A method for directly using excess sludge as a carbon source to in-situ enhance the total nitrogen removal in an anaerobic ammonium oxidation system

Abstract

A method for directly using excess sludge as a carbon source to in-situ enhance the total nitrogen removal in an anaerobic ammonium oxidation system, comprising the following steps: In an anaerobic environment, set up and operate a reactor, inoculate sludge into it, control the concentrations of NH₄⁺-N and NO₂⁻-N in the influent of the reactor and the hydraulic retention time, and at the same time recycle the generated nitrogen gas through a gas circulation pump. When the denitrification performance of the reactor reaches stability, at an appropriate temperature and pH, regularly add a certain amount of excess sludge to the reactor. The in-situ slow release of microbial products in the excess sludge well solves the problem of the inhibition of the activity of anaerobic ammonium oxidizing bacteria by high-concentration organic matter, promotes the reaction rates of anaerobic ammonium oxidation and denitrification, improves the removal of NO₃⁻ in the anaerobic ammonium oxidation system, reduces the accumulation of by-product nitrate during the anaerobic ammonium oxidation process, and thus improves the comprehensive denitrification performance of the system.

Description

Technical Field

[0001] The present invention relates to the field of wastewater treatment, and particularly to a method for directly using excess sludge as a carbon source to in-situ enhance the total nitrogen removal in an anaerobic ammonium oxidation system. Background Art

[0002] In recent years, anaerobic ammonium oxidation has shown excellent environmental protection and energy-saving potential in the field of wastewater treatment, and has received extensive attention due to its low energy consumption and minimal sludge production. Under anaerobic conditions, this process can efficiently convert nitrite and ammonia nitrogen into nitrogen gas, thereby saving up to 60% of the aeration energy consumption and eliminating the dependence on external organic carbon sources. However, the by-product nitrate of this process results in a total nitrogen removal efficiency of less than 89%. To improve the total nitrogen removal, heterotrophic denitrification is often implemented by adding external carbon sources (such as methanol, ethanol, and acetic acid, etc.), but this will significantly increase the cost and complexity of the system, and may introduce secondary pollution due to residual organic matter. These commercial carbon sources may also stimulate the growth of heterotrophic bacteria, which may lead to an imbalance between heterotrophic denitrification and anaerobic ammonium oxidation.

[0003] As the main by-product in the sewage treatment process, the traditional disposal methods of excess sludge such as landfill and incineration not only increase the operating cost, but also have a negative impact on the environment. Excess sludge contains a large amount of organic matter, showing great potential for resource recovery. In addition, excess sludge is an important source of microbial products, which can provide nutrients such as polysaccharides, proteins, and humic substances to support the growth of low-abundance heterotrophic microorganisms (such as heterotrophic denitrifying bacteria). Given the poor direct biodegradability of excess sludge, pretreatment methods such as hydrothermal, ozone, and enzymatic hydrolysis (fermentation) are usually required to enhance its solubility, but these methods will increase the operation complexity and cost, and may rapidly release high-concentration organic matter, inhibiting the activity of anaerobic ammonium oxidation bacteria and thus affecting the efficiency of total nitrogen removal in the anaerobic ammonium oxidation system. Summary of the Invention

[0004] In order to overcome the deficiencies of the above prior art, the purpose of the present invention is to provide a method for directly using excess sludge as a carbon source to in-situ enhance the total nitrogen removal in an anaerobic ammonium oxidation system, avoiding the inhibition problem of the activity of anaerobic ammonium oxidation bacteria by high-concentration organic matter, and improving the comprehensive nitrogen removal performance of the system.

[0005] The purpose of the present invention is achieved by the following technical solutions:

[0006] A method for directly using excess sludge as a carbon source to in-situ enhance the total nitrogen removal in an anaerobic ammonium oxidation system, comprising the following steps:

[0007] (1), In an anaerobic environment, set up and operate a reactor, inoculate sludge into it, and control the influent NH4 + -N and NO2 -The concentration of -N and the hydraulic retention time are adjusted, and the generated nitrogen gas is recycled through a gas circulation pump.

[0008] (2) After the denitrification performance of the reactor reaches stability, a certain amount of excess sludge is added to the reactor at an appropriate temperature and pH.

[0009] Preferably, the reactor is an expanded granular sludge bed reactor.

[0010] Preferably, the inoculated sludge is from an anaerobic ammonium oxidation reactor treating municipal sewage.

[0011] Preferably, the circulation flow rate of the nitrogen gas is 1 - 3 L / h.

[0012] More preferably, the circulation flow rate of the nitrogen gas is 1.5 L / h.

[0013] Preferably, the hydraulic retention time is 12 h.

[0014] Preferably, the concentration of influent NH4 + -N is 50 - 100 mg / L, and the concentration of influent NO2 - -N is 66 - 132 mg / L.

