A double biofilm sewage treatment process for deep denitrification and dephosphorization coupled with sludge reduction

Abstract

The double biofilm sewage treatment process for deep denitrification and dephosphorization coupled with sludge reduction belongs to the technical field of sewage treatment. The process is composed of an anoxic biofilm reaction tank, an aerobic biofilm reaction tank and a ferric autotrophic denitrification biofilter, and high-efficiency denitrification and dephosphorization of sewage is achieved through the double biofilm sewage treatment process. In the front-end biofilm reaction tank, denitrification and dephosphorization and in-situ sludge reduction are mainly carried out, and in the ferric autotrophic denitrification biofilter, deep denitrification and dephosphorization are mainly carried out. The protozoa and metazoan food chain of the aerobic biofilm reaction tank is used to prey on the residual sludge, achieving the effect of zero residual sludge production. By adjusting the reflux ratio of the ferric ion-containing reflux liquid generated by the ferric autotrophic denitrification biofilter to change the concentration of ferric ions, the number and community structure of microorganisms are effectively controlled, and the control of sludge predation is achieved, improving the sludge reduction effect. The process has obvious effect, can be operated stably for a long time, and is suitable for engineering application.

Description

Technical Field

[0001] This invention relates to the fields of wastewater treatment and sludge treatment technology, specifically a wastewater treatment process that combines deep nitrogen and phosphorus removal with in-situ sludge reduction. Background Technology

[0002] Due to urbanization and economic development, the amount of urban wastewater generated and treated has increased significantly in recent years. Simultaneously, the standards for wastewater discharge and the control of byproducts from the treatment process have become increasingly stringent. Many wastewater treatment plants face the challenge of upgrading and retrofitting their processes. Furthermore, the low carbon-to-nitrogen ratio of municipal wastewater is unfavorable for activated sludge treatment. Additionally, the activated sludge process generates a large amount of sludge, and this amount increases with the volume of treated wastewater. The treatment of this excess sludge presents drawbacks such as high costs, imperfect technology, and the potential for secondary pollution.

[0003] To address increasingly stringent municipal wastewater discharge standards and reduce the amount of residual sludge generated during treatment, researchers have proposed numerous solutions. Patent CN202410752286.2 employs a biological treatment process for low C / N wastewater, integrating anaerobic and aerobic processes to effectively improve nitrogen and phosphorus removal efficiency. However, this process requires post-treatment, necessitating the construction of additional operating units and increasing operating costs. Patent CN201711429308.8 utilizes a biofilm-enhanced denitrification process, further optimizing the micro-ecological environment with biological packing material, achieving good denitrification results. However, this process still faces the problem of residual sludge treatment. Patent CN201810999406.3 employs a plug-flow coupled wastewater treatment device with fixed post-biofilm carrier packing material. However, this device still requires the addition of phosphorus removal chemicals and regular sludge removal, leaving the residual sludge problem unresolved. This invention eliminates the need for additional sludge treatment equipment and external carbon sources. Addressing the low C / N ratio of municipal wastewater and the large amount of residual sludge generated by existing activated sludge processes, it applies a dual biofilm wastewater treatment process to significantly reduce the generation of residual sludge while performing deep nitrogen and phosphorus removal on wastewater, thus meeting the needs of modern wastewater treatment plants. Summary of the Invention

[0004] To address the shortcomings of existing technologies and achieve efficient nitrogen and phosphorus removal from wastewater while simultaneously reducing sludge volume in situ, this invention designs a dual-biofilm wastewater treatment process that couples deep nitrogen and phosphorus removal with sludge reduction. The structure of this wastewater treatment process is shown in the attached figure. Figure 1As shown in the diagram, the process flow is as follows: The effluent from the primary sedimentation tank 1 enters the anoxic biofilm reactor 3 via the lift pump 2, and then flows into the aerobic biofilm reactor 4. The effluent from the primary biofilm reactor flows into the iron autotrophic denitrification biofilter 5. The effluent from the aerobic biofilm reactor is returned to the anoxic biofilm reactor via the return liquid 1 through the return device 6. Part of the effluent from the iron autotrophic denitrification biofilter is returned to the anoxic biofilm reactor via the return liquid 2 through the return device 7.

