Method for Deep Synergistic Denitrification of Municipal Sewage with Secondary Inlet Water as Electron Donor

Abstract

The present invention relates to a method for deep synergistic denitrification of urban sewage using secondary influent as an electron donor. The method comprises: S1, a startup phase: S11, using the secondary effluent from the urban sewage treatment plant as the inlet of a denitrification filter, and inoculating the denitrification filter with hydrolytic acidifying bacteria, denitrifying bacteria, and anaerobic ammonia oxidizing bacteria; S12, using a mixture of the secondary effluent from the urban sewage treatment plant and filtered secondary influent as the inlet of the denitrification filter, and adjusting the ratio of the secondary effluent to the secondary influent to increase the ammonia nitrogen concentration of the influent in a stepwise manner to 6.5 mg / L; S2, a stabilization phase: pumping the mixture of the secondary effluent and the secondary influent, with an ammonia nitrogen concentration of 6.5 mg / L, into the denitrification filter for treatment. This method does not require the addition of any external chemicals, reduces carbon source demand, and can reduce the total nitrogen in the secondary effluent of the urban sewage treatment plant to 0.51 mg / L, achieving a removal rate of 97.68%. It can be used in the field of deep denitrification treatment of urban sewage.

Description

Technical Field

[0001] The present invention relates to the field of sewage treatment, and in particular to a method for deep synergistic denitrification of urban sewage using secondary influent as an electron donor. Background Art

[0002] Excessive nitrogen discharged into slow-flowing water bodies such as rivers and lakes can accelerate eutrophication and produce substances harmful to aquatic plants and animals. To reduce nitrogen emissions and improve water quality, my country has built numerous urban sewage treatment plants and established strict total nitrogen emission standards, such as the "Pollutant Discharge Standard for Urban Sewage Treatment Plants" (GB 18918-2002) (total nitrogen ≤ 15 mg / L). Some key regions have enacted even stricter local standards, such as the "Emission Limits of Major Water Pollutants from Urban Sewage Treatment Plants" (DB 5301 / T43-2020), which sets a total nitrogen emission standard of 5 mg / L. Some regions even require compliance with the Class III standard in the "Surface Water Environmental Quality Standard" (GB 3838-2002) (total nitrogen ≤ 1 mg / L). It is difficult for urban sewage treatment plants to achieve these total nitrogen standards in their effluent through secondary biological treatment alone, so deep denitrification of urban sewage is necessary.

[0003] The Chinese patent publication number CN116282521A, "A method for deep synergistic denitrification of urban sewage based on an improved denitrification filter," uses a modified denitrification filter. During startup, the quartz sand filler of the modified denitrification filter is covered with a biofilm containing manganese oxidizing bacteria, denitrifying bacteria, hydrolytic acidifying bacteria, and anaerobic ammonia oxidizing bacteria, as well as biological manganese oxides. The filter is used to deeply treat urban sewage, and the total nitrogen in the effluent after treatment is 1.47 mg / L, with a removal rate of 93.38%. Although this method has a high removal rate for total nitrogen and does not require an external carbon source, the total nitrogen in the effluent does not drop below 1 mg / L, and divalent manganese needs to be added to generate biological manganese oxides. In addition, because this method uses refractory organic matter and the oxidation and hydrolysis products of refractory organic matter as carbon sources, the denitrification rate is low. Moreover, the startup phase takes at least 199 days, which is time-consuming.

[0004] Therefore, there is an urgent need for a deep denitrification technology for urban sewage that does not require any external chemical agents, has a high total nitrogen removal rate, low operating costs, does not produce secondary pollution, and has a short start-up time. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the existing technology and provide a method for deep synergistic denitrification of urban sewage using secondary influent as an electron donor. It does not require the addition of any chemical agents, has a high total nitrogen removal rate, low operating costs, does not produce secondary pollution, and has a short startup time.

