Synchronous nitrogen and phosphorus removal sewage treatment method based on secondary calcification modified siderite coupled sulfur autotrophic denitrification

Abstract

The invention relates to a synchronous nitrogen and phosphorus removal sewage treatment method based on secondary calcification modified siderite coupled sulfur autotrophic denitrification. According to the method, active sites and buffer capacity of siderite are improved by using calcination and calcium-based modification processes, nitrate reduction is driven by sulfur autotrophic denitrifying flora, and phosphate is fixed by using a synergistic precipitation effect of iron and calcium ions. According to the system, a neutral pH environment is effectively maintained, inhibition of acidification on microbial activity is avoided, generation of intermediate products is reduced, the denitrification efficiency is remarkably improved, efficient phosphorus removal is synchronously realized, and meanwhile, a reactor with a novel structure is adopted, so that filler hardening can be effectively prevented, and a supporting effect is achieved. The sewage treatment method adopted by the invention does not need additional carbon sources or chemical agents, is high in process integration level, is suitable for treatment of decentralized sewage, industrial wastewater and eutrophic water bodies, and has the advantages of low operation cost, environmental friendliness, easiness in engineering and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sewage treatment, and particularly relates to a method for simultaneous nitrogen and phosphorus removal from sewage based on secondary calcification modified siderite coupled with sulfur autotrophic denitrification. BACKGROUND

[0002] With the acceleration of urbanization, low C / N ratio (carbon-nitrogen ratio less than 5) wastewater treatment has become a difficulty in the field of sewage treatment. Traditional heterotrophic denitrification requires additional carbon source, which is high in cost and easy to cause secondary pollution; sulfur autotrophic denitrification does not require organic carbon source, but has problems such as acidification inhibition, accumulation of sulfate and insufficient simultaneous phosphorus removal capacity. Existing mineral-based sulfur autotrophic technology (such as pyrite and limestone system) can partially remove nitrogen, but the phosphorus removal efficiency is low (generally less than 60%), and high sulfate generation and pH fluctuation limit its application.

[0003] Siderite (FeCO3) can theoretically provide electron donor, inorganic carbon source and phosphorus removal function due to its Fe 2+ and CO3 2- contents, but the specific surface area of natural siderite is low and it is easy to be passivated, resulting in insufficient phosphorus adsorption efficiency. Low-grade siderite (iron grade ≤40%) is often abandoned due to high smelting cost, and the traditional roasting process is high in energy consumption (≥300 kWh per ton of ore), and the CO2 emission increases by 15%-20%. In the existing technology, calcium-based materials (such as limestone) can adjust the pH of the denitrification system, but calcium-based materials cannot directly participate in nitrogen and phosphorus removal. In addition, the synergistic mechanism of sulfur autotrophic and iron autotrophic has not been fully explored, and the coupling mechanism of microbial metabolism and mineral action also needs to be further clarified.

[0004] Siderite has certain autotrophic denitrification and phosphorus removal potential due to its Fe(II) content, but the specific surface area of natural siderite is small and the phosphorus adsorption efficiency is low. Existing researches are mostly focused on mineral systems such as limestone and pyrite, and high-efficiency simultaneous nitrogen and phosphorus removal has not been achieved. Therefore, it has become a major trend to develop a mineral composite system that can simultaneously solve pH imbalance and enhance the ability of phosphorus and nitrogen removal for wastewater treatment.

[0005] In view of the above problems, it is urgent to develop a high-efficiency, low-cost and environment-friendly simultaneous nitrogen and phosphorus removal technology. The present application breaks through the bottleneck of the existing technology by combining calcium-based modified siderite with sulfur autotrophic denitrification system, combining material modification, microbial regulation and multi-element synergistic mechanism, and provides an innovative solution for low C / N ratio wastewater treatment.

