achieve functions such as water flow guidance, stable biofilm attachment, nitrogen release, and retention of active biofilm after backwashing at the particle scale.

[0009] Literature CN118479644A discloses a method for preparing sulfur-based autotrophic denitrification packing and rapidly starting an autotrophic denitrification process, while literature CN114573103A discloses a method for preparing and applying a high-efficiency denitrification composite packing. Both methods involve the preparation of sulfur-based, iron-based, carbon-based, or mineral-based composite sulfur-based denitrification packing, which can achieve denitrification or simultaneous denitrification and phosphorus removal in wastewater with low carbon-to-nitrogen ratios to a certain extent. However, existing technologies struggle to simultaneously achieve functions such as directional flow guidance, exposure of active components on the pore wall, stable biofilm formation within the pores, nitrogen release, and retention of active biofilm after backwashing at the particle scale. Problems remain, including limited mass transfer, insufficient biofilm stability, poor gas production release, and limited recovery capacity after backwashing.

[0010] In actual operation, sulfur autotrophic denitrification filter media may also face problems such as insufficient reaction interface, limited mass transfer, biofilm aging, increased filter bed pressure difference, and poor nitrogen release. Elemental sulfur has low solubility in water; if the active components on the particle surface and inside are not sufficiently exposed, the contact efficiency between nitrate and electron donors is likely to be low. After long-term operation of the filter bed, the biofilm on the outer surface of the particles may thicken, age, or block the channels between particles; if the nitrogen produced by sulfur autotrophic denitrification cannot be discharged in time, it may also accumulate in the filter bed, causing local gas blockage, short-flow, or operational instability. For scenarios requiring simultaneous phosphorus removal, relying solely on sulfur-based materials is usually insufficient to achieve both stable denitrification and phosphorus removal.

[0011] To improve mass transfer and biofilm formation performance, existing technologies often employ methods such as loading sulfur sources onto porous carriers, foaming, mechanical drilling, regular channel molding, or composite particle granulation to prepare sulfur autotrophic denitrification packing materials. Porous structures can increase specific surface area and facilitate microbial attachment; however, common porous structures are often random micropores, honeycomb pores, or regular through-holes. These types of pore structures may present problems during filter operation, such as clogging due to excessively small pore size, insufficient biofilm stability due to overly regular pores, and limited biofilm retention after backwashing. Foamed porous materials may also suffer from decreased particle strength, uneven pore structure, or increased breakage rate after prolonged backwashing. While mechanical drilling or mold-forming can create pores, the process is relatively complex, and the coupling between the pore structure and the exposure of internal particle components, microbial attachment, and gas release is insufficient.

[0012] Furthermore, current research on sulfur-based composite filter media focuses primarily on formulation combinations of sulfur sources, iron sources, alkaline materials, carbon-based materials, or mineral carriers. During actual granulation, due to differences in hydrophilicity / phobicity, density, particle size, and water absorption properties among the sulfur-based, iron-based, carbon-based, mineral framework, and binder components, water droplet encapsulation, gas-liquid nuclei aggregation, or localized dissolution zones may form internally or on the surface as particles agglomerate, roll, compact, and shrink in water. If this process can be utilized, allowing the aqueous phase to act not only as a granulation medium but also as a pore-forming medium, it may be possible to form functional porous structures on the particle surface directly related to the preparation process.

[0013] However, existing technologies typically do not incorporate factors such as water droplet templates, gas-liquid nucleus escape, localized dissolution phase migration, and pre-solidification of particle surfaces during aqueous granulation into the design of functional pore formation mechanisms for filter media. They also fail to fully utilize the resulting single-sided open pores, blind pores, shallow concave pores, or irregular main pore structures. For filter media particle groups with inconsistent particle sizes, inconsistent pore sizes, and at least some particles possessing only one dominant pore, existing technologies generally do not systematically utilize these features as functional structures to improve flow conduction, biofilm formation, gas release, and backwash recovery performance. Therefore, it is necessary to provide a novel method for preparing autotrophic sulfur denitrification filter media. Summary of the Invention

[0014] The technical problem to be solved by this invention is to overcome the shortcomings of existing sulfur autotrophic denitrification filter media, which mostly rely on melt blowing, foaming agent pore formation, or mechanical pore formation. These shortcomings include strong randomness of pore structure, insufficient exposure of functional components on pore walls, limited particle-scale flow-guiding biofilm formation and gas release capacity, and insufficient retention of active biofilm after backwashing. This invention provides an aqueous phase granulation in-situ porous sulfur autotrophic denitrification filter media and its preparation method. By forming water droplet templates, gas-liquid nuclei, or locally migratory phases during the aqueous phase granulation process, dominant flow biofilm formation pores are formed in situ on the particle surface, thereby improving the mass transfer, biofilm formation, gas release, and synergistic phosphorus removal performance of the filter media. This can effectively solve the problems in the background technology.

[0015] To solve the above-mentioned technical problems, the present invention provides the following technical solution: an aqueous phase granulation in-situ porous sulfur self-trophic denitrification filter material and its preparation method, comprising the following steps:

[0016] Sulfur-based electron donors, iron-based electron donors, carbon-based biofilm components, mineral framework components, and binders are mixed to obtain mixed powders or wet mixtures.

[0017] The mixed powder or wet mixture is placed in an aqueous granulation environment for rolling, stirring, shearing or spraying granulation, so that the mixed powder or wet mixture agglomerates in the aqueous phase to form wet granular preforms, wherein the aqueous phase serves as both the granulation medium and the pore-forming medium.

[0018] In the aqueous granulation process, the differences in hydrophilicity, density, particle size and water absorption properties among sulfur-based electron donors, iron-based electron donors, carbon-based film-forming components, mineral framework components and binders are used to form water droplet templates or gas-liquid nuclei inside or on the surface of wet granular blanks.

[0019] During the rolling, collision, compaction and / or shrinkage of wet granular blanks, the surface of the wet granular blanks undergoes gelation, solidification, hydration or densification before the interior, so as to form a solidified zone on the surface of the particles and keep the water droplet template or gas-liquid nucleus and / or the locally dissolved phase in a migratory state.

[0020] After the solidified zone on the particle surface is formed, the water droplet template or gas-liquid nucleus and / or the local dissolution phase escape outward along a single preferential release path, thereby forming a dominant flow film attachment pore in situ on the surface of at least part of the wet particle blank. The dominant flow film attachment pore is a one-sided open hole, blind hole, shallow concave hole, semi-through hole or irregular concave hole located on one side of the particle surface, and is not a regular through hole that penetrates the entire filter material particle.

[0021] The wet granular preform that forms the main flow film attachment pores is dried, cured or cured at a temperature not exceeding 80°C, and then screened to obtain filter media particle groups.

[0022] Among the porous filter media particles in the obtained filter media particle group, more than 50% of the porous filter media particles have only one main flow biofilm pore, and the pore wall of the main flow biofilm pore is exposed with sulfur-based electron donors, iron-based electron donors, carbon-based biofilm components and / or mineral framework components.

[0023] Furthermore, the main flow biofilm pores are not formed by mechanical drilling, mold core rod hole formation, 3D printing hole formation, or integral foaming hole formation with foaming agent; the main flow biofilm pores are formed in situ by the escape of water droplet templates or gas-liquid nuclei, local dissolution phase migration, and / or particle shrinkage during aqueous granulation; the main flow biofilm pores are not a honeycomb porous structure covering the surface of filter media particles, nor are they a bubble structure formed by integral melting of sulfur-based electron donors followed by air blowing.

[0024] Furthermore, the sulfur-based electron donor includes one or more of elemental sulfur, biogenic sulfur, sulfur paste, ferrous sulfide, pyrite, and pyrrhotite;

[0025] The iron-based electron donors include one or more of the following: siderite, ferrous carbonate, zero-valent iron, iron powder, pyrite, pyrrhotite, iron oxide, and iron hydroxide.

[0026] The carbon-based biofilm component includes one or more of the following: biochar, activated carbon, graphite powder, coke powder, carbonized sludge powder, and carbon fiber.

[0027] The mineral framework components include one or more of the following: bentonite, kaolin, diatomite, zeolite, clay, silicates, cement clinker powder, and volcanic rock powder.

[0028] The binder includes one or more of the following: alginate, chitosan, starch, polyvinyl alcohol, carboxymethyl cellulose, silica sol, water glass, humate, lignin sulfonate, and bentonite slurry.

[0029] Furthermore, a water-soluble pore-forming regulator is added to the mixed powder or wet mixture;

[0030] The water-soluble pore-forming regulator includes one or more of the following: soluble salts, starch microparticles, polyvinyl alcohol microparticles, carbonate microparticles, and soluble cellulose particles.

[0031] The water-soluble pore-forming regulator is used to absorb water, swell, partially dissolve, or form a locally migratory phase during the aqueous granulation process, so as to promote the formation of the water droplet template or gas-liquid core, and / or increase the probability of the formation of the dominant flow biofilm pores.

[0032] The water-soluble pore-forming regulator is not used to cause the wet granular preform to foam as a whole to form a uniform honeycomb pore structure.

[0033] Furthermore, the mixed powder or wet mixture also contains eccentrically migratable pore-forming cores, which include one or more of the following: soluble components, water-absorbing and swelling components, alkalinity-slowing components, carbon-based roughening components, and fiber-anchoring components. During the aqueous granulation process, the eccentrically migratable pore-forming cores, due to their different density, water-absorbing and swelling properties, and / or hydrophilicity / hydrophobicity compared to the wet granular preform, shift or accumulate towards the surface of the wet granular preform along the eccentric migration direction. After the solidification zone on the particle surface is formed, the soluble components in the eccentrically migratable pore-forming cores... The components, expansion components, or locally mobile phases migrate, dissolve, or escape outward along the escape path, thereby forming the dominant flow biofilm pores in situ on one side of the filter media particle surface together with the water droplet template or gas-liquid core. The pore walls of the dominant flow biofilm pores have a functional gradient structure and an in-pore biofilm-retaining microstructure. The functional gradient structure includes a carbon-based biofilm enrichment zone, a sulfur-based denitrification reaction zone, an iron-based phosphorus removal reaction zone, and an alkalinity slow-release microzone. The in-pore biofilm-retaining microstructure includes microprotrusions or microgrooves, rough interlocking points, and / or fiber anchoring points, which are used to retain at least part of the active biofilm in the pores during backwashing.

