Conditioner for river and lake dredged sediment geotube dewatering and simultaneous fermentation and preparation method thereof

Abstract

The application discloses a conditioner for sludge dewatering and synchronous fermentation and a preparation method thereof, and the conditioner is granular and sequentially comprises an inner core, an outer shell and a coating from inside to outside, wherein the mass fraction of the inner core is 1.5-2 parts, the inner core is pressed from coconut shell, and the density of the pressed coconut shell is 0.45-0.50 g / cm 3 ; the outer shell is composed of natural sand, corn shaft powder and a compound microbial agent, and the mass fractions of the three are 6-8 parts, 2-2.5 parts and 0.5-1 part respectively, wherein the natural sand has a fineness modulus of 2.5-3.0, and the mass fraction ratio of the inner core to the outer shell is 1:(5-6); the compound microbial agent is composed of streptococcus thermophilus and thermophilic actinomycetes, and the mass ratio of the two is 1:1; and the coating is composed of ethylene-vinyl acetate copolymer and polyvinyl alcohol, and the mass fractions of the two are 0.6-0.8 parts and 0.15-0.2 parts respectively. The conditioner can significantly shorten the sludge dewatering period and reduce the comprehensive treatment cost of the sludge.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of river and lake sediment treatment and disposal, in particular to a conditioner for dewatering and simultaneous fermentation of river and lake dredged sediment in geotextile tubes and a preparation method thereof. BACKGROUND

[0002] Ecological dredging is an important means to remove internal source pollution in rivers and lakes, but dredging will inevitably produce a large amount of high-moisture sediment. The usual treatment method is to dewater and reduce the volume of the sediment before safe landfill, but this treatment method not only occupies the limited capacity of the landfill, but also wastes the sediment resources themselves, because most of the river and lake sediment is rich in organic matter and nitrogen and phosphorus nutrients, and can be used as green planting soil after fermentation treatment, realizing resource utilization.

[0003] Currently, there are related studies on preparing green soil from river and lake sediment, mainly by simply connecting the dewatering process of the sediment and the process of preparing green soil from the fermented sediment, i.e., first dewatering the sediment to the designed moisture content requirement, and then transporting it to the designated site for fermentation treatment. For example, Chinese Patent Publication No. CN113142014A discloses a kind of alkaline river sediment-based garden green soil and its preparation method, which mixes furfural residue, straw powder, chitosan and other materials with the dewatered sediment by plate and frame filter pressing, and then carries out composting fermentation. Chinese Patent Publication No. CN110604031A discloses a method for producing garden plant soilless culture medium by composting river sediment, which adds garden solid waste, mushroom residue, traditional Chinese medicine residue and other materials to the dewatered sediment, and then carries out aerobic fermentation by strip pile or forced aeration type composting, and finally adds perlite, vermiculite and other auxiliary materials to obtain the soilless culture medium. Both methods are for fermentation of dewatered sediment, without considering the mutual reinforcement benefits of dewatering and simultaneous fermentation of the sediment, and there are problems of long construction period, high cost and difficulty in large-scale application.

[0004] The inventors have found that, if the dewatering process of the geotextile tube is used, the fermentation material can be directly filled into the geotextile tube to realize the simultaneous treatment of dewatering and fermentation of the sediment, wherein the fermentation material can promote the reduction of the moisture content of the sediment, and the geotextile tube for dewatering the sediment can provide a place for the sediment fermentation, the whole process can greatly shorten the construction period and reduce the cost of preparing green soil from the sediment. The key to realizing this simultaneous treatment process is to find a fermentation material that can adapt to the dewatering of the sediment, and there is no related research at home and abroad at present. SUMMARY

[0005] To realize the above-mentioned dewatering and simultaneous fermentation technology of the sediment, one object of the present application is to provide a conditioner for dewatering and simultaneous fermentation of river and lake dredged sediment in geotextile tubes, which is simple in process, environmentally friendly and cost-saving.

[0006] Another object of the present application is to provide a preparation method of the conditioner.

[0007] To this end, the present application provides the following technical solutions:

[0008] A conditioner for dewatering and synchronous fermentation of river and lake dredging sludge geotextile bags, the conditioner is granular, sequentially comprising a core, a shell and a coating, wherein:

[0009] The core has a mass fraction of 1.5-2 parts and is pressed from coconut shell, and the density of the pressed coconut shell is 0.45-0.50 g / cm 3 ;

[0010] The shell is composed of natural sand, corn cob powder and a composite microbial agent, and the mass fractions of the three are 6-8 parts, 2-2.5 parts and 0.5-1 part respectively, wherein the natural sand has a fineness modulus of 2.5-3.0, the mass fraction ratio of the core to the shell is 1:(5-6) (the volume ratio of the shell to the core is about 0.65:0.35), and the composite microbial agent is composed of Streptococcus thermophilus and thermophilic actinomycetes, and the mass ratio of the two is 1:1.

