A method for starting up a sulfur autotrophic activated sludge process

Abstract

This invention discloses a start-up method for a sulfur autotrophic activated sludge process, comprising: inoculation of activated sludge; internal circulation of activated sludge; a first stage of sulfur autotrophic denitrification acclimatization, wherein the supernatant recirculation ratio of the first stage is ≥400%, and the influent flow rate of nitrate nitrogen wastewater is ≤40% of the design flow rate; a second stage of sulfur autotrophic denitrification acclimatization, wherein the supernatant recirculation ratio of the second stage is greater than or equal to the supernatant recirculation ratio of the first stage; and a third stage of sulfur autotrophic denitrification acclimatization, wherein the supernatant recirculation ratio of the third stage is greater than or equal to the supernatant recirculation ratio of the second stage. The start-up procedure ends after the effluent nitrate nitrogen removal rate reaches the required level. According to the method of this invention, by combining a high proportion of recirculation with low load and low influent nitrate nitrogen wastewater, sufficient agitation of the sludge can be achieved, improving the proliferation rate of sulfur autotrophic denitrifying microorganisms while avoiding sludge loss, thus enabling rapid start-up in UASB denitrification denitrification units with a small to medium aspect ratio.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a start-up method for a sulfur autotrophic activated sludge process. Background Technology

[0002] Sulfur autotrophic denitrification is a process that utilizes chemoautotrophic microorganisms under anaerobic conditions to produce reduced sulfur (e.g., S2O3). 2- S 0 S 2- This process uses sulfur as an electron donor to reduce oxidized nitrogen to nitrogen gas (N2) and generate sulfate. It solves the problems of difficult carbon source addition and high cost in deep denitrification, making it a promising deep denitrification process. Currently, research on sulfur autotrophic denitrification mainly focuses on sulfur autotrophic denitrification filters using sintered sulfur particles of different sizes as electron donors, and there are also engineering implementation cases. However, research on pure activated sludge sulfur autotrophic denitrification processes using reduced sulfur as an electron donor is relatively limited.

[0003] Although autotrophic denitrifying bacteria are widely distributed, they have strict requirements for their living environment and are easily lost. Therefore, the sulfur autotrophic activated sludge process generally suffers from a long start-up period. Current research on activated sludge sulfur autotrophic denitrification reactors mainly focuses on upflow anaerobic sludge blanket (UASB) and anaerobic baffled reactor (ABR) designs. These two reactors primarily rely on an effective influent distribution system. The upward flow velocity generated by the influent and recirculation keeps the sludge in a fluidized state, allowing elemental sulfur to directly contact the denitrifying biofilm, resulting in the acquisition of soluble reduced sulfur / sulfur compounds through surface binding or extracellular enzymes.

[0004] In UASB reactors, a relatively large aspect ratio provides hydraulic stirring and good sludge settling, which is crucial for ensuring efficient operation. The relatively small diameter of the UASB reactor allows for better mixing in activated sludge processes by adjusting the upward flow velocity, and provides sufficient time for sludge to settle along the effluent flow path, significantly reducing the possibility of sludge loss. However, UASB reactors with large aspect ratios are difficult to implement in engineering practice. For UASB reactors with small to medium aspect ratios, poor mixing and sludge loss are problems faced from the initial acclimation stage of the sulfur autotrophic activated sludge process. Therefore, it is necessary to improve the sulfur autotrophic activated sludge process. Summary of the Invention

[0005] This invention is based on the inventor's discoveries and understanding of the following facts and problems:

[0006] Traditional activated sludge processes typically control the internal / external recirculation ratio below 400%. However, applying this empirical recirculation ratio to an upflow reactor-based sulfur autotrophic activated sludge process can lead to insufficient upward flow velocities from the influent and recirculation, resulting in inadequate sludge mixing. This leads to poor mass transfer between the substrate and sludge, insufficient microbial activity, low denitrification rates, and the sludge gradually turning black, ultimately causing acclimation failure. To achieve ideal mixing and rapid start-up, it is necessary to increase the influent flow rate and nitrate nitrogen load. This significantly increases the upward flow velocity and gas production. Under high upward flow velocity and gas production, sludge loss is likely to occur, which can also lead to acclimation failure.

[0007] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a start-up method for a sulfur autotrophic activated sludge process. By combining a high proportion of recirculation with low influent flow and low-load nitrate nitrogen wastewater, the sludge can be thoroughly agitated, achieving a good mixing state, improving the proliferation rate of sulfur autotrophic denitrifying microorganisms, and simultaneously preventing sludge loss. This enables rapid start-up in UASB denitrification denitrification units with a small to medium aspect ratio.

[0008] This invention provides a start-up method for a sulfur autotrophic activated sludge process, comprising the following steps:

[0009] Step S1, Inoculation of activated sludge: Inoculate activated sludge into the UASB denitrification unit;

[0010] Step S2, internal circulation of activated sludge: The inoculated activated sludge is internally circulated in the UASB denitrification unit.

[0011] Step S3, the first stage of sulfur autotrophic denitrification acclimatization: nitrate nitrogen wastewater is introduced into the UASB denitrification denitrification unit at a low influent flow rate, and the supernatant reflux ratio of the first stage is adjusted to ≥400%; wherein, the influent flow rate of the nitrate nitrogen wastewater is ≤40% of the design flow rate of the UASB denitrification denitrification unit;

[0012] Step S4, the second stage of sulfur autotrophic denitrification acclimatization: continue to introduce nitrate nitrogen wastewater and add sulfur source, wherein the influent flow rate of nitrate nitrogen wastewater, nitrate nitrogen load and the S / N ratio of sulfur source to nitrate nitrogen wastewater remain unchanged, and adjust the supernatant reflux ratio of the second stage to be greater than or equal to the supernatant reflux ratio of the first stage.

[0013] Step S5, the third stage of sulfur autotrophic denitrification acclimatization: continue to introduce nitrate nitrogen wastewater and add sulfur source, wherein the influent flow rate of nitrate nitrogen wastewater, nitrate nitrogen load and the S / N ratio of sulfur source to nitrate nitrogen wastewater remain unchanged, adjust the supernatant reflux ratio of the third stage to be greater than or equal to the supernatant reflux ratio of the second stage, and end the start-up procedure after the effluent nitrate nitrogen removal rate reaches the requirement.

