Sulfur-pyrite synergistic nitrogen and phosphorus removal composite filler as well as preparation method and application thereof

Abstract

The invention provides a sulfur-pyrite synergistic nitrogen and phosphorus removal composite filler as well as a preparation method and application thereof. The sulfur-pyrite synergistic nitrogen and phosphorus removal composite filler is of a three-dimensional porous structure prepared by melting and granulating sulfur and pyrite. Firstly, pyrite powder is subjected to acidification pretreatment, surface oxides are washed away, the pyrite powder is added into molten sulfur after being dried and screened, the pyrite powder is rapidly stirred to be uniform, and the pyrite powder is naturally cooled to be prepared into composite particles. Sulfur and pyrite with the main component of FeS2 in the composite filler serve as electron donors for autotrophic denitrification, iron ions generated through oxidation can react with phosphate radicals to form iron phosphate precipitates, and therefore the purpose of synchronous nitrogen and phosphorus removal is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and particularly relates to a sulfur-pyrite synergistic denitrification and phosphorus removal composite filler, its preparation method and application, which are applicable to the deep denitrification and phosphorus removal of low-carbon nitrogen ratio sewage. Background Art

[0002] In the field of wastewater treatment, the deep denitrification and phosphorus removal of low C / N wastewater is a key problem in controlling water eutrophication. Traditional heterotrophic denitrification technology relies on external carbon sources (such as methanol), which is inefficient and costly in low-carbon wastewater. Sulfur autotrophic denitrification (SAD) uses elemental sulfur as an electron donor. Although it does not require a carbon source, for every 1 mg of nitrate nitrogen (NO3 - -N) removed, 5.71 mg of sulfate (SO4 2- ) is generated, leading to a risk of secondary pollution. At the same time, the hydrogen ions (H + ) generated by the reaction significantly reduce the system pH, requiring frequent addition of alkalinity regulators, and phosphate (PO4 3- ) cannot be removed synchronously. Pyrite autotrophic denitrification (PAD) utilizes the Fe 3+ released by the oxidation of FeS2 to form FePO4 precipitation with PO4 3- , which has the function of phosphorus removal. However, due to the slow dissolution of pyrite and low denitrification rate, and the formation of a passivation layer on the surface of the filler by the generated Fe(OH)3, the operation stability is poor and frequent maintenance is required.

[0003] Existing technologies have tried to combine sulfur and pyrite for synergistic denitrification and phosphorus removal, but there are still significant defects in practical applications. For example, Patent CN202410799265A is based on a polysulfone skeleton composite filler, relying on organic materials, with high costs and a risk of secondary pollution. Patent CN114685100A discloses a preparation method of a sulfur-pyrite composite denitrification filler, which uses starch as a binder to fuse sulfur and pyrite through extrusion granulation to achieve acid-base neutralization and reduce sulfate generation. However, long-term operation will lead to the loss of the filler, and the structural stability and long-term operation performance of the filler need to be improved by optimizing the choice of binder (such as replacing gelatinized starch).

[0004] Therefore, there is an urgent need to develop an efficient and low-cost inorganic composite filler to solve the above problems, which needs to meet the following core requirements at the same time: one is to achieve efficient synchronous denitrification and phosphorus removal; the second is to control the generation of by-product sulfate and maintain pH stability, reducing the addition of chemical agents; the third is to ensure long-term operation stability. Summary of the Invention

[0005] The purpose of this study is to improve the problems existing in the prior art and provide a preparation method and application of a sulfur-pyrite synergistic denitrification and phosphorus removal composite filler. Through the synergistic effect of sulfur autotrophic denitrification and pyrite autotrophic denitrification, synchronous denitrification and phosphorus removal, pH self-regulation and low sulfate generation are achieved, and long-term stable operation is maintained.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A preparation method of a sulfur-pyrite synergistic denitrification and phosphorus removal composite filler, comprising the following steps:

[0008] Step 1: The pyrite powder is pretreated by pickling to remove surface oxides;

[0009] Step 2: The sulfur powder is heated to a molten state at 160-180 °C;

[0010] Step 3: The pickled pyrite powder is added to the molten sulfur, and rapidly and continuously stirred until evenly mixed;

[0011] Step 4: Naturally cool and form to obtain a sulfur-pyrite composite filler.

[0012] Preferably, in Step 1, the pyrite powder is sieved through a 150-200 mesh sieve.

[0013] Preferably, in Step 1, the pyrite powder is soaked in a 10% (v / v) hydrochloric acid solution for 2 hours to remove the surface-formed oxides, and rinsed with deionized water until the pH value of the cleaning solution is close to 7. The cleaned pyrite powder is placed in a vacuum drying oven and dried at 20 °C for 24 hours.

[0014] Preferably, in Step 2, the sulfur powder is sieved through a 150-200 mesh sieve.

[0015] Preferably, in Step 2, the temperature is raised to 160-170 °C.