[0006] CN107176702A discloses a sewage treatment method for strengthening sulfur autotrophic denitrification process simultaneous nitrogen and phosphorus removal, which uses pyrite, sulfur and siderite to strengthen the wastewater denitrification process and improve the effect of simultaneous nitrogen and phosphorus removal. However, the method is prone to cause effluent sulfate > 150 mg / L, phosphorus removal rate < 60%, and cannot overcome the problems of easy compaction of filler and influence on sewage treatment effect. In comparison, the present application has higher ability of simultaneous nitrogen and phosphorus removal, and solves the defects of previous methods that cannot buffer pH and the cumbersome process of adding multiple minerals. Compared with the common sulfur / limestone denitrification system using limestone to adjust pH and act as carbon source, the present application has the problem of high concentration of effluent sulfate and calcium ions. The calcium-based modified siderite sulfur autotrophic system in the present application can well overcome this problem and maintain stable pH adjustment and stable carbon source supply through siderite. SUMMARY

[0007] The present application aims to provide a calcium-based modified siderite and sulfur coupled autotrophic denitrification system and a simultaneous nitrogen and phosphorus removal sewage treatment method based on calcium-based modified siderite coupled sulfur autotrophic denitrification, which buffers pH, improves electron donor diversity and adsorption capacity, realizes simultaneous efficient nitrogen and phosphorus removal, and overcomes the problems of acidification and poor phosphorus removal ability of traditional sulfur autotrophic denitrification process.

[0008] The object of the present application is achieved at least by one of the following technical solutions.

[0009] The present application provides a simultaneous nitrogen and phosphorus removal sewage treatment method based on secondary calcification modified siderite coupled sulfur autotrophic denitrification, which uses calcium-based modified siderite, sulfur and sulfur autotrophic denitrification bacteria to strengthen wastewater denitrification, realizes the wastewater nitrogen and phosphorus removal process, and includes the following steps:

[0010] Step (1), reactor filler preparation: sulfur and calcium-based modified siderite particulate matter are taken respectively, mixed uniformly and added to a reaction container;

[0011] Step (2), adding wastewater: adding the wastewater to be treated to the reaction container in step (1);

[0012] Step (3), adding bacterial solution: adding sulfur autotrophic denitrification bacterial solution to the reaction container in step (2);

[0013] Step (4), autotrophic denitrification process: blowing protective gas into the mixed culture solution in step (3) and sealing with a cover, and performing autotrophic denitrification reaction. Sulfur is used as sulfur source and calcium-based modified siderite is used as carbon source. The combined action of calcium-based modified siderite and sulfur strengthens the sulfur autotrophic denitrification bacteria, and improves the utilization rate of the bacteria on calcium-based modified siderite.

[0014] Further, the purity of the sulfur and calcium-based modified siderite is more than 80%.

[0015] Further, the volume ratio of the sulfur and the calcium-based modified siderite is 1:1-3:1.

[0016] Further, the nitrate nitrogen concentration of the wastewater to be treated is not higher than 100 mg / L, and the phosphate concentration is not higher than 50 mg / L. If the actual wastewater has a nitrate nitrogen concentration and a phosphate concentration greater than the above concentration range, it can be diluted and then treated.

[0017] Further, the sulfur and the calcium-based modified siderite exist in the form of particulates in the denitrification process, the particle size of the sulfur is 0.5-3 mm, and the particle size of the calcium-based modified siderite is 0.5-3 mm. The reactor is provided with sulfur and calcium-based modified siderite particulates.

[0018] Further, the volume of the sulfur autotrophic denitrifying bacteria liquid accounts for 2%-15% of the volume of the wastewater.

[0019] Further, the protective gas is nitrogen or argon.

[0020] Further, the sulfur autotrophic denitrifying bacteria liquid is rich in sulfur autotrophic denitrifying bacteria sludge and has been domesticated for more than 7 days.

[0021] Further, the preparation method of the calcium-based modified siderite comprises the following steps:

[0022] (1) Selection of raw materials: natural siderite ore (FeCO3, purity ≥80%) is selected, crushed, and sieved, and particles with a particle size of 5-60 mesh are taken;

[0023] (2) Modification treatment: after the natural siderite is crushed and sieved, it is immersed in a Ca(OH)2 solution or a CaCl2 solution with a mass concentration of 1-3 mol / L, and then oscillation reaction is carried out in a shaking table with a rotation speed of 50-300 rpm for 12-24 h. After that, the soaked siderite is taken out, dried, and then calcined in a muffle furnace in an air atmosphere at 300-600°C for 1-4 h;

[0024] (3) Secondary calcification: CaCl2 solution is used for soaking treatment, and the slow-release effect of calcium is increased through two calcifications to solve the problem of too fast dissolution of traditional single-element modified calcium. Specifically, the siderite is soaked in a CaCl2 solution with a concentration of 1-3 mol / L, and then oscillation reaction is carried out in a shaking table with a rotation speed of 50-300 rpm for 12-24 h. After that, the soaked siderite is taken out, dried, and then placed in a muffle furnace to obtain calcium-based modified siderite after cooling;

[0025] As a preferred technical solution of the present application, a simultaneous nitrogen and phosphorus removal wastewater treatment method based on secondary calcification modified siderite coupled with sulfur autotrophic denitrification has the following specific steps:

[0026] (1) Material pretreatment: grind the sulfur to 5-10 mesh, dry and wait for use; re-screen the calcium-based modified siderite to ensure that the particle size is between 5-60 mesh.

