Method for simultaneously realizing nitrogen oxide emission reduction of black and odorous sediment and denitrogenation by anaerobic ammonia oxidation

Abstract

This invention discloses a method for simultaneously reducing nitrous oxide emissions and removing nitrogen from black and odorous sediment. The invention proposes a staged, batch-based nitrate addition method. Results show that this method achieves the same black and odorous sediment removal effect as the traditional one-time addition method, and can reduce the nitrous oxide emission rate by up to approximately 96.84%. Furthermore, the anaerobic ammonia oxidation process is initiated earlier, on day 21. This indicates that the staged, batch-based addition method can effectively reduce the accumulation and emission of nitrous oxide during nitrate remediation of sediment and promote the initiation of the anaerobic ammonia oxidation process, thereby improving remediation efficiency.

Description

Technical Field

[0001] This invention relates to the field of environmental engineering, and in particular to a method for remediating black and odorous sediment by simultaneously reducing nitrous oxide emissions and removing nitrogen through anaerobic ammonia oxidation, thereby inhibiting the generation and release of ammonia nitrogen from the sediment. Background Technology

[0002] Bottom sediment acts as a sink for pollutants when water bodies are polluted, with large amounts of pollutants continuously accumulating in it. When the water environment is improved through remediation, the bottom sediment becomes a source of pollutant release, leading to recurring black and odorous water. Therefore, to effectively treat black and odorous water and achieve long-term cleanliness, it is essential to effectively remove pollutants from the bottom sediment.

[0003] The key pollutants in the sediment that directly contribute to black and odorous conditions are sulfides (AVS) and ferrous iron (Fe). 2+ ) and ammonia nitrogen (NH4) +Currently, conventional sediment remediation methods can be divided into in-situ remediation and ex-situ remediation. Ex-situ remediation most commonly involves sediment dredging, but this method requires a large amount of engineering work, and the disturbance during dredging can lead to further release of pollutants from the sediment. Furthermore, the sediment produced by dredging requires a large land area, making it unsuitable for large-scale use. In-situ remediation refers to removing pollutants directly within the river channel without removing the contaminated sediment. This reduces sediment disturbance, is economically cost-effective, and better meets practical needs. Among these methods, in-situ addition of nitrates (mainly calcium nitrate, potassium nitrate, and sodium nitrate) is a widely used method. It has advantages such as rapid elimination of black and odorous conditions, high economic efficiency, and minimal in-situ disturbance, while also improving the redox potential and transparency of the water. The main principle of this method is that after nitrates are added to the black and odorous sediment, the reduction process driven by microorganisms drives the reduction of sulfides and ferrous iron in the sediment, thereby eliminating the black and odorous conditions. However, its effectiveness in removing ammonia nitrogen from the sediment is unstable. This is because the addition of nitrates can stimulate the reduction of dissimilar nitrates to ammonium (DNRA) in the sediment, leading to an increase in ammonia nitrogen and further exacerbating ammonia nitrogen pollution. On the other hand, the nitrite produced during nitrate reduction can stimulate the anammox process in the sediment, thereby removing ammonia nitrogen. Compared to other pollutants, ammonia nitrogen is highly soluble in water. If ammonia nitrogen is not completely removed from the sediment, it is more likely to diffuse into the overlying water bodies, increasing the risk of black and odorous regeneration. Therefore, controlling the conversion of added nitrates to the Anammox process is a problem that needs to be addressed in sediment remediation. However, anammox bacteria often grow slowly, and the Anammox process in this method can take hundreds of days to start, resulting in low remediation efficiency. Furthermore, nitrous oxide, an intermediate byproduct of nitrate reduction, is a potent greenhouse gas, with a greenhouse effect 296 times greater than that of carbon dioxide. Sulfides, which are abundant in black and odorous sediments, have a strong inhibitory effect on the reduction of nitrous oxide. The large amounts of nitrate added by existing research methods lead to a large emission of nitrous oxide, which significantly increases "carbon emissions" during the remediation of black and odorous sediments. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and deficiencies of the prior art and provide a low-carbon and efficient remediation method that simultaneously achieves nitrous oxide emission reduction and anaerobic ammonia oxidation denitrification during the remediation process of black and odorous sediment. The objective of this invention is achieved through the following technical solution: A method for simultaneously achieving nitrous oxide oxidation for emission reduction and anaerobic ammonia oxidation for nitrogen removal in black and odorous sediment includes the following steps: (1) Taking the black and odorous sediment in a specific area as the treatment target, the black and odorous sediment was sampled and tested in situ to determine key indicators such as moisture content and content of black and odorous substances; (2) Based on the sampling and testing results in step (1), the amount of nitrate to be added is calculated. Within an appropriate temperature range, the nitrate is added in portions to the sediment in which the black and odorous condition has been identified in step (1) to achieve in-situ low-carbon remediation of the black and odorous sediment. (3) Based on the changes in sulfide concentration in step (2), when the sulfide concentration remains stable, calculate the amount of nitrate to be added and continue to add the second stage nitrate to the sediment in step (2) at once, so as to simultaneously suppress the emission of nitrous oxide from the black and odorous sediment and start the anaerobic ammonia oxidation denitrification.

