A method for determining the dewatering process of dredging sludge based on the physical and chemical properties of river and lake sludge

Abstract

The present invention relates to the field of water pollution control, and specifically to a method for determining a dehydration process for dredged sludge based on the physical and chemical properties of river and lake sludge. Given that the amount of dredging of river, lake and reservoir sludge is currently large, and the current selection of dehydration and solidification agents and solidification processes for dredged sludge of different properties is unclear, a method for preliminary selection of the types of dredged sludge agents, formulations and solidification processes for river, lake and reservoir dredging based on the physical and chemical properties of the sludge is proposed. The method mainly analyzes the physical indicators of the sludge to be dredged, which are the sludge class size, and the chemical indicators of the sludge to be dredged, which are the organic matter content of the sludge. Based on the above results, the physical indicators and chemical indicators of the sludge to be dredged are divided into grades, and the dosage and ratio of the sludge solidification agent can be preliminarily determined, and the sludge solidification process can be determined. This method plays an important role in the ratio and process of solidification agents for dredged sludge from rivers, lakes and reservoirs, and can not only save capital investment, but also improve the efficiency of dredged sludge treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of water pollution control, and in particular to a method for determining a dredging sludge dewatering process based on the physical and chemical properties of river and lake sludge. Background Art

[0002] Numerous studies, both domestic and international, have shown that even after external sources are effectively controlled, the continued release of endogenous lake sediment can still impact lake eutrophication for decades. Sediment dredging (or dredging) is a common method for managing endogenous sediment. Sediment dredging primarily involves the use of large-scale dredging equipment to remove heavily polluted sediment from river and lake systems, thereby reducing endogenous pollution, lowering endogenous releases, and improving water quality. Sediment dredging, or dredging, has become a crucial method for managing rivers and lakes in my country and is being implemented in many of the country's rivers and lakes.

[0003] Since the dredged sludge has a high water content and large reserves, it is not suitable for direct on-site stacking, resource reuse, or long-distance transportation. Therefore, the dredged sludge from rivers and lakes must first be dehydrated and solidified. The dewatering disposal technologies for dredged sludge from rivers and lakes mainly include geotextile tube bag method, mechanical dewatering method (including belt filter press method, plate and frame filter press method and centrifuge method), chemical solidification method and other methods. In comparison, mechanical dewatering method is a commonly used sludge disposal method in dredging projects such as rivers and lakes (including reservoirs) in my country. Among them, the centrifuge dewatering method has problems such as high energy consumption and the water content of the mud cake after treatment is still relatively high. In practice, it is rarely used. Therefore, the belt filter press method and the plate and frame filter press method in the mechanical dewatering method are currently the two most commonly used technologies in mechanical dewatering.

[0004] During the desilting sludge disposal process, the type of reagents added and the selection of mechanical dewatering processes have a significant impact on the disposal cost, construction schedule, and subsequent resource recovery of the sludge. Deep sludge dewatering technology is widely used in municipal sewage treatment plants. However, the physical and chemical properties of sludge from municipal sewage treatment plants (high in organic matter and primarily composed of fine particles) differ significantly from those from desilting sludge from rivers and lakes. The sludge from desilting rivers and lakes exhibits the following key characteristics: ① The particle size composition of sludge varies significantly. River and lake sediments are deposited over long periods of time through natural hydrological and hydrodynamic selection, forming on the bottoms of lakes and rivers. As a result, the particle size composition of river and lake sludge can be dominated by fine particles, often referred to as silty, or by coarse particles, often referred to as sandy, or a mixture of fine and sandy particles. ② The organic matter content of river and lake sediments is generally low, with some areas of heavy pollution experiencing excessive or contaminated organic matter content. The above characteristics of river and lake sediments will significantly affect the flocculation effect of the agent and the sludge disposal efficiency of the subsequent mechanical dewatering process.

[0005] Currently, the mechanical dewatering methods (belt filter press and plate and frame filter press) used to treat river and lake dredged sediments present the following problems: ① The dosage form and ratio of the added agents are generally rather uninformed, without considering the differences in sediment size composition. River and lake dredged sediments are large in volume and have significant differences in size composition. Current mechanical dewatering processes do not fully consider the differences in the types of added agents and the proportions of the components that may result from differences in sludge size composition. Coarse and fine particles, or sludge compositions of varying properties, inevitably require different types and proportions of flocculants. Furthermore, the organic matter content of river and lake dredged sediments is generally low (<3%), with the organic matter content exceeding 3% in some areas. Higher organic matter content, however, contains more interfering functional groups that will inevitably react with the flocculant, affecting its efficiency. For sludge with such high organic matter content, the agent ratio needs to be adjusted. ② Targeted mechanical dewatering processes are not used for different silt properties, resulting in low silt disposal efficiency, impacting the progress and cost of silt removal and solidification projects. As mentioned above, the differences in particle size composition of river and lake silt are the most significant characteristics of river and lake sediments. This determines the type and combination of reagents to be added, which will inevitably affect the selection of subsequent silt solidification processes. Currently, most river and lake silt removal processes lack the step of selecting mechanical dewatering processes based on different silt properties, resulting in suboptimal subsequent sediment disposal.

