Five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration

Abstract

The invention discloses a five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration, and relates to the field of sewage treatment. The invention discloses a five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration. The five-stage sewage treatment method comprises the following steps: S1, sewage sequentially flows through a primary sedimentation tank, an anaerobic section, a first-stage anoxic section, a first-stage aerobic section, a second-stage anoxic section and a second-stage aerobic section; s2, a secondary anoxic section receives residual sludge hydrolysate backflow of the primary sedimentation tank and the secondary sedimentation tank, hydrolytic acidification pretreatment is carried out, an endogenous carbon source is released, and a carbon source required by denitrification is supplemented; s3, adopting variable-frequency dynamic aeration control in a second-stage aerobic section, and adjusting the aeration frequency according to the DO concentration gradient; through five-stage biochemical reaction tank flow optimization (anaerobic phosphorus release-anoxic denitrification-aerobic nitrification-secondary anoxic deep denitrification-secondary aerobic oxidation) and in combination with multi-source carbon source synergy, the nitrogen and phosphorus removal efficiency is remarkably improved, and the problems of carbon source competition, nitrate inhibition and poor low-temperature adaptability of a traditional process are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, and particularly relates to a five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration. Background Art

[0002] As a mainstream biological nitrogen and phosphorus removal technology, the traditional A2 / O process has the following defects:

[0003] Insufficient carbon source and competition: Insufficient carbon source in the denitrification stage leads to low nitrogen removal efficiency (TN removal rate < 70%), and the competition between polyphosphate-accumulating organisms (PAOs) and denitrifying bacteria for the carbon source intensifies the inhibition of phosphorus release.

[0004] Nitrate inhibition: Nitrate carried by sludge reflux enters the anaerobic section, interfering with the release and absorption of phosphorus.

[0005] Rigid operation parameters: Fixed hydraulic retention time (HRT) and aeration mode are difficult to adapt to water quality fluctuations, resulting in high energy consumption (0.45 - 0.55 kWh / m 3 ).

[0006] Poor low-temperature adaptability: The activity of traditional bacteria declines at low temperatures, and the nitrogen removal efficiency significantly decreases in winter.

[0007] Although existing improved processes (such as multi-stage A / O, step-feed) can improve the nitrogen removal effect by increasing the anoxic section, they still require a large amount of external carbon source (such as sodium acetate) to be added, and lack intelligent control, resulting in high operating costs; Summary of the Invention

[0008] The purpose of the present invention is to solve the problems in the prior art, and a five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration is proposed.

[0009] To solve the above technical problems, the basic concept of the technical solution adopted by the present invention is:

[0010] A five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration includes the following steps:

[0011] S1. Sewage flows through the primary sedimentation tank, anaerobic section, first-stage anoxic section, first-stage aerobic section, second-stage anoxic section, and second-stage aerobic section in sequence;

[0012] S2. The second-stage anoxic section receives the reflux of the hydrolyzed liquid of the excess sludge from the primary sedimentation tank and the secondary sedimentation tank, and performs hydrolysis acidification pretreatment to release endogenous carbon source and supplement the carbon source required for denitrification;

[0013] S3. The second-stage aerobic section adopts variable-frequency dynamic aeration control, and adjusts the aeration frequency according to the DO concentration gradient;

[0014] S4. Based on the real-time monitoring of COD / TN at the inlet of the secondary anoxic section, trigger the dosing of the external carbon source difference amount, and the dosing position is the inlet of the secondary anoxic section;

[0015] S5. The mixed liquor reflux adopts hierarchical variable frequency control:

[0016] The reflux ratio of the first anoxic section is 200% - 350%, and it is dynamically adjusted according to the NO3 - -N concentration at the end of the first aerobic section);

[0017] The reflux ratio of the secondary anoxic section is 100% - 150%;

[0018] S6. Integrate a membrane fouling warning module in the control system of the MBR membrane bioreactor. When the rising rate of the transmembrane pressure difference (TMP) > 0.5 kpa / day, automatically start chemical backwashing.

[0019] Preferably, in step S1, the hydraulic retention time distribution is as follows: 1.2 - 1.8 hours for the anaerobic section, 1.8 - 2.2 hours for the first anoxic section, 3.5 - 4.5 hours for the first aerobic section, 1.3 - 1.7 hours for the secondary anoxic section, 1.5 - 2 hours for the secondary aerobic section, and the total HRT is 10 - 12 hours.

[0020] Preferably, in step S2, the hydrolysis acidification conditions are as follows: the hydrolysis acidification time is 2 - 4 hours, the pH is controlled at 5.5 - 6.5, and the temperature is maintained at 25 - 35°C.