[0005] The key indicators mentioned in step (1) are the moisture content, density, and total amount of ferrous oxide, sulfides, and ammonia nitrogen in the sediment.

[0006] The black and odorous sediment mentioned in step (1) is sedimentary sediment containing ammonia nitrogen, sulfides and ferrous components that accumulate in the water body.

[0007] The black and smelly sediment described in step (1) contains microorganisms of the anaerobic ammonia-oxidizing bacteria genus.

[0008] The nitrate mentioned in step (2) is calcium nitrate tetrahydrate.

[0009] The amount of nitrate added in step (2) is calculated according to the formula, which is as follows: Total nitrate nitrogen / total sulfide and ferrous iron in sediment = 0.2–0.4; Among them, total nitrate nitrogen is the amount of nitrogen-containing element in nitrate, and the total amount of sulfide and ferrous iron in the sediment is the sum of the amounts of sulfide and ferrous iron in the sediment.

[0010] Preferably, the amount of nitrate added is calculated according to a formula, the specific formula of which is as follows: The ratio of total nitrate nitrogen to sediment sulfides and ferrous iron is 0.3.

[0011] The nitrate in step (2) is added in 2 to 6 times; preferably 4 times.

[0012] The nitrates in step (2) are added in installments at intervals of 4 to 17 days; preferably on days 0, 4, 12, and 29.

[0013] The constant temperature mentioned in step (2) is to maintain a temperature of 28–32°C.

[0014] The amount of nitrate added in step (3) is calculated according to the formula, which is as follows: The ratio of total nitrate nitrogen to the total amount of sulfides, ferrous oxide, and ammonia nitrogen in the sediment is 0.9–1.5; preferably 0.9. Among them, total nitrate nitrogen is the amount of nitrogen-containing elements in nitrate, and the total amount of sulfide, ferrous iron and ammonia nitrogen in sediment is the sum of the amounts of sulfide, ferrous iron and ammonia nitrogen in sediment.

[0015] The second stage of nitrate addition in step (3) is 21 to 29 days after the first addition; preferably, it is added on the 21st day.

[0016] The method for simultaneously reducing nitrous oxide emissions and removing nitrogen from anaerobic ammonia oxidation in black and odorous sediments, on the one hand, utilizes the preferential oxidation of sulfides in sediments by controlling the nitrate addition method, thereby reducing the inhibition of sulfides on subsequent denitrification steps, increasing the microbial process of nitrous oxide reduction in the sediment, and significantly increasing the abundance of nitrous oxide reductase in the sediment, thus reducing nitrous oxide emissions from the sediment. At the same time, the subsequent products of sulfide oxidation also promote the increase of microorganisms that can couple and utilize multiple forms of sulfur oxidation and nitrous oxide reduction, enhancing the nitrous oxide reduction potential of the system. On the other hand, the oxidation of sulfides in black and odorous sediments can also reduce the growth inhibition of anaerobic ammonia oxidizing bacteria, and the nitrous oxide accumulated during the sulfide oxidation stage can further stimulate the growth of anaerobic ammonia oxidizing bacteria in the sediment, accelerating the start of the anaerobic ammonia oxidation process and improving the efficiency of sediment black and odorous remediation. After the anaerobic ammonia oxidizing bacteria in the sediment have accumulated and grown, nitrates are added again to provide substrate to promote the anaerobic ammonia oxidation process in the sediment. Meanwhile, the anaerobic ammonia oxidation process in the sediment can compete with the denitrification process for substrate nitrite, causing nitrogenous substances to be converted into nitrogen gas rather than converted into nitrous oxide emissions. This simultaneously achieves nitrous oxide emission reduction and anaerobic ammonia oxidation denitrification in the remediation process of black and odorous sediment, thus achieving low-carbon and efficient remediation of black and odorous sediment.

