Denitrification membrane biofilm reactor using carbon dioxide as the sole carbon source and use method thereof

Abstract

A denitrifying membrane biofilm reactor with carbon dioxide as the sole carbon source and a method for using the same relate to the technical field of sewage treatment. The purpose of the present invention is to solve the problem that the additional addition of an organic carbon source in the current conventional sewage treatment process increases operating costs and causes secondary pollution, as well as the problem that traditional carbon dioxide-driven autotrophic denitrification requires the addition of additional electron donors, low denitrification efficiency, and slow microbial growth. The present invention uses carbon dioxide as the sole carbon source to drive denitrification, produces intermediate products (volatile fatty acids mainly based on acetic acid) as electron donors to reduce nitrates, and the average denitrification efficiency can reach 97.8%, and the highest denitrification rate is 447.6 mg-N / L / d. The present invention can obtain a denitrifying membrane biofilm reactor with carbon dioxide as the sole carbon source and a method for using the same.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, in particular to a denitrifying membrane biofilm reactor using carbon dioxide as the sole carbon source and a use method thereof. Background Art

[0002] Denitrification is an important process for wastewater treatment to remove nitrogen-containing compounds such as nitrates. Traditional heterotrophic denitrification often relies on the addition of organic carbon sources, such as methanol and ethanol, as electron donors, which not only increases treatment costs but may also cause secondary pollution. In addition, denitrification is highly dependent on organic carbon sources and is easily affected by fluctuations in water quality, leading to problems such as unstable denitrification efficiency. Carbon dioxide, as a major greenhouse gas, has a wide range of sources and exists in large quantities in the environment. If denitrification can be carried out using carbon dioxide as a carbon source, it can achieve resource utilization while treating wastewater, with significant environmental and economic benefits.

[0003] At present, denitrification driven by carbon dioxide is mainly autotrophic denitrification, with carbon dioxide as the carbon source, sulfide, hydrogen and iron as electron donors, and nitrate as the electron acceptor. Traditional autotrophic denitrification still has many problems: (1) The growth and metabolism of microorganisms using carbon dioxide as the carbon source are generally slow. The growth rate of autotrophic denitrifying bacteria is relatively slow, and the cell doubling time is long, resulting in a long start-up time for the denitrification process and a low overall reaction rate. It requires a larger reactor volume and a longer hydraulic retention time, which increases the floor space and construction cost of the treatment facility; (2) The carbon dioxide fixation efficiency is low. Carbon dioxide molecules are stable, and microorganisms need to consume more energy and reducing power to fix them as cellular substances. In actual denitrification processes, the carbon dioxide fixation efficiency is often low, and most of the carbon dioxide cannot be fully utilized, resulting in carbon source waste and reduced denitrification efficiency; (3) Electron donor limitation. Common electron donors such as hydrogen and sulfide have problems such as insufficient supply, high cost or danger in actual applications, which limits the large-scale application of autotrophic denitrification processes using carbon dioxide as the carbon source. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems that the additional addition of organic carbon sources in the current conventional sewage treatment process increases operating costs and causes secondary pollution, and that traditional carbon dioxide-driven autotrophic denitrification requires the addition of additional electron donors (hydrogen, iron, etc.), has low denitrification efficiency and slow microbial growth. A denitrifying membrane biofilm reactor with carbon dioxide as the sole carbon source and a method for its use are provided.

[0005] A denitrification membrane biofilm reactor using carbon dioxide as the sole carbon source comprises a water inlet device 1, a gas containing device 2, a hollow fiber membrane assembly 7, a main reactor 9, a carbon dioxide high-pressure gas device 10, and a water outlet liquid sealing device 11;

[0006] The water inlet device 1 is provided with an air inlet and a water outlet, the main reactor 9 is provided with a main reactor water inlet 8, a main reactor water outlet 6, a main reactor air inlet, a main reactor circulation water inlet 13 and a main reactor circulation water outlet 12, and a magnetic stirrer is provided at the bottom of the main reactor 9;

