Method for enhancing the treatment effect of a biological reactor by using sludge gasification residues

Abstract

This invention belongs to the field of wastewater biological treatment technology and discloses a method for enhancing the treatment effect of a bioreactor using sludge gasification residue. The method includes the following steps: a) drying, grinding, and sieving the sludge gasification residue to obtain sludge gasification residue with a particle size <80 μm; b) modifying the sludge gasification residue with a particle size <80 μm using polyethyleneimine; c) adding the modified sludge gasification residue to the bioreactor. Under anoxic and aerobic conditions, a biofilm forms on the sludge gasification residue, inhibiting filamentous bacterial expansion, promoting sludge floc granulation, and degrading and removing pollutants from the wastewater. This invention utilizes the modified sludge gasification residue, which forms a biofilm on the residue, inhibiting filamentous bacterial expansion, and promoting sludge floc granulation within 20-30 days, shortening the sludge granulation cycle and improving nitrogen and phosphorus removal efficiency.

Description

Technical Field

[0001] This invention belongs to the field of wastewater biological treatment technology and relates to a method for enhancing the treatment effect of a bioreactor by utilizing sludge gasification residue. It is applicable to bioreactors for urban domestic sewage and industrial organic wastewater. Background Technology

[0002] In biological wastewater treatment processes, adding biofilm carriers to bioreactors is one of the core methods to improve treatment efficiency. Biofilm carriers are materials that provide a carrier for microbial attachment, growth, and reproduction. They can enhance the retention of microorganisms and the interception of pollutants, increase the biomass of microorganisms in the reactor, improve the reactor's resistance to shock loads, and thus fully leverage the advantages of biological treatment and stabilize effluent quality.

[0003] Currently, biofilm carriers commonly used in wastewater biological treatment are classified into inorganic and organic types based on their material properties. Inorganic carriers are mostly granular materials, including quartz sand, ceramsite, slag, and activated carbon. However, quartz sand and activated carbon are relatively expensive, and ceramsite and slag have insufficient biofilm adhesion performance and compatibility with nitrogen and phosphorus removal processes. Organic carriers include natural materials such as agar and sodium alginate, as well as chemically synthesized materials such as polyethylene (PE) and polyurethane foam (PUF). However, they are easily degraded by microorganisms, have short service lives, and frequent replacements can significantly increase reactor operating costs.

[0004] With the continuous improvement of wastewater nitrogen and phosphorus removal standards, existing carrier systems are gradually showing insufficient adaptability: 1) Insufficient synergy in wastewater nitrogen and phosphorus removal: The simultaneous nitrification-denitrification efficiency (SND) of conventional carrier-free bioreactors is low, the rate matching of nitrification, denitrification and phosphorus removal processes is poor, and excessive growth of filamentous bacteria is prone to occur in the later stage, resulting in loose microbial floc structure, affecting the treatment efficiency of the reactor and the stability of effluent quality. 2) Limited optimization effect of existing carriers on microbial flocs: Existing carriers are difficult to effectively promote the compaction of microbial flocs in bioreactors, and cannot form a stable sludge particle structure, thus affecting the reactor's shock resistance and operational stability.

[0005] Sludge gasification residue, as the main solid byproduct of sludge gasification treatment, has an extremely low resource utilization rate. The industry primarily treats it through stockpiling and landfilling, which not only wastes resources but also easily leads to environmental problems such as land occupation and secondary pollution. Furthermore, the particle size of commonly used carriers in the industry is concentrated in the 50-300 μm range. Research on the nitrogen and phosphorus removal efficiency of small-particle-size carriers (below 50 μm) is relatively scarce, failing to fully explore the potential advantages of small-particle-size carriers for microbial attachment and pollutant mass transfer. This has become one of the key factors restricting the optimization of wastewater biological treatment processes. Summary of the Invention

[0006] This invention addresses the technical problems of low SND efficiency and inability to form stable sludge particles in existing biofilm carriers of bioreactors. It provides a method to enhance the treatment effect of bioreactors using sludge gasification slag. By using modified sludge gasification slag, a biofilm is formed on the sludge gasification slag, which inhibits the expansion of filamentous bacteria and promotes sludge floc granulation in 20-30 days, shortening the sludge granulation cycle and improving the nitrogen and phosphorus removal effect.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a method for enhancing the treatment effect of a bioreactor using sludge gasification residue, comprising the following steps:

[0009] a. The sludge gasification residue is dried, ground and sieved to obtain sludge gasification residue with a particle size of <80 μm;

[0010] b. Modification of sludge gasification residue with a particle size <80 μm using polyethyleneimine;

[0011] c. The modified sludge gasification residue is added to the bioreactor. Under anoxic and aerobic conditions, a biofilm forms on the sludge gasification residue, which inhibits the expansion of filamentous bacteria, promotes the granulation of sludge flocs, and degrades and removes pollutants in the wastewater.