[0014] The advantages and technical effects of the start-up method of the sulfur autotrophic activated sludge process in this embodiment of the invention are as follows: 1. In the method of this embodiment, after the activated sludge is inoculated into the UASB denitrification unit, the internal circulation of the activated sludge can consume the residual organic matter and dissolved oxygen in the activated sludge, which is conducive to the formation of a good autotrophic and anoxic environment, providing a good environmental foundation for the subsequent sulfur autotrophic denitrification acclimatization; 2. In the method of this embodiment, a large proportion of recirculation is used in each stage of sulfur autotrophic denitrification acclimatization, and the recirculation ratio increases sequentially in each stage, so that a good environment can be maintained during the start-up of the sulfur autotrophic activated sludge process. 1. Good mixing state improves mass transfer between substrate and sludge; 2. The embodiment of the present invention uses low influent flow rate combined with large reflux ratio, which can achieve rapid start-up and avoid sludge loss caused by high upward flow velocity; 3. The embodiment of the present invention is less affected by the influent temperature of nitrate nitrogen wastewater and can achieve rapid start-up for influent with a wide temperature range; 4. The method of the embodiment of the present invention solves the contradiction between poor sludge mixing state and sludge loss during the start-up process in the same reactor, and solves the problem of slow proliferation rate of autotrophic denitrifying bacteria and long start-up cycle in sulfur autotrophic denitrification systems in the prior art.

[0015] In some embodiments, in step S3, the supernatant reflux ratio of the first stage is adjusted to ≥400% and less than the supernatant reflux ratio of the second stage; and / or, in step S4, the supernatant reflux ratio of the second stage is adjusted to be greater than or equal to the supernatant reflux ratio of the first stage and less than 2000%; and / or, in step S5, the supernatant reflux ratio of the third stage is adjusted to be greater than or equal to the supernatant reflux ratio of the second stage and less than 2500%.

[0016] In some embodiments, in step S3, the influent flow rate of the nitrate nitrogen wastewater is ≤3L / h.

[0017] In some embodiments, in step S3, the upward flow velocity is 2.7 to 4.9 m / h; and / or in step S4, the upward flow velocity is 2.9 to 7.5 m / h; and / or in step S5, the upward flow velocity is 3.1 to 8.8 m / h.

[0018] In some embodiments, the height-to-diameter ratio of the UASB denitrification device is greater than or equal to 8, preferably greater than or equal to 8 and less than or equal to 20.

[0019] In some embodiments, when the height-to-diameter ratio of the UASB denitrification unit is less than or equal to 12, the nitrate nitrogen load is ≤2.5 mg-NO3. - -N / g-VSS / hr.

[0020] In some embodiments, in step S3, the first stage of acclimatization is completed when the effluent nitrate nitrogen removal rate reaches 60%; and / or, in step S4, the second stage of acclimatization is completed when the effluent nitrate nitrogen removal rate reaches 80%; and / or, in step S5, the third stage of acclimatization is completed when the effluent nitrate nitrogen removal rate reaches 85%; and / or in steps S3, S4, or S5, the S / N mass ratio of the sulfur source to the nitrate nitrogen wastewater is controlled to be ≥5:1; and / or the influent temperature of the nitrate nitrogen wastewater is 6–25°C.

[0021] In some embodiments, in step S1, the activated sludge contains sulfur-autotrophic microorganisms; the mixed liquor suspended solids (MLSS) concentration of the activated sludge is ≥8 g / L, and the mixed liquor volatile suspended solids (MLVSS) concentration of the activated sludge is ≥40%.

[0022] In some embodiments, the UASB denitrification device includes: an upflow anaerobic sludge blanket (UASB) reactor, a raw water tank, an influent pump, and a return pump; the UASB reactor, the raw water tank, and the influent pump operate continuously; the UASB denitrification device includes a lower columnar reaction zone and an upper sedimentation zone, the bottom of the UASB denitrification device has an inlet and a bottom return port, and the top has an outlet and a top return port; the UASB denitrification device includes a return pipe, the return pump is installed on the return pipe, one end of the return pipe is connected to the bottom return port, and the other end is connected to the top return port.

[0023] In some embodiments, in step S2, the inoculated activated sludge is internally circulated in the UASB denitrification unit, including: turning on the return pump to return the water in the activated sludge to the UASB denitrification unit through the return pipe for internal circulation; wherein, during the internal circulation process, the upward flow velocity of the water is 1 to 3 m / h, and the internal circulation time is 1 to 3 days.

[0024] In some embodiments, in step S3, the nitrate nitrogen wastewater includes effluent from the secondary sedimentation tank of a wastewater treatment plant and additives; the additives include nitrate nitrogen agents, preferably, the additives also include trace elements, sodium bicarbonate and potassium dihydrogen phosphate; the nitrate nitrogen agents include at least one of potassium nitrate or sodium nitrate.

[0025] In some embodiments, in step S3, the sulfur source includes at least one of sodium thiosulfate or elemental sulfur, preferably sodium thiosulfate. Attached Figure Description

[0026] Figure 1 A schematic flow diagram of the start-up method of the sulfur autotrophic activated sludge process based on a UASB reactor in an embodiment of the present invention is shown.

[0027] Figure 2 A schematic diagram showing the results of nitrate nitrogen and sulfate operation during the start-up phase of the method in Example 1 is shown. Detailed Implementation

[0028] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0029] In the following description, when referring to the accompanying drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0030] like Figure 1 As shown, this embodiment of the invention provides a start-up method for a sulfur autotrophic activated sludge process based on a UASB reactor, including steps S1 to S5.

[0031] Step S1: Inoculate the activated sludge into the UASB denitrification unit.

