Calcium nitrate slow-release filler for strengthening restoration of black and odorous bottom mud of river channel and preparation method thereof

Abstract

The invention discloses a calcium nitrate slow-release filler for strengthening restoration of black and odorous bottom mud of a river channel and a preparation method of the calcium nitrate slow-release filler. The calcium nitrate slow-release filler is prepared by physically mixing Ca (NO3) 2.4 H2O, PVA (Polyvinyl Alcohol) and sodium carboxymethyl cellulose. The calcium nitrate slow-release filler disclosed by the invention not only can controllably slowly release calcium nitrate and prevent the calcium nitrate from quickly escaping to overlying water to cause secondary pollution after being put into the bottom mud, but also can provide an electron acceptor for the bottom mud, effectively remove sulfide and ferrous ions in the black and odorous bottom mud and relieve the black and odorous phenomenon of the bottom mud in urban river channels; the method has a wide application prospect in the restoration of the black and odorous bottom mud of the river channel.

Description

Technical Field

[0001] This invention belongs to the field of river black and odorous sediment remediation technology, and relates to a calcium nitrate slow-release filler for enhancing the remediation of river black and odorous sediment and its preparation method. Background Technology

[0002] Urban waterways, as an important component of the urban ecosystem, serve multiple functions, including landscape creation, flood control and drainage, navigation and transportation, and pollution disposal. However, with rapid economic development and accelerated urbanization, urban waterway systems are generally facing serious ecological degradation problems, with black and odorous water bodies being particularly prominent. Therefore, developing efficient technologies for the treatment of black and odorous water pollution in urban waterways is of significant practical importance.

[0003] From the perspective of pollution mechanism, the black and odorous phenomenon in rivers mainly stems from the long-term excessive input of organic pollutants, which leads to the large-scale consumption of dissolved oxygen in the water and the formation of an anaerobic environment. Under anaerobic conditions, organic pollutants are difficult to degrade effectively and are deposited in the bottom sediment. At the same time, inorganic sulfides are reduced to ferrous sulfide (a blackening substance) and hydrogen sulfide (an odor-causing substance), which together lead to the black and odorous phenomenon in the river bottom sediment.

[0004] Among existing treatment technologies, chemical oxidation is widely used due to its rapid effectiveness. Nitrate-based oxidants, in particular, have attracted significant attention due to their oxidation-reduction potential being second only to oxygen, and their ability to be used as electron acceptors by various functional microorganisms for denitrification. Studies have shown that nitrates can both promote the degradation of organic matter by heterotrophic bacteria through denitrification and stimulate autotrophic bacteria to obtain energy through sulfur oxidation, thus possessing a dual effect in eliminating black and odorous pollution. Currently, related patented technologies (such as CN102432078 and CN102267788) mainly employ methods such as direct addition of calcium nitrate or preparation of slow-release agents by combining it with materials like cement. However, these methods have significant drawbacks: calcium nitrate is easily soluble in water, and direct addition leads to agent loss and low utilization efficiency, and residual nitrates may cause secondary pollution; while using hardened materials such as cement as slow-release carriers may cause new pollution to the sediment. Therefore, developing a novel, environmentally friendly, slow-release nitrate filler with slow-release properties is of great significance for enhancing the remediation of black and odorous sediment in rivers. Summary of the Invention

[0005] To address the problems of excessively rapid oxidant release rate and short action period in existing black and odorous sediment remediation technologies, this invention provides a calcium nitrate slow-release filler and its preparation method for enhancing the remediation of black and odorous river sediment. This invention utilizes calcium nitrate tetrahydrate (Ca(NO3)2·4H2O), polyvinyl alcohol (PVA), and sodium carboxymethyl cellulose (CMC-Na) to prepare the calcium nitrate slow-release filler. Its application in the remediation of black and odorous river sediment enables efficient and long-lasting oxidation of reducing substances in the sediment.

[0006] The technical solution of the present invention is as follows:

[0007] The preparation method of calcium nitrate slow-release filler for enhancing the remediation of black and odorous river sediment includes the following steps:

[0008] (1) Heat the Ca(NO3)2·4H2O particles until they melt and become liquid;

[0009] (2) Dissolve PVA powder in water by heating and stirring at a mass ratio of 3:40 to obtain a PVA solution;

[0010] (3) The PVA solution and liquid Ca(NO3)2·4H2O are mixed evenly under heating conditions at a mass ratio of 1:35 to form a viscous solution;

[0011] (4) First, dry the raw black and odorous sediment and then sieve it. Then, mix sodium carboxymethyl cellulose and black and odorous sediment at a mass ratio of 1:10~20. Add the viscous solution from step (3), mix thoroughly, make pellets, dry, and obtain calcium nitrate slow-release filler for strengthening the remediation of black and odorous sediment in rivers.

[0012] Furthermore, in step (1) or (3), the heating temperature is 50~55℃.

[0013] Furthermore, in step (2), the heating temperature is 50~70℃.

