Method for improving micro-ecological environment of urban black and odorous river sediment

Abstract

The application belongs to the technical field of urban water environment treatment and repair, and discloses a method for improving the micro-ecological environment of black and odorous river sediment in cities. The method comprises the following steps: step 1: according to the AVS content in the black and odorous sediment to be repaired, 1.6-1.8 times of the theoretical calculation amount of calcium nitrate is added; and step 2: after the reaction of calcium nitrate is completed, 1.3-2.0 times of the theoretical calculation amount of calcium peroxide (CaO2) is added. According to the differences between the AVS and ferrous reaction processes of the black and odorous sediment and the differences between the oxidation capacities of calcium nitrate and CaO2, calcium nitrate is added first, and then CaO2 is added, so that the removal of ferrous, AVS and organic matter in the black and odorous sediment is strengthened, the chemical agents are used scientifically and efficiently, and the micro-ecological environment of the black and odorous sediment is continuously and effectively improved.

Description

[0001] This invention belongs to the field of urban water environment management and restoration technology, specifically relating to a method for improving the micro-ecological environment of bottom sediment in urban black and odorous rivers. Background Technology

[0002] Urban river ecosystems are continuous, dynamic, and open ecosystems, easily polluted by nutrients, organic matter, and heavy metals. In recent years, with the continuous improvement of relevant policies and regulations, the illegal discharge of external industrial wastewater and domestic sewage into urban rivers has been effectively controlled. However, endogenous pollutants in riverbed sediments have gradually become the main cause of the recurrence of blackening and foul odors in the overlying water. Therefore, how to quickly remediate polluted sediments, improve the micro-ecological environment of the sediments, and continuously and effectively improve the quality of urban water environment has become a highly concerned issue in recent years.

[0003] Nitrate addition is a common method for in-situ bioremediation of polluted river sediments. Nitrate drives autotrophic denitrifying microorganisms in the sediment to oxidize acid volatile sulfides (AVS) and stimulates heterotrophic microorganisms to oxidize sediment organic matter. However, relevant technical methods for calculating nitrate dosage only emphasize the oxidation of AVS in the sediment, paying less attention to the impact of high concentrations of ferrous sulfate in polluted river sediments. Ferrous sulfate oxidation is also considered the cause of the sediment color change from black to brown; therefore, the amount of chemical agents consumed in ferrous sulfate oxidation cannot be ignored. In addition, in actual remediation projects, nitrates are often difficult to achieve the remediation target at an effective concentration. Remediation often requires the addition of 2-3 times the theoretical dosage of nitrates, but excessive use of nitrates greatly increases environmental risks.

[0004] Calcium peroxide (CaO2) can slowly release oxygen molecules into water, significantly improving the oxygen-deficient state of water bodies. It is another commonly used chemical agent in the in-situ treatment of black and odorous river sediments. In addition to its oxygen-releasing function, CaO2 produces H2O2, which, under the catalysis of iron minerals, generates hydroxyl radicals (H2O2 + Fe) with a higher redox potential. 2+ →Fe 3+ +OH · +OH - This allows for more effective oxidation of ferrous iron, AVS, and organic matter in the sediment. Patent CN102432078A prepared a composite suspension of CaO2 and calcium nitrate to quickly eliminate black and odorous substances in sediment, providing a good solution to the problem of excessive calcium nitrate addition. However, when the prepared composite suspension is added to the black and odorous sediment to be remediated, the more oxidizing CaO2 is consumed preferentially over calcium nitrate, which is not conducive to the subsequent oxidation of ferrous iron and recalcitrant organic matter in the sediment, making it difficult to achieve efficient utilization of chemical agents.

[0005] The technical problem solved by this invention is to address the high concentration of ferrous iron and sulfides in black and odorous sediments. Based on the characteristics of each chemical agent, the invention focuses on solving the synergistic sequence, timing, and dosage of CaO2 and calcium nitrate in the process of synergistically improving the micro-ecological environment of black and odorous sediments, so as to achieve efficient and scientific improvement of the micro-ecological environment of black and odorous sediments. Summary of the Invention

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: a method for improving the micro-ecological environment of urban black and odorous riverbed sediment, specifically including the following steps: Step 1, according to the AVS content in the black and odorous sediment to be repaired, the theoretical dosage of calcium nitrate is determined according to the theoretical dosage formula (1);

[0007] (1)

[0008] Step 2: After the calcium nitrate has reacted completely, the theoretical dosage of CaO2 is determined based on the amount of unreacted AVS (calculated as 10% of the initial AVS) and the ferrous content, according to the theoretical dosage formula (2).

[0009] (2)

[0010] In equations (1) and (2) above, —Theoretical amount of calcium nitrate to be added, g / kg;

[0011] —Theoretical amount of calcium peroxide to be added, g / kg;

[0012] —The content of original AVS in the sediment, g / kg;

[0013] —The content of original ferrous iron in the sediment, g / kg;

[0014] —Molar mass of calcium nitrate;

[0015] —The valence of N is from arrive Changes;

[0016] —The valence of S is from arrive Changes;

[0017] —molar mass of S;

[0018] —The change in the oxidation state of Fe from Fe(II) to Fe(III);

[0019] —Molar mass of Fe;

[0020] —molar mass of O;

[0021] —O's oxidation state is from arrive The changes.

