Accurate sewage denitrification control method based on active fermentation primary sedimentation system

Abstract

The invention provides a sewage denitrification accurate control method based on an active fermentation primary sedimentation system, and belongs to the technical field of environmental engineering. The high-efficiency active fermentation primary sedimentation system provided by the invention is obtained by adding active sludge reflux and micro-aerobic aeration area modification on the basis of a traditional primary sedimentation tank, and the investment and construction cost can be effectively reduced; on the basis, according to the inflow water quality and water temperature conditions, process operation parameters are accurately controlled through micro-aerobic and active fermentation, efficient conversion of refractory organics in inflow water of a sewage treatment plant can be guaranteed, and deep denitrification treatment of sewage can be achieved under the condition that no additional carbon source is added.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental engineering, and in particular relates to a precise control method for sewage denitrification based on an active fermentation primary sedimentation system, which is mainly used for the development of internal carbon sources in sewage treatment. Background Art

[0002] According to the "2022 Urban and Rural Construction Statistical Yearbook" of the Ministry of Housing and Urban-Rural Development, the scale of urban sewage treatment in my country has reached 216.06 million cubic meters / day, and the amount of dry sludge generated has reached 13.7 million tons / year. The main goal of urban sewage treatment is to remove nitrogen, phosphorus and organic matter. The activated sludge process is the main method for urban sewage treatment in my country. Most of the denitrifying functional microorganisms are heterotrophic bacteria. Due to the low carbon-nitrogen ratio of the influent, it is usually necessary to add carbon sources in the denitrification stage to ensure the denitrification activity of the denitrifying functional bacteria, so that the effluent water quality meets the total nitrogen emission standards. As the effluent water quality standards of sewage treatment plants continue to improve, it is conservatively estimated that the amount of carbon source added for denitrification in my country's sewage treatment exceeds 7.66 million tons / year, which not only greatly increases the cost of sewage treatment, but also increases indirect carbon emissions. The "Implementation Opinions on Promoting Synergistic Efficiency Improvement in Pollution Reduction and Carbon Reduction in Wastewater Treatment" jointly issued by the National Development and Reform Commission, the Ministry of Housing and Urban-Rural Development and other departments requires the coordinated promotion of pollutant reduction and greenhouse gas emission reduction in the entire wastewater treatment process, the implementation of water conservation and efficiency improvement at the source, energy conservation and carbon reduction in the treatment process, and resource utilization of sewage sludge, to comprehensively improve the comprehensive efficiency of sewage treatment and create a green and low-carbon benchmark sewage treatment plant with efficient and circular utilization of energy resources.

[0003] Organic matter in sewage is divided into biodegradable organic matter and difficult-to-degrade organic matter. Biodegradable organic matter mainly includes soluble proteins, polysaccharides, volatile fatty acids, etc., which can be directly used by denitrification microorganisms to accelerate the denitrification reaction rate; difficult-to-degrade organic matter includes macromolecular proteins, long-chain fatty acids, aromatic compounds and other insoluble macromolecular organic matter, which cannot be directly used by denitrification microorganisms. Therefore, making full use of difficult-to-degrade organic matter in sewage and efficiently converting it into small molecular organic matter such as volatile fatty acids (VFA) and glucose, and then achieving efficient denitrification without the need to add additional chemical carbon sources, will effectively reduce the cost of sewage treatment denitrification and reduce indirect carbon emissions.

[0004] Under the severe situation of global climate change, transforming the difficult-to-degrade organic matter in sewage as a denitrification carbon source and achieving deep denitrification of low carbon-nitrogen ratio sewage without an external carbon source is of great significance for building a resource-saving and environmentally friendly society and achieving sustainable development. Summary of the invention

[0005] The present invention provides a precise control method for sewage denitrification based on an active fermentation primary sedimentation system. The method can accurately control process operating parameters through microaerobic and active fermentation according to the influent water quality and water temperature, thereby ensuring the efficient conversion of difficult-to-degrade organic matter in the influent of the sewage treatment plant and achieving deep denitrification treatment of sewage without an external carbon source.

