Method for promoting rapid granulation of sludge based on ferric trichloride conditioning and enhancing natural drying of biological membrane

Abstract

The invention discloses a method for promoting rapid granulation of sludge by conditioning and strengthening natural drying of a biological membrane based on ferric trichloride. The method comprises the steps of rapid biofilm formation of a polyurethane sponge filler, conditioning of ferric trichloride, natural drying of the biological membrane, acquisition of a sludge aggregate, sludge granulation and the like. According to the technical scheme, rapid granulation of the sludge in actual municipal wastewater can be achieved, and the method has the advantages of being easy to operate, high in efficiency, low in energy consumption and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment, and in particular relates to a method for promoting rapid granulation of sludge by strengthening the natural drying of biofilm through conditioning with ferric chloride. Background Art

[0002] Aerobic granular sludge (AGS) is a promising new biological wastewater treatment technology that has garnered extensive attention and research in recent years. Compared to conventional flocculent sludge, aerobic granular sludge offers advantages such as superior settling performance and efficient pollutant removal, making it a key development direction for biological wastewater treatment. Although numerous studies have been published on AGS, the technology still faces challenges such as a long granulation cycle and demanding operational control requirements. In particular, the formation of aerobic granular sludge in actual municipal wastewater takes an extended period. For example, Ni et al. (Granulation of activated sludge in a pilot-scale sequencing batch reactor for the treatment of low-strength municipal wastewater) used actual municipal wastewater to cultivate aerobic granular sludge, achieving sludge granulation after 300 days of operation. Pronk et al. (Full-scale performance of the aerobic granular sludge process for sewage treatment) reported that aerobic granular sludge cultivation took approximately five months at the Garmerwolde wastewater treatment plant in the Netherlands. Therefore, how to quickly cultivate aerobic granular sludge in actual municipal sewage remains a bottleneck problem that needs to be solved urgently in the engineering application of this technology.

[0003] Polyurethane sponge fillers can quickly form biofilms. Some scholars have used polyurethane sponge fillers to promote the rapid formation of aerobic granular sludge. However, this technology still faces the following challenges in practical applications: (1) The combination of aerobic granular sludge and carrier biofilm is prone to problems such as filler clogging and uneven mass transfer, which adversely affects the formation of aerobic granular sludge and the treatment effect of the system; (2) The long-term operation of the carrier biofilm is complicated, and the filler is easy to lose. It is necessary to set up an interception device or fix the carrier filler, which is not conducive to the stable operation of the aerobic granular sludge system. In addition, Liu Jun et al.'s study (Improving aerobic sludge granulation in sequential batch reactor by natural drying: Effluent sludge recovery and feeding back into reactor) proposed to form sludge aggregates of different sizes and promote the formation of aerobic granular sludge by first dehydrating the loose sludge, then spreading it flat, and then drying it. However, this method is complex to operate, inefficient, and has a long cycle, making it unsuitable for actual production. Therefore, it is of great practical significance and economic value to achieve the rapid formation of aerobic granular sludge simply and efficiently through technological innovation and coupling integration. Summary of the Invention

[0004] To address the challenges of the prior art, the present invention aims to provide a method for rapidly granulating sludge by enhancing the natural drying of biofilms using ferric chloride. This method can rapidly cultivate aerobic granular sludge in actual municipal wastewater, offering advantages such as simple operation, good stability, and low energy consumption.

[0005] The present invention is specifically implemented through the following technical solutions:

[0006] A method for promoting rapid sludge granulation based on ferric chloride conditioning to strengthen the natural drying of biofilm, comprising the following steps:

[0007] (1) Rapid biofilm formation: Polyurethane sponge filler is used to quickly form biofilm in the biochemical pool of the sewage treatment plant;

[0008] (2) Ferric chloride conditioning: ferric chloride solution is used to spray and condition the biofilm on the polyurethane sponge filler;

[0009] (3) Natural drying: The biofilm after spray conditioning is allowed to dry naturally;

[0010] (4) Obtaining sludge aggregates: squeezing the soft polyurethane sponge filler to cause the conditioned and dried biofilm to fall off and form sludge aggregates;

[0011] (5) Sludge granulation: The sludge aggregates are inoculated in a sequencing batch reactor, and the operating parameters are adjusted based on the characteristics of the sludge aggregates to achieve rapid aerobic granulation.

