A sludge dewatering system

Abstract

This invention provides a sludge dewatering system, including a screw press dewatering machine, a sludge pump, a dosing pump, a stirrer, and a controller. The inlet of the screw press dewatering machine is connected to the outlets of the sludge pump and the dosing pump via pipelines. The outlet of the sludge pump is equipped with a sludge flow meter, the outlet of the dosing pump is equipped with a dosing flow meter, and the filtrate outlet of the screw press dewatering machine is equipped with a filtrate flow meter. The controller is electrically connected to the sludge pump, the dosing pump, the stirrer, the sludge flow meter, the dosing flow meter, and the filtrate flow meter. The screw press dewatering machine has a screw pitch of 3-4 mm, a screw shaft diameter of 40-55 mm, a screw shaft compression ratio of 2-3.5, a screw shaft rotation speed of 3-7 rpm, and an outlet pressure of 0.02-0.04 MPa. The sludge dewatering system of the present invention can adjust the moisture content of the dewatered sludge to between 85% and 95%, provided that the sludge feed rate is stable at 400-680 kg·ds / h and the sludge feed moisture content is between 99% and 96%.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment, and in particular relates to a sludge dewatering system. Background Technology

[0002] In foreign countries, natural drying and filter press were the most common methods for sludge dewatering in earlier years. Centrifugal dewatering and filter press dewatering have gradually become dominant. The dewatered sludge obtained through these devices has a moisture content of 60-80%, which limits various subsequent treatment methods and approaches. Furthermore, because sludge moisture content is difficult to measure, it is difficult to adjust the dewatering effect online under normal circumstances, leading to energy and resource waste. Therefore, developing automatic detection and intelligent control equipment for sludge dewatering moisture content, achieving effective control of sludge moisture content between 85% and 95%, and meeting the moisture content requirements of various subsequent treatments, is an effective means to solve the problems of energy waste and high costs.

[0003] The primary sludge at the Jinan Wastewater Treatment Plant is thickened using gravity hydrolysis. However, due to the large volume of residual sludge, gravity thickening efficiency is low, resulting in a low final dewatering rate. Some water is lost with the sludge, leading to persistently high sludge production.

[0004] The current sludge treatment process of Jingu Wastewater Treatment Plant is as follows: (1) The sludge in the biological tank has a moisture content of 99%, (2) The sludge in the equalization tank has a moisture content of 98%, (3) The sludge at the outlet of the dewatering machine has a moisture content of 80%, and (4) The sludge entering the Jinan Sludge Plant's mixing station is diluted in the sludge coarse adjustment tank to reach a secondary dilution of 90%-92%, which causes high costs for the transportation of chemicals, equipment, and vehicles.

[0005] The sludge treatment process at this plant involves transferring treated sludge to the Jinnan sludge treatment plant for disposal. Pipeline transportation is used initially, but due to its lack of mobility, high energy consumption, and expensive maintenance, it's difficult to maintain stable and continuous operation for extended periods, necessitating the use of truck transportation. However, transporting the sludge to the nearby sludge digestion plant by truck further increases operating costs. Upon arrival at the sludge treatment plant, sufficient moisture content must be ensured for anaerobic digestion; therefore, the sludge is diluted, increasing the moisture content from 80% to 90% before subsequent anaerobic digestion can proceed. Consequently, significant ineffective dewatering occurs between the dewatering and digestion steps, leading to the following problems:

[0006] 1. Significant energy waste. Ineffective dewatering (over-dewatering) and the steps of increasing the moisture content of sludge before digestion undoubtedly result in a large amount of energy waste.

[0007] 2. High chemical costs. The dosage of polyacrylamide used for sludge conditioning is severely wasted, leading to increased chemical costs.

[0008] 3. High transportation costs. The sludge after dewatering and concentration has a low water content and lacks fluidity, making it unsuitable for pipeline transportation. Truck transportation significantly increases the cost of transporting the sludge.