[0027] (2) Reactor construction: use an organic glass column as an upflow anaerobic biological filter; use calcium-based modified siderite as biological filler and layer it in the column filter through a partition, with a porosity of 25%-50%; set a 10mm thick hollow partition on the inlet of the water hopper, which is the same diameter as the reactor, to support and facilitate filler replacement and backwashing. Add fillers in the column reactor at a volume ratio of sulfur: calcium-based modified siderite = 1:1-3:1; inoculate with an appropriate amount of sulfur autotrophic denitrifying bacteria.

[0028] (3) Inoculation of bacteria: inoculate the enriched denitrifying bacteria evenly into the reactor, with an inoculation amount of 2%-15%; monitor daily samples, and when the total nitrogen removal rate is higher than 75% for 7 consecutive days, it is considered that the domestication is complete; after the inoculation period ends, use the same medium to continuously feed water for 20 days to complete the biofilm formation.

[0029] (4) Control of operating parameters: blow protective gas into the mixed culture medium and seal it with a lid, and the reactor is operated in an oxygen-free environment (DO <0.2mg / L), with a total nitrogen concentration of 1-80mg / L, a phosphorus concentration of 0.1-20mg / L, an HRT of 4-24 hours, a temperature of 20-30℃, and a system pH of 6.0-8.5.

[0030] (5) Operation and maintenance: backwash between different operating stages to prevent internal filler from hardening; regularly sample and analyze the water quality, including NO3 - -N, NO2 - -N, NH4 + -N, TP, SO4 2- , COD and pH value and other indicators.

[0031] The above technical solution provides a water treatment method for simultaneous and efficient denitrification and phosphorus removal, which is particularly suitable for the treatment of low C / N ratio (C / N <5) wastewater, has the advantages of simple process, stable operation, high removal efficiency, and can be widely applied in the fields of sewage deep treatment, surface water remediation and groundwater pollution control.

[0032] The simultaneous denitrification and phosphorus removal sewage treatment method based on secondary calcification modified siderite coupled with sulfur autotrophic denitrification provided by the application has the following beneficial effects:

[0033] 1. A method for simultaneous nitrogen and phosphorus removal from wastewater based on secondary calcification modified siderite coupled with sulfur autotrophic denitrification, which significantly enhances the system's nitrogen removal capacity, especially under low C / N ratio wastewater treatment conditions, with a substantial improvement in denitrification efficiency compared to traditional sulfur autotrophic denitrification processes.

[0034] 2. A method for simultaneous nitrogen and phosphorus removal from wastewater based on secondary calcification modified siderite coupled with sulfur autotrophic denitrification, in which the calcium-based modified siderite simultaneously serves as a filler carrier and a phosphorus removal material, achieving efficient phosphorus removal through Fe-P and Ca-P synergistic precipitation mechanisms, solving the technical problem of ineffective phosphorus removal in traditional sulfur autotrophic denitrification systems, and avoiding the complexity of setting up additional phosphorus removal units.

[0035] 3. A method for simultaneous nitrogen and phosphorus removal from wastewater based on secondary calcification modified siderite coupled with sulfur autotrophic denitrification, which can effectively alleviate system acidification. The release of calcium ions in calcium-based modified siderite can effectively neutralize the acidic substances produced during the reaction, maintaining the system pH within the optimal growth range of sulfur autotrophic denitrification bacteria, significantly enhancing the system's pH buffering capacity, and ensuring microbial activity and long-term stable operation of the system.

[0036] 4. A method for simultaneous nitrogen and phosphorus removal from wastewater based on secondary calcification modified siderite coupled with sulfur autotrophic denitrification, which increases the specific surface area and active sites of the calcium-based modified siderite, effectively solving the problem of natural siderite surface passivation, improving the material's reaction activity and service life, and enhancing its function as an electron donor and carbon source.