[0007] The gas outlet of the gas containing device 2 is connected to the gas inlet of the water inlet device 1 through a pipeline; the water outlet of the water inlet device 1 is connected to the main reactor water inlet 8 of the main reactor 9 through a pipeline; the main reactor water outlet 6 of the main reactor 9 is connected to the water inlet of the water outlet liquid sealing device 11 through a pipeline;

[0008] The main reactor 9 is provided with a hollow fiber membrane assembly 7, the gas outlet of the carbon dioxide high-pressure gas device 10 is connected to the main reactor air inlet of the main reactor 9 through a pipeline, and the main reactor air inlet of the main reactor 9 is connected to the hollow fiber membrane assembly 7; the main reactor circulation water outlet 12 of the main reactor 9 is connected to the main reactor circulation water inlet 13 through a pipeline.

[0009] The method of using a denitrifying membrane biofilm reactor with carbon dioxide as the only carbon source is as follows:

[0010] Step S1: First, start the water inlet peristaltic pump 3 to add water into the main reactor 9 through the water inlet device 1, then inoculate the main reactor 9 with a microbial seed solution, and at the same time supplement the culture medium, nitrate nitrogen, and nitrite nitrogen into the main reactor 9, wherein the volume ratio of the microbial seed solution to the culture medium is 1:1; introduce carbon dioxide into the hollow fiber membrane assembly 7 in the main reactor 9 through the carbon dioxide high-pressure gas device 10, then start the magnetic stirrer and the circulating peristaltic pump 4, control the speed of the circulating peristaltic pump 4 to 55 rpm, and control the temperature in the main reactor 9 to 29.5-30.5°C;

[0011] The culture medium is composed of 0.075g / L KH2PO4, 0.2g / L MgSO4·7H2O, 0.3g / L CaCl2·2H2O, 0.09g / L NH4Cl, 0.5mL / L acidic trace elements and 0.2mL / L alkaline trace elements. The acidic trace elements are 2.085g / L FeSO4·7H2O, 0.12g / L CoCl2·6H2O, 0.068g / L Zn SO4·7H2O, 0.5g / L MnCl2·4H2O, 0.32g / L CuSO4·5H2O, 0.095g / L NiCl2·6H2O, 0.014g / L H3BO4 and 100mmol HCl, and the alkaline trace elements are composed of 0.4g / L NaOH, 0.05g / L NaWO4·2H2O, 0.242g / L KMnO4 and 0.67g / L SeO2;

[0012] Step S2: After the nitrate nitrogen and nitrite nitrogen are exhausted, sodium nitrate is added to the main reactor 9, and the rotation speed of the magnetic stirrer is controlled to 200 rpm. The main reactor 9 is operated for a total of 121 days.

[0013] Principle of the present invention:

[0014] With carbon dioxide as the sole carbon source, microorganisms in the membrane bioreactor undergo denitrification by producing intermediate volatile fatty acids. The volatile fatty acids are primarily acetic acid, accompanied by a small amount of propionic acid. As the nitrate nitrogen loading increases, no volatile acids remain, indicating that the denitrification process is achieved through the biological conversion of carbon dioxide into intermediate volatile acids, which then act as electron donors for the efficient reduction of nitrate.

[0015] Beneficial effects of the present invention:

[0016] (1) The present invention uses carbon dioxide as the sole carbon source to drive denitrification, and produces intermediate products (volatile fatty acids, mainly acetic acid) as electron donors to reduce nitrate. The average denitrification efficiency can reach 97.8%, and the highest denitrification rate is 447.6 mg-N / L / d. This invention is different from autotrophic denitrification in that although the denitrification process also uses carbon dioxide as the sole carbon source, no exogenous electron donors are added. Instead, volatile acids produced endogenously by the bioconversion of carbon dioxide are used as denitrification electron donors, which greatly improves the rate and efficiency of denitrification and provides technical support for sustainable sewage treatment and the realization of carbon source self-sufficiency and carbon neutrality in sewage treatment.

