A method for dewatering river and lake bottom sediment, the resulting mud cake, and its applications.

Abstract

This invention provides a method for dewatering river and lake bottom sediment, a mud cake, and its uses. The dewatering method involves mixing algal mud with river and lake bottom sediment and then dewatering the mixture. This method improves the dewatering performance of river and lake bottom sediment while avoiding environmental pollution during the dewatering process. Furthermore, the mud cake and filtrate obtained after dewatering are neutral or weakly alkaline, requiring no further deep treatment. They can be used for planting vegetation, constructing ecological slope protection, and preparing planting soil, thus promoting the resource utilization of bottom sediment and the development of a circular economy.

Description

Technical Field

[0001] This invention relates to the field of sludge treatment, disposal and resource utilization, and in particular to a method for dewatering river and lake bottom sediment, sludge cake and its uses. Background Technology

[0002] Environmental dredging is currently the main method for ex-situ remediation of endogenous pollution in rivers and lakes. While it can effectively control endogenous pollution in lakes and lakes, it also generates a large amount of river and lake sediment, requiring significant land resources for sediment disposal sites. However, in my country, the scarcity and contradictions surrounding sediment disposal site resources have become a key factor restricting the smooth implementation of environmental dredging projects, hindering the normal progress of comprehensive river and lake management and development. Therefore, a crucial step in the treatment and disposal of river sediment is reducing the high water content in the sediment to decrease its volume and the required storage space. Dewatering is the primary step in the safe treatment and disposal of sediment, mainly referring to the removal of water from sediment flocs, thereby reducing the amount of sediment requiring final disposal and lowering sediment disposal costs. Mechanical dewatering, natural drying, geotextile bag dewatering, and vacuum preloading are some of the commonly used methods for dewatering and solidifying bottom sediment. However, due to the high hydrophilicity and water retention of bottom sediment in silt layers, there are problems such as "two highs and one low" (high water content, high compressibility, and low permeability) and excessively high N and P concentrations, which bring great difficulties to the dewatering of bottom sediment in actual engineering.

[0003] The water in sediment is divided into bound water and unbound water, with the content of bound water being one of the main factors limiting sediment dewatering capacity. However, due to the strong water-holding capacity of fine sediment particles and the ionization of organic functional groups in the sludge, the sediment surface carries a negative charge, causing electrostatic repulsion between sediment particles. This significantly reduces the dewatering effect. Therefore, conditioning the sediment before dewatering can achieve better results. Currently, deep sediment dewatering often requires the use of sediment dewatering agents such as iron salts and aluminum salts to condition the sediment, releasing capillary water, attached water, and internal water. After improving the sediment's dewatering performance, further dewatering is achieved using equipment such as filter presses.

[0004] Chinese patent CN201910302670.1 discloses a method for the synergistic deep dewatering of cyanobacterial sludge and municipal sludge, comprising the following steps: S1: mixing cyanobacterial sludge and municipal sludge at a dry weight ratio of 1:1 to 1:3; S2: adding quicklime to the mixture of cyanobacterial sludge and municipal sludge, stirring evenly for 0.25 hours; S3: continuing to add polyferric sulfate, ferric chloride, and polyacrylamide, stirring evenly; S4: conveying the prepared mixture of cyanobacterial sludge and municipal sludge to a filter press for filtration. Although this method can solve the problems of difficult dewatering of cyanobacterial sludge and the low calorific value of subsequent incineration of municipal sludge, the method adds a large amount of lime, which pollutes the environment during the dewatering process. Furthermore, the dewatered sludge cake and filtrate are highly alkaline and require further treatment, which is not conducive to the subsequent resource utilization of the bottom sludge.

[0005] Chinese patent CN201910543191.9 discloses an integrated method for the co-treatment of sludge and algal sludge, comprising the following steps: dilution, conditioning, dewatering, drying, and incineration. The method is characterized by a mixing step preceding the dilution step, which involves mixing sludge and algal sludge at an oven-dry weight ratio of 1:1 to 1:3. While this method can solve the problems of difficult dewatering of cyanobacteria sludge and the low calorific value of subsequent incineration of municipal sludge, it actually adds a large amount of lime, causing environmental pollution during dewatering. Furthermore, the dewatered sludge cake and filtrate are highly alkaline and require further treatment, hindering the subsequent resource utilization of the sediment. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for dewatering river and lake bottom sediment, mud cake and its uses, in order to solve the problems in the prior art.

[0007] To achieve the above and other related objectives, the present invention is obtained through the following technical solution.

[0008] This invention provides a method for dewatering river and lake bottom sediment, which involves mixing algal mud with river and lake bottom sediment and then dewatering it.

[0009] Preferably, the water content of the algae mud is 70-95%.

[0010] Preferably, the water content of the river and lake bottom sediment is 90-98%.

[0011] Preferably, the algal mud is obtained by crushing algae.

[0012] More preferably, the algae are selected from one or more of cyanobacteria, red algae, cryptophytes, dinoflagellates, golden algae, yellow algae, diatoms, brown algae, euglenoids, green algae, and charophytes.

