Method for improving micro-ecological environment of bottom mud of urban black and odorous river channel

Abstract

The invention belongs to the technical field of urban water environment treatment and restoration, and discloses a method for improving the micro-ecological environment of bottom mud of an urban black and odorous river. The method specifically comprises the following steps that 1, calcium nitrate with the amount 1.6-1.8 times of theoretical calculation amount is added according to the AVS content in the black and odorous bottom mud to be repaired; 2, after the calcium nitrate reacts, calcium peroxide (CaO2) with the amount 1.3-2.0 times of the theoretical calculation amount is added. According to different reaction processes of AVS and ferrous iron in the black and odorous bottom mud and different oxidation capacities of calcium nitrate and CaO2, calcium nitrate is added firstly, and then CaO2 is added, so that removal of ferrous iron, AVS and organic matters in the black and odorous bottom mud is enhanced, chemical agents are scientifically and efficiently used, and the micro-ecological environment of the black and odorous bottom mud is continuously and effectively improved.

Description

[0001] The invention belongs to the technical field of urban water environment governance and restoration, and specifically relates to a method for improving the microecological environment of urban black and smelly riverbed mud. Background Art

[0002] The urban river ecosystem is a continuous, dynamic, and open ecosystem that is susceptible to pollution by nutrients, organic matter, and heavy metals. In recent years, with the continuous improvement of relevant policies and regulations, the illegal discharge of exogenous industrial wastewater and domestic sewage in urban rivers has been effectively controlled, and endogenous pollutants in river sediments have gradually become the main cause of the black and odorous water bodies above the river. Therefore, how to quickly repair polluted sediments, improve the sediment microecological environment, and continuously and effectively improve the quality of urban water environment has become a problem that has attracted much attention in recent years.

[0003] Adding nitrate is one of the common methods for in situ bioremediation of black and smelly river sediments. Nitrate can drive autotrophic denitrifying microorganisms in the sediment to oxidize acid volatile sulfides (AVS) in the sediment, and stimulate heterotrophic microorganisms to oxidize sediment organic matter. However, in the relevant technical methods for calculating the amount of nitrate, only the oxidation of AVS in the sediment is emphasized, and less attention is paid to the impact of high concentrations of ferrous iron in black and smelly river sediments. The oxidation of ferrous iron is also considered to be the reason why the color of the sediment changes from black to brown. Therefore, the amount of chemical agents consumed by ferrous iron oxidation cannot be ignored. In addition, in actual remediation projects, it is often difficult for nitrate to reach the remediation target at an effective concentration. It is often necessary to add 2-3 times the theoretical amount of nitrate for remediation, but the use of excessive nitrate will greatly increase environmental risks.

[0004] Calcium peroxide (CaO 2 ) can slowly release oxygen molecules in water, significantly improving the hypoxia of water bodies. It is another commonly used chemical agent in the in-situ treatment of black and smelly river sediments. In addition to the oxygen release function, CaO 2 Produces H 2 O 2 Under the catalysis of iron minerals, hydroxyl radicals (H 2 O 2 +Fe 2+ →Fe 3+ +OH · +OH - ), so that it can more effectively oxidize ferrous iron, AVS and organic matter in the sediment. Patent CN102432078A converts CaO 2 A composite suspension was prepared with calcium nitrate to quickly eliminate the black and smelly sludge in the bottom mud, which provides a good idea for solving the problem of excessive addition of calcium nitrate. However, when the prepared composite suspension was added to the black and smelly sludge to be repaired at the same time, CaO with stronger oxidation ability 2It is consumed before calcium nitrate, which is not conducive to the subsequent oxidation of ferrous iron and non-degradable organic matter in the sediment, making it difficult to achieve efficient utilization of chemical agents.

[0005] The technical problem solved by the present invention is to solve the problem of high concentration of ferrous iron and sulfide in black and smelly sludge according to the characteristics of various chemical agents. 2 The issues of synergistic sequence, timing and synergistic dosage in the process of synergistically improving the microecological environment of black and smelly sludge with calcium nitrate are addressed to achieve efficient and scientific improvement of the microecological environment of black and smelly sludge. Summary of the invention

[0006] To achieve the above objectives, the present invention is implemented by the following technical scheme: A method for improving the microecological environment of urban black and smelly riverbed mud, specifically comprising the following steps: Step 1, according to the AVS content in the black and smelly mud to be repaired, according to the theoretical dosage formula (1), determining the theoretical dosage of calcium nitrate; (1) Step 2: After the calcium nitrate reaction is complete, the amount of unreacted AVS (calculated as 10% of the initial AVS) and the ferrous content are used to determine the CaO according to the theoretical dosage formula (2). 2 Theoretical dosage: (2) In the above formulas (1) and (2), —Theoretical amount of calcium nitrate added, g / kg; —Theoretical amount of calcium peroxide added, g / kg; —The original AVS content in the sediment, g / kg; —The original ferrous iron content in the sediment, g / kg; —molar mass of calcium nitrate; —N’s valence is arrive changes; —S valence from arrive changes; — molar mass of S; —The change of Fe valence from Fe(II) to Fe(III); — molar mass of Fe; — molar mass of O; —O's valence is arrive changes.