[0014] Furthermore, in step (4), the mesh size of the sieve is 200 mesh.

[0015] Furthermore, in step (4), the drying temperature is 45 ℃ and the drying time is 24 h.

[0016] The present invention provides a calcium nitrate slow-release filler prepared by the above preparation method.

[0017] The present invention also provides the application of the above-mentioned calcium nitrate slow-release filler in the enhanced remediation of black and odorous sediment in river channels.

[0018] Furthermore, the dosage of calcium nitrate slow-release packing is 3.34 g to 10.53 g / L of black and odorous sediment.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) The calcium nitrate slow-release packing material prepared by the present invention can achieve rapid sedimentation and full contact with the bottom sediment in the water environment, effectively avoiding the problem of ineffective release of calcium nitrate in the upper water phase.

[0021] (2) The calcium nitrate slow-release packing material prepared in this invention has a significant oxidizing effect on black and odorous sediment. Its slow-release characteristics can not only promote the degradation of organic matter by heterotrophic denitrifying bacteria in the sediment, but also activate the oxidation function of autotrophic denitrifying bacteria on sulfides, thereby achieving efficient treatment of black and odorous pollution.

[0022] (3) The slow-release mechanism of the calcium nitrate slow-release filler prepared by the present invention can control the release rate of nitrate, which not only prevents water pollution caused by excessive nitrate entering the aqueous phase, but also significantly reduces the amount of nitrate used, effectively solving the problems of directly adding calcium nitrate.

[0023] (4) The raw materials used in the calcium nitrate slow-release filler prepared in this invention are all environmentally friendly materials. The sediment is black and odorous river sediment, realizing in-situ utilization of the material; polyvinyl alcohol, as a biodegradable polymer, can effectively enhance the slow-release effect by forming a dense molecular network structure; sodium carboxymethyl cellulose has thickening and gelling functions and high water absorption, which can encapsulate calcium nitrate particles and slow down their dissolution and diffusion rate. This all-natural component formulation design completely avoids the secondary pollution problems that may be caused by traditional granulation materials (such as cement). Attached Figure Description

[0024] Figure 1 This is a photograph of the calcium nitrate slow-release packing material.

[0025] Figure 2 SEM image of the calcium nitrate slow-release packing material prepared in Example 1;

[0026] Figure 3 Figure showing the changes in apparent characteristics of sediment after adding calcium nitrate slow-release filler;

[0027] Figure 4 Figure showing the change in ORP after adding calcium nitrate slow-release packing to the sediment;

[0028] Figure 5 Graph showing the change in removal effect of calcium nitrate slow-release filler after adding calcium nitrate slow-release filler to the sediment;

[0029] Figure 6 This is a diagram showing the release pattern of calcium nitrate slow-release packing material in a muddy aqueous phase. Detailed Implementation

[0030] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples and accompanying drawings. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0031] Example 1

[0032] The preparation method of calcium nitrate slow-release filler for enhancing the remediation of black and odorous river sediment includes the following steps:

[0033] Step 1: Dry in a 45 ℃ oven, sieve through a 200 mesh, air dry at room temperature, and store for later use.

[0034] (1) Heat the Ca(NO3)2·4H2O particles to 50 °C so that they melt into a liquid state.

[0035] (2) Mix polyvinyl alcohol powder and water at a mass ratio of 3:40, heat to 70 °C and stir continuously to dissolve.

[0036] (3) The PVA solution is added to the liquid Ca(NO3)2·4H2O at a mass ratio of 1:35 to form a viscous solution.

[0037] (4) First, dry the black and smelly bottom mud in an oven at 45 ℃ and then sieve it through a 200-mesh screen. Then, mix sodium carboxymethyl cellulose and black and smelly bottom mud at a mass ratio of 1:20, and then mix it thoroughly with a viscous solution. Cut it into pellets (Φ= 1 cm) by machine or manually, and dry the pellets in an oven at 45 ℃ for 24 h to obtain calcium nitrate slow-release filler.

[0038] Figure 1 This is a photograph of the calcium nitrate slow-release packing material prepared in Example 1.

[0039] Figure 2 This is a SEM image of the calcium nitrate slow-release packing material prepared in Example 1. Figure 2 As shown, the outer surface of the calcium nitrate slow-release filler is relatively smooth with few pores, thus achieving a better slow-release effect on calcium nitrate. During the mixing of nitrate and PVA solution, the nitrate is encapsulated within the molecular gaps of the PVA. The calcium nitrate slow-release filler fills the pores of the particles, further reducing the probability of nitrate contact with water.

[0040] Example 2

[0041] Sediment from the polluted, black river was collected and placed in a 3 L beaker. It was allowed to settle naturally at room temperature to form a sediment column approximately 2 L high. About 1 L of river water was then added, and the column was allowed to stabilize for one week to obtain the initial experimental sediment column. Figure 3 Then, the calcium nitrate slow-release packing material prepared in Example 1 was set up according to different concentration gradients. 6.680 g, 14.050 g, and 21.061 g (corresponding to N / (Fe+S) ratios of 0.2, 0.4, and 0.6, respectively) were weighed and added sequentially to experimental mud columns labeled PVA1, PVA2, and PVA3 as treatment groups. A blank control group was also set up. The phenotype, redox potential (ORP), acid volatile sulfur (AVS, characterizing sulfides), ferrous content, and nitrate concentration in the aqueous phase were monitored.

