A harmless treatment process for river and lake bottom sludge

Abstract

The present invention relates to the technical field of sediment chemical reagent treatment, and specifically to a harmless treatment process for river and lake sediment. The treatment process of the present invention overcomes the problems of high metal content, excessive organic compounds, pesticides and other substances in the sediment treated by traditional treatment processes. First, the sediment is measured, surveyed and cached, and inorganic solid waste and sand grains are removed by size screening; then, preliminary flocculation is carried out by using a Venturi-structured pipeline and a six-way valve type injector, and primary dehydration is carried out by screw extrusion and track type pressure filtration; after detection and analysis, medicament treatment is carried out on the exceeding-standard substances, and the content of pollutants is reduced by means of the synergistic action of oxidation-adsorption-chelation; finally, secondary dehydration, forming and steam hydrothermal curing are carried out; the indexes of the treated sediment meet the standards, the metal migration amount is low, and it can be used for landscaping, realizing harmlessness and resource utilization; through process innovation, the reaction efficiency of the reagent and the sediment is optimized, and the environmental protection benefit is remarkable.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical reagent treatment of sediment, and in particular to a harmless treatment process for river and lake sediment. Background Art

[0002] With the acceleration of urbanization and industrialization, river and lake sediment pollution has become an urgent environmental challenge. As a vital component of aquatic ecosystems, river and lake sediments absorb large amounts of pollutants from industrial wastewater, domestic sewage, and surface runoff, becoming reservoirs for harmful substances such as heavy metals, organic pesticides, organic matter, and E. coli.

[0003] Currently, existing sediment treatment technologies have numerous limitations. Conventional physical treatment methods, such as simple screening and dewatering, can only remove large particles and some water from the sediment. They are unable to remove the abundant heavy metals and organic pollutants present in the sediment. Consequently, treated sediment can still pollute soil, water, and other environmental factors during subsequent disposal.

[0004] In terms of chemical treatment technology, some methods use a large amount of chemical reagents to remove pollutants. For example, some methods that use acid and alkali to adjust the pH value can change the existence form of heavy metals to a certain extent, but they can easily cause drastic changes in the chemical properties of the sediment, affecting its subsequent resource utilization; excessive oxidants will react with minerals, humus, etc. in the sediment to produce complex chemical reactions. These reactions not only consume a large amount of reagents, but may also destroy the original structure of the sediment and release the originally fixed heavy metal ions, which in turn increases the pollution risk of the sediment. At the same time, some intermediate products generated by the reaction, such as organic free radicals and metal complexes, are unstable in nature and may be further converted into more toxic substances, causing secondary pollution to the environment. In addition, the large amount of chemical reagents remaining after the reaction will also affect the subsequent resource utilization of the sediment, reducing its application value in agriculture, landscaping and other fields.

[0005] Furthermore, existing technologies lack systematic and coordinated design in the overall design of the sediment treatment process. Each treatment step is independent of the others, failing to fully leverage the strengths of different treatment methods. This results in low treatment efficiency and makes it difficult to achieve the dual goals of harmless sediment treatment and resource utilization. Therefore, the development of an efficient, environmentally friendly sediment treatment technology that achieves resource utilization is urgent.

[0006] Therefore, a harmless treatment process for river and lake sediments was proposed. Summary of the invention

[0007] The purpose of the present invention is to provide a harmless treatment process for river and lake bottom sludge. The bottom sludge is obtained through measurement and investigation and cached. Inorganic solid waste and sand grains are removed by size screening. Then, preliminary flocculation is carried out using a Venturi-structured pipeline and a six-way valve type sampler, and primary dehydration is performed through screw extrusion and track-type pressure filtration. After detection and analysis, chemicals are added to the substances exceeding the standard, and the content of pollutants is reduced by the synergistic effect of oxidation-adsorption-chelating. Finally, secondary dehydration, shaping, and hydrothermal curing are carried out. The treated bottom sludge meets all the standards, has a low metal migration amount, can be used for landscaping, realizing harmlessness and resource utilization. Through process innovation, the reaction efficiency of the reagent and the bottom sludge is optimized, and the environmental protection benefit is remarkable.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] The present invention provides a harmless treatment process for river and lake bottom sludge, and the process is as follows:

[0010] S1 Bottom sludge collection and caching;

[0011] S2 Size screening;

[0012] S3 Flocculation screening;

[0013] The interfaces of the six-way valve type sampler are A, B, C, D, E, and F in clockwise order. In working mode one, polyethylene oxide solution is pumped in. In working mode two, polyacrylamide solution is pumped in, and the pretreated bottom sludge is obtained through reaction.

[0014] S4 Primary dehydration;

[0015] S5 Detection and analysis;

[0016] S6 Chemical addition;

[0017] S61 Primary chemical addition;

[0018] Hydrogen peroxide solution and ferrous sulfate solution are added at pH 6.0. A composite NH2-MIL-101 suspension, a dithiocarbamate solution, a thiocarboxylic acid chitosan solution, and an activated carbon suspension are added in sequence, and the reaction pH is adjusted to 7.0.

[0019] S62 Secondary chemical addition;

[0020] Calcium chloride solution, calcium hydroxide suspension, sodium hypochlorite solution, and potassium permanganate solution are added simultaneously. After reacting for 1 h, polyaluminum chloride solution is added. After the reaction, polyacrylamide solution is added to obtain the chemically treated bottom sludge.

[0021] S7 Secondary dehydration;

[0022] S8 Shaping treatment;

[0023] S9 Hydrothermal curing.