[0017] (2) The present invention utilizes a membrane biofilm reactor to supply carbon dioxide, which not only increases the contact area between microorganisms and the carbon source in the liquid phase, but also provides more attachment sites for microorganisms in the reactor, trapping microorganisms and facilitating their growth and reproduction. The reactor startup time is shortened to only 10-15 days. The reactor also significantly enhances the stability and shock load resistance of the system, ensuring efficient and stable operation of the reactor even when the hydraulic retention time is 0.5 days. In addition, by controlling the carbon dioxide partial pressure, the carbon dioxide utilization efficiency can be improved, promoting the growth and metabolic activity of microorganisms in the membrane biofilm reactor, thereby significantly improving the operating efficiency of the denitrification membrane biofilm reactor using carbon dioxide as the sole carbon source.

[0018] The invention can obtain a denitrification membrane biofilm reactor using carbon dioxide as the sole carbon source and a use method thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic structural diagram of a denitrifying membrane biofilm reactor in which carbon dioxide is the sole carbon source of the present invention is shown, wherein 1 represents a water inlet device, 2 represents a gas containing device, 3 represents a water inlet peristaltic pump, 4 represents a circulating peristaltic pump, 5 represents a gas sampling port, 6 represents a water outlet of the main reactor, 7 represents a hollow fiber membrane assembly, 8 represents a water inlet of the main reactor, 9 represents a main reactor, 10 represents a carbon dioxide high-pressure gas device, 11 represents a water outlet liquid seal device, 12 represents a circulating water outlet of the main reactor, and 13 represents a circulating water inlet of the main reactor;

[0020] Figure 2 A graph showing changes in nitrate influent load and nitrate removal rate over operating time in Example 2;

[0021] Figure 3 A graph showing the changes in volatile fatty acids over operating time in Example 2. DETAILED DESCRIPTION

[0022] Specific embodiment 1: In this embodiment, a denitrification membrane biofilm reactor with carbon dioxide as the sole carbon source includes a water inlet device 1, a gas containing device 2, a hollow fiber membrane assembly 7, a main reactor 9, a carbon dioxide high-pressure gas device 10 and a water outlet liquid seal device 11;

[0023] The water inlet device 1 is provided with an air inlet and a water outlet, the main reactor 9 is provided with a main reactor water inlet 8, a main reactor water outlet 6, a main reactor air inlet, a main reactor circulation water inlet 13 and a main reactor circulation water outlet 12, and a magnetic stirrer is provided at the bottom of the main reactor 9;

[0024] The gas outlet of the gas containing device 2 is connected to the gas inlet of the water inlet device 1 through a pipeline; the water outlet of the water inlet device 1 is connected to the main reactor water inlet 8 of the main reactor 9 through a pipeline; the main reactor water outlet 6 of the main reactor 9 is connected to the water inlet of the water outlet liquid sealing device 11 through a pipeline;

[0025] The main reactor 9 is provided with a hollow fiber membrane assembly 7, the gas outlet of the carbon dioxide high-pressure gas device 10 is connected to the main reactor air inlet of the main reactor 9 through a pipeline, and the main reactor air inlet of the main reactor 9 is connected to the hollow fiber membrane assembly 7; the main reactor circulation water outlet 12 of the main reactor 9 is connected to the main reactor circulation water inlet 13 through a pipeline.

[0026] Specific embodiment 2: The difference between this embodiment and specific embodiment 1 is that the water inlet device 1 is a water inlet bottle.

[0027] The other steps are the same as those in the first embodiment.

[0028] Specific embodiment three: The difference between this embodiment and specific embodiment one or two is that the gas containing device 2 is an air bag.

[0029] The other steps are the same as those in the first or second embodiment.

[0030] Specific embodiment 4: The difference between this embodiment and specific embodiments 1 to 3 is that the water outlet liquid sealing device 11 is a water outlet liquid sealing bottle.

[0031] The other steps are the same as those in Specific Embodiments 1 to 3.

[0032] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that a gas phase sampling port 5 is provided on the main reactor 9 .

[0033] The other steps are the same as those in Specific Embodiments 1 to 4.

[0034] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the carbon dioxide high-pressure gas device 10 is a carbon dioxide high-pressure gas cylinder.

[0035] The other steps are the same as those in Specific Embodiments 1 to 5.