[0006] In summary, from the current international technology for the disposal and solidification of desilted sludge from rivers and lakes, there is no targeted proportioning of reagents and selection of suitable mechanical dewatering processes based on the properties of the desilted sludge from rivers and lakes. This extensive reagent proportioning and subsequent selection of sludge solidification processes will inevitably lead to many unfavorable factors such as low sludge disposal efficiency and increased costs. Therefore, the present invention mainly targets the significant differences in the properties of sludge that are prevalent in my country's rivers, lakes and reservoirs, and specifically proposes reagent dosage forms and proportions, and recommends a reasonable sludge dewatering and solidification process. This method plays an important role in the proportioning and process of solidifying reagents for desilted sludge from rivers, lakes and reservoirs, can save capital investment, and can improve the efficiency of desilted sludge treatment in rivers and lakes. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for determining a dredging sludge dewatering process based on the physical and chemical properties of river and lake sludge, so as to solve the problems in the prior art.

[0008] In order to solve the above technical problems, the present invention provides the following technical solution: a method for determining a dredging sludge dewatering process based on the physical and chemical properties of river and lake sludge, comprising the following steps:

[0009] S1: Take the dehydrated sludge from rivers, lakes and reservoirs, and separate them into layers at equal intervals for future use;

[0010] S2: Grain size classification of the desilted sediment to be dewatered at different layers, calculating the median particle size D50 of the desilted sediment, and classifying the desilted sediment into three types based on the median particle size D50: coarse sediment, fine sediment, and sediment of medium coarse and fine particles; and analyzing the organic matter content of the sediment;

[0011] S3: taking any one of the coarse-grained sediment, fine-grained sediment, and medium-coarse-fine-grained sediment after screening and impurity removal, drying and measuring the moisture content, and adjusting the solid content to 10-30% according to the moisture content to obtain a slurry;

[0012] S4: Prepare polyaluminium chloride into PAC agent and anionic polyacrylamide into APAM agent; prepare the agents and determine the dehydration process according to the physical and chemical properties of the dredged sludge in S3.

[0013] Furthermore, in S1, the spacing between the desilted sediment layers is 20-25 cm.

[0014] Furthermore, in S2, the method for grading the particle size of dredged sediment is: according to the proportion of particles less than 16 μm, the proportion of particles less than 16 μm between 0-50% is coarse-grained sediment; the proportion of particles less than 16 μm above 65% is fine-grained sediment; the proportion of particles less than 16 μm between 50-65% is medium-coarse-fine sediment.

[0015] Furthermore, in S4, the concentration of polyaluminium chloride in the PAC agent is 10-25 g / L.

[0016] Furthermore, in S4, the concentration of anionic polyacrylamide in the APAM agent is 0.5-1 g / L.

[0017] Furthermore, in S4, the molecular weight of the anionic polyacrylamide is 10-12 million.

[0018] Furthermore, in S4, when the dredged sludge to be dehydrated is coarse-grained sludge, the volume addition amount of the PAC agent is 3-4% of the sludge, and belt filter press dehydration is adopted.

[0019] Furthermore, in S4, when the dredged sludge to be dewatered is medium-coarse-fine particle sludge or fine particle sludge, and the organic matter content in the dredged sludge to be dewatered is less than or equal to 2.5%, the volume addition amount of the PAC agent is 2-3% of the mud, and the volume addition amount of the APAM agent is 6-8% of the mud, and plate and frame filter pressing is used for dehydration.

[0020] Furthermore, in S4, when the dredged sludge to be dehydrated is medium-coarse-fine particle sludge or fine particle sludge, and the organic matter content of the sludge is 2.5-3%, the volume addition amount of the PAC agent is 4-5% of the sludge, and the volume addition amount of the APAM agent is 10-12% of the sludge, and plate and frame filter pressing is used for dehydration.