[0012] In the above technical solution, the dosage of the modified sludge gasification residue is 200~1000 mg / L.

[0013] In the above technical solution, the particle size of the sludge gasification residue in step a is <40 μm, 40~60 μm, or 60~80 μm, with <40 μm sludge gasification residue being preferred for modification and addition to the bioreactor.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] This invention uses sludge gasification residue as a biofilm carrier: 1) Sludge gasification residue has excellent biofilm adhesion performance. Particle and biofilm adhesion can be observed 10 days after addition. Later, it can densify the sludge flocs in the reactor and form stable particles, effectively inhibiting the excessive growth of filamentous bacteria, solving the problem of loose floc structure in blank reactors, and improving the reactor's resistance to shock loads. 2) Sludge gasification can significantly transform heavy metals from easily migrating forms into stable residues, achieving effective passivation and solidification. Sludge gasification residue has stable chemical properties, is not easily degraded by microorganisms, and has a much longer service life than organic carriers. Simultaneously, as a granular material, it has good contact with wastewater and microorganisms in the reactor, allowing for direct addition without modifying existing reactors, demonstrating strong process adaptability. 3) The long service life of the sludge gasification residue carrier reduces the frequency and cost of carrier replacement. At the same time, it improves the reactor's nitrogen and phosphorus removal efficiency, enhances the stability of effluent water quality, and reduces subsequent treatment costs and compliance rectification costs caused by water quality fluctuations. 4) It enables the resource utilization of sludge gasification residue, reducing the storage, transportation, and other treatment costs for enterprises. A single plant can save tens to hundreds of thousands of yuan in annual solid waste treatment costs depending on the amount of sludge gasification residue generated. 5) It does not require modification of existing bioreactors, making it easy to quickly promote in small and medium-sized wastewater treatment plants. After promotion, it can further reduce the overall wastewater treatment cost of the industry. Attached Figure Description

[0016] Figure 1 Microscopic images of sludge samples from reactors R1 to R4 after 2, 14, and 87 days of sludge gasification residue addition.

[0017] Figure 2 The synchronous nitrification and denitrification rates of each reactor at different operating times in the first stage.

[0018] Figure 3 The specific denitrification rate is the value of each reactor at different operating times during the first stage.

[0019] Figure 4 The specific nitrification rate is the value of each reactor at different operating times in the first stage.

[0020] Figure 5 The specific phosphorus release of each reactor at different operating times in the first stage.

[0021] Figure 6 The specific phosphorus uptake of each reactor at different operating times in the first stage. Detailed Implementation

[0022] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the test methods in the following embodiments are conventional methods.

[0023] Simultaneous nitrification-denitrification efficiency (SND efficiency): is a key indicator for measuring the synergistic effect of nitrification and denitrification during biological nitrogen removal from wastewater.

[0024] Specific denitrification rate: The amount of denitrification reaction per unit mass of microorganisms per unit time, expressed in mg / (g·h), reflecting the denitrification capacity of microorganisms.

[0025] Specific nitrification rate: The amount of nitrification reaction per unit mass of microorganisms per unit time, expressed in mg / (g·h), reflecting the nitrification capacity of microorganisms.

[0026] Specific phosphorus release: The amount of phosphorus released per unit mass of polyphosphate-accumulating bacteria under anaerobic conditions, expressed in mg / g, reflecting the anaerobic phosphorus release capacity of polyphosphate-accumulating bacteria.

[0027] Specific phosphorus uptake rate: The amount of phosphorus absorbed by a unit mass of polyphosphate-accumulating bacteria under aerobic conditions, expressed in mg / g, reflecting the aerobic phosphorus uptake capacity of polyphosphate-accumulating bacteria.

[0028] Sludge pyrolysis gasification residue (SSGA) is the solid residue after sludge is pyrolyzed and gasified at 400~1100℃. It has the following chemical composition: SiO2 14.4~36.2%, Al2O3 4.0~14.9%, Fe2O3 5.4~15.6%, CaO 4.7~49.9%, P2O5 0.1~26.8% and other inorganic oxides. It has a porous structure and a specific surface area of ​​15~30 m². 2 / g, density 1.2~1.8 g / cm³ 3 .