[0005] The process unit consists of an anoxic biofilm reactor, an aerobic biofilm reactor, and an iron-autotrophic denitrification filter. The front end comprises the anoxic and aerobic biofilm reactors. The anoxic reactor primarily performs denitrification, while the aerobic reactor primarily performs nitrification to remove ammonia nitrogen from the wastewater. It also provides a favorable growth environment for protozoa and metazoa, which prey on the excess sludge produced by the system, thus achieving in-situ sludge reduction. The rear end of the process is an iron-autotrophic denitrification biofilter, whose packing material is covered with a biofilm formed by iron-autotrophic denitrifying bacteria, providing deep denitrification and phosphorus removal from the front-end effluent. Return effluent 1 is mainly for nitrification liquor recirculation, returning the water containing nitrate and nitrite nitrogen from the aerobic biofilm reactor to the anoxic biofilm reactor for denitrification treatment. Return liquid 2 mainly involves the return of water containing iron ions. Return liquid 2 is returned to the front-end biofilm reactor, which further enhances the denitrification capacity of the front-end biofilm reactor by promoting electron transfer. At the same time, iron ions have a certain control effect on protozoa and metazoa. Iron ions can control the number and community structure of microorganisms, avoiding damage to the functional flora of the aerobic biofilm reactor. It can also regulate the sludge predation ability of protozoa and metazoa, thus controlling the sludge reduction performance of the process.

[0006] This invention utilizes a dual-biofilm wastewater treatment process that couples deep nitrogen and phosphorus removal with sludge reduction. The technical requirements are as follows: Fixed biological bed packing is used in both the anoxic and aerobic biofilm reactors. The optimal solution is a fixed biological bed packing assembled from MBR curtain-type fabric, placed in both the anoxic and aerobic biofilm reactors at the front end. The filling ratio of the biological bed carrier should be between 20% and 80%, with the optimal filling ratio being between 60% and 80%. The iron autotrophic denitrification biofilter packing is mixed by direct particle mixing. A mixture of limestone, siderite, and magnetite is uniformly mixed and filled into the iron autotrophic denitrification biofilter device. The optimal biofilter packing is a mixture of limestone, siderite, and magnetite of the same particle size, directly mixed and filled at a volume ratio of 1:2:1 (V / V / V). The aerobic biofilm reactor is continuously aerated to ensure that the dissolved oxygen level is controlled between 1 and 5 mg / L; the power of the booster pump is adjusted to ensure that the hydraulic retention time between the aerobic and anoxic biofilm reactors is controlled between 12 and 24 hours; the operating parameters of the reflux device are controlled to ensure that the reflux ratio of reflux liquid 1 is controlled between 60 and 120%, and the reflux ratio of reflux liquid 2 is controlled between 60 and 100%.

[0007] The technical principle of this invention is as follows: In treating pollutants in wastewater, this invention applies a dual biofilm wastewater treatment process, discovering its ability to deeply remove pollutants from water bodies. The downstream iron-autotrophic denitrifying biofilter not only enhances the overall system's nitrogen and phosphorus removal capabilities, achieving deep nitrogen and phosphorus removal from the wastewater, but also, the iron ions in the reflux liquid 2 enrich the interspecies electron transfer mechanisms of microorganisms, promoting the electron transfer rate of microorganisms and significantly increasing the activity of denitrifying bacteria in the upstream biofilm reactor, especially the denitrifying bacteria in the anoxic biofilm reactor. Simultaneously, it enriches the denitrifying bacteria in the anoxic biofilm reactor and the nitrifying bacteria in the aerobic biofilm reactor, thereby improving the treatment performance of the biofilm reactor. By controlling the reflux ratio of reflux liquid 2, the denitrification capacity of the biofilm reactor, especially the denitrification capacity of the anoxic biofilm reactor, can be regulated.

