Process for synchronously realizing deep denitrification and in-situ sludge reduction

Abstract

The invention relates to a process for synchronously realizing deep denitrification and in-situ sludge reduction, and belongs to the field of biological sewage treatment. A device involved in the process mainly comprises a water inlet barrel, a UASB reactor, a middle water tank and an SBR reactor which are connected in sequence; wherein the UASB reactor is respectively provided with two water inlets, raw water enters from the first water inlet, the first water inlet is positioned at the bottom of the UASB reactor, and the second water inlet is arranged on the side wall of the UASB reactor; and outlet water of the SBR is connected with the UASB reactor through a second water inlet by a water outlet bucket. The UASB reactor is divided into an anaerobic zone and an anoxic zone due to the position of the second water inlet; and low-oxygen aeration is adopted in the SBR reactor to realize synchronous nitrification and denitrification. According to the process, organic matters in raw water can be effectively utilized to achieve the purpose of deep denitrification, and in-situ reduction of sludge can be realized by synchronous nitrification and denitrification in the SBR reactor.

Description

Technical Field

[0001] The invention relates to a process for simultaneously realizing deep denitrification and in-situ sludge reduction, and belongs to the field of biological sewage treatment. Background Art

[0002] With the progress of society and the improvement of people's living standards, the amount of sewage generated has also increased. Elements such as nitrogen and phosphorus in sewage entering the water body will cause water pollution problems such as eutrophication, so sewage treatment is crucial, and the current national sewage treatment discharge standards are becoming more and more stringent. Due to the low C / N ratio of domestic sewage, the organic matter in the raw water is not enough for the denitrification process, so the traditional biological sewage process of the sewage treatment plant needs to invest a lot of carbon source and energy to remove pollutants in the sewage. This will greatly increase the treatment cost of the sewage treatment plant. In addition, a large amount of residual sludge will be generated, which will further increase the burden on the disposal of residual sludge in the sewage treatment plant. Therefore, a sewage treatment method that does not require an external carbon source to achieve deep denitrification and can reduce the output of residual sludge is of great significance to the field of sewage treatment.

[0003] Traditional nitrification is NH4 + -N is oxidized to NO2 by ammonia oxidizing bacteria (AOB) in the presence of oxygen - -N, NO2 - -N is then oxidized to NO3 by nitrite oxidizing bacteria (NOB) - -N, traditional denitrification is NO3 - -N is reduced to N2 by denitrifying bacteria under anoxic conditions and with a carbon source. The synchronous short-range nitrification and denitrification process is based on NH4 + -N nitrification process and NO2 - -N denitrification process occurs simultaneously in the same reactor and under the same environmental conditions. Synchronous short-range nitrification and denitrification is generally carried out under low dissolved oxygen conditions. Compared with traditional nitrification and denitrification, synchronous short-range nitrification and denitrification can save 25% of aeration volume and 40% of carbon source, increase the denitrification rate by 63%, and reduce the production of residual sludge by 300%.

[0004] Anaerobic ammonium oxidation process uses NH4 + -N and NO2 - -N is the substrate to react and generate NO3 - -N and N2, no carbon source is required, and the sludge production is low. It is the most economical sewage treatment method and can save the operating costs of sewage treatment plants. However, due to the long generation time of anaerobic ammonium oxidizing bacteria, there is competition with heterotrophic bacteria for substrates and living space. This patent uses granular sludge to retain anaerobic ammonium oxidizing bacteria and reduce the competition with heterotrophic bacteria.

[0005] The present invention connects the UASB reactor with the SBR reactor. The UASB reactor is divided into an anaerobic zone and an anoxic zone according to the influent. Granular sludge is cultivated in the UASB reactor, and part of the anaerobic ammonium oxidizing granular sludge is inoculated. The anaerobic ammonium oxidizing bacteria are used to convert NH4 + -N and NO2 refluxed from SBR - -N reacts to remove nitrogen from sewage. In addition, digestive bacteria remove organic matter from raw water in the anaerobic zone and store it in the body as an internal carbon source for denitrification in the anoxic zone to further remove nitrogen. The SBR reactor adopts a low-oxygen aeration strategy to achieve synchronous short-term nitrification and denitrification. Since the organic matter in the raw water is limited, the organic matter in the raw water is already less when it enters the SBR. Therefore, the occurrence of synchronous short-term nitrification and denitrification will consume the carbon source inside the sludge. Due to the limited carbon source, synchronous short-term nitrification and denitrification can remove part of the nitrogen, and can also accumulate part of the nitrogen. NO2 - -N. The entire system does not require an external carbon source, which can solve the problem of insufficient carbon source for domestic sewage, achieve deep denitrification while saving energy and making full use of the carbon source in the raw water, and will not produce excess sludge. The sludge concentration in the SBR reactor will gradually decrease, achieving the purpose of in-situ sludge reduction. Summary of the invention

