Method and device for producing high-quality carbon source for short-cut denitrification by directionally regulating and fermenting sludge

Abstract

The invention belongs to the technical field of sewage sludge treatment and recycling, and provides a method and a device for producing a high-quality carbon source for short-cut denitrification by directional regulation and fermentation of sludge. The method comprises the following steps: (1) adding sludge with the solid content of 2-5% into a reaction tank of a device for producing short-cut denitrification by directional regulation and control of sludge fermentation, sealing the reaction tank, and aerating the sludge in the reaction tank under a stirring condition to realize directional fermentation; the aeration flow is controlled to be 6-120 L / (kg VSS.h), the gas introduced by aeration is air, and the pressure intensity of the reaction tank is controlled to be normal pressure; and (2) carrying out solid-liquid separation on the fermentation liquor obtained after directional fermentation in the step (1) to obtain a liquid phase which is the high-quality carbon source for short-cut denitrification and contains volatile fatty acid with acetic acid as a main component. According to the method, directional acetic acid production through sludge fermentation can be realized on the basis of not additionally adding medicaments, the medicament cost is reduced, the process operation is simplified, and the yield of volatile fatty acid and the acetic acid proportion during sludge fermentation are improved.

Description

Technical Field

[0001] This invention belongs to the field of wastewater and sludge treatment and resource utilization technology, and relates to a method and apparatus for producing high-quality carbon sources for short-cut denitrification through sludge-directed fermentation. Background Technology

[0002] Nitrogen pollution leads to eutrophication and blackening of water bodies, making nitrogen removal a crucial task for urban wastewater treatment plants. With increasingly stringent total nitrogen discharge standards for urban wastewater treatment plants, and the fact that the carbon-to-nitrogen ratio of the wastewater itself often fails to meet the requirements for deep denitrification, the addition of exogenous carbon sources is essential. Currently, commonly used exogenous carbon sources in wastewater treatment plants include acetate, methanol, and compound carbon sources. Among these, acetate is frequently used as a high-quality exogenous carbon source for conventional denitrification or anaerobic ammonia oxidation denitrification of high-nitrogen wastewater in wastewater treatment plants, offering high denitrification efficiency, but it suffers from excessively high costs. Although traditional biological nitrification / denitrification processes are widely used in existing technologies, they suffer from high energy and chemical consumption, low treatment efficiency, and difficulty in achieving low-carbon operation. In comparison, anammox is a more environmentally friendly and low-carbon technology. Compared with traditional nitrification / denitrification processes, anammox can reduce oxygen demand by 62.5%, carbon source requirement by 100%, sludge production by 87%, and carbon emissions by 85%, making it a promising biological nitrogen removal technology. However, during the anammox reaction, 11% of nitrogen is still converted to nitrate nitrogen, which also needs to be removed. Short-cut denitrification can reduce nitrate nitrogen to nitrite nitrogen, which can then be completely removed through anammox with residual ammonia nitrogen or ammonia nitrogen from other sources, increasing the nitrogen removal rate to 100%. However, short-cut denitrification often relies heavily on acetic acid, a volatile fatty acid (VFA), meaning acetic acid is also a high-quality carbon source for short-cut denitrification. Other VFAs besides acetic acid result in lower or no nitrite accumulation rates.

[0003] Currently, there are reports of using anaerobic fermentation to generate VFAs from primary sludge, chemically enhanced primary treatment sludge, high-load activated sludge, chemically enhanced high-load sludge, secondary sludge, and MBR membrane tank sludge from municipal wastewater treatment plants. However, the VFA produced by these methods has a low proportion of acetic acid, and the total amount of VFA is insufficient, leading to residual COD and other problems when used for denitrification. Therefore, increasing the VFA yield and the proportion of acetic acid in sludge fermentation is crucial for the realization and maintenance of conventional biological denitrification and short-cut denitrification reactions.