[0032] In some embodiments, the height-to-diameter ratio of the UASB denitrification unit is greater than or equal to 8, preferably 8 ≤ height-to-diameter ratio ≤ 20, more preferably 8 ≤ height-to-diameter ratio ≤ 12, for example, 10. When the height-to-diameter ratio of the denitrification unit is too small, sludge loss is likely to occur, while when the height-to-diameter ratio is too large, it is difficult to implement in engineering practice. The method of this invention, using a UASB denitrification unit with a small to medium height-to-diameter ratio, has good prospects for industrial application.

[0033] In some embodiments, the UASB denitrification device is the denitrification device disclosed in Chinese patent application CN106630134A.

[0034] In some embodiments, the UASB denitrification unit includes an upflow anaerobic sludge blanket (UASB) reactor, a raw water tank, an influent pump, and a return pump, and operates in a continuous mode. In some embodiments, the UASB denitrification unit has a vertical upflow structure, divided into a lower columnar reaction zone and an upper sedimentation zone. The bottom of the UASB denitrification unit has an inlet and a bottom return port, and the top (outlet weir) has an outlet and a top return port.

[0035] In some embodiments, the UASB denitrification unit is further equipped with a reflux pipe, a reflux pump is installed on the reflux pipe, one end of the reflux pipe is connected to the bottom reflux port, and the other end is connected to the top reflux port.

[0036] In some embodiments, the activated sludge is a sludge-water mixture containing sulfur-autotrophic microorganisms. The mixed liquor suspended solids (MLSS) concentration of the activated sludge is ≥8 g / L, preferably 8 to 20 g / L; the mixed liquor volatile suspended solids (MLVSS) concentration is ≥40%.

[0037] In some embodiments, the activated sludge is the residual sludge from the secondary sedimentation tank of a municipal wastewater treatment plant, but in this case, the abundance and activity of sulfur autotrophic microorganisms are not high.

[0038] In some embodiments, after step S1, the method further includes: allowing the activated sludge to stand to separate the sludge from the water, thereby obtaining a higher mixed liquor suspended solids concentration (MLSS).

[0039] Step S2 involves internally circulating the inoculated activated sludge within the UASB denitrification unit.

[0040] In this embodiment of the invention, after the activated sludge is inoculated into the denitrification and nitrogen removal device, the internal circulation of the activated sludge can consume the residual organic matter and dissolved oxygen therein, forming a good autotrophic and anoxic environment, which provides a good foundation for subsequent treatment stages.

[0041] In some embodiments, step S2 includes: activating the return pump to return water from the activated sludge-water mixture to the UASB denitrification unit through the return pipe for internal circulation. During internal circulation, the upward flow velocity of the water is 1 to 3 m / h, and the internal circulation time is 1 to 3 days. By controlling the flow rate of the peristaltic pump in the UASB denitrification unit, the water in the activated sludge can be internally circulated from the return pipe to the UASB denitrification unit. Simultaneously, the activated sludge is slightly agitated during the water circulation process, which consumes residual organic matter and dissolved oxygen in the activated sludge, creating a favorable autotrophic and anoxic environment.

[0042] Step S3: Perform the first stage of sulfur autotrophic denitrification acclimatization: introduce nitrate nitrogen wastewater into the UASB denitrification denitrification unit and add sulfur source, adjust the first stage supernatant reflux ratio to ≥400%, wherein the influent flow rate of nitrate nitrogen wastewater is ≤40% of the design flow rate of the UASB denitrification denitrification unit.

[0043] In some embodiments, the supernatant reflux ratio of the first stage is adjusted to ≥400%, preferably ≥600%, for example, 600%, 900%, 1000%, or 1080%. If the reflux ratio of the first stage is too small, it is not conducive to the formation of a good mixed state in the UASB denitrification unit, and the sludge is prone to blackening, leading to start-up failure.

[0044] In some embodiments, in step S3, the influent flow rate is ≤ 40% of the design flow rate of the UASB denitrification unit. For example, the influent flow rate of nitrate nitrogen wastewater is ≤ 3L / h, such as 2L / h or 3L / h. When the influent flow rate of nitrate nitrogen wastewater is too high, sludge loss is likely to occur. This invention uses a low influent flow rate for startup, which can avoid the problem of sludge loss in reactors with small to medium aspect ratios.

[0045] The embodiments of the present invention employ a high proportion of reflux combined with a small influent volume, which not only prevents the sludge in the reactor from being lost, but also allows the sludge to be fully agitated, thereby improving the mixing state of the inoculated activated sludge in the UASB denitrification unit.

[0046] In some embodiments, in step S3, the upward flow velocity is 2.7–4.9 m / h, preferably 3.9–4.4 m / h, for example 3.98 m / h or 4.38 m / h. The upward flow velocity can be calculated using the influent flow rate and reflux ratio in the device. When the upward flow velocity is too low, the agitation effect on the sludge is poor, and the sludge cannot reach a good mixing state, which can easily lead to start-up failure. When the upward flow velocity is too high, sludge loss is likely to occur, which may also lead to acclimatization failure. In the embodiments of the present invention, the acclimatization process uses a large reflux ratio and a small influent flow rate, which can obtain a high upward flow velocity, thus forming a good mixing state and ensuring that sludge is not lost in devices with small to medium diameter ratios, thereby shortening the start-up time.

[0047] In some embodiments, the nitrate nitrogen wastewater is artificially prepared nitrate nitrogen-containing water. When the height-to-diameter ratio of the UASB denitrification unit is greater than or equal to 8 and less than or equal to 12, the nitrate nitrogen load of the nitrate nitrogen-containing water is controlled at 2.5 mg-NO3. - -N / g-VSS / hr or less, preferably 2.1 mg-NO3 - -N / g-VSS / hr or less, more preferably (1.45±0.18)~(1.94±0.16) mg-NO3 -The nitrate nitrogen loading in the nitrate nitrogen-containing water is between -N / g and -VSS / hr. For example, when the height-to-diameter ratio is 10, the nitrate nitrogen loading is (1.94±0.16) mg-NO3. - -N / g-VSS / hr. When the nitrate nitrogen load in the nitrate nitrogen feedwater is too high, the gas production is large, which easily leads to sludge loss. This invention controls the nitrate nitrogen load at a low level, which can achieve rapid start-up at low concentrations, avoiding the sludge loss problem caused by gas production during high-concentration start-up, especially in UASB reactors with small aspect ratios. It can also stably and gradually reach the optimal denitrification state, thereby further improving the start-up effect.