[0011] The coating is composed of ethylene-vinyl acetate copolymer and polyvinyl alcohol, and the mass fractions of the two are 0.6-0.8 parts and 0.15-0.2 parts respectively.

[0012] Preferably, the diameter of the conditioner granules is 4-6 mm, and the density is 1.1-1.2 g / cm 3 .

[0013] The coconut shell fiber powder has a moderate degree of decomposition, an ash content ratio of 6-8%, a bulk density of 0.1-0.15 g / cm 3 , and an EC value (salt content) of 1.30-2.60 mS / cm; the coconut shell fiber powder is washed with clean water for 3-5 times, the EC value of the coconut shell is controlled to be ≤0.5 mS / cm, and then the coconut shell is dried to a water content of ≤15%.

[0014] The corn cob powder is obtained by grinding the cob of corn after removing the kernels through a 120-mesh sieve, and has a water content of 3-5 wt%.

[0015] Preferably, the water content of the composite microbial agent is ≤8 wt%, and the effective viable bacterial count is ≥20 billion CFU / gram.

[0016] Preferably, the density of the conditioner granules is 1.1-1.2 g / cm 3 , which is closest to the dredging slurry density, so as to ensure uniform distribution of the conditioner in the slurry and uniformity and sufficiency of the fermentation process.

[0017] A preparation method of the conditioner comprises the following steps:

[0018] S1, core making: the coconut shell is sent to a roller tearing granulator, and is pressed into a spherical shape under a pressure of 2.5-3 Mpa for 5-10 min; the roller tearing granulator can reduce the volume of the coconut shell to 1 / 4-1 / 3 of the original volume, and the roller die diameter can be adjusted in a range of 2 mm-20 cm.

[0019] S2, shell making: the natural sand, corn shaft powder and compound microbial agent are uniformly mixed according to the above-mentioned raw material ratio to obtain a shell material; then the core and the shell material are put into a shot blasting granulator according to a proportion to carry out coating granulation, and the particle diameter is 4-6 mm;

[0020] S3, coating making: the ethylene-vinyl acetate copolymer and polyvinyl alcohol are uniformly mixed according to a ratio, then the particles obtained in the step S2 are added, and the particles are put into a film coating machine to carry out film coating, and the coating thickness is 15-20 mu m.

[0021] The conditioner can be used for dehydrating and synchronously fermenting dredged river and lake sludge (containing about 95% of water, and having a density of 1.12 g / cm 3 ) to prepare green soil, wherein the dredged river and lake sludge contains about 95% of water, and has a density of 1.08 g / cm 3 ); and the conditioner is used in an amount of 1-1.6 kg per square meter of the dredged river and lake sludge.

[0022] According to the requirements of sludge dehydration and preparation of green soil, the conditioner is divided into three layers, and each layer plays a different role, and the specific conditions are as follows:

[0023] The core is selected from compressed and dense coconut shells, which can be rapidly expanded when meeting water, and can absorb 5-10 times of water in volume, so that the water content of the sludge can be adjusted from 85% to 70% or less, so as to meet the subsequent sludge fermentation water content condition; and due to the expansion of the coconut shells, the air permeability of the sludge in the geotube is increased, and the subsequent sludge fermentation ventilation condition is improved; on the other hand, the C / N ratio of the coconut shells is about 120, so that the problem of insufficient carbon source of the sludge in the fermentation process can be solved.

[0024] The shell is composed of natural sand, corn shaft powder and compound microbial agent; the natural sand can be used to improve the infiltration rate index of the green soil prepared from the sludge, because the dredged sludge is mainly silt clay, and the natural infiltration rate value is low, and after the natural sand is introduced, the soil particle size distribution is closer to the natural planting soil; the corn shaft powder in the shell layer plays a role of adhesive to wrap the shell material on the core, and can provide nutrients for the compound microbial agent; and the compound microbial agent in the shell layer is used for the fermentation of the sludge in the geotube.

[0025] Vinyl acetate-ethylene copolymer is used to modify polyvinyl alcohol, effectively improving the water resistance of the film, and the permeability is about 0.66%, which mainly controls the slow entry of water in the sediment into the core layer, ensures the water absorption and swelling of the core after about 2-3 days, and the conditioner cracks.