[0015] More preferably, the concentration of influent NH4 + -N is 100 mg / L, and the concentration of influent NO2 - -N is 132 mg / L.

[0016] Preferably, the excess sludge is from the secondary sedimentation tank of a municipal sewage treatment plant.

[0017] Preferably, the addition amount of the excess sludge is 100 - 400 mL, and the mass ratio of the excess sludge to the total sludge in the reactor is 1:4 - 1:6.

[0018] More preferably, the addition amount of the excess sludge is 200 mL, and the mass ratio of the excess sludge to the total sludge in the reactor is 1:4.7.

[0019] Preferably, in step (2), the appropriate temperature is 28 - 32 °C, and the pH is 6.8 - 7.2.

[0020] Preferably, the device includes a water inlet tank, an expanded granular sludge bed reactor, a water outlet tank, a water inlet pump, a gas circulation pump and a gas bag. The water outlet of the water inlet tank is connected to the water inlet of the expanded granular sludge bed reactor through the water inlet pump. The gas outlet of the gas circulation pump is connected to the gas inlet of the expanded granular sludge bed reactor. The water outlet of the expanded granular sludge bed reactor is connected to the water inlet of the water outlet tank through the water inlet pump. The gas bag is installed at the top of the expanded granular sludge bed reactor. The gas bag is connected to the expanded granular sludge bed reactor through the gas circulation pump. The nitrogen gas generated by the expanded granular sludge bed reactor is recycled through the gas circulation pump.

[0021] Preferably, the effective working volume of the expanded granular sludge bed reactor is 3.2 L.

[0022] The present invention has the following advantages and beneficial effects compared with the prior art:

[0023] (1). The present invention uses untreated excess sludge as a carbon source and adds it to the anaerobic ammonium oxidation system. The in-situ slow release of microbial products in the excess sludge well solves the problem of the inhibition of the activity of anaerobic ammonium oxidation bacteria by high-concentration organic matter. Moreover, the microbial products can be used as an organic carbon source to increase the denitrification rate, and can also provide the abundance and activity of short-cut denitrifying microorganisms, promoting the reaction rates of anaerobic ammonium oxidation and denitrification, and improving the removal of NO3 - in the anaerobic ammonium oxidation system, reducing the accumulation of by-product nitrate in the anaerobic ammonium oxidation process, thereby improving the comprehensive nitrogen removal performance of the system.

[0024] (2). The method disclosed by the present invention avoids any pretreatment steps, reduces the operation complexity and operation cost, and provides an effective alternative method for enhancing nitrogen removal and sludge reduction. Using excess sludge as a substitute for traditional expensive commercial carbon sources reduces the operation cost while recycling the excess sludge, promoting the sustainable development of the environment and economy.

[0025] The principle of the present invention is as follows:

[0026] Under anaerobic conditions, add excess sludge to the reactor. The excess sludge provides heterotrophic denitrifying bacteria and microbial products slowly released by microorganisms. The in-situ slow release solves the problem of the inhibition of the activity of anaerobic ammonium oxidation bacteria by high-concentration organic matter. The microbial products can be used as an electron donor for heterotrophic denitrifying bacteria in the anaerobic ammonium oxidation system. The role of heterotrophic denitrification can effectively reduce NO3 -Accumulation. Moreover, the microbial products slowly released from the excess sludge are rich in CHON and CHONS compounds, which are unsaturated and reducing, making them preferentially used as electron donors in the denitrification process. In addition to denitrification, the presence of electron transfer mediators (such as humic substances) in the microbial products also promotes the anammox activity, and a stable process of anammox-coupled denitrification can be established, which is beneficial to the improvement of the anammox process and total nitrogen removal. Description of the Drawings

[0027] Figure 1 It is a schematic diagram of the device in the embodiment of the present invention.

[0028] Figure 2 For the NH4 + -N concentration curve of the reactor effluent over time.

[0029] Figure 3 For the NO2 - -N concentration curve of the reactor effluent over time.

[0030] Figure 4 For the NO3 - -N concentration curve of the reactor effluent over time.

[0031] Figure 5 It is the TNRE curve of the reactor effluent over time.

[0032] Markings of each component in the drawings:

[0033] 1 - influent tank, 2 - influent pump, 3 - expanded granular sludge bed reactor, 4 - effluent tank, 5 - gas circulation pump, 6 - gas bag. Detailed Embodiment

[0034] The invention object of the present invention will be further described in detail below in conjunction with the drawings and specific embodiments. The embodiments cannot be elaborated one by one here, but the implementation manners of the present invention are not limited to the following embodiments.