[0021] Preferably, for the temperature and pH value in the hydrolysis acidification, both are controlled by the hydrolysis acidification system. The hydrolysis acidification system includes a heating device and an automatic acid-base addition system. The heating device adopts a dual-track system of waste heat recovery and active heating for the hydrolysis acidification tank, that is, first uses the heat dissipation of the blower or the waste heat of the sewage to maintain the water temperature, and if the temperature does not meet the standard, auxiliary heating is carried out through a heat pump.

[0022] Preferably, the automatic acid-base addition system: real-time monitors the pH value in the hydrolysis acidification tank through a PH online probe, and triggers the acid-base adder to adjust the acidity and alkalinity only when the pH value exceeds 5.5 - 6.5.

[0023] Preferably, cold-tolerant denitrifying bacteria are added to the secondary anoxic section, and the initial dosing amount is 0.1% - 0.3% of the total amount of activated sludge; regularly detect the denitrification rate in the secondary anoxic section at low temperature, and if the rate drops by more than 20%, trigger the replenishment of the bacterial agent.

[0024] Preferably, in step S4, the added external carbon source is sodium acetate or glucose.

[0025] Preferably, a mechanical stirring device is provided in the anaerobic section, and the anaerobic section is naturally enriched with the medium for Aggregatibacter, and the medium is a mixed solution of sodium acetate, potassium dihydrogen phosphate and trace metal ions.

[0026] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art: the present invention;

[0027] 1. The five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration significantly improves the nitrogen and phosphorus removal efficiency by optimizing the five-stage biochemical reaction pool process (anaerobic phosphorus release → anoxic denitrification → aerobic nitrification → secondary anoxic deep denitrification → secondary aerobic oxidation) and combining multi-source carbon sources synergistically, and solves the problems of carbon source competition, nitrate inhibition and poor low-temperature adaptability of traditional processes;

[0028] 2. Optimize the energy consumption by DO gradient aeration, extend the membrane life and reduce the operation and maintenance costs by MBR membrane pollution early warning (transmembrane pressure difference monitoring + automatic backwashing);

[0029] 3. Introduce a strategy of periodically adding cold-tolerant bacteria agents to ensure that the TN removal rate is stably > 85% at low temperatures (10 - 15 °C). BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In the drawings:

[0031] Figure 1 is a schematic flow chart of a five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration proposed by the present invention;

[0032] Figure 2 is a schematic diagram of the hydrolysis acidification principle of a five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration proposed by the present invention;

[0033] Figure 3 is a schematic diagram of the variable-frequency aeration principle of a five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration proposed by the present invention;

[0034] Figure 4 is a schematic diagram of external carbon addition of a five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration proposed by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0035] The following further describes the present invention in detail with reference to the drawings and embodiments, so that those skilled in the art can implement it according to the description in the specification.

[0036] It should be understood that the terms such as "having", "comprising" and "including" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0037] In the description of the present invention, the orientation or positional relationship indicated by the terms "lateral", "longitudinal", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation on the present invention.

[0038] Referring to Figures 1-4 , a five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration, comprising the following steps:

[0039] S1. The sewage flows through the anaerobic section, the first anoxic section, the first aerobic section, the second anoxic section, and the second aerobic section of the biochemical reaction tank in sequence;

[0040] The hydraulic retention time of the biochemical reaction tank is allocated as follows: 1.2 - 1.8 hours for the anaerobic section, 1.8 - 2.2 hours for the first anoxic section, 3.5 - 4.5 hours for the first aerobic section, 1.3 - 1.7 hours for the second anoxic section, and 1.5 - 2 hours for the second aerobic section. The total HRT is 10 - 12 hours;

[0041] And an online monitoring of nitrate nitrogen is added at the end of the first aerobic section. If NO3 - -N > 8mg / L, the reflux ratio of the first anoxic section is automatically increased to 300% - 350% to reduce the load of the second anoxic section;

[0042] S2. The second anoxic section receives the hydrolyzed liquid of the excess sludge from the secondary sedimentation tank and the primary sedimentation tank. The sludge reflux of the two is coordinated, and the coordination ratio is 1:1 or 1:2. Before reflux, it undergoes hydrolysis acidification pretreatment in an anaerobic fermentation tank to increase the endogenous carbon contribution rate to 40% - 50%, further reducing the external carbon source demand; the internal carbon source released by the sludge hydrolysis acidification is used to supplement the carbon source required for denitrification;