[0016] Preferably, in Step 2, the stirring speed is 250±50 rpm and the stirring time is 20-30 seconds.

[0017] Preferably, in Step 3, the mass ratio of sulfur to pyrite is 1:1.

[0018] The present invention also provides a sulfur / pyrrhotite denitrification and phosphorus removal composite biological filler prepared by the above preparation method.

[0019] Furthermore, the present invention provides the application of the above sulfur-pyrite synergistic denitrification and phosphorus removal composite filler in the advanced denitrification and phosphorus removal of sewage.

[0020] Specifically, the application method is: using the sulfur-pyrite synergistic denitrification and phosphorus removal composite filler as a filler in a biological filter or a fixed-bed reactor.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) The pyrite in the raw materials used in the present invention has the characteristics of wide mineral deposit distribution, low mining cost, sufficient market supply, etc. Combined with the optimized filler structure design, the material consumption rate is greatly reduced, the operation and maintenance cycle is extended, and the comprehensive operation cost of the sewage treatment system is significantly reduced;

[0023] (2) The sulfur-pyrite synergistic denitrification and phosphorus removal composite filler of the present invention is a solid-state stable and efficient filler. Through the micro-interface synergistic effect of sulfur element and pyrite, a composite functional material with a three-dimensional porous structure is constructed. It is particularly suitable for the deep denitrification and phosphorus removal of wastewater with a low C / N ratio;

[0024] (3) The sulfur-pyrite synergistic denitrification and phosphorus removal composite filler of the present invention is applied to the deep denitrification and phosphorus removal of sewage through the coupling mechanism of sulfur autotrophic denitrification and iron-mediated phosphorus removal. Without adding external organic carbon sources, it effectively solves the problems of carbon source shortage and excessive sulfate in the effluent when treating low C / N ratio wastewater in depth. Moreover, it has a stable structure and a dynamic pH buffering function, and the denitrification and phosphorus removal effects are excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the SEM image of the sulfur-pyrite synergistic denitrification and phosphorus removal composite filler prepared in Example 1.

[0026] Figure 2 is the concentration graph of NO3 - -N in the effluent during Example 4.

[0027] Figure 3 is the concentration graph of PO4 3- -P in the effluent during Example 4.

[0028] Figure 4 is the concentration graph of NO3 - -N in the effluent during Example 5.

[0029] Figure 5 is the concentration graph of PO4 3- -P in the effluent during Example 5.

[0030] Figure 6 is the concentration graph of NO2 - -N in the effluent during Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will be further described below in conjunction with specific embodiments.

[0032] Example 1

[0033] Preparation method of sulfur-pyrite synergistic denitrification and phosphorus removal composite filler, comprising the following steps:

[0034] The pyrite powder and sulfur powder are screened through a 150-200 mesh sieve;

[0035] The pyrite powder is immersed in a 10% (v / v) hydrochloric acid solution for 2 hours to remove the oxides formed on the surface, and rinsed with deionized water until the pH value of the cleaning solution is close to 7. The cleaned pyrite powder is placed in a vacuum drying oven and dried at 20 °C for 24 hours;

[0036] The sulfur powder is heated to a molten state at 160-170 °C;

[0037] The pickled pyrite powder is added to the molten sulfur (the mass ratio of sulfur to pyrite is 1:1), and rapidly and continuously stirred until evenly mixed. The stirring speed is 250±50 rpm, and the stirring time is 20-30 seconds;

[0038] It is naturally cooled and formed to obtain the sulfur-pyrite synergistic denitrification and phosphorus removal composite filler.

[0039] Figure 1 SEM image of the sulfur-pyrite synergistic denitrification and phosphorus removal composite filler prepared in Example 1, showing the uniform combination of sulfur and pyrite and the porous structure.

[0040] Example 2

[0041] This example is basically the same as Example 1, the only difference being that the mass ratio of sulfur to pyrite is 1:2.

[0042] Example 3

[0043] This example is basically the same as Example 1, the only difference being that the mass ratio of sulfur to pyrite is 2:1.

[0044] Example 4

[0045] 20 g of particle mixtures with different sulfur / pyrite mass ratios (S / P = 1:1, 2:1, 1:2) and synthetic wastewater are respectively added to anaerobic bottles with a working volume of 100 mL, nitrogen is bubbled into them, and the operation is repeated three times to remove the oxygen in the bottles. Then, 20 mL of sulfur autotrophic denitrifying bacteria is inoculated, and they are placed in a shaker and reacted under the conditions of 100 rpm / min and 30 °C. The synthetic wastewater consists of KNO3 0.3697 g / L, KH2PO4 0.0231 g / L, NaHCO3 0.8 g / L, and MgCl2·6H2O 0.1 g / L. The concentrations of NO3 - -N and PO4 3- -P in the synthetic wastewater are 51.24 mg / L and 5.27 mg / L respectively.