[0026] Compared with the existing conditioner, the conditioner has the following beneficial effects:

[0027] 1. The conditioner of the present application makes full use of the strong water absorption and high carbon-nitrogen ratio of coconut shell material, realizes the functions of dewatering and synchronous fermentation of dredged sediment. The conditioner is filled into the geotextile tube simultaneously with the slurry, which significantly shortens the dewatering period of the sediment, and completes the fermentation of the sediment in the geotextile tube without the need for additional fermentation equipment. The total period of the traditional geotextile tube dewatering and fermentation process for preparing green soil is at least 3-4 months, while the conditioner of the present application can shorten the total period to 2 months or less.

[0028] 2. The conditioner of the present application makes full use of the bag capacity released by the tail water discharge after the filling of the geotextile tube is completed, and uses the internal space released by the geotextile tube as a fermentation site for the sediment. Compared with the traditional sediment fermentation process for preparing green soil, the conditioner of the present application does not require investment in civil engineering and factory building, significantly reduces the engineering cost of sediment comprehensive treatment, and enhances the market viability and competitiveness of the technology for preparing green soil from sediment.

[0029] 3. The natural sand in the conditioner can promote the survival of bacteria, has a shelf life of more than 1 year under dry and normal temperature conditions, and can improve the physical structure of the green soil prepared from the sediment, increase the permeability, and further improve the quality of the green soil.

[0030] 4. The conditioner of the present application can be applied to the dewatering engineering of geotextile tube, and the conditioner is filled into the geotextile tube simultaneously with the slurry, which can significantly shorten the dewatering period of the sediment, and complete the fermentation of the sediment in the geotextile tube without the need for additional fermentation equipment. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a structural schematic diagram of the conditioner of the present application. DETAILED DESCRIPTION

[0032] The following specific examples further illustrate the conditioner of the present application, but do not mean that the content of the present application is limited to the scope of the examples.

[0033] Example 1

[0034] Based on a dredging engineering of a river in Harbin City, Heilongjiang Province, a dewatering and synchronous fermentation test of sediment geotextile tube was carried out. The water content of the sediment before dewatering was 95%, and the carbon-nitrogen ratio (C / N) in the sediment was 2.5:1. The effective bag capacity of the geotextile tube used in the test was 60m 3, filling slurry 60m 3 , and 240 kg of conditioning agent was added cumulatively during the filling process. The total period of dewatering and fermentation of the bottom sludge was 45 days.

[0035] The conditioning agent for dewatering and synchronous fermentation of the bottom sludge in the embodiment was prepared by the following method:

[0036] ① Core preparation: First, the coconut husk was washed with clean water for 5 times, and the EC value was controlled to be not more than 0.5 mS / cm, and then dried to a water content of 15%, and the dried coconut husk was sent to a roll tearing granulator, and was pressed into a spherical shape with a diameter of 2-4 mm under a pressure of 2.5 Mpa for 8 min, and the density after compression was about 0.45 g / cm 3 ;

[0037] ② Shell preparation: The natural sand, corn shaft powder and composite microbial agent were mixed uniformly according to a ratio of 6 parts, 2 parts and 0.5 parts, and then 1 part of the core material and 6 parts of the shell material were put into a shot blasting granulator for coating and granulation, and the particle diameter was 4-6 mm;

[0038] ③ Film preparation: The ethylene-vinyl acetate copolymer and polyvinyl alcohol were mixed uniformly according to a mass ratio of 0.6:0.15, and then the particles obtained in step ② were added and put into a film coating machine for film coating, and the film coating thickness was 20 μm.

[0039] The structure of the conditioning agent prepared by the above method is shown in Figure 1 .

[0040] The action mechanism of the conditioning agent of the present application is as follows:

[0041] The conditioning agent of the present application is mainly used in the dewatering engineering of the geotextile tube, and mainly plays a role in two stages.

[0042] The first stage is the dewatering stage of the bottom sludge. The flocculating agent and the conditioning agent enter the geotextile tube together with the dredged slurry, and the flocculating agent plays a role within 2-3 days after the filling of the geotextile tube is completed. During this period, the dewatering of the bottom sludge relies on the self-filtration of the geotextile tube, and the water content of the bottom sludge can be reduced to about 85%, at which time the surface of the geotextile tube is no longer obviously drained. After entering the geotextile tube for 3-5 days, the film on the surface of the conditioning agent gradually melts, the coconut husk core begins to contact water and swell, and the conditioning agent rapidly disintegrates. After absorbing water, the coconut husk can swell to 5-10 times the original volume, and each kilogram of conditioning agent can theoretically absorb about 20 L of water, and the water content of the bottom sludge will be reduced to within 70%.

