A method for increasing the yield of macroaggregates in a sidestream sludge densification process

Abstract

The application discloses a method for improving the yield of large biological aggregates in a side-flow sludge densification process, which comprises sludge activity selection, sludge aggregation and side-flow densification, in a continuous-flow activated sludge system, a large amount of inert substances and decayed sludge are screened out through a sludge activity selector, and sludge with higher activity is preferentially stored in a sludge aggregation tank, and a carbon source is provided into the aggregation tank, the metabolic capacity of the high-activity sludge under anaerobic conditions is stronger, the synthesis and secretion of EPS are carried out in a large amount, the sludge aggregation behavior is enhanced, and the active sludge is quickly adhered to each other to form large biological aggregates with the help of PAM or other cationic flocculants, if microcarriers (MC) are added at the same time, the active sludge quickly occurs colonization behavior, and is aggregated with other sludge to form LBA, and finally forms overflow sludge (OS) synthesis liquid, and then various side-flow activated sludge densification devices are used to complete the intensified separation of LBA or realize sludge granulation.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a method for improving the yield of large bioaggregates in the lateral sludge densification process. Background Technology

[0002] Sequencing batch reactors (SBRs) are the most commonly used and efficient method for cultivating aerobic granular sludge (AGS). In SBRs, the formation of AGS with high biomass, high density, and rapid settling velocity requires multiple complex cycles of filling, reaction, settling, and dewatering. Its efficiency can be affected by several factors, such as wastewater treatment volume, organic loading rate, hydrodynamic shear stress, reactor configuration, sludge retention time (SRT), and hydraulic retention time. With increasing operating loads, the efficient and continuous filling and pumping processes of SBR pumping systems remain a significant challenge, making efficient operation of SBRs for AGS cultivation extremely difficult. Therefore, in recent years, attention has turned to the application of side-stream densified activated sludge (SdAS) technology, also known as bio-physical external selector technology, to form AGS in situ within continuous-flow activated sludge systems.

[0003] SdAS, as a novel intensive strategy for continuous-flow activated sludge granulation, provides a practical approach for in-situ enhanced treatment of existing continuous-flow wastewater treatment plants. Typical upgrade methods only require the installation of a single side-flow densification device, such as using external selection methods like drum screens, hydrocyclones, baffles, stripping, or magnetic fields. Based on the gravity characteristics of granular sludge, the granular sludge is screened to form dense sludge (dAS). It is important to emphasize that "dense sludge" is essentially a mixed-state sludge that bridges the gap between flocculent and granular sludge, where the biomass component is defined as a biological aggregate.

[0004] However, due to insufficient influent carbon sources in most wastewater treatment plants in China, primary sedimentation tanks have been eliminated. This has led to problems such as high sand content and significant impacts from rainwater loads, resulting in limited granulation of activated sludge in most continuous flow activated sludge systems. Furthermore, the activated sludge itself cannot withstand mechanical damage caused by pumping or other equipment. Therefore, large-scale granulation is almost impossible in continuous flow SdAS systems in China, with large bioaggregates (LBAs) exceeding 200 μm playing a crucial role in system settling performance and nitrogen and phosphorus removal. Researchers believe that adding an anaerobic selector to provide a specific feast / famine ratio is key to the success of continuous flow granular sludge technology. However, because the inert components in the activated sludge system possess similar gravitational characteristics to granular sludge and account for over 50%, no matter how the SdAS device is configured and optimized, LBA loss due to inert material accumulation cannot be effectively avoided, with a loss rate reaching 30%–40%. This results in significant waste of energy and resources and fails to effectively enhance the system. Therefore, improving the yield of LBA in the side-flow sludge densification process is a problem that needs to be solved. Summary of the Invention

[0005] The purpose of this invention is to address the low yield of large bioaggregates in side-flow sludge densification technology, and to propose a method to improve the yield of large bioaggregates in the side-flow sludge densification process. This invention can directly select activated sludge with higher activity, discharge decaying sludge and most of the sand and gravel from the system, simultaneously improving the system's activity and the dewatering performance of excess sludge, and efficiently utilizing energy and resources. It avoids ineffective side-flow activated sludge densification processes, fully utilizing carbon sources, PAM (or other cationic flocculants), and MC, significantly increasing the proportion of LBA in the original sludge. Ultimately, it can be directly or arbitrarily coupled with a side-flow activated sludge densification device, increasing the system's LBA yield to 30-40%, providing a guarantee for further sludge densification or granulation.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for improving the yield of large bioaggregates in the side-flow sludge densification process, comprising the following steps:

[0007] Step (1): Concentrate the activated sludge after aerobic phosphorus uptake in the continuous flow system, or directly use a secondary sedimentation tank to settle the sludge. By adjustment, the MLVSS of the activated sludge reaches 5-10 g / L and the MLSS reaches 10-20 g / L. Among them, the VSS of more than 200 μm in the concentrated sludge accounts for 10%-20% of the total sludge volume.