[0006] The present invention realizes synchronous short-range nitrification and denitrification through low-oxygen aeration, and realizes anaerobic ammonia oxidation process in combination with UASB reactor, so as to achieve the purpose of deep denitrification of domestic sewage and in-situ sludge reduction. Raw water enters the UASB reactor from the water inlet tank. In the anaerobic zone, the organic matter in the raw water is anaerobically digested and stored by digestive bacteria, and the effluent enters the SBR reactor. Low-oxygen aeration is used in the SBR reactor, and the DO concentration is controlled at 0.3-0.5 mg / L. The SBR effluent enters the anoxic zone of the UASB reactor through the second water inlet on the side of the UASB reactor through a peristaltic pump for denitrification. Part of the effluent in the SBR reactor is used as the final effluent discharge system. According to the setting of the water inlet position, the bottom 1 / 3 of the UASB reactor is the anaerobic zone. Anaerobic bacteria store organic matter in the sewage in the form of internal carbon sources in the body. The upper 2 / 3 area is the reaction zone of anaerobic ammonia oxidizing bacteria and endogenous denitrifying bacteria. The anaerobic ammonia oxidizing bacteria use the NO2 produced by the SBR - -N, remove NH4 from sewage + -N, while endogenous denitrifying bacteria can remove NO3 produced by anaerobic ammonium oxidizing bacteria - -N. This invention can make full use of the carbon source in the raw water without adding an external carbon source, and low oxygen aeration can reduce the aeration volume, saving operating costs; the use of granular sludge can effectively retain the anaerobic ammonia-oxidizing bacteria in the reactor, and the cost is low. In addition, since synchronous short-range nitrification and denitrification will consume the carbon source inside the sludge, the sludge concentration in the SBR reactor will be gradually reduced, and in-situ sludge reduction can be achieved.

[0007] A process for simultaneously achieving deep denitrification and in-situ sludge reduction, comprising an inlet bucket (1), a UASB reactor (3), an intermediate water tank (5), an outlet tank (6), and an SBR reactor (8); wherein the inlet bucket (1) is connected to a first water inlet (reactor bottom) of the UASB reactor (3) via a first inlet pump (2) and an inlet pipe; the UASB reactor (3) is connected to the intermediate water tank (5) via an outlet pipe; the intermediate water tank (5) is connected to the SBR reactor (8) via a second inlet pump (7) and an inlet pipe; the outlet water in the SBR reactor (8) enters the outlet tank (6), and the outlet tank (6) is connected to a second water inlet on the side wall of the UASB reactor (3) via a reflux pump (4). The SBR reactor (8) uses an aeration pump (11), an aeration pipe and an aeration plate to perform low-oxygen aeration. The aeration pump is connected to a rotor flowmeter (10) to control the intensity of aeration. An agitator (9) is provided in the SBR reactor (8) for mixing mud and water. WTW probes are provided in the SBR reactor (8) and the UASB reactor (3) to monitor the pH value and dissolved oxygen concentration therein.

[0008] The treatment process of urban sewage in this process is as follows: First, the raw water enters the UASB reactor from the first water inlet of the water inlet tank. In the anaerobic zone, the digestive bacteria store the organic matter in the raw water in the form of internal carbon source in the body, and then the effluent after the three-phase separator enters the SBR reactor. The SBR reactor adopts low oxygen aeration, and the dissolved oxygen concentration is controlled at 0.3-0.5 mg / L. Under the action of nitrifying bacteria, NH4 + -N is oxidized to NO2 - -N, part of NO2 - -N is synchronously reduced to N2 by denitrifying bacteria using internal carbon sources. Finally, part of the effluent enters the anoxic zone of the UASB reactor from the second water inlet on the side of the UASB reactor for denitrification, and part of the effluent in the SBR reactor is discharged from the system as the final effluent.