[0034] Further, the water temperature of the aqueous granulation environment is 5-45℃, the pH is 6-9, the stirring speed is 50-800 rpm, the granulation time is 5-120 min, and the water-to-material mass ratio is 0.5:1-20:1; the granulation is one or more of the following: aqueous drum granulation, aqueous disc granulation, underwater stirring granulation, underwater shearing granulation, and underwater spray granulation; the drying temperature is 35-70℃; the curing or maintenance includes one or more of the following: natural maintenance, low-temperature hot air drying, ion crosslinking, silicate curing, alkali-activated curing, and surface coating curing.

[0035] Furthermore, in the obtained filter media particle group, filter media particles with a diameter of 2-10 mm account for more than 60% of the total mass of filter media particles, filter media particles with a diameter of less than 1 mm do not exceed 10% of the total mass of filter media particles, and filter media particles with a diameter of more than 12 mm do not exceed 15% of the total mass of filter media particles;

[0036] The pore size of the main flow biofilm pore is 0.05-5 mm;

[0037] The ratio of the pore size of the main flow biofilm pores to the equivalent particle size of the corresponding filter media particles is 0.01-0.60;

[0038] In the porous filter media particles of the aforementioned filter media particle group, more than 70% of the porous filter media particles have only one main flow biofilm attachment pore.

[0039] Furthermore, to improve the controllability of the formation of the dominant biofilm pores and the operational stability of the filter media, eccentrically migratable pore-forming cores can be added to the mixed powder or wet mixture. These eccentrically migratable pore-forming cores can be granular, agglomerated, gel-like, or multiphase composite granular structures, and include one or more of the following: soluble salts, starch, polyvinyl alcohol, soluble cellulose, carbonates, calcium carbonate, dolomite powder, hydrotalcite minerals, biochar microparticles, activated carbon microparticles, zeolite microparticles, volcanic rock microparticles, chopped carbon fibers, and / or cellulose fibers. The equivalent particle size of the eccentrically migratable pore-forming cores can be 0.05-3 mm, preferably 0.1-1.5 mm. Because the density, water absorption and swelling properties, dissolution properties, or hydrophilicity / hydrophobicity of the eccentrically migratable pore-forming cores differ from those of the wet granular preform, they can shift or accumulate towards the surface of the wet granular preform along the eccentric migration direction under the rolling, collision, compaction, and shrinkage effects during the aqueous granulation process.

[0040] Furthermore, the amount of the eccentrically migrateable pore-forming core added can be 0.5% to 15% of the dry basis mass of the mixed powder or wet mixture, preferably 1% to 8%. The eccentrically migrateable pore-forming core can be obtained by wet agglomeration, extrusion pelletizing, spheroidizing, spray granulation or sieving. The eccentrically migrateable pore-forming core can be a single-layer particle structure or a layered particle structure. When it is a layered particle structure, it can include an outer layer containing carbon-based rough components and / or fiber anchoring components, an intermediate layer containing soluble components or water-absorbing swelling components, and an inner layer containing alkalinity slow-release components and / or iron-based components. When the eccentrically migrateable pore-forming core shifts, dissolves, shrinks or escapes during aqueous granulation and subsequent drying and curing, its different components can remain, be exposed or deposited in the pore opening, middle of the pore wall, bottom of the pore or local area of ​​the pore wall of the main flow biofilm pore, thereby promoting the formation of carbon-based biofilm enrichment zone, sulfur-based denitrification reaction zone, iron-based phosphorus removal reaction zone and alkalinity slow-release micro-zone.

[0041] Furthermore, after the wet granular preform is formed, one or more of the following methods are used: ionic crosslinking, silicate curing, low-temperature pre-drying, surface coating curing, alkali-activated curing, or natural dehydration densification, to form a granular surface curing zone on the surface of the wet granular preform before the interior. At this time, the eccentrically migrateable porous core still retains at least partially the ability to absorb water, swell, soften, dissolve, shrink, or migrate. Subsequently, during drying, curing, or maintenance, the soluble components, expanding components, or locally migrateable components in the eccentrically migrateable porous core will... Escape paths are formed at locations with low resistance on the particle surface, and the phase migrates, dissolves, or escapes outward, thus interacting with the water droplet template or gas-liquid nucleus to form a dominant flow biofilm pore in situ on one side of the filter material particle surface. This dominant flow biofilm pore is not a honeycomb structure formed by the overall foaming of the foaming agent, nor is it a regular channel formed by mechanical drilling, mold core rod, or 3D printing. Instead, it is a unilateral functional pore formed during the aqueous granulation process by the combined action of an eccentrically migratable pore nucleus, water droplet template, or gas-liquid nucleus and / or a locally dissolved phase.

[0042] Furthermore, the pore walls of the main biofilm-bearing pores have a functionally graded structure; along the direction from the pore opening to the pore bottom, the pore walls may include a carbon-based biofilm enrichment zone near the pore opening, a sulfur-based denitrification reaction zone located in the middle or inner side of the pore wall, an iron-based phosphorus removal reaction zone near the pore bottom or a local area of ​​the pore wall, and alkalinity-slow-release micro-zones distributed on the pore wall or pore bottom; the carbon-based biofilm enrichment zone contains biochar, activated carbon, graphite powder, coke powder, carbonized sludge powder, and / or chopped carbon fibers, used to improve the roughness of the pore opening and pore wall and promote microbial attachment; the sulfur-based denitrification reaction zone... The system contains elemental sulfur, biogenic sulfur, sulfur paste, ferrous sulfide, pyrite, and / or pyrrhotite to provide electron donors for sulfur autotrophic denitrification; the iron-based phosphorus removal reaction zone contains siderite, ferrous carbonate, zero-valent iron, iron powder, pyrite, pyrrhotite, iron oxides, and / or iron hydroxides to adsorb, precipitate, or complex with phosphates; the alkalinity slow-release microzone contains calcium carbonate, dolomite, magnesium carbonate, hydrotalcite minerals, or basic silicate components to release alkalinity when the pH in the pores decreases, thereby buffering the acidification effect generated during the sulfur autotrophic denitrification process.

[0043] Furthermore, the pore walls of the main flow biofilm pores also have an internal biofilm-preserving microstructure; the internal biofilm-preserving microstructure includes micro-protrusions or micro-grooves, rough interlocking points and / or fiber anchoring points formed by coarse biochar particles, zeolite particles, volcanic rock particles, diatomite particles, short-cut carbon fibers, cellulose fibers and / or mineral aggregates; the internal biofilm-preserving microstructure is used to weaken the direct shearing effect of water flow or air flow on the biofilm inside the pores during the backwashing of the filter media layer, so that while the aged biofilm on the outer surface of the filter media particles is washed away, at least some of the main flow biofilm pores still retain active biofilm, thereby forming an internal biofilm-preserving enhancement zone and shortening the denitrification function recovery time after backwashing.

[0044] Through the combination of the aforementioned eccentrically movable pore cores, functional gradient structures, alkalinity-slow-release microzones, and in-pore biofilm-preserving microstructures, the dominant flow biofilm-bearing pores no longer exist merely as ordinary pores. Instead, they form a composite micro-reaction space at the particle scale, integrating functions such as water flow introduction, nitrate mass transfer, in-pore biofilm formation, sulfur autotrophic denitrification, iron-based phosphorus removal, local alkalinity buffering, nitrogen release, and biofilm preservation after backwashing. This improves the nitrogen and phosphorus removal stability of the filter media in low C / N ratio wastewater treatment, reduces the risk of gas retention and increased filter bed pressure differential, and enhances operational recovery performance after backwashing.

[0045] Furthermore, a particle group of an aqueous phase granulated in-situ porous sulfur autotrophic denitrification filter material, wherein the filter material particle group includes multiple filter material particles of different sizes.

[0046] At least some of the filter media particles of different sizes include a filter media particle body and a main flow biofilm pore formed on one side of the surface of the filter media particle body;

[0047] The filter media particles comprise sulfur-based electron donors, iron-based electron donors, carbon-based biofilm-forming components, and mineral framework components.

[0048] The main flow membrane attachment pores are single-sided openings, blind holes, shallow concave holes, semi-through holes, or irregular concave holes.

[0049] The main flow membrane pores are not regular through holes that penetrate the entire filter media particle body, nor are they honeycomb porous structures that cover the surface of the filter media particle body.

[0050] The pore walls of the main flow biofilm pores are exposed with sulfur-based electron donors, iron-based electron donors, carbon-based biofilm components and / or mineral framework components.

[0051] The equivalent particle size of filter media particles of different sizes in the filter media particle group is not completely the same, and the pore size of the main flow biofilm pores on filter media particles of different sizes is not completely the same.

[0052] Further, the equivalent particle size of the filter media particles is 1-15 mm; the pore size of the main flow biofilm pore is 0.05-5 mm; the ratio of the pore size of the main flow biofilm pore to the corresponding equivalent particle size of the filter media particles is 0.01-0.60; filter media particles with a particle size of 2-10 mm account for more than 60% of the total mass of the filter media particle group; filter media particles with a particle size of less than 1 mm account for less than 10% of the total mass of the filter media particle group; filter media particles with a particle size of more than 12 mm account for less than 15% of the total mass of the filter media particle group; and among the filter media particles having the main flow biofilm pore, more than 50% of the filter media particles have only one main flow biofilm pore.

[0053] Furthermore, a method for denitrification and phosphorus removal from wastewater using a particle group of aqueous phase granulated in-situ porous autotrophic sulfur denitrification filter media includes the following steps:

[0054] The wastewater to be treated flows through an aqueous granulation in-situ porous filter media layer filled with the filter media particle group.

[0055] The nitrate nitrogen in the wastewater to be treated enters the gaps between the filter media particles and the main flow biofilm pores, and comes into contact with the sulfur-based electron donor and the biofilm attached to the pore wall to undergo sulfur autotrophic denitrification and generate nitrogen gas.