[0013] More preferably, the crushing process is performed using one or more of jet, ultrasonic, and high-pressure methods.

[0014] If too much algae mud is used, the organic matter content will be too high, resulting in poor dewatering of the river and lake bottom sediment; if too little algae mud is used, the dewatering effect of the river and lake bottom sediment will also be poor. Preferably, the algae mud and the river and lake bottom sediment are mixed at a dry matter ratio of 1:(1-10). For example, the ratio can be 1:(1-3), 1:(3-5), 1:(5-7), 1:(7-10), and more preferably 1:(3-5).

[0015] Preferably, before dewatering, the river and lake sediment is further conditioned using inorganic flocculants and / or skeleton materials.

[0016] More preferably, the inorganic flocculant is selected from iron salts and / or aluminum salts.

[0017] More preferably, the iron salt is selected from one or more of polyferric chloride, polyferric sulfate, ferric nitrate, ferric chloride, and ferric sulfate.

[0018] More preferably, the aluminum salt is selected from one or more of polyaluminum chloride, polyaluminum sulfate, aluminum chloride, and aluminum sulfate.

[0019] More preferably, the skeleton material is selected from one or more of fly ash, biochar, slag powder, etc.

[0020] More preferably, the particle size of the skeleton material is between 1 mm and 5 mm.

[0021] More preferably, based on the mass of river and lake bottom sediment, the amount of inorganic flocculant added is 5-50‰. For example, it can be 5-10‰, 10-20‰, 20-30‰, or 30-50‰.

[0022] More preferably, based on the mass of river and lake bottom sediment, the amount of skeleton material added is 0.1 to 1‰. For example, it can be 0.1 to 0.5‰ or 0.5 to 1‰.

[0023] Preferably, sedimentation and separation are performed before dehydration.

[0024] More preferably, the settling time is at least 30 minutes.

[0025] More preferably, the sedimentation time is 30–120 min.

[0026] Preferably, the dewatering treatment uses plate and frame dewatering and / or geotextile bag dewatering.

[0027] More preferably, the dehydration pressure is 1.0-1.2 MPa.

[0028] More preferably, the dehydration time is 30–50 min. For example, it can be 30–40 min or 40–50 min.

[0029] The present invention also discloses a mud cake formed by the dehydration method described above.

[0030] Preferably, the moisture content of the mud cake is less than 40%.

[0031] The present invention also discloses the use of the mud cake as described above for planting and constructing ecological slope protection.

[0032] The present invention also discloses the use of algal mud as a dewatering agent for dewatering river and lake bottom sediments, as described above.

[0033] This invention discloses a method for dewatering river and lake bottom sediment, the resulting mud cake, and its uses, which have the following beneficial effects:

[0034] 1) No organic flocculants or strong alkaline compounds such as calcium oxide were added. The use of eco-friendly algae mud improved the dewatering performance of river and lake bottom sediments and also avoided environmental pollution during the dewatering process. Furthermore, the use of algae mud, inorganic flocculants, and skeleton materials on river and lake bottom sediments not only has a synergistic dewatering effect, but also improves the mechanical strength of the mud cakes obtained after dewatering.

[0035] 2) Using algae as raw material, the waste is utilized as a resource. At the same time, the dewatering method has a wide range of applications and is not subject to various restrictions. It can be widely used for the treatment of river and lake bottom sediment. The mud cake and filtrate obtained after dewatering are neutral or weakly alkaline and do not require further deep treatment. They can be used for planting, constructing ecological slope protection, and compounding planting soil, which is conducive to the resource utilization of bottom sediment and the development of the circular economy. Detailed Implementation

[0036] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0037] It should be noted that the process equipment or apparatus not specifically mentioned in the following embodiments are all conventional equipment or apparatus in the art.

[0038] Furthermore, it should be understood that the one or more method steps mentioned in this invention do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated; moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered as within the scope of the invention.

[0039] The algae used in the following embodiments and comparative examples of this application are specifically selected from algae in the riparian zone of Chaohu Lake, which were harvested between August and September, and are mainly blue-green algae.

[0040] Example 1

[0041] This embodiment provides a specific method for dewatering river and lake sediment. The river and lake sediment is from a river and lake in the suburbs of Shanghai (95% water content), and the algae is harvested from Chaohu Lake. The specific steps are as follows:

[0042] (1) The collected algae were crushed and filtered using ultrasound to obtain algal mud (90% water content);

[0043] (2) Mix the algal mud with the river and lake bottom mud in a dry weight ratio of 1:1;

[0044] (3) After settling for 30 minutes, mud and water are separated. The settled sludge is dewatered by a plate and frame filter press with a dewatering pressure of 1.2 MPa and a dewatering time of 40 minutes.

[0045] Example 2

[0046] This embodiment provides a specific method for dewatering river and lake bottom sediment, which is basically the same as that in embodiment 1. The only difference is that in step (2), the algal mud and river and lake bottom sediment are mixed evenly in a dry weight ratio of 1:3.

[0047] Example 3

[0048] This embodiment provides a specific method for dewatering river and lake bottom sediment, which is basically the same as that in embodiment 1. The only difference is that in step (2), the algal mud and river and lake bottom sediment are mixed evenly at a dry weight ratio of 1:5.