[0024] Preferably, it is calculated in milligrams per liter of chemically treated sediment;

[0025] In S61, the ratio of the polyethylene oxide solution to the chemically treated sediment is 10 - 15:1; the ratio of the polyacrylamide solution to the chemically treated sediment is 150 - 250:1; the ratio of the hydrogen peroxide solution to the chemically treated sediment is 180 - 220:1; the ratio of the ferrous sulfate solution to the chemically treated sediment is 450 - 500:1; the ratio of the composite NH2-MIL-101 suspension to the chemically treated sediment is 260 - 320:1; the ratio of the dithiocarbamate solution to the chemically treated sediment is 4800 - 5100:1; the ratio of the thiocarboxylic acid chitosan solution to the chemically treated sediment is 800 - 1050:1;

[0026] In S62, the ratio of the calcium chloride solution to the chemically treated sediment is 90 - 150:1; the ratio of the calcium hydroxide suspension to the chemically treated sediment is 45 - 60:1; the ratio of the sodium hypochlorite solution to the chemically treated sediment is 3500 - 4000:1; the ratio of the potassium permanganate solution to the chemically treated sediment is 1800 - 2200:1; the ratio of the polyaluminum chloride solution to the chemically treated sediment is 130 - 150:1; the ratio of the polyacrylamide solution to the chemically treated sediment is 40 - 60:1.

[0027] Preferably, in S3 flocculation screening, in working mode one, the polyethylene oxide solution is pumped in by F, passes through A and D in sequence, and is pumped into the Venturi structure pipeline by E; when switched to working mode two, the polyacrylamide solution is pumped in by C and is pumped into the Venturi structure pipeline by C.

[0028] Preferably, in S61, in working mode one, the hydrogen peroxide solution is pumped in by F. After initially pumping in 10 L, it passes through A and D in sequence, and is sealed by E. Then it is switched to working mode two, the ferrous sulfate solution is pumped in by C, and the hydrogen peroxide solution and the ferrous sulfate solution between A and D are mixed at C, and finally pumped into the connection between the converging section and the throat of the Venturi structure pipeline.

[0029] Preferably, in S62, in the state of working mode one, the polyaluminum chloride solution is pumped in by F, passes through A and D in sequence, and is sealed by E; when switched to working mode two, the polyacrylamide solution is pumped in by C, the polyaluminum chloride solution and the polyacrylamide solution are mixed at C, and finally pumped into the Venturi structure pipeline to obtain the chemically treated sediment.

[0030] Preferably, the steps of S2 size screening are as follows: The sediment in the buffer pool is size-screened by a vibrating screen screening device to separate the inorganic solid waste, and stones, branches, and plastic inorganic waste with a diameter greater than 15 mm are screened out; screening is carried out with a sieve hole size of 1.5 mm to remove sand grains to obtain the preliminarily screened sediment.

[0031] Preferably, the conditions for hydrothermal curing of S9 are as follows: under the condition of 280 °C, the die-casting bottom sludge is cured with water vapor for 3 h to obtain the cured bottom sludge.

[0032] Preferably, the composite NH2-MIL-101 suspension is obtained by mixing composite NH2-MIL-101 and deionized water; the composite NH2-MIL-101 is obtained by reacting terephthalic acid, 2-aminoterephthalic acid and iron oxide nanoparticles, or directly purchasing the product with the commercial information CAS 1189182-85-1.

[0033] Preferably, the thio-carboxylic acid chitosan solution is obtained by mixing thio-carboxylic acid chitosan and deionized water; the thio-carboxylic acid chitosan is obtained by reacting chitosan with a deacetylation degree of 90% with thioacetic acid.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] 1. Through S2 size screening, stones, branches, plastic inorganic solid wastes larger than 10 - 20 mm and sand grains of 0.1 - 2 mm can be effectively separated, reducing the interference of impurities on subsequent treatment; the combination of S3 flocculation screening and S4 primary dehydration reduces the water content of the bottom sludge from 85% to 45%, creating good conditions for subsequent treatment. In the S6 chemical addition link, by precisely controlling the dosage and addition sequence of various chemical reagents such as hydrogen peroxide, ferrous sulfate, and composite NH2-MIL-101, and using the synergistic mechanisms of oxidation-adsorption-chelation, precipitation-flocculation, and disinfection oxidation, the contents of heavy metals, organic compounds, and Escherichia coli in the bottom sludge are effectively reduced; after treatment, the total zinc content is 380 - 442 mg / kg, the total cadmium is 3.2 - 4.1 mg / kg, glyphosate is 65 - 84 mg / kg, and the coliform value is 0.004 - 0.007 mg / kg, etc., all meeting the standard of "Sludge Disposal for Greening in Urban Sewage Treatment Plants" GB / T 23486, realizing the harmless treatment of the bottom sludge and greatly reducing the environmental pollution risk of the bottom sludge.