[0037] 5. Reduced operating costs: No additional organic carbon source is needed, and natural mineral materials are used as key functional fillers, which are widely available and low in price, significantly reducing system operating costs and improving economic feasibility.

[0038] 6. Reduced accumulation of intermediate products: Optimized system design and operating parameter control effectively inhibit the accumulation of harmful intermediate products such as nitrite, improving the safety and stability of the treated water.

[0039] 7. Strong adaptability: The system can be operated stably within a wide range of hydraulic retention times, and has strong adaptability to fluctuations in water quality, especially suitable for treating low C / N ratio wastewater and phosphorus-containing wastewater.

[0040] 8. High process integration: The nitrogen and phosphorus removal functions are integrated into a single reactor, simplifying the process flow, reducing land area and equipment investment, and facilitating practical engineering application and promotion.

[0041] 9. Environmentally friendly: uses green and sustainable materials, avoids using chemical agents for phosphorus removal, reduces the risk of secondary pollution, and meets environmental protection requirements.

[0042] 10. Microbial ecology optimization: calcium-based modified siderite provides a more suitable microenvironment for sulfur autotrophic denitrifying bacteria, promoting the enrichment and stability of functional bacterial flora, and enhancing the microbial ecological stability of the system.

[0043] 11. Low sludge yield: as an autotrophic biological treatment process, the sludge yield of the system is significantly lower than that of traditional heterotrophic denitrification processes, reducing the cost of residual sludge treatment.

[0044] 12. Strong impact load resistance: the reactor has a novel structure, and through the layered packing design and the high buffering effect of calcium-based modified siderite, the system's resistance to water quality and quantity fluctuations is significantly enhanced, maintaining stable treatment effect.

[0045] 13. Wide application range: this method is not only suitable for advanced treatment of tail water in municipal wastewater treatment plants, but also can be applied to the treatment of various nitrogen and phosphorus-containing wastewater such as groundwater, mine acid wastewater, and agricultural non-point source pollution, with broad application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 The design schematic of the reactor for the invention based on secondary calcium-modified siderite coupled with sulfur autotrophic denitrification for simultaneous nitrogen and phosphorus removal from wastewater.

[0047] Figure 2 The denitrification and phosphorus removal efficiency analysis graph of the invention under different sulfur and siderite ratios. (a) is the change of total nitrogen concentration under different sulfur and siderite ratios, (b) is the change of total phosphorus concentration under different sulfur and siderite ratios, and (c) is the change of COD and sulfate concentration under different sulfur and siderite ratios.

[0048] Figure 3 The running effect comparison graph of the invention under different HRTs in actual reactors and compared with other existing processes for 90 days of continuous operation, named sulfur autotrophic denitrification (SAD), siderite sulfur autotrophic denitrification (SSAD), and calcium-based modified siderite sulfur autotrophic denitrification (SCAD). (a) is the change of nitrate nitrogen concentration in the influent and effluent of SAD / SSAD / SCAD continuous operation, (b) is the change of total phosphorus concentration in the influent and effluent of SAD / SSAD / SCAD continuous operation, (c) is the change of sulfate concentration in the influent and effluent of SAD / SSAD / SCAD continuous operation, and (d) is the change of pH value in the influent and effluent of SAD / SSAD / SCAD continuous operation.

[0049] Figure 4XPS full scan (a) and XRD pattern (b) of Siderite, Siderite-Ca used in the continuous operation of the present application in actual reactor and existing Siderite sulfur autotrophic reactor for 90 days at different HRT.

[0050] Figure 5 The reactor structure used in the embodiments of the present application. DETAILED DESCRIPTION

[0051] The specific embodiments of the present application are further described below. It should be noted that the description of the embodiments is intended to help understand the present application, but does not constitute a limitation on the present application. In addition, the technical features involved in each of the embodiments of the present application described below can be combined with each other as long as they do not conflict with each other. Any technology implemented based on the above description of the present application falls within the scope of the present application, and the following examples are completed using conventional prior art unless otherwise specified; the raw materials and devices used are conventional commercially available products unless otherwise specified.