[0008] Regarding the reduction of excess sludge, this invention utilizes a dual biofilm system, significantly reducing the generation of excess sludge at its source. Simultaneously, protozoa / metazoa are inoculated into the aerobic biofilm reactor, ensuring that all excess sludge generated by the dual biofilm system is preyed upon. Within this system, this invention reveals the regulatory role of iron ions on protozoa / metazoa in the upstream aerobic biofilm reactor. Since iron ions have a certain controlling and regulatory effect on microorganisms, the iron ions contained in the return liquid 2 also control the quantity and community structure of microorganisms. Iron ions cause succession in the microorganism community, with protozoa such as ciliates and metazoa such as nematodes and rotifers, which are highly adaptable to iron ions, gradually becoming the dominant species, thus stabilizing the operation of this excess sludge predation system. By controlling the return ratio of the return liquid 2 in this system, the sludge reduction capacity of the system can be further regulated.

[0009] The iron ion concentration inside the front-end biofilm reactor plays a regulatory role in the denitrification and sludge reduction capabilities of this process. During implementation, the reflux ratio of the return liquid 2 should be controlled to prevent excessive iron ion concentration in the biofilm reactor. The reflux ratio should be maintained at approximately 60%-100% to ensure that the iron ion concentration has a positive promoting effect on the biofilm reactor.

[0010] Specific process implementation steps:

[0011] Step 1: Fixed biological bed packing material is loaded into the anoxic and aerobic biofilm reactors at a filling ratio of 20%–80%. Iron ore packing material is uniformly mixed and used as a biofilm composite carrier, then filled into the iron autotrophic denitrification biological filter. Primary sedimentation wastewater is continuously fed into this dual biofilm treatment process. Activated sludge is exogenously inoculated into the anoxic and aerobic biofilm reactors for biofilm formation. Autotrophic denitrifying bacteria are inoculated into the iron autotrophic denitrification filter for biofilm formation. After successful biofilm formation, the dual biofilm system is constructed according to the process diagram.

[0012] Step 2: Start the booster pump 2, reflux device 6, and reflux device 7. The effluent from the primary sedimentation tank 1 enters the anoxic biofilm reactor 3 via the booster pump 2, and then flows into the aerobic biofilm reactor 4. The effluent from the upstream biofilm reactor flows into the iron autotrophic denitrification biofilter 5. The effluent from the aerobic biofilm reactor is refluxed back to the anoxic biofilm reactor via reflux device 6 (reflux liquid 1), and a portion of the effluent from the iron autotrophic denitrification biofilter is refluxed back to the anoxic biofilm reactor via reflux device 7 (reflux liquid 2). The water treated by this dual biofilm process is discharged in compliance with standards.

[0013] Step 3: Determine the optimal filling rate, optimal hydraulic retention time, dissolved oxygen concentration in the aerobic biofilm reactor, optimal filling ratio of the composite packing material in the iron autotrophic denitrification filter, and optimal reflux ratio of reflux liquid 1 to reflux liquid 2 based on the specific site conditions. After commissioning, continuously and efficiently treat municipal sewage.

[0014] Based on the above technical solution, compared with existing known technologies, it has the following advantages:

[0015] This dual-biofilm process enables deep nitrogen and phosphorus removal from municipal wastewater, effectively reducing its turbidity and demonstrating strong pollutant treatment performance. Furthermore, the establishment of this dual-biofilm system ensures high pollutant treatment capacity while maintaining low sludge production, guaranteeing the system's long-term operational potential.

[0016] Through microbial predation technology, a food chain / food web mainly composed of residual sludge and protozoa / metazoa is formed in the aerobic biofilm reactor, which greatly improves the sludge reduction capacity in situ of this dual biofilm wastewater treatment process. It can achieve long-term sludge discharge without secondary pollution, reducing sludge treatment costs and operational difficulty in practical applications.