[0021] Compared with existing technologies, the present invention achieves the following beneficial effects: it clarifies the types of mechanical dewatering agents for different properties of river and lake dredged sediment, and primarily uses sediment particle size classification as an important reference indicator. When the sludge is primarily coarse-grained, only polyaluminum chloride is required, and belt filter press dewatering is recommended. When the sludge is medium- to fine-grained, a combination of PAC and APAM agents is required, with the specific ratio of PAC to APAM agents refined based on the organic matter content of the sludge. Plate and frame filter press is recommended as the preferred method for mechanical dewatering.

[0022] The main innovations of this program are as follows:

[0023] (1) For the first time, the core physical and chemical properties of sediment, such as particle size and organic matter content, were used to define the types of conditioning agents, and the main mechanical dewatering method for coarse-grained dredged sediment (belt filter press) was determined;

[0024] (2) The types of reagent ratios when there is a difference in organic matter content in medium-coarse and fine-grained sediments and fine-grained sediments, as well as their ratios to mud concentration, were further refined, and the mechanical dewatering process for medium-coarse and fine-grained sediments, mainly using the plate and frame filter press method, was clarified;

[0025] This method uses a method to pre-evaluate the physical indicator particle size and chemical indicator organic matter content of the sludge before dehydration, defines the types of dehydration agents and mechanical dehydration methods for sludge of different properties, avoids the dilemma of blindly using agents, significantly saves investment, and makes sludge dehydration and solidification more scientific and reasonable, ensuring the smooth implementation of dredging and silt consolidation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 This is the trend diagram of the moisture content and specific resistance of the mud cake under different polyaluminium chloride dosages;

[0028] Figure 2 This is a graph showing the change trend of the water content and specific resistance of the medium-grained sediment cake under the combined action of anionic polyacrylamide and polyaluminium chloride;

[0029] Figure 3This is a graph showing the change trend of the moisture content and specific resistance of the fine-grained sediment cake under the combined action of anionic polyacrylamide and polyaluminium chloride;

[0030] Figure 4 This is a schematic diagram of the change curve of sediment moisture content and filtration resistance with different particle size compositions;

[0031] Figure 5 This is the relationship between the specific resistance and water content of polyaluminium chloride / anionic polyacrylamide conditioned sediment in different organic matter sediments;

[0032] Figure 6 This is the relationship between the moisture content of the dewatered cake from the belt filter press and the composition of the sediment particle size;

[0033] Figure 7 This is the relationship between the plate and frame filter press dewatering effect and output of sludge of different diameters;

[0034] Figure 8 It is a flow chart of the dredging and solidification process. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0036] The raw materials used in the present invention and their sources are as follows: polyaluminium chloride was purchased from Shuibiqing Environmental Protection Technology Co., Ltd., with an aluminium oxide content of 30%; anionic polyacrylamide was purchased from Tangda Water Purification, with a molecular weight of 12 million.

[0037] Example 1: Investigate the effect of reagent addition on the filtration resistance and water content of sludge of different diameters.

[0038] Table 1 Particle size distribution of different types of sediment particles

[0039]

[0040] Through the analysis of sediment particle size, three types of experimental sediments with different particle sizes were screened out, namely fine-grained mud with particles less than 16μm accounting for 73.63%, medium-coarse-grained mud with particles less than 16μm accounting for 55.18%, and coarse-grained mud with particles less than 16μm accounting for 36.74%, and adjusted into homogeneous mud with a solid content of 10%.

[0041] (1) Take 100 mL of coarse granular sludge in a 250 mL beaker, add 20 g / L PAC agent with volume fractions of 0, 0.5%, 1%, 2%, 3%, and 4% respectively (corresponding to PAC dosage of 0, 0.1 g / L, 0.2 g / L, 0.4 g / L, 0.6 g / L, and 0.8 g / L in the sludge), stir rapidly at a speed of 200 r / min for 1 min, and then stir slowly at a speed of 50 r / min for 3 min to complete the flocculation reaction. The filtration resistance of the flocculated sludge and the moisture content of the dewatered cake are measured using the following sludge resistance measuring device. The results are as follows Figure 1 and as shown in Table 2.

