A method for desalination of high-salt cow manure

Abstract

The application discloses a high-salt dairy cow excrement and urine desalination method, and belongs to the technical field of environmental protection and resource utilization. The desalination method comprises the following steps: after solid-liquid separation of dairy cow excrement and urine, a chemical precipitant is added to the separated liquid urine for chemical precipitation, and then membrane filtration and electrodialysis are performed to obtain desalted liquid urine; crushed crop straws are added to the separated solid manure residue, the desalted liquid urine is sprayed after mixing, compost fermentation is performed, and salt in the solid manure residue is removed by spraying clean water regularly during the fermentation process, so that low-salt solid products are finally obtained; and the molar ratio of calcium hydroxide to sodium carbonate in the chemical precipitant is 1:(1-2). The desalination method can effectively remove salt in high-salt dairy cow excrement and urine, has high desalination efficiency, and has stable treatment effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environmental protection and resource utilization, in particular to a desalination method of high-salt cow dung and urine. BACKGROUND

[0002] In modern cow breeding, due to the use of feed additives and specific breeding environment, the salt content (sodium chloride, magnesium sulfate and phosphate) in cow dung and urine is often high. If the high-salt cow dung and urine is directly discharged without proper treatment, it will not only cause serious salt pollution to the surrounding soil and water body, destroy the ecological balance, but also limit its resource utilization in agricultural production.

[0003] Traditional desalination technologies, such as evaporation pond method and chemical precipitation method, often require a long treatment period and a large area of land occupation, which is difficult for the rapidly increasing cow farms to timely process a large amount of dung and urine, resulting in an increase in the risk of accumulation and environmental pollution. Advanced desalination technologies, such as reverse osmosis and electrodialysis, have high processing efficiency, but the initial equipment investment and operation and maintenance costs are huge. In the above processes, the power consumption accounts for a large proportion, and long-term operation is a heavy economic burden for the farm. Some chemical treatment methods can effectively remove salt, but harmful chemicals may be used or produced in the process, which may cause soil and water pollution if not properly disposed of, and even affect the safety of crops and human health. At the same time, waste disposal is also a difficult problem.

[0004] In view of the problems existing in the prior art, it is an important link to explore and develop a new, efficient, low-cost and environmentally friendly desalination technology for cow dung and urine, which is also an important link to reduce costs, reduce environmental side effects, realize efficient recycling of dung and urine resources, and promote the sustainable development of the breeding industry. SUMMARY

[0005] The purpose of the present application is to provide a desalination method of high-salt cow dung and urine to solve the problems existing in the prior art. The desalination method provided by the present application can effectively remove the salt in high-salt cow dung and urine, has high desalination efficiency and stable treatment effect.

[0006] To achieve the above purpose, the present application provides the following solutions:

[0007] The present application provides a desalination method of high-salt cow dung and urine, comprising the following steps:

[0008] After the cow dung and urine are subjected to solid-liquid separation, a chemical precipitant is added to the separated liquid urine for chemical precipitation, and then membrane filtration and electrodialysis are performed to obtain desalted liquid urine;

[0009] The pulverized crop straw is added to the separated solid dung residue, the desalted liquid urine is sprayed after mixing, compost fermentation is carried out, and the salt in the solid dung residue is removed by spraying clean water regularly during the fermentation process, so that a low-salt solid product is finally obtained.

[0010] The molar ratio of calcium hydroxide and sodium carbonate in the chemical precipitant is 1:(1-2).

[0011] Further, when the chemical precipitant is added to the separated liquid urine, the amount-of-substance ratio of calcium ions to magnesium ions in the urine is 1:1.

[0012] Further, the pressure of the membrane filtration is 1.5-2.0 MPa, and the filtration time is 1-1.5 h.

[0013] Further, the electric field strength of the electrodialysis is 20-25 V / cm, and the time is 2-2.5 h.

[0014] Further, the mass ratio of the solid dung residue to the crop straw is 5:(2-3).

[0015] Further, the height of the compost is 2 m.

[0016] Further, the fermentation time is 15 days, and the temperature is 50 DEG C.

[0017] Further, the compost fermentation is turned over every 2 days.

[0018] Further, the clean water is sprayed every 4 days.