[0004] In existing technologies, there are reports on the use of enhanced anaerobic fermentation of sludge to produce acid for denitrification in wastewater. For example, CN116286321A discloses a micro-aeration anaerobic digester based on ORP control, which adds iron ore powder to the reactor tank to eliminate residual reactive oxygen free radicals and provide a good living environment for facultative anaerobic microorganisms. This reactor improves the performance of anaerobic digestion and methanogenesis by adding iron ore powder and micro-aeration, but does not mention that it can improve the performance of acetic acid production. CN117185606A discloses a method for enhancing the anaerobic fermentation of excess sludge to produce acid by coupling ferrate and nitrite. This method requires the addition of potassium ferrate and sodium nitrite for sludge pretreatment, which has the problem of high reagent costs, and the method does not optimize the yield and ratio of acetic acid. CN116692954A discloses a method for preparing Fe-Fe2O3 core-shell material and anaerobic fermentation of sludge. The implementation of this method depends on adding Fe-Fe2O3 core-shell material prepared by a specific method. However, the preparation process of Fe-Fe2O3 core-shell material requires the use of a variety of reagents, including ferric salts and reducing agents, which is complicated.

[0005] Overall, the methods reported in the above literature have two shortcomings: (1) When regulating the fermentation of sludge, attention is not paid to increasing the acetic acid production and the acetic acid ratio in VFA, the application of fermentation liquid is narrow and cannot be applied to short-cut denitrification reaction; (2) It depends on pretreatment conditions such as added reagents, the consumption of reagents is high and the operation is complicated. Summary of the Invention

[0006] To address the issues that existing methods for enhancing anaerobic fermentation of sludge to produce acid for wastewater denitrification rely on pretreatment with external chemicals and fail to focus on increasing the yield and proportion of acetic acid during sludge fermentation, this invention provides a method and apparatus for the targeted controlled fermentation of sludge to produce a high-quality carbon source for short-cut denitrification. This method achieves targeted acetic acid production from sludge fermentation without the addition of external chemicals, reducing chemical costs, simplifying process operations, and increasing the yield of volatile fatty acids and the proportion of acetic acid in volatile fatty acids during sludge fermentation.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for producing a high-quality carbon source for short-cut denitrification through targeted fermentation of sludge includes the following steps:

[0009] ① Add sludge with a solid content of 2% to 5% to the reaction tank of the device for directional fermentation of sludge to produce short-cut denitrification. Seal the reaction tank and aerate the sludge in the reaction tank under stirring conditions to achieve directional fermentation. Control the aeration flow rate to 6 to 120 L / (kg VSS·h), the gas introduced for aeration is air, and control the pressure of the reaction tank to atmospheric pressure.

[0010] ② After completing the directional fermentation in step ①, the fermentation broth is subjected to solid-liquid separation. The resulting liquid phase is a high-quality carbon source for short-cut denitrification. This liquid phase contains volatile fatty acids with acetic acid as the main component.

[0011] In step ① of the above method's technical solution, the sludge added to the reaction tank comes from at least one of the following: mixed concentrated sludge from urban sewage treatment plants, solids from domestic sewage after biological-chemical flocculation sedimentation, sludge from the primary sedimentation tank of sewage treatment plants, sludge from the secondary sedimentation tank of sewage treatment plants, sludge from the thickening tank of sewage treatment plants, and concentrated biochemical sludge from industrial wastewater treatment plants.

[0012] In step ① of the above method's technical solution, it is preferable to control the aeration flow rate to be 30~100 L / (kg VSS·h).

[0013] In step ① of the above method, the purpose of applying stirring is to promote the mixing of the mixture in the reaction tank. The stirring speed can usually be controlled at 10~100 rpm. At the same time, the aeration operation can assist mechanical stirring to promote the mixing of the mixture in the reaction tank.

[0014] In step ① of the above method's technical solution, the aeration operation can directionally regulate the anaerobic hydrolysis acidification and fermentation of sludge. By regulating the redox potential of the fermentation system through aeration, the proportion of acetic acid in the sludge hydrolysis acidification products can be increased, generating a high-quality carbon source with a high proportion of acetate.

[0015] Furthermore, in step ① of the above method, the sludge in the reaction tank is aerated using intermittent or continuous air supply. When step ① aerates the sludge in the reaction tank using intermittent air supply, a single cycle of intermittent air supply includes an aeration phase and a non-aeration phase. The duration of the aeration phase accounts for 10% to 75% of the total duration of a single cycle, preferably 25% to 75% of the total duration of a single cycle. Typically, the total duration of a single cycle is 40 to 90 minutes, for example, 60 minutes.

[0016] In step ① of the above method's technical solution, a dissolved oxygen concentration sensor or a redox potential sensor can be installed in the reaction tank, and the aeration flow rate and / or aeration mode can be adjusted according to the dissolved oxygen concentration sensor or redox potential. Preferably, the dissolved oxygen concentration in the mixture in the reaction tank is controlled between 0.01 and 0.3 mg / L, or the redox potential (ORP) of the mixture in the reaction tank is controlled between -200 and 50 mV.