[0006] In order to achieve the above-mentioned purpose, the present invention provides a precise control method for sewage denitrification based on an active fermentation primary sedimentation system. The active fermentation primary sedimentation system is arranged before a conventional biological tank and a secondary sedimentation tank, and includes a primary sedimentation tank, an online monitoring instrument, an aeration system / pipeline and an activated sludge return pipeline. Based on the inlet temperature and COD concentration in the primary sedimentation tank, the activated sludge return ratio, sludge discharge volume and micro-aerobic ventilation ratio in the primary sedimentation tank are precisely controlled to achieve deep denitrification of low carbon-nitrogen ratio sewage without an external carbon source.

[0007] It is understandable that the high-efficiency active fermentation primary sedimentation system provided by the present invention adds activated sludge return and micro-aerobic aeration zone on the basis of conventional horizontal flow primary sedimentation tanks, and accurately controls the activated sludge return ratio, sludge discharge volume, micro-aerobic ventilation ratio and other process operation parameters according to the inlet water temperature and COD concentration, so as to achieve deep denitrification of low carbon-nitrogen ratio sewage without external carbon source. Among them, by returning activated sludge and providing a micro-aerobic environment, the types of hydrolysis and acidification functional microorganisms in the primary sedimentation tank can be enriched, the abundance and activity of key microbial populations can be improved, and the macromolecular organic matter that is difficult to degrade in sewage and primary sedimentation tank sludge can be quickly hydrolyzed to produce small-molecule organic matter that is easily utilized by denitrification functional microorganisms, which can increase the concentration of dissolved organic matter and volatile fatty acids in the inlet water of the subsequent biological treatment system, thereby achieving deep denitrification of low carbon-nitrogen ratio sewage without external carbon source.

[0008] Preferably, the activated sludge in the primary sedimentation tank comes from the activated sludge return from the biological tank or the secondary sedimentation tank, and the activated sludge is returned to the water inlet pipe of the primary sedimentation tank to be fully mixed with the inlet water. It can be understood that the activated sludge includes organic matter, inorganic matter and attached microorganisms. The sludge from the biological tank and the secondary sedimentation tank is called activated sludge in the industry; the primary sedimentation tank usually has very few microorganisms, and its sludge is mainly organic and inorganic, which is called primary sedimentation sludge.

[0009] Preferably, a variable frequency pump and a flow meter are respectively provided on the activated sludge return pipeline of the biological tank or the secondary sedimentation tank to control the sludge flow rate of the activated sludge returning to the primary sedimentation tank.

[0010] Preferably, a COD and temperature online monitoring instrument is provided on the water inlet pipe of the primary sedimentation tank to monitor the COD concentration and temperature of the inlet water;

[0011] An online sludge concentration monitoring instrument, a variable frequency pump and a flow meter are installed at the bottom of the primary sedimentation tank to control the sludge concentration at the bottom of the primary sedimentation tank.

[0012] Preferably, the primary sedimentation tank includes a micro-aerobic aeration zone, which is an area at the bottom of the primary sedimentation tank where a perforated or microporous aeration system / pipeline is arranged, and the area is from the water inlet to the 15% to 50% area, preferably the 25% to 35% area;

[0013] The perforated or microporous aeration system / pipeline is equipped with an air flow meter and a blower valve, and the aeration volume at the bottom of the primary sedimentation tank is controlled by adjusting the valve opening.

[0014] Preferably, the hydraulic retention time of the high-efficiency active fermentation primary sedimentation system is 1.5 to 3.5 hours, preferably 2.5 hours.

[0015] As a preferred method, according to the inlet water temperature and COD concentration in the primary sedimentation tank in the primary sedimentation system, the activated sludge return ratio, sludge discharge volume and microaerobic ventilation ratio in the primary sedimentation tank are accurately controlled to achieve deep denitrification of low carbon-nitrogen ratio sewage without an external carbon source. Specifically, the method includes:

[0016] When the inlet water temperature T≤10℃, the activated sludge return ratio W is controlled to be 〔1+(C-500) / (C+500)〕×5%, and the frequency conversion pump of the biological pool or the secondary sedimentation tank and the flow meter of the activated sludge return pipeline are used to adjust the pump operation frequency, and the flow rate of the activated sludge returning to the primary sedimentation tank is controlled to be Q×W; the micro-aerobic zone ventilation ratio A is controlled to be 〔1+(C-500) / (C+500)〕×0.35, and the air flow meter on the microporous aeration system / pipeline is combined to adjust the blower valve opening to control the aeration volume at the bottom of the primary sedimentation tank to be V×A×R; the bottom sludge concentration is controlled to be 18000-19000mg / L, and the sludge discharge volume is increased when the sludge concentration is greater than 19000mg / L, and the sludge discharge volume is reduced when the sludge concentration is less than 18000mg / L;