[0036] 2. By using a Venturi-structured pipeline in conjunction with a six-way valve type injector, reagents are added at the tapered section and the throat. Utilizing a high-speed, low-pressure environment and a special flow regime, the reagents are rapidly dispersed and thoroughly mixed with the sediment, enhancing the treatment efficiency. This design optimizes the reaction process between the chemical reagents and the sediment. During the S9 steam hydrothermal curing stage, the curing conditions of 280°C steam transform the metals in the cured sediment from unstable states to residual states, significantly reducing the metal migration amount. The metal zinc migration amount is 21.1 mg / Kg and cadmium is 0.12 mg / Kg. The process of the present invention effectively stabilizes the metals in the sediment, reduces their migration and release into the environment, and avoids secondary pollution to the soil and water bodies. The treated cured sediment can be directly used for afforestation of forest lands, nursery gardens, grasslands, and road slopes, realizing the resource utilization of the sediment, which is of great significance in environmental protection and resource recycling. Brief Description of the Drawings

[0037] Figure 1 It is a process diagram for the harmless treatment of river and lake sediment of the present invention;

[0038] Figure 2 It is a state diagram of working mode 1 of the six-way valve type injector of the present invention;

[0039] Figure 3 It is a state diagram of working mode 2 of the six-way valve type injector of the present invention. Detailed Description of the Invention

[0040] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0041] Please refer to Figures 1 to 3 , the present invention provides a harmless treatment process for river and lake sediment, and the technical solutions are as follows:

[0042] Example 1

[0043] As Figure 1 shown, the treatment process is as follows:

[0044] S1 Sediment collection and caching

[0045] According to the design method of patent CN106638456B, gradually conduct measurement, survey, detection, determination of dredging work volume, and ecological dredging to obtain the sediment, and temporarily store the sediment in the caching pool; the volume of the caching pool is 100 cubic meters.

[0046] S2 Size screening

[0047] Use a vibrating screen screening device to screen the sediment in the buffer pool by size and separate the inorganic solid waste in it for subsequent separate treatment (stones, branches, and plastic inorganic solid waste with a diameter greater than 15 mm are screened out, and sand grains are removed by screening with a sieve hole size of 1.5 mm); the moisture content of the preliminarily screened sediment is 85%; the screening frequency is maintained in the range of 15 - 30 Hz.

[0048] S3 Flocculation Screening

[0049] There is a Venturi-structured pipeline in front of the pretreatment tank. The pipeline is divided into a converging section, a throat, and a diverging section. A six-way valve type injector is set at the connection of the converging section and the throat. The interfaces are A, B, C, D, E, and F in clockwise order. In the first working mode: The drag reducer polyethylene oxide solution (dosage concentration 12 mg / L) is pumped in from F and pumped into the Venturi-structured pipeline from E. After initially pumping in 10 L, it is then switched to the second working mode. The cationic polyacrylamide solution (dosage concentration 150 mg / L) is pumped in from C and pumped into the Venturi-structured pipeline from C; the flow rate at the inlet of the converging section is 1.2 m / s, the flow rate in the throat is 3.5 m / s, and the flow rate at the outlet of the diverging section is 0.6 m / s.

[0050] Working mode one: As Figure 2 shown, B and C are connected, A is connected to F, E is connected to D, and A is connected to D; the pipeline connecting A and D is a transparent pipeline, and the state and situation of the chemical reagents in it can be observed at any time; it flows in from F, passes through A and D in sequence, and finally flows out from E. Working mode two: As Figure 3 shown, B is connected to A, A is connected to F, A is connected to D, D is connected to C, and E is connected to F.

[0051] The flocculated sediment flowing out of the diverging section and flocculated is subjected to secondary screening and filtration to remove the flocculated substances to obtain the pretreated sediment.

[0052] S4 Primary Dewatering

[0053] The pretreated sediment is passed through a screw extrusion dewatering machine and a belt filter press in sequence. The screw extrusion dewatering machine has a rotation speed of 12 r / min and a pressure of 0.5 MPa in the feeding section, a rotation speed of 10 r / min and a pressure of 0.8 MPa in the extrusion section, and a rotation speed of 6 r / min and a pressure of 1.2 MPa in the pressing section; the belt filter press has a pressure of 0.2 MPa in the gravity dewatering area, a filter belt speed of 5 m / min, a pressure of 0.7 MPa in the wedge pre-pressing area, a filter belt speed of 3 m / min, a pressure of 1.5 MPa in the high-pressure pressing area, and a filter belt speed of 1.5 m / min; the filter belt mesh number is 500 mesh. After being treated by the screw extrusion dewatering machine, the moisture content of the sediment is 68%. After passing through the belt filter press again, the moisture content of the primary dewatered sediment is 45%.

[0054] S5 Detection and Analysis

[0055] If it meets the standard, it directly enters S7; if it does not meet the standard, it enters S6 for treatment. The contents of heavy metals, organic matters, organic pesticides, and Escherichia coli are detected and analyzed. After sample treatment, the detection and analysis are carried out. Among them, referring to the substance limit requirements specified in GB / T 23486-2009 "Sludge Disposal in Urban Sewage Treatment Plants - Quality of Sludge for Greening in Gardens and Landscapes", for total zinc < 500 mg / kg, total nickel < 200 mg / kg, total copper < 400 mg / kg, total cadmium < 5 mg / kg, total mercury < 5 mg / kg, total arsenic < 50 mg / kg, total lead < 300 mg / kg, total chromium < 400 mg / kg, hexavalent chromium < 10 mg / kg, DDT < 2 mg / kg, hexachlorocyclohexane < 2 mg / kg, glyphosate < 100 mg / kg, dichlorvos < 1.0 mg / kg, polychlorinated biphenyls < 0.5 mg / kg, toluene < 50 mg / kg, benzo(a)pyrene < 0.3 mg / kg, and coliform value < 0.01 mg / kg, after the primary dewatered sludge is pressed by a plate and frame press and mixed with inorganic solid waste, it is digested and mixed into powder, mechanically formed and hydrothermally cured, and directly used for greening of forest land, nursery gardens, grasslands, and road slopes;

[0056] The actual detected contents of the sludge substances are as follows: total zinc 1126 mg / kg, total nickel 80 mg / kg, total copper 125 mg / kg, total cadmium 276 mg / kg, total mercury 14 mg / kg, total arsenic 32 mg / kg, total lead 125 mg / kg, total chromium 316 mg / kg, hexavalent chromium 8 mg / kg, DDT not detected, hexachlorocyclohexane 0.5 mg / kg, glyphosate 324 mg / kg, dichlorvos 1.6 mg / kg, polychlorinated biphenyls 0.1 mg / kg, toluene 175 mg / kg, benzo(a)pyrene 0.8 mg / kg; coliform value 0.16 mg / kg; the contents of some substances do not meet the requirements, and further treatment is carried out.