[0017] In step ① of the above method's technical solution, the residence time of sludge in the reaction tank can usually be controlled to be 3-5 days.

[0018] In step ① of the above method's technical solution, the temperature inside the reaction vessel is controlled to be 10~35 ℃.

[0019] In step ① of the above method, the pH value of the sludge can be in the slightly acidic or neutral range, for example, between pH 6 and 8. Generally, the mixed concentrated sludge from urban sewage treatment plants, the solids after biological-chemical flocculation sedimentation of domestic sewage, the sludge from the primary sedimentation tank of sewage treatment plants, the sludge from the secondary sedimentation tank of sewage treatment plants, the sludge from the thickening tank of sewage treatment plants, and the concentrated biochemical sludge from industrial wastewater treatment plants can basically meet this pH condition. Therefore, the method described in this invention usually does not require special adjustment of the pH value of the sludge.

[0020] In step ② of the above method's technical solution, the solid-liquid separation method includes gravity sedimentation, centrifugation, plate and frame filtration, or belt filtration.

[0021] In step ② of the above method, the mass percentage of acetic acid in the volatile fatty acids in the liquid phase obtained by solid-liquid separation reaches more than 47 wt%. For example, in some specific embodiments, the mass percentage of acetic acid in the volatile fatty acids reaches 47.4 wt% to 80.6%.

[0022] In the above-mentioned method, the yield of volatile fatty acids reached a level of 73 mg COD / g VSS or higher, and the yield of acetic acid reached a level of 41 mg COD / g VSS or higher. For example, in some specific embodiments, the yield of volatile fatty acids reached a level of 73.8~87.3 mg COD / g VSS, and the yield of acetic acid reached a level of 41.4~59.5 mg COD / g VSS.

[0023] The present invention also provides an apparatus for implementing the above method, but the apparatus for implementing the above method is not limited to the apparatus with the following structure, which is only one of many apparatuses that can implement the above water treatment method.

[0024] A device for the directional controlled fermentation of sludge to produce a high-quality carbon source for short-range denitrification includes a reaction tank, a stirrer, a sensor, a gas source, a gas diffuser, and a programmable logic controller.

[0025] The reaction vessel is a cylindrical body sealed at both ends. The reaction vessel is equipped with an outlet with a one-way exhaust valve, a sludge inlet, and a fermentation product outlet. The stirring part of the agitator is located inside the reaction vessel, and the sensing part of the sensor is located inside the reaction vessel. The gas source is connected to the gas diffuser inside the reaction vessel via pipes and gas flow controllers, gas solenoid valves, and gas one-way valves installed on the pipes. The gas source, gas solenoid valves, agitator, and sensor are respectively connected to signal transmitters, and the signal transmitters are connected to programmable logic controllers.

[0026] In the above-mentioned technical solution, the reaction vessel is a cylindrical or rectangular body closed at both ends, and the material of the reaction vessel can be metal, concrete or plastic.

[0027] In the above-mentioned device, the agitator can be a top-mounted agitator or an underwater propulsion device (fermentation tank agitator).

[0028] In the above-mentioned device, the part of the stirrer that performs the stirring function is usually located above the gas diffuser.

[0029] In the above-mentioned device, the sensor is a redox potential sensor or a dissolved oxygen sensor.

[0030] In the above-mentioned device, the gas diffuser is a pipe with a plurality of aeration holes or microporous aeration discs.

[0031] Furthermore, the gas diffuser is located near the bottom of the reaction vessel.

[0032] Furthermore, when the gas diffuser is a pipe with a plurality of aeration holes, the diameter of the aeration holes is typically 0.25 to 2 mm, for example, 0.25 mm, 0.5 mm, 1 mm, 2 mm, etc., and the distance between adjacent aeration holes on the pipe is 5 to 100 mm, for example, 5 mm, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, etc.

[0033] In the above-mentioned device, the programmable logic controller is used to control the intermittent opening and closing or continuous opening of the gas solenoid valve, the gas supply flow rate, and the stirring rate according to the received sensor signals.

[0034] Furthermore, the technical solution of the above-mentioned device also includes a human-machine interface terminal, which is connected to the programmable logic controller via signals.