[0009] 4. Repeated processes. The repeated dehydration and water addition processes increase the costs of manpower, materials, and time.

[0010] Repeated dewatering and dilution processes not only result in waste of technology, but also in significant waste of chemicals, energy, labor, and equipment, increasing costs. Furthermore, current sludge dewatering equipment cannot effectively control or detect the moisture content, leading to ineffective dewatering (over-dewatering). Summary of the Invention

[0011] In view of this, the present invention aims to provide a sludge dewatering system to achieve precise control and real-time monitoring of sludge moisture content.

[0012] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0013] A sludge dewatering system includes a screw press dewatering machine, a sludge pump, a dosing pump, a mixer, and a controller. The inlet of the screw press dewatering machine is connected to the outlets of the sludge pump and the dosing pump via pipelines. The outlet of the sludge pump is equipped with a sludge flow meter, the outlet of the dosing pump is equipped with a dosing flow meter, and the filtrate outlet of the screw press dewatering machine is equipped with a filtrate flow meter. The controller is electrically connected to the sludge pump, the dosing pump, the mixer, the sludge flow meter, the dosing flow meter, and the filtrate flow meter. The screw press dewatering machine has a screw pitch of 3-4 mm, a screw shaft diameter of 40-55 mm, a screw shaft compression ratio of 2-3.5, a screw shaft rotation speed of 3-7 rpm, and an outlet pressure of 0.02-0.04 MPa.

[0014] The flow rates of each stage in the sludge dewatering system of the present invention satisfy the following formula:

[0015]

[0016] Q 滤液 Q is the required flow rate of the filtrate to be discharged. 进泥 The flow rate of sludge entering the screw press dewatering machine is monitored by a sludge flow meter located at the sludge pump outlet. 进泥 The moisture content of the sludge entering the screw press dewatering machine is a fixed value that remains relatively stable within the testing period. It is derived from laboratory data and data recorded manually on-site. Q 药量 The amount of chemical solution entering the screw press dewatering machine is monitored by a flow meter located at the outlet of the dosing pump. 出泥 To achieve the target moisture content of the sludge discharged from the screw press dewatering machine, SS 滤液The density of suspended solids in the discharged filtrate is expressed in g / L and is a constant value over a certain period of time. The 1 in the formula represents the concentration of dissolved suspended solids in the sludge, which is generally around 1 g / L in urban wastewater treatment plants.

[0017] Based on the above formula, it can be deduced that in order to achieve the target moisture content of the discharged sludge, the target flow rate Q of the discharged filtrate needs to be controlled. 目标滤液值 as follows:

[0018]

[0019] A filtrate flow meter installed at the filtrate outlet of the screw press dewatering machine monitors the real-time flow rate of the discharged filtrate and the target filtrate flow rate Q. 目标滤液值 In comparison, the controller adjusts the speed of the screw press dewatering machine to achieve the target flow rate Q of the filtrate. 目标滤液值 .

[0020] Furthermore, the flocculant dosage of the screw press dewatering machine is 0.5-1.5 kg / t ds.

[0021] Furthermore, the moisture content of the sludge fed into the screw press dewatering machine is 97.5%-98.5%.

[0022] Furthermore, the inlet flow rate of the screw press dewatering machine is 3.7-4 m³ / h. 3 / h.

[0023] Furthermore, the screw press dewatering machine is equipped with an FDR sensor, which is electrically connected to the controller. The FDR sensor can sense the moisture content of the sludge entering the screw press dewatering machine, and the controller adjusts the rotation speed of the screw press dewatering machine based on the change in moisture content to achieve the target flow rate Q of the filtrate. 目标滤液值 This ensures that the discharged sludge reaches the target moisture content.

[0024] Furthermore, the screw press dewatering machine is also equipped with an online turbidity meter for real-time monitoring of the suspended solids density of the discharged filtrate, and the online turbidity meter is electrically connected to the controller.