[0006] In order to solve the above technical problems, the technical solution of the present invention is: a method for deep synergistic denitrification of urban sewage using secondary influent as an electron donor, the method comprising:

[0007] S1, startup phase:

[0008] S11, using the secondary effluent from the municipal sewage treatment plant as the inlet water for the denitrification filter, and inoculating the denitrification filter with hydrolytic acidifying bacteria, denitrifying bacteria, and anaerobic ammonium oxidizing bacteria. The hydrolytic acidifying bacteria and denitrifying bacteria were inoculated once every three days, for a total of four times; the anaerobic ammonium oxidizing bacteria were inoculated once every seven days.

[0009] S12, after the effluent ammonia nitrogen is stabilized, a mixture of the secondary effluent from the municipal sewage treatment plant and the filtered secondary influent is used as the influent for the denitrification filter, and the ratio of the secondary effluent to the secondary influent is adjusted to increase the influent ammonia nitrogen concentration in a stepwise manner to 6.5 mg / L. During the stepwise increase in the influent ammonia nitrogen concentration, the next increase is performed after the effluent ammonia nitrogen is stabilized, and anaerobic ammonia-oxidizing bacteria are inoculated until the effluent ammonia nitrogen is finally stabilized;

[0010] S2, stable phase:

[0011] The mixture of secondary effluent with an ammonia nitrogen concentration of 6.5 mg / L and secondary influent is pumped into the denitrification filter as influent for treatment. The hydraulic retention time is 4-6 hours and the backwash cycle is 6-8 days.

[0012] Furthermore, in step S1, the bacterial solution inoculated each time is 300 mL, and the bacterial concentrations of hydrolytic acidifying bacteria, denitrifying bacteria and anaerobic ammonia oxidizing bacteria are 10 g / L-15 g / L, 10 g / L-13 g / L and 5 g / L-8 g / L, respectively.

[0013] Furthermore, in step S12, in the process of increasing the influent ammonia nitrogen concentration in a stepwise manner, the influent ammonia nitrogen concentration is increased to 1 mg / L, 2 mg / L, 3 mg / L, 5 mg / L, and 6.5 mg / L in sequence.

[0014] Furthermore, the stability of effluent ammonia nitrogen means that the ammonia nitrogen concentration in the water does not fluctuate by more than 10% relative to the average ammonia nitrogen concentration within 10 to 12 consecutive days.

[0015] Furthermore, in step S2, each backwashing time is 3-5 minutes, and the backwashing intensity is 10-12 L / (s·m 2 ).

[0016] Furthermore, the denitrification filter includes:

[0017] A pool body, wherein a water inlet is provided at the bottom of the pool body and a water outlet is provided at the upper end of the pool body;

[0018] A supporting layer, the supporting layer being disposed within the pool body and leaving a space between the supporting layer and the bottom of the pool body;

[0019] A packing layer, the packing layer is located on the supporting layer and below the water outlet; wherein,

[0020] The supporting layer and the filler layer are both made of quartz sand, and the particle size of the quartz sand in the supporting layer is larger than that of the quartz sand in the filler layer.

[0021] Furthermore, the particle size of the quartz sand of the supporting layer is 1-2 cm, and the particle size of the quartz sand of the filler layer is 2-4 mm.

[0022] Furthermore, the thickness of the supporting layer is 10 cm, and the thickness of the filler layer is 70 cm.

[0023] After adopting the above technical solution, the present invention has the following advantages:

[0024] (1) No external chemical agents are required, the operating cost is extremely low, and no secondary pollution is generated: the present invention uses organic matter and ammonia nitrogen in the secondary influent as electron donors for partial denitrification-anaerobic ammonium oxidation and deep synergistic denitrification by denitrification; denitrifying bacteria use the organic matter in the secondary influent as a carbon source to reduce the nitrate nitrogen in the secondary effluent to nitrite nitrogen, and then the anaerobic ammonium oxidizing bacteria use the ammonia nitrogen in the secondary influent as an electron donor to reduce the generated nitrite nitrogen to nitrogen gas, and finally the remaining nitrite nitrogen is further denitrified to nitrogen gas by the denitrifying bacteria using the organic matter in the secondary influent as a carbon source. Therefore, the present invention does not require the addition of any external chemical agents, the operating cost is extremely low, and no secondary pollution is generated;