[0035] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0036] 1. This invention provides a method for the targeted regulation of sludge fermentation to produce a high-quality carbon source for short-cut denitrification. This method is simple to operate, requiring neither the addition of costly chemical agents nor the provision of high-temperature and high-pressure conditions. It only requires appropriate aeration of the sludge to directionally increase the yield of volatile fatty acids and the proportion of acetic acid in the fermented sludge, thereby increasing acetic acid production. Compared with existing methods for enhanced anaerobic fermentation of sludge to produce acid, this invention has the advantages of low chemical and energy consumption, simple and safe operation, and green and low-carbon operation.

[0037] 2. Experiments have confirmed that the fermentation broth obtained by the method described in this invention can achieve a volatile fatty acid yield of 87.3 mg COD / g VSS and an acetic acid yield of 59.5 mg COD / g VSS. The mass percentage of acetic acid in the volatile fatty acids in the fermentation broth can reach 80.6%.

[0038] 3. The present invention also provides an apparatus for implementing the method described herein. The apparatus has a simple structure and can automatically adjust the aeration time and aeration flow rate based on the measurement results of the sensor through a programmable logic controller, so as to easily achieve the optimization of working conditions with the goal of increasing the yield and proportion of acetic acid. It is easy to implement and easy to promote. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of a device for producing a high-quality carbon source for short-range denitrification through sludge-directed controlled fermentation.

[0040] Figure 2 This is a diagram showing the effect of short-cut denitrification of fermentation broth obtained using the method described in this invention.

[0041] Explanation of reference numerals in the attached diagram: 11—Reaction vessel, 12—One-way exhaust valve, 13—Sludge inlet, 14—Fermentation product outlet, 21—Agitator, 31—Sensor, 32—Gas source, 33—Gas flow controller, 34—Gas solenoid valve, 35—Gas check valve, 36—Gas diffuser, 41—Signal transmitter, 42—Programmable logic controller, 43—Human-machine interface. Detailed Implementation

[0042] The following examples further illustrate the method and apparatus for producing high-quality carbon sources for short-cut denitrification using sludge-directed controlled fermentation, as provided by the present invention. It should be noted that the following examples are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above description are still within the scope of protection of the present invention.

[0043] Example 1

[0044] In this embodiment, a structure of an apparatus for the directional controlled fermentation of sludge to produce a high-quality carbon source for short-cut denitrification is provided, and its schematic diagram is shown below. Figure 1 As shown, the device includes a reaction vessel 11, a stirrer 21, a sensor 31, a gas source 32, a gas diffuser 36, and a programmable logic controller 42.

[0045] The reaction tank 11 is a cylindrical body closed at both ends. The upper part of the reaction tank 11 has an air inlet, an air outlet, and a sludge inlet 13. The lower part of the reaction tank 11 has a fermentation product outlet 14. A one-way exhaust valve 12 is installed at the air outlet. During operation, air introduced into the reaction tank 11 is discharged through the one-way exhaust valve 13. The agitator 21 is a top-mounted agitator. The agitator's impeller is located inside the reaction tank 11 and is driven by a motor. The axis of the drive shaft connecting the impeller and the motor coincides with the axis of the reaction tank. The sensor 31 is a redox potential sensor, and its sensing part is located inside the reaction tank 11. The gas source 32, via pipe fittings and a gas flow controller 33, a gas solenoid valve 34, and a gas one-way valve 35 mounted on the pipe fittings, passes through the air inlet and connects to a gas diffuser 36 located inside the reaction tank 11. The gas diffuser 36 is a stainless steel pipe with several aeration holes. The diameter of each aeration hole is 1 mm, and the distance between adjacent aeration holes is 5 mm. The gas diffuser 36 is located near the bottom of the reaction vessel, and the agitator is positioned above the gas diffuser 36. The gas source 32, gas solenoid valve 34, agitator 21, and sensor 31 are all connected to a signal transmitter 41. The signal transmitter 41 is connected to a programmable logic controller 42, which controls the intermittent or continuous opening and closing of the gas solenoid valve, the gas supply flow rate, and the agitation rate based on the received signals from the sensors. The programmable logic controller 42 is also connected to a human-machine interface 43.

[0046] Example 2

[0047] In this embodiment, a method for producing a high-quality carbon source for short-cut denitrification through sludge-directed controlled fermentation is provided, and the steps are as follows:

[0048] Step 1: Add sludge with a solids content of 2% to 5% to the reaction tank of the sludge-directed controlled fermentation production short-cut denitrification device, seal the reaction tank, and aerate the sludge in the reaction tank under stirring conditions to achieve directional fermentation; control the aeration flow rate to 6 to 120 L / (kg VSS·h), the gas introduced for aeration is air, and control the pressure of the reaction tank to atmospheric pressure.

