Preparation method and application of biological carrier for advanced sewage treatment

Abstract

The invention discloses a preparation method and application of a biological carrier for advanced sewage treatment, and belongs to the field of advanced sewage treatment. The preparation method of the biological carrier comprises the following steps: (1) drying the white mud, and then grinding and sieving; (2) heating sulfur until the sulfur becomes liquid, then adding the white mud sieved in the step (1), and stirring and mixing; and (3) cooling after stirring and mixing in the step (2) are completed, and then crushing and sieving to obtain the biological carrier. In the preparation process of the biological carrier, few raw materials are used, operation is easy, the obtained biological carrier has very high compressive strength, the state of the carrier can be kept under continuous washing, smashing and disintegration are avoided, the unexpected technical effect is achieved, and a good foundation is laid for expanding the actual use range of the biological carrier.

Description

Technical Field

[0001] This invention relates to a method for preparing a biological carrier for advanced wastewater treatment and its application, belonging to the field of advanced wastewater treatment. Background Technology

[0002] Traditional activated sludge processes have significant bottlenecks in the removal of nitrogen and phosphorus from secondary effluent, especially for wastewater with low carbon-to-nitrogen ratios, which is difficult to meet the Class A standard requirements of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918-2002).

[0003] In existing technologies, deep nitrogen and phosphorus removal often rely on external carbon sources or chemical agents, which not only significantly increases treatment costs but may also pose a risk of secondary pollution. Sulfate autotrophic denitrification is an autotrophic nitrogen removal process that does not require the addition of a carbon source. It has advantages such as low sludge production, low investment costs, and high nitrogen removal efficiency. However, the sulfur autotrophic denitrification process requires the supply of alkalinity.

[0004] White mud, a byproduct of calcium carbonate deep processing parks and the paper industry, is produced in large quantities. Its main component is CaCO3, and its surface contains residual alkali such as Na2CO3. Currently, there are few resource utilization pathways for white mud. Traditional recycling processes involve pre-treating the white mud to remove alkali, which increases energy consumption and complexity. Therefore, white mud can be used to supplement alkalinity for the sulfur autotrophic denitrification process.

[0005] Currently, patent CN 118949836 A discloses a method for preparing high-load denitrification packing particles using industrial by-products. This method utilizes bio-derived sulfur (a by-product of biological desulfurization towers) and white mud (a by-product of papermaking) to prepare porous packing particles for high-load denitrification. However, the raw materials used in this preparation process are quite complex, and the product's compressive strength is low, resulting in a lack of reliability in practical use.

[0006] Furthermore, patent CN 109019877 A discloses a nitrogen and phosphorus removal active biological carrier, its preparation method, and its application. This nitrogen and phosphorus removal active biological carrier is formed from existing sulfur and siderite through a physical process. The substrate is sulfur, and a large number of siderite particles are embedded on the surface and inside. The mass ratio of sulfur to siderite is 1-9:9-1. However, the compressive strength of the obtained biological carrier is not high, which does not meet the requirements of practical applications. Summary of the Invention

[0007] Technical issues

[0008] White clay can be used to prepare a filler to supplement alkalinity in the sulfur autotrophic denitrification process. However, due to its soft texture, the resulting filler often has low strength and is easily crushed and disintegrated, which is not conducive to practical use. Therefore, there is a need to provide a high-strength white clay filler.

[0009] Technical content

[0010] To address the aforementioned problems, this invention provides a method for preparing a biological carrier for advanced wastewater treatment and its application. This method uses sulfur and white mud to prepare a biological carrier, thereby enhancing the denitrification and phosphorus removal capabilities of a sulfur autotrophic system and maintaining the system's acid-base balance. Furthermore, the biological carrier obtained by this invention possesses high compressive strength, resisting friction and impact without disintegrating, and can be used long-term in the sulfur autotrophic denitrification process to provide alkalinity replenishment.

[0011] The present invention provides a biological carrier for advanced wastewater treatment, the biological carrier being composed of sulfur and white mud in a mass ratio of 1 to 7:1.

[0012] Furthermore, the mass ratio of sulfur to white mud in the biological carrier is 3 to 5:1.

[0013] Furthermore, the particle size of the biological carrier is 1–8 mm.

[0014] Preferably, the particle size of the biological carrier is 3-5 mm.

[0015] Furthermore, the sulfur used in the biological carrier is a known type of sulfur, such as sublimed sulfur.

[0016] Furthermore, the white mud in the biological carrier is a byproduct generated during the production process of the calcium carbonate deep processing park, which includes complexes such as cellulose, lignin, and calcium carbonate, with a water content between 40% and 60%.