[0017] When 10℃<water inlet temperature T≤15℃, control the activated sludge return ratio W=〔1+(C-500) / (C+500)〕×4.5%, adjust the pump operation frequency through the frequency conversion pump of the biological pool or secondary sedimentation tank and the flow meter of the activated sludge return pipeline, and control the flow rate of the activated sludge returning to the primary sedimentation tank to Q×W; control the micro-aerobic zone ventilation ratio A=〔1+(C-500) / (C+500)〕×0.3, and control the aeration volume at the bottom of the primary sedimentation tank to V×A×R by adjusting the blower valve opening in combination with the microporous aeration system / air flow meter on the pipeline; control the bottom sludge concentration to 17500-18500mg / L, increase the sludge discharge when the sludge concentration is greater than 18500mg / L, and reduce the sludge discharge when the sludge concentration is less than 17500mg / L;

[0018] When 15℃<water inlet temperature T≤20℃, control the activated sludge return ratio W=〔1+(C-500) / (C+500)〕×4%, adjust the pump operation frequency through the frequency conversion pump of the biological pool or the secondary sedimentation tank and the flow meter of the activated sludge return pipeline, and control the flow rate of the activated sludge returning to the primary sedimentation tank to be Q×W; control the micro-aerobic zone ventilation ratio A=〔1+(C-500) / (C+500)〕×0.25, and control the aeration volume at the bottom of the primary sedimentation tank to be V×A×R by adjusting the blower valve opening in combination with the microporous aeration system / air flow meter on the pipeline; control the bottom sludge concentration to be 17000-18000mg / L, increase the sludge discharge when the sludge concentration is greater than 18000mg / L, and reduce the sludge discharge when the sludge concentration is less than 17000mg / L;

[0019] When 20℃<water inlet temperature T≤25℃, control the activated sludge return ratio W=〔1+(C-500) / (C+500)〕×3.5%, adjust the pump operation frequency through the frequency conversion pump of the biological pool or the secondary sedimentation tank and the flow meter of the activated sludge return pipeline, and control the flow rate of the activated sludge returning to the primary sedimentation tank to be Q×W; control the micro-aerobic zone ventilation ratio A=(1+(C-500) / (C+500))×0.2, and control the aeration volume at the bottom of the primary sedimentation tank to be V×A×R by adjusting the blower valve opening in combination with the air flow meter on the microporous aeration system / pipeline; control the bottom sludge concentration to be 16500-17500mg / L, increase the sludge discharge when the sludge concentration is greater than 17500mg / L, and reduce the sludge discharge when the sludge concentration is less than 16500mg / L;

[0020] When the inlet water temperature T>25℃, control the activated sludge return ratio W=〔1+(C-500) / (C+500)〕×3%, adjust the pump operation frequency through the frequency conversion pump of the biological pool or the secondary sedimentation tank and the flow meter of the activated sludge return pipeline, and control the flow rate of the activated sludge returning to the primary sedimentation tank to be Q×W; control the micro-aerobic zone ventilation ratio A=(1+(C-500) / (C+500))×0.15, and adjust the blower valve opening in combination with the air flow meter on the microporous aeration system / pipeline to control the aeration volume at the bottom of the primary sedimentation tank to be V×A×R; control the bottom sludge concentration to be 16000-17000mg / L. When the sludge concentration is greater than 17000mg / L, increase the sludge discharge volume, and when the sludge concentration is less than 16000mg / L, reduce the sludge discharge volume;

[0021] Where C represents the influent COD concentration, in mg / L; Q represents the influent flow rate of the primary sedimentation tank, in m 3 / h; V represents the volume of the primary sedimentation tank, in m 3 ; R represents the proportion of the aeration area at the bottom of the primary sedimentation tank; the ventilation ratio is the ratio of the ventilation volume per minute to the sewage volume, unit vvm.

[0022] Preferably, the carbon-nitrogen ratio in the low carbon-nitrogen ratio sewage is less than 3:1.