[0057] The six-port valve type injector sets a PID controller. Based on the initial detected contents of pollutants in the sludge and the treatment target, a relationship model between pollutant content and reagent dosage is established. The pre-feedback controller calculates the required increased dosage of chemical reagents according to the model and controls the pump at the corresponding interface of the dynamic reagent injector to increase the dosage.

[0058] S6 Chemical Reagent Addition

[0059] S61 Primary Chemical Reagent Addition

[0060] Adjust the pH of the sediment to 6.0, then add hydrogen peroxide solution (dosage concentration 200 mg / L), ferrous sulfate solution (dosage concentration 480 mg / L), and maintain the temperature at 45 °C before adding the ferrous sulfate solution; and add the mixed composite NH2-MIL-101 suspension (dosage concentration 320 mg / L) and dithiocarbamate solution (dosage concentration 4800 mg / L) through another pipeline. After reacting for 20 min, add the thiocarboxylic acid chitosan solution (dosage concentration 800 mg / L), react for 10 min, and finally add the activated carbon suspension (dosage concentration 6000 mg / L), and react at room temperature for 5 h. After the reaction is completed, adjust the pH to 7.0;

[0061] Pump the hydrogen peroxide solution by F. After initially pumping 10 L, seal it with E, then switch to working mode 2. Pump the ferrous sulfate solution by C. The hydrogen peroxide solution and the ferrous sulfate solution are mixed in equal volumes at the C outlet, and finally pump them into the venturi-structured pipeline by C. The adding positions of the above reagents are all at the interfaces of the converging section and the throat;

[0062] S62 Secondary dosing

[0063] At the same time, add calcium chloride solution (dosage concentration 130 mg / L), calcium hydroxide suspension (dosage concentration 50 mg / L), sodium hypochlorite solution (dosage concentration 3500 mg / L), potassium permanganate solution (dosage concentration 1800 mg / L). After fully reacting for 1 h, add polyaluminum chloride solution (130 mg / L). After reacting for 20 min, add polyacrylamide solution (40 mg / L). After flocculation, filter to remove the generated flocculation precipitate, and remove the composite NH2-MIL-101 and the oxidized iron by magnetic separation. The obtained flocculant is separated from the composite NH2-MIL-101, and finally the chemically treated sediment is obtained; the magnetic separation intensity is 400 mT, and the magnetic separation time is 20 min;

[0064] Pump the polyaluminum chloride solution by F, pass through A and D in sequence, and finally seal it with E. After initially pumping 10 L, then switch to working mode 2. Pump the polyacrylamide solution by B. Before pumping into the venturi-structured pipeline by C, the polyaluminum chloride solution and the polyacrylamide solution are mixed in equal volumes at the C inlet, and finally pump them into the venturi-structured pipeline by C to obtain the chemically treated sediment; when the reagent stored between the feedback ends A and D of the PID controller is less than 300 mL, stop the treatment, switch to working state 1, and switch back to working state 2 after replenishing the reagent.

[0065] S7 Secondary dehydration

[0066] After adding calcium oxide suspension (dosage concentration 60 mg / L) to the chemically treated sediment, use a plate and frame filter press to remove water and drain the remaining water. The water content of the obtained secondary dehydrated sediment is 36.8%;

[0067] S8 Molding treatment

[0068] Add the inorganic solid waste in S2 to the secondary dewatered sludge, and mix to obtain the material to be molded; place the material to be molded in a die-casting machine, and die-cast to obtain die-cast sludge;

[0069] S9 Hydrothermal curing

[0070] Under the condition of 280 °C, use water vapor to cure the die-cast sludge for 3 h to finally obtain cured sludge; the cured sludge can be directly used for landscaping, and can be used for forest land, nursery garden, grassland, and road slope greening.

[0071] The following chemical reagent concentrations are the concentrations in the Venturi structure pipeline itself. The following chemical reagents are all dissolved or dispersed by mixing with water. Among them, the concentration of hydrogen peroxide solution is 20 g / L, the concentration of ferrous sulfate solution is 50 g / L, the concentration of composite NH2-MIL-101 suspension is 100 g / L, the concentration of dithiocarbamate solution is 100 g / L, the concentration of thiocarboxylic acid chitosan solution is 100 g / L, the concentration of activated carbon suspension is 2000 g / L; the concentration of calcium chloride solution is 111 g / L; the concentration of calcium hydroxide suspension is 37 g / L; the concentration of sodium hypochlorite (available chlorine) solution is 50 g / L; the concentration of potassium permanganate solution is 30 g / L; the concentration of polyaluminum chloride solution is 100 g / L; the concentration of polyacrylamide solution is 10 g / L; the concentration of polyethylene oxide solution is 20 g / L; the concentration of cationic polyacrylamide solution is 5 g / L; the concentration of calcium oxide suspension is 35 g / L.