[0042] Table 2 Relationship between PAC dosage, specific resistance and water content in coarse-grained sediment

[0043] PAC dosage (g / L) Mud cake moisture content (%) <![CDATA[Specific resistance (×10 10 cm / g)]]> 0 50.57 42.52 0.1 40.74 28.2 0.2 30.47 20.54 0.4 29.74 11.11 0.6 28.68 6.26 0.8 28.98 4.30

[0044] (2) Take 100 mL of medium-sized sludge in a 250 mL beaker, first add 2% and 3% of 10 g / L PAC agent (corresponding to PAC dosage of 0.2 g / L and 0.3 g / L in sludge), and stir rapidly for 1 min; then add 1%, 2%, 3%, 4%, and 5% of 500 mg / L APAM agent (corresponding to APAM dosage of 5 mg / L, 10 mg / L, 15 mg / L, 20 mg / L, and 25 mg / L in sludge), stir rapidly for 1 min at 200 r / min on a magnetic stirrer, and then stir slowly for 3 min at 50 r / mind to complete the flocculation reaction. The filtration resistance of the flocculated sludge and the moisture content of the dewatered cake are measured using a sludge resistance measuring device. The results are shown in Figure 2. Figure 2 and shown in Table 3.

[0045] Table 3 Relationship between PAC dosage, specific resistance and water content in granular sediment

[0046]

[0047]

[0048] (3) Take 100 mL of fine-grained sludge in a 250 mL beaker, first add 1%, 2%, and 3% of 25 g / L PAC agent (corresponding to PAC dosage of 0.25 g / L, 0.5 g / L, and 0.75 g / L in the sludge), stir rapidly for 1 min, then add 0%, 2%, 4%, 6%, 8%, and 10% of 500 mg / L APAM agent (corresponding to APAM dosage of 0, 10 mg / L, 20 mg / L, 30 mg / L, 40 mg / L, and 50 mg / L in the sludge), stir rapidly for 1 min at a speed of 200 r / min on a magnetic stirrer, and then stir slowly for 3 min at a speed of 50 r / mind to complete the flocculation reaction. The filtration resistance of the flocculated sludge and the moisture content of the dewatered cake are measured using a sludge resistance measuring device. The results are as follows: Figure 3 and as shown in Table 4.

[0049] Table 4 Relationship between PAC dosage, specific resistance and water content in fine-grained sediment

[0050]

[0051] (4) The relationship between the ratio of polyaluminium chloride and different types of polyacrylamide agents and the proportion of fine particle size in the sediment was investigated. As mentioned above, the higher the proportion of fine particles in the sediment, the more difficult it is to dehydrate, which can be directly reflected by the two indicators of specific resistance and water content. The flocculation experiment was carried out on the mud with different proportions of sediment particles using a filtration device. The dosage of PAC agent was 500mg / L, and the dosage of APAM and CPAM was 20mg / L. The results are shown in Figure 2. Figure 4 and as shown in Table 5.

[0052] Table 5 The conditioning effect of polyaluminium chloride and cationic and anionic polyacrylamide combinations with different proportions of mud particles

[0053]

[0054] Example 2: Investigate the effect of adding reagents on the moisture content of sediments with different organic matter contents.

[0055] Take fine-grained sediments with different organic matter contents, prepare mud according to the method in Example 1, add different concentrations of reagents, and carry out filtration experiments. The moisture content of the filtered mud cake and the filtration resistance are shown in Tables 6-7 and Figure 5As shown. Among them, the experimental sediment mainly selected fine-grained silt sediment in the southern part of Chaohu desilting area, with an average organic matter content of 2.35%. Therefore, the particle size composition and nitrogen and phosphorus pollution levels of the same batch of sediments are consistent. Humic acid, a typical representative of sediment organic matter, is added to the original homogeneous sediment as the organic matter in the sediment. The addition amount is controlled at 0.5%, 1.0%, and 1.5% of the dry mud, respectively recorded as low organic matter, medium organic matter, and high organic matter conditioned sediment. After quantitative addition and mixing, it is placed for more than 24 hours. The solid content of the adjusted sediment is consistent with the dewatering experimental sediment slurry in the previous article (10% solid content). The two core indicators of sediment filtration resistance and dewatering cake moisture content are used to study the effect of different organic matter content in the sediment on the dewatering effect of the flocculant.

[0056] Table 6 Treatment effects of different doses of APAM on low organic matter sediment

[0057]

[0058] Table 7 Treatment effects of different doses of PAC and APAM on organic matter sludge

[0059]

[0060] Table 8 Treatment effects of different doses of PAC and APAM on high organic matter sediment

[0061]

[0062] Example 3: The dewatering effects of belt filter press and plate and frame filter press on sediments with different particle sizes were investigated.