[0017] The biological carrier for advanced wastewater treatment provided by this invention is applied in wastewater treatment.

[0018] Furthermore, the application is as a filler to provide alkalinity supplementation for sulfur autotrophic denitrification.

[0019] The present invention also provides a method for preparing a biological carrier for advanced wastewater treatment, the method comprising:

[0020] (1) Dry the white clay, then grind and sieve it;

[0021] (2) Heat the sulfur until it becomes liquid, then add the sieved white mud from step (1) and stir to mix.

[0022] (3) After the mixing in step (2) is completed, the mixture is cooled, then crushed and sieved to obtain the biological carrier.

[0023] Furthermore, in step (1), the drying process involves drying at 90–110°C for 0.5–5 hours.

[0024] Furthermore, the mesh size of the sieve in step (1) is 30 to 50 mesh.

[0025] Furthermore, the heating temperature in step (2) is 130-150℃.

[0026] Furthermore, in step (2), the mass ratio of sulfur to white mud is 1 to 7:1.

[0027] Preferably, the mass ratio of sulfur to white mud in step (2) is 3 to 5:1.

[0028] Furthermore, in step (2), the mixing is carried out at a mixing speed of 300-500 rpm for 60-500 seconds.

[0029] Furthermore, in step (3), the mesh size of the sieve is 1 to 8 mm.

[0030] Preferably, the mesh size of the sieve in step (3) is 3-5 mm.

[0031] Beneficial effects

[0032] (1) Compared with the prior art, the preparation process of the biological carrier of the present invention uses less raw materials, is simple to operate, and the obtained biological carrier has a strong compressive strength of up to 72.8N. It can maintain the state of the carrier under continuous scouring without being crushed or disintegrated, achieving unexpected technical effects and laying a good foundation for expanding the practical application range of the biological carrier.

[0033] (2) The biological carrier obtained by the present invention can achieve good nitrogen and phosphorus removal effects. The removal rate of nitrate can reach more than 95%, the removal rate of total phosphorus can reach more than 90%, the pH can be stabilized at around 6.8, and it can operate stably for more than 300 days, which proves that the biological carrier can effectively replenish alkalinity and maintain excellent sewage treatment effect. Attached Figure Description

[0034] Figure 1 This is the result of the compressive strength test. Detailed Implementation

[0035] Source of raw materials

[0036] The white clay was sourced from a calcium carbonate deep processing park in Guangxi, while the sulfur was a commercially available product.

[0037] Detection methods

[0038] Nitrate and total phosphorus were determined using a UV spectrophotometer (DR6000).

[0039] The compressive strength was determined using a computer-controlled electronic universal testing machine (QJ211S-5kN).

[0040] The shake-flask experiment was conducted as follows: 15g of white mud-sulfur composite packing was added to a 250mL Erlenmeyer flask, along with 200mL of nitrate wastewater and 15mL of anoxic tank sludge. The flask was shaken at 100rpm in a shaker at 25℃. Samples were taken every 12 hours to determine the nitrate and total phosphorus concentrations and calculate the removal rate.

[0041] Example 1

[0042] Biological carriers were prepared by mixing 75% sulfur and 25% white mud according to the following mass ratio:

[0043] (1) Place the white clay in a 105℃ oven for 1 hour to dehydrate and dry it, and grind it until it passes through a 30-mesh sieve.

[0044] (2) Place the sulfur in a mold and heat it on a hot plate at 150°C until the sulfur becomes liquid.

[0045] (3) Add the white clay from (1) into the mold and mix it with liquid sulfur. The mass ratio of sulfur to white clay is 3:1. Start the mixer and stir at 300 rpm for 180 seconds to mix evenly.

[0046] (4) Turn off the heating plate, remove the mold, and let it stand for 30 minutes to cool down;

[0047] (5) After cooling, pour out the solid mixture of sulfur and white mud and put it into a crusher to crush for 5 minutes;

[0048] (6) Pour out the crushed particles and pass them through a 3-5 mm sieve to obtain the biological carrier.

[0049] Example 2

[0050] The biological carrier from Example 1 was filled into a fixed-bed reactor at a filling ratio of 60%, and anaerobic sludge was inoculated. Artificially prepared water containing 30 mg / L nitrate and 2 mg / L phosphate was used as the influent; no alkalinity supplementation was added.

[0051] After startup, the reactor was gradually reduced from 10 hours to 1.5 hours and operated stably for 300 days. The nitrate removal rate reached over 95%, the total phosphorus removal rate reached over 85%, and the pH remained stable at around 6.8. Therefore, the prepared biological carrier exhibits excellent nitrogen and phosphorus removal effects without alkalinity supplementation, and the effluent maintains a stable neutral pH, providing a suitable living environment for microorganisms. Furthermore, the biological carrier did not show any signs of rupture or precipitation, demonstrating a well-structured composition.

