Method for regulating heavy metal distribution in sludge hydrothermal treatment process

Abstract

The application discloses a method for regulating heavy metal distribution in a sludge hydrothermal treatment process, which comprises the following steps: step 1, mixing citric acid or tannic acid with sludge, adjusting the water content, and mixing in a polypropylene lining; step 2, placing the polypropylene lining in step 1 into a stainless steel hydrothermal reaction kettle for high-temperature treatment; and step 3, when the reaction kettle is cooled to room temperature, opening the reaction kettle to take out the reacted product, and separating the mixture of solid phase and aqueous phase. By regulating the type and concentration of the hydrothermal conditioner, the migration of heavy metals in the liquid and solid phases in the hydrothermal process is controlled, and a reference basis is provided for the disposal of heavy metals in sludge.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection technology, specifically relating to a method for regulating the distribution of heavy metals during the hydrothermal treatment of sludge. Background Technology

[0002] With the acceleration of urbanization in my country, the amount of sewage treated in major cities is constantly increasing, and the amount of urban sludge produced is also increasing year by year. It is estimated that it will reach 90 million tons by 2025. Sludge contains a large number of pathogens, organic matter, heavy metals and other pollutants. Improper disposal can lead to serious environmental risks. Sludge reduction and harmless treatment are urgent problems that my country needs to solve. At present, traditional technologies such as landfill, incineration, composting and anaerobic digestion are used to treat sludge, but there are problems with cost, environmental protection and efficiency. Moreover, the heavy metals contained in sludge are difficult to be degraded by microorganisms and heavy metal enrichment will occur during the treatment process, threatening the ecological environment. How to control the distribution of heavy metals in the sludge treatment process also affects the development of sludge treatment technology. Therefore, finding a safe, efficient and low-cost sludge heavy metal treatment technology is in line with the current development trend of the sludge treatment field.

[0003] Hydrothermal reactions utilize water as a reactant, solvent, and catalyst. During this process, macromolecular organic matter in sludge undergoes a series of reactions, including hydrolysis, decarboxylation, polymerization, and aromatization. This effectively reduces the toxicity and leaching concentration of heavy metals, alters the binding mode between sludge and heavy metals, and consequently changes the phase distribution and chemical form of heavy metals in the sludge. Therefore, hydrothermal technology has broad application prospects in the treatment of heavy metals in sludge. However, due to the complex properties of sludge, heavy metal migration and transformation are prone to occur during hydrothermal processes. How to further regulate heavy metal migration is a question worth considering. Summary of the Invention

[0004] Sludge has a complex composition, and heavy metals migrate and transform during hydrothermal processes. Based on this, this application provides a method for controlling the distribution of heavy metals in sludge during hydrothermal processes. This method involves co-hydrothermally heating sludge contaminated with chromium and a conditioner to regulate the migration of chromium during the hydrothermal process.

[0005] The technical solution of this invention is:

[0006] A method for regulating the distribution of heavy metals in the hydrothermal process of sludge includes the following steps:

[0007] Step 1: Mix citric acid and tannic acid of different concentrations with sludge, adjust the moisture content to 50%-90%, and then mix them thoroughly in a polypropylene liner.

[0008] Step 2: Place the polypropylene liner from Step 1 into a stainless steel hydrothermal reactor for high-temperature treatment. Set the reaction time to 60-240 min and the temperature to 120-180℃.

[0009] Step 3: After the reactor cools to room temperature, open the reactor and take out the reaction product. Separate the solid phase and the aqueous-liquid phase mixture, wash the solid phase with deionized water, and dry and store the solid product.

[0010] Step 4: Determine the chromium content in the solid and liquid components of the sludge hydrothermal solution obtained in Step 3.

[0011] Step 5: Analyze the acid-soluble / exchangeable chromium content, reducible chromium content, oxidizable chromium content, and residual chromium content of the hydrothermal solid obtained in Step 3 using the BCR analysis method.

[0012] Step 6: Based on the analysis results of Step 4 and Step 5, calculate the content ratio of acid-soluble / exchangeable components, reducible components, oxidizable components and residual components of chromium.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] 1. When citric acid is used as a hydrothermal conditioning agent in this invention, it promotes the migration of chromium into the liquid during hydrothermal treatment. The resulting hydrothermal solid will lead to an increase in acid-soluble components, making the hydrothermal solid composition unstable and increasing the risk of leaching of heavy metal chromium.

[0015] 2. When tannic acid is used as a hydrothermal conditioning agent in this invention, it promotes the migration of chromium to the solid during hydrothermal treatment. The resulting hydrothermal solid will reduce the acid-soluble components, stabilize the composition of the hydrothermal solid, and reduce the risk of leaching of heavy metal chromium.

[0016] 3. The addition of conditioner during the hydrothermal process reduces the bound water in the sludge, and the hydrophobicity of the solids obtained by hydrothermal treatment increases, which is beneficial for solid-liquid separation.

[0017] 4. The hydrothermal process increases the dissolution of macromolecular substances in the sludge, resulting in a significant volume reduction effect.