[0056] The nitrogen gas is released through the gap between the main flow membrane pores and the filter media particles;

[0057] The phosphate in the wastewater to be treated is brought into contact with the iron-based electron donor and / or the conversion product of the iron-based electron donor to achieve synergistic phosphorus removal through adsorption, precipitation or complexation.

[0058] When the pressure difference of the filter media reaches the set value or the running time reaches the set cycle, the in-situ porous filter media layer of the aqueous phase granulation is backwashed to remove the aged biofilm on the outer surface of the filter media particles and to retain the active biofilm in at least some of the main flow biofilm pores.

[0059] Furthermore, the wastewater to be treated includes secondary effluent from wastewater treatment plants, wastewater treatment plant tailwater, low carbon-to-nitrogen ratio wastewater from industrial parks, effluent from deep treatment of rural domestic sewage, or pollution reduction water flowing into lakes and reservoirs.

[0060] The influent TN of the wastewater to be treated is 5-50 mg / L, and the influent NO3 is... - -N is 3-40 mg / L, influent TP is 0.1-5 mg / L, and influent COD is 10-100 mg / L;

[0061] The hydraulic retention time of the wastewater denitrification and phosphorus removal method is 0.5-8 h, the filtration rate is 0.5-12 m / h, the operating pH is 6.0-8.5, and the influent DO is 0-2.0 mg / L;

[0062] The backwashing cycle is 12-168 h, and the backwashing intensity is 3-20 L / (m). 2 ·s);

[0063] During operation, anoxic microzones are formed within the main flow biofilm pores, and the pore walls serve as the attachment interface for sulfur autotrophic denitrifying bacteria, sulfur-converting bacteria, and / or iron-converting bacteria.

[0064] Furthermore, a deep nitrogen and phosphorus removal system for wastewater includes: an influent unit; a sulfur autotrophic denitrification filter; an aqueous phase granulation in-situ porous filter media layer disposed within the sulfur autotrophic denitrification filter; a filter media support layer disposed below the aqueous phase granulation in-situ porous filter media layer; an effluent unit; an exhaust unit; and a backwashing unit; wherein the aqueous phase granulation in-situ porous filter media layer is filled with the filter media particle group;

[0065] The autotrophic denitrification filter tank for sulfur includes, in sequence along the water flow direction, a low oxygen consumption zone, a main denitrification zone, a synergistic phosphorus removal zone, and an effluent polishing zone.

[0066] The exhaust unit is used to exhaust nitrogen generated during sulfur autotrophic denitrification, and the main flow membrane pores are used as microchannels for nitrogen release at the particle size of the filter media.

[0067] The backwashing unit is used to input backwashing water and / or backwashing gas into the aqueous granulation in-situ porous filter media layer to flush away the aged biofilm on the outer surface of the filter media particles and to retain active biofilm in at least a portion of the main flow biofilm pores.

[0068] The system also includes an online monitoring and control unit, which is used to monitor pH, ORP, and NO3. - -N, SO4 2- Fe 2+ The system can adjust one or more parameters among TP, DO, and filter bed differential pressure, and adjust the influent flow rate, filtration rate, backwash cycle, and / or backwash intensity based on the monitoring results.

[0069] Compared with the prior art, the beneficial effects of the present invention are:

[0070] 1. This invention uses water as both the granulation medium and the pore-forming medium. During the agglomeration of sulfur-based electron donors, iron-based electron donors, carbon-based biofilm-forming components, mineral framework components, and binders in the aqueous phase, the differences in hydrophilicity / hydrophobicity, density, particle size, and water absorption properties of each component are utilized to form water droplet templates, gas-liquid nuclei, or locally migratory phases inside or on the surface of the wet particle blanks. Subsequently, by first solidifying the particle surface and allowing the migratory phase to escape outward along the preferred release path, dominant flow biofilm pores are formed in situ on the surface of the filter media particles. This method differs from methods such as molten sulfur blowing pore formation, foaming agent integral foaming pore formation, and mechanical drilling. It can form a functional pore structure coupled with the particle granulation process under milder preparation conditions, reducing the impact of high-temperature melting or post-processing pore formation on the exposure state of filter media components and the stability of particle structure.

[0071] 2. The dominant flow biofilm pores formed in this invention are located on one side of the filter media particle surface and can be manifested as single-sided open pores, blind pores, shallow concave pores, semi-through pores, or irregular concave pores, rather than regular through pores that penetrate the entire filter media particle or honeycomb pore structures that cover the particle surface; this pore structure forms relatively clear pore openings, pore walls, and locally recessed spaces at the particle scale, which is conducive to water flow entering the pores and can provide a relatively stable attachment interface for microorganisms; compared with ordinary random micropores or integral foamed pores, these dominant flow biofilm pores are more conducive to the formation of local flow guidance, biofilm formation within the pores, and gas release areas, thereby improving the mass transfer and biofilm formation conditions of the filter media during operation;

[0072] 3. Since the main flow biofilm pores are formed by the solidification of the particle surface followed by the escape of water droplet templates, gas-liquid nuclei, or local dissolution phases, the pore walls can expose sulfur-based electron donors, iron-based electron donors, carbon-based biofilm components, and / or mineral framework components. When the wastewater to be treated enters the main flow biofilm pores or flows near the pore opening, nitrate nitrogen can contact the sulfur-based electron donors and attached biofilm at the pore walls, and iron-based components and their conversion products can also undergo adsorption, precipitation, or complexation with phosphate. Therefore, this invention does not simply increase the overall porosity of the filter media, but improves the effective contact opportunities in the process of sulfur autotrophic denitrification and synergistic phosphorus removal by exposing the active components on the pore walls and constructing local reaction interfaces within the pores.

[0073] 4. In the filter media particle group obtained by the present invention, at least some of the porous filter media particles have only one main flow biofilm pore, and the pore size on particles of different sizes may not be exactly the same; this structure enables the filter media layer to form non-uniform local reaction spaces at different particle scales while maintaining particle packing stability and hydraulic channels; the flow velocity in the main flow biofilm pore is usually lower than that in the main water flow channels between particles, which is conducive to the formation of anoxic micro-zones in the pores and provides attachment sites for sulfur autotrophic denitrifying bacteria, sulfur conversion bacteria and / or iron conversion bacteria; at the same time, the nitrogen gas generated during denitrification can be released through the main flow biofilm pore and particle gaps, which helps to reduce local gas resistance and mass transfer unevenness caused by gas retention;

[0074] 5. During the backwashing process of the filter media layer, the aged biofilm on the outer surface of the particles is easily washed away by water or air flow. However, the main flow biofilm pores, due to their concave structure and pore wall shielding effect, can retain part of the active biofilm inside the pores. After backwashing, the active biofilm retained in the pores can serve as the biological basis for subsequent recovery of operation, which is beneficial to shorten the functional recovery time of the filter media layer. In summary, the present invention, through the combination of structure and process of "aqueous phase granulation in situ pore formation - single-sided main flow biofilm pores - exposure of active components on the pore wall - biofilm formation and gas release inside the pores - biofilm retention after backwashing", makes the filter media more suitable for deep denitrification and synergistic phosphorus removal treatment of wastewater with low carbon-to-nitrogen ratio. Attached Figure Description

[0075] Figure 1 This is a schematic diagram of the in-situ pore-forming process for the aqueous phase granulation of the sulfur self-trophic denitrification filter material of the present invention;

[0076] Figure 2 This is a schematic diagram of the aqueous phase granulation equipment and granulation process of the present invention;

[0077] Figure 3 This is a schematic diagram illustrating the mechanism by which the water droplet template or gas-liquid nucleus escapes to form the dominant flow membrane pores according to the present invention;

[0078] Figure 4 This is a schematic diagram of the filter media particle group with non-uniform particle size and non-uniform pore size according to the present invention.

[0079] Figure 5 This is an enlarged structural schematic diagram of a single aqueous phase granulation in-situ porous filter material particle of the present invention;

[0080] Figure 6 This is a schematic diagram of the short-range sulfur cycle micro-reaction zone within the main flow biofilm pores of the present invention;

[0081] Figure 7 This is a schematic diagram of the sulfur self-trophic denitrification filter media application system of the present invention;

[0082] Figure 8 This is a schematic diagram showing the normal operation and backwashing states of the application system of this invention;

[0083] Figure 9 This is a schematic diagram illustrating the process of forming the dominant flow biofilm pores by regulating the eccentrically migrateable pore-forming cores according to the present invention.

[0084] Figure 10 This is a schematic diagram of the functional gradient pore wall and the microstructure of the membrane retention pores in the main flow membrane pores of the present invention.

[0085] In the diagram: 1. Wet granular preform; 2. Water droplet template or gas-liquid core; 3. Particle surface solidification zone; 4. Main flow biofilm pores; 5. Filter media particle group; 6. Aqueous granulation container; 7. Stirring or rolling granulation mechanism; 8. Raw material inlet; 9. Outlet; 10. Filter media particles of different sizes; 11. Filter media particle body; 12. Pore wall; 13. Sulfur-based electron donor; 14. Iron-based electron donor; 15. Carbon-based biofilm component; 16. Mineral framework component; 17. Anoxic microzone within the pore; 18. Biofilm; 19. Functional bacteria community within the pore; 20. Inlet water unit; 21. Low oxygen consumption zone; 22. Main denitrification zone; 23. Synergistic phosphorus removal zone; 24. Effluent polishing zone; 25. Sulfur autotrophic denitrification filter, 26 Aqueous phase granulation in-situ porous filter media layer, 27 Filter media support layer, 28 Effluent unit, 29 Exhaust unit, 30 Backwashing unit, 31 Online monitoring and control unit, 32 In-pore retained active biofilm, 33 Eccentric migratory pore core, 34 Eccentric migration direction, 35 Soluble component, expanding component or locally migratory phase, 36 Escape path, 37 Carbon-based biofilm enrichment zone, 38 Sulfur-based denitrification reaction zone, 39 Iron-based phosphorus removal reaction zone, 40 Alkalinity slow-release microzone, 41 In-pore membrane retention microstructure, 42 Micro-protrusions or micro-grooves, 43 Fiber anchoring points, 44 In-pore membrane reinforcement zone. Detailed Implementation

[0086] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. The following embodiments are used to illustrate the technical solutions of the present invention, so that those skilled in the art can implement the present invention accordingly, and are not intended to limit the scope of protection of the present invention. Without departing from the technical concept of the present invention, those skilled in the art can make appropriate adjustments to the type of raw materials, the ratio, the granulation method, the solidification method and the operating parameters according to the source of raw materials, the quality of water to be treated, the scale of the filter bed and the operating conditions.