[0072] Examples 2-4

[0073] Different from Example 1, the concentrations of the following chemical reagents are changed, as shown in Table 1 and Table 2 specifically. The concentration unit in the table is the mass of the chemical reagent in each liter of primary dewatered sludge.

[0074] Table 1 Chemical reagent dosing concentrations during primary dosing and secondary dosing

[0075]

[0076] Table 2 Chemical reagent dosing concentrations during primary dosing and secondary dosing

[0077]

[0078] Comparative Example 3

[0079] Different from Example 1, replace the composite NH2-MIL-101 with an aqueous sodium persulfate solution with a dosing concentration of 320 mg / L, and the concentration of the aqueous sodium persulfate solution itself is 5 g / L.

[0080] Comparative Example 4

[0081] Different from Example 1, the thiocarboxylic acid chitosan solution was replaced with a carboxylic acid chitosan solution at the same dosing concentration.

[0082] Comparative Example 5

[0083] Different from Example 1, the thiocarboxylic acid chitosan solution was not added.

[0084] Preparation Example 1

[0085] The preparation method of composite NH2-MIL-101 is as follows: Weigh 0.1 mol of terephthalic acid and 0.1 mol of 2-aminoterephthalic acid, and dissolve them together in 1000 mL of N,N-dimethylformamide to form a mixed solution A; Weigh 0.1 mol of ferric chloride hexahydrate ( ), dissolve it in 50 mL of DMF to form solution B; Slowly add solution B to solution A, stir evenly, then transfer it to a reaction kettle and react at 180 °C for 36 h; After the reaction is completed, naturally cool it to room temperature to obtain NH2-MIL-101 crystals, and obtain NH2-MIL-101 by centrifugation, washing 3 times with DMF and ethanol respectively, and drying;

[0086] Weigh 10 g of NH2-MIL-101 and 20 g of iron oxide nanoparticles (100 nm), disperse them in 1000 mL of deionized water, and ultrasonically treat for 45 min to make the iron oxide nanoparticles uniformly adsorbed on the surface of NH2-MIL-101; Then add 0.15 g of sodium persulfate;

[0087] Stir and react the above mixed solution at 40 °C for 18 h to make the sodium persulfate undergo a chemical bonding reaction with the amino groups or other active sites on the surface of NH2-MIL-101, and at the same time the iron oxide nanoparticles are also combined with NH2-MIL-101 through physical adsorption and chemical reactions to form a composite product; After the reaction is completed, separate the product by centrifugation, wash it 3 times with deionized water and ethanol respectively, and dry it at 70 °C to obtain composite NH2-MIL-101.

[0088] Preparation Example 2

[0089] The preparation method of chitosan thio-carboxylate is as follows: Dissolve 65 g of chitosan with a deacetylation degree of 90% in 1000 mL of acetic acid solution with a mass concentration of 5% to obtain a chitosan solution; dissolve 76.2 g of thioacetic acid in methanol to obtain a thioacetic acid solution with a mass fraction of 1 mol / L; drop the chitosan solution into 200 mL of thioacetic acid solution at a speed of 5 drops / s, react at 45 °C for 5 h to obtain a chitosan thio-carboxylate solution; then filter, wash with water, and dry to obtain chitosan thio-carboxylate.

[0090] Experimental Example 1

[0091] The chemically treated sludge obtained by the above several schemes was tested for metal content, organic matter content, and coliform value. The final test results are shown in Table 3 and Table 4. The concentration unit of the substances in the table is mg / kg.

[0092] Table 3 Test Results of Examples 1-4 and Comparative Example 1

[0093]

[0094] Table 4 Test Results of Comparative Examples 2-5

[0095]

[0096] By adjusting the dosage of chemical reagents, the substance content in the sludge is changed. Except for the substances that already meet the requirements, the content of the originally excessive substances is also reduced within the standard range. Under the conditions of Examples 1-4, the total zinc content is 380-442 mg / kg, the total cadmium is 3.2-4.1 mg / kg, the total mercury is 1.5-2.0 mg / kg, glyphosate is 65-84 mg / kg, dichlorvos is 0.4-0.6 mg / kg, toluene is 28-36 mg / kg, benzo(a)pyrene is 0.1-0.2 mg / kg, and the coliform value is 0.004-0.007 mg / kg. By adjusting the concentrations of the added hydrogen peroxide solution, ferrous sulfate solution, composite NH2-MIL-101 suspension, dithiocarbamate solution, chitosan thio-carboxylate solution, activated carbon suspension, calcium chloride solution, calcium hydroxide suspension, sodium hypochlorite solution, and potassium permanganate solution, good removal effects on metals, organic substances, and Escherichia coli are achieved. Under acidic conditions FE + Catalyze hydrogen peroxide to generate hydroxyl radicals, whose oxidation potential is as high as 2.8 V, and can non-selectively degrade organic pollutants; composite NH2-MIL-101 has a high specific surface area (>1000 m 2 / g) and amino-modified pores selectively adsorb heavy metals and hydrophobic organic substances. At the same time, the sodium persulfate contained in it releases SO4 after activation -· Free radicals degrade the adsorbed organic matter on the surface of MOF to avoid the oxidation effect caused by directly adding sodium persulfate, which affects the Fenton reaction; the amino group (-NH2) of chitosan in thiocarboxylic acid chitosan enhances the reductive adsorption of Cr 6+ (C 6+ → Cr 3+ ). At the same time, after thiolation, the degradation ability of organic compounds increases; sodium hypochlorite oxidizes organochlorine pesticides (BHC, DDT) to CO2 and Cl - ; potassium permanganate degrades stubborn organic matter such as benzo(a)pyrene, inactivates Escherichia coli (oxidizes the cell membrane), and oxidizes the previously added divalent iron for subsequent magnetic separation and removal; the Al 3+ of polyaluminum chloride compresses the double electric layer, and the long-chain structure of polyacrylamide bridges particles to form dense flocs (size > 500 μm). The flocs wrap residual heavy metals and organic matter for easy pressure filtration and separation. In Comparative Example 1, the content of substances increased, and the removal efficiency of substances improved, but too many unnecessary components were easily introduced into the sediment and were difficult to be effectively removed in the sediment; in Comparative Example 2, the content of chemical reagents decreased, and the removal effects on metals, organic compounds and Escherichia coli decreased; in Comparative Example 3, the composite NH2-MIL-101 was replaced with an aqueous solution of sodium persulfate with a dosing concentration of 320 mg / L, and there was no obvious effect on the removal of heavy metals, but the removal effects on organic compounds such as glyphosate and dichlorvos decreased, and the removal ability of Escherichia coli decreased; in Comparative Example 4, it was replaced with carboxylic acid chitosan (without -SH group), and the adsorption and removal effects on metals and organic compounds decreased; in Comparative Example 5, thiocarboxylic acid chitosan was not added, and the adsorption and removal effect further decreased. Through the synergy of oxidation-adsorption-chelating, precipitation-flocculation and disinfection oxidation, the good removal of metals, organic compounds and Escherichia coli is jointly achieved.