[0035] Embodiment 1

[0036] A device for directly using excess sludge as a carbon source to in-situ enhance the total nitrogen removal of an anammox system, including an influent tank 1, an influent pump 2, an expanded granular sludge bed reactor 3, an effluent tank 4, a gas circulation pump 5 and a gas bag 6.

[0037] The influent tank 1 is located on the left side of the expanded granular sludge bed reactor 3. The outlet of the influent tank 1 is connected to the inlet of the expanded granular sludge bed reactor 3 through the influent pump 2. The gas outlet of the gas circulation pump 5 is connected to the gas inlet of the expanded granular sludge bed reactor 3. The outlet of the expanded granular sludge bed reactor 3 is connected to the inlet of the effluent tank 4. The effective working volume of the expanded granular sludge bed reactor 3 is 3.2 L. The gas bag 6 is installed on the top of the expanded granular sludge bed reactor 3. The gas bag 6 is connected to the expanded granular sludge bed reactor 3 through the gas circulation pump 5. The nitrogen gas generated by the expanded granular sludge bed reactor 3 is recycled through the gas circulation pump 5.

[0038] Example 2

[0039] In the first stage, the device disclosed in Example 1 was used in this example to operate the expanded granular sludge bed reactor to prepare simulated wastewater. The influent NH4 + -N and NO2 - -N concentrations were controlled at 100 mg / L and 132 mg / L respectively, and the hydraulic retention time was controlled at 12 h. The N2 in the gas bag was recycled through the gas circulation pump at a flow rate of 1.5 L / h. The inoculated sludge was obtained from the municipal wastewater treated by the anaerobic ammonium oxidation reactor.

[0040] When the denitrification performance of the reactor reached stability, it entered the second stage. 200 mL of excess sludge was directly added to the reactor from the bottom of the reactor at one time (the reactor in this example was named R-WAS). The excess sludge came from the secondary sedimentation tank of the municipal wastewater treatment plant. The temperature of the wastewater in the reactor was 28 °C and the pH was 6.8.

[0041] Comparative Example 1

[0042] No excess sludge was added in this comparative example, and other technical features were the same as those in Example 1 (the reactor in this comparative example was named R-CON).

[0043] Figures 2 - 5 is the change curve of the component concentrations of the effluents of the R-WAS and R-CON reactors over time. It can be seen Figures 2 - 5 that in the first stage (no excess sludge was added to both), the performance of R-WAS and R-CON gradually stabilized and their total nitrogen removal efficiencies were close (86.6%). In the second stage, when excess sludge was added to the R-WAS reactor, the NO3 - -N in the effluent of R-WAS immediately dropped to 3.9 mg / L, significantly lower than 27.9 mg / L observed in R-CON; correspondingly, the TNRE of R-WAS was 94.1% higher than that of R-CON (86.6%); in R-WAS, NH4 could not be detected in the effluent +-N, indicating that the addition of excess sludge does not inhibit the activity of anaerobic ammonium oxidation bacteria, but enhances the overall total nitrogen removal of the anaerobic ammonium oxidation system.

[0044] The above specific embodiments are preferred embodiments of the present invention and do not limit the present invention. Any other changes or other equivalent replacement methods made without departing from the technical solution of the present invention are included in the protection scope of the present invention.

Claims

1. A method for directly using excess sludge as a carbon source to in-situ enhance the total nitrogen removal of an anaerobic ammonium oxidation system, characterized in that, It includes the following steps: (1) In an anaerobic environment, set up and operate a reactor, inoculate sludge into it, control the concentrations of NH4 + -N and NO2 - -N in the influent of the reactor and the hydraulic retention time, and at the same time recycle the generated nitrogen gas through a gas circulation pump; (2) After the denitrification performance of the reactor reaches stability, a certain amount of excess sludge is added to the reactor at an appropriate temperature and pH; The addition amount of the excess sludge is 100 - 400 mL, and the mass ratio of the excess sludge to the total sludge in the reactor is 1:4 - 1:6; The hydraulic retention time is 12 h; In step (2), the appropriate temperature is 28 - 32 °C, and the pH is 6.8 - 7.2; The inoculated sludge is from an anaerobic ammonium oxidation reactor for treating municipal wastewater; The concentration of influent NH4 + -N is 50 - 100 mg / L, and the concentration of influent NO2 - -N is 66 - 132 mg / L; The excess sludge is from the secondary sedimentation tank of a municipal wastewater treatment plant.

2. The method for removing total nitrogen from an in-situ enhanced anaerobic ammonium oxidation system according to claim 1, characterized in that, The reactor is an expanded granular sludge bed reactor.

3. The method for in-situ enhancing the total nitrogen removal of the anaerobic ammonium oxidation system according to claim 1, characterized in that, The circulation flow rate of the nitrogen is 1 - 3 L / h.

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