[0009] The present invention provides a process for simultaneously achieving deep denitrification and in-situ sludge reduction, which is characterized by the following contents:

[0010] Synchronous short-term nitrification and denitrification start-up stage: inoculate the full-process nitrification sludge of the municipal sewage plant into the SBR reactor (8), and maintain the sludge concentration at 3500-4500 mg / L; adopt a low oxygen aeration strategy, control the dissolved oxygen concentration at 0.3-0.5 mg / L, the hydraulic retention time is 6h, and no active sludge discharge. At this stage, the NH4 + This stage can be considered to be successfully started when the -N concentration is lower than 5 mg / L, TN loss is observed under hypoxic conditions, and the nitrite accumulation rate in the effluent reaches more than 80%.

[0011] UASB reactor startup stage: inoculate anaerobic digestion sludge and part of anaerobic ammonium oxidation granular sludge in the UASB reactor, the sludge concentration is controlled at 5000-7000 mg / L, the temperature is maintained at 30-35℃ by a temperature control device, and the hydraulic retention time is controlled at 20-24h. The influent uses artificial water distribution, and the NH4 + -N and NO2 - The ratio of -N concentration is controlled at 1:1.32 to facilitate the growth of anaerobic ammonia-oxidizing bacteria. At this stage, when red granular sludge is observed in the reactor and the simultaneous removal rate of ammonia nitrogen and nitrite reaches more than 80%, this stage can be considered to be successfully started.

[0012] Normal operation stage: After the synchronous short-range nitrification and denitrification and the formation of granular sludge, the UASB reactor and the SBR reactor are connected in series, and the influent is the actual domestic sewage. According to the NO2 - -N concentration adjusts the reflux ratio to 50%-100% so that NH4 + -N and NO2 - -N concentration ratio is controlled at 1:1~1.32 and operates continuously. When COD≤50mg / L in the effluent of SBR reactor, NH4 + -N≤5mg / L, TN≤15mg / L, after maintaining for 30-40 days, the system can be considered to have reached a stable state. After stabilization, it will continue to operate according to the following parameters: the temperature of the UASB reactor is 30-35℃, and the hydraulic retention time is 20-24h; the dissolved oxygen concentration of the SBR reactor is 0.3-0.5mg / L, the hydraulic retention time is 6h, and there is no active sludge discharge; the reflux ratio of the SBR effluent back to the UASB reactor is 50%-100%.

[0013] A second water inlet is set at 1 / 4 to 1 / 3 of the side wall of the UASB reactor, dividing the UASB reactor into an anaerobic zone and an anoxic zone. The anaerobic zone is below the second water inlet and is used to store organic matter in the raw water. The anoxic zone is above the second water inlet and denitrifies the nitrite and nitric nitrogen returned from the SBR and performs anaerobic ammonia oxidation to achieve denitrification.

[0014] The dissolved oxygen concentration in the SBR reactor is set to 0.3-0.5 mg / L, and simultaneous nitrification and denitrification are achieved under low oxygen conditions to remove part of the nitrogen. At the same time, the sludge concentration in the reactor is gradually reduced due to the consumption of the internal carbon source of the sludge, thereby achieving in-situ sludge reduction.

[0015] The process of the present invention for simultaneously achieving deep denitrification and in-situ sludge reduction has the following advantages over the existing processes:

[0016] (1) The present invention divides UASB into anaerobic zone and anoxic zone according to the water inlet position, so that the UASB reactor has the dual functions of removing organic matter and denitrification. Compared with AOA or OA process, it can fully and effectively utilize the carbon source in the raw water, achieve deep denitrification, and reduce the reaction volume and floor space.

[0017] (2) The present invention adopts a low-oxygen aeration strategy to achieve short-range nitrification. Compared with full-range nitrification, it can save part of the aeration volume, save energy, and reduce the operating costs of sewage treatment products.