[0025] (2) Fast rate of deep synergistic denitrification: In this denitrification filter, denitrifying bacteria use easily degradable dissolved organic matter in the secondary influent as a carbon source, and the denitrification reaction rate is fast, which is conducive to improving the rate of deep synergistic denitrification of partial denitrification-anaerobic ammonium oxidation and denitrification;

[0026] (3) Excellent total nitrogen removal effect: total nitrogen was reduced from approximately 22 mg / L to 0.51 mg / L, with a removal rate of 97.68%. The total nitrogen in the effluent met the Class III standard in the "Surface Water Environmental Quality Standard" (GB 3838-2002);

[0027] (4) Reduced carbon source demand: In this denitrification filter, by achieving partial denitrification-anaerobic ammonium oxidation and deep synergistic denitrification by denitrification, the deep denitrification effect is improved and the carbon source demand is reduced. Theoretically, 2.86 mg of COD is required to reduce 1 mg of nitrate nitrogen to nitrogen gas, and 1.14 mg of COD is required to reduce 1 mg of nitrate nitrogen to nitrite nitrogen; however, partial denitrification-anaerobic ammonium oxidation is used to remove 1 mg of total nitrogen (nitrate nitrogen + ammonia nitrogen) and only about 0.74 mg of COD is required. The present invention actually consumes 1.30 mg of COD to remove 1 mg of total nitrogen, which is much lower than the theoretical COD consumption of denitrification;

[0028] (5) Reduced the operating cost of secondary biochemical treatment in urban sewage treatment plants: The intercepted suspended organic matter is anaerobic fermented to produce biogas, which is then used to generate electricity to provide electricity for urban sewage treatment plants. Part of the secondary influent does not undergo secondary biochemical treatment, which reduces the operating cost of secondary biochemical treatment;

[0029] (6) The startup time is shortened: on the one hand, various strains are inoculated simultaneously, which shortens the inoculation time. On the other hand, due to the fast deep synergistic denitrification rate, the time for the influent ammonia nitrogen concentration to be increased stepwise to 6.5 mg / L is shortened. In the present invention, the startup time is 140 days, while in the patent with publication number CN116282521A, the strains are inoculated in sequence, and it takes at least 39 days to inoculate the strains, and it takes 160 days for the influent ammonia nitrogen concentration to be increased stepwise to 7 (the 160 days are from the paper "Advanced synergetic nitrogen removal of municipal wastewater using oxidation products of refractory organic matters in secondary effluent by biogenic manganese oxides as carbon source" published on the content of the patent with publication number CN116282521A). The startup time takes at least 199 days. Therefore, the present invention greatly shortens the time required for the startup phase. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a diagram of a system for deep treatment of urban sewage including a denitrification filter tank according to the present invention;

[0031] Figure 2 This is a diagram showing the removal effect of COD during treatment in an embodiment of the present invention;

[0032] Figure 3 This is a diagram showing the effect of removing ammonia nitrogen as the treatment proceeds in an embodiment of the present invention;

[0033] Figure 4 This is a diagram showing the effect of nitrate nitrogen removal during treatment in an embodiment of the present invention;

[0034] Figure 5 This is a diagram showing the effect of total nitrogen removal during treatment in an embodiment of the present invention;

[0035] Figure 1 Among them, 1. Water tank; 2. Pump; 3. Water inlet valve; 4. Denitrification filter; 4-1. Tank body; 4-2. Support layer; 4-3. Filling layer; 4-4. Water inlet; 4-5. Water outlet; 5. Backwash valve. DETAILED DESCRIPTION

[0036] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments in conjunction with the accompanying drawings.