[0043] Among them, the sludge reflux undergoes hydrolysis acidification pretreatment before reflux. The hydrolysis acidification time is 2 - 4 hours, the pH is controlled at 5.5 - 6.5, and the temperature is maintained at 25 - 35°C;

[0044] The hydrolysis acidification pretreatment requires an independent hydrolysis acidification tank, equipped with a PH adjustment and heating device. The heating device adopts a dual-track system of waste heat recovery and active heating for the hydrolysis acidification tank, that is, first uses the heat dissipation of the blower or the waste heat of the sewage to maintain the water temperature, and if the temperature does not meet the standard, auxiliary heating is carried out through a heat pump;

[0045] The PH adjustment adopts an automatic acid-base addition system, and the pH value in the hydrolysis acidification tank is monitored in real time through a PH online probe, and the adjustment is triggered only when the pH value exceeds 5.5 - 6.5;

[0046] Specifically, double-line heating is adopted: one is to utilize the waste heat of the variable-frequency blower in the secondary aerobic section and the sewage waste heat in the secondary anoxic section to heat the sludge hydrolysis liquid in the hydrolysis acidification tank through a plate heat exchanger; the other is to set up a heat pump for heating.

[0047] The heating priority is controlled in stages through the PLC system. At the first-level control, the waste heat of the variable-frequency blower and the sewage waste heat are preferentially utilized, and the water temperature is maintained by adjusting the flow rate of the plate heat exchanger through frequency conversion.

[0048] At the second-level control, when the waste heat and the residual heat are insufficient and the temperature is lower than 25 degrees, the sewage heat pump is started to supplement the heat.

[0049] S3. The variable-frequency dynamic control of the aeration intensity is adopted in the secondary aerobic section, and the frequency conversion adjustment adopts the DO concentration gradient control: when the DO concentration is 0.8 - 1.5 mg / L, the aeration frequency is 60% - 80% (to promote nitrification); when the DO concentration is 1.5 - 2.5 mg / L, the aeration frequency is reduced to 30% - 50% (for energy saving).

[0050] Among them, the variable-frequency dynamic aeration control is achieved through the following methods:

[0051] An on-line dissolved oxygen sensor is set in the secondary aerobic section and fed back to the aeration control system in real time:

[0052] When the DO concentration is in the range of 0.8 - 1.5 mg / L, the variable-frequency blower is started to increase the aeration volume to the rated power, so that the aeration frequency is 60% - 80% (to promote nitrification);

[0053] When the DO concentration is in the range of 1.5 - 2.5 mg / L, the aeration power is reduced to 30% - 50% (for energy saving);

[0054] Among them, the on-line dissolved oxygen sensor is configured with dual redundancy, one main sensor and the other calibration sensor. When a fault occurs, it automatically switches and alarms to improve the reliability of the system;

[0055] S4. Based on the real-time monitoring of the COD / TN of the influent water in the secondary anoxic section, the addition of the external carbon source difference amount is triggered, and the addition position is the inlet of the secondary anoxic section, with an error ≤ ±5%; the external carbon source added is sodium acetate or glucose.

[0056] The added amount of the carbon source difference = [(target COD / N * influent YN) - actual COD] / effective COD equivalent of the carbon source. For example: if the TN of the influent water in the secondary anoxic section is 20 mg / L, the measured COD is 60 mg / L, and the target COD / N is 5, then the COD to be supplemented = 5 × 20 - 60 = 40 mg / L; if sodium acetate (effective COD equivalent ≈ 1.07 g COD / g sodium acetate) is used, the added amount is 40 / 1.07 ≈ 37.4 mg / L;

[0057] S5. The return of the mixed liquor adopts hierarchical variable-frequency control, where:

[0058] The return ratio of the mixed liquor in the first anoxic section is 200% - 300%, and the return point is located at the end of the first aerobic section;

[0059] The return ratio of the mixed liquor in the second anoxic section is 100% - 150%, and the return point is located at the end of the second aerobic section;

[0060] The mixed liquor return pump is replaced with a "variable-frequency pump + flow sensor", and the return ratio is adjusted in real time according to the monitored nitrate nitrogen data;

[0061] Synergy of nitrification and denitrification: In the first aerobic section and the second aerobic section, ammonia nitrogen (NH4 + ) is converted into nitrate (NO3 - ) through nitrification, while in the first anoxic section and the second anoxic section, nitrate (NO3 - ) is converted into nitrogen gas (N2) and escapes through denitrification.