[0023] Preferably, the concentration of dissolved organic matter in the influent is increased by 20-35%, and the concentration of volatile fatty acids (VFA) is increased by 10-30%.

[0024] Compared with the prior art, the advantages and positive effects of the present invention are:

[0025] The high-efficiency active fermentation primary sedimentation system provided by the present invention is obtained by adding activated sludge return and micro-aerobic aeration zone to the traditional primary sedimentation tank, which can effectively reduce the investment and construction cost; on this basis, according to the influent water quality and water temperature, the process operation parameters are accurately controlled through micro-aerobic and active fermentation, which can ensure the efficient conversion of difficult-to-degrade organic matter in the influent of the sewage treatment plant, and can increase the concentration of dissolved organic matter in the influent of the biological pool of the sewage treatment plant by 20-35%, and increase the concentration of volatile fatty acids (VFA) by 10-30%, thereby further reducing the operation cost on the basis of achieving deep denitrification of sewage treatment without adding an external carbon source. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of a high-efficiency active fermentation primary sedimentation system provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Example 1

[0029] A sewage treatment plant in a coastal city in the north has a treatment capacity of 50,000 cubic meters per day. The biological treatment unit adopts a three-stage AO+MBBR process (aerobic-anaerobic+moving bed biofilm reactor process). The efficient active fermentation primary sedimentation system is based on the transformation of the original horizontal flow sedimentation tank. The activated sludge comes from the activated sludge return from the secondary sedimentation tank and flows back to the primary sedimentation tank inlet pipe; the biological pool (3) (the biological pool is the largest structure in the sewage treatment process, and its volume is usually about 10 times that of the primary sedimentation tank and the secondary sedimentation tank. Figure 1In order to highlight the technical features of the primary sedimentation tank, the size is shown schematically here) or the activated sludge return pipe (12) of the secondary sedimentation tank (4) is respectively provided with a variable frequency pump (6) and a flow meter (5) to control the sludge flow of the activated sludge returning to the primary sedimentation tank (2); the water inlet pipe (1) of the primary sedimentation tank is provided with a COD online monitoring instrument (7) and a temperature online monitoring instrument (11) to monitor the COD concentration and temperature of the inlet water; the bottom of the primary sedimentation tank is provided with a sludge concentration online monitoring instrument (13), a flow meter (14) and a variable frequency pump (not shown) to control the sludge concentration at the bottom of the primary sedimentation tank. A microporous aeration device (10) is arranged at the bottom of the area from the water inlet to 30% of the high-efficiency active fermentation primary sedimentation system, the hydraulic retention time is 2.5h, and the capacity of the primary sedimentation tank is 5200m 3 .

[0030] The COD concentration of the influent of the high-efficiency active fermentation primary sedimentation system is monitored by online monitoring instruments, which is C (in mg / L) and the water temperature T (in °C). The influent flow rate Q of the primary sedimentation tank is 2000-2200m 3 / h, the volume of the primary sedimentation tank V is 5000m 3 , according to the influent water quality and water temperature, determine the process operating parameters according to the following settings:

[0031] When T≤10, the activated sludge return ratio W=〔1+(C-500) / (C+500)〕×5%, the frequency conversion pump (6) of the biological pool or the secondary sedimentation tank and the flow meter (5) of the activated sludge return pipeline are used to adjust the pump operation frequency, and the flow rate of the activated sludge returned to the primary sedimentation tank is controlled to be Q×W; the microaerobic zone ventilation ratio A=〔1+(C-500) / (C+500)〕×0.35, combined with the microporous aeration system / pipeline (10) on The air flow meter (not shown) controls the aeration volume at the bottom of the primary sedimentation tank to 5200×A×30% by adjusting the opening of the valve (not shown) of the blower (8); controls the bottom sludge concentration to 18000-19000 mg / L, and controls the bottom sludge concentration by the sludge discharge volume of the primary sedimentation tank. When the sludge concentration is greater than 19000 mg / L, the sludge discharge volume is increased by the sludge discharge pump (9), and when the sludge concentration is less than 18000 mg / L, the sludge discharge volume is reduced.