[0017] The recirculation of reflux liquid 2 promoted the denitrification performance of both the anoxic and aerobic biofilm reactors, especially the denitrification performance of the anoxic biofilm reactor. Simultaneously, it played a role in controlling and regulating the protozoa and metazoa in the aerobic biofilm reactor, creating a dynamic balance between sludge growth and microbial predation.

[0018] This method is simple to operate, safe and economical, suitable for practical engineering applications, and deserves widespread promotion. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the process principle described in this invention.

[0020] Figure label annotations: 1-Primary sedimentation tank; 2-Lift pump; 3-Anoxic biofilm reactor; 4-Aerobic biofilm reactor; 5-Iron autotrophic denitrification biological filter; 6-Recirculation device 1; 7-Recirculation device 2.

[0021] Figure 2The diagram illustrates the pollutant removal performance of the influent and effluent in the anoxic and aerobic biofilm reactors during the implementation of this invention, under the following conditions: MBR curtain material filling rate of 60%, internal recirculation ratio of 100%, hydraulic retention time of 16 h, dissolved oxygen concentration of 4 mg / L in the aerobic reactor, use of limestone, siderite and magnetite composite packing material with a filling ratio of 1:2:1 (V / V / V), optimal recirculation ratio of 100% for recirculation liquid 1, and optimal recirculation ratio of 60% for recirculation liquid 2.

[0022] Figure 3 The diagram illustrates the sludge reduction under the following conditions during the implementation of this invention: the MBR curtain filling rate in the anoxic biofilm reactor and the aerobic biofilm reactor is 60%, the internal recirculation ratio is 100%, the hydraulic retention time is 16 h, the dissolved oxygen concentration in the aerobic reactor is 4 mg / L, the limestone, siderite and magnetite composite packing material with a filling ratio of 1:2:1 (V / V / V) is used, the optimal recirculation ratio of recirculation liquid 1 is 100%, and the optimal recirculation ratio of recirculation liquid 2 is 60%.

[0023] Figure 4 The diagram illustrates the pollutant removal performance of the influent and effluent in the anoxic and aerobic biofilm reactors during the implementation of this invention, under the following conditions: MBR curtain material filling rate of 60%, internal recirculation ratio of 100%, hydraulic retention time of 16 h, dissolved oxygen concentration of 4 mg / L in the aerobic reactor, use of limestone, siderite and magnetite composite packing material with a filling ratio of 1:2:1 (V / V / V), optimal recirculation ratio of 100% for recirculation liquid 1 and 80% for recirculation liquid 2.

[0024] Figure 5 The diagram illustrates the sludge reduction under the following conditions during the implementation of this invention: the MBR curtain packing filling rate in the anoxic biofilm reactor and the aerobic biofilm reactor is 60%, the internal recirculation ratio is 100%, the hydraulic retention time is 16 h, the dissolved oxygen concentration in the aerobic reactor is 4 mg / L, the limestone, siderite and magnetite composite packing material with a filling ratio of 1:2:1 (V / V / V) is used, the optimal recirculation ratio of recirculation liquid 1 is 100%, and the optimal recirculation ratio of recirculation liquid 2 is 80%.

[0025] Figure 6 The diagram shows the pollutant removal performance of the influent and effluent under the following conditions during the implementation of this invention: MBR curtain filling rate of 60%, internal recirculation ratio of 100%, hydraulic retention time of 16h, dissolved oxygen concentration of 4mg / L in the aerobic reactor, use of limestone, siderite and magnetite composite packing material with a filling ratio of 1:2:1 (V / V / V), and optimal recirculation ratio of 100% for both recirculation liquid 1 and recirculation liquid 2.