[0052] Figure 1 The design schematic of the reactor for simultaneous nitrogen and phosphorus removal of sewage treatment based on secondary calcification modified siderite coupled with sulfur autotrophic denitrification of the present application. An upflow anaerobic biological filter is used, which contains sulfur autotrophic denitrifying bacteria liquid, which is rich in sulfur autotrophic denitrifying bacteria sludge, and the filter material in the reactor is mixed and uniform sulfur and calcium-based modified siderite particles. A hollow partition with a thickness of 10 mm or more is provided at the top of the water inlet hopper, which has the same diameter as the reactor, which serves as a support and facilitates the replacement and backwashing of the mineral filler. Backwashing is performed at each stage to prevent the internal filler from being hardened.

[0053] Example 1

[0054] (1) The natural siderite was crushed and sieved, and the particles with a particle size of 0.5 mm were selected. 20 g of dry siderite was immersed in 100 mL of 0.5 mol / L Ca(OH)2 solution, and oscillated at 25°C and 150 rpm for 24 hours. After filtration and drying, the dried siderite was placed in a muffle furnace and calcined at 450°C in air for 4 hours, and then cooled to obtain calcium-based modified siderite.

[0055] (2) The calcium-based modified siderite (SID) was placed in a bottle, 100 mL of wastewater was added, and 10 mL of 4.12 g VSS / L acclimated sludge was inoculated in each bottle. The water quality was NO3 --N 60mg / L, TP 5mg / L, COD 100mg / L, pH 7.0±0.2. The experiment used sulfur and SID particles with a particle size of 0.5mm. Four different sulfur / calcium-modified siderite addition ratios (volume ratio) were set up: 4mL sulfur; 4mL calcium-modified siderite; 2mL each of sulfur and calcium-modified siderite; and 3mL sulfur and 1mL calcium-modified siderite. These four groups were treated with S... 0 SID, S 0 SID = 1:1, S 0 SID = 3:1 indicates.

[0056] This embodiment compares different sulfur (S) 0 The operational effects of varying the dosage ratio of calcium-modified siderite (SID) to sulfur autotrophic denitrification technology were verified, demonstrating the synergistic effect of SID coupled with calcium-modified siderite in the treatment of low C / N ratio wastewater. Figure 2 As shown, in the system where only sulfur is added (S 0 Group), nitrate (NO3) - The removal rate of NO3- (NO3-N) reached 98%, but the removal rate of nitrite (NO2) was still low. - Within 2-3 days, nitrates significantly accumulated to 6 mg / L, requiring additional reaction time to eliminate intermediate products. In contrast, the system with only calcium-modified siderite (SID group), lacking a sulfur source, achieved only a 65% nitrate removal rate, with nitrite continuously accumulating to 8 mg / L, indicating that a single material cannot achieve efficient denitrification. In comparison, the synergistic addition of sulfur and calcium-modified siderite significantly improved pollutant removal efficiency: the sulfur:siderite = 3:1 group achieved complete nitrate removal (100%) within 5 days, with a peak nitrite level of only 1.8 mg / L and a COD removal rate of 85%; the sulfur:calcium-modified siderite = 1:1 group achieved simultaneous nitrogen and phosphorus removal, with a nitrate removal rate of 98%, a total phosphorus (TP) removal rate of 95%, ammonia nitrogen concentration stable below 0.8 mg / L, and pH maintained between 6.8 and 7.2, avoiding the acidification problem of traditional sulfur autotrophic systems.

[0057] Regarding phosphorus removal efficiency, only calcium-modified siderite addition (SID group) depends on Fe. 2+ It combines with phosphate to form a precipitate, and TP drops to 0.1 mg / L within 1 day (removal rate 99%), but its denitrification capacity is insufficient; while when sulfur and calcium-modified siderite are added together, the sulfur:calcium-modified siderite ratio of 1:1 group releases Ca through the calcium-modified siderite. 2+ Further formation of hydroxyapatite (Ca 10(PO4)6(OH)2), the TP removal rate was stable at 95% in 5 days, and no secondary dissolution occurred. The TP removal rate of the sulfur: calcium-based modified siderite = 3:1 group was slightly lower, at 76%. The synergistic effect of sulfur and calcium-based modified siderite significantly reduced the risk of by-products: the amount of sulfate generated in the sulfur: calcium-based modified siderite = 3:1 group (320 mg / L) was reduced by 25% compared to the single sulfur group (430 mg / L), and the system stability was significantly improved.