[0049] Example 4

[0050] This embodiment provides a specific method for dewatering river and lake sediment. The river and lake sediment is from a river and lake in the suburbs of Shanghai (95% water content), and the algae is harvested from Chaohu Lake. The specific steps are as follows:

[0051] (1) The collected algae are broken down by ultrasound and filtered to obtain algal mud;

[0052] (2) Mix the algal mud with the river and lake bottom mud at a dry weight ratio of 1:5;

[0053] (3) Add polyaluminum chloride and mix well. The amount added is 50‰.

[0054] (4) After settling for 30 minutes, mud and water are separated. The settled sludge is dewatered by a plate and frame filter press. The dewatering pressure is 1.2 MPa and the dewatering time is 40 minutes.

[0055] Example 5

[0056] This embodiment provides a specific method for dewatering river and lake bottom sediment, which is basically the same as that in embodiment 4. The only difference is that in step (2), the algal mud and river and lake bottom sediment are mixed evenly at a dry weight ratio of 1:5; in step (3), polyaluminum chloride and skeleton material are added and mixed evenly, with the addition amount being 50‰ and the addition amount of skeleton material being 1‰.

[0057] Example 6

[0058] This embodiment provides a specific method for dewatering river and lake bottom sediment, which is basically the same as that in embodiment 4. The only difference is that in step (2), the algal mud and river and lake bottom sediment are mixed evenly at a dry weight ratio of 1:10; and in step (3), the amount of polyaluminum chloride added is 5‰.

[0059] Comparative Example 1

[0060] This comparative example is the same as Example 1, except that municipal sludge is used instead of river and lake sediment, and the municipal sludge has a water content of 95%.

[0061] The moisture content of the sludge cakes obtained after dewatering in Examples 1-6 and Comparative Example 1 was tested using the following methods, and the results are shown in Table 1. The river and lake sediments from Examples 1-6 were directly dewatered without conditioning and used as a control experiment. Similarly, the municipal sludge from Comparative Example 1 was directly dewatered without conditioning and used as a control experiment.

[0062] The moisture content test method is as follows: the dewatered mud cake is dried to constant weight at 105-110℃, the weight of the mud cake before and after drying is weighed, and the moisture content is calculated by the calculation formula.

[0063] The calculation formula is: Moisture content of mud cake = (Weight of mud cake before drying - Weight of mud cake after drying) / Initial weight of mud cake * 100%.

[0064] The pH of the filtrates obtained after dehydration of Examples 1-4 and Comparative Example 1 was tested using pH, and the test results are shown in Table 1.

[0065] The shear strength of mud cakes obtained after dewatering treatment of Examples 1-6, Comparative Example 1, original river and lake bottom sediment, and municipal sludge was tested. The test results are shown in Table 1.

[0066] The testing method is as follows:

[0067] Direct shear specimens were collected from the dewatered soil cake using the ring sampler method. After removal, excess soil outside the ring sampler was cleaned, smoothed, and immediately sealed with plastic wrap to prevent moisture evaporation. The direct shear specimens were subjected to a rapid shear test within 24 hours of collection. This test used a ZJ-type strain-controlled direct shear apparatus (four-unit) manufactured by Nanjing Soil Instrument Factory. The vertical pressure was set to 50 kPa, and the shear rate was 0.8 mm / min. The shear strength was automatically collected and generated by a geotechnical testing microcomputer-controlled data acquisition and processing system via sensors.

[0068] Table 1

[0069]

[0070]

[0071] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. The use of algal mud as a dewatering agent for dewatering river and lake bottom sediment, characterized in that, The algae mud is mixed with river and lake bottom sediment and then dehydrated; the water content of the algae mud is 70-95%; the water content of the river and lake bottom sediment is 90-98%; the algae mud and the river and lake bottom sediment are mixed at a dry weight ratio of 1:(1-10), and the algae mud is obtained by crushing algae.

2. The use according to claim 1, characterized in that, The algae are selected from one or more of the following: cyanobacteria, red algae, cryptophytes, dinoflagellates, golden algae, yellow algae, diatoms, brown algae, euglenoids, green algae, and charophytes. And / or, the crushing process may be selected from one or more of jet, ultrasonic and high pressure methods.

3. The use according to claim 1, characterized in that, Before dewatering, the river and lake sediment is further conditioned using inorganic flocculants and / or skeleton materials.

4. The use according to claim 3, characterized in that, The inorganic flocculant is selected from iron salts and / or aluminum salts; And / or, the skeleton material is selected from one or more of fly ash, biochar, slag powder, etc.; And / or, the particle size of the skeleton material is between 1 mm and 5 mm; And / or, based on the mass of river and lake bottom sediment, the amount of inorganic flocculant added is 5 to 50‰; And / or, based on the mass of river and lake bottom sediment, the amount of skeleton material added is 0.1 to 1‰.

5. The use according to claim 1, characterized in that, Before dehydration, sedimentation and separation processes are performed; And / or, the dewatering treatment may be performed using plate and frame dewatering and / or geotextile bag dewatering.

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