[0032] When 10 < T ≤ 15, control the return ratio of activated sludge W = [1 + (C - 500) / (C + 500)] × 4.5%. Through the variable-frequency pump in the biological pool or secondary sedimentation tank and the flowmeter on the activated sludge return pipeline, adjust the pump operation frequency to control the flow rate of activated sludge returning to the primary sedimentation tank as Q × W. Control the aeration ratio A in the micro-aerobic zone = [1 + (C - 500) / (C + 500)] × 0.3. Combine with the air flowmeter on the microporous aeration system / pipeline and adjust the opening of the blower valve to control the aeration volume at the bottom of the primary sedimentation tank as 5200 × A × 30%. Control the bottom sludge concentration at 17500 - 18500 mg / L. Control the bottom sludge concentration through the sludge discharge volume of the primary sedimentation tank. When the sludge concentration is greater than 18500 mg / L, increase the sludge discharge volume; when the sludge concentration is less than 17500 mg / L, decrease the sludge discharge volume.

[0033] When 15 < T ≤ 20, control the return ratio of activated sludge W = [1 + (C - 500) / (C + 500)] × 4%. Through the variable-frequency pump in the biological pool or secondary sedimentation tank and the flowmeter on the activated sludge return pipeline, adjust the pump operation frequency to control the flow rate of activated sludge returning to the primary sedimentation tank as Q × W. Control the aeration ratio A in the micro-aerobic zone = [1 + (C - 500) / (C + 500)] × 0.25. Combine with the air flowmeter on the microporous aeration system / pipeline and adjust the opening of the blower valve to control the aeration volume at the bottom of the primary sedimentation tank as 5200 × A × 30%. Control the bottom sludge concentration at 17000 - 18000 mg / L. Control the bottom sludge concentration through the sludge discharge volume of the primary sedimentation tank. When the sludge concentration is greater than 18000 mg / L, increase the sludge discharge volume; when the sludge concentration is less than 17000 mg / L, decrease the sludge discharge volume.

[0034] When 20 < T ≤ 25, control the return ratio of activated sludge W = [1 + (C - 500) / (C + 500)] × 3.5%. Through the variable-frequency pump in the biological pool or secondary sedimentation tank and the flowmeter on the activated sludge return pipeline, adjust the pump operation frequency to control the flow rate of activated sludge returning to the primary sedimentation tank as Q × W. Control the aeration ratio A in the micro-aerobic zone = [1 + (C - 500) / (C + 500)] × 0.2. Combine with the air flowmeter on the microporous aeration system / pipeline and adjust the opening of the blower valve to control the aeration volume at the bottom of the primary sedimentation tank as 5200 × A × 30%. Control the bottom sludge concentration at 16500 - 17500 mg / L. Control the bottom sludge concentration through the sludge discharge volume of the primary sedimentation tank. When the sludge concentration is greater than 17500 mg / L, increase the sludge discharge volume; when the sludge concentration is less than 16500 mg / L, decrease the sludge discharge volume.

[0035] When T>25, the activated sludge return ratio W is controlled to be 〔1+(C-500) / (C+500)〕×3%, and the frequency conversion pump of the biological pool or the secondary sedimentation tank and the flow meter of the activated sludge return pipeline are used to adjust the pump operation frequency, and the flow rate of the activated sludge returning to the primary sedimentation tank is controlled to be Q×W; the micro-aerobic zone ventilation ratio A is controlled to be 〔1+(C-500) / (C+500)〕×0.15, and the air flow meter on the microporous aeration system / pipeline is used to adjust the blower valve opening to control the aeration volume at the bottom of the primary sedimentation tank to be 5200×A×30%; ​​the bottom sludge concentration is controlled to be 16000-17000 mg / L, and the bottom sludge concentration is controlled by the sludge discharge volume of the primary sedimentation tank. When the sludge concentration is greater than 17000 mg / L, the sludge discharge volume is increased, and when the sludge concentration is less than 16000 mg / L, the sludge discharge volume is reduced.