[0049] Step 2: The fermentation broth obtained after the directional fermentation in Step 1 is subjected to solid-liquid separation. The resulting liquid phase is a high-quality carbon source for short-cut denitrification. This liquid phase contains volatile fatty acids (VFAs) with acetic acid as the main component.

[0050] More specifically, this embodiment uses the apparatus described in Example 1 for directional fermentation. The solids content of the sludge is 5%, and the sludge originates from the mixed concentrated sludge of a municipal wastewater treatment plant. The specific operation is as follows:

[0051] ① Sludge is added from the sludge inlet to the reaction tank of the sludge-directed fermentation production short-cut denitrification device. The reaction tank is sealed, and stirring is applied at a speed of 50 r / min by a stirrer. Under normal temperature (10~35 ℃) conditions, the air output from the gas source is continuously aerated by passing through a gas flow controller, a gas solenoid valve, and a gas one-way valve into the gas diffuser to achieve directional fermentation.

[0052] In this step, aeration is carried out at an aeration flow rate of 96 L / (kg VSS·h). The opening and closing of the gas solenoid valve (aeration or stopping aeration) is adjusted according to the oxidation-reduction potential (ORP) of the mixed liquor in the reaction tank. The ORP is always controlled between -200 and 50 mV. When the ORP reaches 50 mV, the gas solenoid valve is closed to stop aeration. When the ORP is lower than -200 mV, the gas solenoid valve is opened to aeration. The gas introduced for aeration is air. During the operation of the device, the air introduced into the reaction tank is discharged from the reaction tank through a one-way exhaust valve after reacting with the sludge. The pressure of the reaction tank is controlled at atmospheric pressure, and the residence time of the sludge in the reaction tank is controlled at 5 days.

[0053] ② The fermentation mixture obtained after the directional fermentation in step ① is discharged from the fermentation product outlet, and then solid-liquid separation is performed. The resulting liquid phase (fermentation broth) is a high-quality carbon source for short-cut denitrification. This liquid phase contains VFA with acetic acid as the main component.

[0054] Take the fermentation broth obtained in step ②, measure the VFA concentration and acetic acid concentration, calculate the VFA yield, acetic acid percentage (the proportion of acetic acid in VFA), and acetic acid yield. The results are shown in Table 1.

[0055] Example 3

[0056] In this embodiment, a method for producing a high-quality carbon source for short-cut denitrification through sludge-directed controlled fermentation is provided, and the steps are as follows:

[0057] Step 1: Add sludge with a solids content of 2% to 5% to the reaction tank of the sludge-directed controlled fermentation device for producing short-cut denitrification. Seal the reaction tank and aerate the sludge in the reaction tank under stirring conditions to achieve directional fermentation. Control the aeration flow rate to 6 to 120 L / (kg VSS·h), and the gas introduced for aeration is air. Control the pressure of the reaction tank to atmospheric pressure.

[0058] Step 2: After the directional fermentation in Step 1 is completed, the fermentation broth is subjected to solid-liquid separation. The resulting liquid phase (fermentation broth) is a high-quality carbon source for short-cut denitrification. This liquid phase contains VFA with acetic acid as the main component.

[0059] More specifically, this embodiment uses the apparatus described in Example 1 for directional fermentation. The sludge has a pH of 8 and a solids content of 5%, and the sludge originates from mixed concentrated sludge from a municipal wastewater treatment plant. The specific operation is as follows:

[0060] ① Sludge is added from the sludge inlet to the reaction tank of the sludge-directed fermentation production short-cut denitrification device. The reaction tank is sealed, and stirring is applied by a stirrer at a speed of 50 r / min. Under room temperature (15~30 ℃) conditions, the air output from the gas source is fed into the gas diffuser through a gas flow controller, a gas solenoid valve, and a gas one-way valve for intermittent aeration to achieve directional fermentation.

[0061] In this step, intermittent aeration is used, with a single cycle duration of 60 minutes, consisting of a 30-minute aeration phase and a 30-minute non-aeration and mixing phase. The aeration flow rate during the aeration phase is 48 L / (kg VSS·h). The aeration phase is performed first, followed by the non-aeration phase. The gas introduced for aeration is air. During operation, the air introduced into the reaction tank reacts with the sludge and is then discharged through a one-way exhaust valve. The pressure in the reaction tank is maintained at atmospheric pressure, and the sludge residence time in the reaction tank is controlled to be 5 days. Under the aeration conditions in this step, the ORP of the mixed liquor in the reaction tank can be adjusted between -200 and 50 mV.