[0063] Figure 6 The relationship between the sediment particle size and the moisture content of the mud cake in the actual production of the belt filter press in the Chaohu desilting pilot project. Figure 7 The relationship between the plate and frame filter press dewatering effect and output of different particle size sludge is shown in the figure. The two sludge solidification processes have the same sludge flocculation treatment. The specific process flow is: first, the sludge in the sedimentation tank is sucked into the homogenization tank by a slurry pump, and a certain concentration of PAC agent (concentration is about 2.5%) and APAM agent (concentration is about 0.5‰) is added. The solid content of the sludge in the homogenization tank is about 15%. Then it is pumped into the filter press or plate and frame filter press for extrusion dehydration. The specific process is as follows: Figure 8 shown.

[0064] It can be seen that the moisture content of the dewatered cake is closely correlated with the proportion of sediment particles smaller than 16μm. The initial desilting area was located far from shore, where the sediment particle size was small and primarily fine-grained. Therefore, the particle size analysis showed a high proportion of particles smaller than 16μm, generally exceeding 70%. Sediment samples collected on April 7, 2022, had the highest proportion of particles smaller than 16μm, at 82.87%, and the dewatered cake moisture content was also the highest. Dewatering performance was suboptimal for both dewatering units, with dewatered cake moisture contents of 57.53% and 53.53%, respectively. As the desilting project progressed northward toward the nearshore area, sediment particle size increased, the proportion of particles smaller than 16μm began to decrease, and the dewatered cake moisture content also began to decrease significantly. Sediment samples collected on September 7, 2022, had a median particle size of 16.3μm and particles smaller than 16μm accounted for 49.27%, typical of coarse-grained sandy mud. As a result, the two belt dewatering machines achieved the lowest levels of dewatering, achieving 35.16% and 34.27% respectively. The actual sediment dewatering results were consistent with the laboratory simulation results, indicating that sediment particle size is a significant factor influencing sediment dewatering. The smaller the sediment particle size, and the greater the proportion of particles smaller than 16μm, the more difficult it is to dewater.

[0065] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0066] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for determining a dredging sludge dewatering process based on the physical and chemical properties of river and lake sludge, characterized in that: The following steps are involved: S1: Take the dehydrated sludge from rivers, lakes and reservoirs, and separate them into layers at equal intervals for future use; S2: Grain size classification of the desilted sediment to be dewatered at different layers, calculating the median particle size of the desilted sediment, and classifying the desilted sediment into three types based on the median particle size: coarse-grained sediment, fine-grained sediment, and sediment of medium coarse and fine particles; and analyzing the organic matter content of the sediment; S3: taking any one of the coarse-grained sediment, fine-grained sediment, and medium-coarse-fine-grained sediment after screening and impurity removal, drying and measuring the moisture content, and adjusting the solid content to 10-30% according to the moisture content to obtain a slurry; S4: Prepare polyaluminium chloride into PAC agent; prepare anionic polyacrylamide into APAM agent, add agents according to the physical and chemical properties of the dredged sludge in S3, and determine the dehydration process; In S4, when the dredged sludge to be dewatered is coarse-grained sludge, the volume addition amount of PAC agent is 3-4% of the mud, and belt filter press dehydration is adopted; when the dredged sludge to be dewatered is medium-coarse-fine granular sludge or fine-grained sludge, and the organic matter content in the dredged sludge with belt dehydration is less than or equal to 2.5%, the volume addition amount of PAC agent is 2-3% of the mud, and the volume addition amount of APAM agent is 6-8% of the mud, and plate and frame filter press dehydration is adopted; when the dredged sludge to be dewatered is medium-coarse-fine granular sludge or fine-grained sludge, and the organic matter content of the sludge is 2.5-3%, the volume addition amount of PAC agent is 4-5% of the mud, and the volume addition amount of APAM agent is 10-12% of the mud, and plate and frame filter press dehydration is adopted.

2. The method for determining a dredging sludge dewatering process based on the physical and chemical properties of river and lake sludge according to claim 1, characterized in that: In S1, the spacing between dredged sediment layers is 20-25 cm.

3. The method for determining a dredging sludge dewatering process based on the physical and chemical properties of river and lake sludge according to claim 1, characterized in that: In S2, the method for grading the particle size of dredged sediment is as follows: according to the proportion of particles less than 16 μm, the proportion of particles less than 16 μm between 0-50% is coarse-grained sediment; the proportion of particles less than 16 μm above 65% is fine-grained sediment; the proportion of particles less than 16 μm between 50-65% is medium-coarse-fine sediment.

4. The method for determining a dredging sludge dewatering process based on the physical and chemical properties of river and lake sludge according to claim 1, characterized in that: In S4, the concentration of polyaluminium chloride in the PAC agent is 10-25 g / L; the concentration of anionic polyacrylamide in the APAM agent is 0.5-1 g / L.

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