[0097] Examples 5 and 6

[0098] Different from Example 1, the dosage of the flocculant for flocculation screening and secondary dosing changed, as shown in Table 5 specifically.

[0099] Table 5 Dosage concentrations of flocculant and drag reducer

[0100]

[0101] Comparative Example 6

[0102] Different from Example 1, in the secondary dosing of S62, the polyaluminum chloride solution and polyacrylamide solution were added 10 minutes after the reaction.

[0103] Comparative Example 7

[0104] Different from Example 1, in S3, the drag reducer polyethylene oxide solution and the cationic polyacrylamide solution are not added to the preliminarily screened sludge through a six-way valve injector. Instead, the drag reducer polyethylene oxide solution and the cationic polyacrylamide solution are mixed in equal volume and then added to the preliminarily screened sludge.

[0105] Comparative Example 8

[0106] Different from Example 1, in the first chemical addition process of S61, the ferrous sulfate solution and the hydrogen peroxide solution are not added to the preliminarily screened sludge through a six-way valve injector. Instead, they are mixed in advance and then added.

[0107] Comparative Example 9

[0108] Different from Example 1, the ferrous sulfate solution is not added to the preliminarily screened sludge through a six-way valve injector first. Instead, the ferrous sulfate solution is first introduced into the pipeline, and after 10 minutes of introduction, the hydrogen peroxide solution is introduced while the ferrous sulfate solution continues to be introduced.

[0109] Comparative Example 10

[0110] Different from Example 1, during the treatment process, the injection port of the chemical reagent is not at the connection between the converging section and the throat of the Venturi structure pipeline, but is set at the front end of the converging section.

[0111] Comparative Example 11

[0112] Different from Example 1, in the second chemical addition of S62, the polyaluminum chloride solution is added first, and after reacting for 5 minutes, the polyacrylamide solution is added. Finally, the calcium chloride solution, calcium hydroxide suspension, sodium hypochlorite solution, and potassium permanganate solution are added simultaneously.

[0113] Comparative Example 12

[0114] Different from Example 1, the order of the second chemical addition in S62 and the first chemical addition in S61 is replaced, and the specific addition conditions remain unchanged.

[0115] Comparative Example 13

[0116] Different from Example 1, S3 flocculation screening and S4 primary dehydration are not carried out, and the chemical addition stage is directly entered.

[0117] Comparative Example 14

[0118] Different from Example 1, the S9 steam hydrothermal curing step is not carried out, but air drying and curing are carried out under the sun.

[0119] Experimental Example 2

[0120] The chemical compositions of the chemically treated sludges obtained in Example 1, 5, 6 and Comparative Examples 6 - 13 were tested, and the test results are shown in Tables 6 and 7.

[0121] Table 6 Substance content of chemically treated sediment in Examples 1, 5, 6 and Comparative Examples 7-8

[0122]

[0123] Table 7 Substance content of chemically treated sediment in Comparative Examples 9-13

[0124]

