A mixed nutrient denitrification filler, a preparation method and application thereof

Abstract

The application provides a mixed nutrient denitrification filler and a preparation method and application thereof, and relates to the technical field of sewage treatment. The mixed nutrient denitrification filler is composed of waste tire particles and pyrite particles, and is arranged in layers in a filter tank. The preparation method comprises the following steps: respectively weighing waste tire particles and pyrite particles according to proportions, and filling the layered filler according to a layered arrangement mode. The application is the application of the mixed nutrient denitrification filler in denitrification and phosphorus removal in sewage biochemical treatment. The mixed nutrient denitrification filler is composed of waste tire particles and pyrite particles, high-efficiency denitrification is achieved, the organic carbon and sulfur autotrophic mixed denitrification can achieve a high denitrification rate, and the microbial community abundance of the mixed nutrient denitrification filter tank is increased.

Description

[0001] Cross-references to related applications

[0002] This application claims priority and benefit to Chinese Patent Application No. 202610801921.0, filed with the China National Intellectual Property Administration on June 4, 2026, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This application relates to the field of wastewater treatment technology, and in particular to a mixed nutrient denitrification packing material, its preparation method, and its application. Background Technology

[0004] Biological denitrification can be divided into two types: autotrophic denitrification, which is carried out by autotrophic denitrifying microorganisms, and heterotrophic denitrification, which is carried out by heterotrophic denitrifying microorganisms. Mixed nutrient denitrification refers to the simultaneous occurrence of both autotrophic and heterotrophic denitrification processes during denitrification.

[0005] Traditional biological denitrification technology is one of the effective methods for removing nitrate nitrogen from water bodies, with advantages such as short start-up time, fast reaction rate, and large treatment capacity. However, it requires a sufficient organic carbon source to maintain the reaction rate. When the organic carbon source is insufficient, incomplete denitrification can easily occur, leading to NO2 emissions. - The accumulation of sludge, coupled with excessive addition, leads to secondary pollution as microorganisms cannot fully utilize the nutrients. Traditional heterotrophic denitrification processes require external carbon sources, which are limited by organic carbon sources, thus increasing sludge production and operation and maintenance costs.

[0006] In contrast, autotrophic denitrification produces less sludge, reducing the risk of filter clogging, and does not require an external organic carbon source, effectively removing nitrate nitrogen from water. Therefore, autotrophic denitrification is a more feasible option. In sulfur autotrophic denitrification, alkalinity consumption is an essential step, but the alkalinity of the influent is usually insufficient to meet the reaction requirements, leading to a decrease in pH and negatively impacting the activity of functional microorganisms. Therefore, an additional buffer system is needed to counteract the pH drop caused by alkalinity consumption. Furthermore, directly discharging the large amounts of SO4 generated by sulfur autotrophic denitrification... 2- It will also have adverse effects on the ecological environment and human health, therefore reducing alkalinity consumption and SO4 levels is important. 2- The generation of sulfur is a key factor in constructing an autotrophic denitrification filter.

[0007] Mixed nutrient denitrification is a method to reduce H+ + and SO4 2-The idea is to generate and enhance the nitrogen removal efficiency of filters. Mixed nutrient denitrification refers to the coexistence of autotrophic and heterotrophic denitrification processes within the same system, where both inorganic and organic carbon sources can serve as electron donors, and the two denitrification processes can occur simultaneously. By adding a certain amount of organic carbon source to wastewater, suitable environmental conditions for mixed nutrient denitrification can be achieved, thus realizing a win-win situation between the two denitrification processes.

[0008] Current mixed-nutrient denitrification technologies primarily utilize elemental sulfur, sulfur-based minerals, and pyrite-iron-based minerals as inorganic electron donor sources, and activated carbon and agricultural waste as organic electron donor sources to construct a mixed-nutrient system. However, existing mixed-nutrient denitrification packings suffer from an imbalance in the release rates of electron donors from different sources, leading to difficulties in efficiently and stably providing electrons and resulting in low nitrogen removal efficiency. Summary of the Invention

[0009] To address the problem of unbalanced electron donor release rates from different sources in mixed nutrient denitrification packing materials, which leads to difficulties in efficiently and stably providing electrons and low nitrogen removal efficiency, this application provides a mixed nutrient denitrification packing material, its preparation method, and its application.