[0052] This indicates that the biological carrier has shown good performance and reliable structure in long-term experiments, and has broad application prospects.

[0053] Comparative Example 1

[0054] To investigate the denitrification and phosphorus removal effects of biological carriers with different particle sizes, the preparation method of Example 1 was followed, and the sieve pore size in step (6) was adjusted to 1-3 mm and 5-8 mm under the same mass ratio of sulfur to white mud. Then, three biological carriers with different particle sizes were selected for comparison of denitrification and phosphorus removal effects. The final results are shown in Table 1 below.

[0055] In a 48-hour shake-flask experiment, the removal rates of biological carriers with particle sizes of 1-3 mm and 3-5 mm were both over 90% under influent conditions of nitrate 60 mg / L and total phosphorus 2 mg / L, while the removal effect of biological carriers with particle sizes of 5-8 mm was weaker.

[0056] Table 1

[0057] 1-3mm 3-5mm 5-8mm Nitrate removal rate (%) after 48 hours 100 97.78 73.61 Total phosphorus removal rate (%) after 48 hours 98.75 91.48 78.31

[0058] Comparative Example 2

[0059] Based on the application of the obtained biological carriers in biofilters, it is necessary to determine the packing porosity of biological carriers of different particle sizes. 500g each of the three different particle sizes of biological carriers from Comparative Example 1 was weighed into beakers, and water was poured in until it just covered the biological carriers. The total mass of the beakers before and after pouring water was measured, and the mass of the poured water was calculated. The ratio of the volume of the poured water to the packing volume of the biological carriers is the porosity. The results are shown in Table 2 below. The porosity of the three particle sizes of biological carriers differs significantly. In biofilters, too small a porosity increases the risk of filter clogging, while too large a porosity leads to insufficient biological attachment. Therefore, a porosity of 3-5mm for biological carriers is more suitable.

[0060] Table 2

[0061] 1-3mm 3-5mm 5-8mm Porosity (%) 38.13 45.18 54.31

[0062] Comparative Example 3

[0063] To clarify the effect of the mixing ratio of sulfur and white mud in the biological carrier on the denitrification and phosphorus removal effect, referring to the preparation method of Example 1, the mass ratio of sulfur and white mud was adjusted to 1:1, 5:1, and 7:1 under the same particle size of 3-5 mm. The obtained biological carrier was then used to verify the denitrification and phosphorus removal effect. The final results are shown in Table 3 below.

[0064] In a 48-hour shake-flask experiment, the biological carriers with mass ratios of 3:1 and 5:1 exhibited superior nitrogen and phosphorus removal effects. With influent containing 60 mg / L nitrate and 2 mg / L total phosphorus, the 3:1 and 5:1 groups achieved removal rates of over 85% for nitrate and over 90% for total phosphorus. Therefore, a mass ratio of 3:1 and 5:1 for sulfur and white mud is a suitable mixing ratio for biological carriers.

[0065] Table 3

[0066]

[0067]

[0068] Comparative Example 4

[0069] During the operation and transportation of biological filters, the strength of the biological carrier is crucial, as it affects the service life of the biological carrier and transportation losses. Therefore, a comparison of the compressive strength of two other types of biological carriers was conducted.

[0070] 1. Biological carrier A was prepared according to Example 1 in patent CN 118949836 A, and the specific method is as follows:

[0071] (1) Filter the 1L bio-derived sulfur waste liquid by-product of the bio-desulfurization tower, wash it with 1L of deionized water, dry it, and grind it into bio-derived sulfur particles with a particle size D50=9μm.

[0072] (2) Grind and mix 100g of bio-derived sulfur particles, 400g of white mud (a byproduct of papermaking), and 20g of alumina to obtain a mixture;

[0073] (3) Place the uniform mixture into a disc granulator and spray 60g of 20% epoxy resin emulsion during rotation until it slowly grows into 5mm particles.

[0074] (4) The 1-5 mm particles obtained above are screened out, soaked in NaOH solution with pH=14 for 2 hours, and the water temperature is maintained at 50℃. After washing and drying, porous packing particles with high load denitrification are obtained.

[0075] 2. Biological carrier B was prepared according to Example 1 of patent CN 109019877 A, and the specific method is as follows:

[0076] (1) Melt the sulfur into a liquid state at 140℃;

[0077] (2) Maintain the above temperature, add siderite to the above liquid sulfur at a mass ratio of 1:1, and stir at a stirring speed of 450 rpm for 2 minutes to obtain a mixture.