[0048] In some embodiments, the influent temperature of nitrate nitrogen wastewater is 6–25°C, preferably 15–25°C, and more preferably 22–25°C. The method of this embodiment is less affected by the influent temperature and can achieve rapid start-up for influent within a wide temperature range.

[0049] In some embodiments, in step S3, nitrate nitrogen wastewater is introduced into the UASB denitrification denitrification unit through the inlet and continuously discharged through the outlet.

[0050] In some embodiments, the first stage of acclimatization is completed when the effluent nitrate removal rate reaches 60%.

[0051] In some embodiments, the sulfur source includes at least one of sodium thiosulfate or elemental sulfur, preferably sodium thiosulfate. In step S3, the S / N mass ratio of the sulfur source to nitrate nitrogen wastewater is controlled to be ≥5:1, preferably in the range of 5:1 to 8:1, and more preferably 5:1. The preferred S / N mass ratio in this embodiment of the invention is beneficial to the sulfur autotrophic denitrification acclimatization process, while also saving the amount of electron donor sodium thiosulfate used.

[0052] In some embodiments, nitrate nitrogen wastewater includes effluent from the secondary sedimentation tank of a wastewater treatment plant and additives.

[0053] In some embodiments, the additive includes a nitrate nitrogen agent; the nitrate nitrogen agent includes at least one of potassium nitrate or sodium nitrate. Further, the additive also includes trace elements, sodium bicarbonate, or potassium dihydrogen phosphate.

[0054] In some embodiments, the chemical oxygen demand (COD) concentration of the effluent from the secondary sedimentation tank of the wastewater treatment plant is 15 to 50 mg / L, the total nitrogen concentration is 10 to 20 mg / L, the ammonia nitrogen concentration is 0.1 to 2.5 mg / L, the total phosphorus concentration is 0.3 to 1.0 mg / L, and the pH value is 7.4 to 8.2.

[0055] Step S4, carry out the second stage of sulfur autotrophic denitrification acclimatization: continue to introduce nitrate nitrogen wastewater and add sulfur source, wherein the influent flow rate of nitrate nitrogen wastewater, nitrate nitrogen load and S / N ratio remain unchanged, and adjust the supernatant reflux ratio of the second stage to be greater than or equal to the supernatant reflux ratio of the first stage.

[0056] In some embodiments, the same concentration of nitrate wastewater and sulfur source as in step S3 is introduced into the UASB denitrification unit.

[0057] In some embodiments, in step S4, nitrate nitrogen wastewater is introduced into the UASB denitrification denitrification unit through the inlet and continuously discharged through the outlet.

[0058] In some embodiments, the second stage of acclimatization is completed when the effluent nitrate removal rate reaches 80%.

[0059] In some embodiments, in step S4, the upward flow velocity is 2.9 to 7.5 m / h, preferably 4.5 to 7.3 m / h, for example 4.7 m / h or 7.26 m / h.

[0060] In some embodiments, the second-stage supernatant reflux ratio is: 400% ≤ second-stage supernatant reflux ratio ≤ 2000%, preferably 500% ≤ second-stage supernatant reflux ratio ≤ 1800%; for example, 650%, 1080%, 1500% or 1724%.

[0061] Step S5: Conduct the third stage of sulfur autotrophic denitrification acclimatization: Continue to introduce nitrate nitrogen wastewater and add sulfur source, wherein the influent flow rate of nitrate nitrogen wastewater, nitrate nitrogen load and S / N ratio remain unchanged, adjust the supernatant reflux ratio of the third stage to be greater than or equal to the supernatant reflux ratio of the second stage, and end the start-up procedure after the effluent nitrate nitrogen removal rate reaches the requirements.

[0062] In some embodiments, the same concentration of nitrate wastewater and sulfur source as in step S3 is introduced into the UASB denitrification unit.

[0063] In some embodiments, in step S5, nitrate nitrogen wastewater is introduced into the UASB denitrification denitrification unit through the inlet and continuously discharged through the outlet.

[0064] In some embodiments, the third stage of acclimatization is completed when the effluent nitrate removal rate reaches 85%.

[0065] In some embodiments, in step S5, the upward flow velocity is 3.1 to 8.8 m / h, preferably 5.1 to 8.6 m / h, for example 5.18 m / h or 8.59 m / h.

[0066] In some embodiments, the third-stage supernatant reflux ratio is 400% ≤ 2500%, preferably 550% ≤ 2200%, for example, 700%, 1200%, 1800%, or 2059%.

[0067] In some embodiments, to enable faster startup of the sulfur autotrophic denitrification system, a supernatant recirculation port is installed below the effluent weir. Adjusting the supernatant recirculation ratio allows for regulation of the system's upward flow velocity, thereby improving the mixing effect between sludge and wastewater and ensuring a more stable denitrification process. The supernatant recirculation ratios for the first, second, and third stages can be adjusted based on the weight of the activated sludge flocs (i.e., sludge concentration (MLSS) * sludge layer volume). Adjusting the recirculation ratio using the method provided in this embodiment prevents sludge loss from the reactor while simultaneously ensuring sufficient sludge agitation.