[0087] like Figure 1 As shown, the preparation process of the aqueous phase granulation in-situ porous sulfur autotrophic denitrification filter material of the present invention includes the following steps: raw material preparation, aqueous phase granulation, forming wet granular blank 1, forming water droplet template or gas-liquid core 2, surface layer first solidification, gas-liquid core or locally migratory phase escapes along the preferred path, forming the main flow film pores in situ 4, low temperature drying or solidification, and sieving to obtain filter material particle group 5.

[0088] like Figure 2 As shown, aqueous granulation can be carried out in aqueous granulation container 6; a stirring or rolling granulation mechanism 7 is provided in aqueous granulation container 6, the raw material is added through raw material inlet 8, and the granulated particles are discharged through outlet 9; the aqueous granulation method can be one or more of aqueous roller granulation, aqueous disc granulation, underwater stirring granulation, underwater shearing granulation, and underwater jet granulation; in this process, the aqueous phase is not only used to wet, disperse and agglomerate the raw material, but also serves as the medium source for forming water droplet templates or gas-liquid nuclei 2.

[0089] I. Raw Material Composition and Pretreatment

[0090] The raw materials of the filter media of the present invention include sulfur-based electron donor 13, iron-based electron donor 14, carbon-based biofilm component 15, mineral framework component 16 and binder.

[0091] The sulfur-based electron donor 13 can be selected from one or more of elemental sulfur, biological sulfur, sulfur paste, ferrous sulfide, pyrite, and pyrrhotite; the sulfur-based electron donor 13 is used to provide an electron donor for the sulfur autotrophic denitrification process.

[0092] The iron-based electron donor 14 can be selected from one or more of siderite, ferrous carbonate, zero-valent iron, iron powder, pyrite, pyrrhotite, iron oxide, and iron hydroxide. The iron-based electron donor 14 can participate in iron-related reactions, and its conversion products can adsorb, precipitate, or complex with phosphate, thereby achieving synergistic phosphorus removal.

[0093] The carbon-based biofilm component 15 can be selected from one or more of biochar, activated carbon, graphite powder, coke powder, carbonized sludge powder, and carbon fiber; the carbon-based biofilm component 15 is used to improve the roughness of the surface of the filter media particles and the pore wall 12, and improve the conditions for microbial attachment.

[0094] The mineral framework component 16 can be selected from one or more of bentonite, kaolin, diatomite, zeolite, clay, silicate, cement clinker powder, and volcanic rock powder; the mineral framework component 16 is used to improve the molding stability, erosion resistance and filter bed support performance of the filter media particles.

[0095] The binder may be selected from one or more of alginate, chitosan, starch, polyvinyl alcohol, carboxymethyl cellulose, silica sol, water glass, humate, lignin sulfonate, and bentonite slurry; the binder is used to enable the components to form wet granular blanks 1 during the aqueous granulation process and to maintain the granular morphology during subsequent curing or drying.

[0096] In one embodiment, the mixed powder or wet mixture, by dry basis mass, comprises: 10-70 parts of sulfur-based electron donor 13, 5-50 parts of iron-based electron donor 14, 1-30 parts of carbon-based biofilm-forming component 15, 5-60 parts of mineral framework component 16, and 0.5-20 parts of binder; each powder raw material can be pre-crushed and sieved, typically using 40-300 mesh powder; for cases requiring improved particle framework strength, mineral framework component 16 can employ different particle size distributions; for cases requiring improved pore wall roughness and biofilm-forming ability, carbon-based biofilm-forming component 15 can be selected from biochar or activated carbon powder with rough surfaces and well-developed pores; the mixing time of each raw material can be 5-30 minutes to ensure uniform dispersion of functional components.

[0097] To adjust the formation probability of the dominant flow biofilm pores 4, a water-soluble pore-forming agent can be added to the mixed powder or wet mixture. The water-soluble pore-forming agent can be selected from one or more of soluble salts, starch microparticles, polyvinyl alcohol microparticles, carbonate microparticles, and soluble cellulose particles. During the aqueous granulation process, the water-soluble pore-forming agent can absorb water, swell, partially dissolve, or form a locally migratory phase, thereby promoting the formation of water droplet templates or gas-liquid nuclei 2. This water-soluble pore-forming agent is not used to make the wet granular preform 1 foam as a whole to form a uniform honeycomb pore structure, but to promote the formation of the local dominant flow biofilm pores 4.

[0098] II. Aqueous phase granulation and in-situ pore formation process

[0099] The prepared mixed powder or wet mixture is added to the aqueous granulation container 6, and then rolled, stirred, sheared or sprayed into granules in the aqueous phase. The aqueous granulation environment can be controlled as follows: water temperature 5-45℃, pH 6-9, stirring speed 50-800rpm, granulation time 5-120min, water-to-material mass ratio 0.5:1-20:1; preferably, the water-to-material mass ratio is 3:1-10:1, the stirring speed is 200-500rpm, and the granulation time is 30-60min.

[0100] During the aqueous granulation process, the powder is first wetted by water and forms initial agglomerates. Subsequently, under the action of rolling, collision, shearing and compaction, it gradually forms wet granular blank 1. Due to the differences in hydrophilicity / hydrophobicity, density, particle size, wettability and water absorption of the sulfur-based electron donor 13, iron-based electron donor 14, carbon-based film-forming component 15, mineral framework component 16 and binder, local areas of the wet granular blank 1 are prone to forming water droplet embedding areas, gas-liquid entrainment areas or local dissolution areas. The above-mentioned areas are referred to as water droplet templates or gas-liquid cores 2 in this invention, and may also include local migratory phases formed by water-soluble pore-forming regulators.

[0101] In a further embodiment, to improve the formation probability and pore wall functionalization degree of the unilateral dominant flow biofilm pores 4, eccentrically migratable pore-forming cores 33 can be added to the mixed powder or wet mixture. The eccentrically migratable pore-forming cores 33 include one or more of the following: soluble components, water-absorbing and swelling components, alkalinity-slowing components, carbon-based roughening components, and fiber anchoring components. During aqueous granulation, the eccentrically migratable pore-forming cores 33, due to their different density, water-absorbing and swelling properties, and / or hydrophilicity / hydrophobicity compared to the main body of the wet granular preform 1, shift or accumulate towards the surface of the wet granular preform 1 along the eccentric migration direction 34. After the solidification zone 3 is formed on the particle surface, the eccentrically migratable cores... Soluble components, expanding components, or locally migratory phases 35 in the core 33 migrate, dissolve, or escape outward along the escape path 36, thereby forming a dominant flow biofilm pore 4 in situ on one side of the filter media particle surface together with the water droplet template or gas-liquid core 2. The pore wall 12 of the dominant flow biofilm pore 4 has a functional gradient structure and an in-pore biofilm-retaining microstructure 41. The functional gradient structure includes a carbon-based biofilm enrichment zone 37, a sulfur-based denitrification reaction zone 38, an iron-based phosphorus removal reaction zone 39, and an alkalinity slow-release microzone 40. The in-pore biofilm-retaining microstructure 41 includes microprotrusions or microgrooves 42, rough interlocking points, and / or fiber anchoring points 43, which are used to retain at least part of the active biofilm in the pores during backwashing.

[0102] In one specific embodiment, the functionally graded structure can be formed through layered loading of eccentrically migratable pore-forming cores, local migration and deposition of components of different particle sizes, stepwise feeding, or local residual effects on the pore wall. For example, sulfur-based electron donors, iron-based electron donors, mineral framework components, and binders can be first used to form wet particle blanks in an aqueous phase, and then an outer layer mixture containing carbon-based biofilm-forming components, chopped fibers, and eccentrically migratable pore-forming cores can be added, making it easier for the carbon-based biofilm-forming components and fiber anchoring components to accumulate on the particle surface or near the pore opening of the main biofilm-forming pores; alternatively, a composite pore-forming core containing soluble salts, starch, calcium carbonate, and chopped fibers can be used, allowing the soluble salts and starch to migrate, dissolve, or shrink during drying or curing, while calcium carbonate, chopped fibers, biochar microparticles, or coarse mineral particles remain at least partially on the pore wall, thereby forming alkalinity-slow-release microzones, micro-protrusions, rough intercalation points, or fiber anchoring points.

[0103] Functionally graded structures and in-pore biofilm microstructures can be confirmed through cross-sectional observation, stereomicroscopy, scanning electron microscopy, elemental surface distribution analysis, energy dispersive spectroscopy, or statistical microscopic imaging. Specifically, carbon-based biofilm enrichment zones can be confirmed by the enrichment state of carbon-based particles or fibers near the pore opening; sulfur-based denitrification reaction zones can be confirmed by the exposure state of sulfur elements or sulfur-containing mineral particles in the middle or inner side of the pore wall; iron-based phosphorus removal reaction zones can be confirmed by the exposure state of iron elements or iron-based particles in localized areas of the pore wall; alkalinity-slow-release microzones can be confirmed by the distribution state of carbonate particles, calcium-magnesium components, or basic silicate components on the pore wall or bottom; and in-pore biofilm microstructures can be confirmed by micro-protrusions, micro-grooves, rough interlocking points, or fiber anchoring points on the pore wall.

[0104] After backwashing, the retention of active biofilm in the main flow biofilm pores can be evaluated by stereomicroscopy, scanning electron microscopy, biofilm staining, ATP content determination, protein content determination, or image area statistics. Compared with the outer surface of the filter media particles, the main flow biofilm pores are more likely to retain some active biofilm after backwashing due to the concave space, pore wall shielding effect, and biofilm-preserving microstructure inside the pores, thus providing a biological attachment basis for the subsequent restoration of nitrogen and phosphorus removal functions.