[0010] In a first aspect, this application provides a mixed nutrient denitrification packing material, which is composed of waste tire particles and pyrite particles, and is arranged in layers in the filter bed.

[0011] Optionally, the raw materials include the following volumetric filling ratios: 34% to 66% waste tire pellets and 34% to 66% pyrite pellets.

[0012] Optionally, the raw materials include the following volumetric filling ratio: 60%~66% waste tire pellets and 34%~40% pyrite pellets.

[0013] Optionally, the particle size of the waste tire particles ranges from 4 to 6 mm.

[0014] Optionally, the pyrite particles have a particle size range of 1 to 3 mm.

[0015] Optionally, the layered arrangement is a two-layer arrangement, with the waste tire particles located in the lower layer and the pyrite particles located in the upper layer.

[0016] In this arrangement, water flows from bottom to top through the tire layer. The organic matter released by the tires provides electron donors for heterotrophic denitrification, rapidly removing most of the nitrates and generating alkalinity. The water then flows into the pyrite layer, where sulfur autotrophic denitrification further removes residual nitrates and consumes alkalinity, bringing the effluent pH closer to neutral. Because the waste tire particles are larger than the pyrite particles, the lower layer of tire particles creates larger pores, which facilitates uniform water distribution; the upper layer of pyrite particles creates smaller pores, acting as a filter and secondary distributor. Under appropriate empty bed flow rates, the interface between the two layers remains stable.

[0017] Optionally, the layered arrangement is a three-layer arrangement, consisting of a lower pyrite particle layer, a middle waste tire particle layer, and an upper pyrite particle layer from bottom to top, with the lower pyrite particle layer and the upper pyrite particle layer having the same amount.

[0018] In this arrangement, the lower pyrite particle layer serves as a support layer, providing a stable hydraulic distribution. It also acts as the first stage of sulfur autotrophic denitrification, releasing iron ions that combine with influent phosphate to form precipitates. The middle waste tire particle layer acts as a slow-release organic carbon source, rapidly removing most nitrates and generating alkalinity. The upper pyrite particle layer serves as the second stage of sulfur autotrophic denitrification, further removing residual nitrates and utilizing the organic matter diffusing upwards from the middle layer for mixed nutrient denitrification, while simultaneously consuming excess alkalinity. Because pyrite has a much higher density than waste tires, the lower pyrite particle layer settles stably at the bottom under gravity, while the upper pyrite particle layer covers the waste tire particle layer, sandwiching it in between. Even under upward hydraulic impact, the waste tire particles cannot float through the upper pyrite particle layer, nor can the pyrite particles sink through the tire layer, thus achieving a long-term stable stratified structure.

[0019] Secondly, this application provides a method for preparing the mixed nutrient denitrification packing material, wherein waste tire particles and pyrite particles are weighed in proportion and filled with the layered packing material in a layered arrangement.

[0020] For the two-layer arrangement, first fill the bottom of the filter pool with waste tire particles to the designed height, and then fill the top with pyrite particles to the designed height.

[0021] For the three-layer arrangement, first fill the bottom of the filter bed with pyrite particles to the lower layer design height, then fill with waste tire particles to the middle layer design height, and finally fill with pyrite particles to the upper layer design height, with the amount of pyrite particles in the lower layer being equal to that in the upper layer.

[0022] Thirdly, this application provides the application of the mixed nutrient denitrification packing material in the biological treatment of wastewater for nitrogen and phosphorus removal.

[0023] Optionally, the wastewater biochemical treatment adopts an upward flow influent method, and the empty bed retention time is 5-10 hours.