[0037] A method for deep synergistic denitrification of urban sewage using secondary influent as an electron donor, the method comprising:

[0038] S1, startup phase:

[0039] S11, using the actual secondary effluent from the urban sewage treatment plant as the inlet water of the denitrification filter 4, and inoculating hydrolytic acidifying bacteria, denitrifying bacteria and anaerobic ammonium oxidizing bacteria in the denitrification filter 4, the bacterial concentrations of hydrolytic acidifying bacteria, denitrifying bacteria and anaerobic ammonium oxidizing bacteria are 10g / L-15g / L, 10g / L-13g / L, and 5g / L-8g / L, respectively, and each inoculation of the bacterial solution is 300mL. The hydrolytic acidifying bacteria and denitrifying bacteria are inoculated once every 3 days, for a total of 4 times; the anaerobic ammonium oxidizing bacteria are inoculated once every 7 days;

[0040] S12, after the effluent ammonia nitrogen is stable, the mixture of the actual secondary effluent of the urban sewage treatment plant and the filtered secondary influent is used as the influent of the denitrification filter 4, and the ratio of the secondary effluent and the secondary influent is adjusted to make the influent ammonia nitrogen concentration 1 mg / L. When the effluent ammonia nitrogen is stable, the influent ammonia nitrogen concentration is increased to 2 mg / L, 3 mg / L, 5 mg / L, and 6.5 mg / L in sequence. In the process of increasing the influent ammonia nitrogen concentration, each time the effluent ammonia nitrogen is stable, the next increase is made. The stability of the effluent ammonia nitrogen means that the ammonia nitrogen concentration in the water does not fluctuate by more than 10% relative to the average ammonia nitrogen concentration within 10 to 12 consecutive days. The anaerobic ammonia oxidizing bacteria are inoculated until the effluent ammonia nitrogen is finally stable;

[0041] It should be noted that when the ammonia nitrogen concentration of the influent is increased in a step-by-step manner, the concentrations are not limited to those introduced above, but can also be 1 mg / L, 3 mg / L, 5 mg / L, 6.5 mg / L or 2 mg / L, 4 mg / L, 5 mg / L, 6.5 mg / L, etc.

[0042] S2, stable phase:

[0043] The mixture of secondary effluent and secondary influent with an ammonia nitrogen concentration of 6.5 mg / L is pumped into the denitrification filter as influent. The hydraulic retention time is 4-6 hours, the backwash cycle is 6-8 days, each backwash time is 3-5 minutes, and the backwash intensity is 10-12 L / (s·m 2 ).

[0044] Specifically, the organic matter in the secondary effluent of a municipal sewage treatment plant is a difficult-to-degrade organic matter, because these organic matter are not removed during the secondary biochemical treatment process of the municipal sewage treatment plant. The main form of nitrogen in the secondary effluent is nitrate nitrogen, which also contains a certain amount of organic nitrogen (such as protein, microorganisms), ammonia nitrogen, and nitrite nitrogen. The hydrolytic acidifying bacteria inoculated in the denitrification filter 4 convert the organic nitrogen in the secondary effluent into ammonia nitrogen (ammoniation), and at the same time convert the difficult-to-degrade organic matter into easily degradable organic matter. The inoculated denitrifying bacteria use the easily degradable organic matter produced and the easily degradable organic matter in the secondary influent as carbon sources to reduce the nitrate nitrogen in the secondary effluent to nitrite nitrogen, and the inoculated anaerobic ammonia-oxidizing bacteria use the ammonia nitrogen produced by ammoniation and the ammonia nitrogen in the secondary influent as electron donors to reduce the produced nitrite nitrogen to nitrogen gas, and the remaining nitrite nitrogen is further reduced to nitrogen gas by the denitrifying bacteria. After the secondary influent is filtered (filtration pore size: 30-50 μm), the remaining easily degradable dissolved organic matter is used as a carbon source for denitrification, which can increase the rate of denitrification. By increasing the proportion of the secondary influent, sufficient electron donors can be provided for partial denitrification-anaerobic ammonium oxidation and deep synergistic denitrification by denitrification. In addition, this embodiment can also use secondary influent with different carbon-nitrogen ratios (COD / TN) to provide electron donors for deep synergistic denitrification. By adjusting the contribution rate of partial denitrification-anaerobic ammonium oxidation and denitrification to total nitrogen removal, it can adapt to secondary influent with different carbon-nitrogen ratios, thereby achieving efficient and low-cost removal of total nitrogen. If the carbon-nitrogen ratio in the secondary influent is high, efficient and low-cost removal of total nitrogen can be achieved by increasing the contribution rate of denitrification to total nitrogen; if the carbon-nitrogen ratio in the secondary influent is low, efficient and low-cost removal of total nitrogen can be achieved by increasing the contribution rate of partial denitrification-anaerobic ammonium oxidation to total nitrogen. This embodiment is also applicable to treating secondary effluent with different total nitrogen concentrations, because the secondary influent contains sufficient organic matter and ammonia nitrogen to provide electron donors for deep synergistic denitrification. Therefore, the present invention has a high application prospect.