[0068] The start-up method for the sulfur autotrophic activated sludge process based on a UASB reactor in this invention embodiment can effectively start up the sulfur autotrophic denitrification system in a UASB denitrification unit with a small aspect ratio and under low nitrate nitrogen load, with a short start-up time. Specifically, in this invention embodiment, after the activated sludge is inoculated into the denitrification unit, the internal circulation of the activated sludge can consume the residual organic matter and dissolved oxygen, forming a good autotrophic and anoxic environment, providing a good foundation for subsequent treatment stages. Secondly, under nitrate nitrogen load, the method of this invention embodiment abandons the traditional experience of controlling the internal / external recirculation ratio of activated sludge processes to below 400%, and adopts an acclimatization method with a high proportion of recirculation and a progressively increasing recirculation ratio in each stage. This ensures that the sulfur autotrophic activated sludge process maintains a good mixing state during start-up, improves the mass transfer between the substrate and sludge, and mitigates the sludge loss problem. For existing autotrophic bacterial processes that require maintaining a good mixing state but also face the problem of sludge loss due to gas production, the method of this invention solves this contradiction during startup within the same reactor. It addresses both the issue of poor mixing leading to suboptimal mass transfer between the substrate and sludge, resulting in sludge blackening, and the problem of sludge loss due to the combined effects of rising flow velocity and gas production. This method overcomes the problems of slow proliferation rate of autotrophic denitrifying bacteria and long startup cycles in existing autotrophic denitrification systems, enabling rapid startup of the autotrophic denitrification system and ensuring its stable operation. It is particularly suitable for deep denitrification treatment of secondary effluent from urban wastewater treatment plants.

[0069] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0070] Example 1

[0071] The denitrification device disclosed in Chinese patent application CN106630134A is used. It is an upflow reactor made of plexiglass with an effective volume of 12L. The bottom of the reactor is equipped with a reflux inlet, a water inlet, a sludge discharge outlet, and a water distribution plate. A peristaltic pump is used for water intake and reflux. The UASB denitrification device has a height of 0.8m, a height-to-diameter ratio of 10, and an effective volume of 0.004m³. 3 .

[0072] Step 1: Inoculate the reactor with activated sludge. The activated sludge is excess sludge from the secondary sedimentation tank of a municipal wastewater treatment plant in Beijing. After inoculation, the activated sludge inoculation concentration in the reactor is MLSS = 8.49 g / L and MLVSS = 48.20%.

[0073] Step 2: Start the internal circulation using a peristaltic pump, adjust the upward flow rate to 2.5 m / h, and run the circulation for 2 days without adding water. This allows the activated sludge to consume residual organic matter and dissolved oxygen, creating a favorable autotrophic and anoxic environment.

[0074] Step 3: First stage of sulfur autotrophic denitrification acclimatization

[0075] The effluent from the secondary sedimentation tank of a wastewater treatment plant was used. The characteristics of the secondary effluent from this wastewater treatment plant were: COD concentration 15–50 mg / L, total nitrogen (TN) concentration 10–20 mg / L, ammonia nitrogen concentration 0.1–2.5 mg / L, total phosphorus (TP) concentration 0.3–1.0 mg / L, and pH value approximately 7.4–8.2. Sodium nitrate and sodium thiosulfate were further added to maintain the nitrate nitrogen load in the influent at 1.94 ± 0.16 mg-NO3. - -N / g-VSS / hr, S / N mass ratio controlled at 5:1. In this stage, the influent flow rate is controlled at 2L / h, HRT = 2h, influent temperature between 15 and 21℃, and pH between 6.88 and 7.32. The reflux ratio is set to 1080%, the upflow velocity is 4.38m / h, and the unit operates for 17 days. NO3 - -N removal rate reached over 60%, completing the first stage of sulfur autotrophic denitrification acclimatization.

[0076] Step 4: Second stage of sulfur autotrophic denitrification acclimatization

[0077] Continue to introduce wastewater and a sulfur source, controlling the nitrate nitrogen load and S / N ratio in the influent to be the same as in step 3, increasing the reflux ratio to 1724%, and setting the upflow velocity to 7.26 m / h, allowing the unit to continue operating for 9 days. NO3 - -N removal rate reached over 80%, completing the second stage of sulfur autotrophic denitrification acclimatization.

[0078] Step 5: The third stage of sulfur autotrophic denitrification acclimatization

[0079] Continue to introduce wastewater and add sulfur sources to control NO3 in the influent. - The NO3- concentration and S / N ratio are the same as in step 3. As microorganisms continue to accumulate, the sludge flocs gradually increase in size and density, and their color gradually turns white. The mixing state in the reactor gradually deteriorates, and short-circuiting occurs. The reflux ratio is increased to 2059%, and the upflow velocity is 8.59 m / h, allowing the device to continue operating for another 15 days. - -N removal rate reached over 85%, completing the third stage of sulfur autotrophic denitrification acclimatization.

[0080] Step 6: End the startup process.

[0081] In this embodiment, the sulfur autotrophic denitrification system was started up in 41 days.

[0082] like Figure 2 As shown, in this embodiment, the initiation of the acclimatization process can be divided into two stages:

[0083] The first stage, from 0 to 17 days, is the sulfur autotrophic denitrification acclimatization period, with influent NO3... - The average concentration of -N was 38.30 mg / L, and NO3... - The average removal rate of nitrogen (N) was 58.65%; the average influent sulfate concentration was 368.75 mg / L, the average effluent sulfate concentration was 606.00 mg / L, the average sulfate production was 237.25 mg / L, and the autotrophic removal rate increased to 86.55%.

[0084] The second and third stages of sulfur autotrophic denitrification acclimatization take 18 to 40 days, with influent NO3... - The average concentration of -N was 38.40 mg / L, and NO3... - The average removal rate of nitrogen (N) was 76.01%; the average influent sulfate concentration was 406.00 mg / L, the average effluent sulfate concentration was 573.50 mg / L, the average sulfate production was 167.50 mg / L, and the autotrophic removal rate increased to 93.24%.

[0085] When the process reached day 41, the denitrification inflection point appeared, and NO3... - The average removal rate of -N was 87.06%, and the autotrophic removal rate rose to 94.07%, indicating a successful start-up.

[0086] Example 2

[0087] The method is the same as in Example 1, except that the inlet water temperature in step 3 is 6–10°C. The specific operation of steps 3-5 is as follows:

[0088] Step 3: First stage of sulfur autotrophic denitrification acclimatization: The influent flow rate is controlled at 2 L / h, and the nitrate nitrogen load in the influent is maintained at 1.94 ± 0.16 mg-NO3. - -N / g-VSS / hr, reflux ratio of 1080%, run for 18 days, NO3 - -N removal rate reached over 60%, completing the first stage of sulfur autotrophic denitrification acclimatization.