[0043] The second stage is a sediment fermentation stage. The coconut husk can establish a support skeleton inside the soil while absorbing water, which can effectively improve the air permeability of the dredged sediment and create an environment for aerobic fermentation of the composite microbial agent. Because the density of the conditioner is close to that of the dredged slurry, the conditioner in the geotube is uniformly dispersed in the sediment, which can ensure the uniformity of fermentation. After 30-45 days, the dredged sediment can be fermented into green planting soil, and finally the bag is broken and sieved.

[0044] After the geotube slurry filling is completed, columnar soil samples are periodically collected from the geotube sleeve, and the sediment moisture content and conditioner state are detected. The sampling frequency is 1 day, 2 days, 3 days, 5 days, 15 days, 30 days, and 45 days, and the results are shown in Table 1. Compared with the traditional geotube dewatering process, the sediment dewatering efficiency is significantly improved (the traditional geotube dewatering to a moisture content of 60% requires 3-6 months), and the sediment moisture content meets the requirements of external transportation and loading at 30 days.

[0045] Table 1 Test Results

[0046] Sampling time (day) Mud water content (%) Conditioner state 1 90.2 Un-disintegrated 2 88.5 Un-disintegrated 3 85.1 Un-disintegrated 5 72.3 Fully disintegrated 15 61.5 Fully disintegrated 30 50.5 Fully disintegrated 45 45.6 Fully disintegrated

[0047] After 45 days, the geotube is broken, the product is crushed, and samples are taken for green soil index detection, as shown in Table 2. The green soil prepared from dredged sediment meets the requirements of “Green Planting Soil” CJ / T340-2016. Compared with the traditional dredged sediment fermentation process (soil infiltration rate is 60-80 mm / h), the soil infiltration rate is significantly improved to 152.44 mm / h.

[0048] Table 2 Test Results

[0049] Serial number Detection index Unit Greening soil after treatment 1 pH Non-dimensional 7.82 2 Salt content g / kg 4.36 3 Organic matter mg / kg 45 4 Soil infiltration rate mm / h 152.44 5 Hydrolytic nitrogen mg / kg 145 6 Available phosphorus mg / kg 9.5 7 Available potassium mg / kg 201.3 8 Available magnesium mg / kg 163.1 9 Available calcium mg / kg 301.32 10 Available iron mg / kg 121.12 11 Available copper mg / kg 1.24 12 Available zinc mg / kg 2.49

[0050] Example 2

[0051] Based on the Baiyangdian dredging project in Xiong'an New Area, a sediment geotube dewatering and simultaneous fermentation test was carried out. The sediment moisture content before dewatering was 90%, and the average C / N ratio of the sediment was 3.5:1. The effective utilization bag capacity of the geotube used in the test was 90 m 3 , and the filling slurry was 90 m 3 . During the filling process, 450 kg of conditioner was added cumulatively. The total period of sediment dewatering and fermentation was 42 days.

[0052] The conditioner for sediment dewatering and simultaneous fermentation in this example was prepared by the following method:

[0053] ① Kernel production: First, wash the coconut husk with clean water for 5 times, control the EC value not to exceed 0.5mS / cm, then dry it to a moisture content of 15%. The dried coconut husk is fed into a roller shredder and pressed into balls with a diameter of 2-4mm under a pressure of 2.6Mpa for 10 minutes. The density after compression is about 0.48g / cm 3 ;

[0054] ② Shell production: natural sand, corn cob powder, and composite microbial agent are mixed evenly in a ratio of 7 parts, 2.5 parts, and 0.9 parts, and then 1 part of kernel material and 6 parts of shell material are put into a shot blasting granulator for shelling and granulation. The particle diameter is 4-6mm.

[0055] ③ Coating preparation: vinyl acetate-ethylene copolymer and polyvinyl alcohol are evenly mixed in a ratio of 0.6:0.15 by mass, and then the particles obtained in step ② are added and placed in a coating machine for coating. The coating thickness is 20 μm.

[0056] After the geotube bag was filled with mud, columnar soil samples were collected regularly from the cuff of the geotube bag to test the moisture content of the bottom mud and the status of the conditioner. The sampling frequency was 1 day, 2 days, 3 days, 5 days, 15 days, 30 days, and 45 days. The results are shown in Table 3.