[0045] In addition, after the secondary influent is filtered (filtration pore size: 30-50μm), the intercepted suspended organic matter can produce biogas through anaerobic fermentation, and then provide electricity for the urban sewage treatment plant through biogas power generation. The increased ratio of ammonia nitrogen / COD in the filtered secondary influent is conducive to increasing the contribution rate of partial denitrification-anaerobic ammonia oxidation to total nitrogen removal, that is, increasing the amount of ammonia nitrogen removed, as well as the rate of denitrification and deep synergistic denitrification. After filtering and intercepting the suspended organic matter in the secondary influent, the consumption of the secondary influent increases, and this part of the secondary influent does not undergo secondary biochemical treatment, thereby reducing the operating cost of the secondary biochemical treatment; at the same time, as the consumption of the secondary influent increases, the amount of suspended organic matter intercepted by filtration also increases accordingly, which can provide more electricity for the urban sewage treatment plant.

[0046] After treatment using the method described in this example, total nitrogen was reduced from approximately 22 mg / L to 0.46-0.64 mg / L, with a removal rate of 97.10%-97.90%. The average concentration was 0.51 mg / L, with an average removal rate of 97.68%. The effluent total nitrogen met the Class III standard in the Environmental Quality Standard for Surface Water (GB 3838-2002).

[0047] This embodiment effectively solves the problem of deep denitrification of urban sewage requiring the addition of electron donors (such as carbon sources, inorganic substances (reduced sulfur, hydrogen, Fe 2+ This system addresses the challenges of high operating costs, secondary pollution, and poor total nitrogen removal, achieving low-cost, efficient total nitrogen removal. After treatment in denitrifying filters, the secondary effluent from urban sewage treatment plants can be reduced from Class IB in the "Pollutant Discharge Standard for Urban Sewage Treatment Plants" (GB 18918-2002) to Class III in the "Environmental Quality Standard for Surface Water" (GB 3838-2002). This system has high application value and is conducive to widespread application.

[0048] like Figure 1 As shown, the denitrification filter 4 includes:

[0049] The pool body 4-1 has a water inlet 4-4 at the bottom and a water outlet 4-5 at the upper end.

[0050] The supporting layer 4-2 is disposed in the tank body 4-1 and has a space between the supporting layer 4-2 and the bottom of the tank body 4-1;

[0051] The packing layer 4-3 is located on the supporting layer 4-2 and below the water outlet 4-5; wherein,

[0052] The supporting layer 4-2 and the filling layer 4-3 are both made of quartz sand, and the particle size of the quartz sand of the supporting layer 4-2 is larger than that of the quartz sand of the filling layer 4-3.

[0053] In this embodiment, the quartz sand of the supporting layer 4-2 has a particle size of 1-2 cm, and the quartz sand of the packing layer 4-3 has a particle size of 2-4 mm. Of course, the particle sizes of the quartz sand of the supporting layer 4-2 and the packing layer 4-3 are not limited to these. The thickness of the supporting layer can be, but is not limited to, 10 cm, and the thickness of the packing layer can be, but is not limited to, 70 cm.

[0054] like Figure 1 As shown, the water tank 1 is connected to the water inlet 4-1 of the denitrification filter 4 through the pump 2. An inlet valve 3 is provided between the pump 2 and the water inlet 4-1. In addition, the water inlet 4-1 is also connected to a backwash pipe, and a backwash valve 5 is provided on the backwash pipe.