[0018] (3) Since the generation time of anaerobic ammonium oxidizing bacteria is relatively long, granular sludge can effectively retain anaerobic ammonium oxidizing bacteria. At the same time, due to the formation process of granular sludge, anaerobic ammonium oxidizing bacteria grow inside the particles, which can protect the anaerobic ammonium oxidizing bacteria from the impact and influence of organic matter in the influent.

[0019] (4) Since the simultaneous nitrification and denitrification process in the SBR reactor requires a carbon source, and the amount of carbon source entering it is relatively small, the carbon source inside the sludge will be consumed, resulting in a gradual decrease in the sludge concentration in the reactor. Not only will no excess sludge be produced, but in-situ reduction can also be achieved, without the need to consider the treatment of excess sludge, thereby reducing operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the results of a process that simultaneously achieves deep denitrification and in-situ sludge reduction. Figure 1 Middle: 1 is the water inlet barrel, 2 is the first water inlet pump, 3 is the UASB reactor, 4 is the reflux pump, 5 is the intermediate water tank, 6 is the water outlet barrel, 7 is the second water inlet pump, 8 is the SBR reactor, 9 is the agitator, 10 is the rotor flowmeter, and 11 is the aeration pump.

[0021] A process for simultaneously achieving deep denitrification and in-situ sludge reduction comprises an inlet bucket (1), a UASB reactor (3), an intermediate water tank (5), an outlet tank (6), and an SBR reactor (8); wherein the inlet bucket (1) is connected to a first water inlet (reactor bottom) of the UASB reactor (3) via a first inlet pump (2) and an inlet pipe; the UASB reactor (3) is connected to the intermediate water tank (5) via an outlet pipe; the intermediate water tank (5) is connected to the SBR reactor (8) via a second inlet pump (7) and an inlet pipe; the outlet water in the SBR reactor (8) enters the outlet tank (6), and the outlet tank (6) is connected to a second water inlet on the side wall of the UASB reactor (3) via a reflux pump (4). The SBR reactor (8) uses an aeration pump (11), an aeration pipe and an aeration plate to perform low-oxygen aeration. The aeration pump is connected to a rotor flowmeter (10) to control the intensity of aeration. An agitator (9) is provided in the SBR reactor (8) for mixing mud and water. WTW probes are provided in the SBR reactor (8) and the UASB reactor (3) to monitor the pH value and dissolved oxygen concentration therein.

[0022] Test system such as Figure 1 As shown, the effective volume of the UASB reactor is 5.6 L, the effective volume of the SBR reactor is 10 L, and both reactors are made of plexiglass.

[0023] The specific operations are as follows:

[0024] 1) Synchronous short-cut nitrification and denitrification start-up stage: Inoculate the full-process nitrification sludge of the municipal sewage plant into the SBR reactor (8), and maintain the sludge concentration at 3500-4500 mg / L; adopt a low oxygen aeration strategy, control the dissolved oxygen concentration at 0.3-0.5 mg / L, and the hydraulic retention time is 6 hours, without active sludge discharge. At this stage, the NH4 + This stage can be considered to be successfully started when the -N concentration is lower than 5 mg / L, TN loss is observed under hypoxic conditions, and the nitrite accumulation rate in the effluent reaches more than 80%.

[0025] 2) UASB reactor startup stage: inoculate anaerobic digestion sludge and part of anaerobic ammonium oxidation granular sludge in the UASB reactor, the sludge concentration is controlled at 5000-7000 mg / L, the temperature is maintained at 30-35℃ by a temperature control device, and the hydraulic retention time is controlled at 20-24h. The influent uses artificial water distribution, and the NH4 + -N and NO2 - The ratio of -N concentration is controlled at 1:1.32 to facilitate the growth of anaerobic ammonia-oxidizing bacteria. At this stage, when red granular sludge is observed in the reactor and the simultaneous removal rate of ammonia nitrogen and nitrite reaches more than 80%, this stage can be considered to be successfully started.