[0057] Table 3 Test results

[0058] Sampling time (day) Mud water content (%) Conditioner state 1 89.2 Un-disintegrated 2 87.5 Un-disintegrated 3 84.6 Un-disintegrated 5 68.4 Fully disintegrated 15 59.1 Fully disintegrated 30 53.5 Fully disintegrated 42 41.6 Fully disintegrated

[0059] Compared with the traditional geotube dehydration process, the sludge dehydration efficiency is significantly improved (it takes 3-6 months for the traditional geotube to be dehydrated to a moisture content of 60%), and the sludge moisture content can meet the requirements for external transportation and loading within 30 days.

[0060] After 42 days, the geotube bags were broken open, the products were crushed, and samples were taken for green soil index testing, as shown in Table 4.

[0061] Table 4 Test results

[0062] Serial number Detection index Unit Greening soil after treatment 1 pH Non-dimensional 7.62 2 Salt content g / kg 3.36 3 Organic matter mg / kg 53 4 Soil infiltration rate mm / h 115.13 5 Hydrolytic nitrogen mg / kg 121 6 Available phosphorus mg / kg 7.7 7 Available potassium mg / kg 185.1 8 Available magnesium mg / kg 173.3 9 Available calcium mg / kg 255.14 10 Available iron mg / kg 110.32 11 Available copper mg / kg 1.05 12 Available zinc mg / kg 2.15

[0063] All indicators of the greening soil prepared from desilted sediment meet the requirements of "Greening Planting Soil" CJ / T340-2016. Compared with the traditional desilted sediment fermentation process (soil infiltration rate of 60-80mm / h), the soil infiltration rate is significantly improved to 115.13mm / h.

Claims

1. A conditioning agent for dehydration and simultaneous fermentation of geotechnical tube bags for dredged mud from rivers and lakes, characterized by: The conditioner is in granular form and comprises a core, an outer shell and a coating from the inside out, wherein: The core has a mass fraction of 1.5 to 2 parts and is made of coconut husks. The density of the coconut husks after pressing is 0.45 to 0.50 g / cm 3 ; The shell is composed of natural sand, corn cob powder, and a composite bacterial agent, with the mass proportions of the three being 6-8 parts, 2-2.5 parts, and 0.5-1 parts, respectively. The fineness modulus of the natural sand is 2.5-3.0, and the mass ratio of the kernel to the shell is 1:(5-6). The composite bacterial agent is composed of thermophilic Streptococcus and thermophilic actinomycetes, with the mass ratio of the two being 1:

1. The coating is composed of vinyl acetate-ethylene copolymer and polyvinyl alcohol, and the mass proportions of the two are 0.6-0.8 parts and 0.15-0.2 parts respectively.

2. The conditioning agent according to claim 1, characterized in that: The diameter of the conditioning agent particles is 4~6mm and the density is 1.1~1.2g / cm 3 .

3. The conditioning agent according to claim 1, characterized in that: The coconut husk is prepared from coconut shell fiber powder, the ash ratio of the coconut shell fiber powder is 6% to 8%, and the bulk density is 0.1 to 0.15 g / cm 3 , EC value is 1.30~2.60mS / cm; after washing with clean water 3~5 times, control the EC value of coconut bran to ≤0.5 mS / cm, and then dry it to a moisture content ≤15%.

4. The conditioning agent according to claim 1, characterized in that: The corn cob powder is obtained by grinding corn cobs after removing the kernels and passing them through a 120-mesh sieve, and has a water content of 3-5 wt%.

5. The conditioning agent according to claim 1, characterized in that: The water content of the composite bacterial agent is ≤8wt%, and the effective viable bacteria count is ≥2 billion CFU / g.

6. The conditioning agent according to claim 1, characterized in that: The density of the conditioning agent particles is 1.1-1.2 g / cm 3 .

7. A method for preparing the conditioner according to any one of claims 1 to 6, comprising the following steps: S1, kernel preparation: the coconut husk is fed into a roller shredder pelletizer and pressed into a ball shape at a pressure of 2.5-3 MPa for 5-10 minutes; S2, shell preparation: natural sand, corn cob powder, and composite microbial agent are mixed uniformly according to the raw material ratio to obtain shell material; then the kernel and shell material are placed in a shot blasting granulator according to the proportion to be shelled and granulated, and the particle diameter is 4-6 mm; S3, coating preparation: the vinyl acetate-ethylene copolymer and polyvinyl alcohol are mixed evenly according to a ratio, and then the particles obtained in step S2 are added and placed in a coating machine for coating, with a coating thickness of 15-20 μm.

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