[0062] ② The fermentation mixture obtained after the directional fermentation in step ① is discharged from the fermentation product outlet, and then solid-liquid separation is performed. The resulting liquid phase is a high-quality carbon source for short-cut denitrification. This liquid phase contains VFA with acetic acid as the main component.

[0063] Take the fermentation broth obtained in step ②, measure the VFA concentration and acetic acid concentration, and calculate the VFA yield, acetic acid percentage and acetic acid yield.

[0064] Comparative Example 1

[0065] The operation of this comparative example is basically the same as that of Example 2, except that no aeration operation is performed. The VFA production, acetic acid ratio and acetic acid production of this comparative example are shown in Table 1.

[0066] Table 1. VFA yield, acetic acid percentage, and acetic acid yield in Examples 2-7 and Comparative Example 1

[0067]

[0068] As shown in Table 1, compared with Comparative Example 1 which was not aerated, the VFA yield in the fermentation broth obtained under aeration conditions in Examples 2-3 was significantly higher. At the same time, the proportion of acetic acid in VFA and the yield of acetic acid were also higher. This indicates that the method of the present invention can increase the proportion of acetic acid in VFA while increasing the yield of VFA.

[0069] Example 4

[0070] In this embodiment, the effect of using the fermentation broth obtained in Example 2 in short-cut denitrification was investigated. Specifically, the fermentation broth from Example 2 was used in a batch test for denitrification of sludge from the aeration tank of a municipal wastewater treatment plant, and the steps are as follows:

[0071] (1) Take the sludge mixture from the gas supply tank of the municipal sewage treatment plant, and concentrate it at 4 ℃ for 8 h. Skim off the supernatant to obtain concentrated sludge.

[0072] (2) Take an appropriate amount of the concentrated sludge after cleaning and add it to the microbial activity test device. Then add pure water to dilute it to a volume of 1.5 L. Control the sludge concentration in the diluted mixture to 2.5 g VSS / L. Add an appropriate amount of macro-element stock solution and micro-element stock solution.

[0073] (3) The denitrification reaction was carried out under hypoxic and stirring conditions, and the temperature of the microbial activity test device was maintained at 25 °C and the pH was maintained at 8.5.

[0074] (4) After stirring for 30 min under anaerobic conditions, potassium nitrate stock solution and fermentation broth obtained in Example 5 were added. The initial nitrate nitrogen concentration in the resulting mixture was controlled to be about 30 mg N / L, and the initial VFA concentration was 90 mg COD / L, i.e., the carbon-nitrogen ratio was 3 mg COD / mg N.

[0075] (5) Continue stirring under anaerobic conditions, take 10 mL of the mixture every 20-30 min, filter, and test the concentration of nitrate nitrogen and nitrite nitrogen in the filtrate.

[0076] In the short-cut denitrification process of this embodiment, the accumulation of nitrite is as follows: Figure 2 As shown in the figure, there is a significant accumulation of nitrite during the denitrification treatment of municipal sludge, indicating a clear short-cut denitrification phenomenon. This suggests that using the fermentation broth obtained by the method described in this invention as a carbon source for long-term acclimatization of municipal sludge may yield mature short-cut denitrification sludge.

[0077] Example 5

[0078] In this embodiment, a method for producing a high-quality carbon source for short-cut denitrification through sludge-directed controlled fermentation is provided, and the steps are as follows:

[0079] Step 1: Add sludge with a solids content of 2% to 5% to the reaction tank of the sludge-directed controlled fermentation production short-cut denitrification device, seal the reaction tank, and intermittently aerate the sludge in the reaction tank under room temperature and stirring conditions to achieve directional fermentation; control the aeration flow rate to 6 to 120 L / (kg VSS·h), the gas introduced for aeration is air, and control the pressure of the reaction tank to atmospheric pressure.

[0080] Step 2: After the directional fermentation in Step 1 is completed, the fermentation broth is subjected to solid-liquid separation. The resulting liquid phase (fermentation broth) is a high-quality carbon source for short-cut denitrification. This liquid phase contains VFA with acetic acid as the main component.