[0058] Overall, under the condition of considering nitrogen and phosphorus removal simultaneously, S 0 The addition of SID is indispensable, and the two achieve simultaneous nitrogen and phosphorus removal by denitrification, S 0 The SID = 3:1 group performed best in terms of nitrate removal, while the S 0 The SID = 1:1 group had an advantage in terms of balanced removal of nitrogen and phosphorus. And in the S 0 At the dosage of SID = 3:1, the regulation of heterotrophic denitrification is achieved simultaneously, and the removal of COD in low C / N ratio wastewater can achieve efficient and synergistic removal of carbon, nitrogen, and phosphorus pollutants. By adjusting the dosage ratio of sulfur and calcium-based modified siderite (preferably 1:1 or 3:1), the technology can simultaneously achieve a nitrate removal rate of >98%, a total phosphorus removal rate of >95%, and a COD removal rate of >85% in 5 days, with self-buffering of pH (6.8-7.5) and nitrite accumulation of less than 2.5 mg / L, without the need for external carbon source or chemical agents, providing an efficient, economical, and stable solution for low C / N ratio wastewater.

[0059] Example 2

[0060] (1) After crushing the natural siderite, sieve the particles with a particle size of about 0.5, 1, and 3 mm, immerse them in 100 mL of 0.5 mol / L Ca(OH)2 solution, oscillate at 25°C and 100 rpm for 24 hours, filter and dry, and then place them in a muffle furnace for calcination at 500°C in an air atmosphere for 4 hours. After cooling, calcium-based modified siderite is obtained.

[0061] (2) Reactor design: organic glass column (diameter 10 cm, height 55 cm), layered filling of fillers (upper layer 0.5 mm, middle layer 1 mm, lower layer 3 mm calcium-based modified siderite), each layer filled with a porosity of 40%;

[0062] (4) Set up three reactor systems for comparison of nitrogen and phosphorus removal efficiency: named as simple sulfur autotrophic denitrification system (SAD), siderite sulfur autotrophic denitrification system (SSAD), and calcium-based modified siderite sulfur autotrophic denitrification system (SCAD), respectively.

[0063] (5) Addition ratio: Set SSAD, and in the SCAD system, the volume ratio of siderite, calcium-modified siderite and sulfur is 3:1, and the filling height is 45cm; in the SAD system, add the same volume of sulfur, but do not add siderite.

[0064] (6) Inoculate with sulfur autotrophic bacterial solution (Thiobacillus 65% and Sulfurimonas 18%), with the bacterial solution accounting for 10% of the total volume.

[0065] (7) Reactor Operation: SAD, SSAD, and SCAD each use peristaltic pumps to draw wastewater from the same reservoir for treatment. The reactors have continuous inflow and outflow, and the reaction cycle is set to 30 days. Effluent quality, including NO3, is sampled and analyzed daily at set times. - -N, NO2 - -N, NH4 + -N, TP, SO4 2- Indicators such as COD and pH value. Operating conditions: The influent water quality is shown in Table 1 below.

[0066] Table 1. Composition of Influent Water Quality

[0067]

[0068] like Figure 3 As shown, the SCAD system achieved a total nitrogen removal rate of up to 93.4% (HRT = 24h), significantly better than SAD (83.5%) and SSAD (87%). Even with the HRT shortened to 16h, SCAD maintained a total nitrogen removal rate of 86%, while SAD and SSAD decreased to 77% and 81.9%, respectively. Nitrite (NO2) - The phosphorus accumulation was lowest in SCAD (1.715±0.471 mg / L at HRT=4h), a reduction of 24%-25% compared to SAD (2.257 mg / L) and SSAD (2.296 mg / L). The SCAD system achieved a total phosphorus removal rate of up to 98.8% (HRT=24h), with an effluent TP concentration below 0.2 mg / L; even at HRT=4h, it maintained 81.5%, far exceeding SAD (20.3%) and SSAD (42.3%). Calcium-modified siderite achieves efficient phosphorus fixation through the reaction of Ca, Fe, and phosphate to form a precipitate. Even with HRT shortened to 16h, the TP removal rate of SCAD remained stable at 81.5%, while SSAD and SAD were only 42.3% and 20.3%, respectively. No secondary phosphorus leaching occurred during long-term operation (90 days), indicating that the chemical stability of calcium-phosphorus precipitation is significantly better than that of traditional iron-based adsorption.