[0022] In a preferred embodiment of the present invention, in step 1, the amount of calcium nitrate added is 1.6 to 1.8 times the theoretical amount.

[0023] As a preferred embodiment of the present invention, in step 2, the amount of CaO2 added is 1.3 to 2.0 times the theoretical amount.

[0024] The present invention improves the micro-ecological environment of black and odorous sediment. Its feature is that, based on the characteristic that AVS in black and odorous sediment is preferentially oxidized over ferrous iron, calcium nitrate, which has a weaker oxidizing ability, is added first (the amount of calcium nitrate added is determined in step 1) to remove more than 90% of AVS.

[0025] The present invention improves the micro-ecological environment of black and odorous sediment. Its feature is that after most of the AVS is oxidized, based on the characteristic that CaO2 generates H2O2, which can react with ferrous iron to generate hydroxyl radicals with stronger oxidizing power, the recalcitrant substances in the black and odorous sediment are oxidized more efficiently. The amount of CaO2 added is determined according to step 2.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] (1) The method provided by the present invention is simple to operate. Based on theoretical calculations, calcium nitrate and CaO2 are added, which can save the cost of reagents, reduce investment, and increase efficiency. It can effectively improve the micro-ecological environment of black and odorous bottom sediment.

[0028] (2) Based on the different characteristics of the AVS oxidation and ferrous oxidation reaction processes, calcium nitrate was added first, followed by CaO2, to give full play to the characteristics of each agent and achieve efficient utilization of chemical agents, while also achieving the goal of strengthening the removal of pollutants in black and odorous sediment.

[0029] (3) When calcium nitrate oxidizes ferrous iron, it lowers the pH of the system, exacerbating the environmental risks associated with calcium nitrate addition. Furthermore, the reaction has a high free energy, making it difficult for the reaction to occur (Fe). 2+ + 0.2NO3 - +2.4H₂O→Fe(OH)₃+0.1N₂+1.8H + ▲G=-101kJ / mol, NO3 - +10H + +8e- →NH4 + +3H₂O▲G=-679kJ / mol). Co-addition of CaO₂ not only accelerates the reaction process but also reduces the amount of calcium nitrate used, thus mitigating the environmental risks associated with excessive calcium nitrate addition.

[0030] (4) By synergistically adding CaO2, the present invention utilizes the alkali-producing process of CaO2 reacting with water to make the water body weakly alkaline, thereby inhibiting the generation of acidic odorous gas (H2S) and controlling the occurrence of odorous smell.

[0031] (5) By synergistically adding CaO2, the high concentration of ferrous iron in the sediment is oxidized, causing the sediment color to change from black to brown, thus eliminating the blackening substances in the sediment. Attached Figure Description

[0032] Figure 1 The removal of AVS from the sediment after adding calcium nitrate in step 1.

[0033] Figure 2 The removal of ferrous iron from the sediment during step 1 (addition of calcium nitrate).

[0034] Figure 3 The removal of AVS from the sediment during step 2, when calcium nitrate and CaO2 were added.

[0035] Figure 4 The removal of ferrous iron from the sediment during step 2, when calcium nitrate and CaO2 were added. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to specific embodiments and accompanying drawings. Obviously, the specific embodiments described are only for illustrating the present invention and are not intended to limit the present invention. Example

[0037] The sediment used in this experiment was taken from riverbed sediment in a certain city and tested in a small-scale laboratory.

[0038] The collected black and odorous sediment samples were homogenized, impurities were removed by sieving, and 400g of each sample was weighed into five 250 mL serum bottles. After two weeks of sealed storage, samples were taken for determination of AVS, ferrous iron, and water content. The initial AVS content in the five bottles was approximately 3500 mg / kg, the initial ferrous iron content was approximately 13.1 g / kg, and the water content was approximately 84.5%.

[0039] According to the theoretical dosage formula (1) for calcium nitrate, four gradients of calcium nitrate dosage were set, which were 0.8, 1.0, 1.2 and 1.6 times the theoretical dosage. The calcium nitrate was added to bottles 1, 2, 3 and 4 respectively. Bottle 5 was used as a control and no calcium nitrate was added. The AVS and ferrous iron content in the five bottles were monitored on days 1, 2, 3, 5, 10 and 15 of the reaction.

[0040] The results showed that, compared with the blank control group, the addition of calcium nitrate significantly reduced the sulfide content in the sediment, and the reduction in sulfides increased with the increase in dosage. When the calcium nitrate dosage was 1.0 times the theoretical calculation value, AVS was oxidized by 65.1%, and when the calcium nitrate dosage was 1.6 times the theoretical calculation value, AVS was oxidized by 74.6%. This indicates that calculating the dosage of chemical agents solely based on AVS content has limitations, and the calcium nitrate consumed by the high concentration of ferrous iron in the sediment cannot be ignored. Furthermore, when the calcium nitrate dosage was 1.6 times the theoretical calculation value, only a portion of the ferrous iron was oxidized, indicating that AVS is preferentially oxidized before ferrous iron. This further demonstrates that controlling the oxidation process of AVS and ferrous iron through the control of the agent addition process in this invention is scientifically sound and reasonable. Example

[0041] The sediment used in this experiment was taken from riverbed sediment in a certain city and tested in a small-scale laboratory.