[0012] Furthermore, in the step (1), the polyurethane sponge filler has a thickness of 1-2 cm, a pore density of 45-60 ppi, and a rapid biofilm formation time of 5-15 days. After the biofilm formation is completed, the biofilm biomass per gram of polyurethane sponge filler reaches 0.85-1.25 g, and the water content of the biofilm is 90%-95% after the filler is allowed to stand for 10-20 minutes and drained.

[0013] Furthermore, in step (2), the treatment is performed by spraying ferric chloride solution with an aerosol spray, the concentration of the ferric chloride solution is 4.5-5.5 mol / L, and the spraying amount of ferric chloride is 10-20 mg FeCl3 / g biomass (equivalent to 2.28-8.24 mL FeCl3 / m 2 polyurethane filler).

[0014] Furthermore, the natural drying in step (3) is carried out by natural hanging, and the natural drying time is 12-36 hours.

[0015] Furthermore, in step (4), the dried biofilm is removed by mechanical or manual squeezing of the filler to form the desired sludge aggregates.

[0016] The sludge aggregates obtained by the steps (1) to (4) of the present invention have a moisture content of 80% to 90%, an average particle size of 150 to 300 μm, and an SVI of 1. 30 20-35mL / g, SVI 30 / SVI5 is 0.75-0.85; the structural strength of sludge aggregates with a particle size greater than 200 μm is 0.05-0.10 min -1 , the sedimentation rate is 30-80m / h.

[0017] Furthermore, in step (5), 1500-2500 mg / L of sludge aggregates are inoculated in the sequencing batch reactor, and the sedimentation time is 3-6 minutes. After running for 1-2 cycles, 1500-2500 mg / L of sludge aggregates are inoculated again, and the sedimentation time is 5-10 minutes. Then, the reactor is started to operate normally, the sedimentation time is set to 5-10 minutes, and it is run for 20-60 days to achieve aerobic sludge granulation.

[0018] The average particle size of the granulated sludge obtained in step (5) of the present invention is 300-600 μm; SVI 30 20-35mL / g; SVI 30 / SVI5≥0.90.

[0019] The average particle size of the sludge aggregates obtained by the present invention is 1-2 times higher than that of the original flocculent sludge; the obtained sludge aggregate SVI 30 Compared with the original floc sludge SVI 30 Reduced by 30%-50%; SVI of sludge aggregates obtained 30 / SVI5 compared with original floc sludge SVI 30 / SVI5 increased by 15%-20%; the active ammonia nitrogen degradation rate of the obtained sludge aggregate decreased by 65%-70% compared with the active ammonia nitrogen degradation rate of the original sludge, but the ammonia nitrogen degradation activity could be restored after 3-5 days of operation.

[0020] The advantages of the present invention are:

[0021] 1. Advantages of polyurethane sponge filler rapid film formation:

[0022] Polyurethane sponge with high pore density has a three-dimensional interconnected porous structure and a high specific surface area, which can provide a good ecological site for microbial biofilm attachment and promote the rapid formation of biofilm through physical interception and adhesion.

[0023] 2. Advantages of ferric chloride conditioning:

[0024] (1) Charge neutralization

[0025] The surface of activated sludge usually carries a negative charge (due to surface functional groups such as carboxyl and phosphate groups), which leads to electrostatic repulsion between particles and makes it difficult to aggregate. 3+ , Fe 3+ Its hydrolysis products carry strong positive charges, which can neutralize the negative charges on the surface of sludge particles, reduce the repulsive potential energy between particles (i.e., reduce the Zeta potential), and make the particles more likely to collide and combine.

[0026] (2) Adsorption bridging effect

[0027] Fe 3+ Further hydrolysis generates hydroxyl complexes (such as Fe(OH)3 colloids). These colloids have a large specific surface area and abundant surface active sites. They can connect multiple sludge particles through physical or chemical adsorption to form a "particle-colloid-particle" network structure (adsorption bridge), significantly increasing the floc size.

[0028] (3) Regulation of extracellular polymers (EPS)

[0029] EPS in sludge is the key to maintaining aggregate structure. 3+ It can complex with carboxyl, hydroxyl and other groups in EPS to form a more stable three-dimensional network structure and enhance the mechanical strength of the flocs.

[0030] Therefore, spraying saturated ferric chloride can simply and effectively promote sludge aggregation, promote sludge EPS secretion, increase sludge aggregation intensity, and strengthen sludge aggregation during drying.