[0018] 5. This invention proposes a method for regulating the distribution of heavy metals during hydrothermal processes. By controlling the type and concentration of hydrothermal conditioning agents, the migration of heavy metals in liquid and solid forms during hydrothermal processes can be controlled, providing a reference for the treatment of heavy metals in sludge. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with preferred embodiments.

[0020] Example 1:

[0021] A method for regulating the distribution of heavy metals in the hydrothermal process of sludge includes the following steps:

[0022] Step 1: Take a certain amount of sludge, adjust the moisture content to 90%, add a certain concentration (0-0.24 mmol / g sludge) of citric acid and mix it into 100 ml of polypropylene liner.

[0023] Step 2: Place the polypropylene liner from Step 1 into a stainless steel hydrothermal reactor for high-temperature treatment. Set the reaction time to 120 minutes and the temperature to 180°C.

[0024] Step 3: After the reactor cools to room temperature, open the reactor and take out the reaction product. Separate the solid phase and the aqueous-liquid phase mixture, wash the solid phase with deionized water, and dry and store the solid product.

[0025] Step 4: The content of chromium in the solid and liquid components of the sludge hydrothermal solution obtained in Step 3 was determined by atomic absorption spectrometry, and the distribution ratio was calculated. The calculation results are shown in Table 1.

[0026] Table 1. Distribution of Chromium in Solid and Liquid Substances of Sludge Treated with Citric Acid Hydrothermal Conditioning

[0027]

[0028] Step 5: Extract the acid-soluble / exchangeable chromium, reducible chromium, oxidizable chromium, and residual chromium from the hydrothermal solid obtained in Step 3 using BCR analysis, and measure the extracted chromium speciation content using atomic absorption spectrometry. BCR analysis is a standard operating method; its principles and procedures will not be elaborated here.

[0029] Step 6: Based on the analysis results of Step 4 and Step 5, calculate the proportions of the acid-soluble / exchangeable component (F1), the reducible component (F2), the oxidizable component (F3), and the residual component (F4) of chromium. The calculation results are shown in Table 2.

[0030] Table 2. Distribution ratio of chromium speciation in solid and liquid sludge treated with citric acid hydrothermal conditioning

[0031]

[0032] Example 2

[0033] A method for regulating the distribution of heavy metals in the hydrothermal process of sludge includes the following steps:

[0034] Step 1: Take a certain amount of sludge, adjust the moisture content to 90%, add a certain concentration (0-0.24 mmol / g sludge) of tannic acid and mix it into 100 ml of polypropylene liner.

[0035] Step 2: Place the polypropylene liner from Step 1 into a stainless steel hydrothermal reactor for high-temperature treatment. Set the reaction time to 120 minutes and the temperature to 180°C.

[0036] Step 3: After the reactor cools to room temperature, open the reactor and take out the reaction product. Separate the solid phase and the aqueous-liquid phase mixture, wash the solid phase with deionized water, and dry and store the solid product.

[0037] Step 4: The content of chromium in the solid and liquid components of the sludge hydrothermal solution obtained in Step 3 was determined by atomic absorption spectrometry, and the distribution ratio was calculated. The calculation results are shown in Table 3.

[0038] Table 3. Distribution of Chromium in Tannic Acid Hydrothermal Conditioning Sludge (Solid and Liquid)

[0039]

[0040]

[0041] Step 5: Extract the acid-soluble / exchangeable chromium, reducible chromium, oxidizable chromium, and residual chromium from the hydrothermal solid obtained in Step 3 using BCR analysis, and measure the extracted chromium speciation content using atomic absorption spectrometry. BCR analysis is a standard operating method; its principles and procedures will not be elaborated here.

[0042] Step 6: Based on the analysis results of Step 4 and Step 5, calculate the proportions of the acid-soluble / exchangeable component (F1), the reducible component (F2), the oxidizable component (F3), and the residual component (F4) of chromium. The calculation results are shown in Table 4.

[0043] Table 4. Distribution ratio of chromium speciation in solid and liquid components of tannic acid hydrothermal conditioning sludge.

[0044]

[0045] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, without departing from the principle of the present invention, it is also applicable to substances such as livestock and poultry manure and soil containing heavy metals, and several improvements and modifications can be made. These improvements and modifications are also within the protection scope of the present invention.

Claims

1. A method for regulating the distribution of heavy metals during the hydrothermal treatment of sludge, characterized in that, Includes the following steps: Step 1: Mix tannic acid with sludge, adjust the moisture content, and mix thoroughly in a polypropylene liner; the amount of tannic acid added is 0.03-0.12 mmol / g sludge; Step 2: Place the polypropylene liner from Step 1 into a stainless steel hydrothermal reactor for high-temperature treatment. Step 3: After the reactor cools to room temperature, open the reactor and remove the reaction product to separate the solid phase and the aqueous phase mixture.

2. The method for regulating the distribution of heavy metals during the hydrothermal treatment of sludge according to claim 1, characterized in that, In step 2, the high-temperature treatment time is 60-240 minutes, and the temperature is 120-180℃.

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