[0042] The collected black and odorous sediment samples were homogenized, impurities were removed by sieving, and 400g of each sample was weighed into five 250mL serum bottles. After two weeks of sealed storage, samples were taken for determination of AVS, ferrous iron, and water content. The initial AVS content in the five bottles was approximately 3900mg / kg, the initial ferrous iron content was approximately 13.9g / kg, and the water content was approximately 83.4%.

[0043] According to the theoretical dosage formula (1), the calcium nitrate dosage was set to 1.6 times the theoretical dosage and added to bottles 1, 2, 3 and 4 respectively. The AVS and ferrous iron content in the four bottles were monitored on days 1, 2, 3, 5 and 7 of the reaction.

[0044] Based on the AVS and ferrous iron content measured in the sediment on day 8, and according to the theoretical CaO2 dosage formula (2), the CaO2 dosage was set to be 1.0 and 2.0 times the theoretical dosage, respectively, and added to bottles 3 and 4. The AVS and ferrous iron content in bottles 3 and 4 were continuously monitored.

[0045] Control experiment: Based on the oxidation of all remaining AVS and ferrous iron in bottles 1 and 2, the theoretical dosage of calcium nitrate was calculated. Calcium nitrate dosages of 1.0 and 2.0 times the theoretical dosage were added to bottles 1 and 2 respectively. The AVS and ferrous iron content in bottles 1 and 2 were continuously monitored.

[0046] Blank control: Bottle No. 5 contains neither calcium nitrate nor CaO2 as a blank control.

[0047] The results showed that after the addition of calcium nitrate, compared with the blank control group, approximately 84.7% of AVS in bottles 1-4 was oxidized. After the synergistic addition of CaO2, the remaining AVS in bottles 3 and 4 was completely oxidized, and approximately 75% of the ferrous iron was oxidized. In the control experimental group, approximately 90% of AVS was oxidized, and approximately 50% of the ferrous iron was oxidized.

[0048] The results showed that, under the same total dosage of reagents, CaO2 synergistically enhanced the removal of AVS and ferrous iron in the sediment, effectively eliminating the black and odorous phenomenon of the sediment. The above embodiments are preferred embodiments of the present invention, but the present invention is not limited thereto. Those skilled in the art can substitute and modify the specific embodiments or technical features of the present invention under the guidance of the present invention. It should be particularly noted that all similar substitutions and modifications still fall within the protection scope of the present invention.

Claims

1. A method for improving the micro-ecological environment of bottom sediment in urban black and odorous rivers, characterized in that: Specifically, the following steps are included: Step 1: Based on the content of acid volatile sulfides (AVS) in the black and odorous sediment to be repaired, determine the theoretical dosage of calcium nitrate (Ca(NO3)2) according to the theoretical dosage formula (1); （1） Step 2: After the calcium nitrate has reacted completely, calculate based on the amount of unreacted AVS (calculated as 10% of the initial AVS) and ferrous iron (Fe). 2+ Based on the content of calcium peroxide (CaO2), the theoretical dosage of calcium peroxide (CaO2) is determined according to the theoretical dosage formula (2). （2） In equations (1) and (2) above, —Theoretical amount of calcium nitrate to be added, g / kg; —Theoretical amount of calcium peroxide to be added, g / kg; —The content of original AVS in the sediment, g / kg; —Primitive Fe in bottom sediment 2+ The content, g / kg; —Molar mass of calcium nitrate; —The change in the valence of N from to ; —The change in the valence of S from to ; —molar mass of S; —The oxidation state of Fe changes from Fe 2+ To Fe 3+ Changes; —Molar mass of Fe; —molar mass of O; —The change in the oxidation state of O from to ; According to the fact that AVS is preferentially over Fe in black and odorous sediment 2+ Due to the oxidation process, calcium nitrate, which has a weaker oxidizing ability, is first added to remove more than 90% of AVS. The amount of calcium nitrate added is determined according to step 1. After most of the AVS has been oxidized, based on the fact that CaO2 produces H2O2, which can react with Fe... 2+ The CaO2 is used to generate hydroxyl radicals with stronger oxidizing power, and the addition of CaO2 can more efficiently oxidize the recalcitrant substances in the black and odorous sediment. The amount of CaO2 added is determined according to step 2.

2. The method for improving the micro-ecological environment of urban black and odorous riverbed sediment according to claim 1, characterized in that: In step 1, the amount of calcium nitrate added is 1.6 to 1.8 times the theoretical amount.

3. The method for improving the micro-ecological environment of urban black and odorous riverbed sediment according to claim 1, characterized in that: In step 2, the amount of CaO2 added is 1.3 to 2.0 times the theoretical amount.

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