[0026] 3) Normal operation stage: After the synchronous short-range nitrification and denitrification and the formation of granular sludge, the UASB reactor and the SBR reactor are connected in series, and the influent is the actual domestic sewage. According to the NO2 - -N concentration adjusts the reflux ratio to 50%-100% so that NH4 + -N and NO2 - -N concentration ratio is controlled at 1:1~1.32 and operates continuously. When COD≤50mg / L in the effluent of SBR reactor, NH4 + -N≤5mg / L, TN≤15mg / L, after maintaining for 30-40 days, the system can be considered to have reached a stable state. After stabilization, it will continue to operate according to the following parameters: the temperature of the UASB reactor is 30-35℃, and the hydraulic retention time is 20-24h; the dissolved oxygen concentration of the SBR reactor is 0.3-0.5mg / L, the hydraulic retention time is 6h, and there is no active sludge discharge; the reflux ratio of the SBR effluent back to the UASB reactor is 50%-100%.

Claims

1. A process for simultaneously achieving deep denitrification and in-situ sludge reduction, characterized in that: The device used in the process comprises a water inlet barrel (1), a UASB reactor (3), an intermediate water tank (5), a water outlet tank (6), and an SBR reactor (8); wherein the water inlet barrel (1) is connected to the first water inlet (bottom of the reactor) of the UASB reactor (3) via a first water inlet pump (2) and a water inlet pipe; the UASB reactor (3) is connected to the intermediate water tank (5) via a water outlet pipe; the intermediate water tank (5) is connected to the SBR reactor (8) via a second water inlet pump (7) and a water inlet pipe; The effluent enters an outlet water tank (6), which is connected to a second water inlet on the side wall of the UASB reactor (3) via a reflux pump (4); the SBR reactor (8) uses an aeration pump (11), an aeration pipe and an aeration disk for low-oxygen aeration, and the aeration pump is connected to a rotor flowmeter (10) to control the intensity of aeration. An agitator (9) is provided in the SBR reactor (8) for mixing mud and water, and WTW probes are provided in the SBR reactor (8) and the UASB reactor (3) to monitor the pH value and dissolved oxygen concentration therein.

2. A process for simultaneously achieving deep denitrification and in-situ sludge reduction according to claim 1, characterized in that: 1) Synchronous short-cut nitrification and denitrification start-up stage: The full-process nitrification sludge of the municipal sewage plant was inoculated into the SBR reactor (8), and the sludge concentration was maintained at 3500-4500 mg / L; a low oxygen aeration strategy was adopted, that is, the dissolved oxygen concentration was controlled at 0.3-0.5 mg / L, the hydraulic retention time was 6 h, and no active sludge discharge was performed; at this stage, the NH4 + -When the N concentration is lower than 5 mg / L, TN loss is observed under hypoxic conditions, and the nitrite accumulation rate in the effluent reaches more than 80%, this stage is considered to be successfully started; 2) UASB reactor startup stage: inoculate anaerobic digestion sludge and part of anaerobic ammonium oxidation granular sludge in the UASB reactor, the sludge concentration is controlled at 5000-7000 mg / L, the temperature is maintained at 30-35℃ by a temperature control device, and the hydraulic retention time is controlled at 20-24h; NH4 + -N and NO2 — The ratio of N mass concentration was controlled at 1:1.32 to facilitate the growth of anaerobic ammonia-oxidizing bacteria. At this stage, when red granular sludge was observed in the reactor and the simultaneous removal rate of ammonia nitrogen and nitrite reached more than 80%, it was considered that this stage was successfully started. 3) Operation phase: After the synchronous short-range nitrification and denitrification and the formation of granular sludge, the UASB reactor and the SBR reactor are connected in series, and the influent is the actual domestic sewage. According to the NO2 - -N concentration adjusts the reflux ratio to 50%-100% so that NH4 + -N and NO2 — The ratio of N mass concentration is controlled at 1:1~1.32 and operated continuously; when COD≤50mg / L in the effluent of SBR reactor, NH4 + -N≤5mg / L, TN≤15mg / L, after maintaining for 30-40 days, the system is considered to have reached a stable state. After stabilization, it will continue to operate according to the following parameters: the temperature of the UASB reactor is 30-35℃, and the hydraulic retention time is 20-24h; the dissolved oxygen concentration of the SBR reactor is 0.3-0.5mg / L, the hydraulic retention time is 6h, and there is no active sludge discharge; the reflux ratio of the SBR effluent back to the UASB reactor is 50%-100%.

Images