[0017] The above-mentioned method for simultaneously reducing nitrous oxide emissions and promoting anammox denitrification in black and odorous sediment is applied in the treatment of black and odorous sediment to simultaneously reduce nitrous oxide emissions and promote anammox denitrification. The present invention has the following advantages and effects compared with the prior art: This invention proposes a phased and batch-based nitrate addition method. Results show that the phased and batch-based nitrate addition method has the same black and odorous removal effect on sediment as the traditional one-time addition method, and can reduce the nitrous oxide emission rate by up to about 96.84%. Moreover, the anaerobic ammonia oxidation process is initiated earlier, on day 21. This indicates that the phased and batch-based addition method can effectively reduce the accumulation and emission of nitrous oxide during the nitrate remediation process of sediment, promote the initiation of the anaerobic ammonia oxidation process in the sediment, and improve the remediation efficiency. Attached Figure Description

[0018] Figure 1 This refers to the changes in nitrate nitrogen concentration in different treatment groups in Example 1.

[0019] Figure 2This refers to the changes in sediment sulfide concentration in different treatment groups in Example 1.

[0020] Figure 3 This refers to the changes in ferrous concentration in the sediment of different treatment groups in Example 1.

[0021] Figure 4 This refers to the changes in ammonia nitrogen concentration in the sediment of different treatment groups in Example 1.

[0022] Figure 5 This refers to the changes in the abundance of anaerobic ammonia oxidizing bacteria in different treatment groups in Example 1.

[0023] Figure 6 This refers to the change in nitrate concentration in the sediment of the system in Example 2.

[0024] Figure 7 This refers to the change in ORP of the bottom sediment in the system in Example 2.

[0025] Figure 8 This refers to the change in AVS concentration in the bottom sediment of the system in Example 2.

[0026] Figure 9 This refers to the change in ferrous concentration in the bottom sediment of the system in Example 2.

[0027] Figure 10 These are the results of metagenomic sequencing statistical analysis in Example 2.

[0028] Figure 11 This is a graph showing the trend of relative abundance changes of denitrifying microorganisms in Example 2. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0030] Unless otherwise specified in the following implementation plan, the test conditions are generally as per standard test conditions or the test conditions recommended by the reagent company. Unless otherwise specified, all materials and reagents used are commercially available. Example

[0031] According to the mechanistic formula of anaerobic ammonium oxidation, the substrate for anaerobic ammonium oxidation is NH4. + and NO2 - Therefore, providing sufficient substrate NH4 + and NO2 - This promotes the growth of anaerobic ammonia-oxidizing bacteria in the sediment, thereby facilitating the initiation of the anaerobic ammonia oxidation process. However, existing studies generally employ a one-time excessive addition of nitrate, taking advantage of the sulfur autotrophic denitrification process due to the influence of sulfur. 2- and NO3 - Inhibition of NO2- The cumulative effect and the high concentration of NH4 in the black and smelly sediment itself + Ultimately, this method achieves the elimination of black and odorous sediment and denitrification. The staged nitrate addition method proposed in this study separates the oxidation processes of sulfides and ferrous oxide from the ammonia nitrogen oxidation process, thus fully utilizing the NO2 generated during the initial sulfur autotrophic denitrification process. - The cumulative stimulation of anaerobic ammonia-oxidizing bacteria growth, while avoiding S 2- Growth inhibition of anaerobic ammonia-oxidizing bacteria in the later stages of oxidation.

[0032] Existing research indicates that when the calcium nitrate dosage ratio (n(N) / n(S+Fe)) is around 1.2, rapid oxidation of sulfides in the sediment can be achieved. Here, n(N) represents the amount of nitrogen in the added calcium nitrate, and n(S+Fe) represents the initial sulfur content in the black and odorous sediment. 2- and Fe 2+ The sum of the amounts of substances. Therefore, this experiment selected the nitrate addition ratio in the first stage as n(N) / n(S+Fe)≈1.2, and explored the anaerobic ammonium oxidation effect under different nitrate addition amounts in the second stage.