[0046] As Figure 2 and 3 shown, the nitrate and phosphate in the three groups of effluents were completely removed, and the removal rate was the fastest when the mass ratio of sulfur to pyrite was 1:1. Therefore, the prepared composite particles had the best denitrification and phosphorus removal effects.

[0047] Example 5

[0048] The domesticated sulfur autotrophic denitrifying bacteria were inoculated into three upflow anaerobic biological filters, and layered pyrite and sulfur particles, mixed pyrite and sulfur particles, and the sulfur-pyrite synergistic denitrification and phosphorus removal composite filler prepared in Example 1 were added. The reactors were R1, R2, and R3 respectively. Synthetic wastewater containing NO3 - -N 30 mg / L and PO4 3- 3 mg / L was used as the influent and pumped into the reactors. During the reaction, the temperature was controlled by a heating belt and maintained at 28±2°C to ensure stable microbial activity. It was divided into two major stages. In the first stage, the hydraulic retention times were 18 h, 12 h, 6 h, and 3 h, and the influent NO3 - -N was 30 mg / L and PO4 3- was 3 mg / L; in the second stage, the influent NO3--N concentration was 30, 60, and 90 mg / L, the hydraulic retention time was the optimal hydraulic retention time in the first stage, and the influent PO4 3- concentration remained unchanged.

[0049] As Figure 4 and 5 shown, the effluent NO3 - -N and PO4 3- -P concentrations in the R3 reactor were both lower than those in R1 and R2. When the HRT was 12 h, the effluent NO3 - -N concentration was only 0.39±0.05 mg / L, and the effluent PO4 3- -P concentration was only 0.24±0.04 mg / L, and the average removal efficiencies were as high as 98.70% and 91.88% respectively. However, due to the weak shock load resistance of the sulfur and pyrite dispersed filler systems used in R1 and R2, with the shortening of the HRT, the denitrification and phosphorus removal performance deteriorated sharply and could not meet the requirements of the above two indicators in the discharge standards at the same time. When the influent NO3 - -N concentration increased to 60 mg / L, the NO3 - -N removal amounts in the R1, R2, and R3 reactors increased to 42.1, 53.72, and 57.99 mg / L respectively. Since other operating conditions were the same, the greater the influent NO3 - -N concentration, the more NO3 - -N was removed. At this time, the denitrification load of R3 increased to 115.98 gN / (m 3·d), the TN removal rate still remained at 98.84%. In contrast, the TN removal rates of R1 and R2 decreased to 71.71% and 91.55% respectively. And the removal rate of PO4 3- -P in R3 was 96.15%. As Figure 6 shown, there was no obvious accumulation of NO2 - -N in R3, and the system operated stably.

[0050] It can be seen that the sulfur-pyrite synergistic denitrification and phosphorus removal composite filler prepared in Example 1 is feasible, efficient and operates stably when applied to the biological filter.

[0051] In summary, the present invention uses a method of melting and granulating sulfur and pyrite to prepare a sulfur-pyrite synergistic denitrification and phosphorus removal composite filler. Through the sulfur-iron interface synergistic effect, it solves problems such as alkalinity consumption, sulfate pollution and low phosphorus removal efficiency of single processes, and shows excellent denitrification and phosphorus removal performance when treating low C / N ratio wastewater.

Claims

1. A preparation method of a sulfur-pyrite synergistic denitrification and phosphorus removal composite filler, characterized in that, It includes the following steps: Step 1: The pyrite powder is pretreated by pickling to remove surface oxides; Step 2: The sulfur powder is heated to a molten state at 160 - 180 °C; Step 3: The pickled pyrite powder is added to the molten sulfur, and the mixture is continuously stirred rapidly until evenly mixed; Step 4: It is naturally cooled and formed to obtain a sulfur - pyrite composite filler.

2. The preparation method according to claim 1, wherein: The particle size of the sulfur powder and the pyrite powder is 150 - 200 mesh, and the mass ratio of sulfur to pyrite is 1:

1.

3. The preparation method according to claim 1, wherein: In Step 1, the pickling pretreatment is carried out by soaking in 10% (v / v) hydrochloric acid for 2 hours, and then washing with deionized water until neutral. The washed pyrite powder is placed in a vacuum drying oven and dried at 20 °C for 24 hours.

4. A sulfur - pyrite synergistic denitrification and phosphorus removal composite filler, which is prepared by the preparation method described in any one of Claims 1 - 3.

5. Use of the sulfur-pyrite synergistic denitrification and phosphorus removal composite filler according to claim 4 in advanced denitrification and phosphorus removal of sewage, characterized in that: The filler is used as an electron donor in a biological filter or a fixed - bed reactor to simultaneously remove nitrate and phosphate.

6. The application according to claim 5, characterized in that: The denitrification load of the filler ≥ 100 g N / (m 3 ·d), and the TP removal rate ≥ 90%.

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