Sulfur-based autotrophic expanded bed process

Abstract

The invention discloses a sulfur-based autotrophic expanded bed process which comprises the following steps: S1, a reactor is filled with a sulfur-iron composite filler, the mass ratio of sulfur to iron of the filler is 1: 1, and the average particle size is 1-2 mm; s2, controlling the ascending velocity by adjusting the reflux ratio, and dynamically adjusting the bed expansion rate to 40-95% according to a formula R = 0.78 xQ ^ 0.62 (R is the expansion rate, and Q is the ascending velocity); s3, when the pH value is 6.8-7.8, dissolving oxygen lt; under the condition of 0.3 mg / L, denitrification synergy of anaerobic ammonium oxidation bacteria and denitrifying bacteria is synchronously realized; s4, when the NOx concentration of the effluent is gt; when the expansion rate is 15 mg / L, starting a strengthening mode (the expansion rate is gt; 85%), otherwise, switching to an economic mode (swelling rate lt; 60%). According to the improvement effect of the expansion rate on the nitrogen removal capacity of the sulfur autotrophic denitrification reactor, the reflux ratio is adjusted to improve the ascending velocity of the reactor, the bed expansion rate is changed, and the nitrogen removal efficiency of microorganisms in the reactor is improved so as to meet different nitrogen removal requirements.

Description

Technical Field

[0001] The present invention relates to the field of sewage treatment, and particularly to a sulfur-based autotrophic expanded bed process. Background Art

[0002] Nitrogen, as one of the main inducements for water eutrophication, has been widely concerned. At present, the nitrogen capacity of ecological water bodies in most regions has tended to be saturated and is on the verge of the risk of eutrophication outbreak. The nutrient content (nitrate nitrogen, ammonia nitrogen, and phosphate) in the secondary effluent of sewage treatment plants is relatively low, but it is also sufficient to cause the eutrophication of natural water bodies, which has become increasingly obvious in the water quality changes of some inland basins and lakes in recent years. Due to the limited self-purification ability of water bodies, the environmental capacity of such regions is becoming saturated day by day. Gradually increasing the total nitrogen emission limit of surrounding sewage discharge units is a powerful measure to prevent further water quality deterioration. Therefore, the total nitrogen discharge standard of sewage treatment plants has been continuously improved. For example, the total nitrogen was increased from 15 mg·L-1 in the national standard to 10 mg·L-1 in 2012, and it was required that the total nitrogen in the effluent reach 5 mg·L-1 for discharge in 2020.

[0003] The sulfur autotrophic denitrification technology is a denitrification technology that has received much attention at present, mainly due to the outstanding advantages of the low cost of elemental sulfur and the dual roles of electron donor and biological carrier. The fixed-bed reactor with sulfur particles as fillers has a simple structure and is the most common form of sulfur autotrophic denitrification process, and there is a lot of operation experience in actual water plants. However, this process has disadvantages such as long startup time, low removal rate, and the risk of blockage, which limit its application scenarios. In the fixed-bed reactor, the mass transfer between the filler and the liquid is mainly diffusion, which limits the contact efficiency between the substrate and the electron donor. At the same time, as the thickness of the biofilm increases, the mass transfer resistance further increases, the products are difficult to discharge in time, resulting in blockage, and the effective mass transfer area on the surface of the filler is reduced. In order to maintain a high denitrification efficiency, a fluidized-bed reactor has been developed. This process improves the shear force between the fluid and the particles by changing the flow regime, increases the convective mass transfer efficiency, and at the same time, the suspended state maximizes the surface area of the particles exposed to the fluid, further promoting mass transfer. However, it also has limitations such as high operating cost, strict requirements for the particle size of the filler, and complex flow regime control. For sewage treatment plants that have established a fixed-bed process, the main challenge is that the limited denitrification of the packed bed is difficult to meet the increasingly strict emission standards. For sewage treatment plants mainly treating domestic sewage, the high denitrification ability of the fluidized bed may lead to problems of performance surplus and resource waste under low-concentration influent conditions, and at the same time, it will also bring higher demolition and renovation costs and operating costs, making it difficult to achieve the balance between economy and efficiency.

[0004] Some adaptive processes have been developed for the sulfur autotrophic denitrification process in the prior art, such as: the combined process of anaerobic ammonia oxidation and sulfur autotrophic denitrification, sulfur autotrophic denitrification biological filter, the coupled process of sulfide reduction and denitrification, etc.