[0033] The experimental sediment was collected from Haifeng County, Shanwei City, Guangdong Province (115.38441271E, 22.98071058N). Before the experiment, the density of the original sediment was measured to be approximately 1.317 g / cm³. 3 The experiment was conducted in 250 mL serum bottles containing 200 mL of a mud-water mixture with a mud-water volume ratio of 1:1 (the wet weight of the added bottom mud was approximately 131.7 g). Before the experiment, the moisture content of the bottom mud, as well as the concentrations of AVS (acid volatile sulfides) and ferrous sulfate (calculated based on the dry weight of the bottom mud), were measured, and the actual amount of calcium nitrate added was calculated based on the addition ratio.

[0034] Table 1 Initial physicochemical characteristics of black and odorous sediment and calcium nitrate dosage in the first stage

[0035] The experiment included three nitrate treatment groups: R1: Calcium nitrate tetrahydrate (1.13g) was added in the first stage, with n(N) / n(Fe+S)≈1.2. R2: In the first stage, 1.13 g of calcium nitrate tetrahydrate was added, with n(N) / n(Fe+S)≈1.2. After the sulfide concentration in the black and odorous sediment stabilized following oxidation (day 21), the amount of calcium nitrate tetrahydrate to be added in the second stage was calculated based on the AVS, ferrous, and ammonia nitrogen concentrations measured that day. The addition ratio was n(N) / n(Fe+S+NH4). + The calculated dosage of calcium nitrate tetrahydrate is 0.34g, with a ratio of approximately 0.9. R3: In the first stage, 1.13 g of calcium nitrate tetrahydrate was added, with n(N) / n(Fe+S)≈1.2. After the concentration of sulfides in the black and odorous sediment stabilized following oxidation, the second stage of n(N) / n(Fe+S+NH4) addition was started simultaneously with the R2 system. + 0.57g of calcium nitrate tetrahydrate approximately 1.5g In addition to the three nitrate treatment groups mentioned above, a blank CK (no treatment) was added as a control group.

[0036] After the mud was loaded and calcium nitrate was added, nitrogen gas was introduced into the four experimental groups for 1 minute and then sealed to maintain an anaerobic environment. After the mud and water were thoroughly mixed, they were placed in a 30°C constant temperature incubator for static culture and awaited periodic sampling and testing.

[0037] After the experiment began, the concentrations of nitrate nitrogen, ammonia nitrogen, AVS, and ferrous iron in different experimental groups were periodically measured. The detection methods followed the national standard methods. Sediment microbial samples were also periodically collected to detect changes in the abundance of anaerobic ammonia-oxidizing bacteria. The abundance of microbial genera was obtained by clustering after 16S rRNA sequencing using Shanghai Meiji Biomedical Technology Co., Ltd. The experimental results are as follows: Figures 1-5 As shown.

[0038] according to Figures 1-5 It is known that the addition of nitrate promotes the oxidation of sulfides and ferrous iron in the system. In the nitrate-added systems, AVS (ammonia sulfide) showed significant oxidation in the first 7 days, while ferrous iron showed significant oxidation in the first 21 days. In the R1 system, AVS decreased by 88.88% on day 7 and by 56.91% on day 21. In contrast, in the R2 and R3 systems with phased addition, AVS decreased by 88.16% and 88.20% respectively on day 7, and by 94.11% and 97.09% respectively on day 84. Furthermore, significant oxidation of ferrous iron was detected in the R2 and R3 systems on day 21, with decreases of 56.92% and 50.56% respectively.

[0039] Compared to the control system, the ammonia nitrogen content in the nitrate-added system showed a slight decrease in the first stage. On day 21, ammonia nitrogen levels in systems R1, R2, and R3 decreased by 32.20%, 27.15%, and 25.16%, respectively. After the addition of the second stage of nitrate on day 21, the ammonia nitrogen levels in systems R2 and R3 continued to decrease, reaching 72.08% and 93.48% decreases, respectively, on day 84. However, in system R1, which did not receive nitrate in the second stage, ammonia nitrogen levels rebounded, increasing by 31.61% on day 84 compared to day 21. This indicates that staged nitrate addition can promote rapid oxidation of ammonia nitrogen in the sediment under anaerobic conditions, possibly due to the rapid initiation of anaerobic ammonia oxidation.

