A sludge-based water-retaining agent and preparation method thereof

Abstract

The invention discloses a sludge-based water-retaining agent and a preparation method thereof, and relates to the technical field of environmental engineering. The invention pre-treats the sludge by adding a conditioning agent to the sludge, and then uses physical and chemical means to perform elutriation-flocculation-centrifugal-drying on the sludge to prepare a green high-performance sludge-based water-retaining agent, which well realizes the reduction and resource utilization of the excess sludge. The invention has a low economic cost and avoids possible secondary pollution problems, solves the problem of efficient resource utilization of the excess sludge in urban sewage plants, and takes into account the dual indicators of economic benefits and environmental benefits.

Description

Technical Field

[0001] The invention relates to the technical field of environmental engineering, and in particular to a sludge-based water-retaining agent and a preparation method thereof. Background Art

[0002] Soil water conservation is an important measure to maintain ecological balance, improve agricultural production efficiency and ensure sustainable use of water resources. In arid and semi-arid areas, soil moisture is a key factor limiting plant growth and agricultural production. Therefore, soil water conservation is particularly important.

[0003] Soil water-retaining agents are a type of functional polymer materials with strong hydrophilicity and high water absorption and water retention capacity. At present, the water-retaining materials on the market are mainly polyvinyl alcohol, polyacrylamide and polyacrylic acid salts or starch-grafted acrylate materials. Although these materials have the advantages of strong water-retaining performance and long water-retaining life, they are difficult to promote on a large scale in actual use because of the problems such as the biological toxicity of degradation products (such as acrylamide monomer) and the rapid decline of water-retaining effect.

[0004] With the acceleration of urbanization, the demand for urban sewage treatment continues to rise. As an inevitable by-product of sewage biochemical treatment, the output of residual sludge is also increasing. Converting sludge into a soil water retaining agent with high water absorption rate and strong water retention capacity is an effective measure to realize the resource utilization of sludge, reduce sludge volume and improve soil water retention. Summary of the invention

[0005] The purpose of the present invention is to provide a sludge-based water-retaining agent and a preparation method thereof, so as to solve the problems existing in the above-mentioned prior art, quickly break down the bacterial cells in the residual sludge, and efficiently separate and extract EPS to reduce the sludge volume and improve the physical and chemical properties of the sludge, so that the residual sludge is converted into a green bio-based water-retaining agent, thereby providing a new technical means for solving the current problem of reducing and recycling the residual sludge.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] The present invention provides a method for preparing a sludge-based water-retaining agent, comprising the following steps:

[0008] (1) adding polyhexamethylene biguanide to concentrated excess sludge and stirring the mixture to obtain pretreated sludge;

[0009] (2) performing a primary washing on the pretreated sludge to remove fine particles until the viscosity of the supernatant sludge drops below 5.0 mPa·s;

[0010] (3) subjecting the sludge treated in step (2) to ultrasonic treatment;

[0011] (4) washing the sludge after ultrasonic treatment again to obtain liquid phase a and precipitated sludge a;

[0012] (5) washing the precipitated sludge a to obtain a liquid phase b and precipitated sludge b;

[0013] (6) The liquid phase a and the liquid phase b are mixed, tannic acid and polyacrylamide are added to the obtained mixed solution, the solid phase is collected by centrifugation, and dried to obtain the sludge-based water-retaining agent.

[0014] Furthermore, the concentrated excess sludge is concentrated excess sludge from a municipal sewage treatment plant.

[0015] Furthermore, the power of the ultrasonic treatment is 500-1000W.

[0016] Furthermore, the ultrasonic treatment time is 10-15 min.

[0017] Furthermore, the amount of tannic acid added is 2%-5% of the mass of the mixed solution; and the amount of polyacrylamide added is 10-30 mg / L based on the volume of the mixed solution.

[0018] Furthermore, the water used for the primary washing and the secondary washing is the effluent from the sewage treatment plant.

[0019] Furthermore, the moisture content after drying is ≤10%.

[0020] The present invention also provides a sludge-based water-retaining agent prepared by the above preparation method.

[0021] The present invention further provides application of the sludge-based water-retaining agent in soil water retention.

[0022] The residual sludge is mainly composed of bacteria. The main components of the substances secreted outside the cells during the growth and placement of these bacteria are high molecular polymers, including polysaccharides, proteins, nucleic acids, humic acid and other substances. These substances are called extracellular polymeric substances (EPS). EPS can be regarded as a natural high molecular polymer with strong hydrophilicity.

[0023] According to the different degrees of binding between EPS and bacterial cells, it can be further divided into soluble EPS (SolubleEPS), loose EPS (Loosely Bound EPS, LB-EPS) and tight EPS (Tightly Bound EPS, TB-EPS). However, since soluble EPS and LB-EPS are looser in structure and lower in molecular weight than TB-EPS, they are relatively easy to be degraded by microorganisms and are not suitable for making soil water-retaining agents. TB-EPS is bound to the cell wall and has a tighter structure. It is a key component in forming the sludge floc structure and is less susceptible to microbial degradation, making it suitable for preparation as a soil water-retaining agent.