[0025] Compared with existing technologies, the sludge dewatering system of the present invention has the following advantages:

[0026] (1) The sludge dewatering system of the present invention can adjust the moisture content of the dewatered sludge between 85% and 95% under the premise that the sludge feed rate is stable at 400-680 kg·ds / h and the sludge feed moisture content is between 99% and 96%.

[0027] (2) The sludge dewatering system of the present invention can measure the concentration ratio online, thereby indirectly monitoring the sludge moisture content online in real time;

[0028] (3) The sludge dewatering system of the present invention uses a screw press for dewatering, which greatly reduces energy consumption, with a comprehensive reduction rate of more than 51%. Attached Figure Description

[0029] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0030] Figure 1 This is a schematic diagram illustrating the effect of different screw pitches on the moisture content of the discharged mud, as described in an embodiment of the present invention.

[0031] Figure 2 This is a schematic diagram illustrating the effect of different spiral shaft diameters on the sludge moisture content according to an embodiment of the present invention.

[0032] Figure 3 This is a schematic diagram illustrating the effect of different compression ratios on the moisture content of the discharged mud, as described in an embodiment of the present invention.

[0033] Figure 4 This is a schematic diagram illustrating the effect of different outlet pressures on the moisture content of the discharged mud, as described in an embodiment of the present invention.

[0034] Figure 5 This is a schematic diagram illustrating the effect of different rotation speeds on the moisture content of the discharged mud, as described in an embodiment of the present invention.

[0035] Figure 6 This is a schematic diagram illustrating the effect of the influent sludge moisture content on the effluent sludge moisture content according to an embodiment of the present invention;

[0036] Figure 7 This is a schematic diagram illustrating the effect of different influent volumes on the moisture content of the discharged sludge, as described in an embodiment of the present invention.

[0037] Figure 8 This is a schematic diagram comparing the theoretical and actual values ​​of the sludge moisture content described in an embodiment of the present invention.

[0038] Figure 9 This is a schematic diagram illustrating the FDR sludge moisture content monitoring principle according to an embodiment of the present invention;

[0039] Figure 10 This is a schematic diagram illustrating the theoretical moisture content of the FDR measurement method described in this embodiment of the invention.

[0040] Figure 11 This is a schematic diagram comparing the theoretical moisture content of the FDR determination method described in this embodiment of the invention with the national standard determination. Detailed Implementation

[0041] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0042] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0043] Example of verifying parameters of screw press

[0044] 1. Screw pitch

[0045] The pitch of the screw significantly affects the helix angle, and the size of the helix angle, in turn, influences the sludge propulsion process to varying degrees, jointly determining the final sludge propulsion state. If the diameter of the entire blade and the overall throughput of the equipment can be determined, changing the pitch value can effectively alter the sliding state of the sludge during movement, potentially leading to changes in the velocity distribution. Generally, during the design process, the following two factors must be fully considered: the friction between the propeller and the sludge, and the relationship between the components of different velocities.

[0046] Given the two necessary conditions mentioned above, if the first condition is required, then the particle will be subjected to this axial force. The axial force is minimal at the root of each propeller blade. Furthermore, for the second case, since the particles corresponding to each type of sludge have different distribution relationships during movement, it is necessary to design to minimize their axial propulsion speed; the axial speed at different points should be greater than the circumferential speed.

[0047] First, sludge with an initial moisture content of 99.2% was selected for treatment. The screw shaft speed was maintained at 5 rpm, the screw shaft diameter was 40 mm, and the screw pitch was adjusted to 1–5 mm. The obtained dewatering data are shown in Table 1. Figure 1 As shown:

[0048] Table 1. Effect of different screw pitches on the moisture content of discharged mud.