[0125] The sediment obtained by the process of the present invention meets the requirements for substance content under the conditions of Examples 1, 5, and 6. In S62, the oxidant is first reacted for a sufficient time, so that the subsequently added polyaluminum chloride solution and polyacrylamide solution can exert a good flocculation effect, and the fine particles in the sediment are condensed and settled through adsorption bridging, electrical neutralization, and other effects. Metal ions will be removed as these particles flocculate and settle; the flocs formed by the flocculant can adsorb organic compounds, causing them to precipitate with the flocs; they can also condense tiny particles containing E. coli together and remove them through subsequent filtration and other operations; in Comparative Example 6, the reaction time is too short, and the oxidant produces an oxidative decomposition effect on the flocculant, thereby reducing the removal effect of metals, pesticides, organic matter, and E. coli. In Comparative Example 7, the drag reducer polyethylene oxide solution and the cationic polyacrylamide solution are mixed in equal volumes and then added, which destroys the synergistic effect of step-by-step addition through a six-way valve injector. When the two are mixed in advance, their polymer chains will entangle with each other. The cationic groups of cationic polyacrylamide attract polyethylene oxide molecular chains through electrostatic action, bringing the distance between the molecular chains closer, and then flocculation occurs. In sediment treatment, this flocculation may cause flocs to form prematurely and too large, which is not conducive to uniform dispersion in the sediment, reducing the wrapping and flocculation effect on the sediment particles; the cationic groups of cationic polyacrylamide will hydrolyze in aqueous solution, creating an acidic environment. The presence of metal ions in the sediment after a single dosing will catalyze the degradation reaction of polyethylene oxide. The acidic environment generated by the hydrolysis of cationic polyacrylamide may also accelerate the breakage of polyethylene oxide molecular chains, reducing its molecular weight, thereby weakening the drag reduction performance of polyethylene oxide. The flocculation and sedimentation of metal ions are affected, and the content of metals such as total zinc, total cadmium, and total mercury increases. This addition method makes the flocculant unable to effectively adsorb organic compounds, resulting in an increase in the content of organic compounds, such as glyphosate and dichlorvos. Comparative Example 8 Because the Fenton reagent is mixed in advance, hydrogen peroxide and ferrous ions generate hydroxyl radicals in advance, which cannot be effectively oxidized subsequently. Therefore, the removal effect of organic compounds decreases, and the removal effect on metal elements is not significant. In Comparative Example 9, ferrous sulfate solution was first introduced and then hydrogen peroxide solution was introduced, which changed the process of the Fenton reaction. Excessive ferrous ions consumed the oxidant in the system, reducing the removal effect of organic matter such as glyphosate and dichlorvos.In Comparative Example 10, the injection port is arranged at the front end of the tapered section, which changes the mixing and reaction environment of the chemical reagent in the Venturi-structured pipeline, resulting in a decrease in the removal effect of substances. In the Venturi structure, when the fluid flows through the tapered section, the flow rate gradually increases and the pressure gradually decreases. At the throat, the flow rate reaches the maximum and the pressure reaches the minimum. Adding reagents at the tapered section and the throat can utilize this high-speed and low-pressure environment to quickly disperse the reagents. The low-pressure environment helps the reagents to come into full contact with the sediment, avoiding local aggregation of the reagents. The special flow pattern at the tapered section and the throat can generate strong turbulence and shear force, which can quickly disperse the added reagents and mix them fully with the sediment, improving the contact treatment effect between the chemical reagent and the sediment. In Comparative Example 11, polyaluminum chloride solution is added first, and polyacrylamide solution is added after 5 minutes of reaction. The two form a complex, resulting in a decrease in flocculation ability. Then, substances such as oxidants are added, reducing the removal effect of substances. The added calcium ions preferentially precipitate some heavy metals, reducing the consumption of oxidants. PAC is added after the oxidation reaction to avoid being oxidized and decomposed. However, the addition sequence in Comparative Example 11 is opposite to that in Example 1, so the removal effect of substances decreases. In Comparative Example 12, the removal effect of substances is the worst. In the S61 stage, organic matter and exchangeable heavy metals are removed through Fenton reaction and chelation. S62 is carried out first, and Ca(OH)2 precipitation wraps the pollutants, hindering the oxidation / chelation reaction, and the treatment efficiency drops precipitously. In Comparative Example 13, S3 flocculation screening and S4 primary dehydration are not carried out, and it directly enters the dosing stage, interfering with the removal of metals, organic pesticides, organic compounds, and Escherichia coli.

[0126] Experimental Example 3

[0127] Test of metal migration content: The solidified sediment obtained in Example 1 and Comparative Example 14 was crushed and ground, and passed through a 200-mesh sieve. An acetic acid solution with a pH of 2.88 was used as the extraction solution, and the solid-liquid ratio (w / v) was 1:20. After oscillating and extracting for 18 h, the metal substance content was as shown in Table 8. The migration limits of zinc, chromium, cadmium, nickel, and lead in SW-846 are 25 mg / Kg, 5 mg / Kg, 0.5 mg / Kg, 1 mg / Kg, and 5 mg / Kg, respectively.

[0128] Table 8 Metal migration test results

[0129]

[0130] Under the steam hydrothermal curing in the harmless treatment process of river and lake sediment, under the conditions of Example 1, the migration amount of zinc is 21.1 mg / Kg, the migration amount of chromium is 3.74 mg / Kg, the migration amount of cadmium is 0.12 mg / Kg, the migration amount of nickel is 0.64 mg / Kg, and the migration amount of lead is 2.8 mg / Kg. In Comparative Example 14, no heat curing is carried out, and the migration amount of metals increases. By setting the steam curing conditions at 280 °C, the metals in the solidified sediment are converted from acetic acid-extractable state, reducible state and oxidizable state to residual state, and the stable metals are not easily migrated out of the solidified sediment, thus reducing environmental pollution.