[0105] like Figure 3 As shown, the process of water droplet templates or gas-liquid nuclei 2 escaping to form the dominant flow biofilm pores 4 can be divided into four stages: Stage A is the formation of wet particle blanks 1; Stage B is the formation of water droplet templates or gas-liquid nuclei 2 inside or on the surface of wet particle blanks 1; Stage C is the gelation, solidification, hydration, densification or coating solidification of the surface of wet particle blanks 1 before the interior, forming the particle surface solidification zone 3, at which time the internal water droplet templates or gas-liquid nuclei 2 still maintain a certain migration ability; Stage D is the outward escape of water droplet templates or gas-liquid nuclei 2 and / or the locally dissolved phase along the position with less resistance on the particle surface, thereby forming the dominant flow biofilm pores 4 on one side of the particle surface.

[0106] To make the surface curing process more stable, one or more of the following methods can be used: After the wet particle blank 1 is formed, it can be left to stand for 5-60 minutes; low-speed pre-drying can be used to dehydrate and densify the particle surface; ionic crosslinking can be used to form a preliminary crosslinking layer on the particle surface using binders such as alginate and chitosan; silicate curing, alkali-activated curing, or surface coating curing can be used to form a particle surface curing zone 3 first. For example, when the binder contains alginate, the wet particle blank 1 can be briefly contacted with a calcium salt solution to form a crosslinking layer on the outer layer of the particle first; when the binder contains silica sol or water glass, the particle surface can be densified first by standing, low-temperature drying, or silicate curing.

[0107] After the solidification zone 3 on the particle surface is formed, the wet particle blank 1 is dried, solidified or cured; the drying temperature is not higher than 80℃, preferably 35-70℃; the drying can be carried out in stages, for example, pre-drying at room temperature to 35℃ for 0.5-2h, and then continuing to dry at 35-70℃ for 4-24h; this method helps to avoid the overall melting and migration of the sulfur-based electron donor 13, and at the same time allows the water droplet template or gas-liquid core 2 to escape along a single preferential release path during particle shrinkage, forming the main flow film attachment hole 4.

[0108] The main flow membrane attachment holes 4 formed by the present invention are not formed by mechanical drilling, mold core rod hole formation, three-dimensional printing hole formation, or integral foaming hole formation by foaming agent, nor are they formed by gas blowing after integral melting of sulfur-based electron donor 13; the main flow membrane attachment holes 4 are usually located on one side of the surface of filter material particles, and can be single-sided open holes, blind holes, shallow concave holes, semi-through holes, or irregular concave holes, not regular through holes that penetrate the entire filter material particle body 11, nor honeycomb porous structures that are distributed throughout the surface of filter material particles.

[0109] III. Filter Media Particle Structure and Detection Methods

[0110] like Figure 4 As shown, the obtained filter media particle group 5 includes multiple filter media particles 10 with different particle sizes; at least some of the filter media particles 10 with different particle sizes include a filter media particle body 11 and a main flow biofilm pore 4 formed on one side of the surface of the filter media particle body 11; the equivalent particle size of the filter media particles 10 with different particle sizes may not be completely the same, and the pore size of the main flow biofilm pore 4 on the different filter media particles may not be completely the same.

[0111] like Figure 5 As shown, a single filter media particle includes a filter media particle body 11, pore walls 12, sulfur-based electron donors 13, iron-based electron donors 14, carbon-based biofilm-forming components 15, mineral framework components 16, and main flow biofilm-forming pores 4; it should be noted that... Figure 5 The anoxic microzones 17 and biofilm 18 shown are the state of the filter media during water treatment operation or after biofilm formation, and are not structures that must already exist when the filter media is prepared. After the filter media is prepared, the pore walls 12 of the main flow biofilm formation pores 4 are exposed with sulfur-based electron donors 13, iron-based electron donors 14, carbon-based biofilm formation components 15 and / or mineral framework components 16. During operation, biofilm 18 can gradually attach to the pore walls 12, and anoxic microzones 17 can be formed in the main flow biofilm formation pores 4.

[0112] To facilitate the confirmation of the product structure, the following testing method can be used: Randomly select no less than 100 filter media particles, observe the surface morphology of the particles under a stereomicroscope, record the number of particles with the main flow biofilm pores 4, and count the number of main flow biofilm pores 4 on each porous filter media particle; convert the pore projection area of ​​the main flow biofilm pores 4 into the equivalent circle diameter, and use it as the pore diameter of the main flow biofilm pores 4; convert the outer contour projection area of ​​the filter media particles into the equivalent circle diameter, and use it as the equivalent particle size of the filter media particles; then calculate the ratio of the pore diameter of the main flow biofilm pores 4 to the equivalent particle size of the corresponding filter media particles.

[0113] For some filter media particles, they can be cut or split along the direction of the main flow biofilm pore 4 to observe the depth of the pore, the pore wall morphology, and whether it penetrates the entire particle. If the pore opening is located on the surface of the filter media particle, the pore wall 12 extends into the filter media particle body 11, and does not form a regular through hole that penetrates the entire particle, it can be identified as a one-sided open hole, blind hole, shallow concave hole, semi-through hole, or irregular concave hole of the present invention. The exposure of sulfur-based electron donor 13, iron-based electron donor 14, carbon-based biofilm component 15, and / or mineral framework component 16 at the pore wall 12 can be confirmed by microscopic observation or elemental analysis.

[0114] In one embodiment, the equivalent particle size of the filter media particles is 1-15 mm, the pore size of the main flow biofilm pore 4 is 0.05-5 mm, and the ratio of the pore size of the main flow biofilm pore 4 to the equivalent particle size of the corresponding filter media particles is 0.01-0.60. Preferably, filter media particles with a particle size of 2-10 mm account for more than 60% of the total mass of the filter media particle group 5, filter media particles with a particle size of less than 1 mm account for less than 10%, and filter media particles with a particle size of more than 12 mm account for less than 15%. Among the filter media particles with the main flow biofilm pore 4, more than 50% of the filter media particles have only one main flow biofilm pore 4, and more preferably more than 70%.

[0115] IV. Wastewater Deep Nitrogen and Phosphorus Removal Systems and Application Methods

[0116] like Figure 7 As shown, in one application, the filter media particle group 5 can be used in a deep denitrification and phosphorus removal system for wastewater; the system may include an influent unit 20, a sulfur autotrophic denitrification filter 25, an aqueous phase granulation in-situ porous filter media layer 26 disposed in the sulfur autotrophic denitrification filter 25, a filter media support layer 27 disposed below the aqueous phase granulation in-situ porous filter media layer 26, an effluent unit 28, an exhaust unit 29, and a backwashing unit 30; wherein, the aqueous phase granulation in-situ porous filter media layer 26 is filled with the filter media particle group 5; Figure 7 The system structure shown is used to illustrate one application environment of the filter media particle group 5, and does not limit the filter media particle group 5 to be used only in this system.

[0117] In one specific operating mode, the sulfur autotrophic denitrification filter 25 can sequentially form a low-oxygen consumption zone 21, a main denitrification zone 22, a synergistic phosphorus removal zone 23, and an effluent polishing zone 24 along the water flow direction; the low-oxygen consumption zone 21 is used to reduce the influence of dissolved oxygen in the influent on the subsequent sulfur autotrophic denitrification process; the main denitrification zone 22 is used to drive the sulfur autotrophic denitrification reaction through sulfur-based electron donors 13; the synergistic phosphorus removal zone 23 is used to adsorb, precipitate, or complex phosphate through iron-based electron donors 14 and their conversion products; the effluent polishing zone 24 is used to further reduce suspended solids, residual phosphorus, residual iron, or turbidity.

[0118] Exhaust unit 29 can be used to exhaust nitrogen gas generated during sulfur autotrophic denitrification; backwash unit 30 can be used to input backwash water and / or backwash gas into the aqueous phase granulation in-situ porous filter media layer 26 to flush away the aging biofilm on the outer surface of the filter media particles; the system can also be equipped with an online monitoring and control unit 31 to monitor pH, ORP, and NO3. - -N, SO4 2- Fe 2+ The system can adjust one or more parameters among TP, DO, and filter bed differential pressure, and adjust the influent flow rate, filtration rate, backwash cycle, and / or backwash intensity based on the monitoring results.

[0119] like Figure 6 As shown, during the operation of the filter media, the NO3 in the wastewater to be treated... - -N enters the main flow biofilm-attached pore 4 or passes near the pore opening, contacting the sulfur-based electron donor 13 on the pore wall 12 and the biofilm 18 attached to the pore wall 12; the biofilm 18 may contain pore-forming functional bacteria 19, which may include one or more of sulfur autotrophic denitrifying bacteria, sulfur-converting functional bacteria, and iron-converting functional bacteria; the sulfur-based electron donor 13 can participate in S within the pore. 0 Sx 2- SO4 2- Nitrate nitrogen is converted into nitrogen gas through sulfur autotrophic denitrification, and the nitrogen gas can be released outward through the main flow membrane pores 4 and the gaps between filter media particles.

[0120] like Figure 8 As shown, under normal operating conditions, water flows through the in-situ porous filter media layer 26 formed by aqueous granulation, and nitrogen gas generated by sulfur autotrophic denitrification can be released through the main flow biofilm pores 4 and the gaps between particles. Under backwashing conditions, backwash water and / or backwash gas enter the filter media layer from the backwashing unit 30 to wash away the aged biofilm on the outer surface of the filter media particles. Due to the concave structure and pore wall shielding effect of the main flow biofilm pores 4, at least some of the main flow biofilm pores 4 can retain the active biofilm 32 inside the pores. After backwashing, the active biofilm 32 retained in the pores can serve as the biological basis for subsequent recovery of operation.

[0121] The wastewater to be treated can be secondary effluent from wastewater treatment plants, wastewater treatment plant tailwater, low C / N ratio wastewater from industrial parks, effluent from advanced treatment of rural domestic sewage, or pollution reduction water flowing into lakes and reservoirs; the influent TN can be 5-50 mg / L, and the influent NO3 can be... - -N can be 3-40 mg / L, influent TP can be 0.1-5 mg / L, and influent COD can be 10-100 mg / L; during operation, the hydraulic retention time can be 0.5-8 h, the filtration rate can be 0.5-12 m / h, the operating pH can be 6.0-8.5, and the influent DO can be 0-2.0 mg / L; the backwash cycle can be 12-168 h, and the backwash intensity can be 3-20 L / m 2 ·s.