[0029] Example 1

[0030] 1.1 Pretreatment of sludge gasification residue

[0031] The raw sludge gasification residue was dried, ground, and sieved to obtain sludge gasification residue with three particle sizes: <40 μm, 40~60 μm, and 60~80 μm, which were then sealed for later use.

[0032] 1.2 Modification of sludge gasification residue

[0033] The above-mentioned sludge gasification residues of different particle sizes were modified using polyethyleneimine (PEI) or ferric chloride (FeCl3) as follows: 1) PEI solutions with mass gradient concentrations of 0.5%, 0.75%, 1%, 1.5%, and 2% were prepared; FeCl3 solutions with molar gradient concentrations of 0.02 mol / L, 0.04 mol / L, 0.06 mol / L, 0.08 mol / L, 0.1 mol / L, and 0.2 mol / L were prepared, and the pH of each FeCl3 solution was adjusted to 2.7 ± 0.05; a deionized water solution was used as a control group. 2) 3 g of sludge gasification residues of three or more particle sizes were respectively placed into 50 mL of the above-mentioned solutions of corresponding concentrations, stirred at room temperature for 1 h with a magnetic stirrer, filtered, washed, and dried at 80℃ for 2 h. 3) The Zeta potential of all particles was measured.

[0034] The results showed that the potential of the <40 μm sludge gasification slag modified with 0.75% PEI (-1.9084 mV) was higher than that of the control group (-2.1157 mV), and not significantly different from that of the 40–60 μm and 60–80 μm sludge gasification slag modified with 0.75% PEI. This is because PEI modification can impart surface viscosity and stable charge characteristics to the sludge gasification slag particles, effectively improving the physicochemical properties of the carrier surface and compensating for the lack of biocompatibility of the original gasification slag.

[0035] 1.3 The role of sludge gasification residue in the investigation of a gradual addition strategy was adopted.

[0036] A sequencing batch reactor (SBR) was used, consisting of four groups (R1, R2, R3, and R4), each with an effective volume of 10 L and a height-to-diameter ratio (H / D) of 2.18 to ensure good hydraulic flow. The influent to the SBR was simulated municipal sewage, with the composition shown in Table 1. The pH of the simulated municipal sewage was controlled at 7.8–8.0. The inoculum sludge was flocculent activated sludge from the aeration tank of a wastewater treatment plant in Zhengzhou (SRT approximately 15–30 days). The initial sludge concentration (MLSS) was controlled at 3000–4000 mg / L, the MLVSS / MLSS ratio was approximately 0.65–0.75, the initial SVI was 150–200 mL / g, and the settling performance was generally good.

[0037] Table 1 Composition of simulated urban domestic sewage

[0038]

[0039] The sequencing batch reactor (SBR) was operated as follows: one operating cycle was 6 hours, with 4 cycles per day, including 1 hour of influent (stirring for the first 15 minutes), 1 hour of settling (stirring for the last 15 minutes), 2 hours of aeration (aeration + stirring), 5 minutes of sedimentation, 10 minutes of effluent discharge, and 105 minutes of settling. The stirring speed was 100 pm, and the dissolved oxygen concentration was 3-5 mg / L. 3.8 L of effluent was discharged per cycle, leaving a residual volume of 1.5 L. The reactor temperature was maintained at 20-28°C, and the initial pH was 7.5. The acclimation of the inoculum sludge was completed after 60 days of operation according to this protocol.

[0040] The gradual addition strategy uses sludge gasification residue of three particle sizes modified with 0.75% PEI.

[0041] 1.3.1 First-stage screening of suitable particle size for sludge gasification residue

[0042] Phase 1 Dosing Plan: No sludge gasification residue is added to R1. For R2-R4, 10 g of modified sludge gasification residue (<40 μm, 40-60 μm, and 60-80 μm respectively) is added (equivalent to 1 g per L of reactor). After addition, the mixture in the reactor is thoroughly stirred to ensure uniform distribution of the sludge gasification residue within the reactor, without sedimentation or accumulation. Phase 1 operation will run from December 24, 2024 to March 30, 2025.

[0043] 1) Sludge floc samples were collected from each sequencing batch reactor after 2 days (December 25, 2024), 14 days (January 6, 2025), and 87 days (March 20, 2025) of adding sludge gasification residue to the reactor. The structure of microbial flocs, biofilm attachment, and microbial growth status (such as the growth of filamentous bacteria) were observed under a microscope.

[0044] Figure 1 Microscopic images of sludge samples from reactors R1 to R4 after 2, 14, and 87 days of sludge gasification residue addition. It can be seen that the sludge gasification residue, as a biofilm carrier, possesses excellent biofilm adhesion performance. Particle and biofilm adhesion can be observed as early as 14 days after addition. Later, it can densify the sludge flocs within the reactor and form stable particles, effectively inhibiting the excessive growth of filamentous bacteria.