[0040] To verify the initiation of anaerobic ammonia oxidation in the sediment of the staged dosing system, high-throughput sequencing was performed on sediment samples. Comparison of the microbial community structure revealed that the samples contained anaerobic ammonia-oxidizing bacteria. Candidatu_ Brocadia , Candidatu_ Annamoxoglobus and Brocadiaceae The relative abundance of these bacteria was extremely low (<0.025%) at the beginning of the experiment. In subsequent experiments, the relative abundance of anaerobic ammonia oxidizing bacteria in the CK and R1 systems did not change significantly, while the R2 and R3 systems showed an increasing trend starting from day 14. In the R2 system, the relative abundance of anaerobic ammonia oxidizing bacteria increased rapidly from day 21 to day 49, with the highest detected abundance occurring on day 49 (0.19%), after which it gradually decreased. In the R3 system, the rapid increase in the relative abundance of anaerobic ammonia oxidizing bacteria occurred from day 49 to day 56, with the highest detected abundance on day 56 (0.15%), after which it decreased. Based on the increase in the abundance of anaerobic ammonia oxidizing bacteria and the decrease in ammonia nitrogen in the sediment, it can be concluded that anaerobic ammonia oxidation had already started in the R2 and R3 systems by day 21.

[0041] Meanwhile, based on the changes in headspace nitrous oxide concentration in the experimental system, we calculated the nitrous oxide emission rate at different stages of the experiment. The emission rate calculation formula is as follows: V max =24×(c1×V-c0×V) / (m×T) In the formula, V max 24 represents the nitrous oxide emission rate, in mg / (kg*d); V represents the headspace volume of the system, in L; c0 represents the nitrous oxide concentration in the headspace gas monitored during the first sampling, in mg / L; c1 represents the nitrous oxide concentration in the headspace gas monitored during the second sampling, in mg / L; m represents the mass of the mud-water mixture in the system, in kg; and T represents the number of hours between the two samplings, in h.

[0042] Nitrous oxide concentration was determined using an Agilent 7890B gas chromatograph with an ECD detector at a detection temperature of 300℃, a column temperature of 60℃, and a carrier gas of 99.999% high-purity argon / methane (95% argon + 5% methane) at a flow rate of 40 mL / min. The results are shown in Table 2.

[0043] Table 2. Nitrous oxide emission rates at different stages of the experiment (unit: mg / (kg*d))

[0044] The experimental results show that the nitrous oxide emission rate of the CK system remained basically in a negative emission state, while the nitrate treatment system was in a state of large emissions for the first 21 days. However, after the R2 and R3 systems entered the anaerobic ammonium oxidation start-up stage, the systems gradually entered a state of negative nitrous oxide emissions. This is because the anaerobic ammonium oxidation process can compete with the nitrous oxide production process for the substrate NO2. - This reduces nitrous oxide emissions. Simultaneously, we observed that the R2 system reached a negative nitrous oxide emission state faster than the R3 system, indicating that the second-stage addition ratio was n(N) / n(Fe+S+NH4). + A ratio of approximately 0.9 is more conducive to the reduction of nitrous oxide emissions. Furthermore, considering the increasing trend of anaerobic ammonia oxidizing bacteria abundance, the R2 system shows a faster increase in abundance and a higher peak abundance. This also indicates that the second-stage addition ratio is n(N) / n(Fe+S+NH4). + A ratio of approximately 0.9 is more conducive to enhancing the anaerobic ammonia oxidation potential of sediment. Therefore, in the process of calcium nitrate remediation of black and odorous sediment, a staged addition method can efficiently remove key black and odorous substances such as sulfides, ferrous oxide, and ammonia nitrogen from the sediment. Furthermore, when the second stage addition ratio is n(N) / n(Fe+S+NH4), the effect is even more pronounced. + When )≈0.9, the nitrous oxide emissions during the black and odorous elimination process are even lower. Example

[0045] The experiment in Example 1 showed that adding nitrate in the first stage of black and odorous sediment treatment could achieve good results. However, the nitrate treatment group exhibited significant nitrous oxide emissions from days 7 to 21, increasing greenhouse gas emissions during the sediment oxidation process. Comparative observation of the results from treatment groups R2 and R3 revealed that after anaerobic ammonia oxidation began in the sediment, the treatment group with lower nitrate dosage experienced a faster decrease in nitrous oxide than the group with higher dosage. This suggests that excessive nitrate addition may have led to incomplete denitrification, producing nitrous oxide. Therefore, this example further improves the treatment method by adjusting the addition to a step-by-step approach based on the R1 experimental group to achieve better pollution control results.