[0031] 3. Advantages of polyurethane sponge filler film formation coupled with natural drying:

[0032] The natural drying process relies on environmental conditions (such as light and ventilation) and does not require additional energy input, which reduces equipment investment and operation and maintenance costs; the polyurethane sponge is corrosion-resistant and has good anti-aging properties, can be reused for a long time, and reduces the frequency of replacement; natural drying is simple, and the efficiency of sludge natural drying is improved; after natural drying, the sludge EPS secretion increases, the sludge aggregation becomes more firm, and the strength of the sludge aggregates is significantly improved; after natural drying, the moisture content of the sludge aggregates decreases significantly, and the sludge specific gravity is further increased.

[0033] 4. Sludge aggregates obtained after conditioning, drying and squeezing with ferric chloride:

[0034] The average particle size of the sludge aggregates obtained after extrusion is 150-300μm, SVI 30 20-35mL / g, SVI 30 / SVI5 is 0.75-0.85, and the structural strength of sludge aggregates with a particle size greater than 200 μm is 0.05-0.10 min -1 The sedimentation rate is 30-80m / h, and it basically has particle characteristics; the sludge aggregates are inoculated in a sequencing batch reactor and cultured in actual municipal sewage for 3-6 days. The ammonia nitrogen degradation rate returns to normal, the effluent water quality is good, and the activity recovers quickly.

[0035] 5. Inoculate sludge aggregates twice and apply shorter settling time:

[0036] A single inoculation of a low sludge volume and a short settling time enhances the selection of sludge aggregates with good settling performance. Double inoculation of sludge aggregates maintains a high sludge concentration within a short settling time, ensuring system treatment efficiency. Short settling times force slow-settling flocculent sludge to be discharged with the effluent, retaining only sludge aggregates with excellent settling performance. This "natural selection" mechanism promotes the formation of granular sludge, improving sludge density and settling efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Comparison diagram of the activated flocculent sludge in the biochemical pond (a), the sludge aggregates prepared in Example 1 (b), and the aerobic granulated sludge after 30 days of operation in actual municipal sewage (c). DETAILED DESCRIPTION

[0038] In order to make the technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0039] Example 1:

[0040] A polyurethane sponge filler (50 cm*50 cm) with a thickness of 1 cm and a pore density of 45 ppi was selected, and 1 ml of ferric chloride (4.5 mol / L) was sprayed on it, and the drying time was 12 h.

[0041] The steps include:

[0042] ①Put the polyurethane sponge filler into the aerobic pool of the sewage treatment plant for biofilm formation. The biofilm formation time of the filler is 15 days.

[0043] ② Take the polyurethane sponge filler out of the aerobic tank and hang it to drain for 16 minutes.

[0044] ③Spray 1ml of saturated ferric chloride (4.5mol / L).

[0045] ④ Dry with natural ventilation for 12 hours.

[0046] ⑤ After drying, the dried biofilm was squeezed off by mechanical squeezing, and the average particle size of the obtained sludge aggregates was 175μm, SVI 30 35mL / g, SVI 30 / SVI5 is 0.76.

[0047] ⑥Use actual municipal sewage (COD: 120-350mg / L, NH4 + -N: 15-45mg / L, PO4 3- -P: 2-8 mg / L), the above sludge aggregates were inoculated in a sequencing batch reactor, the first inoculation was 1500 mg / L, the sedimentation time was set to 3 minutes, and after running for 2 cycles, 1500 mg / L was inoculated again, the sedimentation time was set to 5 minutes, and the operation was carried out for 30 days to obtain a granular sludge with an average particle size of 325 μm; SVI 30 35mL / g; SVI 30 / SVI5 was 0.91, achieving sludge granulation.

[0048] Figure 1 The figure is a comparison of the activated flocculent sludge in the biochemical pool, the sludge aggregates prepared in this example, and the aerobic granular sludge after being cultured in actual municipal sewage and operated for 30 days.

[0049] Example 2:

[0050] Select a polyurethane sponge filler (50cm*50cm) with a thickness of 2cm and a pore density of 45ppi, spray 1ml of saturated ferric chloride (5.5mol / L), and dry it for 36h.

[0051] The steps include:

[0052] ①Put the polyurethane sponge filler into the aerobic pool of the sewage treatment plant for biofilm formation. The biofilm formation time of the filler is 15 days.

[0053] ② Take the polyurethane sponge filler out of the aerobic tank and let it hang for 16 minutes.

[0054] ③Spray 1ml of ferric chloride (5.5mol / L).