[0024] In summary, this application includes at least one of the following beneficial effects: 1. This invention uses waste tire pellets and pyrite pellets to form a mixed nutrient denitrification packing material, which is easily degraded by microorganisms and utilized by denitrifying bacteria, achieving a high-efficiency denitrification effect. The organic carbon and sulfur autotrophic mixed denitrification can achieve a high nitrogen removal efficiency, increasing the abundance of microbial community in the mixed nutrient denitrification filter. The community structure of the biological filter is complex and stable, significantly reducing or even eliminating the need for additional liquid organic carbon sources.

[0025] 2. This invention utilizes tire waste and natural materials to provide organic carbon sources and alkaline substances, achieving sustainable resource utilization, being green and environmentally friendly, and posing no harm to humans or the environment.

[0026] 3. This invention uses pyrite and tire leachate as electron donors, which can solve the problems that may occur in traditional sulfur autotrophic filters, such as acidification and excessive sulfate in the effluent. Compared with traditional denitrification filters, this invention uses mixed nutrient denitrification packing material, which has a more stable denitrification effect, produces less sulfate, and has a partial phosphorus removal effect. The effluent is more stable, with low operating costs and low transportation and storage risks. Attached Figure Description

[0027] Figure 1 The graphs show the changes in nitrate concentration in the effluent of the mixed nutrient denitrification filters of Examples 1-3 and Comparative Examples 1-2 of the present invention over time. Figure 2 The graphs show the changes in effluent phosphate concentration over time in the mixed nutrient denitrification filters of Examples 1-3 and Comparative Examples 1-2 of the present invention. Figure 3 The graphs show the changes in sulfate concentration in the effluent of the mixed nutrient denitrification filters of Examples 1-3 and Comparative Examples 1-2 over time. Figure 4 The total ion chromatogram of leachate from waste tire particles; Figure 5 for Figure 4 Mass spectra of the corresponding chromatographic peaks. Detailed Implementation

[0028] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0029] The theoretical basis for mixed-nutrient denitrification is that the alkalinity produced by heterotrophic denitrification can be utilized by autotrophic denitrification. By combining sulfur autotrophic and heterotrophic denitrification, excess organic carbon sources can be consumed as electron donors, thereby reducing SO4. 2- This reduces the amount of organic carbon source added and lowers the concentration of sulfate in the effluent.

[0030] As the most typical pollutant in black pollution, tires possess characteristics such as high strength and heat resistance, making them difficult to degrade under natural conditions. Waste tires are composed of synthetic and natural rubber, textiles, antioxidants, carbon black, metals, as well as plasticizers, zinc oxide, sulfur, and other organic and inorganic substances, giving them high recycling value. Therefore, in their research on mixed-nutrient denitrification, the inventors considered using waste tires as an organic carbon source for heterotrophic denitrification to supplement the insufficient organic carbon in the filter bed; moreover, the alkalinity generated by heterotrophic denitrification is precisely consumed by sulfur autotrophic denitrification, and the acidification caused by sulfur autotrophic denitrification is neutralized by the alkalinity generated by heterotrophic denitrification. Based on this, the technical solution of this invention was formed.

[0031] This invention provides a mixed-nutrient denitrification packing material composed of waste tire particles and pyrite particles, arranged in a stratified manner in the filter bed, with the waste tire particles in the lower layer and the pyrite particles in the upper layer. The waste tire particles act as a slow-release organic carbon source, gradually degrading under the action of microorganisms and continuously releasing small-molecule organic matter, providing electron donors for heterotrophic denitrifying bacteria. The pyrite particles act as an inorganic sulfur source, undergoing chemical and biological oxidation under the action of sulfur-oxidizing bacteria, releasing ferrous ions and low-valence sulfur, providing electron donors for autotrophic denitrifying bacteria. The simultaneous presence of both electron donors in the same system forms a dual supply pathway of organic and inorganic electrons. Furthermore, the metabolic products generated during heterotrophic denitrification, such as small-molecule organic acids, promote the dissolution and biological oxidation of pyrite, allowing the release rate of inorganic electron donors to adaptively match the supply rate of organic electron donors. This avoids the problems of insufficient supply or excessive accumulation that can easily occur with a single electron donor, thus ensuring the continuous and stable denitrification process.