[0036] For example, the inlet water temperature of the sedimentation tank was 22.5℃, the COD concentration was 523mg / L, the total nitrogen was 73mg / L, and the inlet flow rate was 2100m 3 / h, then the activated sludge return ratio W = [1 + (523-500) / (523 + 500)] × 3.5% = 3.58%. Through the frequency conversion pump of the biological pool or the secondary sedimentation tank and the flow meter of the activated sludge return pipeline, the pump operating frequency is adjusted to control the flow rate of the activated sludge returning to the primary sedimentation tank to Q × W = 2100 × 3.58% = 75.15m 3 / h; control the ventilation ratio of the micro-aerobic zone A = [1 + (523-500) / (523 + 500)] × 0.2 = 0.204, and adjust the blower valve opening by combining the microporous aeration system / air flow meter on the pipeline to control the aeration volume at the bottom of the primary sedimentation tank to 5200 × 0.204 × 30% = 318m 3 / h; control the bottom sludge concentration to 16500-17500mg / L, and control the bottom sludge concentration by the sludge discharge volume of the primary sedimentation tank. When the sludge concentration is greater than 17500mg / L, increase the sludge discharge volume, and when the sludge concentration is less than 16500mg / L, reduce the sludge discharge volume. After the active fermentation primary sedimentation system, the dissolved organic matter in the influent increased from 127.5mg / L to 151.2mg / L, an average increase of about 18.6%; VFA increased from 40.3mg / L to 58.8mg / L, an increase of about 45.9%. Deep denitrification of sewage treatment without external carbon source is achieved, and the total nitrogen in the effluent of the sewage treatment plant is 8.5mg / L.

[0037] The inlet water temperature of the primary sedimentation tank is 17.0℃, the COD concentration is 475mg / L, the total nitrogen is 82mg / L, and the inlet flow rate is 2050m 3 / h, then the activated sludge return ratio W is controlled to be W = [1 + (475-500) / (475 + 500)] × 4% = 3.90%. Through the frequency conversion pump of the biological pool or the secondary sedimentation tank and the flow meter of the activated sludge return pipeline, the pump operating frequency is adjusted to control the flow rate of the activated sludge returning to the primary sedimentation tank to be Q × W = 2050 × 3.90% = 79.90m 3 / h; control the ventilation ratio of the micro-aerobic zone A = [1 + (475-500) / (475 + 500)] × 0.25 = 0.244, and adjust the blower valve opening by combining the microporous aeration system / air flow meter on the pipeline to control the aeration volume at the bottom of the primary sedimentation tank to 5200 × 0.244 × 30% = 381m 3 / h; control the bottom sludge concentration to 17000-18000mg / L, and control the bottom sludge concentration by the sludge discharge volume of the primary sedimentation tank. When the sludge concentration is greater than 18000mg / L, increase the sludge discharge volume, and when the sludge concentration is less than 17000mg / L, reduce the sludge discharge volume. After the active fermentation primary sedimentation system, the dissolved organic matter in the influent increased from 119.6mg / L to 143.5mg / L, an average increase of about 20.0%; VFA increased from 38.4mg / L to 53.2mg / L, an increase of about 38.5%. Deep denitrification of sewage treatment without external carbon source is achieved, and the total nitrogen in the effluent of the sewage treatment plant is 11.2mg / L.

[0038] The inlet water temperature of the primary sedimentation tank is 9.2℃, the COD concentration is 567mg / L, the total nitrogen is 85mg / L, and the inlet flow rate is 2120m 3 / h, then the activated sludge return ratio W = [1 + (567-500) / (567 + 500)] × 5% = 5.31%. Through the frequency conversion pump of the biological pool or the secondary sedimentation tank and the flow meter of the activated sludge return pipeline, the pump operating frequency is adjusted to control the flow rate of the activated sludge returning to the primary sedimentation tank to Q × W = 2120 × 5.31% = 112.57m 3 / h; control the ventilation ratio of the micro-aerobic zone A = [1 + (567-500) / (567 + 500)] × 0.35 = 0.372, and adjust the blower valve opening by combining the microporous aeration system / air flow meter on the pipeline to control the aeration volume at the bottom of the primary sedimentation tank to 5200 × 0.372 × 30% = 580m 3 / h; control the bottom sludge concentration to 18000-19000mg / L, and control the bottom sludge concentration by the sludge discharge volume of the primary sedimentation tank. When the sludge concentration is greater than 19000mg / L, increase the sludge discharge volume, and when the sludge concentration is less than 18000mg / L, reduce the sludge discharge volume. After the active fermentation primary sedimentation system, the dissolved organic matter in the influent increased from 145.3mg / L to 175.8mg / L, an average increase of about 21.0%; VFA increased from 50.1mg / L to 73.2mg / L, an increase of about 46.1%. Deep denitrification of sewage treatment without external carbon source is achieved, and the total nitrogen in the effluent of the sewage treatment plant is 13.5mg / L.