[0062] Core significance of return: Return the nitrate-rich mixed liquor at the end of the first aerobic section and the second aerobic section to the first anoxic section and the second anoxic section to provide reaction substrates (NO3 - ) for denitrifying bacteria, and at the same time use influent or endogenous carbon sources (such as organic matter) as electron donors to complete nitrogen removal.

[0063] S6. Addition of cold-resistant denitrifying bacteria agent: Add cold-resistant denitrifying bacteria agent to the second anoxic section. The components of the agent are a composite bacterial community of Pseudomonas and Denitrifying bacillus, and the initial addition amount is 0.1% - 0.3% of the total amount of activated sludge;

[0064] Regularly detect the denitrification rate in the second anoxic section at low temperature. If the rate drops by more than 20%, it is necessary to trigger the replenishment of the bacteria agent;

[0065] Quantitatively detect the gene copy number of cold-resistant bacteria in the sludge by fluorescence quantitative PCR, set a threshold, and replenish when it is lower than 50% of the initial addition amount;

[0066] Replenishment trigger conditions: When the denitrification rate is lower than the set threshold, or the gene copy number of cold-resistant bacteria is lower than 50% of the initial value, or the water temperature continuously remains below 15°C for more than 7 days, automatic replenishment is triggered;

[0067] During long-term operation, by detecting the denitrification rate or the gene abundance of cold-resistant bacteria in the second anoxic section, dynamically replenish the bacteria agent to the target proportion (0.1% - 0.3%). The calculation formula for the replenishment amount is: Replenishment amount = (Target proportion - Current proportion) * Total amount of activated sludge;

[0068] When the water temperature continuously remains below 15°C, automatically increase the target proportion to 0.3% - 0.5%;

[0069] S7. The end of the secondary aerobic section is coupled with the MBR membrane bioreactor. The membrane module of the MBR membrane bioreactor is a polyvinylidene fluoride hollow fiber membrane, and the membrane flux is controlled at 15 - 25 L / (m 2 .h);

[0070] A membrane fouling warning module is integrated in the control system of the MBR membrane bioreactor. When the rising rate of the transmembrane pressure difference (TMP) > 0.5 kPa / day, chemical backwashing is automatically started;

[0071] S8. A mechanical stirring device is set in the anaerobic section, and a natural enrichment culture medium of A. phosphatis is formed through the anaerobic section. The culture medium is a mixed solution of sodium acetate, potassium dihydrogen phosphate and trace metal ions;

[0072] Illustrate with examples;

[0073] Example 1: Municipal sewage treatment;

[0074] Sewage properties: COD = 300 mg / L, TN = 50 mg / L, TP = 5 mg / L, water temperature 15 - 25 °C.

[0075] Operation steps:

[0076] Process parameter settings:

[0077] HRT distribution: Anaerobic section 1.5 h → First anoxic section 2 h → First aerobic section 4 h → Second anoxic section 1.5 h → Second aerobic section 1 h (total HRT 10 h);

[0078] Sludge reflux ratio 25%, hydrolysis acidification time 3 h (pH 6.0, temperature 30 °C);

[0079] Mixed liquor reflux ratio: 250% in the first anoxic section, 120% in the second anoxic section.

[0080] Frequency conversion dynamic control:

[0081] The DO in the second aerobic section is set at 0.8 - 2.5 mg / L, and the aeration frequency is automatically adjusted according to the real-time DO;

[0082] If the influent TN in the second anoxic section = 20 mg / L, the measured COD = 60 mg / L, and the target COD / N = 5, then the additional COD required = 5×20 - 60 = 40 mg / L; if sodium acetate is used (effective COD equivalent ≈ 1.07 g COD / g sodium acetate), then the dosage is 40 / 1.07 ≈ 37.4 mg / L

[0083] Treatment effect:

[0084] Effluent quality: TN < 5 mg / L, TP < 0.3 mg / L, reaching the first-class A standard;

[0085] Carbon source consumption: 4.8 mg / L, energy consumption 0.36 kWh / m 3 .

[0086] Example 2: Industrial wastewater treatment (coupled BMR);

[0087] Sewage properties: COD = 600 mg / L, TN = 80 mg / L, TP = 8 mg / L, containing refractory organic matter;

[0088] Improvement measures: MBR integration: Connect a PVDF membrane module after the secondary aerobic section, i.e., an MBR membrane bioreactor (membrane flux 20 L / (m 2 ·h)), the effluent is directly filtered, and at the same time, a membrane fouling early warning module is integrated into the system of the MBR membrane bioreactor. When the rising rate of the transmembrane pressure difference (TMP) > 0.5 kPa / day, chemical enhanced backwashing is automatically started;

[0089] Low-temperature adaptability: Add 0.2% (activated sludge volume) of cold-resistant denitrifying bacteria agent to adapt to the low temperature in winter (10 - 15 °C);

[0090] Operation steps: Sludge reflux ratio 30%, hydrolysis acidification time 4 h (pH 5.5, temperature 25 °C); Dynamically aerate to control DO at 1.0 - 2.0 mg / L to reduce membrane fouling;

[0091] Treatment effect: Effluent quality: COD < 30 mg / L, TN < 8 mg / L, TP < 0.5 mg / L; The membrane fouling cycle is extended to 30 days, and the backwashing frequency is reduced by 40%.