[0045] 2) Sludge floc samples were collected from the reactors after 3 days (December 26, 2024), 17 days (January 9, 2025), 24 days (January 16, 2025), 66 days (February 27, 2025), 74 days (March 7, 2025), 80 days (March 13, 2025), and 87 days (March 20, 2025) following the addition of sludge gasification residue. The particle size of the sludge flocs was measured, and the results are shown in Table 2. It can be seen that although the particle size of R3 and R4 increases relatively quickly, combined with... Figure 1 R3 and R4 sludge gasification residues adhered to the outside of the particles, failing to achieve a core structure based on the sludge gasification residue powder. Therefore, modified sludge gasification residues with a particle size <40 μm (400 mesh) were selected. These residues have a high degree of size matching with sludge flocs, allowing them to embed within the flocs to form a "core-shell" structure, which is more conducive to binding with sludge. Furthermore, the porous structure of the sludge gasification residues provides numerous attachment sites for microorganisms, promoting the secretion of extracellular polymeric substances (EPS). The Fe, Ca, and Al oxides within the residues can form coordination bonds with the carboxyl and hydroxyl groups in the EPS, significantly enhancing the strength of the particle structure.

[0046] Table 2. Sludge floc particle size at different sampling times in the first stage

[0047]

[0048] 3) Effluent samples were collected from each reactor group after 7 days (December 30, 2024), 10 days (January 2, 2025), 17 days (January 9, 2025), 25 days (January 17, 2025), 64 days (February 25, 2025), 71 days (March 4, 2025), and 78 days (March 11, 2025) following the addition of sludge gasification residue. Key nitrogen and phosphorus removal indicators such as SND efficiency, specific denitrification rate, specific nitrification rate, specific phosphorus release, and specific phosphorus uptake were detected and calculated. The impact of sludge gasification residue of different particle sizes on reactor treatment efficiency was analyzed.

[0049] The average values ​​of nitrogen and phosphorus removal indicators for each reactor during the first stage of operation are shown in Table 3. It can be seen that adding modified sludge gasification slag with a particle size of <40 μm to R2 can significantly improve the reactor's SND efficiency, specific phosphorus release, and specific phosphorus uptake rate. This is because the P2O5 content in the sludge gasification slag can reach 10-20%, which is gradually released during wastewater treatment, assisting in phosphorus removal while achieving internal phosphorus resource recycling; the abundant CaO (4.7-49.9%) and A2O3 (4.0-14.9%) in the sludge gasification slag can react with phosphates, assisting in chemical phosphorus removal, and increasing the total phosphorus removal rate to 85-95%.

[0050] Table 3. Average values ​​of nitrogen and phosphorus removal indicators for the first stage of transport (R1-R4)

[0051]

[0052] Figure 2 The values ​​represent the simultaneous nitrification and denitrification (SND) rates of each reactor at different operating times during the first stage. It can be seen that R1 has the lowest SND efficiency and R2 has the highest SND efficiency during the first stage of operation.

[0053] Figure 3 The values ​​represent the specific denitrification rates of each reactor at different operating times during the first stage. It can be seen that R1 exhibits the highest specific denitrification rate during the first stage of operation.

[0054] Figure 4 The values ​​represent the specific nitrification rates of each reactor at different operating times during the first stage. It can be seen that R1 has the highest specific nitrification rate in the initial hour of aeration, while R3 exhibits the best nitrification effect throughout the entire aeration process.

[0055] Figure 5 The values ​​represent the specific phosphorus release of each reactor at different operating times during the first stage. It can be seen that R2 exhibits the highest specific phosphorus release during the first stage of operation.

[0056] Figure 6 The values ​​represent the specific phosphorus uptake of each reactor at different operating times during the first stage. It can be seen that R2 has the highest specific phosphorus uptake in the first hour of aeration, while R3 exhibits the best phosphorus uptake and nitrification effect throughout the entire aeration process.

[0057] In summary, considering SND efficiency, nitrogen and phosphorus removal rates, and sludge particle size, R2 exhibits the best treatment performance.

[0058] 1.3.2 Second-stage screening of modified gasification slag addition amount

[0059] Phase II Dosing Plan: In R1, 2 g of <40 μm sludge gasification residue will be added; in R2, 6 g of <40 μm sludge gasification residue will continue to be added; R3 and R4 will be shut down. Phase II operation will run from April 3, 2025 to April 30, 2025.