[0046] The experimental sediment was collected from Haifeng County, Shanwei City, Guangdong Province (115.38447976E, 22.98106616N). Before the experiment, the density of the original sediment was measured to be approximately 1.249 g / cm³. 3The experiment was conducted in a 250 mL feed bottle containing 200 mL of a mud-water mixture with a mud-to-water volume ratio of 1:1 (the wet weight of the added bottom mud was approximately 124.9 g). A 200 mL gas collection bag was connected to one end of the feed bottle, and a three-way valve to the other. When adding nitrate, the corresponding mass of nitrate was weighed, dissolved in water, and quantitatively drawn using a 1 mL syringe before being injected into the feed bottle through the three-way valve. After injection, the experimental setup was placed in a 30°C incubator. Based on previous experimental results, the total nitrate addition ratio was selected as n(N) / n(S+Fe)≈1.2. Before the experiment, the concentrations of AVS (acid volatile sulfides) and ferrous iron in the bottom mud were measured, and the actual amount of calcium nitrate added was calculated based on the addition ratio.

[0047] Table 3 Initial physicochemical properties of bottom sediment and total calcium nitrate dosage

[0048] This experiment controlled the frequency of nitrate addition in batches. Based on different addition methods, one blank control group and two nitrate treatment groups were set up, namely: R1 (blank control group); the device contained only 200 ml of mud-water mixture; R2 (Batch Dosing Treatment Group): In addition to the blank control group, calcium nitrate tetrahydrate was added at a ratio of n(N) / n(Fe+S)=0.3 on days 0, 4, 12 and 29, for a total of 4 additions (0.36g each time). R3 (single dose treatment group): On day 0, calcium nitrate tetrahydrate (1.45g) with n(N) / n(Fe+S)=1.2 was added once, based on the blank control group.

[0049] Each treatment group had three parallel systems. During the experiment, a destructive sampling method was used to periodically detect the redox potential (ORP), nitrate, acid volatile sulfide (AVS), and ferrous concentration in different systems. The concentration of nitrous oxide gas in the headspace of the system was monitored simultaneously, the emission rate of nitrous oxide gas in the headspace of the system was calculated, and corresponding sediment samples were sent to Shanghai Meiji Biomedical Technology Co., Ltd. to obtain changes in gene abundance in the sediment using metagenomic sequencing.

[0050] The concentration of nitrous oxide was determined using an Agilent 7890B gas chromatograph with an ECD detector at a detection temperature of 300℃ and a column temperature of 60℃. The carrier gas was 99.999% high-purity argon / methane (95% argon + 5% methane), and the flow rate was 40 mL / min. The experiment lasted approximately two months, and the results are as follows: Figures 6-11 As shown in Table 4.

[0051] Table 4. Changes in headspace nitrous oxide emission rates among different treatment groups (unit: mg / (kg*d))

[0052] according to Figure 7 It can be seen that both batch-addition and one-time addition of nitrate can effectively increase the ORP value of black and odorous sediment, restoring the sediment to an oxidized state. However, at the end of the experimental period (day 63), the ORP of the batch-addition treatment group remained >40 mV, while the ORP of the one-time addition treatment group was <-50 mV, indicating a significant decrease in the oxidized state of the sediment. This suggests that the batch-addition method has a better effect on maintaining the oxidized state of the sediment.

[0053] The changes in AVS and ferrous iron content indicate that batch-addition of nitrate has the same oxidation effect as one-time addition. On day 56, the AVS removal rates of R2 and R3 systems were 91.34% and 96.12%, respectively, and the ferrous iron removal rates were 63.33% and 61.28%, respectively. This shows that under the condition of a fixed total nitrate addition, changing the nitrate addition method does not affect the overall removal effect of key black and odorous indicators AVS and ferrous iron in the sediment. In other words, the batch-addition method does not affect the oxidation effect of black and odorous sediment.