[0005] In the field of sulfur autotrophic denitrification, there is still a lack of an economical, efficient and flexible packed bed process. The potential advantage of the expanded bed in improving mass transfer makes it an important direction for optimizing the sulfur autotrophic denitrification process. In addition, with the improvement of environmental emission standards, the sulfur autotrophic denitrification process not only needs to meet the nitrogen removal efficiency requirements, but also needs to provide advantages in economy and sustainability. The expected low cost, high efficiency and flexibility brought by the development of the sulfur autotrophic denitrification expanded bed technology highly coincide with this demand. Summary of the Invention

[0006] The purpose of the present invention is to provide a sulfur-based autotrophic expanded bed process to solve the technical problems of low denitrification efficiency and high operating cost in the prior art.

[0007] To achieve the above-mentioned invention purpose, the technical solution of the present invention is:

[0008] A sulfur-based autotrophic expanded bed process, comprising the following steps:

[0009] S1. Fill the reactor with sulfur-iron composite filler, the mass ratio of sulfur to iron in the filler is 1:1, and the average particle size is 1-2 mm;

[0010] S2. Control the upward flow rate by adjusting the reflux ratio, and dynamically adjust the bed expansion rate to 40-95% according to the formula R = 0.78xQ∧0.62 (R is the expansion rate, Q is the upward flow rate);

[0011] S3. Under the conditions of pH 6.8-7.8 and dissolved oxygen <0.3 mg / L, synchronously achieve the denitrification synergy of anaerobic ammonium-oxidizing bacteria and denitrifying bacteria;

[0012] S4. When the NOx concentration in the effluent > 15 mg / L, start the enhanced mode (expansion rate > 85%), otherwise switch to the economic mode (expansion rate < 60%).

[0013] Preferably, in step S1, the sulfur-iron composite filler is in a lump shape, a block shape, a spherical shape or an irregular shape.

[0014] Preferably, in step S1, the sulfur-iron composite filler accounts for 10-90% of the volume of the expanded bed filter.

[0015] Preferably, the sulfur-iron composite filler is prepared by the following steps:

[0016] a) Mix elemental sulfur (purity ≥ 99%) and zero-valent iron powder (particle size 50-100 μm) in a mass ratio of 1:1;

[0017] b) Add a binder (polyvinyl alcohol solution, concentration 5%-8%), and form it into a lump shape or a granular shape in a granulator;

[0018] c) After hot air curing at 60-80°C, a porous composite filler is formed.

[0019] Preferably, in step b), the porosity of the porous composite filler is 35%-45%.

[0020] Preferably, in step S4, the frequency of the reflux pump is dynamically adjusted through the double feedback of an on-line turbidimeter and a differential pressure sensor;

[0021] Economic mode (effluent NOx concentration ≤ 15 mg / L): control the expansion rate at 40%-60%, and the upward flow rate at 8-12 m / h;

[0022] Enhanced mode (effluent NOx concentration > 15 mg / L): increase the expansion rate to 85%-95%, and the upward flow rate to 15-20 m / h.

[0023] Preferably, in step S3, a low-oxygen stimulation is implemented every 24 hours: instantaneously increase the dissolved oxygen to 0.5-0.8 mg / h and maintain it for 10-15 minutes.

[0024] The beneficial effects of the present invention are as follows:

[0025] 1. In the present invention, according to the improvement effect of the expansion rate on the nitrogen removal ability of the sulfur autotrophic denitrification reactor, the reflux ratio is adjusted to increase the upward flow rate of the reactor, change the bed expansion rate, and improve the nitrogen removal efficiency of the microorganisms inside the reactor to meet different nitrogen removal requirements.

[0026] 2. In the present invention, due to the setting of an on-line turbidimeter and a pressure sensor, a multi-parameter on-line monitoring and intelligent speed regulation system can be integrated to achieve precise control of the expansion rate, enabling it to be flexibly transferred under different application scenarios and process conditions, further enhancing its practicability and promotion value; and reducing energy consumption by 40%-50% and extending the filler regeneration cycle to twice that of the traditional process. Detailed Embodiments

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0028] The described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0029] Example 1

[0030] A sulfur-based autotrophic expanded bed process includes the following steps:

[0031] S1. Fill the reactor with sulfur-iron composite filler. The mass ratio of sulfur to iron in the filler is 1:1, and the average particle size is 1 - 2 mm. Among them, the sulfur-iron composite filler is in the shape of a mass, block, spherical-like or irregular shape, and the sulfur-iron composite filler accounts for 10 - 90% of the volume of the expanded bed filter.

[0032] The sulfur-iron composite filler is prepared through the following steps:

[0033] a) Mix elemental sulfur (purity ≥ 99%) and zero-valent iron powder (particle size 50 - 100 μm) at a mass ratio of 1:1.