[0055] ④ Dry by natural ventilation for 36 hours.

[0056] ⑤ After drying, the dried biofilm was squeezed off by mechanical squeezing, and the average particle size of the obtained sludge aggregates was 280μm, SVI 30 25mL / g, SVI 30 / SVI5 is 0.82.

[0057] ⑥Use actual municipal sewage (COD: 120-350mg / L, NH4 + -N: 15-45mg / L, PO4 3- -P: 2-8 mg / L), the above sludge aggregates were inoculated in a sequencing batch reactor, the first inoculation was 1500 mg / L, the sedimentation time was set to 3 minutes, and after running for 2 cycles, 1500 mg / L was inoculated again, the sedimentation time was set to 5 minutes, and the reactor was run for 45 days to obtain a granular sludge with an average particle size of 510 μm; SVI 30 22mL / g; SVI 30 / SVI5 was 0.94, achieving sludge granulation.

[0058] Example 3:

[0059] Select a polyurethane sponge filler (50cm*50cm) with a thickness of 1cm and a pore density of 60ppi, spray 2ml of ferric chloride (4.5mol / L), and dry it for 12h.

[0060] The steps include:

[0061] ①Put the polyurethane sponge filler into the aerobic pool of the sewage treatment plant for biofilm formation. The biofilm formation time of the filler is 5 days.

[0062] ② Take the polyurethane sponge filler out of the aerobic tank and hang it to drain for 14 minutes.

[0063] ③Spray 2ml of saturated ferric chloride (4.5mol / L).

[0064] ④ Dry with natural ventilation for 12 hours.

[0065] ⑤ After drying, the dried biofilm was squeezed off by mechanical squeezing, and the average particle size of the obtained sludge aggregates was 255μm, SVI 30 28mL / g, SVI 30 / SVI5 is 0.79.

[0066] ⑥Use actual municipal sewage (COD: 120-350mg / L, NH4 + -N: 15-45mg / L, PO4 3- -P: 2-8 mg / L), the above sludge aggregates were inoculated in a sequencing batch reactor, the first inoculation was 1500 mg / L, the sedimentation time was set to 3 minutes, and after running for 2 cycles, 1500 mg / L was inoculated again, the sedimentation time was set to 5 minutes, and the operation was carried out for 55 days to obtain a granulated sludge with an average particle size of 530 μm; SVI 30 24mL / g; SVI 30 / SVI5 was 0.93, achieving sludge granulation.

[0067] Example 4:

[0068] Select a polyurethane sponge filler (50cm*50cm) with a thickness of 2cm and a pore density of 60ppi, spray 2ml of ferric chloride (5.5mol / L), and dry it for 36h.

[0069] The steps include:

[0070] ①Put the polyurethane sponge filler into the aerobic pool of the sewage treatment plant for biofilm formation. The biofilm formation time of the filler is 5 days.

[0071] ② Take the polyurethane sponge filler out of the aerobic tank and hang it to drain for 14 minutes.

[0072] ③Spray 2ml of saturated ferric chloride (5.5mol / L).

[0073] ④ Dry by natural ventilation for 36 hours.

[0074] ⑤ After drying, the dried biofilm was squeezed off by mechanical squeezing, and the average particle size of the obtained sludge aggregates was 290μm, SVI 30 22mL / g, SVI 30 / SVI5 is 0.84.

[0075] ⑥Use actual municipal sewage (COD: 120-350mg / L, NH4 +-N: 15-45mg / L, PO4 3- -P: 2-8 mg / L), the above sludge aggregates were inoculated in a sequencing batch reactor, the first inoculation was 1500 mg / L, the sedimentation time was set to 3 minutes, and after running for 2 cycles, 1500 mg / L was inoculated again, the sedimentation time was set to 5 minutes, and the reactor was run for 35 days. The average particle size of the granulated sludge was 591 μm; SVI 30 20mL / g; SVI 30 / SVI5 is 0.95, achieving sludge granulation.

[0076] Comparative Example 1:

[0077] Using actual municipal sewage (COD: 120-350mg / L, NH4 + -N: 15-45mg / L, PO4 3- -P: 2-8 mg / L), activated floc sludge from the biochemical pool of the sewage treatment plant was inoculated in a sequencing batch reactor. The first inoculation was 1500 mg / L, the sedimentation time was set to 3 minutes, and after running for 2 cycles, 1500 mg / L was inoculated again, the sedimentation time was set to 5 minutes, and the average particle size of the sludge obtained was 134 μm; SVI 30 75mL / g; SVI 30 / SVI5 is 0.63. After 89 days of operation, the average particle size of the granulated sludge is 335μm; SVI 30 33mL / g; SVI 30 / SVI5 is 0.90, achieving sludge granulation.