[0122] like Figure 9 As shown, in a preferred embodiment, an eccentric, migratable pore-forming core 33 can also be introduced during the aqueous phase granulation process. Figure 9 State A in the text represents the state in which the eccentrically migrateable core 33 enters the wet granular blank 1 or is distributed inside the wet granular blank 1; Figure 9 State B in the text indicates that the eccentrically migrateable porous core 33, under the influence of rolling, collision, compaction, water absorption and expansion and hydrophilic and hydrophobic interfaces during the aqueous granulation process, shifts towards the surface of the wet granular blank 1 along the eccentric migration direction 34, while the surface of the wet granular blank 1 forms the granular surface solidification zone 3 before the interior. Figure 9 The C state in the text represents the state in which the soluble component, expanding component, or locally migratory phase 35 in the eccentrically migratory pore core 33 migrates, dissolves, or escapes outward along the escape path 36, and forms the dominant flow biofilm pore 4 in situ on one side of the filter material particle surface; through the above process, the formation probability and pore size controllability of the single-sided dominant flow biofilm pore 4 can be improved.

[0123] like Figure 10 As shown, in a preferred embodiment, the pore wall 12 of the main flow biofilm pore 4 has a functional gradient structure and an in-pore biofilm-retaining microstructure 41. The functional gradient structure may include a carbon-based biofilm enrichment zone 37 near the pore opening, a sulfur-based denitrification reaction zone 38 located in the middle or inner side of the pore wall, an iron-based phosphorus removal reaction zone 39 near the bottom of the pore or a local area of ​​the pore wall, and alkalinity-slow-release micro-regions 40 distributed on the pore wall or bottom. The carbon-based biofilm enrichment zone 37 is used to improve the roughness of the pore opening and pore wall and promote biofilm attachment. The sulfur-based denitrification reaction zone 38 is used to provide electron donors for sulfur autotrophic denitrification. The iron-based phosphorus removal reaction zone 39 is used to fix phosphate in the wastewater to be treated. The alkalinity-slow-release micro-regions 40 are used to buffer in-pore acidification. The in-pore biofilm-retaining microstructure 41 may include micro-protrusions or micro-grooves 42, rough interlocking points and / or fiber anchoring points 43, which are used to retain at least part of the active biofilm in the pore during backwashing and form an in-pore biofilm-retaining enhancement zone 44.

[0124] Example 1

[0125] This embodiment prepares an aqueous phase granulation in-situ porous sulfur autotrophic denitrification filter material with elemental sulfur, pyrite and biochar as the main functional components.

[0126] Take 40 parts of elemental sulfur powder, 20 parts of pyrite powder, 10 parts of biochar powder, 18 parts of bentonite, 10 parts of zeolite powder, and 2 parts of sodium alginate by dry basis weight. After each powder raw material is pulverized, it is passed through a 100-mesh sieve and mixed for 15 minutes to obtain a mixed powder. Among them, elemental sulfur powder serves as a sulfur-based electron donor 13, pyrite powder serves as an iron-based electron donor 14 and also has the function of sulfur-containing minerals, biochar powder serves as a carbon-based film-forming component 15, bentonite and zeolite powder serve as mineral framework components 16, and sodium alginate serves as a binder.

[0127] Add clean water to the aqueous granulation container 6, control the water temperature at 25℃ and the pH at 7.0-7.5; add the mixed powder into the aqueous granulation container 6 through the raw material inlet 8, control the water-to-material mass ratio at 5:1, the stirring speed at 300 rpm, and the granulation time at 45 min; during the granulation process, the mixed powder gradually agglomerates to form wet granular blanks 1; due to the different wettability and water absorption of elemental sulfur powder, biochar powder, pyrite powder, bentonite and sodium alginate, water droplet templates or gas-liquid cores 2 are formed inside or on the surface of some wet granular blanks 1.

[0128] After granulation, the wet granule blank 1 is taken out and placed in a 1% calcium chloride solution for 5 minutes to allow the alginate on the surface of the granules to undergo ionic cross-linking, forming a solidified zone 3 on the surface of the granules. Then, the granules are taken out to drain, left to stand at room temperature for 30 minutes, and then dried in hot air at 45°C for 12 hours, followed by natural curing for 24 hours. During the drying and shrinkage process, some water droplet templates or gas-liquid nuclei 2 escape outward along the part of the granule surface with less resistance, forming a dominant flow film attachment pore 4 on the surface of the granules.

[0129] After drying, the granules are sieved, and the granules with a diameter of 2-10 mm are retained as filter material granule group 5. The fine powder with a diameter of less than 1 mm is reused for the next batch of granulation, and the granules with a diameter of more than 12 mm are crushed and reused. The obtained filter material granules are observed under a stereomicroscope, and at least some of the filter material granules have dominant flow biofilm pores 4 in the form of unilateral open pores, shallow concave pores or irregular concave pores on their surface. When the pores are cut and observed, the pore wall 12 is a rough pore wall formed by non-cutting, and sulfur-based electron donors 13, iron-based electron donors 14, carbon-based biofilm components 15 and / or mineral framework components 16 are exposed.

[0130] Example 2

[0131] This embodiment prepares an aqueous phase granulation in-situ porous sulfur autotrophic denitrification filter material with added water-soluble pore-forming regulator.

[0132] Take 35 parts of elemental sulfur powder, 10 parts of zero-valent iron powder, 15 parts of pyrrhotite powder, 8 parts of activated carbon powder, 20 parts of kaolin, 8 parts of diatomaceous earth, 2 parts of carboxymethyl cellulose, and 2 parts of starch microparticles according to dry basis mass. After crushing and sieving, the above raw materials are mixed for 20 minutes to obtain a mixed powder. The starch microparticles are used as a water-soluble pore-forming regulator to absorb water, swell, and form a locally migratory phase during the aqueous granulation process.

[0133] The mixed powder was added to the aqueous granulation container 6, and the water temperature was controlled at 20℃, the pH at 7.0, the water-to-powder mass ratio at 8:1, the stirring speed at 400 rpm, and the granulation time at 60 min. During the granulation process, carboxymethyl cellulose improved the agglomeration of the powder, kaolin and diatomaceous earth provided skeletal support, starch microparticles formed local expansion zones in the wet granular blank 1, and the wetting difference between elemental sulfur powder and activated carbon powder and hydrophilic mineral powder further promoted the formation of water droplet templates or gas-liquid nuclei 2.

[0134] After granulation, the wet granule blank 1 is left to stand at room temperature for 20 minutes to allow the outer layer of the granules to be initially densified; then it is pre-dried at 35°C for 1 hour, then dried at 60°C for 8 hours, and naturally cured for 24 hours; during the drying process, the water droplet template or gas-liquid core 2 and the local migratory phase formed by starch microparticles migrate outward or escape, forming the main flow film pores 4 on the surface of the granules; in this embodiment, no foaming agent is used, nor is the entire granule foamed to form a uniform honeycomb pore structure.

[0135] The obtained filter media particles are screened to obtain filter media particle group 5; the main flow biofilm pores 4 are mainly blind pores, shallow concave pores or irregular concave pores, and zero-valent iron powder, pyrrhotite powder, activated carbon powder and mineral skeleton particles are exposed at pore wall 12; this filter media is suitable for the treatment of low carbon-to-nitrogen ratio wastewater that needs to take into account both nitrate nitrogen removal and phosphate removal.

[0136] Example 3

[0137] This embodiment prepares an in-situ porous sulfur autotrophic denitrification filter material using a silica sol and water glass composite bonding system.

[0138] Take 30 parts of bio-sulfur, 20 parts of siderite powder, 10 parts of carbonized sludge powder, 20 parts of volcanic rock powder, 15 parts of bentonite, 3 parts of silica sol, and 2 parts of water glass according to dry basis mass, and mix them to obtain a wet mixture. Bio-sulfur serves as a sulfur-based electron donor 13, siderite powder serves as an iron-based electron donor 14, carbonized sludge powder serves as a carbon-based biofilm component 15, volcanic rock powder and bentonite serve as mineral framework components 16, and silica sol and water glass serve as binders.

[0139] The wet mixture is added to the aqueous granulation container 6 and granulated by underwater shear granulation. The water temperature is controlled at 30℃, the pH is 8.0, the water-to-material mass ratio is 3:1, the shearing and stirring speed is 500 rpm, and the granulation time is 30 min. During the granulation process, the wet mixture is sheared, tumbled and agglomerated in the aqueous phase to form wet granular blanks 1. As the silica sol and water glass gradually condense and solidify on the outer layer of the particles, the particle surface solidification zone 3 is formed first, while the internal water droplet template or gas-liquid core 2 remains in a migratory state.

[0140] After granulation, the wet granule blank 1 is dried at 50℃ for 10 hours and then naturally cured for 48 hours. During the drying and curing process, water droplet templates or gas-liquid nuclei 2 escape along the preferential release path on one side of the particle surface to form the main flow film attachment pores 4. After sieving, particles with a particle size of 2-10 mm are retained as filter material particle group 5.

[0141] The filter media particles have good skeletal stability and are suitable for use in filter beds that require periodic backwashing. The pore walls 12 of the main flow biofilm pores 4 are exposed to one or more of biological sulfur, siderite, carbonized sludge powder and volcanic rock powder, which can provide a sulfur autotrophic denitrification reaction interface, an iron-based phosphorus removal interface and a microbial attachment interface during operation.

[0142] Example 4: Hole Structure Confirmation Method

[0143] The pore structure of the filter media particle group 5 prepared in Example 1 was confirmed. No less than 100 filter media particles were randomly selected, and the pore structure on the particle surface was observed under a stereomicroscope. The number of porous filter media particles and the number of main flow biofilm pores 4 on each porous filter media particle were recorded. For pore diameter measurement, the equivalent circle diameter obtained by converting the pore projection area of ​​the main flow biofilm pore 4 was used as the pore diameter. For particle size measurement, the equivalent circle diameter obtained by converting the outer contour projection area of ​​the particle was used as the equivalent particle size.