[0049]

[0050] As the screw pitch increased from 1mm to 5mm, the sludge moisture content gradually increased, but the rate of increase slowed down until it stabilized. The experiment revealed that while the moisture content changed extremely slowly with increasing screw pitch, it still showed a gradual upward trend. This differs slightly from the general design of dewatering screw presses and thickening screw presses. In dewatering screw presses, a denser screw pitch is used to ensure a final moisture content of 80%, allowing for slow sludge movement and slight disturbance, mixing, and agitation. This process relies on the balance between sludge and water, ensuring that the sludge flocs do not break apart and that the surrounding water breaks the air-water film in time. In thickeners, the pitch is wider, reaching 8-10mm. This ensures that the sludge flocs are not broken apart and that the suspended solids in the filtered water are low, thus increasing the thickener's processing efficiency.

[0051] Experiments show that a screw pitch of 3-4 mm generally meets the requirements for this dehydration process. This approach can be implemented in customized machinery modifications, with the screw pitch customized according to these requirements.

[0052] 2. Helical shaft diameter

[0053] The overall lift angle of the device is determined by factors such as the diameter and pitch of the propeller shaft. Therefore, multiple factors need to be considered during testing. When determining the propeller shaft diameter, considering the direction of sludge movement and velocity distribution characteristics, the main focus is on determining the frictional force between the propeller rotation and the sludge. Secondly, the relationship between the speeds of different components must be analyzed.

[0054] Sludge with an initial moisture content of 99.2% was selected for treatment. The screw shaft speed was maintained at 5 rpm, and the screw shaft diameters were 40, 45, 50, and 55 mm. The screw pitch was adjusted to 1 mm. The obtained dewatering data are shown in Table 2. Figure 2 As shown:

[0055] Table 2. Effect of different screw shaft diameters on the moisture content of discharged mud.

[0056]

[0057] When the diameter of the screw shaft increases from 40mm to 55mm, the moisture content of the discharged mud gradually increases, ranging from 85.5% to 93.1%. The moisture content of the discharged mud varies more between 40-50mm and between 50-55mm, and is relatively stable.

[0058] 3-screw shaft compression ratio

[0059] Different compression ratios significantly affect the pressure edge of the corresponding filter screen flow field, resulting in concentrated sludge with varying moisture contents. The trend of fluid pressure change inside the equipment is the same when only the screw shaft compression ratio is changed. That is, the pressure increases gradually from the inlet to the outlet. As the compression ratio increases, the fluid pressure inside the device rises. A higher compression ratio indicates greater pressure on the sludge inside the device, resulting in a more significant dewatering effect.

[0060] The results are shown in Table 3 and Figure 3 As shown, the sludge moisture content decreases non-linearly with increasing compression ratio. As the screw shaft compression ratio gradually increases, the rate of decrease in sludge moisture content begins to slow down. When the compression ratio is 3.0, the effect of the compression ratio on the dewatering effect gradually weakens. With an outlet pressure of 0.03 MPa and a screw shaft speed of 5 rpm, the sludge moisture content reaches a maximum of 89.3% when the screw shaft compression ratio reaches its maximum value of 3.5.

[0061] Table 3. Effect of different compression ratios on the moisture content of discharged sludge.

[0062] Serial Number Compression ratio Export pressure Screw shaft speed Sludge moisture content 1 2.0 0.03Mpa 5rpm 85.2％ 2 2.5 0.03Mpa 5rpm 87.7％ 3 3.0 0.03Mpa 5rpm 89.2％ 4 3.5 0.03Mpa 5rpm 89.3％

[0063] 4. Export pressure

[0064] The outlet pressure of the screw press can be controlled by adjusting the distance between the mud outlet and the back pressure plate. To study the effect of outlet pressure on the moisture content of the discharged mud, tests were conducted at different outlet pressures of 0.02 MPa, 0.03 MPa, 0.04 MPa, and 0.05 MPa. The test results are shown in Table 4. Figure 4 As shown, the sludge moisture content decreases with increasing outlet pressure. The relationship between moisture content and outlet pressure is non-linear; the decreasing trend of moisture content gradually increases with increasing outlet pressure. When the outlet pressure reaches its maximum value of 0.05 MPa, the sludge moisture content is 87.5%. However, in actual operating conditions, when the outlet pressure is adjusted to 0.05 MPa, the distance between the back pressure plate and the sludge outlet significantly affects normal sludge discharge. Therefore, in actual operating conditions, the maximum outlet pressure selected is 0.04 MPa, at which point the sludge moisture content is 90.2%.