[0078] Comparative Example 2:

[0079] A polyurethane sponge filler with a thickness of 1 cm and a pore density of 45 ppi was selected, and the drying time was 12 h.

[0080] The steps include:

[0081] ①Put the polyurethane sponge filler into the aerobic pool of the sewage treatment plant for biofilm formation. The biofilm formation time of the filler is 15 days.

[0082] ② Take the polyurethane sponge filler out of the aerobic tank and hang it to drain for 15 minutes.

[0083] ③ Dry with natural ventilation for 12 hours.

[0084] ④ After drying, the dried biofilm was squeezed off by mechanical squeezing, and the average particle size of the obtained sludge aggregates was 155μm, SVI 30 40mL / g, SVI 30 / SVI5 is 0.72.

[0085] ⑤Use actual municipal sewage (COD: 120-350mg / L, NH4 + -N: 15-45mg / L, PO4 3- -P: 2-8 mg / L), the above sludge aggregates were inoculated in a sequencing batch reactor, the first inoculation was 1500 mg / L, the sedimentation time was set to 3 minutes, and after running for 2 cycles, 1500 mg / L was inoculated again, the sedimentation time was set to 5 minutes, and the operation was carried out for 30 days. The average particle size of the sludge obtained was 240 μm; SVI 30 38mL / g; SVI 30 / SVI5 is 0.83. After 65 days of operation, the average particle size of the granulated sludge is 300μm; SVI 30 35mL / g; SVI 30 / SVI5 was 0.91, achieving sludge granulation.

[0086] The embodiment described above is only a preferred solution of the present invention and does not limit the present invention in any form. Other variations and modifications are possible without exceeding the technical solution described in the claims.

Claims

1. A method for promoting rapid sludge granulation by strengthening the natural drying of biofilm by conditioning with ferric chloride, characterized in that: The following steps are involved: (1) Rapid biofilm formation: Polyurethane sponge filler is used to quickly form biofilm in the biochemical pool of the sewage treatment plant; (2) Ferric chloride conditioning: ferric chloride solution is used to spray and condition the biofilm on the polyurethane sponge filler; (3) Natural drying: The biofilm after spray conditioning is allowed to dry naturally; (4) Obtaining sludge aggregates: squeezing the soft polyurethane sponge filler to cause the conditioned and dried biofilm to fall off and form sludge aggregates; (5) Sludge granulation: The sludge aggregates are inoculated in a sequencing batch reactor, and the operating parameters are adjusted based on the characteristics of the sludge aggregates to achieve rapid aerobic granulation.

2. The method according to claim 1, characterized in that The thickness of the polyurethane sponge filler in step (1) is 1-2 cm, and the pore density is 45-60 ppi.

3. The method according to claim 1, characterized in that The rapid biofilm formation time in step (1) is 5-15 days.

4. The method according to claim 1, wherein After the biofilm is formed in step (1), the biofilm biomass per gram of polyurethane sponge filler reaches 0.85-1.25g; and after the filler is left to stand for 10-20 minutes and drained, the water content of the biofilm is 90%-95%.

5. The method according to claim 1, wherein In the step (2), a ferric chloride solution is sprayed with aerosol, and the concentration of the ferric chloride solution is 4.5-5.5 mol / L.

6. The method according to claim 1, wherein The spraying adjustment amount of ferric chloride sprayed in the step (2) is 10-20 mgFeCl3 / g biomass.

7. The method according to claim 1, characterized in that The natural drying in step (3) is carried out by natural hanging, and the natural drying time is 12-36 hours.

8. The method according to claim 1, characterized in that In the step (4), the dried biofilm is removed by mechanical or manual squeezing of the filler.

9. The method according to claim 1, characterized in that In the step (5), 1500-2500 mg / L of sludge aggregates are inoculated in the sequencing batch reactor, and the sedimentation time is 3-6 minutes. After running for 1-2 cycles, 1500-2500 mg / L of sludge aggregates are inoculated again, and the sedimentation time is 5-10 minutes. Then, the reactor is started to operate normally, and the sedimentation time is set to 5-10 minutes. After running for 20-60 days, aerobic sludge granulation can be achieved.

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