Method for in-situ enhancing total nitrogen removal of anaerobic ammonia oxidation system by directly utilizing excess sludge as carbon source

Abstract

A method for in-situ enhancement of total nitrogen removal of an anaerobic ammonia oxidation system by directly using excess sludge as a carbon source comprises the following steps: in an anaerobic environment, setting and operating a reactor, inoculating sludge into the reactor, controlling the concentrations of NH4 < + >-N and NO2 <->-N in inlet water of the reactor and hydraulic retention time, and meanwhile, recycling generated nitrogen through a gas circulating pump, when the denitrification performance of the reactor is stable, a certain amount of excess sludge is regularly added into the reactor at proper temperature and pH. The in-situ slow release of microbial products in the excess sludge well solves the inhibition problem of high-concentration organic matters on the activity of anaerobic ammonium oxidation bacteria, promotes the reaction rate of anaerobic ammonium oxidation and denitrification, improves the removal of NO3 <-> in an anaerobic ammonium oxidation system, reduces the accumulation of by-product nitrate in the anaerobic ammonium oxidation process, and improves the denitrification efficiency. Therefore, the comprehensive denitrification performance of the system is improved.

Description

Technical Field

[0001] The invention relates to the field of wastewater treatment, and in particular to a method for directly utilizing excess sludge as a carbon source to in-situ enhance 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 attracted widespread attention due to its low energy consumption and minimal sludge production. Under anaerobic conditions, the process can efficiently convert nitrite and ammonia nitrogen into nitrogen gas, thereby saving up to 60% of aeration energy consumption and eliminating dependence on external organic carbon sources. However, the byproduct nitrate of this process results in a total nitrogen removal efficiency of less than 89%. In order to improve the removal of total nitrogen, heterotrophic denitrification is often implemented by adding external carbon sources (such as methanol, ethanol, and acetic acid), but this significantly increases 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 reproduction of heterotrophic bacteria, which may lead to an imbalance between heterotrophic denitrification and anaerobic ammonium oxidation.

[0003] As the main by-product of sewage treatment, the traditional disposal methods of residual sludge, such as landfill and incineration, not only increase operating costs, but also have a negative impact on the environment. Residual sludge contains a large amount of organic matter, showing great potential for resource recovery. In addition, residual sludge is an important source of microbial products, which can provide nutrients such as polysaccharides, proteins and humus, and support the growth of low-abundance heterotrophic microorganisms (such as heterotrophic denitrifiers). In view of the poor direct biodegradability of residual sludge, it is usually necessary to use pretreatment methods such as hydrothermal, ozone and enzymatic hydrolysis (fermentation) to enhance its solubility, but these methods will increase the complexity and cost of operation, and may quickly release high concentrations of organic matter, inhibit the activity of anaerobic ammonia-oxidizing bacteria, and thus affect the efficiency of total nitrogen removal in the anaerobic ammonia-oxidizing system. Summary of the invention

[0004] In order to overcome the deficiencies of the above-mentioned prior art, the object of the present invention is to provide a method for directly utilizing residual sludge as a carbon source to in situ enhance the total nitrogen removal of the anaerobic ammonium oxidation system, thereby avoiding the inhibition of the activity of anaerobic ammonium oxidizing bacteria by high concentrations of organic matter and improving the comprehensive denitrification performance of the system.

[0005] The purpose of the present invention is achieved through the following technical solutions: A method for directly utilizing excess sludge as a carbon source to enhance the removal of total nitrogen in an anaerobic ammonium oxidation system in situ comprises the following steps: (1) In an anaerobic environment, set up and operate a reactor, inoculate it with sludge, and control the NH influent of the reactor. 4 + -N and NO 2 --N concentration and hydraulic retention time, while the generated nitrogen is recycled through a gas circulation pump; (2) When the denitrification performance of the reactor reaches stability, a certain amount of residual sludge is added to the reactor at an appropriate temperature and pH.

[0006] Preferably, the reactor is an expanded granular sludge bed reactor.

[0007] Preferably, the inoculum sludge comes from an anaerobic ammonium oxidation reactor for treating municipal sewage.

[0008] Preferably, the circulation flow rate of the nitrogen is 1-3 L / h.

[0009] More preferably, the circulation flow rate of the nitrogen is 1.5 L / h.

[0010] Preferably, the hydraulic retention time is 12 h.

[0011] Preferably, the influent NH 4 + -N concentration is 50~100 mg / L, the influent NO 2 - The concentration of -N is 66~132mg / L.

[0012] More preferably, the influent NH 4 + -N concentration is 100 mg / L, the influent NO 2 - The concentration of -N was 132 mg / L.

[0013] Preferably, the excess sludge comes from the secondary sedimentation tank of a municipal sewage treatment plant.