[0036] Specific embodiment seven: The difference between this embodiment and specific embodiments one to six is ​​that the power source on the pipeline between the water outlet of the water inlet device 1 and the main reactor water inlet 8 of the main reactor 9 is the water inlet peristaltic pump 3.

[0037] The other steps are the same as those in Specific Embodiments 1 to 6.

[0038] Specific embodiment eight: The difference between this embodiment and specific embodiments one to seven is that the power source on the pipeline between the main reactor circulation water outlet 12 and the main reactor circulation water inlet 13 of the main reactor 9 is a circulation peristaltic pump 4.

[0039] The other steps are the same as those in Specific Embodiments 1 to 7.

[0040] Specific embodiment 9: The method for using the denitrification membrane biofilm reactor with carbon dioxide as the only carbon source in this embodiment is carried out according to the following steps:

[0041] Step S1: First, start the water inlet peristaltic pump 3 to add water into the main reactor 9 through the water inlet device 1, then inoculate the main reactor 9 with a microbial seed solution, and at the same time supplement the culture medium, nitrate nitrogen, and nitrite nitrogen into the main reactor 9, wherein the volume ratio of the microbial seed solution to the culture medium is 1:1; introduce carbon dioxide into the hollow fiber membrane assembly 7 in the main reactor 9 through the carbon dioxide high-pressure gas device 10, then start the magnetic stirrer and the circulating peristaltic pump 4, control the speed of the circulating peristaltic pump 4 to 55 rpm, and control the temperature in the main reactor 9 to 29.5-30.5°C;

[0042] The culture medium is composed of 0.075g / L KH2PO4, 0.2g / L MgSO4·7H2O, 0.3g / L CaCl2·2H2O, 0.09g / L NH4Cl, 0.5mL / L acidic trace elements and 0.2mL / L alkaline trace elements. The acidic trace elements are 2.085g / L FeSO4·7H2O, 0.12g / L CoCl2·6H2O, 0.068g / L Zn SO4·7H2O, 0.5g / L MnCl2·4H2O, 0.32g / L CuSO4·5H2O, 0.095g / L NiCl2·6H2O, 0.014g / L H3BO4 and 100mmol HCl, and the alkaline trace elements are composed of 0.4g / L NaOH, 0.05g / L NaWO4·2H2O, 0.242g / L KMnO4 and 0.67g / L SeO2;

[0043] Step S2: After the nitrate nitrogen and nitrite nitrogen are exhausted, sodium nitrate is added to the main reactor 9, and the rotation speed of the magnetic stirrer is controlled to 200 rpm. The main reactor 9 is operated for a total of 121 days.

[0044] Specific embodiment ten: This embodiment differs from specific embodiment nine in that: in step S1 , when inoculating the microbial seed liquid and supplementing the culture medium, argon gas is continuously introduced into the main reactor 9 for aeration.

[0045] The other steps are the same as those in the ninth embodiment.

[0046] The following examples are used to verify the beneficial effects of the present invention:

[0047] Example 1: A denitrification membrane biofilm reactor with carbon dioxide as the sole carbon source, comprising a water inlet bottle, an air bag, a hollow fiber membrane assembly 7, a main reactor 9, a carbon dioxide high-pressure gas cylinder, and a water outlet liquid sealing bottle;

[0048] The water inlet bottle is provided with an air inlet and a water outlet, the main reactor 9 is provided with a main reactor water inlet 8, a main reactor water outlet 6, a main reactor air inlet, a main reactor circulation water inlet 13 and a main reactor circulation water outlet 12, a magnetic stirrer is provided at the bottom of the main reactor 9, and a gas phase sampling port 5 is provided on the main reactor 9;

[0049] The air outlet of the air bag is connected to the air inlet of the water inlet bottle through a pipeline; the water outlet of the water inlet bottle is connected to the main reactor water inlet 8 of the main reactor 9 through a pipeline, and a water inlet peristaltic pump 3 is provided on the pipeline; the main reactor water outlet 6 of the main reactor 9 is connected to the water inlet of the water outlet liquid seal bottle through a pipeline;

[0050] The main reactor 9 is provided with a hollow fiber membrane assembly 7, the gas outlet of the carbon dioxide high-pressure cylinder is connected to the main reactor air inlet of the main reactor 9 through a pipeline, and the main reactor air inlet of the main reactor 9 is connected to the hollow fiber membrane assembly 7; the main reactor circulation water outlet 12 of the main reactor 9 is connected to the main reactor circulation water inlet 13 through a pipeline, and a circulating peristaltic pump 4 is provided on the pipeline.