[0081] More specifically, this embodiment uses the apparatus described in Example 1 for directional fermentation. The sludge parameters are as follows: pH value of 7, solids content of 2%, and the sludge originates from the solids of domestic sewage after biological-chemical flocculation and sedimentation. The specific operation is as follows:

[0082] ① Sludge is added from the sludge inlet to the reaction tank of the sludge-directed fermentation production short-cut denitrification device. The reaction tank is sealed, and stirring is applied by a stirrer at a speed of 10 r / min. Under room temperature (15~30 ℃) conditions, the air output from the gas source is fed into the gas diffuser through a gas flow controller, a gas solenoid valve, and a gas one-way valve for intermittent aeration to achieve directional fermentation.

[0083] In this step, the duration of a single intermittent aeration cycle is controlled to be 60 min, including a 6-min aeration phase and a 54-min non-aeration mixing phase. The aeration flow rate during the aeration phase is 120 L / (kg VSS·h). The aeration phase is performed first, followed by the non-aeration phase. The gas introduced for aeration is air. During the operation of the device, the air introduced into the reaction tank reacts with the sludge and is then discharged from the reaction tank through a one-way exhaust valve. The pressure in the reaction tank is controlled to be atmospheric pressure, and the residence time of the sludge in the reaction tank is controlled to be 3 days. Under the aeration conditions of this step, the ORP of the mixed liquor in the reaction tank can be adjusted between -200 and 50 mV.

[0084] ② The fermentation mixture obtained after the directional fermentation in step ① is discharged from the fermentation product outlet, and then solid-liquid separation is performed. The resulting liquid phase is a high-quality carbon source for short-cut denitrification. This liquid phase contains VFA with acetic acid as the main component.

[0085] Example 6

[0086] In this embodiment, a method for producing a high-quality carbon source for short-cut denitrification through sludge-directed controlled fermentation is provided, and the steps are as follows:

[0087] Step 1: Add sludge with a solids content of 2% to 5% to the reaction tank of the sludge-directed controlled fermentation production short-cut denitrification device, seal the reaction tank, and intermittently aerate the sludge in the reaction tank under room temperature and stirring conditions to achieve directional fermentation; control the aeration flow rate to 6 to 120 L / (kg VSS·h), the gas introduced for aeration is air, and control the pressure of the reaction tank to atmospheric pressure.

[0088] Step 2: After the directional fermentation in Step 1 is completed, the fermentation broth is subjected to solid-liquid separation. The resulting liquid phase (fermentation broth) is a high-quality carbon source for short-cut denitrification. This liquid phase contains VFA with acetic acid as the main component.

[0089] More specifically, this embodiment uses the apparatus described in Example 1 for directional fermentation. The sludge parameters are as follows: pH value 8.5, solids content 3.5%, and the sludge originates from the solids of domestic sewage after biological-chemical flocculation and sedimentation. The specific operation is as follows:

[0090] ① Sludge is added from the sludge inlet to the reaction tank of the sludge-directed fermentation production short-cut denitrification device. The reaction tank is sealed, and stirring is applied at a speed of 100 r / min by a stirrer. Under room temperature (15~30 ℃) conditions, the air output from the gas source is fed into the gas diffuser through a gas flow controller, a gas solenoid valve, and a gas one-way valve for intermittent aeration to achieve directional fermentation.

[0091] In this step, the duration of a single intermittent aeration cycle is controlled to be 60 min, including a 45-min aeration phase and a 15-min non-aeration mixing phase. The aeration flow rate during the aeration phase is 30 L / (kg VSS·h). The aeration phase is performed first, followed by the non-aeration phase. The gas introduced for aeration is air. During the operation of the device, the air introduced into the reaction tank reacts with the sludge and is then discharged from the reaction tank through a one-way exhaust valve. The pressure in the reaction tank is controlled to be atmospheric pressure, and the residence time of the sludge in the reaction tank is controlled to be 4 days. Under the aeration conditions of this step, the ORP of the mixed liquor in the reaction tank can be adjusted between -200 and 50 mV.

[0092] ② The fermentation mixture obtained after the directional fermentation in step ① is discharged from the fermentation product outlet, and then solid-liquid separation is performed. The resulting liquid phase is a high-quality carbon source for short-cut denitrification. This liquid phase contains VFA with acetic acid as the main component.

[0093] In summary, this invention effectively overcomes some shortcomings of existing methods for enhancing anaerobic fermentation of sludge to produce acid, and thus possesses high industrial application value. The above embodiments are merely illustrative of the principles and effects of this invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of this invention. Therefore, all equivalent modifications or changes made without departing from the spirit and technical concept disclosed in this invention should still be covered by the claims of this invention.