[0007] As a preferred technical solution of the present invention, in step 1, the dosage of calcium nitrate is 1.6 to 1.8 times the theoretical dosage.

[0008] As a preferred technical solution of the present invention, in step 2, CaO 2 The dosage is 1.3~2.0 times the theoretical dosage.

[0009] The present invention is used to improve the microecological environment of black and smelly sludge, and is characterized in that, according to the characteristic that AVS in the black and smelly sludge is oxidized before ferrous iron, calcium nitrate with weaker oxidation ability is first added (the dosage of calcium nitrate is determined in step 1) to remove more than 90% of AVS.

[0010] The present invention is used to improve the microecological environment of black and smelly sludge, characterized in that after most of the AVS is oxidized, according to CaO 2 Produces H 2 O 2 It can react with ferrous iron to generate hydroxyl free radicals with stronger oxidizing ability, and more efficiently oxidize the difficult-to-degrade substances in the black and smelly sludge, CaO 2 The dosage is determined according to step 2.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] (1) The method provided by the present invention is simple to operate and is based on theoretical calculations to add calcium nitrate and CaO 2 It can save the cost of chemicals, reduce investment, has high efficiency, and can economically and effectively improve the microecological environment of black and smelly sludge.

[0013] (2) According to the different characteristics of the AVS oxidation and ferrous oxidation reaction processes, calcium nitrate is added first and CaO is added later. 2 , giving full play to the characteristics of each agent, realizing the efficient utilization of chemical agents, and at the same time achieving the purpose of strengthening the removal of pollutants in black and smelly sludge.

[0014] (3) When calcium nitrate oxidizes ferrous iron, it will lower the pH of the system, exacerbating the environmental risk of calcium nitrate addition. At the same time, the free energy of the reaction is high, and the reaction is not easy to occur (Fe 2+ + 0.2NO 3 - +2.4H 2 O→Fe(OH) 3 +0.1N 2 +1.8H +▲G=-101kJ / mol, NO 3 - +10H + +8e - →NH 4 + +3H 2 O▲G=-679kJ / mol). Co-dosing of CaO 2 It not only speeds up the reaction process, but also reduces the amount of calcium nitrate used and reduces the environmental risk of excessive calcium nitrate addition.

[0015] (4) The present invention adds CaO 2 , using CaO 2 The alkali-producing process of reacting with water makes the water body weakly alkaline, which inhibits the acidic odorous gas (H 2 S) to control the occurrence of bad odor.

[0016] (5) The present invention adds CaO 2 , oxidizing the high concentration of ferrous iron in the sediment, changing the color of the sediment from black to brown, and eliminating the blackening substances in the sediment. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the removal of AVS in the sludge added with calcium nitrate in step 1.

[0018] Figure 2 This is the removal of ferrous iron from the sludge added with calcium nitrate in step 1.

[0019] Figure 3 Add calcium nitrate and CaO for step 2 2 Removal of AVS from sediment.

[0020] Figure 4 Add calcium nitrate and CaO for step 2 2 Removal of ferrous iron from sediments. DETAILED DESCRIPTION

[0021] The technical scheme in the embodiments of the present invention is clearly and completely described below in combination with the specific embodiments and the accompanying drawings. Obviously, the specific embodiments described are only used to illustrate the present invention, rather than to limit the present invention. Example

[0022] The sediment used in this implementation was taken from the river sediment in a certain city and a small test was carried out in the laboratory.

[0023] The black and smelly sludge samples were homogenized, and after impurities were sieved out, 400 g were weighed into 5 250 mL serum bottles, sealed and stored for two weeks, and then samples were taken for the determination of AVS, ferrous iron and water content. The initial AVS content in the 5 bottles was measured to be about 3500 mg / kg, the initial ferrous iron content was about 13.1 g / kg, and the water content was about 84.5%.

[0024] According to the theoretical calcium nitrate dosage formula (1), the calcium nitrate dosage was set to four gradients of 0.8, 1.0, 1.2, and 1.6 times the theoretical dosage, and 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 contents in the five bottles were monitored on days 1, 2, 3, 5, 10, and 15 of the reaction.