[0019] The present application discloses the following technical effects:

[0020] The present application adopts the technology of combining electrodialysis and membrane filtration, which can effectively remove the salt in high-salt cow dung and urine, has high desalination efficiency, stable treatment effect, and environmental protection and energy saving in the whole desalination process, without secondary pollution, and the purified liquid and concentrated liquid after treatment can be reasonably utilized to realize the recycling of resources.

[0021] The method of the present application is simple to operate, low in running cost, and easy to popularize and apply in actual production. DETAILED DESCRIPTION

[0022] The present application will now be described in detail with reference to a number of exemplary embodiments, which should not be considered as limiting the present application, but rather as being illustrative of certain aspects, features and embodiments of the present application.

[0023] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. Additionally, for a range of values of, for example, concentration, intensity, and the like, every intermediate value of that range is specifically contemplated as being included in the present application. The upper and lower limits of these intervening values are also contemplated in the same way, subject to any specifically excluded range in the stated disclosure and claims. These smaller ranges are not admitted to be prior art by virtue of their inclusion in the described range.

[0024] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned herein are incorporated by reference to disclose and describe the methods and / or materials in connection with which the documents are cited. In case of conflict, the content of the present specification will control.

[0025] Various modifications and changes can be made to the specific embodiments of the present application described herein without departing from the scope or spirit of the application. Other embodiments of the application will be apparent to those of ordinary skill in the art from the description and examples presented herein. The description and examples are illustrative only.

[0026] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", "contains", "containing", or variations thereof, are intended to be open-ended terms that mean including, but not limited to.

[0027] The present application takes a large-scale dairy farm in Yinchuan City, Ningxia Hui Autonomous Region as an experimental site to collect the cow urine and dung in the farm. The collected cow urine and dung samples are randomly divided into 6 parts, and the desalination method of the present application examples 1-3 and comparative examples 1-3 is used to desalinate the cow urine and dung in the farm.

[0028] Example 1 A desalination method of high-salt cow urine and dung

[0029] (1) Pretreatment

[0030] The collected high-salt cow urine and dung is subjected to solid-liquid separation to obtain solid dung residue and liquid urine. The solid dung residue mainly contains undigested fiber and organic matter, etc., while the liquid urine dissolves a large amount of salt and other water-soluble substances.

[0031] (2) Chemical precipitation

[0032] Chemical precipitants (prepared by calcium hydroxide and sodium carbonate according to the molar ratio of 1:1) are added according to the molar ratio of calcium ions and magnesium ions in urine as 1:1, and stirred thoroughly to ensure uniform contact between the precipitants and the ions in the solution, and to promote the progress of the precipitation reaction. After stirring is completed, the reaction is carried out for 0.5 h. Through this step, most of the calcium and magnesium ions in the liquid urine can be effectively removed, reducing the difficulty and cost of subsequent treatment. The reactions involved in the chemical precipitation process are as follows:

[0033] Ca(OH)2+Mg 2+ →Ca 2+ +Mg(OH)2↓

[0034] Na2CO3+Ca 2+ →2Na + +CaCO3↓

[0035] (3) Membrane filtration

[0036] The liquid urine treated by chemical precipitation is filtered through a nanofiltration membrane filtration system. The nanofiltration membrane has a unique pore size structure and selective separation performance, which can block larger molecular weight organic matter and multivalent ions, while allowing monovalent ions and small molecule substances to pass through. In the filtration process, the salt, residual organic matter and other impurities in the liquid urine are further removed, improving the purity and quality of the liquid urine. The pressure during membrane filtration is 1.5 MPa, and the treatment time is 1.5 h.

[0037] (4) Electrodialysis

[0038] The liquid urine filtered by the nanofiltration membrane is sent to the electrodialysis device for desalination treatment. The electrodialysis device is composed of alternating arrangement of cation and anion exchange membranes, and under the action of direct current, the anions and cations in the solution move to the anode and cathode respectively. Cations pass through the cation exchange membrane, and anions pass through the anion exchange membrane, thereby realizing the separation and removal of salt. This process can efficiently reduce the salt content in the liquid urine to achieve the purpose of desalination. In the process of electrodialysis, the electric field strength is 20 V / cm, and the treatment time is 2 h.