[0042] like Figure 3 As shown, after adding calcium nitrate slow-release packing material, the color of the bottom sediment changed significantly from black to yellow after 30 days, indicating that the main blackening substances in the bottom sediment were oxidized. At the same time, it was observed that a large number of pores were generated in the upper, middle and lower layers of the bottom sediment, indicating that nitrate ions in the bottom sediment participated in the abnormal denitrification process and were reduced to nitrogen gas, which was released from the bottom sediment.

[0043] like Figure 4 As shown, regarding the redox potential of sediment, after 60 days of adding calcium nitrate slow-release packing, the blank group increased from the initial -185 mV to -160 mV, while the ORP of PVA1, PVA2, and PVA3 groups increased to -2.5, 25, and 43 mV, respectively. This indicates that after adding the packing, the sediment environment changed from a significantly reduced state to an oxidized state, and the sediment oxidation effect was significant.

[0044] like Figure 5 As shown, for the target pollutants, sulfides (AVS) and ferrous iron in the sediment, the degradation effects of AVS and ferrous iron in the sediment of groups PVA2 and PVA3 were similar. AVS decreased from 6500 mg / kg to about 450 mg / kg, with a removal rate of 93%, and tended to stabilize after 30 days of reaction. Ferrous iron decreased from 7500 ug / g to about 2500 ug / g, with a removal rate of 67%. Subsequently, the electron donor will mainly act on the ferrous iron in the sediment, indicating that the addition of calcium nitrate slow-release filler can effectively remove black and odorous pollutants.

[0045] like Figure 6 As shown, regarding the nitrate concentration in the aqueous phase, after 60 days of packing material addition, the PVA1 and PVA2 groups had their packing material depleted after 35 days, with nitrate concentrations as low as approximately 2.5 and 20 mg / L, respectively, at 60 days, indicating good nitrate release control. In the PVA3 group, due to excessive packing material addition failing to fully consume the electron acceptor, the nitrate concentration in the overlying water reached 320 mg / L, indicating that calcium nitrate was slowly released from the slow-release packing material.

[0046] In summary, this invention physically combines Ca(NO3)2·4H2O, PVA, and CMC-Na, utilizing in-situ river black and odorous sediment as raw material to obtain a novel, highly efficient, stable, and environmentally friendly slow-release filler. This filler effectively enhances the treatment effect of river black and odorous sediment and has potential application value in the field of sediment treatment. This composite slow-release filler containing Ca(NO3)2·4H2O, PVA, and CMC-Na solves the problem of calcium nitrate reagents being easily dissolved and dispersed into the overlying water when directly exposed. It maximizes the flow of electrons released from calcium nitrate to nitrates and converts them into nitrogen gas. The dosage of the calcium nitrate slow-release filler can be determined according to the actual engineering application. Appropriately increasing the dosage of the composite material can significantly improve the treatment effect, but a balance between cost and benefit is necessary.

[0047] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of protection of this application is limited to these examples; within the framework of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of one or more embodiments of this application as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing calcium nitrate slow-release filler for strengthening the remediation of black and odorous river sediment, characterized in that, The method comprises the following steps: (1) heating Ca(NO3)2·4H2O particles to melt into a liquid state; (2) heating and stirring PVA powder in water to obtain a PVA solution according to a mass ratio of 3:40; (3) mixing the PVA solution with the liquid-state Ca(NO3)2·4H2O under heating conditions according to a mass ratio of 1:35 to form a viscous solution; (4) first drying and sieving the black and odorous sediment, then fully stirring sodium carboxymethyl cellulose and the black and odorous sediment according to a mass ratio of 1:10-20, and then adding the viscous solution of step (3) and fully stirring and mixing to obtain a pellet, and drying to obtain a calcium nitrate slow-release filler for strengthening the repair of black and odorous sediment in a river channel.

2. The production method according to claim 1, characterized by, In step (1) or (3), the heating temperature is 50-55℃.

3. The preparation method according to claim 1, characterized in that, In step (2), the heating temperature is 50-70℃.

4. The method of claim 1, wherein, In step (4), the mesh number of the sieve is 200.

5. The preparation method according to claim 1, characterized in that, In step (4), the drying temperature is 45℃, and the drying time is 24 h.

6. The calcium nitrate slow-release filler prepared by the preparation method according to any one of claims 1-5.

7. The application of the calcium nitrate slow-release filler according to claim 6 in strengthening the repair of black and odorous sediment in a river channel.

8. Use according to claim 7, characterized in that, The dosage of the calcium nitrate slow-release filler is 3.34 g-10.53 g / L of black and odorous sediment.

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