[0008] Step (2): Adjust and set the SRT of the continuous flow system to 5-10 days, and calculate the total amount of residual sludge per day based on MLSS.

[0009] Step (3): Based on the MLSS of the concentrated sludge, obtain the total flow rate of the feed sludge (FS) and the running time of the sludge activation selector, which is 1.2 to 1.5 times the total amount of residual sludge.

[0010] Step (4): Pump the FS into the sludge activation selector. The sludge activation selector consists of a hydrocyclone and a pump set. By setting the configuration parameters and operating parameters of the hydrocyclone, the VSS / SS of the underflow sludge (US) reaches 10% to 30%. This part of the sludge contains more inert substances and low-activity sludge. As the waste sludge 1 (WAS1) discharge system, the VSS / SS of the overflow sludge (OS) reaches 60% to 90%. It is mainly the preferred sludge with high activity. Then, it is pumped into the sludge collection tank with a stirring device.

[0011] Step (5): Add carbon source, PAM (or other cationic flocculant) and microcarrier (MC) to the sludge collection tank. Use a stirring device to mix them thoroughly with OS. The stirring speed is 10-80 rpm. Mix each batch for 10-60 min to provide shear force to the activated sludge to quickly form LBA. The amount of carbon source added is converted to COD of 0.17-0.33 gCOD / L·h, the amount of PAM added is 0.1-1.0 mg / L, and the amount of MC added is 0.1-0.5 g / g VSS.

[0012] Step (6): After stirring, the OS synthesis liquid is pumped into various side-flow activated sludge densification devices through a pump assembly. By utilizing the size characteristics or rapid settling characteristics of LBA itself, LBA in the OS synthesis liquid is quickly screened and separated. Finally, the proportion of LBA in FS is increased from 10-20% to 30-40%. It can then be directly returned to the continuous flow activated sludge system, while the sludge flocs that do not form LBA are discharged from the system as waste sludge 2 (WAS2).

[0013] Step (7): When the total amount of sludge in WAS1 and WAS2 reaches the set total amount of remaining sludge, the sludge activation selector will stop operating and the remaining OS mixture in the sludge collection tank will be gradually processed.

[0014] Furthermore, in step (1), the continuous flow system includes anaerobic / aerobic, anaerobic / anoxic / aerobic, and anoxic / anaerobic / aerobic processes.

[0015] Furthermore, in step (1), the activated sludge system based on MBR in the continuous flow system adjusts the sludge concentration to the working range.

[0016] Furthermore, in step (4), the FS is pumped into the sludge activation selector in a sequential batch manner, with each batch processing flow rate being 10% to 20% of the total amount of residual sludge.

[0017] Furthermore, in step (4), each group of sludge activation selectors is equipped with at least two hydrocyclones, adjusted according to the actual treatment capacity. The inlet flow rate of each group is 3-8% of the system influent flow rate, and the overflow and underflow flow rate split ratio is 70-95% / 5-30%. The hydrocyclone includes a column, a cone, a feed inlet, an overflow outlet, and an underflow outlet. The diameter D of the column is between 50 and 150 mm, and the column height-to-diameter ratio L1 / D is 1-1.5. The height-to-diameter ratio L2 / D of the cone is 3.5-5, and the cone angle is 6-8°. The feed inlet is a cuboid structure, with an inlet area S / column diameter D. 2 The value is 0.060~0.067. The feed inlet tangentially enters the column, and the overflow portion is embedded in the column, with an embedded portion length L. v The diameter D of the column is 0.10 to 0.15 mm, and the remaining part of the overflow port protrudes from the column, with a protrusion length L. o The diameter D of the column is 0.57, and the diameter D of the overflow outlet is... o The diameter D of the column is 0.3 to 0.5 mm; the underflow outlet is connected to the conical inlet, and the length L of the underflow outlet is... u The diameter D of the column is 0.57, and the diameter of the bottom outlet is D. u The diameter D of the cylinder is 0.05 to 0.1.