[0026] Figure 7The diagram illustrates the sludge reduction under the following conditions during the implementation of this invention: the MBR curtain packing filling rate in the anoxic biofilm reactor and the aerobic biofilm reactor is 60%, the internal recirculation ratio is 100%, the hydraulic retention time is 16 h, the dissolved oxygen concentration in the aerobic reactor is 4 mg / L, the limestone, siderite and magnetite composite packing material with a filling ratio of 1:2:1 (V / V / V) is used, and the optimal recirculation ratio of recirculated liquid 1 and recirculated liquid 2 is 100%. Detailed Implementation

[0027] Example 1: Improving the system's deep pollutant removal capacity and sludge reduction effect under the condition of a 60% reflux ratio in reflux liquid 2.

[0028] Step (1) Assemble the fixed biological bed carrier, which is assembled from MBR curtain fabric, into the anoxic biofilm reactor and the aerobic biofilm reactor at a filling rate of 60%. Mix limestone, siderite and magnetite in a volume ratio of 1:2:1 (V / V / V) to form iron ore filler, and mix and fill it into the iron autotrophic denitrification biological filter.

[0029] Step (2) Based on step (1), start the dual biofilm treatment process. Inoculate activated sludge in both the anoxic and aerobic biofilm reactors to form biofilms. Add activated sludge to the biofilm reactor, turn on the stirring device in the anoxic tank and the aeration device in the aerobic zone, and use a circulating water pump to keep the inside of the biofilm reactor in a circulating state for biofilm formation. The circulation time is 24 hours. Add autotrophic denitrifying bacteria solution to the iron autotrophic denitrifying biofilter and control the upward flow velocity of the bacterial solution in the filter to 0.0300 m / s for biofilm formation. The biofilm formation time in the biofilter is 24 hours.

[0030] Step (3): Based on step (2), connect the aerobic biofilm reactor, the anoxic biofilm reactor, and the iron autotrophic denitrification biological filter according to the process flow diagram to continuously treat municipal wastewater. Adjust the lift pump to make the hydraulic retention time of the biofilm reactor 16h, adjust the internal circulation pump to make the internal return ratio 100%, and adjust the aeration pump to make the dissolved oxygen concentration of the aerobic reactor 4mg / L. Adjust the return pump to make the return ratio of return liquid 1 100% and adjust the return pump to make the return ratio of return liquid 2 60% and run continuously and stably for 25 days respectively. On the same day, the COD, ammonia nitrogen, total nitrogen, and phosphate concentrations of the influent and effluent of the system are tested, and the sludge condition before and after the system operation is measured.

[0031] Example 2: Improving the system's deep pollutant removal capacity and sludge reduction effect under the condition of 80% reflux ratio of reflux liquid 2.

[0032] Step (1) Assemble the fixed biological bed carrier, which is assembled from MBR curtain fabric, into the anoxic biofilm reactor and the aerobic biofilm reactor at a filling rate of 60%. Mix limestone, siderite and magnetite in a volume ratio of 1:2:1 (V / V / V) to form iron ore filler, and mix and fill it into the iron autotrophic denitrification biological filter.

[0033] Step (2) Based on step (1), start the dual biofilm treatment process. Inoculate activated sludge in both the anoxic and aerobic biofilm reactors to form biofilms. Add activated sludge to the biofilm reactor, turn on the stirring device in the anoxic tank and the aeration device in the aerobic zone, and use a circulating water pump to keep the inside of the biofilm reactor in a circulating state for biofilm formation. The circulation time is 24 hours. Add autotrophic denitrifying bacteria solution to the iron autotrophic denitrifying biofilter and control the upward flow velocity of the bacterial solution in the filter to 0.0300 m / s for biofilm formation. The biofilm formation time in the biofilter is 24 hours.