[0039] After one year of continuous operation, the influent COD concentration ranged from 300-700 mg / L, the influent total nitrogen concentration ranged from 70-120 mg / L, and the influent temperature ranged from 9-25°C with seasonal changes. After the active fermentation primary sedimentation system, the dissolved organic matter in the influent increased from an average of 135.2 mg / L (average value throughout the year) to an average of 158.6 mg / L (average value throughout the year), an average increase of about 17.3%; VFA increased from an average of 45.1 mg / L to an average of 71.3 mg / L, an average increase of about 58.1%. Deep denitrification of sewage treatment without external carbon source was achieved, and the average total nitrogen value of the sewage treatment plant effluent was 12.7 mg / L.

Claims

1. A precise control method for wastewater denitrification based on an active fermentation primary sedimentation system, characterized in that: The active fermentation primary sedimentation system is installed before the conventional biological tank and the secondary sedimentation tank, and includes the primary sedimentation tank, online monitoring instruments, an aeration system / pipeline and an activated sludge return pipeline. Based on the inlet temperature and COD concentration in the primary sedimentation tank, the activated sludge return ratio, sludge discharge volume and micro-aerobic ventilation ratio in the primary sedimentation tank are precisely controlled to achieve deep denitrification of low carbon-nitrogen ratio sewage without an external carbon source.

2. The precise control method according to claim 1, characterized in that: The activated sludge in the primary sedimentation tank comes from the activated sludge return from the biological tank or the secondary sedimentation tank. The activated sludge is returned to the inlet pipe of the primary sedimentation tank to be fully mixed with the inlet water.

3. The precise control method according to claim 2, characterized in that: The activated sludge return pipe of the biological tank or the secondary sedimentation tank is respectively provided with a variable frequency pump and a flow meter to control the sludge flow rate of the activated sludge returning to the primary sedimentation tank.

4. The precise control method according to claim 2, characterized in that: The inlet pipe of the primary sedimentation tank is equipped with COD and temperature online monitoring instruments to monitor the COD concentration and temperature of the inlet water; An online sludge concentration monitoring instrument, a variable frequency pump and a flow meter are installed at the bottom of the primary sedimentation tank to control the sludge concentration at the bottom of the primary sedimentation tank.

5. The precise control method according to claim 1, characterized in that: The primary sedimentation tank includes a micro-aerobic aeration zone, which is an area at the bottom of the primary sedimentation tank where a perforated or microporous aeration system / pipeline is arranged, and the area is from the water inlet to the 15% to 50% area, preferably the 25% to 35% area; The perforated or microporous aeration system / pipeline is equipped with an air flow meter and a blower valve, and the aeration volume at the bottom of the primary sedimentation tank is controlled by adjusting the valve opening.

6. The precise control method according to any one of claims 1 to 5, characterized in that: The hydraulic retention time of the high-efficiency active fermentation primary sedimentation system is 1.5 to 3.5 hours, preferably 2.5 hours.