[0032] Heterotrophic denitrification generates alkalinity while reducing nitrate, causing the system's pH to tend to rise. Conversely, sulfur autotrophic denitrification consumes alkalinity while oxidizing sulfides, causing the system's pH to tend to fall. When both occur simultaneously within the same packing system, the alkalinity generated by heterotrophic denitrification is precisely consumed by sulfur autotrophic denitrification, while the acidification caused by sulfur autotrophic denitrification is neutralized by the alkalinity generated by heterotrophic denitrification. This endogenous acid-base feedback balance mechanism allows the entire filter bed to automatically maintain its pH within a neutral range suitable for microbial growth, eliminating the need for additional buffers such as lime or sodium bicarbonate, and avoiding the problem of decreased microbial activity due to acidification in traditional sulfur autotrophic filters.

[0033] Ferrous ions released during the biological oxidation of pyrite can be further converted into ferric ions under micro-aerobic or anoxic conditions. These ferric ions combine with phosphate ions in wastewater to form insoluble ferric phosphate precipitates, thereby removing phosphorus from the water. Simultaneously, the ferric hydroxide colloid formed by the hydrolysis of ferric ions also has a strong phosphate adsorption capacity. The organic matter generated from the degradation of waste tire particles promotes the biological oxidation rate of pyrite, increasing the release of ferric ions, and may also form organic-iron complexes with ferric ions, further improving the phosphate removal efficiency. Therefore, the packing material of this invention possesses synergistic phosphorus removal functions while denitrifying.

[0034] The packing material of this invention employs a layered arrangement with waste tire particles at the bottom and pyrite particles at the top. The waste tire particles, with their lower density and larger particle size, serve as a support layer to achieve uniform water distribution. Simultaneously, the slowly released organic matter diffuses upwards, providing a partial carbon source for microorganisms in the upper layer. The pyrite particles, with their higher density and smaller particle size, accumulate in the upper layer to form the main reaction zone. Water flows from bottom to top, first through the tire layer and then through the pyrite layer, creating a gradient distribution of organic carbon source concentration along the water flow direction. This facilitates the spatial niche differentiation of denitrifying bacteria of different nutrient types, thereby improving overall reaction efficiency.

[0035] During long-term operation, a large number of denitrifying microorganisms gradually accumulate on the surface and in the gaps between the packing particles. These microorganisms include both heterotrophic and sulfur-autotrophic denitrifying bacteria, forming a complex mixed-nutrient microbial community. A metabolic intertrophic relationship is established between the two types of bacteria; the carbon dioxide produced by the metabolism of heterotrophic denitrifying bacteria can serve as an inorganic carbon source for the growth of autotrophic bacteria; and the intermediate products produced by the metabolism of autotrophic bacteria may also be utilized by some heterotrophic bacteria. This mixed-nutrient microbial community has stronger environmental adaptability and resistance to shock loads than a monotrophic community, thus ensuring the stable operation of the filter under fluctuating influent water quality conditions. Therefore, the packing material of this invention increases the abundance of the microbial community in the mixed-nutrient denitrification filter, and the community structure is complex and stable.

[0036] The technical solution of the present invention will be further described below through specific embodiments and comparative examples.

[0037] This invention employs a continuous flow denitrification experimental apparatus as the device for packing mixed nutrient denitrification packing material, thereby constituting a reactor for conducting continuous flow denitrification experiments. The continuous flow denitrification experimental apparatus is constructed of plexiglass (500 mm high, 80 mm inner diameter) and is sealed at the bottom. Example 1:

[0038] First, the waste tires and pyrite are pre-treated.

[0039] The pretreatment process for waste tire pellets is as follows: After removing the metal rings and textile layers from the waste tires, they are crushed using a jaw crusher and sieved through 4mm and 6mm standard sieves to obtain pellets with a particle size of 4~6mm; they are then soaked in 0.1mol / L NaOH solution for 24h to remove surface oil stains, rinsed with deionized water until neutral, and air-dried for later use.