[0014] Preferably, the amount of the excess sludge added is 100-400 mL, and the mass ratio of the excess sludge to the total sludge in the reactor is 1:4-1:6.

[0015] More preferably, the amount of the excess sludge added is 200 mL, and the mass ratio of the excess sludge to the total sludge in the reactor is 1:4.7.

[0016] Preferably, the suitable temperature in step (2) is 28-32°C, and the pH is 6.8-7.2.

[0017] Preferably, the device includes an inlet tank, an expanded granular sludge bed reactor, an outlet tank, an inlet pump, a gas circulation pump and an air bag, the water outlet of the inlet tank is connected to the water inlet of the expanded granular sludge bed reactor through the inlet pump, the air outlet of the gas circulation pump is connected to the air 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 outlet tank through the inlet pump, the air bag is installed on the top of the expanded granular sludge bed reactor, the air bag is connected to the expanded granular sludge bed reactor through the gas circulation pump, and the nitrogen generated by the expanded granular sludge bed reactor is recycled through the gas circulation pump.

[0018] Preferably, the effective working volume of the expanded granular sludge bed reactor is 3.2 L.

[0019] The present invention has the following advantages and beneficial effects compared with the prior art: (1) The present invention uses untreated excess sludge as a carbon source to add to the anaerobic ammonium oxidation system. The in-situ slow release of microbial products in the excess sludge effectively solves the problem of high concentrations of organic matter inhibiting the activity of anaerobic ammonium oxidizing bacteria. In addition, 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-range denitrifying microorganisms, promote the reaction rate of anaerobic ammonium oxidation and denitrification, and increase the NO in the anaerobic ammonium oxidation system. 3 - The removal of nitrate reduces the accumulation of by-product nitrate during the anaerobic ammonium oxidation process, thereby improving the comprehensive denitrification performance of the system.

[0020] (2) The method disclosed in the present invention avoids any pretreatment steps, reduces operational complexity and running costs, and provides an effective alternative method for enhancing denitrification and sludge reduction. The excess sludge is used as a substitute for the traditional expensive commercial carbon source, which reduces the running cost and recycles the excess sludge, promoting the sustainable development of the environment and the economy.

[0021] The principle of the present invention is as follows: Under anaerobic conditions, excess sludge is added to the reactor. The excess sludge provides heterotrophic denitrifying bacteria and microbial products that are slowly released by microorganisms. The in-situ slow release solves the problem of high concentrations of organic matter inhibiting the activity of anaerobic ammonium oxidizing bacteria. Microbial products can serve as electron donors for heterotrophic denitrifying bacteria in the anaerobic ammonium oxidation system. The role of heterotrophic denitrification can effectively reduce NO in the anaerobic ammonium oxidation process. 3 -The microbial products slowly released by the residual sludge are rich in CHON and CHONS compounds, which are unsaturated and reductive, making them preferentially used as electron donors in the denitrification process. In addition to denitrification, the presence of electron transfer mediators (such as humus substances) in microbial products also promotes anaerobic ammonium oxidation activity, and a stable anaerobic ammonium oxidation coupled denitrification process can be established, which is beneficial to the improvement of the anaerobic ammonium oxidation process and total nitrogen removal. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of a device in an embodiment of the present invention.

[0023] Figure 2 is the NH 4 + -N concentration variation with time.

[0024] Figure 3 NO in the reactor effluent 2 - -N concentration variation with time.

[0025] Figure 4 NO in the reactor effluent 3 - -N concentration variation with time.

[0026] Figure 5 This is a curve of TNRE of reactor effluent changing with time.

[0027] The markings of the components in the accompanying drawings: 1-water inlet tank, 2-water inlet pump, 3-expanded granular sludge bed reactor, 4-water outlet tank, 5-gas circulation pump, 6-air bag. DETAILED DESCRIPTION

[0028] The purpose of the present invention is further described in detail below with reference to the accompanying drawings and specific examples. The examples cannot be described one by one here, but the implementation methods of the present invention are not therefore limited to the following examples.

[0029] Example 1 A device for directly utilizing residual sludge as a carbon source to in-situ enhance total nitrogen removal in an anaerobic ammonium oxidation system comprises an inlet pool 1, an inlet pump 2, an expanded granular sludge bed reactor 3, an outlet pool 4, a gas circulation pump 5 and an air bag 6.