[0144] Several filter media particles with dominant flow biofilm attachment pores 4 are cut along the direction of the pores to observe whether the pores penetrate the entire filter media particle body 11. Upon observation, the dominant flow biofilm attachment pores 4 that meet the requirements of this invention are single-sided open pores, blind pores, shallow concave pores, semi-through pores, or irregular concave pores formed on one side of the surface of the filter media particle, and are not regular through pores that penetrate the entire filter media particle body 11, nor are they honeycomb porous structures. For particles that do not meet the requirements of particle size, pore size, or single pore structure, they can be removed, crushed, or reused during the screening and sorting process.

[0145] Through the above testing and sorting, filter media particle group 5 that meets the following structural requirements can be obtained: the equivalent particle size of the filter media particles is 1-15mm, the pore size of the main flow biofilm attachment pore 4 is 0.05-5mm, and the ratio of the pore size of the main flow biofilm attachment pore 4 to the equivalent particle size of the corresponding filter media particles is 0.01-0.60; among the filter media particles with the main flow biofilm attachment pore 4, more than 50% of the filter media particles have only one main flow biofilm attachment pore 4.

[0146] Example 5: Application of wastewater denitrification and phosphorus removal

[0147] The filter media particle group 5 prepared in Example 1 or Example 2 is filled into Figure 7 In the aqueous phase granulation in-situ porous filter media layer 26 shown, a filter media support layer 27 is set below the filter media layer; the wastewater to be treated is secondary effluent from a wastewater treatment plant or low C / N ratio tailwater, with an influent TN of 5-50 mg / L and NO3... - -N is 3-40 mg / L, TP is 0.1-5 mg / L, COD is 10-100 mg / L; during operation, the hydraulic retention time is controlled at 0.5-8h, the filtration rate is 0.5-12m / h, the operating pH is 6.0-8.5, and the influent DO is 0-2.0 mg / L.

[0148] After the wastewater enters the in-situ porous filter media layer 26, part of the water flows through the gaps between the filter media particles, while the other part flows into the main flow biofilm pores 4 or passes near the pore openings. Nitrate nitrogen comes into contact with the sulfur-based electron donors 13 on the pore wall 12 and the biofilm 18 attached to the pore wall 12, undergoing a sulfur autotrophic denitrification reaction and generating nitrogen gas. The generated nitrogen gas is released through the main flow biofilm pores 4 and the gaps between the filter media particles, and can be discharged by the exhaust unit 29. Phosphate in the wastewater to be treated comes into contact with the iron-based electron donors 14 and their conversion products, achieving synergistic phosphorus removal through adsorption, precipitation, or complexation.

[0149] In the initial stage of operation, a low-load water intake method can be used to start biofilm formation, so that the biofilm 18 gradually forms on the outer surface of the filter media particles and on the pore wall 12 of the main flow biofilm pore 4. After the biofilm stabilizes, the water intake load is gradually increased according to the water quality. During operation, anoxic micro-zones 17 can be formed in the main flow biofilm pore 4, and the pore wall 12 serves as the attachment interface for sulfur autotrophic denitrifying bacteria, sulfur conversion bacteria and / or iron conversion bacteria.

[0150] When the pressure difference of the filter media reaches the set value, or the operating time reaches the set cycle, the in-situ porous filter media layer 26 of the aqueous phase granulation is backwashed; the backwashing cycle can be 12-168 hours, and the backwashing intensity can be 3-20 L / m. 2•s; During backwashing, the aged biofilm on the outer surface of the filter media particles is washed away, and at least part of the active biofilm 32 is retained in the main flow biofilm pores 4; After backwashing, the water is re-injected and the active biofilm 32 retained in the pores can continue to serve as the attachment basis for sulfur autotrophic denitrification and synergistic phosphorus removal reactions.

[0151] Example 6: Eccentrically Migratory Porous Core-Controlled Aqueous Phase Granulation In-situ Porous Autotrophic Sulfur Denitrification Filter Material

[0152] This embodiment prepares an aqueous granulation in-situ porous sulfur autotrophic denitrification filter material with an eccentric migratable pore core 33, functionally gradient pore walls, and an internal membrane microstructure 41.

[0153] Take 35 parts of elemental sulfur powder, 15 parts of pyrite powder, 10 parts of siderite powder, 8 parts of biochar powder, 1 part of chopped carbon fiber, 15 parts of bentonite, 10 parts of zeolite powder, 3 parts of sodium alginate, and 3 parts of calcium carbonate powder according to dry basis mass, and mix them evenly to obtain the basic mixed powder. Among them, elemental sulfur powder and pyrite powder are used as sulfur-based electron donors 13, siderite powder and pyrite powder are used as iron-based electron donors 14, biochar powder and chopped carbon fiber are used as carbon-based film-forming components 15, bentonite and zeolite powder are used as mineral framework components 16, sodium alginate is used as a binder, and calcium carbonate powder is used as an alkalinity slow-release component.

[0154] Specifically, 40-60 parts by weight of starch, 20-40 parts by weight of sodium chloride, 10-30 parts by weight of calcium carbonate powder, 2-8 parts by weight of polyvinyl alcohol, and 0.2-2 parts by weight of chopped carbon fiber are mixed with an appropriate amount of water to form a wet mass. The wet mass is then extruded, granulated, spheroidized, or wet-screened to obtain granular eccentrically migrateable porous cores 33. Subsequently, the cores are pre-dried at 35-45°C for 0.5-2 hours and screened to obtain eccentrically migrateable porous cores 33 with an equivalent particle size of 0.3-1.2 mm. The amount of eccentrically migrateable porous cores 33 added is 1%-8% of the dry basis mass of the basic mixed powder. Sodium chloride and starch are used to form soluble components, expanding components, or locally migrateable phases 35 during aqueous granulation and subsequent drying. Calcium carbonate powder is used to form alkalinity-slow-release micro-regions 40, and chopped carbon fiber is used to form fiber anchoring points 43 at the pore walls 12 of the main flow film-attached pores 4.

[0155] The basic mixed powder and the eccentrically migrateable porous core 33 are added together into the aqueous granulation container 6. The water temperature is controlled at 20-30℃, the pH is controlled at 6.5-8.0, the water-to-powder mass ratio is controlled at 4:1-8:1, the stirring speed is controlled at 250-450 rpm, and the granulation time is controlled at 30-60 min. During the aqueous granulation process, the basic mixed powder gradually agglomerates to form a wet granular blank 1. Under the action of particle rolling, collision, compaction and water absorption expansion, the eccentrically migrateable porous core 33 shifts to the surface of the wet granular blank 1 along the eccentric migration direction 34, and forms an eccentrically migrateable phase together with the local water droplet template or gas-liquid core 2.

[0156] After granulation, the wet granule blank 1 is placed in a calcium chloride solution with a mass fraction of 0.5%-2% for 3-10 minutes to allow the alginate on the surface of the granules to undergo ionic cross-linking, forming a solidified zone 3 on the surface of the granules. The granules are then removed and drained, and dried at a low temperature of 35-60℃ for 8-16 hours. During the drying, shrinkage and local dissolution process, the soluble components, expanding components or locally migratory phases 35 in the eccentric migratory core 33 form an escape path 36 along the position with less resistance on the surface of the granules, and migrate or escape outward, forming a dominant flow film attachment pore 4 on one side of the filter media granule surface.

[0157] The obtained main flow biofilm pore 4 has a functional gradient structure and an internal biofilm-retaining microstructure 41 on its pore wall 12; biochar powder and chopped carbon fibers are enriched near the pore opening to form a carbon-based biofilm enrichment zone 37; elemental sulfur powder and pyrite powder are exposed in the middle of the pore wall to form a sulfur-based denitrification reaction zone 38; siderite powder and pyrite powder are exposed at the bottom of the pore or in a local area of ​​the pore wall to form an iron-based phosphorus removal reaction zone 39; calcium carbonate powder is distributed on the pore wall or at the bottom of the pore to form an alkalinity slow-release microzone 40; coarse biochar particles, zeolite particles and chopped carbon fibers form micro-protrusions or micro-grooves 42, rough interlocking points and fiber anchoring points 43 at the pore wall, constituting an internal biofilm-retaining microstructure 41.

[0158] When this filter media is used for low C / N ratio wastewater treatment, nitrate nitrogen in the wastewater enters the main flow biofilm pores 4 or flows near the pore openings, and comes into contact with the sulfur-based electron donors 13 and attached biofilm 18 at the pore wall 12, resulting in sulfur autotrophic denitrification. Phosphate comes into contact with the iron-based electron donors 14 and their conversion products at the pore wall 12, achieving synergistic phosphorus removal through adsorption, precipitation, or complexation. The alkalinity slow-release micro-zones 40 release alkalinity when the local pH in the pore decreases, thus buffering the acidification effect during the sulfur autotrophic denitrification process. The nitrogen gas generated by denitrification is released through the main flow biofilm pores 4 and the gaps between the filter media particles. During backwashing, the aged biofilm on the outer surface of the filter media particles is washed away, while the presence of micro-protrusions or micro-grooves 42, rough interlocking points, and fiber anchoring points 43 in the main flow biofilm pores 4 can form a biofilm-retaining enhancement zone 44 within the pores, retaining at least part of the active biofilm within the pores, which is beneficial for the rapid recovery of nitrogen and phosphorus removal functions after backwashing.

[0159] Based on the above embodiments, the sulfur-based electron donor 13 can be replaced by elemental sulfur with biogenic sulfur, sulfur paste, ferrous sulfide, pyrite, or pyrrhotite; the iron-based electron donor 14 can be replaced by pyrite, zero-valent iron, or siderite with ferrous carbonate, iron powder, iron oxide, or iron hydroxide; the carbon-based biofilm component 15 can be replaced by biochar or activated carbon with graphite powder, coke powder, carbonized sludge powder, or carbon fiber; the mineral framework component 16 can be replaced by bentonite, zeolite, kaolin, or diatomite with clay, silicate, cement clinker powder, or volcanic rock powder; the binder can be selected from alginate, carboxymethyl cellulose, silica sol, water glass, bentonite slurry, or a combination thereof, depending on the particle strength and curing method.