[0089] Step 4: Second stage of sulfur autotrophic denitrification acclimatization: Influent flow rate and nitrate nitrogen load remain constant, reflux ratio is 1724%, operation for 7 days, NO3 - -N removal rate reached over 80%, completing the second stage of sulfur autotrophic denitrification acclimatization.

[0090] Step 5: Third stage of sulfur autotrophic denitrification acclimatization: Influent flow rate and nitrate nitrogen load remain constant, reflux ratio is 2059%, operation for 22 days, NO3 - -N removal rate reached over 85%, completing the third stage of sulfur autotrophic denitrification acclimatization.

[0091] In this embodiment, the sulfur autotrophic denitrification system was started up in 47 days.

[0092] Example 3

[0093] The method is the same as in Example 1, except that the inlet water temperature in step 3 is 22–25°C. The specific operation of steps 3-5 is as follows:

[0094] Step 3: First stage of sulfur autotrophic denitrification acclimatization: The influent flow rate is controlled at 2 L / h, and the nitrate nitrogen load in the influent is maintained at 1.94 ± 0.16 mg-NO3. - -N / g-VSS / hr, reflux ratio 1080%, run for 14 days, NO3 - -N removal rate reached over 60%, completing the first stage of sulfur autotrophic denitrification acclimatization.

[0095] Step 4: Second stage of sulfur autotrophic denitrification acclimatization: Influent flow rate and nitrate nitrogen load remain constant, reflux ratio is 1920%, operation for 7 days, NO3 - -N removal rate reached over 80%, completing the second stage of sulfur autotrophic denitrification acclimatization.

[0096] Step 5: Third stage of sulfur autotrophic denitrification acclimatization: Influent flow rate and nitrate nitrogen load remain constant, reflux ratio is 2050%, operation for 16 days, NO3 - -N removal rate reached over 85%, completing the third stage of sulfur autotrophic denitrification acclimatization.

[0097] In this embodiment, the sulfur autotrophic denitrification system was started up in 37 days.

[0098] Example 4

[0099] The method is the same as in Example 1, except that the nitrate nitrogen loading in the influent in step 3 is maintained at 1.45 ± 0.18 mg NO3. - -N / g-VSS / hr. The specific operation of steps 3-5 is as follows:

[0100] Step 3: First stage of sulfur autotrophic denitrification acclimatization: Influent flow rate controlled at 2L / h, reflux ratio at 1080%, run for 18 days, NO3 - -N removal rate reached over 60%, completing the first stage of sulfur autotrophic denitrification acclimatization.

[0101] Step 4: Second stage of sulfur autotrophic denitrification acclimatization: Influent flow rate and nitrate nitrogen load remain constant, reflux ratio is 1920%, operation for 11 days, NO3 - -N removal rate reached over 80%, completing the second stage of sulfur autotrophic denitrification acclimatization.

[0102] Step 5: Third stage of sulfur autotrophic denitrification acclimatization: Influent flow rate and nitrate nitrogen load remain constant, reflux ratio is 2050%, operation for 21 days, NO3 - -N removal rate reached over 85%, completing the third stage of sulfur autotrophic denitrification acclimatization.

[0103] In this embodiment, the sulfur autotrophic denitrification system was started up in 50 days.

[0104] Example 5

[0105] The method is the same as in Example 1, except that the UASB denitrification unit has a height of 1.6m, a height-to-diameter ratio of 20, and an effective volume of 0.008m³. 3 The influent flow rate in steps 3-5 is controlled at 3 L / h, and the nitrate nitrogen load in the influent is maintained at 3.06 ± 0.15 mg-NO3. - -N / g-VSS / hr, and the reflux ratios are different. The specific operation of steps 3-5 is as follows:

[0106] Step 3: First stage of sulfur autotrophic denitrification acclimatization: Influent flow rate controlled at 3 L / h, reflux ratio at 400%, upflow velocity at 2.99 m / h, run for 21 days, NO3 - -N removal rate reached over 60%, completing the first stage of sulfur autotrophic denitrification acclimatization.

[0107] Step 4: Second stage of sulfur autotrophic denitrification acclimatization: Influent flow rate and nitrate nitrogen load remain constant, reflux ratio is 500%, upflow velocity is 3.58 m / h, operation for 13 days, NO3... --N removal rate reached over 80%, completing the second stage of sulfur autotrophic denitrification acclimatization.

[0108] Step 5: Third stage of sulfur autotrophic denitrification acclimatization: Influent flow rate and nitrate nitrogen load remain constant, reflux ratio is 550%, upflow velocity is 3.88 m / h, operation for 14 days, NO3... - -N removal rate reached over 85%, completing the third stage of sulfur autotrophic denitrification acclimatization.

[0109] In this embodiment, the sulfur autotrophic denitrification system was started up in 48 days.

[0110] Example 6

[0111] The method is the same as in Example 1, except that the reflux ratio in steps 3-5 is different. The specific operation of steps 3-5 is as follows:

[0112] Step 3: First stage of sulfur autotrophic denitrification acclimatization: Influent flow rate controlled at 2L / h, reflux ratio at 600%, upflow velocity at 2.79m / h, run for 20 days, NO3 - -N removal rate reached over 60%, completing the first stage of sulfur autotrophic denitrification acclimatization.

[0113] Step 4: Second stage of sulfur autotrophic denitrification acclimatization: Influent flow rate and nitrate nitrogen load remain constant, reflux ratio is 650%, upflow velocity is 2.99 m / h, operation for 10 days, NO3... - -N removal rate reached over 80%, completing the second stage of sulfur autotrophic denitrification acclimatization.

[0114] Step 5: Third stage of sulfur autotrophic denitrification acclimatization: Influent flow rate and nitrate nitrogen load remain constant, reflux ratio is 700%, upflow velocity is 3.18 m / h, operation for 22 days, NO3... - -N removal rate reached over 85%, completing the third stage of sulfur autotrophic denitrification acclimatization.

[0115] In this embodiment, the sulfur autotrophic denitrification system was started up in 52 days.