[0054] The concentration of nitrous oxide in the headspace gas of each system was monitored during the experiment, and the headspace gas volume of each system was measured to calculate the nitrous oxide emission rate in the system. Table 4 shows that the nitrous oxide emission rate of the batch nitrate dosing treatment group (R2 system) was significantly lower than that of the single-dose treatment group (R3 system). The maximum nitrous oxide emission rate of the R2 system occurred on day 2, at 45.27 mg / (kg*d); the maximum emission rate of the R3 system occurred on day 4, at 1431.92 mg / (kg*d). The batch dosing treatment group reduced the nitrous oxide emission rate by up to approximately 96.84%, indicating that the batch dosing method can significantly reduce the nitrous oxide emission rate during the oxidation process of black and odorous sediment. Based on metagenomic sequencing results, nitrogen cycle-related genes were screened, and the significant differences were analyzed using STAMP software. Figure 10 (A) It was found that the abundance of nitrous oxide reductase (nosZ) in the R2 system was significantly higher than that in the R3 system, indicating that the nitrous oxide reduction capacity of the R2 system was significantly stronger than that of the R3 system. Further screening of sulfur oxidation process genes and Spearman correlation analysis with denitrification process genes yielded the following results (…). Figure 10(B) shows that in the R1 system, the nosZ gene did not show a significant correlation with genes involved in sulfur oxidation. In the R2 system, nosZ showed a significant positive correlation with genes involved in sulfur disproportionation oxidation (phsBC), persulfate oxidation (soxX), sulfide ion oxidation (asrAB and cysJ), and sulfite oxidation (soeC). In the R3 system, nosZ showed a significant positive correlation only with genes involved in sulfide ion oxidation (sir, asrA, cysJ, and fccA). The nitrogen-sulfur gene correlation analysis reflects the microbial nitrogen-sulfur coupling process in the system. This indicates that in the R2 system, after batch addition, nitrate preferentially oxidized sulfide ions, leading to an increase in microbial processes utilizing other forms of sulfur for denitrification, providing more pathways for nitrous oxide reduction and facilitating nitrous oxide consumption. In contrast, in the R3 system, due to the inhibitory effect of sulfide ions, only microbial processes capable of simultaneously utilizing sulfide ions for denitrification existed, resulting in a single pathway for nitrous oxide reduction in the sediment, while denitrification continued, leading to nitrous oxide emissions. Coupled sulfur-oxidizing and denitrifying microorganisms in the R2 system norank_f__ Rhodocyclaceae The relative abundance trend is also consistent with the above analysis. Figure 11 This genus is believed to have the ability to simultaneously utilize multiple sulfur forms for oxidation and denitrification. Its relative abundance in the R2 system remains above 3%, reaching a maximum of 11.6%; while in the R3 system, its relative abundance remains below 3%, with a maximum of only 2.2%.

[0055] Based on literature review and analysis, it is believed that the batch-addition method increases the electron donor-to-acceptor ratio in the early stage of sediment oxidation. This ratio is a key parameter affecting nitrous oxide production during nitrate reduction; increasing this ratio can reduce nitrous oxide production during incomplete denitrification. Simultaneously, the black and odorous sediment contains a large amount of sulfides, which inhibit nitrous oxide reductase (NOR) enzymes. nosZ Reducing the single-dose nitrate dosage can decrease the amount of nitrous oxide produced in the earlier steps of denitrification, preventing nitrous oxide accumulation and emissions due to production exceeding consumption. When most sulfides are oxidized, nitrous oxide reductase activity recovers, increasing the microbial processes in the sediment that utilize various forms of sulfur for nitrous oxide reduction, significantly enhancing the sediment's nitrous oxide reduction capacity. Therefore, we can see that the maximum nitrous oxide emission rate in the R2 system occurs on day 2. Subsequent additions of the same nitrate dosage (days 4, 12, and 29) lead to slightly increased nitrous oxide emission rates, but these rates are all significantly lower than the emission rate during the first addition.

[0056] In the later stages of the experiment, we observed a significant decrease in the nitrous oxide emission rate across all treatment groups, leading to nitrous oxide absorption. This is because the system was completely closed, allowing microorganisms in the sediment to further utilize dissolved nitrous oxide for subsequent denitrification. As the nitrous oxide concentration in the water decreased, according to Fick's Law, nitrous oxide would dissolve from the gas phase into the liquid phase, resulting in a continuous decrease in the headspace nitrous oxide concentration. However, in actual in-situ remediation of black and odorous sediment, the large amount of nitrous oxide produced by a single nitrate addition would escape into the atmosphere and cannot be removed during subsequent denitrification. Therefore, a phased addition method can effectively reduce the accumulation of nitrous oxide during in-situ remediation of black and odorous sediment, preventing large-scale nitrous oxide escape and thus effectively reducing carbon emissions during the remediation process.