[0069] The optimal environment SCAD system realizes double regulation through the synergistic effect of calcium-based modified siderite and sulfur. Among them, sulfur, as the core electron donor of sulfur autotrophic denitrifying bacteria, drives the denitrification metabolic process; and the continuous dissolution of CaCO3 in calcium-based modified siderite (CaCO3+2H + →Ca 2+ +CO2+H2O) releases HCO3 - specifically neutralizes H + produced by sulfur oxidation to form a pH buffer coupling mechanism. The synergistic effect of the two stabilizes the system pH at 6.84-7.46, while building a complete metabolic chain of continuous supply of electron donors and immediate neutralization of acidic by-products, significantly improving the biological activity compared with the single modified siderite system, and realizing the dynamic balance of the metabolic microenvironment of the sulfur autotrophic bacteria group.

[0070] In comparison, the pH of the SAD system drops to 6.32 (close to the lower limit of tolerance of the bacteria group) at HRT=4h, and the pH of the SSAD system is only maintained at 6.45 due to the limited dissolution of siderite (FeCO3). In addition, the sulfate production of SCAD (106±25.9mg / L at HRT=4h) is more stable than that of SAD (72.6mg / L) and SSAD (99.1mg / L), with a reduction of 30%-40% in fluctuation range, indicating that calcium-based materials promote the complete oxidation of sulfur (S 0 →SO4 2- ), reducing the accumulation of intermediate products such as S2O3 2- , SO3 2- , etc.

[0071] The present application verifies the significant advantages of the calcium-based secondary modified siderite coupled with the sulfur autotrophic denitrification system through examples: through the multi-dimensional synergistic effect of Ca 2+ and Fe 2+ with sulfur (S 0 electron supply / Ca 2+ -Fe 2+ chemical regulation), simultaneous realization of efficient denitrification (total nitrogen removal rate >93%), deep phosphorus removal (TP removal rate >98%), pH self-buffering (6.8-7.5), and sulfur metabolic stability, suitable for efficient treatment of low C / N ratio wastewater, meeting the requirements of the first level A standard of the “Urban Wastewater Treatment Plant Pollutant Discharge Standard”.

[0072] Example 3

[0073] On the basis of Example 2, after the end of the operation stage, the SSAD (siderite) and SCAD filler (siderite-Ca) were collected for XRD and XPS analysis to explore the composition and composition change of the filler.

[0074] As Figure 4As shown in (a), XPS full-spectrum analysis reveals a high peak value in Siderite-Ca near a binding energy of 347 eV, proving that Ca... 2+ Successful doping of Fe. The Fe 2p peak decreased compared to Siderite, indicating that Fe in SCAD... 2+ The increased solubility of Fe indicates that 2+ Participated in PO4 3- -P precipitation reaction. And in the XRD pattern ( Figure 4 (b) Compared to the initial Siderite-Ca without reactor input, the crystallinity of the Siderite-Ca after 90 days of operation in SSAD and SCAD deteriorated, and the content of calcium-modified siderite decreased sharply. This indicates that most of the calcium-modified siderite participated in the system's denitrification and dephosphorization reactions, while some was converted into byproducts such as goethite (α-FeO(OH)). The 104 crystal facet corresponding to calcite (CaCO3) also demonstrates the successful loading of calcium. The quartz SiO2 corresponding to the 101 crystal facet is an impurity present in natural siderite. The 200 crystal facet may correspond to a small amount of pyrite, due to dissolved Fe. 2+ Intermediate products of sulfur oxidation (S) 2- ), polysulfides (S n 2- Secondary minerals formed through long-term contact with these minerals. Hydroxyapatite, represented by the 104 crystal facet, demonstrates the binding of calcium groups to phosphates as the primary mechanism for phosphate removal.

[0075] Figure 5 This is the reactor structure used in the embodiments of the present invention. Through the layered packing design and the efficient buffering effect of calcium-modified siderite, the system's resistance to fluctuations in water quality and quantity is significantly enhanced, maintaining a stable treatment effect.