[0039] (5) Solid manure residue treatment

[0040] The solid manure residue separated in step (1) is treated by composting.

[0041] The solid manure separated in step (1) is added with crop straw crushed to a length of less than 5 cm (mass ratio of solid manure to crop straw is 5:3), and then the desalted liquid urine prepared in step (4) is sprayed thereon to perform compost fermentation, with a stacking height of 2 m, a fermentation time of 15 days, a fermentation temperature of 50°C, and turning over every 2 days to increase the air permeability and uniformity of the stack and promote the activity of microorganisms. Meanwhile, an appropriate amount of water is sprayed every 4 days to fully dissolve the salt in the manure. After the composting is completed, the compost product is washed with clean water to further remove the salt therein, and a low-salt solid product is obtained. The wastewater from washing the manure is collected and mixed with the liquid urine separated in step (1) to perform the recycling treatment of steps (2)-(5).

[0042] Example 2: A desalination method for high-salt cow urine and manure

[0043] (1) Pretreatment

[0044] The collected high-salt cow urine and manure is subjected to solid-liquid separation to obtain solid manure and liquid urine.

[0045] (2) Chemical precipitation

[0046] A chemical precipitant (prepared from calcium hydroxide and sodium carbonate at a molar ratio of 1:1.5) is added according to a molar ratio of calcium ions to magnesium ions in the urine of 1:1, and is fully stirred to ensure uniform contact between the precipitant and the ions in the solution and promote the precipitation reaction. After stirring, the reaction is performed for 0.75 h.

[0047] (3) Membrane filtration

[0048] The liquid urine treated by chemical precipitation is filtered through a nanofiltration membrane filtration system. The pressure during membrane filtration is 2.0 MPa, and the treatment time is 1 h.

[0049] (4) Electrodialysis

[0050] The liquid urine filtered by the nanofiltration membrane is sent to an electrodialysis device for desalination treatment. During electrodialysis, the electric field strength is 25 V / cm, and the treatment time is 2.5 h.

[0051] (5) Solid manure treatment

[0052] The solid manure separated in step (1) is subjected to composting treatment.

[0053] The solid manure separated in step (1) is added with crop straw crushed to a length of less than 5 cm (mass ratio of solid manure to crop straw is 5:2), and the desalted liquid urine prepared in step (4) is sprayed thereon after being uniformly mixed, and compost fermentation is performed, with a stacking height of 2 m, a fermentation time of 15 days, a fermentation temperature of 50°C, and turning over every 2 days to increase the air permeability and uniformity of the stack and promote the activity of microorganisms. Meanwhile, an appropriate amount of water is sprayed every 4 days to fully dissolve the salt in the manure. After the composting is completed, the compost product is rinsed with clean water to further remove the salt therein, and a low-salt solid product is obtained. The wastewater from rinsing the manure is collected and mixed with the liquid urine separated in step (1) to perform the recycling treatment of steps (2)-(5).

[0054] Example 3: A desalination method for high-salt cow urine and dung

[0055] (1) Pretreatment

[0056] The collected high-salt cow urine and dung is subjected to solid-liquid separation to obtain solid manure and liquid urine.

[0057] (2) Chemical precipitation

[0058] A chemical precipitant (prepared from calcium hydroxide and sodium carbonate at a molar ratio of 1:2) is added according to a molar ratio of calcium ions to magnesium ions in the urine of 1:1, and is fully stirred to ensure uniform contact between the precipitant and the ions in the solution and promote the precipitation reaction. After stirring, the reaction is performed for 0.5 h.

[0059] (3) Membrane filtration

[0060] The liquid urine after the chemical precipitation treatment is filtered through a nanofiltration membrane filtration system. The pressure during the membrane filtration is 1.5 MPa, and the treatment time is 1 h.

[0061] (4) Electrodialysis

[0062] The liquid urine after the nanofiltration membrane filtration is sent to an electrodialysis device for desalination treatment. In the electrodialysis process, the electric field strength is 20 V / cm, and the treatment time is 2.5 h.

[0063] (5) Solid manure treatment

[0064] The solid manure separated in step (1) is subjected to composting treatment.