[0040] The pretreatment process for pyrite particles is as follows: after crushing and ball milling, natural pyrite ore is sieved using 1mm and 3mm standard sieves to obtain particles with a particle size of 1~3mm; the surface oxide layer is removed by soaking in 0.5mol / L hydrochloric acid for 24h, then rinsed with deionized water until neutral, and dried under nitrogen protection for later use.

[0041] Waste tire pellets (4-6 mm in diameter) and pyrite pellets (1-3 mm in diameter) were weighed separately. A water distribution zone with a height of 10 mm was set up at the bottom of the continuous flow denitrification experimental device. The filter bed body was supported by a porous plexiglass partition above the water distribution zone. The waste tire pellets were then filled onto the plexiglass partition, and the pyrite pellets were then filled on top of the waste tire pellets to form a layered packing. The waste tire pellets accounted for 34% of the height, and the pyrite pellets accounted for 66%. Example 2:

[0042] Example 2 is basically the same as Example 1, except that the height of waste tire particles accounts for 50% and the height of pyrite particles accounts for 50%. Example 3:

[0043] Example 3 is basically the same as Example 1, except that the height of waste tire particles accounts for 66% and the height of pyrite particles accounts for 34%. Example 4:

[0044] Example 4 uses the same total amount of material as Example 1, but adopts a three-layer arrangement, from bottom to top: a lower pyrite particle layer, a middle waste tire particle layer, and an upper pyrite particle layer; the lower pyrite particle layer accounts for 33% of the height, the middle waste tire particle layer accounts for 34% of the height, and the upper pyrite particle layer accounts for 33% of the height.

[0045] Comparative Example 1: Comparative Example 1 used waste tire pellets as filler throughout.

[0046] Comparative Example 2: Comparative Example 2 used pyrite particles as filler throughout.

[0047] It should be noted that the total height of the packing in Examples 1-4 and Comparative Examples 1-2 is the same, the only difference being the type of packing and the percentage of the packing height.

[0048] The continuous-flow denitrification experimental apparatus utilizes a peristaltic pump for continuous upward water intake, and a peristaltic pump is used to pump out the effluent at the same flow rate as the intake water. Artificial water preparation uses tap water as a base, with the addition of NH4Cl, KNO3, and KH2PO4 to increase nitrate nitrogen (NO3). - The concentration of -N) was 40 mg / L, and the phosphate (PO4) concentration was... 3- The concentration of phosphorus nitrogen (P) was 10 mg / L, and the ammonia nitrogen concentration in the influent was approximately 2 mg / L. A trace element mixture (0.1% by volume) was added to meet the normal metabolic needs of the microorganisms. The trace element mixture was prepared with the following compounds in the following amounts: 1.5 mg FeSO4·7H2O, 0.5 mg ZnSO4·7H2O, 0.15 mg MnCl2·4H2O, 0.1 mg H3BO3, 0.2 mg CoCl2·6H2O, 0.2 mg CuCl2·2H2O, 0.1 mg NiCl2·6H2O, 0.24 mg Na2MoO4·2H2O, and 5 mg Na2·EDTA. Water was added to a final volume of 1000 mL, and the mixture was filtered through a 0.22 μm membrane. The empty bed residence time (EBCT) of the reactor was controlled to be 7 h.

[0049] Table 1. Volumetric filling ratio of filler particles in each embodiment and comparative example.

[0050] The reactor effluent water quality was tested, including nitrate, phosphate, and sulfate concentrations. The test results are as follows: Figure 1-3 As shown.

[0051] from Figures 1-3It can be seen that in the early stage of reactor startup, the effluent quality fluctuates to some extent because the microorganisms are in the adaptation period. As the proportion of waste tire particles gradually increases, the concentration of organic matter in the system rises, the heterotrophic denitrification ratio increases accordingly, and at the same time, it provides a more favorable symbiotic environment for the sulfur autotrophic denitrifying bacteria.