[0116] Example 7

[0117] The method is the same as in Example 1, except that the reflux ratio in steps 3-5 is different. The specific operation of steps 3-5 is as follows:

[0118] Step 3: First stage of sulfur autotrophic denitrification acclimatization: Influent flow rate controlled at 2L / h, reflux ratio at 900%, upflow velocity at 3.98m / h, run for 20 days, NO3 - -N removal rate reached over 60%, completing the first stage of sulfur autotrophic denitrification acclimatization.

[0119] Step 4: Second stage of sulfur autotrophic denitrification acclimatization: Influent flow rate and nitrate nitrogen load remain constant, reflux ratio is 1080%, upflow velocity is 4.70 m / h, operation for 9 days, NO3 - -N removal rate reached over 80%, completing the second stage of sulfur autotrophic denitrification acclimatization.

[0120] Step 5: Third stage of sulfur autotrophic denitrification acclimatization: Influent flow rate and nitrate nitrogen load remain constant, reflux ratio is 1200%, upflow velocity is 5.18 m / h, operation for 18 days, NO3... - -N removal rate reached over 85%, completing the third stage of sulfur autotrophic denitrification acclimatization.

[0121] In this embodiment, the sulfur autotrophic denitrification system was started up in 47 days.

[0122] Comparative Example 1

[0123] The method is the same as in Example 1, except that the reflux ratio in step 3 is controlled at 200%, and the specific operation is as follows:

[0124] Step 3: First stage of sulfur autotrophic denitrification acclimatization: The influent flow rate is controlled at 2 L / h, and the nitrate nitrogen load in the influent is maintained at 1.94 ± 0.16 mg-NO3. - With a reflux ratio of 200% and a denitrification rate of -N / g-VSS / hr, the sludge turns black after 7 days of operation, indicating a low denitrification rate and insufficient microbial activity in the sludge, signifying a startup failure.

[0125] Comparative Example 2

[0126] The method is the same as in Example 1, except that the reflux ratio in step 3 is controlled at 100%. The specific operation is as follows:

[0127] Step 3: First stage of sulfur autotrophic denitrification acclimatization: The influent flow rate is controlled at 2 L / h, and the nitrate nitrogen load in the influent is maintained at 1.94 ± 0.16 mg-NO3. - With a reflux ratio of 100% and a denitrification rate of -N / g-VSS / hr, the sludge turned black on the third day of operation, indicating a low denitrification rate and insufficient microbial activity in the sludge, signifying a startup failure.

[0128] Comparative Example 3

[0129] The method is the same as in Example 6, except that the influent flow rate in steps 3 to 5 is 7.4 L / h, which is greater than 40% of the device's design flow rate. The specific operating conditions are as follows:

[0130] Step 3: First stage of sulfur autotrophic denitrification acclimatization: The influent flow rate is controlled at 7.4 L / h, the reflux ratio is 600%, and the upflow velocity is 6.97 m / h. Due to the poor retention effect of the inoculated sludge flocs, all the sludge was lost after one day of operation, indicating that the start-up failed.

[0131] In the methods of Examples 1 to 7 of this invention, by employing a large reflux ratio combined with a small influent flow rate during the sulfur autotrophic denitrification acclimatization at each stage, the mixed state within the low aspect ratio reactor is effectively improved, enabling rapid start-up even under low-load nitrate nitrogen wastewater conditions. The sulfur autotrophic denitrification acclimatization in the methods of this invention mainly goes through an adaptation period and an improvement period, gradually entering a stable period after the denitrification inflection point appears. As microorganisms continuously accumulate within the reactor, the mixed state within the reactor gradually deteriorates, leading to instability, i.e., the appearance of NO3. - The fluctuation in the reduction of -N removal efficiency is a critical period for the acclimatization of the sulfur autotrophic activated sludge process. The method of this embodiment effectively adjusts the mixing state in the reactor by sequentially increasing the reflux ratio at each stage, enabling the sulfur autotrophic denitrification system of this embodiment to quickly enter the stable period and complete the start-up, effectively shortening the start-up time. The reactor can be successfully started up within 37 to 52 days.

[0132] In Examples 1 to 3 of this invention, the sulfur autotrophic denitrification acclimatization process under different influent temperatures was compared. It is evident that the sulfur autotrophic denitrification acclimatization method according to this invention is less affected by influent temperature and can achieve rapid start-up over a wide temperature range. Furthermore, even at lower water temperatures, rapid start-up can be achieved.

[0133] Example 4 of the present invention further reduces the nitrate nitrogen load to 1.45 ± 0.18 mg-NO3. - The results below -N / g-VSS / hr demonstrate that the method of the present invention can be started up under low nitrate nitrogen load, improve the reflux ratio at each stage, achieve low concentration start-up, and help avoid sludge loss caused by gas generation during high concentration start-up.

[0134] In Comparative Examples 1 and 2, the reflux ratio was reduced to below 400%. In Comparative Examples 1 and 2, the sludge turned black, indicating startup failure. Comparing Example 1 and Comparative Examples 1 and 2, reducing the reflux ratio to below 400% of the conventional empirical value did not achieve rapid startup of the sulfur autotrophic denitrification system.

[0135] In Comparative Example 3, increasing the influent flow rate to 7.4 L / h resulted in rapid sludge loss and startup failure. Compared to Example 6, this demonstrates that excessive influent flow rate not only fails to adequately agitate the sludge but also leads to rapid sludge loss.

[0136] In summary, to address the issues of poor sludge mixing leading to suboptimal mass transfer between the substrate and sludge, resulting in sludge blackening, and sludge loss due to the combined effects of rising flow velocity and gas production, this invention provides a start-up method for a sulfur autotrophic activated sludge process based on a UASB reactor. This method improves the proliferation rate of sulfur autotrophic denitrifying microorganisms, maintains the microbial biomass within the reactor, minimizes sludge loss, and reduces the start-up cycle of the sulfur autotrophic activated sludge process.