[0060] In the second stage, sludge gasification residue was added to the reactors for 1 day (April 3, 2025), 2 days (April 4, 2025), 5 days (April 7, 2025), 15 days (April 17, 2025), 22 days (April 24, 2025), and 28 days (April 30, 2025). Sludge floc samples were collected from each reactor, and the particle size of the sludge flocs was measured. The results are shown in Table 4. It can be seen that in R1, adding only 2 g of <40 μm sludge gasification residue resulted in a more significant increase in sludge particle size, shortening the sludge granulation cycle from the traditional 60+ days to 20-30 days. In contrast, in R2, a cumulative addition of 16 g of <40 μm sludge gasification residue resulted in a smaller increase in sludge particle size in the second stage compared to the first stage.

[0061] Table 4. Sludge floc particle size at different sampling times in the second stage.

[0062]

[0063] 1.3.3 The third stage examines the effect of modified gasification slag on the formation of sludge particles.

[0064] The third phase of the dosing plan is as follows: 6 g of <40 μm sludge gasification residue will be added to R1; 2 g of <40 μm sludge gasification residue will be added to R2; R3 and R4 will be shut down. The third phase of operation will run from May 12, 2025 to June 11, 2025.

[0065] In the third stage reactor, sludge gasification residue was added for 1 day (May 12, 2025), 10 days (May 21, 2025), 16 days (May 27, 2025), 25 days (June 5, 2025), and 31 days (June 11, 2025). Sludge floc samples were collected from each reactor group, and the particle size of the sludge flocs was measured. The results are shown in Table 5. It can be seen that a total of 8 g of <40 μm sludge gasification residue was added in R1, and a total of 18 g of <40 μm sludge gasification residue was added in R2. Although the particle size of the sludge particles in R1 and R2 further increased, clogging of the aeration discs occurred in both reactors, affecting normal aeration. This indicates that to ensure the normal operation of the reactor, the sludge particle size should be kept within a reasonable range and should not be too large.

[0066] Table 5. Sludge floc particle size at different sampling times in the third stage.

[0067]

[0068] In summary, through three-stage comparative experiments, the optimal dosage of <40 μm sludge gasification residue was determined to be 2 g (equivalent to 0.2 g per 1L reactor). At this dosage, the sludge particle size increased significantly, the granulation cycle was shortened, and the normal operation of the reactor was not affected.

[0069] 1.4 Engineering Examples

[0070] Project Overview: SBR pilot-scale reactor, effective volume 1.4 m³ 3 The inoculated sludge was flocculent activated sludge from the aeration tank of a wastewater treatment plant in Zhengzhou City, with MLSS of 3500 mg / L and SVI of 180 mL / g. The gasification slag parameters were: 0.75% PEI-modified <40 μm sludge gasification slag powder, with a dosage of 200 mg / L.

[0071] After adding gasification slag, samples were taken at different stages of a certain operating cycle and compared with the data before operation without adding gasification slag, as shown in Tables 6 and 7. It can be seen that after adding gasification slag, the removal rate of nitrate nitrogen increased by 3%, the removal rate of phosphate increased by 12%, and the biochemical oxygen demand increased by 1%.

[0072] Table 6. Removal efficiency of nitrate nitrogen and phosphate without gasification slag

[0073]

[0074] Table 7. Removal efficiency of nitrate nitrogen and phosphate from gasified slag

[0075]

[0076] The embodiments described above are merely preferred embodiments of the present invention and are only used to explain the present invention. They are not intended to limit the scope of the present invention. For those skilled in the art, other implementation methods can be easily made by substitution or modification based on the technical content disclosed in this specification. Therefore, all changes and improvements made on the principle of the present invention should be included within the scope of the patent application of the present invention.

Claims

1. A method for enhancing the treatment effect of a bioreactor using sludge gasification slag, characterized in that, Includes the following steps: a. The sludge gasification residue is dried, ground and sieved to obtain sludge gasification residue with a particle size of <80 μm; b. Modification of sludge gasification residue with a particle size <80 μm using polyethyleneimine; c. The modified sludge gasification residue is added to the bioreactor. Under anoxic and aerobic conditions, a biofilm forms on the sludge gasification residue, which inhibits the expansion of filamentous bacteria, promotes the granulation of sludge flocs, and degrades and removes pollutants in the wastewater.

2. The method according to claim 1, characterized in that, The dosage of the modified sludge gasification residue is 200~1000 mg / L.

3. The method according to claim 1, characterized in that, The particle size of the sludge gasification residue mentioned in step a is <40 μm, 40~60 μm, or 60~80 μm.

Images