[0065] Table 4. Effect of different outlet pressures on sludge moisture content

[0066] Serial Number Export pressure Compression ratio Screw shaft speed Sludge moisture content 1 0.02MPa 3.5 5rpm 79.3％ 2 0.03MPa 3.5 5rpm 85.2％ 3 0.04MPa 3.5 5rpm 90.2％ 4 0.05MPa 3.5 5rpm 87.5％

[0067] 5. Screw shaft speed

[0068] The rotational speed of the screw press is related to the operating volume of the equipment. Generally, increasing the rotational speed can increase the processing capacity. However, there are limitations to increasing the rotational speed. Exceeding a certain limit will actually reduce the sludge processing capacity and increase equipment wear and tear. Typically, the rotational speed of the screw press is adjusted according to the change in the liquid level in the sludge mixing tank, reflecting the amount of feed. Increasing the frequency and rotational speed of the dewatering screw press can lead to insufficient compression and an increase in the sludge moisture content.

[66] .

[0069] Rotation speed directly determines the time the sludge is compressed inside the equipment. To investigate the effect of rotation speed on the moisture content of the discharged sludge, sludge with an initial moisture content of 99.2% was selected for treatment at a compression ratio of 3.5 and an outlet pressure of 0.04 MPa. Tests were conducted using different screw shaft rotation speeds of 3 rpm, 4 rpm, 5 rpm, 6 rpm, and 7 rpm. The changes in the moisture content of the discharged sludge corresponding to the five different rotation speeds were obtained, and the results are shown in Table 5. Figure 5 As shown:

[0070] Table 5. Effect of different rotation speeds on the moisture content of discharged sludge.

[0071] Serial Number Screw shaft speed Compression ratio Export pressure Sludge moisture content 1 3rpm 3.5 0.04MPa 91.34％ 2 4rpm 3.5 0.04MPa 89.35％ 3 5rpm 3.5 0.04MPa 88.32％ 4 6rpm 3.5 0.04MPa 87.54％ 5 7rpm 3.5 0.04MPa 86.34％

[0072] As the screw shaft speed decreases, the sludge moisture content decreases non-linearly, while the throughput decreases linearly. The slope of the curve shows that as the speed decreases from 7 rpm to 6 rpm, the decreasing trend in sludge moisture content gradually increases. However, as the speed decreases from 6 rpm to 3 rpm, although the sludge compression time increases, the compression pressure decreases. When the speed drops to 4 rpm, the decreasing trend in sludge moisture content gradually declines. At a compression ratio of 3.5, an outlet pressure of 0.04 MPa, and a screw shaft speed of 3 rpm, the sludge moisture content is 91.34%, and the throughput is 3 m³ / s. 3 / h.

[0073] Flocculant Dosage Validation Example

[0074] With other parameters constant, the dryness of dewatered sludge will vary across different industries. For example, sludge from the paper industry needs to be drier, while sludge from the petroleum industry needs to be wetter. The dosage of PAM in the sludge also has an impact. Generally, cationic PAM is sufficient for sludge dewatering and flocculation. The dosage directly affects the flocculation effect; too low a dosage results in poor flocculation and low sludge dryness, while too high a dosage produces slippery sludge with poor dryness. Appropriate dosage ensures optimal sludge dryness. The stability of sludge inflow concentration and flow rate is also crucial for flocculation. Typically, the sludge concentration transported from the sludge tank fluctuates significantly. Lower sludge concentration leads to increased sludge inflow, which, without intervention, can result in insufficient dosage and poor flocculation. The flocculation dosage should be adjusted according to changes in sludge concentration; as sludge concentration increases, the flocculation dosage should also increase.