[0092] The above embodiments only represent several implementation manners of the present invention, and the description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can be made. These are all equivalent modifications and evolutions of the above embodiments based on the essence of the present invention, and these all belong to the protection scope of the present invention.

Claims

1. A five-stage sewage treatment method based on the series connection of two-stage AO and carbon source regeneration, characterized in that, It includes the following steps: S1. The sewage flows through the primary sedimentation tank, anaerobic section, first-stage anoxic section, first-stage aerobic section, second-stage anoxic section, and second-stage aerobic section in sequence; S2. The second-stage anoxic section receives the reflux of the residual sludge hydrolysis liquid from the primary sedimentation tank and the secondary sedimentation tank, and conducts hydrolysis acidification pretreatment to release endogenous carbon sources and supplement the carbon sources required for denitrification; S3. The second-stage aerobic section adopts variable-frequency dynamic aeration control and adjusts the aeration frequency according to the DO concentration gradient; S4. Based on the real-time monitoring of COD / TN at the inlet of the second-stage anoxic section, the addition of the external carbon source difference amount is triggered, and the addition position is the inlet of the second-stage anoxic section; S5. The mixed liquid reflux adopts hierarchical variable-frequency control: The reflux ratio of the first-stage anoxic section is 200% - 350%, which is dynamically adjusted according to the NO3 - -N concentration at the end of the first-stage aerobic section); The reflux ratio of the second-stage anoxic section is 100% - 150%; S6. A membrane fouling early warning module is integrated in the control system of the MBR membrane bioreactor. When the rising rate of the transmembrane pressure difference (TMP) > 0.5 kpa / day, the chemical backwashing is automatically started.

2. A five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration according to claim 1, characterized in that, The hydraulic retention time distribution in the step S1 is as follows: the anaerobic section is 1.2 - 1.8 hours, the first-stage anoxic section is 1.8 - 2.2 hours, the first-stage aerobic section is 3.5 - 4.5 hours, the second-stage anoxic section is 1.3 - 1.7 hours, the second-stage aerobic section is 1.5 - 2 hours, and the total HRT is 10 - 12 hours.

3. A five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration according to claim 1, characterized in that, The hydrolysis acidification conditions in the step S2 are as follows: the hydrolysis acidification time is 2 - 4 hours, the pH is controlled at 5.5 - 6.5, and the temperature is maintained at 25 - 35 °C.

4. A five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration according to claim 3, characterized in that In the hydrolysis acidification, both the temperature and the pH are controlled by the hydrolysis acidification system. The hydrolysis acidification system includes a heating device and an automatic acid-base addition system. The heating device adopts a dual-track system of waste heat recovery and active heating for the hydrolysis acidification tank, that is, first uses the heat dissipation of the blower or the waste heat of the sewage to maintain the water temperature, and if the temperature does not meet the standard, auxiliary heating is carried out through a heat pump.

5. A five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration according to claim 4, characterized in that, The automatic acid-base addition system: The pH value in the hydrolysis acidification tank is monitored in real time by a pH online probe, and the acid-base adder is triggered to adjust the acidity only when the pH value exceeds 5.5 - 6.

5.

6. A five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration according to claim 1, characterized in that, Cold-resistant denitrifying bacteria are added to the second-stage anoxic section, and the initial addition amount is 0.1% - 0.3% of the total amount of activated sludge; the denitrification rate in the second-stage anoxic section at low temperature is regularly detected. If the rate drops by more than 20%, the addition of the bacterial agent is triggered.

7. A five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration according to claim 1, characterized in that, In the step S4, the added external carbon source is sodium acetate or glucose.

8. A five-stage sewage treatment method based on two-stage AO series connection and carbon source regeneration according to claim 7, characterized in that, A mechanical stirring device is arranged in the anaerobic section, and a natural aggregation scale bacteria culture medium is formed in the anaerobic section by itself. The culture medium is a mixed solution of sodium acetate, potassium dihydrogen phosphate, and trace metal ions.

Images