[0018] Furthermore, in step (5), depending on the yield of LBA, it is selected whether MC needs to be added. MC does not have specific requirements for materials, and waste bio-activated carbon can be preferred. In terms of size: the microcarrier particles have a particle size of 10-100 μm and a particle density of 0.90-1.10 g / mL, and are characterized by being porous and having a high specific surface area of ​​100-1000 m². 2 / g, oxygen-containing functional groups (such as hydroxyl, carboxyl, etc.) are introduced on the surface of the microcarrier to increase its surface hydrophilicity, and the contact angle with water is 30-60°.

[0019] Furthermore, in step (6), the OS synthesis liquid can be connected to the side-flow activated sludge densification device through various suitable lifting methods, and then sludge densification or granulation is carried out.

[0020] The principle of this invention is as follows: In a continuous flow activated sludge system comprising both anaerobic and aerobic processes, activated sludge concentrated to a certain concentration passes through a sludge selector. This allows for the discharge of large amounts of inert matter and decaying sludge from the bottom of the selector, while sludge with higher activity is selected from the overflow and enters the sludge collection tank. After adding COD to the sludge collection tank, the metabolic activity of microorganisms in the highly active sludge under anaerobic conditions is enhanced, leading to the synthesis and secretion of EPS (explosive peroxides) using a large amount of COD. Due to its high activity, the sludge aggregation behavior is enhanced. With the help of PAM (or other cationic flocculants), the activated sludge rapidly adheres to each other to form LBA (flocculated basal body aggregates). If MC is added simultaneously, the activated sludge rapidly colonizes and aggregates with other sludge to form LBA, ultimately forming OS (sludge-on-basin) synthesis liquid. OS synthesis liquid is a mixture of flocculated sludge and sludge with high LBA content. This mixture is then processed through various side-flow activated sludge densification devices to achieve enhanced LBA separation or sludge granulation.

[0021] Beneficial effects:

[0022] (1) By configuring a sludge activation selector, the present invention can directly select activated sludge with higher activity, discharge decayed sludge and most of the sand and gravel from the system, and at the same time improve the activity of the system and the dewatering performance of the remaining sludge.

[0023] (2) This invention will make efficient use of energy and resources, avoid the ineffective side-flow activated sludge densification process, and make full use of carbon source, PAM (or other cationic flocculants) and MC to significantly increase the proportion of LBA in the original sludge.

[0024] (3) The present invention can be directly or arbitrarily coupled with a side-flow activated sludge densification device to increase the LBA yield of the system to 30-40%, providing a guarantee for SdAS technology to further realize sludge densification or granulation. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the principle of the present invention for improving the yield of large bioaggregates in a conventional AAO-secondary sedimentation tank system using a sludge densification technology.

[0026] Figure 2 The changes in MLSS and MLVSS after passing through the sludge activation selector;

[0027] Figure 3 This shows the changes in sludge dewatering performance after passing through the sludge activation selector.

[0028] Figure 4 This represents the change in the relative proportion of live and dead cells after passing through the sludge activation selector. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Combination Figure 1 As shown, this embodiment is used to realize the side-flow sludge densification technology in a conventional AAO-secondary sedimentation tank system, including a grit chamber, primary sedimentation tank, anaerobic tank, anoxic tank, aerobic tank, secondary sedimentation tank, sludge activation selector, sludge aggregation tank, and side-flow activated sludge densification device; the yield of large biological aggregates is improved. The basic overview of the wastewater treatment plant is shown in Table 1.

[0031] Table 1 Basic Overview of Wastewater Treatment Plant

[0032] Processing scale <![CDATA[40,000 m 3 / d]]> Influent COD 200~300mg / L sludge concentration ~4g / L Inlet TP 3~5mg / L SRT 10d Inlet TN 30–50 mg / L Sludge discharge volume 14t / d <![CDATA[Influent NH4 + -N]]> 25~35mg / L