[0052] Compared to Example 1, the average nitrate nitrogen concentration, concentrated phosphate, and sulfate concentration in the effluent during the stabilization period of Example 4 all decreased. The results indicate that placing pyrite on both sides of the tire layer enhances the synergistic effect of denitrification and phosphorus removal, while simultaneously reducing sulfate production.

[0053] Regarding the phosphorus removal mechanism, since microbial assimilation contributes limitedly to phosphate removal, the decrease in phosphate concentration in the system is mainly attributed to the release of Fe during the chemical and biological oxidation of pyrite. 2+ and Fe 3+ These iron ions combine with phosphate to form FePO4 precipitate, or are removed by adsorption of Fe(OH)3 colloids. The addition of organic matter enhances the bio-oxidation process of pyrite, promotes the release of iron ions, and thus improves the phosphorus removal effect.

[0054] In mixed-nutrient denitrification systems, sulfate primarily originates from the sulfur autotrophic denitrification process of pyrite. Trace amounts of sulfur-containing organic matter (such as sulfur and sulfurization accelerators) in waste tire particles may also contribute small amounts of sulfate under microbial action. Simultaneously, the alkalinity generated by heterotrophic denitrification neutralizes the alkalinity consumed by sulfur autotrophic denitrification, maintaining the system pH within a stable range. Therefore, the packing material of this invention achieves a comprehensive effect of highly efficient nitrogen removal, synergistic phosphorus removal, and low sulfate production.

[0055] Figure 4 The total ion chromatogram of leachate from waste tire particles; Figure 5 for Figure 4 The mass spectrum corresponds to the chromatographic peaks. The leachate from waste tire particles was obtained by adding 100g of waste tire particles to every 1L of water and soaking for 48 hours. From... Figure 4-5 It can be seen that the organic matter in the leachate from waste tire particles is mainly concentrated in low molecular weight organic matter that can be utilized by organisms.

[0056] Table 2 lists the heavy metal content of potentially toxic components in the leachate from the aforementioned waste tire particles, as detected by ICP-OES. As can be seen from Table 2, the concentration of metal ions did not meet the limit standards.

[0057] Table 2. Composition of leachate after 48 hours containing 100 g / L, 4-6 mm waste tire particles.

[0058] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A mixed nutrient denitrification packing material, characterized in that, The mixed nutrient denitrification packing is composed of waste tire particles and pyrite particles, and is arranged in layers in the filter bed.

2. The mixed nutrient denitrification packing material according to claim 1, characterized in that, The raw materials include the following volumetric filling ratios: 34%~66% waste tire pellets and 34%~66% pyrite pellets.

3. The mixed nutrient denitrification packing material according to claim 1, characterized in that, The raw materials include the following volumetric filling ratio: 60%~66% waste tire pellets and 34%~40% pyrite pellets.

4. The mixed nutrient denitrification packing material according to claim 1, characterized in that, The particle size range of the waste tire particles is 4~6 mm.

5. The mixed nutrient denitrification packing material according to claim 1, characterized in that, The pyrite particles have a particle size range of 1 to 3 mm.

6. The mixed nutrient denitrification packing material according to claim 1, characterized in that, The layered arrangement consists of two layers, with the waste tire particles located in the lower layer and the pyrite particles located in the upper layer.

7. The mixed nutrient denitrification packing material according to claim 1, characterized in that, The layered arrangement consists of three layers, from bottom to top: a lower pyrite particle layer, a middle waste tire particle layer, and an upper pyrite particle layer. The amount of the lower pyrite particle layer is equal to that of the upper pyrite particle layer.

8. A method for preparing a mixed nutrient denitrification packing material according to any one of claims 1-7, characterized in that, Weigh out waste tire pellets and pyrite pellets according to the specified proportions, and fill them with layered filler material in a layered arrangement.

9. The application of the mixed nutrient denitrification packing material according to any one of claims 1-7 in the denitrification and phosphorus removal of wastewater in biological treatment.

10. The application according to claim 9, characterized in that, The wastewater biochemical treatment adopts an upward flow water inlet method, and the empty bed retention time is 5~10 h.

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