7. The precise control method according to claim 1, characterized in that: According to the inlet water temperature and COD concentration in the primary sedimentation tank in the primary sedimentation system, the activated sludge return ratio, sludge discharge volume and micro-aerobic ventilation ratio in the primary sedimentation tank are accurately controlled to achieve deep denitrification of low carbon-nitrogen ratio sewage without external carbon source. Specifically include: When the inlet water temperature T≤10℃, the activated sludge return ratio W is controlled to be 〔1+(C-500) / (C+500)〕×5%, and the frequency conversion pump of the biological pool or the secondary sedimentation tank and the flow meter of the activated sludge return pipeline are used to adjust the pump operation frequency, and the flow rate of the activated sludge returning to the primary sedimentation tank is controlled to be Q×W; the micro-aerobic zone ventilation ratio A is controlled to be 〔1+(C-500) / (C+500)〕×0.35, and the air flow meter on the microporous aeration system / pipeline is combined to adjust the blower valve opening to control the aeration volume at the bottom of the primary sedimentation tank to be V×A×R; the bottom sludge concentration is controlled to be 18000-19000mg / L, and the sludge discharge volume is increased when the sludge concentration is greater than 19000mg / L, and the sludge discharge volume is reduced when the sludge concentration is less than 18000mg / L; When 10℃<water inlet temperature T≤15℃, control the activated sludge return ratio W=〔1+(C-500) / (C+500)〕×4.5%, adjust the pump operation frequency through the frequency conversion pump of the biological pool or secondary sedimentation tank and the flow meter of the activated sludge return pipeline, and control the flow rate of the activated sludge returning to the primary sedimentation tank to Q×W; control the micro-aerobic zone ventilation ratio A=〔1+(C-500) / (C+500)〕×0.3, and control the aeration volume at the bottom of the primary sedimentation tank to V×A×R by adjusting the blower valve opening in combination with the microporous aeration system / air flow meter on the pipeline; control the bottom sludge concentration to 17500-18500mg / L, increase the sludge discharge when the sludge concentration is greater than 18500mg / L, and reduce the sludge discharge when the sludge concentration is less than 17500mg / L; When 15℃<water inlet temperature T≤20℃, control the activated sludge return ratio W=〔1+(C-500) / (C+500)〕×4%, adjust the pump operation frequency through the frequency conversion pump of the biological pool or the secondary sedimentation tank and the flow meter of the activated sludge return pipeline, and control the flow rate of the activated sludge returning to the primary sedimentation tank to be Q×W; control the micro-aerobic zone ventilation ratio A=〔1+(C-500) / (C+500)〕×0.25, and control the aeration volume at the bottom of the primary sedimentation tank to be V×A×R by adjusting the blower valve opening in combination with the microporous aeration system / air flow meter on the pipeline; control the bottom sludge concentration to be 17000-18000mg / L, increase the sludge discharge when the sludge concentration is greater than 18000mg / L, and reduce the sludge discharge when the sludge concentration is less than 17000mg / L; When 20℃<water inlet temperature T≤25℃, control the activated sludge return ratio W=〔1+(C-500) / (C+500)〕×3.5%, adjust the pump operation frequency through the frequency conversion pump of the biological pool or the secondary sedimentation tank and the flow meter of the activated sludge return pipeline, and control the flow rate of the activated sludge returning to the primary sedimentation tank to be Q×W; control the micro-aerobic zone ventilation ratio A=(1+(C-500) / (C+500))×0.2, and control the aeration volume at the bottom of the primary sedimentation tank to be V×A×R by adjusting the blower valve opening in combination with the air flow meter on the microporous aeration system / pipeline; control the bottom sludge concentration to be 16500-17500mg / L, increase the sludge discharge when the sludge concentration is greater than 17500mg / L, and reduce the sludge discharge when the sludge concentration is less than 16500mg / L; When the inlet water temperature T>25℃, control the activated sludge return ratio W=〔1+(C-500) / (C+500)〕×3%, adjust the pump operation frequency through the frequency conversion pump of the biological pool or the secondary sedimentation tank and the flow meter of the activated sludge return pipeline, and control the flow rate of the activated sludge returning to the primary sedimentation tank to be Q×W; control the micro-aerobic zone ventilation ratio A=(1+(C-500) / (C+500))×0.15, and control the aeration volume at the bottom of the primary sedimentation tank to be V×A by adjusting the blower valve opening in combination with the air flow meter on the microporous aeration system / pipeline; control the bottom sludge concentration to be 16000-17000mg / L, increase the sludge discharge when the sludge concentration is greater than 17000mg / L, and reduce the sludge discharge when the sludge concentration is less than 16000mg / L; Where C represents the influent COD concentration, in mg / L; Q represents the influent flow rate of the primary sedimentation tank, in m 3 / h; V represents the volume of the primary sedimentation tank, in m 3 ; R represents the proportion of the aeration area at the bottom of the primary sedimentation tank; the ventilation ratio is the ratio of the ventilation volume per minute to the sewage volume, unit vvm.

8. The precise control method according to claim 1, characterized in that: The carbon-nitrogen ratio in low carbon-nitrogen ratio sewage is less than 3:

1.

9. The precise control method according to any one of claims 1 to 8, characterized in that: Increase the concentration of dissolved organic matter in the influent by 20-35% and the concentration of volatile fatty acids (VFA) by 10-30%.

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