[0065] The solid fecal residue separated in step (1) is added with crop straw crushed to a length of less than 5 cm (mass ratio of solid fecal residue to crop straw is 5:3), and then the desalted liquid urine prepared in step (4) is sprayed thereon after being uniformly mixed, and compost fermentation is carried out, with a stacking height of 2 m, a fermentation time of 15 days, a fermentation temperature of 50°C, and turning over every 2 days to increase the air permeability and uniformity of the stack and promote the activity of microorganisms. Meanwhile, an appropriate amount of water is sprayed every 4 days to fully dissolve the salt in the fecal residue. After the composting is completed, the compost product is washed with clean water to further remove the salt therefrom, and a low-salt solid compost product is obtained. The wastewater from washing the fecal residue is collected and mixed with the liquid urine separated in step (1) for cyclic treatment according to steps (2)-(5).

[0066] Comparative Example 1

[0067] The same as in Example 2, except that the membrane filtration step in step (3) is omitted.

[0068] Comparative Example 2

[0069] The same as in Example 2, except that in step (2), the chemical precipitant is prepared from calcium hydroxide and sodium carbonate at a molar ratio of 1.5:1.

[0070] Comparative Example 3

[0071] The same as in Example 2, except that after the chemical precipitation in step (2) is completed, the product is first subjected to electrodialysis in step (4) and then membrane filtration in step (3).

[0072] Effect verification

[0073] 1. Desalination effect of liquid urine

[0074] In the desalination methods of Examples 1-3 and Comparative Examples 1-3 of the present application, the characteristic parameters of the liquid urine after desalination treatment in steps (1)-(4) are shown in Table 1.

[0075] Table 1. Characteristic parameters of liquid urine before and after desalination

[0076]

[0077] As shown in Table 1, the salt content of the cow fecal urine treated by Examples 1-3 of the present application is significantly reduced, and the salt removal rate in the liquid urine reaches more than 86%.

[0078] 2. Composting effect of solid fecal residue

[0079] The solid compost products prepared in Examples 1-3 and Comparative Examples 1-3 are used as base fertilizer and applied to corn fields at a usage of 80 kg / acre, and other management methods are the same, and the final corn yield per acre is counted, and the results are shown in Table 2.

[0080] Table 2 Corn yield per acre

[0081] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Yield per mu, kg 1086 1120 1103 739 847 880

[0082] The above embodiments are only to describe the preferred modes of the present application, and are not intended to limit the scope of the present application. Any modification and improvement made by those skilled in the art to the technical solutions of the present application without departing from the design spirit of the present application shall fall within the protection scope of the present application.

Claims

1. A method for desalination of high-salinity dairy manure, characterized by, The method comprises the following steps: After solid-liquid separation of cow urine and feces, a chemical precipitant is added to the separated liquid urine for chemical precipitation, and then membrane filtration and electrodialysis are performed to obtain desalted liquid urine; The pulverized crop straw is added to the separated solid manure residue, the desalted liquid urine is sprayed after mixing, and composting fermentation is performed, and clean water is sprayed regularly during the fermentation process to remove salt in the solid manure residue, and finally a low-salt solid product is obtained. The molar ratio of calcium hydroxide to sodium carbonate in the chemical precipitant is 1:(1-2).

2. The desalination method of claim 1, wherein, When the chemical precipitant is added to the separated liquid urine, the amount-of-substance ratio of calcium ions to magnesium ions in the liquid urine is 1:

1.

3. The desalination method of claim 1, wherein, The pressure of the membrane filtration is 1.5-2.0 MPa, and the filtration time is 1-1.5 h.

4. The desalination method of claim 1, wherein, The electric field strength of the electrodialysis is 20-25 V / cm, and the time is 2-2.5 h.

5. The desalination method of claim 1, wherein, The mass ratio of the solid manure residue to the crop straw is 5:(2-3).

6. The desalination method of claim 1, wherein, The height of the composting is 2 m.

7. The desalination method of claim 1, wherein, The fermentation time is 15 days, and the temperature is 50℃.

8. The desalination method of claim 1, wherein, The composting is turned over every 2 days during the fermentation process.

9. The desalination method of claim 1, wherein, The regular spraying of clean water is spraying of clean water every 4 days.

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