[0034] Step (3): Based on step (2), connect the aerobic biofilm reactor, the anoxic biofilm reactor, and the iron autotrophic denitrification biological filter according to the process flow diagram to continuously treat municipal wastewater. Adjust the lift pump to make the hydraulic retention time of the biofilm reactor 16h, adjust the internal circulation pump to make the internal return ratio 100%, and adjust the aeration pump to make the dissolved oxygen concentration of the aerobic reactor 4mg / L. Adjust the return pump to make the return ratio of return liquid 1 100% and adjust the return pump to make the return ratio of return liquid 2 80% and run continuously and stably for 25 days respectively. On the same day, the COD, ammonia nitrogen, total nitrogen, and phosphate concentrations of the influent and effluent of the system are tested, and the sludge condition before and after the system operation is measured.

[0035] Example 3: Improving the system's deep pollutant removal capacity and sludge reduction effect under the condition of 100% reflux ratio of iron-containing reflux liquid.

[0036] Step (1) Assemble the fixed biological bed carrier, which is assembled from MBR curtain fabric, into the anoxic biofilm reactor and the aerobic biofilm reactor at a filling rate of 60%. Mix limestone, siderite and magnetite in a volume ratio of 1:2:1 (V / V / V) to form iron ore filler, and mix and fill it into the iron autotrophic denitrification biological filter.

[0037] Step (2) Based on step (1), start the dual biofilm treatment process. Inoculate activated sludge in both the anoxic and aerobic biofilm reactors to form biofilms. Add activated sludge to the biofilm reactor, turn on the stirring device in the anoxic tank and the aeration device in the aerobic zone, and use a circulating water pump to keep the inside of the biofilm reactor in a circulating state for biofilm formation. The circulation time is 24 hours. Add autotrophic denitrifying bacteria solution to the iron autotrophic denitrifying biofilter and control the upward flow velocity of the bacterial solution in the filter to 0.0300 m / s for biofilm formation. The biofilm formation time in the biofilter is 24 hours.

[0038] Step (3): Based on step (2), connect the aerobic biofilm reactor, the anoxic biofilm reactor, and the iron autotrophic denitrification biofilter according to the process flow diagram to continuously treat municipal wastewater. Adjust the lift pump to make the hydraulic retention time of the biofilm reactor 16h, adjust the internal circulation pump to make the internal return ratio 100%, and adjust the aeration pump to make the dissolved oxygen concentration of the aerobic reactor 4mg / L. Adjust the return pump to make the return ratio of return liquid 1 100% and adjust the return pump to make the return ratio of return liquid 2 100% respectively, and run continuously and stably for 25 days. On the same day, the COD, ammonia nitrogen, total nitrogen, and phosphate concentrations of the influent and effluent of the system are tested, and the sludge condition before and after the system operation is measured.

[0039] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention and are not intended to limit the present invention.

Claims

1. A dual-biofilm wastewater treatment process for deep nitrogen and phosphorus removal coupled with sludge reduction, characterized in that: The effluent from the primary sedimentation tank is pumped into the anoxic biofilm reactor and then flows into the aerobic biofilm reactor. The effluent treated by the front-end biofilm reactor flows into the iron autotrophic denitrification biofilter. The effluent from the aerobic biofilm reactor is returned to the anoxic biofilm reactor via the first return line, and part of the effluent from the iron autotrophic denitrification biofilter is returned to the anoxic biofilm reactor via the second return line. The second reflux line recirculates iron-containing water and inoculates protozoa / metazoa in the aerobic biofilm reactor, ensuring that all residual sludge produced by the dual biofilm system is preyed upon. Iron ions regulate the protozoa / metazoa in the upstream aerobic biofilm reactor. The anoxic and aerobic biofilm reactors use fixed biological bed packing material, filled at a ratio of 20%–80%. The iron autotrophic denitrification biofilter is constructed using iron ore composite packing material, a mixture of limestone, siderite, and magnetite in a volume ratio of 1:2:

1. The dissolved oxygen level in the aerobic biofilm reactor ranges from 1 to 5 mg / L. The hydraulic retention time in both the aerobic and anoxic biofilm reactors is controlled between 12 and 24 hours. The reflux ratio of the first reflux line is controlled between 60% and 120%, and the reflux ratio of the second reflux line is controlled between 60% and 100%.

Images