[0051] Example 2: A method for using a denitrifying membrane biofilm reactor with carbon dioxide as the sole carbon source is carried out according to the following steps:

[0052] Step S1: First, start the water inlet peristaltic pump 3 to add water to the main reactor 9 through the water inlet device 1, and then inoculate 100 mL of microbial seed liquid into the main reactor 9 (anaerobic digester sludge, farmland drainage ditch bottom mud and Wenchang sewage treatment plant (Harbin) recycled sludge mixed sludge obtained by long-term enrichment culture), and at the same time add 100 mL of culture medium to the main reactor 9; carbon dioxide is introduced into the hollow fiber membrane assembly 7 in the main reactor 9 through the carbon dioxide high-pressure gas device 10, and then the magnetic stirrer and the circulating peristaltic pump 4 are started, the speed of the circulating peristaltic pump 4 is controlled to 55 rpm, and the temperature in the main reactor 9 is controlled to 30°C;

[0053] In step S1, when inoculating the microbial seed solution and supplementing the culture medium, argon gas is continuously introduced into the main reactor 9 for aeration;

[0054] The culture medium is composed of 0.075g / L KH2PO4, 0.2g / L MgSO4·7H2O, 0.3g / L CaCl2·2H2O, 0.09g / L NH4Cl, 0.5mL / L acidic trace elements and 0.2mL / L alkaline trace elements. The acidic trace elements are 2.085g / L FeSO4·7H2O, 0.12g / L CoCl2·6H2O, 0.068g / L Zn SO4·7H2O, 0.5g / L MnCl2·4H2O, 0.32g / L CuSO4·5H2O, 0.095g / L NiCl2·6H2O, 0.014g / L H3BO4 and 100mmol HCl, and the alkaline trace elements are composed of 0.4g / L NaOH, 0.05g / L NaWO4·2H2O, 0.242g / L KMnO4 and 0.67g / L SeO2;

[0055] Step S2: After the nitrate nitrogen and nitrite nitrogen are exhausted, sodium nitrate is added to the main reactor 9, and the speed of the magnetic stirrer is controlled to 200 rpm to ensure that the microorganisms are always in a suspended state, which is conducive to biofilm formation; the operation stage includes a hydraulic retention time (HRT) of 2 days, 1.3 days, 1 day, 0.8 days, 0.67 days and 0.5 days (corresponding to loads of 400 and 450 mg-N / L / d), and the corresponding nitrate nitrogen loads are 100 mg-N / L / d, 150 mg-N / L / d, 200 mg-N / L / d, 250 mg-N / L / d, 300 mg-N / L / d, 400 mg-N / L / d and 450 mg-N / L / d, respectively. The main reactor 9 runs for a total of 121 days.

[0056] Note: Steps S1 and S2 are the operation phase of the main reactor 9; in the enrichment phase before the operation phase, when the total reduction efficiency of nitrate nitrogen and nitrite nitrogen reaches 200 mg-N / L / d, it indicates that the microbial biofilm is successfully formed, and then the culture medium and nitrate are supplemented to the main reactor 9 through the batch operation mode.

[0057] Figure 2The nitrate influent load and nitrate removal rate in Example 2 change with the operating time; under the conditions of an influent concentration of 200 mg-N / L and a nitrate nitrogen load of 100 mg-N / L / d, in the 1-2 stage (0-31 days), that is, when the HRT is 2 days and 1.3 days, the effluent nitrite concentration is less than 0.2 mg-N / L, and denitrification is complete. In the 3rd stage (32-49 days), the HRT of the membrane biofilm reactor is shortened to 1 day, the denitrification rate is 200 mg-N / L / d, and the denitrification efficiency is greater than 94%. In the 5th to 7th stage (50-103 days), the HRT of the reactor is shortened to 0.8 days, 0.67 days and 0.5 days, and nitrate reduction has fluctuated to a certain extent, but eventually the denitrification rate is restored to 99.9%. Under the condition of reactor HRT of 0.5 days, the denitrification potential of the reactor was explored by further increasing the influent concentration. The influent nitrate nitrogen concentration was 225 mg-N / L, that is, the influent load was 450 mg-N / L / d, the average denitrification rate was 436.4 mg-N / L / d, and the denitrification efficiency was 97.0%.