Claims

1. A method for the targeted controlled fermentation of sludge to produce a high-quality carbon source for short-cut denitrification, characterized in that, Includes the following steps: ① Add sludge with a solid content of 2% to 5% to the reaction tank of the device for directional fermentation of sludge to produce short-cut denitrification. Seal the reaction tank and aerate the sludge in the reaction tank under stirring conditions to achieve directional fermentation. Control the aeration flow rate to 6 to 120 L / (kg VSS·h), the gas introduced for aeration is air, and control the pressure of the reaction tank to atmospheric pressure. ② After completing the directional fermentation in step ①, the fermentation broth is subjected to solid-liquid separation. The resulting liquid phase is a high-quality carbon source for short-cut denitrification. This liquid phase contains volatile fatty acids with acetic acid as the main component.

2. The method for producing a high-quality carbon source for short-cut denitrification through sludge-directed fermentation according to claim 1, characterized in that, The sludge added to the reaction tank in step ① comes from at least one of the following: mixed concentrated sludge from urban wastewater treatment plants, solids from domestic sewage after biological-chemical flocculation sedimentation, sludge from the primary sedimentation tank of wastewater treatment plants, sludge from the secondary sedimentation tank of wastewater treatment plants, sludge from the thickening tank of wastewater treatment plants, and concentrated biochemical sludge from industrial wastewater treatment plants.

3. The method for producing a high-quality carbon source for short-cut denitrification through sludge-directed fermentation according to claim 1, characterized in that, In step ①, the sludge in the reaction tank is aerated by intermittent air supply and / or continuous air supply.

4. The method for producing a high-quality carbon source for short-cut denitrification through sludge-directed fermentation according to claim 1, characterized in that, When step ① aerates the sludge in the reaction tank in an intermittent aeration manner, a single cycle of intermittent aeration includes an aeration phase and a non-aeration phase, with the duration of the aeration phase accounting for 10% to 75% of the total duration of a single cycle.

5. The method for producing a high-quality carbon source for short-cut denitrification through sludge-directed controlled fermentation according to any one of claims 1 to 4, characterized in that, In step ①, the concentration of dissolved oxygen in the mixture in the reaction vessel is controlled between 0.01 and 0.3 mg / L, or the redox potential of the mixture in the reaction vessel is controlled between -200 and 50 mV.

6. The method for producing high-quality carbon source for short-cut denitrification through sludge-directed controlled fermentation according to any one of claims 1 to 4, characterized in that, In step ①, the residence time of the sludge in the reaction tank is controlled to be 3-5 days.

7. The method for producing a high-quality carbon source for short-cut denitrification through sludge-directed controlled fermentation according to any one of claims 1 to 4, characterized in that, In step ①, the temperature inside the reaction vessel is controlled at 10~35 ℃.

8. A device for the directional controlled fermentation of sludge to produce a high-quality carbon source for short-cut denitrification, characterized in that, It includes a reaction vessel (11), a stirrer (21), a sensor (31), a gas source (32), a gas diffuser (36), and a programmable logic controller (42). The reaction vessel (11) is a cylindrical body closed at both ends. The reaction vessel (11) is equipped with an outlet with a one-way exhaust valve (12), a sludge inlet (13), and a fermentation product outlet (14). The stirring part of the stirrer (21) is located inside the reaction vessel (11), and the sensing part of the sensor (31) is located inside the reaction vessel (11). The gas source (32) is connected to the gas diffuser (36) inside the reaction vessel (11) via pipe fittings and a gas flow controller (33), a gas solenoid valve (34), and a gas one-way valve (35) installed on the pipe fittings. The gas source (32), the gas solenoid valve (34), the stirrer (21), and the sensor (31) are respectively connected to the signal transmitter (41), and the signal transmitter (41) is connected to the programmable logic controller (42).

9. The apparatus for producing a high-quality carbon source for short-cut denitrification through sludge-directed controlled fermentation according to claim 8, characterized in that, The sensor (31) is a redox potential sensor or a dissolved oxygen sensor.

10. The apparatus for producing a high-quality carbon source for short-cut denitrification through sludge-directed controlled fermentation according to claim 8 or 9, characterized in that, The gas diffuser (36) is a pipe fitting with several aeration holes or microporous aeration discs.

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