[0024] In order to improve the physical and chemical properties of excess sludge, convert it into a soil water-retaining agent with high water absorption rate and strong water-retaining capacity, and at the same time achieve the purpose of reducing the sludge volume, the present invention performs targeted conditioning on the sludge according to its characteristics, and converts the sludge into a high-performance water-retaining material through a reasonable EPS separation-extraction procedure, thereby achieving the reduction and resource utilization of excess sludge.

[0025] More specifically, the preparation method of the sludge-based water-retaining agent of the present invention comprises the following steps:

[0026] (1) Adding 20-50 mg / L of polyhexamethylene biguanide (PHMB) to concentrated excess sludge with a water content of 97%-98% from a municipal sewage treatment plant to condition the excess sludge, and stirring for 20-30 minutes to form pretreated sludge;

[0027] (2) Use the effluent from the sewage treatment plant to perform initial washing on the pretreated sludge to remove fine particles until the viscosity of the supernatant sludge drops below 5.0 mPa·s;

[0028] (3) using an ultrasonic instrument with a power of 500-1000W to perform ultrasonic treatment on the pretreated sludge after the initial washing, and the treatment time for each batch is 10-15 minutes;

[0029] (4) The sludge after the ultrasonic treatment in the previous step is washed again to remove the precipitate (this part is the precipitated sludge a) to obtain a liquid phase part (this part is the liquid phase a);

[0030] (5) Adding effluent from a sewage treatment plant to the precipitated sludge a, the amount of water added being about 50% of the liquid phase a, performing mechanical stirring and then repeating the washing process of step (4) to obtain a precipitated portion (this portion is the precipitated sludge b) and a liquid phase portion (this portion is the liquid phase b), and the precipitated sludge b enters the sludge treatment system of the sewage treatment plant and is transported out for disposal;

[0031] (6) After the liquid phase a and the liquid phase b are combined to form a mixed liquid, 2%-5% of tannic acid and 10-30 mg / L of polyacrylamide (PAM) are added, which is then centrifuged to obtain a solid phase (this portion is the sludge-based water-retaining basic material), and the supernatant of the centrifugation is returned to the sewage treatment plant for treatment as wastewater;

[0032] (7) The sludge-based water-retaining base material is air-dried or oven-dried (preferably at 60-100° C.) until the moisture content is ≤10% to obtain a sludge-based water-retaining agent.

[0033] The present invention pre-treats the sludge by adding a conditioning agent to the sludge, and then uses physical and chemical means to wash, flocculate, centrifuge and dry the sludge to prepare a green high-performance sludge-based water-retaining agent, which well achieves the reduction and resource utilization of excess sludge. The more specific technical principles are as follows:

[0034] PHMB is a widely used bactericide and preservative with broad-spectrum antibacterial activity. It can combine with the negative charges on the cell membranes of microorganisms in sludge, causing the charge on the cell membrane surface to be neutralized, thereby destroying the permeability of the cell membranes of sludge microorganisms. PHMB is also a high-molecular compound. During the washing process, it can promote the sedimentation of large particles in the sludge, improve the sludge washing effect, and prevent large sludge particles from entering the supernatant. During the sludge washing process, soluble EPS and some loose EPS can be effectively removed, leaving tight EPS that is tightly bound to the sludge particles.

[0035] After PHMB pretreatment, due to the change in the permeability of the microbial cell membrane in the sludge, the cell membrane will be destroyed after applying ultrasonic treatment with a power of 500-1000W, resulting in the release of cell contents including soluble polysaccharides, proteins, nucleic acids, etc., and the separation of compact EPS from sludge particles. After the ultrasonically treated sludge is washed, the resulting liquid phase (liquid phase a and liquid phase b) contains fine-particle compact EPS, as well as soluble soluble polysaccharides, proteins, nucleic acids, etc.; after adding tannic acid and polyacrylamide to the liquid phase (liquid phase a and liquid phase b) to flocculate the fine compact EPS, the precipitation product (solid phase) can be obtained by centrifugation in a centrifuge, and the solid phase is dried to obtain a sludge-based water-retaining agent; the centrifuged supernatant is returned to the sewage treatment plant for treatment as wastewater, which can avoid possible secondary pollution problems during the preparation process.

[0036] The present invention discloses the following technical effects:

[0037] The present invention uses environmentally friendly conditioners and flocculants to break down and settle sludge microbial cells, and combines physical means such as elutriation and ultrasonic stripping to achieve green and efficient separation and extraction of compact EPS. The prepared sludge-based water-retaining agent is a natural bio-based material, which is not only structurally stable and not easily degradable, but also friendly to soil environmental microorganisms.