[0034] b) Add an adhesive (polyvinyl alcohol solution, concentration 5% - 8%), and form it into a mass or granular shape in a granulator.

[0035] c) After curing with hot air at 60 - 80 °C, a porous composite filler is formed, and the porosity of the porous composite filler is 35% - 45%.

[0036] S2. Control the upward flow rate by adjusting the reflux ratio, and dynamically adjust the bed expansion ratio to 40 - 95% according to the formula R = 0.78×Q ∧ 0.62 (R is the expansion rate, Q is the upward flow rate).

[0037] S3. Implement low-oxygen stimulation once every 24 hours: Instantly increase the dissolved oxygen to 0.5 - 0.8 mg / h and last for 10 - 15 minutes; under the conditions of pH 6.8 - 7.8 and dissolved oxygen < 0.3 mg / L, simultaneously achieve the nitrogen removal synergy of anaerobic ammonium-oxidizing bacteria and denitrifying bacteria.

[0038] S4. Dynamically adjust the frequency of the reflux pump through the double feedback of an on-line turbidimeter and a differential pressure sensor.

[0039] Economic mode (effluent NOx concentration ≤ 15 mg / L): Control the expansion rate at 40% - 60% and the upward flow rate at 8 - 12 m / h.

[0040] Enhanced mode (effluent NOx concentration > 15 mg / L): Increase the expansion rate to 85% - 95% and the upward flow rate to 15 - 20 m / h.

[0041] Performance comparison of fillers with different particle sizes:

[0042] Table 1

[0043]

[0044] As can be seen from Table 1:

[0045] The mass transfer efficiency of the 1 - 2 mm filler reaches 82% at an expansion rate of 80%, which is 9.3% higher than that of the 2 - 3 mm filler.

[0046] Verification of dynamic regulation effect:

[0047] Table 2

[0048] Operating conditions: inlet NOx concentration 80 mg / L, temperature 20 °C

[0049]

[0050] As can be seen from Table 2:

[0051] The denitrification rate increases by 76% in the enhanced mode, but the energy consumption increases by 65%, which is applicable to the scenario of fluctuating inlet concentration.

[0052] The described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A sulfur-based autotrophic expanded bed process, characterized in that: The following steps are involved: S1. Filling the reactor with a sulfur-iron composite filler, wherein the mass ratio of sulfur to iron in the filler is 1:1 and the average particle size is 1-2 mm; S2, by adjusting the reflux ratio to control the rising flow rate, according to the formula R = 0.78xQ ∧ 0.62 (R is the expansion rate, Q is the rising flow rate) Dynamically adjust the bed expansion rate to 40-95%; S3, under the conditions of pH 6.8-7.8 and dissolved oxygen <0.3mg / L, the denitrification of anaerobic ammonia oxidizing bacteria and denitrifying bacteria is achieved simultaneously; S4. When the outlet water NOx concentration is >15 mg / L, start the enhanced mode (expansion rate >85%), otherwise switch to the economic mode (expansion rate <60%).

2. The sulfur-based autotrophic expanded bed process according to claim 1, characterized in that: In step S1, the ferrosulphide composite filler is in the shape of a lump, a block, a spherical shape or an irregular shape.

3. The sulfur-based autotrophic expanded bed process according to claim 2, characterized in that: In step S1, the ferrosulphur composite filler occupies 10-90% of the volume of the expanded bed filter.

4. The sulfur-based autotrophic expanded bed process according to claim 2, characterized in that: The ferrosulphur composite filler is prepared by the following steps: a) Mix elemental sulfur (purity ≥ 99%) and zero-valent iron powder (particle size 50-100 μm) in a mass ratio of 1:1; b) adding a binder (polyvinyl alcohol solution, concentration 5%-8%) and forming into agglomerates or granules in a granulator; c) After being cured by hot air at 60-80°C, a porous composite filler is formed.

5. The expanded bed reactor system according to claim 4, characterized in that: In step b), the porosity of the porous composite filler is 35%-45%.

6. The expanded bed reactor system according to claim 5, characterized in that: In step S4, the frequency of the reflux pump is dynamically adjusted through dual feedback from the online turbidity meter and the differential pressure sensor; Economic mode (outlet NOx concentration ≤ 15mg / L): control expansion rate 40%-60%, rising flow rate 8-12m / h; Enhanced mode (outlet NOx concentration>15mg / L): increase the expansion rate to 85%-95%, and the rising flow rate to 15-20m / h.

7. The expanded bed reactor system according to claim 6, characterized in that: In step S3, sequential hypoxic stimulation is implemented every 24 hours: dissolved oxygen is transiently increased to 0.5-0.8 mg / h for 10-15 minutes.

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