[0033] Wastewater sequentially passes through a grit chamber, primary sedimentation tank, anaerobic tank, anoxic tank, aerobic tank, and secondary sedimentation tank. After nitrogen and phosphorus removal, it leaves the system. The activated sludge, after aerobic phosphorus uptake, undergoes gravity thickening in the secondary sedimentation tank, resulting in an MLVSS of 6.11 g / L, an MLSS of 12.6 g / L, and a VSS / SS ratio of 0.48. The continuous flow system's SRT is adjusted and set to 10 days. The sludge concentration in the aerobic tank is approximately 4 g / L, resulting in a calculated sludge discharge rate of 14 t / d. The total treatment capacity of the sludge active selector is set to 1.5 × 14 t / d = 21.0 t / d. With a sludge concentration of approximately 12 g / L in the secondary sedimentation tank, the daily treatment flow rate of the sludge active selector is 1750 m³ / d. 3 / d, then the processing capacity is 2×50m 3 / h=100m 3 The sludge activated selector operates for 17.5 hours per day; combined with Figure 2 As shown, when FS is pumped into the sludge activation selector, the initial VSS / SS ratio is 48.4%, and LBA accounts for 11.2% of the total sludge volume of FS. Through selection, the VSS / SS ratio of US decreases to 20.3%, and the MLSS concentration is 25.7 g / L. As the WAS1 discharge system, a total of 9.0 t / d is discharged. The VSS / SS ratio of OS reaches 71.5%, and the MLSS is 9.12 g / L. Due to the crushing effect of the swirling shear force, the LBA in OS accounts for only 7.3% of the total FS sludge volume. Figure 3 As shown, through the sludge activation selector, the CST of the sludge is reduced from 2.5 s / g SS·L⁻¹ to 2.5 s / g SS·L⁻¹. -1 Decreased to 1.5s / g SS·L in the US -1 Dehydration performance improved by 40%; combined with Figure 4 As shown, through the sludge activation selector, the proportion of live cells in the sludge increased from 39.6% in FS to 73.5% in OS, an increase of 33.9% in the proportion of live cells in the sludge. In US, the proportion of necrotic cells increased from 14.8% in FS to 24.0%, while only 5.60% of OS were necrotic cells. Further, the remaining 12.8 t / d of OS was pumped into a sludge collection tank equipped with a stirring device. Further, carbon source, PAM, and MC were added to the sludge collection tank, and the stirring device was used to thoroughly mix them with the OS. The stirring speed was 20 rpm, and each batch was stirred for 30 minutes to provide shear force to the activated sludge to rapidly form LBA. The carbon source dosage, converted to COD, was 0.33 g COD / L·h, the PAM dosage was 0.5 mg / L, and the MC dosage was 0.1 g / g. Based on the shape of the sludge itself, it is expected that the proportion of LBA in the total OS sludge in the preferred sludge can be increased from 7.3% to 50-80%. Furthermore, the OS synthesis liquid after mixing is pumped into various side-flow activated sludge densification devices through a pump assembly. Utilizing the size characteristics or rapid settling characteristics of LBA, the LBA in the OS synthesis liquid is quickly screened and separated. Ultimately, the proportion of LBA in FS is expected to increase from 11.2% to 30-40%. It can then be directly returned to the continuous flow activated sludge system, while the sludge flocs that have not formed LBA are discharged from the WAS2 system, with a total volume of 5t / d. When the total amount of sludge in WAS1 and WAS2 reaches the set total amount of remaining sludge, the operation of the sludge activation selector is stopped, and the remaining OS mixture in the sludge collection tank is gradually treated.