Claims

1. A method for simultaneous nitrogen and phosphorus removal from wastewater based on secondary calcification modified siderite coupled with sulfur autotrophic denitrification, characterized in that: The application discloses a method for simultaneously achieving wastewater denitrification and phosphorus removal by using calcium-based modified siderite, sulfur and sulfur autotrophic denitrification bacteria to strengthen the wastewater denitrification process. Step (1), reactor packing preparation: sulfur and calcium-based modified siderite particles are taken respectively, mixed uniformly and added into a reaction container; Step (2), adding wastewater: adding the wastewater to be treated into the reaction container in step (1); Step (3), adding bacteria liquid: adding the sulfur autotrophic denitrification bacteria liquid into the reaction container in step (2); Step (4), autotrophic denitrification process: protective gas is blown into the mixed culture solution in step (3) and the reaction container is sealed, and autotrophic denitrification reaction is carried out.

2. The process for simultaneous removal of nitrogen and phosphorus from wastewater based on secondary calcification modified siderite coupled with sulfur autotrophic denitrification according to claim 1, characterized in that: The purity of the sulfur and the calcium-based modified siderite is more than 80%, and the volume ratio of the sulfur to the calcium-based modified siderite is 1:1-3:

1.

3. The process for simultaneous removal of nitrogen and phosphorus from wastewater based on secondary calcification modified siderite coupled with sulfur autotrophic denitrification according to claim 1, characterized in that: In the denitrification process, the sulfur and the calcium-based modified siderite exist in the form of particles, the particle size of the sulfur is 0.5-3 mm, the particle size of the calcium-based modified siderite is 0.5-3 mm, and the sulfur and the calcium-based modified siderite particles are placed in multiple layers in the reactor.

4. The process for simultaneous removal of nitrogen and phosphorus from wastewater based on secondary calcification modified siderite coupled with sulfur autotrophic denitrification according to claim 1, characterized in that: The volume of the sulfur autotrophic denitrification bacteria liquid accounts for 2%-15% of the volume of the wastewater.

5. The process for simultaneous removal of nitrogen and phosphorus from wastewater based on secondary calcification modified siderite coupled with sulfur autotrophic denitrification according to claim 1, characterized in that: The protective gas is nitrogen or argon.

6. The process for simultaneous removal of nitrogen and phosphorus from wastewater based on secondary calcification modified siderite coupled with sulfur autotrophic denitrification according to claim 1, characterized in that: The sulfur autotrophic denitrification bacteria liquid is rich in sulfur autotrophic denitrification bacteria sludge and is domesticated for more than 7 days.

7. The process for simultaneous removal of nitrogen and phosphorus from wastewater based on secondary calcification modified siderite coupled with sulfur autotrophic denitrification according to claim 1, characterized in that: The concentration of nitrate nitrogen in the wastewater to be treated ranges from 1 mg / L to 80 mg / L, and the concentration of phosphate phosphorus ranges from 0.1 mg / L to 30 mg / L.

8. The process for simultaneous removal of nitrogen and phosphorus from wastewater based on secondary calcification modified siderite coupled with sulfur autotrophic denitrification according to claim 1, characterized by the fact that: The preparation method of the calcium-based modified siderite comprises the following steps: a) crushing and screening the natural siderite to 5-60 meshes; b) calcining the pretreated siderite at 300-600 DEG C for 1-4 hours; c) oscillating the calcined siderite in a 1-3 mol / L Ca (OH) 2 solution or a CaCl2 solution at a rotating speed of 50-300 rpm for 12-24 hours; d) soaking the siderite in the CaCl2 solution, taking out the soaked siderite, washing and drying to obtain the calcium-based modified siderite.

9. The process for simultaneous removal of nitrogen and phosphorus from wastewater based on secondary calcification modified siderite coupled with sulfur autotrophic denitrification according to claim 1, characterized by the fact that: The reactor is an upflow anaerobic biological filter, and the filter material is filled with the calcium-based modified siderite and the sulfur inside, and the packing porosity reaches 25%-50%.

10. The process for simultaneous removal of nitrogen and phosphorus from wastewater based on secondary calcification modified siderite coupled with sulfur autotrophic denitrification according to claim 1, characterized in that: Under the dosing amount of sulfur: calcium-based modified siderite = 3:1, the autotrophic denitrification reaction can simultaneously achieve the nitrate removal rate of more than 98%, the total phosphorus removal rate of more than 95%, the COD removal rate of more than 85%, the pH self-buffering range of 6.8-7.5 and the nitrite accumulation amount of less than 2.5 mg / L within 5 days.

Images