[0055] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A method for deep synergistic denitrification of urban sewage using secondary influent as an electron donor, characterized in that: Methods include: S1, startup phase: S11, using the secondary effluent from the municipal sewage treatment plant as the inlet water for the denitrification filter, and inoculating the denitrification filter with hydrolytic acidifying bacteria, denitrifying bacteria, and anaerobic ammonium oxidizing bacteria. The hydrolytic acidifying bacteria and denitrifying bacteria were inoculated once every three days, for a total of four times; the anaerobic ammonium oxidizing bacteria were inoculated once every seven days. S12, after the effluent ammonia nitrogen is stabilized, a mixture of the secondary effluent from the municipal sewage treatment plant and the filtered secondary influent is used as the influent for the denitrification filter, and the ratio of the secondary effluent to the secondary influent is adjusted to increase the influent ammonia nitrogen concentration in a stepwise manner to 6.5 mg / L. During the stepwise increase in the influent ammonia nitrogen concentration, the next increase is performed after the effluent ammonia nitrogen is stabilized, and anaerobic ammonia-oxidizing bacteria are inoculated until the effluent ammonia nitrogen is finally stabilized; S2, stable phase: The mixture of the secondary effluent with an ammonia nitrogen concentration of 6.5 mg / L and the secondary influent is pumped into the denitrification filter as influent, with a hydraulic retention time of 4-6 hours and a backwash cycle of 6-8 days; Among them, the filtered secondary influent provides easily degradable organic matter as a carbon source for denitrifying bacteria and ammonia nitrogen as an electron donor for anaerobic ammonia-oxidizing bacteria.

2. The method for deep synergistic denitrification of urban sewage using secondary influent as an electron donor according to claim 1, characterized in that: In step S1, the bacterial solution inoculated each time is 300 mL, and the bacterial concentrations of hydrolytic acidifying bacteria, denitrifying bacteria and anaerobic ammonia oxidizing bacteria are 10 g / L-15 g / L, 10 g / L-13 g / L and 5 g / L-8 g / L respectively.

3. The method for deep synergistic denitrification of urban sewage using secondary influent as an electron donor according to claim 1, characterized in that: In step S12, in the process of increasing the influent ammonia nitrogen concentration in a step-by-step manner, the influent ammonia nitrogen concentration is increased to 1 mg / L, 2 mg / L, 3 mg / L, 5 mg / L, and 6.5 mg / L in sequence.

4. The method for deep synergistic denitrification of urban sewage using secondary influent as an electron donor according to claim 1, characterized in that: The stability of effluent ammonia nitrogen means that the ammonia nitrogen concentration in the water does not fluctuate by more than 10% relative to the average ammonia nitrogen concentration within 10 to 12 consecutive days.

5. The method for deep synergistic denitrification of urban sewage using secondary influent as an electron donor according to claim 1, characterized in that: In step S2, each backwashing time is 3-5 minutes, and the backwashing intensity is 10-12 L / (s·m 2 ).

6. The method for deep synergistic denitrification of urban sewage using secondary influent as an electron donor according to claim 1, characterized in that: The denitrification filter comprises: A pool body, wherein a water inlet is provided at the bottom of the pool body and a water outlet is provided at the upper end of the pool body; a supporting layer, the supporting layer being disposed within the pool body and leaving a space between the supporting layer and the bottom of the pool body; A packing layer, the packing layer is located on the supporting layer and below the water outlet; wherein, The supporting layer and the filler layer are both made of quartz sand, and the particle size of the quartz sand in the supporting layer is larger than that of the quartz sand in the filler layer.

7. The method for deep synergistic denitrification of urban sewage using secondary influent as an electron donor according to claim 6, characterized in that: The particle size of the quartz sand of the supporting layer is 1-2 cm, and the particle size of the quartz sand of the filler layer is 2-4 mm.

8. The method for deep synergistic denitrification of urban sewage using secondary influent as an electron donor according to claim 6, characterized in that: The thickness of the supporting layer is 10 cm, and the thickness of the filler layer is 70 cm.

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