[0030] The water inlet tank 1 is located on the left side of the expanded granular sludge bed reactor 3, the water outlet of the water inlet tank 1 is connected to the water inlet of the expanded granular sludge bed reactor 3 through the water inlet pump 2, the air outlet of the gas circulation pump 5 is connected to the air inlet of the expanded granular sludge bed reactor 3, the water outlet of the expanded granular sludge bed reactor 3 is connected to the water inlet of the water outlet tank 4, the effective working volume of the expanded granular sludge bed reactor 3 is 3.2 L, the air bag 6 is installed on the top of the expanded granular sludge bed reactor 3, the air bag 6 is connected to the expanded granular sludge bed reactor 3 through the gas circulation pump 5, and the nitrogen generated by the expanded granular sludge bed reactor 3 is recycled through the gas circulation pump 5.

[0031] Example 2 In the first stage, this embodiment uses the device disclosed in Example 1 to operate the expanded granular sludge bed reactor to prepare simulated wastewater, and controls the reactor inlet NH 4 + -N and NO 2 - The concentrations of -N were 100 mg / L and 132 mg / L respectively, and the hydraulic retention time was controlled at 12 h. 2 The gas was recirculated at a flow rate of 1.5 L / h by a gas circulation pump. The inoculum sludge was obtained from municipal wastewater treated in the anaerobic ammonium oxidation reactor.

[0032] When the denitrification performance of the reactor reaches stability, it enters the second stage, and 200 mL of residual sludge is directly added into the reactor from the bottom of the reactor at one time (the reactor in this example is named R-WAS). The residual sludge comes from the secondary sedimentation tank of the urban sewage treatment plant. The wastewater temperature in the reactor is 28 °C and the pH is 6.8.

[0033] Comparative Example 1 In this comparative example, no excess sludge was added, and other technical features were the same as those in Example 1 (the reactor in this comparative example was named R-CON).

[0034] Figure 2-Figure 5 The concentration of each component in the effluent of R-WAS and R-CON reactors changes with time. Figure 2-Figure 5 It can be seen that in the first stage (no excess sludge was added to either), the performance of R-WAS and R-CON gradually stabilized and the total nitrogen removal efficiency of the two was close (86.6%). In the second stage, when excess sludge was added to the R-WAS reactor, the effluent NO in the R-WAS 3 - -N immediately dropped to 3.9 mg / L, significantly lower than the 27.9 mg / L observed in R-CON; accordingly, the TNRE of R-WAS was 94.1%, which was higher than the TNRE of R-CON (86.6%); in R-WAS, no NH4 + -N, which indicates that the addition of excess sludge does not inhibit the activity of anaerobic ammonium-oxidizing bacteria, but enhances the comprehensive total nitrogen removal of the anaerobic ammonium-oxidizing system.

[0035] The above specific implementation modes are preferred embodiments of the present invention and cannot be used to limit the present invention. Any other changes or other equivalent replacement methods that do not deviate from the technical solution of the present invention are included in the protection scope of the present invention.

Claims

1. A method for directly utilizing excess sludge as a carbon source to enhance the removal of total nitrogen in an anaerobic ammonium oxidation system in situ, characterized in that: The following steps are involved: (1) In an anaerobic environment, set up and operate a reactor, inoculate it with sludge, and control the NH4 influent of the reactor. + -N and NO2 - -N concentration and hydraulic retention time, while the generated nitrogen is recycled through a gas circulation pump; (2) When the denitrification performance of the reactor reaches stability, a certain amount of residual sludge is added to the reactor at an appropriate temperature and pH.

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 removing total nitrogen from an in-situ enhanced anaerobic ammonium oxidation system according to claim 1, characterized in that: The inoculated sludge comes from an anaerobic ammonium oxidation reactor that treats municipal sewage.

4. The method for removing total nitrogen from an in-situ enhanced anaerobic ammonium oxidation system according to claim 1, characterized in that: The influent NH4 + -N concentration is 50~100 mg / L, the influent NO2 - The concentration of -N is 66~132 mg / L.

5. The method for removing total nitrogen from an in-situ enhanced anaerobic ammonium oxidation system according to claim 1, characterized in that: The hydraulic retention time is 12 h.

6. The method for removing total nitrogen from an in-situ enhanced anaerobic ammonium oxidation system according to claim 1, characterized in that: The circulation flow rate of the nitrogen is 1-3 L / h.

7. The method for removing total nitrogen from an in-situ enhanced anaerobic ammonium oxidation system according to claim 1, characterized in that: The excess sludge comes from the secondary sedimentation tank of a municipal sewage treatment plant.

8. The method for removing total nitrogen from an in-situ enhanced anaerobic ammonium oxidation system according to claim 1, characterized in that: The amount of the excess sludge added is 100-400 mL, and the mass ratio of the excess sludge to the total sludge in the reactor is 1:4-1:

6.

9. The method for removing total nitrogen from an in-situ enhanced anaerobic ammonium oxidation system according to claim 1, characterized in that: The suitable temperature in step (2) is 28-32°C, and the pH is 6.8-7.2.

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