[0057] Experimental results demonstrate that both batch-addition and one-time addition of nitrates achieve the same remediation effect on black and odorous sediment, with the batch-addition method better maintaining the oxidative state of the sediment. Furthermore, batch-addition of nitrates significantly reduces nitrous oxide emissions during the sediment remediation process, decreasing the emission rate by up to approximately 96.84%, making it a green and low-carbon remediation method for black and odorous sediment.

[0058] Based on the methods and results of the above embodiments, this invention has discovered that phased and batch-based nitrate addition can achieve better results in the low-carbon and efficient remediation of black and odorous sediments, and can significantly reduce nitrous oxide emissions. First, the required amount of nitrate to be added in the first stage is calculated based on the sulfide and ferrous content of the black and odorous sediment. A batch-based addition method is used to reduce nitrous oxide emissions during the oxidation process of sulfides and ferrous oxide. After the oxidation of sulfides and ferrous oxide is completed, the second stage of nitrate is added based on the concentrations of sulfides, ferrous oxide, and ammonia nitrogen, to rapidly initiate anaerobic ammonia oxidation in the sediment and reduce nitrous oxide emissions. This promotes the rapid elimination of key black and odorous substances in the sediment, namely sulfides, ferrous oxide, and ammonia nitrogen, ultimately achieving the goal of simultaneously reducing nitrous oxide emissions and removing nitrogen through anaerobic ammonia oxidation in the black and odorous sediment. The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A remediation method for simultaneously achieving nitrous oxide emission reduction and anaerobic ammonia oxidation denitrification of black and odorous sediment, characterized in that Includes the following steps: (1) Taking the black and odorous sediment in a specific area as the treatment target, the black and odorous sediment was sampled and tested in situ to determine key indicators such as moisture content and content of black and odorous substances; (2) Based on the sampling and testing results in step (1), the amount of nitrate added is calculated. Within an appropriate temperature range, the first-stage nitrate is added in batches to the sediment in which the black and odorous condition has been identified in step (1) to achieve in-situ low-carbon remediation of the black and odorous sediment. (3) Based on the changes in sulfide concentration in step (2), when the sulfide concentration remains stable, calculate the amount of nitrate to be added and add the second stage nitrate to the sediment in step (2) at once to simultaneously suppress nitrous oxide emissions from black and odorous sediment and start up anaerobic ammonia oxidation denitrification.

2. The method according to claim 1, characterized in that: The sampling and testing described in step (1) is to test the water content and density of the sediment and the total amount of ferrous oxide, sulfides and ammonia nitrogen contained therein.

3. The method according to claim 1, characterized in that: The black and smelly sediment described in step (1) contains anaerobic ammonia-oxidizing bacteria.

4. The method according to claim 1, characterized in that: The nitrate mentioned in step (2) is calcium nitrate tetrahydrate.

5. The method according to claim 1, characterized in that: The amount of nitrate added in step (2) is calculated according to the formula, which is as follows: Total nitrate nitrogen / total sulfide and ferrous iron in sediment = 0.2–0.4; Among them, total nitrate nitrogen is the amount of nitrogen-containing element in nitrate, and the total amount of sulfide and ferrous iron in the sediment is the sum of the amounts of sulfide and ferrous iron in the sediment.

6. The method according to claim 1, characterized in that: The nitrate in step (2) is added in 2 to 6 portions; The interval between the addition of nitrate in step (2) is 4 to 17 days.

7. The method according to claim 1, characterized in that: The amount of nitrate added in step (3) is calculated according to the formula, which is as follows: The ratio of total nitrate nitrogen to the total amount of sulfides, ferrous oxide, and ammonia nitrogen in the sediment is 0.9–1.5; preferably 0.

9. Among them, total nitrate nitrogen is the amount of nitrogen-containing elements in nitrate, and the total amount of sulfide, ferrous iron and ammonia nitrogen in sediment is the sum of the amounts of sulfide, ferrous iron and ammonia nitrogen in sediment.

8. The method according to claim 1, characterized in that: The second stage of nitrate addition in step (3) is 21 to 29 days after the first addition; preferably, it is added on the 21st day.

9. The method according to any one of claims 1 to 8, characterized in that: The appropriate temperature range mentioned in step (2) is to maintain 28 to 32°C.

10. The application of the simultaneous reduction of nitrous oxide emissions and anaerobic ammonia oxidation denitrification of black and odorous sediment as described in any one of claims 1 to 9 in the treatment of black and odorous sediment.

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