[0034] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the yield of large bioaggregates in a side-flow sludge densification process, characterized in that: Includes the following steps: Step (1): Concentrate the activated sludge after aerobic phosphorus uptake in the continuous flow system, or directly settle the sludge in a secondary sedimentation tank. Adjust the activated sludge so that the MLVSS reaches 5 ~ 10 g / L and the MLSS reaches 10 ~ 20 g / L. Among them, the VSS exceeding 200 μm in the concentrated sludge accounts for 10% ~ 20% of the total sludge volume. Step (2): Adjust and set the SRT of the continuous flow system to 5 ~ 10 days, and calculate the total amount of residual sludge per day based on MLSS; Step (3): Based on the MLSS of the concentrated sludge, obtain the total flow rate of the feed sludge and the running time of the sludge activation selector, which is 1.2 to 1.5 times the total amount of residual sludge. Step (4): Pump the feed sludge into the sludge activation selector. The sludge activation selector consists of a hydrocyclone and a pump set. By setting the configuration parameters and operating parameters of the hydrocyclone, the VSS / SS of the underflow sludge reaches 10% to 30% and is used as a discharge system for excess sludge. The VSS / SS of the overflow sludge reaches 60% to 90% and is then pumped into a sludge collection tank with a stirring device. Step (5): Add carbon source, PAM and microcarrier to the sludge collection tank. Use a stirring device to mix them thoroughly with the overflow sludge. The stirring speed is 10 to 80 rpm. Mix each batch for 10 to 60 minutes to provide shear force to the activated sludge to quickly form large bio-aggregates. The amount of carbon source added is equivalent to 0.17 to 0.33 g COD / L·h, the amount of PAM added is 0.1 to 1.0 mg / L, and the amount of microcarrier added is 0.1 to 0.5 g / g VSS. Step (6): The overflow sludge synthesis liquid after stirring is pumped into various side-flow activated sludge densification devices through a pump assembly. By utilizing the size characteristics or rapid settling characteristics of the large bio-aggregates, the large bio-aggregates in the overflow sludge synthesis liquid are quickly screened and separated. Finally, the proportion of large bio-aggregates in the feed sludge increases from 10-20% to 30-40%. Then, it can be directly returned to the continuous flow activated sludge system, while the sludge flocs that do not form large bio-aggregates are discharged as excess sludge in the secondary discharge system. Step (7): When the total amount of residual sludge one and residual sludge two reaches the set total amount of residual sludge, the operation of the sludge activation selector is stopped, and the remaining overflow sludge mixture in the sludge collection tank is gradually processed.

2. The method for improving the yield of large bioaggregates in the side-flow sludge densification process according to claim 1, characterized in that: In step (1), the continuous flow system includes anaerobic / aerobic, anaerobic / hypoxic / aerobic, and hypoxic / anaerobic / aerobic processes.

3. The method for improving the yield of large bioaggregates in the side-flow sludge densification process according to claim 1, characterized in that: In step (1), the activated sludge system based on MBR in the continuous flow system adjusts the sludge concentration to the working range.

4. The method for improving the yield of large bioaggregates in the side-flow sludge densification process according to claim 1, characterized in that: In step (4), the feeding sludge is pumped into the sludge activation selector in a sequential batch manner, and the flow rate of each batch is 10% to 20% of the total amount of residual sludge.

5. The method for improving the yield of large bioaggregates in the side-flow sludge densification process according to claim 1, characterized in that: In step (4), each sludge activation selector is equipped with at least two hydrocyclones, with each set having an inlet flow rate of 3-8% of the system's influent flow rate, and an overflow-to-bottom flow rate split ratio of 70-95% / 5-30%. Each hydrocyclone comprises a column, a cone, an inlet, an overflow outlet, and a bottom flow outlet. The column diameter D is between 50 and 150 mm, and the column height-to-diameter ratio L1 / D is 1-1.

5. The cone height-to-diameter ratio L2 / D is 3.5-5, and the cone angle is 6-8°. The inlet is a cuboid, with an inlet area S / column diameter D of 0.060-0.

067. The inlet tangentially enters the column, and the overflow outlet is partially embedded in the column, with an embedded length L. v The diameter D of the column is 0.10 ~ 0.15 mm, and the remaining part of the overflow port protrudes from the column, with a protrusion length L. o The diameter D of the column is 0.57, and the diameter D of the overflow outlet is... o The diameter D of the column is 0.3 ~ 0.5; the underflow outlet is connected to the conical outlet, and the length L of the underflow outlet is... u The diameter D of the column is 0.57, and the diameter of the bottom outlet is D. u The diameter D of the cylinder is 0.05 ~ 0.

1.

6. The method for improving the yield of large bioaggregates in the side-flow sludge densification process according to claim 1, characterized in that: In step (5), depending on the yield of the large bio-aggregates, it is determined whether microcarriers need to be added. The microcarriers are selected from discarded bio-activated carbon. In terms of size, the microcarrier particles have a diameter of 10~100 μm and a particle density of 0.90~1.10 g / mL. They are porous and have a high specific surface area of ​​100~1000 m². 2 / g, oxygen-containing functional groups are introduced onto the surface of the microcarrier, resulting in a contact angle of 30~60° with water. o .

7. The method for improving the yield of large bioaggregates in the side-flow sludge densification process according to claim 1, characterized in that: In step (6), the overflow sludge synthesis liquid is connected to the side-flow activated sludge densification device by means of lifting, and then the sludge densification or granulation is carried out.

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