[0078] (3) The above mixture is cooled and solidified in 45°C cooling water through a mixture distributor for 1 minute, and the outflow rate of the mixture from the mixture distributor is controlled to be 3 mL / hole per minute.

[0079] (4) Filter out the formed solid material through a 3-5 mesh sieve to obtain a nitrogen- and phosphorus-removing active biological carrier.

[0080] The compressive strength results are as follows Figure 1As shown, it is evident that the strength of the two proportions of biocarriers prepared by this method is higher than that of sulfur filler, biocarrier A, and biocarrier B. This indicates that this method effectively bonds the white mud and sulfur while maintaining high strength. Biocarrier A, also prepared using white mud and sulfur, and employing epoxy resin as a binder for granulation, does not exhibit a good bonding effect due to the relatively soft nature of the white mud, resulting in a still lower compressive strength for biocarrier A.

[0081] Comparative Example 5

[0082] In the operation of sulfur autotrophic denitrification filters, problems such as bubble retention and caking inevitably occur. Backwashing is typically used in engineering to remove retained nitrogen, metabolic microorganisms, and other substances from the filter. During this process, the biological carriers rub and collide with each other; if their strength is insufficient, the carriers are prone to breakage, affecting the normal operation of the filter. This comparative example uses a bottom-inlet, top-outlet filter column and employs high-intensity influent flushing instead of backwashing to verify the reliability of the biological carriers in actual operation. The biological carriers used include a 3:1 sulfur and white mud biological carrier prepared by this method (hereinafter referred to as the 3:1 biological carrier) and biological carrier A. The specific process is as follows: the 3:1 biological carrier and biological carrier A are filled into a filter column of the same specification at a filling ratio of 60%, and the influent peristaltic pump flow rate is adjusted to 100 L / h for continuous flushing for 5 minutes. The flushing state of the two biological carriers in the filter column is observed.

[0083] (1) The 3:1 biological carrier initially rises in layers with the water flow during the flushing process. Subsequently, the particles begin to suspend in the water flow and rotate due to friction and collision. The remaining sludge in the bed and the sediment produced by phosphorus removal are discharged through the upper outlet. The retained nitrogen is carried out by the high-speed water flow at the beginning, achieving the effect of backwashing and maintaining the denitrification capacity of the filter column.

[0084] (2) Biological carrier A was slightly loosened with the water flow at the beginning of the flushing, but within 1 minute, the particles disintegrated due to the impact and collision of the water flow. The filter column gradually became turbid, and fragments of biological carrier A were distributed, resulting in the failure of the flushing.

[0085] A comparison of the two biological carriers under the same conditions revealed that biological carrier A could not meet the operational requirements of the filter bed during routine flushing, exhibiting poor strength and a tendency to break. In contrast, the 3:1 biological carrier could meet the requirements for routine flushing, possessed better structural strength, and while satisfying phosphorus removal requirements, could also remove calcium phosphate precipitates through flushing, maintaining the filter column's denitrification capacity.

[0086] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A biological carrier for advanced wastewater treatment, characterized in that, The biological carrier is composed of sulfur and white mud in a mass ratio of 1 to 7:1; the particle size of the biological carrier is 1 to 8 mm.

2. The biological carrier according to claim 1, characterized in that, The mass ratio of sulfur to white mud in the biological carrier is 3 to 5:

1.

3. The biological carrier according to claim 1, characterized in that, The biological carrier has a particle size of 3–5 mm.

4. The application of the biological carrier according to any one of claims 1 to 3 in wastewater treatment.

5. A method for preparing a biological carrier according to any one of claims 1 to 3, characterized in that, The preparation method includes: (1) Dry the white clay, then grind and sieve it; (2) Heat the sulfur until it becomes liquid, then add the sieved white mud from step (1) and stir to mix. (3) After the mixing in step (2) is completed, the mixture is cooled, then crushed and sieved to obtain the biological carrier.

6. The preparation method according to claim 5, characterized in that, In step (1), the drying process involves drying at 90–110°C for 0.5–5 hours; the sieve mesh size is 30–50 mesh.

7. The preparation method according to claim 5, characterized in that, In step (2), the heating temperature is 130-150℃; the mass ratio of sulfur to white mud is 1-7:

1.

8. The preparation method according to claim 5, characterized in that, In step (2), the mass ratio of sulfur to white mud is 3 to 5:

1.

9. The preparation method according to claim 5, characterized in that, In step (2), the mixing is carried out at a speed of 300-500 rpm for 60-500 seconds.

10. The preparation method according to claim 5, characterized in that, In step (3), the mesh size of the sieve is 1-8 mm.

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