[0038] The invention has low economic cost and avoids possible secondary pollution problems, solves the problem of efficient resource utilization of excess sludge in urban sewage plants, and takes into account the dual indicators of economic benefits and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0041] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0042] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0043] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0044] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0045] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0046] The present invention is further described in detail below with reference to specific embodiments.

[0047] Example 1

[0048] Preparation of sludge-based water retaining agent:

[0049] (1) 20 mg / L PHMB was added to the residual sludge with a moisture content of 97% for conditioning. After stirring for 30 minutes, the sludge was washed to reduce the viscosity of the supernatant sludge to 4.8 mPa·s. The sludge was ultrasonically treated at 1000 W for 10 minutes and then washed to obtain precipitated sludge a and liquid phase a.

[0050] (2) Add effluent from a sewage treatment plant with a water volume equal to 50% of the liquid phase a, mix with the sludge a, and then wash again to obtain sludge b and liquid phase b.

[0051] (3) After adding 2% tannic acid and 10 mg / L PAM equivalent to the mass of the mixed solution of liquid phase a and liquid phase b, the solid phase is centrifuged to obtain a sludge-based water-retaining basic material. The sludge-based water-retaining basic material is dried (60°C) to a moisture content of 10% to obtain a sludge-based water-retaining agent.

[0052] The sludge-based water retaining agent prepared in Example 1 of the present invention has a high water absorption rate and a high salt water absorption rate. The water absorption capacity of natural water absorption for 10 minutes reaches 680g / g, and the salt water absorption rate is 35g / g; the water release rate is low, and the water retention capacity is strong. The water retention rate for 12h is 96.5%, the water retention rate for 24h is 83%, the water retention rate for 48h is 52%, the water retention rate for 72h is 17%, and the water retention rate for 96h is 3.8%. The heavy metal content of the sludge-based water retaining agent is lower than the "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard (Trial)" (GB 15618-2018).

[0053] Example 2

[0054] Preparation of sludge-based water retaining agent:

[0055] (1) 50 mg / L PHMB was added to the residual sludge with a moisture content of 98% to condition it. After stirring for 20 minutes, it was washed to reduce the viscosity of the supernatant sludge to 4.5 mPa·s. The sludge at this time was subjected to 500 W ultrasonic treatment for 15 minutes and then washed to obtain precipitated sludge a and liquid phase a.

[0056] (2) Add effluent from a sewage treatment plant with a water volume equal to 50% of the liquid phase a, mix with the sludge a, and then wash again to obtain sludge b and liquid phase b.

[0057] (3) After adding 5% of tannic acid and 30 mg / L of PAM to the mixture of liquid phase a and liquid phase b, the solid phase is centrifuged to obtain a sludge-based water-retaining base material. The sludge-based water-retaining base material is dried (60°C) to a moisture content of 6% to obtain a sludge-based water-retaining agent.

[0058] The sludge-based water retaining agent prepared in Example 2 of the present invention has high water absorption rate and high salt water absorption rate, and the water absorption capacity of natural water absorption for 10 minutes reaches 560g / g, and the salt water absorption rate is 27g / g; the water release rate is low, and the water retention capacity is strong, the 12h water retention rate is 92%, the 24h water retention rate is 78%, the 48h water retention rate is 43%, the 72h water retention rate is 12%, and the 96h water retention rate is 3.1%. The heavy metal content of the sludge-based water retaining agent is lower than the "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard (Trial)" (GB 15618-2018).

[0059] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a sludge-based water-retaining agent, characterized in that: The following steps are involved: (1) adding polyhexamethylene biguanide to concentrated excess sludge and stirring the mixture to obtain pretreated sludge; (2) performing a primary washing on the pretreated sludge to remove fine particles until the viscosity of the supernatant sludge drops below 5.0 mPa·s; (3) subjecting the sludge treated in step (2) to ultrasonic treatment; (4) washing the sludge after ultrasonic treatment again to obtain liquid phase a and precipitated sludge a; (5) washing the precipitated sludge a to obtain a liquid phase b and precipitated sludge b; (6) mixing the liquid phase a and the liquid phase b, adding tannic acid and polyacrylamide to the obtained mixed solution, collecting the solid phase by centrifugation, and drying to a water content of ≤10% to obtain the sludge-based water-retaining agent; The concentrated excess sludge is concentrated excess sludge from a municipal sewage treatment plant; The amount of tannic acid added is 2%-5% of the mass of the mixed solution; The amount of polyacrylamide added is 10-30 mg / L based on the volume of the mixed solution; The water used for the initial washing and the secondary washing is the effluent from the sewage treatment plant.

2. The preparation method according to claim 1, characterized in that: The power of the ultrasonic treatment is 500-1000W.

3. The preparation method according to claim 2, characterized in that: The ultrasonic treatment time is 10-15 min.

4. The sludge-based water-retaining agent prepared by the preparation method according to any one of claims 1 to 3.

5. Use of the sludge-based water-retaining agent as claimed in claim 4 in soil water retention.

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