[0137] The method of this invention involves inoculating activated sludge into a UASB denitrification unit. The internal circulation of the activated sludge consumes residual organic matter and dissolved oxygen, promoting a favorable autotrophic and anoxic environment and providing a good environmental foundation for subsequent sulfur autotrophic denitrification acclimatization. This invention's start-up method for sulfur autotrophic activated sludge processes based on a UASB reactor can rapidly and effectively start up a sulfur autotrophic denitrification system in UASB denitrification units with small to medium aspect ratios, particularly an aspect ratio of 10. This invention combines high-proportion recirculation and low influent volume in each stage of sulfur autotrophic denitrification acclimatization, maintaining good mixing during the start-up process, improving mass transfer between the substrate and sludge, and avoiding sludge loss. This solves the contradictions during startup within the same reactor, overcomes the problems of slow proliferation rate of autotrophic denitrifying bacteria and long startup cycle in existing technologies, and enables rapid startup of the autotrophic denitrification system while ensuring its stable operation. It is especially suitable for deep denitrification treatment of secondary effluent from urban wastewater treatment plants.

[0138] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0139] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A start-up method for a sulfur autotrophic activated sludge process, characterized in that, Includes the following steps: Step S1, Inoculation of activated sludge: Inoculate activated sludge into the UASB denitrification unit; The height-to-diameter ratio of the UASB denitrification unit is greater than or equal to 8. Step S2, internal circulation of activated sludge: The inoculated activated sludge is internally circulated in the UASB denitrification unit; the internal circulation time is 1 to 3 days. Step S3, the first stage of sulfur autotrophic denitrification acclimatization: Nitrate nitrogen wastewater is introduced into the UASB denitrification denitrification device, and a sulfur source is added to adjust the first stage supernatant reflux ratio to ≥400%; wherein, the influent flow rate of the nitrate nitrogen wastewater is ≤40% of the design flow rate of the UASB denitrification denitrification device; Step S4, the second stage of sulfur autotrophic denitrification acclimatization: continue to introduce nitrate nitrogen wastewater and add sulfur source, wherein the influent flow rate of nitrate nitrogen wastewater, nitrate nitrogen load and S / N ratio of sulfur source to nitrate nitrogen wastewater remain unchanged, and adjust the supernatant reflux ratio of the second stage to be greater than the supernatant reflux ratio of the first stage; Step S5, the third stage of sulfur autotrophic denitrification acclimatization: continue to introduce nitrate nitrogen wastewater and add sulfur source, wherein the influent flow rate of nitrate nitrogen wastewater, nitrate nitrogen load and S / N ratio of sulfur source to nitrate nitrogen wastewater remain unchanged, adjust the supernatant return ratio of the third stage to be greater than the supernatant return ratio of the second stage, and end the start-up program after the effluent nitrate nitrogen removal rate reaches the requirement. The influent temperature of the nitrate nitrogen wastewater is 6~25℃; In step S3, S4 or S5, the S / N mass ratio of the sulfur source to the nitrate nitrogen wastewater is controlled to be ≥5:

1.

2. The method according to claim 1, characterized in that, In step S4, the supernatant reflux ratio of the second stage is adjusted to be greater than that of the first stage supernatant reflux ratio, but less than 2000%; and / or In step S5, the supernatant reflux ratio of the third stage is adjusted to be greater than that of the second stage supernatant reflux ratio, but less than 2500%.

3. The method according to claim 1 or 2, characterized in that, In step S3, the influent flow rate of the nitrate nitrogen wastewater is ≤3 L / h.

4. The method according to claim 1 or 2, characterized in that, In step S3, the upward flow velocity is 2.7~4.9 m / h; and / or In step S4, the upward flow velocity is 2.9~7.5 m / h; and / or In step S5, the upward flow velocity is 3.1~8.8 m / h.

5. The method according to claim 1 or 2, characterized in that, The height-to-diameter ratio of the UASB denitrification unit is greater than or equal to 8 and less than or equal to 20.

6. The method according to claim 5, characterized in that, When the height-to-diameter ratio of the UASB denitrification unit is less than or equal to 12, the nitrate nitrogen load is ≤2.5 mg-NO3. - -N / g-VSS / hr.

7. The method according to claim 1 or 2, characterized in that, In step S3, when the nitrate and nitrogen removal rate of the effluent reaches 60%, the first stage of acclimatization is completed; and / or In step S4, when the effluent nitrate and nitrogen removal rate reaches 80%, the second stage of acclimatization is completed; and / or In step S5, when the nitrate removal rate of the effluent reaches 85%, the third stage of acclimatization is completed.

8. The method according to claim 1 or 2, characterized in that, In step S1, the activated sludge contains sulfur-autotrophic microorganisms; the concentration of suspended solids in the mixed liquor of the activated sludge is ≥8 g / L, and the concentration of volatile suspended solids in the mixed liquor of the activated sludge is ≥40%.

9. The method according to claim 1 or 2, characterized in that, The UASB denitrification unit includes: a UASB reactor, a raw water tank, an inlet pump, and a return pump; the UASB reactor, the raw water tank, and the inlet pump operate in a continuous operation mode; The UASB denitrification denitrification device includes a lower columnar reaction zone and an upper sedimentation zone. The bottom of the UASB denitrification denitrification device has an inlet and a bottom reflux outlet, and the top has an outlet and a top reflux outlet. The UASB denitrification denitrification device includes a reflux pipe, and the reflux pump is installed on the reflux pipe. One end of the reflux pipe is connected to the bottom reflux port, and the other end is connected to the top reflux port.

10. The method according to claim 9, characterized in that, In step S2, the inoculated activated sludge is internally circulated within the UASB denitrification unit, including: turning on the return pump to return water from the activated sludge to the UASB denitrification unit through the return pipe for internal circulation; wherein, during the internal circulation process, the upward flow velocity of the water is 1~3 m / h; and / or In step S3, the nitrate nitrogen wastewater includes effluent from the secondary sedimentation tank of a wastewater treatment plant and additives; the additives include nitrate nitrogen reagents; the nitrate nitrogen reagents include at least one of potassium nitrate or sodium nitrate; and / or In step S3, the sulfur source includes at least one of sodium thiosulfate or elemental sulfur.

11. The method according to claim 10, characterized in that, In step S3, the additive further includes trace elements, sodium bicarbonate, and potassium dihydrogen phosphate; and / or In step S3, the sulfur source is sodium thiosulfate.

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