[0160] In actual implementation, the raw material ratio, granulation time, stirring speed, drying temperature and backwashing parameters can be adjusted according to the filter media strength, target pore size, treated water quality and filter operation conditions. As long as a wet particle blank 1 can be formed during the aqueous phase granulation process, and escapes through the water droplet template or gas-liquid core 2 and / or local dissolution phase, forming a dominant flow film attachment pore 4 on the surface of the filter media particles, it is an implementation method under the technical concept of this invention.

Claims

1. A method for preparing an in-situ porous sulfur-autotrophic denitrification filter material by aqueous phase granulation, characterized in that, Includes the following steps: Sulfur-based electron donor (13), iron-based electron donor (14), carbon-based biofilm component (15), mineral framework component (16) and binder are mixed to obtain mixed powder or wet mixture; The mixed powder or wet mixture is placed in an aqueous granulation environment for rolling, stirring, shearing or spraying granulation, so that the mixed powder or wet mixture agglomerates in the aqueous phase to form wet granular preforms (1), wherein the aqueous phase is used as both the granulation medium and the pore-forming medium. During the aqueous granulation process, the differences in hydrophilicity, density, particle size and water absorption properties between sulfur-based electron donors (13), iron-based electron donors (14), carbon-based film-forming components (15), mineral framework components (16) and binders are utilized to form water droplet templates or gas-liquid cores (2) inside or on the surface of the wet granular blanks (1). During the rolling, collision, compaction and / or shrinkage of the wet granular blank (1), the surface of the wet granular blank (1) undergoes gelation, solidification, hydration or densification before the interior to form a solidified zone (3) on the surface of the granules, and keeps the water droplet template or gas-liquid core (2) and / or the locally dissolved phase in a migratory state. After the solidified zone (3) on the particle surface is formed, the water droplet template or gas-liquid core (2) and / or the local dissolution phase escape outward along a single preferential release path, thereby forming a dominant flow film attachment hole (4) in situ on the surface of at least part of the wet particle blank (1). The dominant flow film attachment hole (4) is a one-sided open hole, blind hole, shallow concave hole, semi-through hole or irregular concave hole located on one side of the particle surface, and is not a regular through hole that penetrates the entire filter material particle. The wet particle blank (1) that forms the main flow film pores (4) is dried, cured or cured at a temperature not exceeding 80°C, and then screened to obtain filter material particle group (5). Among the porous filter media particles in the obtained filter media particle group (5), more than 50% of the porous filter media particles have only one main flow biofilm pore (4), and the pore wall (12) of the main flow biofilm pore (4) is exposed with sulfur-based electron donors (13), iron-based electron donors (14), carbon-based biofilm components (15) and / or mineral skeleton components (16).

2. The method for preparing an in-situ porous sulfur autotrophic denitrification filter material by aqueous phase granulation according to claim 1, characterized in that: The main flow membrane pores (4) are formed in situ by the escape of water droplet templates or gas-liquid nuclei (2), local dissolution phase migration, and / or particle shrinkage during the aqueous granulation process.

3. The method for preparing an in-situ porous sulfur autotrophic denitrification filter material by aqueous phase granulation according to claim 1, characterized in that: The sulfur-based electron donor (13) includes one or more of elemental sulfur, biological sulfur, sulfur paste, ferrous sulfide, pyrite, and pyrrhotite; The iron-based electron donor (14) includes one or more of the following: siderite, ferrous carbonate, zero-valent iron, iron powder, pyrite, pyrrhotite, iron oxide, and iron hydroxide; The carbon-based biofilm component (15) includes one or more of the following: biochar, activated carbon, graphite powder, coke powder, carbonized sludge powder, and carbon fiber. The mineral framework component (16) includes one or more of the following: bentonite, kaolin, diatomite, zeolite, clay, silicate, cement clinker powder, and volcanic rock powder; The binder includes one or more of the following: alginate, chitosan, starch, polyvinyl alcohol, carboxymethyl cellulose, silica sol, water glass, humate, lignin sulfonate, and bentonite slurry.

4. The method for preparing an in-situ porous sulfur-autotrophic denitrification filter material by aqueous phase granulation according to claim 1, characterized in that: A water-soluble pore-forming regulator is also added to the mixed powder or wet mixture; The water-soluble pore-forming regulator includes one or more of the following: soluble salts, starch microparticles, polyvinyl alcohol microparticles, carbonate microparticles, and soluble cellulose particles. The water-soluble pore-forming regulator is used to absorb water, swell, partially dissolve, or form a locally migratory phase during the aqueous granulation process to promote the formation of the water droplet template or gas-liquid core (2) and / or increase the probability of the formation of the main flow attached membrane pore (4). The water-soluble pore-forming regulator is not used to foam the wet granular preform (1) to form a uniform honeycomb pore structure.

5. The method for preparing an in-situ porous sulfur-autotrophic denitrification filter material by aqueous phase granulation according to claim 1, characterized in that: The aqueous granulation environment has a water temperature of 5-45℃, a pH of 6-9, a stirring speed of 50-800 rpm, a granulation time of 5-120 min, and a water-to-material mass ratio of 0.5:1-20:

1. The granulation is one or more of the following: aqueous drum granulation, aqueous disc granulation, underwater stirring granulation, underwater shearing granulation, and underwater spray granulation. The drying temperature is 35-70℃.

6. The method for preparing an in-situ porous sulfur autotrophic denitrification filter material by aqueous phase granulation according to claim 1, characterized in that: In the obtained filter media particle group (5), filter media particles with a particle size of 2-10 mm account for more than 60% of the total mass of filter media particles, filter media particles with a particle size of less than 1 mm do not exceed 10% of the total mass of filter media particles, and filter media particles with a particle size of more than 12 mm do not exceed 15% of the total mass of filter media particles; The diameter of the main flow membrane attachment pore (4) is 0.05-5 mm; The ratio of the pore size of the main flow membrane pore (4) to the equivalent particle size of the corresponding filter media particles is 0.01-0.60; In the porous filter media particles group (5), more than 70% of the porous filter media particles have only one main flow biofilm pore (4).

7. A particle group of an aqueous phase granulated in-situ porous sulfur autotrophic denitrification filter material, characterized in that, The particle group is a filter material particle group (5) prepared by any one of the preparation methods of claims 1-6, and the filter material particle group (5) includes a plurality of filter material particles (10) with different particle sizes. At least some of the filter media particles (10) of different sizes include a filter media particle body (11) and a main flow biofilm pore (4) formed on one side of the surface of the filter media particle body (11). The filter media particle body (11) includes a sulfur-based electron donor (13), an iron-based electron donor (14), a carbon-based biofilm component (15), and a mineral skeleton component (16). The main flow membrane attachment hole (4) is a single-sided opening hole, a blind hole, a shallow concave hole, a semi-through hole or an irregular concave hole; The main flow membrane pores (4) are not regular through holes that penetrate the entire filter material particle body (11), nor are they honeycomb porous structures that cover the surface of the filter material particle body (11). The pore wall (12) of the main flow biofilm pore (4) exposes the sulfur-based electron donor (13), iron-based electron donor (14), carbon-based biofilm component (15) and / or mineral framework component (16). The equivalent particle size of filter media particles (10) of different sizes in the filter media particle group (5) is not completely the same, and the pore size of the main flow biofilm pores (4) on the filter media particles (10) of different sizes is not completely the same.

8. The particle group of the aqueous phase granulation in-situ porous sulfur autotrophic denitrification filter material according to claim 7, characterized in that: The equivalent particle size of the filter media particles is 1-15 mm; the pore size of the main flow biofilm pore (4) is 0.05-5 mm; the ratio of the pore size of the main flow biofilm pore (4) to the equivalent particle size of the corresponding filter media particles is 0.01-0.60; filter media particles with a particle size of 2-10 mm account for more than 60% of the total mass of the filter media particle group (5); filter media particles with a particle size of less than 1 mm account for less than 10% of the total mass of the filter media particle group (5); and filter media particles with a particle size of more than 12 mm account for less than 15% of the total mass of the filter media particle group (5).

9. A method for wastewater denitrification and phosphorus removal using the particle group of the aqueous phase granulation in-situ porous sulfur autotrophic denitrification filter media as described in claim 7 or 8, characterized in that, Includes the following steps: The wastewater to be treated flows through an in-situ porous filter media layer (26) filled with the filter media particle group (5) in the aqueous phase granulation process. Nitrate nitrogen in the wastewater to be treated enters the gaps between the filter media particles and the main flow biofilm pores (4), and comes into contact with the sulfur-based electron donor (13) and the biofilm (18) attached to the pore wall (12) to undergo sulfur autotrophic denitrification and generate nitrogen gas. The nitrogen gas is released through the gap between the main flow membrane pores (4) and the filter media particles; The phosphate in the wastewater to be treated is brought into contact with the iron-based electron donor (14) and / or the conversion product of the iron-based electron donor (14) to achieve synergistic phosphorus removal through adsorption, precipitation or complexation. When the pressure difference of the filter media reaches the set value or the running time reaches the set cycle, the in-situ porous filter media layer (26) of the aqueous phase granulation is backwashed to remove the aged biofilm on the outer surface of the filter media particles and to retain the active biofilm (32) in at least part of the main flow biofilm pores (4).

10. The method for denitrification and phosphorus removal from wastewater according to claim 9, characterized in that: The wastewater to be treated includes secondary effluent from wastewater treatment plants, wastewater tailwater from wastewater treatment plants, low carbon-to-nitrogen ratio wastewater from industrial parks, deep-treated effluent from rural domestic sewage, or pollution reduction water flowing into lakes and reservoirs. The influent TN of the wastewater to be treated is 5-50 mg / L, and the influent NO3 is... - -N is 3-40 mg / L, influent TP is 0.1-5 mg / L, and influent COD is 10-100 mg / L; The hydraulic retention time of the wastewater denitrification and phosphorus removal method is 0.5-8 h, the filtration rate is 0.5-12 m / h, the operating pH is 6.0-8.5, and the influent DO is 0-2.0 mg / L; The backwashing cycle is 12-168 h, and the backwashing intensity is 3-20 L / (m). 2 ·s); During operation, an oxygen-deficient micro-region (17) is formed in the main flow biofilm pore (4), and the pore wall (12) serves as the attachment interface for sulfur autotrophic denitrifying bacteria, sulfur-converting bacteria and / or iron-converting bacteria.

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