[0058] in conclusion:

[0059] Under the condition of using carbon dioxide as the only carbon source and without adding any exogenous electron donors, the membrane biofilm reactor can achieve long-term stable denitrification and denitrification; the highest average denitrification rate can reach 436.4 mg-N / L / d, which is comparable to the denitrification rate of a pure heterotrophic system.

[0060] Figure 3 The following is a graph showing the changes in volatile fatty acids over operating time in Example 2; during the first stage of the reactor (days 0-16), the total volatile acid concentration was 235.8 mg / L. During the second to sixth stages (days 17-103), when the HRT was shortened to 1.3 days, 1 day, 0.8 day, 0.67 day, and 0.5 day, the total volatile acid concentration in the reactor, mainly acetic acid, gradually decreased to below 60 mg / L, with occasional accumulation of propionic acid. During the seventh stage (days 104-121), the rise in influent concentration was accompanied by a rapid consumption of volatile acids. After two days of operation in this stage, only a small amount of acetic acid remained, and the average effluent concentration was 1.0 mg / L.

[0061] in conclusion:

[0062] The trend of volatile acid effluent concentration change is highly correlated with the nitrate reduction rate during the process of improving the overall efficiency of the reactor, indicating that the production of intermediate volatile acid is an important reason for achieving the denitrification process with carbon dioxide as the only carbon source.

Claims

1. The method for using a denitrifying membrane biofilm reactor with carbon dioxide as the only carbon source is characterized in that The usage is as follows: Step S1: First, start the water inlet peristaltic pump (3) to add water into the main reactor (9) through the water inlet device (1), then inoculate the main reactor (9) with microbial seed liquid, and at the same time supplement the culture medium, nitrate nitrogen and nitrite nitrogen into the main reactor (9), wherein the volume ratio of the microbial seed liquid to the culture medium is 1:1; introduce carbon dioxide into the hollow fiber membrane assembly (7) in the main reactor (9) through the carbon dioxide high-pressure gas device (10), then start the magnetic stirrer and the circulating peristaltic pump (4), control the speed of the circulating peristaltic pump (4) to 55 rpm, and control the temperature in the main reactor (9) to 29.5~30.5℃; use carbon dioxide as the only carbon source to drive denitrification, and use the generated intermediate product acetic acid as an electron donor; The culture medium is composed of 0.075 g / L KH2PO4, 0.2 g / L MgSO4·7H2O, 0.3 g / L CaCl2·2H2O, 0.09 g / L NH4Cl, 0.5 mL / L acidic trace elements and 0.2 mL / L alkaline trace elements, wherein the acidic trace elements are composed of 2.085 g / L FeSO4·7H2O, 0.12 g / L CoCl2·6H2O, 0.068 g / L ZnSO4·7H2O, 0.5 g / L MnCl2·4H2O, 0.32 g / L CuSO4·5H2O, 0.095 g / L NiCl2·6H2O, 0.014 g / L H3BO4 and 100 mmol HCl, and the alkaline trace elements are composed of 0.4 g / L NaOH, 0.05 g / L NaWO4·2H2O, 0.242 g / L KMnO4, and 0.67 g / L SeO2; Step S2: After the nitrate nitrogen and nitrite nitrogen are exhausted, sodium nitrate is added to the main reactor (9), and the speed of the magnetic stirrer is controlled to 200 rpm. The main reactor (9) is operated for a total of 121 days.

2. The method for using the denitrifying membrane biofilm reactor with carbon dioxide as the sole carbon source according to claim 1, characterized in that In step S1, when inoculating the microbial seed solution and supplementing the culture medium, argon gas is continuously introduced into the main reactor (9) for aeration.

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