[0025] The results show that, compared with the blank control group, after adding calcium nitrate, the sulfide content in the sediment is significantly reduced, and as the dosage increases, the more sulfide is reduced. When the calcium nitrate dosage is 1.0 times the theoretical calculated value, AVS is oxidized by 65.1%, and when the calcium nitrate dosage is 1.6 times the theoretical calculated value, AVS is oxidized by 74.6%. This shows that there are limitations in calculating the dosage of chemical agents based only on the AVS content, and the calcium nitrate consumed by the high concentration of ferrous iron in the sediment cannot be ignored. At the same time, when the calcium nitrate dosage is 1.6 times the theoretical calculated value, only part of the ferrous iron is oxidized, indicating that AVS will be oxidized before ferrous iron, further indicating that it is scientific and reasonable to control the oxidation process of AVS and ferrous iron by controlling the agent addition process in the present invention. Example

[0026] The sediment used in this implementation was taken from the river sediment in a certain city and a small test was carried out in the laboratory.

[0027] The black and smelly sludge samples were homogenized, and after impurities were sieved out, 400 g were weighed into 5 250 mL serum bottles, sealed and stored for two weeks, and then samples were taken for determination of AVS, ferrous iron and water content. The initial AVS content in the 5 bottles was measured to be about 3900 mg / kg, the initial ferrous iron content was about 13.9 g / kg, and the water content was about 83.4%.

[0028] 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 contents in the four bottles were monitored on days 1, 2, 3, 5, and 7 of the reaction.

[0029] According to the AVS and ferrous content of the sediment measured on the 8th day, according to CaO 2 Theoretical dosage formula (2), set CaO 2The dosage is 1.0 and 2.0 times of the theoretical dosage, respectively, and is added to bottles 3 and 4. The AVS and ferrous iron contents in bottles 3 and 4 are continuously monitored.

[0030] Control test: Calculate the theoretical dosage of calcium nitrate based on the oxidation of all the remaining AVS and ferrous iron in bottles 1 and 2, and set the dosage of calcium nitrate to 1.0 and 2.0 times the theoretical dosage, respectively, and put it into bottles 1 and 2. Continuously monitor the AVS and ferrous iron content in bottles 1 and 2.

[0031] Blank control: Neither calcium nitrate nor CaO was added to bottle 5 2 As a blank control.

[0032] The results showed that after adding calcium nitrate, the AVS in bottles 1 to 4 was oxidized by about 84.7% compared with the blank control group. 2 After that, the remaining AVS in bottles 3 and 4 were completely oxidized, and the ferrous iron was oxidized by about 75%. In the control group, the AVS was oxidized by about 90%, and the ferrous iron was oxidized by about 50%.

[0033] The results show that under the premise of the same total amount of reagent added, CaO 2 The removal effect of AVS and ferrous iron in the sludge is synergistically enhanced, and the black and smelly phenomenon of the sludge is effectively eliminated. The above embodiment is a preferred embodiment of the present invention, but the present invention is not limited thereto. Those skilled in the art may replace and modify the specific implementation methods or technical features of the present invention under the guidance of the present invention. It should be particularly pointed out that all similar replacement and modification technical solutions still fall within the scope of protection of the present invention.

Claims

1. A method for improving the microecological environment of urban black and smelly riverbed mud, characterized by: The specific steps include: Step 1, according to the acid volatile sulfide (AVS) content in the black and smelly sludge to be repaired, the theoretical dosage of calcium nitrate is determined according to the theoretical dosage formula (1); （1） Step 2, after the calcium nitrate reaction is complete, the theoretical dosage of CaO2 is determined according to the amount of unreacted AVS (calculated as 10% of the initial AVS) and the ferrous content according to the theoretical dosage formula (2); （2） In the above formulas (1) and (2), —Theoretical amount of calcium nitrate added, g / kg; —Theoretical amount of calcium peroxide added, g / kg; —The original AVS content in the sediment, g / kg; —The original ferrous iron content in the sediment, g / kg; —molar mass of calcium nitrate; —N’s valence is arrive changes; —S valence from arrive changes; — molar mass of S; —The change of Fe valence from Fe(II) to Fe(III); — molar mass of Fe; — molar mass of O; —O's valence is arrive changes.

2. A method for improving the microecological environment of urban black and smelly riverbed mud according to claim 1, characterized in that: In the step 1, the dosage of calcium nitrate is 1.6 to 1.8 times the theoretical dosage.

3. A method for improving the microecological environment of urban black and smelly riverbed mud according to claim 1, characterized in that: In step 2, the dosage of CaO2 is 1.3 to 2.0 times the theoretical dosage.

4. A method for improving the microecological environment of urban black and smelly riverbed mud according to claim 1, characterized in that: According to the characteristic that AVS in the black and smelly sludge is oxidized before ferrous iron, calcium nitrate with weaker oxidation ability is added first (the dosage of calcium nitrate is determined in step 1) to remove more than 90% of AVS.

5. A method for improving the microecological environment of urban black and smelly riverbed mud according to claim 1, characterized in that: After most of the AVS is oxidized, based on the characteristic that H2O2 produced by CaO2 can react with ferrous iron to generate hydroxyl radicals with stronger oxidizing ability, the difficult-to-degrade substances in the black and smelly sludge can be oxidized more efficiently. The amount of CaO2 added is determined based on the step 2.

Images