[0131] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A harmless treatment process for river and lake bottom mud, characterized in that: The harmless treatment process includes: Flocculation and screening: A Venturi-structured pipeline is provided in front of the pretreatment tank. The Venturi-structured pipeline is divided into a converging section, a throat, and a diverging section. A six-way valve type sampler is provided at the connection between the converging section and the throat. The interfaces are A, B, C, D, E, and F in clockwise order. In working mode one, B is connected to C, and F - A - D - E are connected in sequence. The polyethylene oxide solution is pumped in from F, passes through A and D in sequence, and is pumped into the Venturi-structured pipeline from E. Then it is switched to working mode two, connected in the manner of D - C - B - A - D, E is connected to F, the polyacrylamide solution is pumped in from C, and is pumped into the Venturi-structured pipeline from C to obtain the pretreatment sludge. Primary dehydration: The pretreatment sludge is dehydrated successively through a screw extrusion dehydrator and a belt filter press. Primary dosing: Chemicals are added to the dehydrated pretreatment sludge. In working mode one, the hydrogen peroxide solution is pumped in from F, passes through A and D in sequence, and is sealed by E. Then it is switched to working mode two, the ferrous sulfate solution is pumped in from C, and the hydrogen peroxide solution and the ferrous sulfate solution between A and D are mixed at C and pumped into the connection between the converging section and the throat of the Venturi-structured pipeline. The composite NH2-MIL-ONE zero one suspension, the dithiocarbamate solution, the thiocarboxylic acid chitosan solution, and the activated carbon suspension are added successively through another pipeline. Secondary dosing: The calcium chloride solution, the calcium hydroxide suspension, the sodium hypochlorite solution, and the potassium permanganate solution are added simultaneously. After reacting for 1 h, the polyaluminum chloride solution is added. After the reaction, the polyacrylamide solution is added to obtain the chemically treated sludge. The preparation method of composite NH2-MIL-101 is as follows: Weigh 0.1 mol of terephthalic acid and 0.1 mol of 2-aminoterephthalic acid, and dissolve them together in 1000 mL of N,N-dimethylformamide to form a mixed solution A; Weigh 0.1 mol of FeCl3 ·6H2O and dissolve it in 50 mL of DMF to form solution B; Slowly add the solution B to the solution A, stir evenly, transfer it to a reaction kettle, and react at 180 °C for 36 h; After the reaction is completed, naturally cool it to room temperature to obtain NH2-MIL-101 crystals, and obtain NH2-MIL-101 by centrifugation, washing with DMF and ethanol, and drying; Weigh 10 g of the NH2-MIL-ONE zero one and 20 g of iron oxide nanoparticles, disperse them in 1000 mL of deionized water, and ultrasonically treat for 45 min to make the iron oxide nanoparticles evenly adsorbed on the surface of the NH2-MIL-ONE zero one. Then add 0.15 g of sodium persulfate. Stir and react at 40 °C for 18 h to cause the sodium persulfate to undergo a chemical bonding reaction with the amino group or other active sites on the surface of the NH2-MIL-ONE zero one. At the same time, the iron oxide nanoparticles are also combined with the NH2-MIL-ONE zero one through physical adsorption and chemical reactions to form a composite product. After the reaction is completed, the product is separated by centrifugation, washed with the deionized water and ethanol, and dried at 70 °C to obtain the composite NH2-MIL-ONE zero one.

2. The harmless treatment process for river and lake bottom mud according to claim 1, characterized in that, The preparation method of thiocarboxylic acid chitosan is as follows: Dissolve 65 g of chitosan with a deacetylation degree of 90% in 1000 mL of acetic acid solution with a mass concentration of 5% to obtain a chitosan solution. Dissolve 76.2 g of thioacetic acid in methanol to obtain a thioacetic acid solution with a mass fraction of 1 mol / L. The chitosan solution is dropped into 200 mL of the thioacetic acid solution at a speed of 5 drops / s and reacted at 45 °C for 5 h to obtain a thiocarboxylic acid chitosan solution. Then it is filtered, washed with water, and dried to obtain the thiocarboxylic acid chitosan.

3. The harmless treatment process for river and lake bottom sludge according to claim 1, wherein: Calculated based on milligrams per liter of the chemically treated sludge; In the first chemical addition, the ratio of the polyethylene oxide solution to the chemically treated sludge is 10 - 15:1; the ratio of the polyacrylamide solution to the chemically treated sludge is 150 - 250:1; the ratio of the hydrogen peroxide solution to the chemically treated sludge is 180 - 220:1; the ratio of the ferrous sulfate solution to the chemically treated sludge is 450 - 500:1; the ratio of the composite NH2-MIL-101 suspension to the chemically treated sludge is 260 - 320:1; the ratio of the dithiocarbamate solution to the chemically treated sludge is 4800 - 5100:1; the ratio of the thiocarboxylic acid chitosan solution to the chemically treated sludge is 800 - 1050:1; In the second chemical addition, the ratio of the calcium chloride solution to the chemically treated sludge is 90 - 150:1; the ratio of the calcium hydroxide suspension to the chemically treated sludge is 45 - 60:1; the ratio of the sodium hypochlorite solution to the chemically treated sludge is 3500 - 4000:1; the ratio of the potassium permanganate solution to the chemically treated sludge is 1800 - 2200:1; the ratio of the polyaluminum chloride solution to the chemically treated sludge is 130 - 150:1; the ratio of the polyacrylamide solution to the chemically treated sludge is 40 - 60:

1.

4. The harmless treatment process of river and lake bottom sludge according to claim 1, characterized in that: In the second chemical addition, in working mode one, the polyaluminum chloride solution is pumped in by F, passes through A and D in sequence, and is sealed by E; when switched to working mode two, the polyacrylamide solution is pumped in by C, the polyaluminum chloride solution and the polyacrylamide solution are mixed at C, and finally pumped into the venturi-structured pipeline to obtain the chemically treated sludge.

5. A harmless treatment process for river and lake bottom sludge according to claim 1, characterized in that: The harmless treatment process further includes hydrothermal curing; the conditions for the hydrothermal curing are: using steam to perform thermal curing on the die-casting sludge to obtain the cured sludge.

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