[0075] Polyacrylamide, abbreviated as PAM, is a commonly used agent in municipal wastewater treatment. Cationic PAM is generally used when treating municipal sludge. Anionic PAM is typically used for auxiliary flocculation in wastewater. Branched PAM is chosen for decolorization. Nonionic PAM is chosen for non-charge-induced flocculation.

[0076] When used for dehydration flocculation, molecular weight is a frequently considered parameter, which is the length of the molecular chain. Higher molecular weights are generally used in centrifugal dehydrators, while belt dehydrators typically achieve good results with a molecular weight of around 4 million. For this study, considering that the dehydration flocculation time is similar to that of a belt dehydrator, polyacrylamide with a molecular weight between 3 million and 6 million was selected for testing. Ionicity generally refers to the charge density after hydrolysis; a relatively common and stable concentration of 40% ionicity was chosen. Finally, through small-scale trials, a reagent with a molecular weight of 5 million and a 40% ionicity was selected.

[0077] By controlling the flow rate of 0.002 PAM to be 0%-100% of the maximum flow rate, it can be found that when the flow rate is at its maximum (100%), the sludge moisture content is the lowest at 85.9%, and when the flow rate is 50%, the sludge moisture content is the highest at 89.2%.

[0078] During the experiment, samples of the concentrated filtrate were taken and tested, with a focus on the suspended solids moisture content. At a PAM dosage of 50%, the suspended solids content was 150 mg / L; at 80% PAM dosage, it was 220 mg / L; and at 100% PAM dosage, it was 350 mg / L. It is evident that as the moisture content gradually increases, the sludge agitation within the screw press becomes greater, and the rapid reduction of the outer water layer causes the sludge to directly contact the friction plates, resulting in more sludge flocs being passively detached and a significant increase in the suspended solids content of the filtrate. Therefore, in controlling the moisture content, it should be more precisely controlled at around 90% to ensure the highest overall solids recovery efficiency. The test results are shown in Table 6.

[0079] Table 6. Effect of different flocculant dosages on sludge moisture content.

[0080] Serial Number Maximum flow rate at 2‰ PAM flow rate: 130 L / h mud content in effluent 1 80％ 87.5％ 2 100％ 85.9％ 3 50％ 89.2％ 4 0％ 88.5％

[0081] Validation Example of Sludge Moisture Content

[0082] To investigate the effect of influent sludge moisture content on effluent sludge moisture content, tests were conducted at a compression ratio of 3.5, an outlet pressure of 0.04 MPa, a screw shaft speed of 3 rpm, and initial moisture contents of 99%, 98%, 95%, 93%, and 90%. The changes in effluent sludge moisture content corresponding to the five different influent sludge moisture contents were obtained, and the test results are shown in Table 7. Figure 6 As shown, controlling the moisture content of the feed mud reveals that when the feed mud moisture content is at its maximum (99%), the output mud moisture content is the highest at 94.34%, while when the feed mud moisture content is 90%, the output mud moisture content is the lowest at 83.34%.

[0083] It can be seen that the concentration ratio of the screw press dewatering system increases with decreasing moisture content of the influent sludge, depending on the solids content of the sludge. This corresponds to the gradual increase in the residence time within the machine. Therefore, in pretreatment sections with a certain concentration capacity, their operation should be strengthened. In this study, the external reflux ratio of the biological tank in the pretreatment process was 50%, and the concentration of the reflux sludge increased to 12,000 mg / L. Simultaneously, physical sedimentation concentration was performed in the physical thickening tank, stabilizing the influent sludge moisture content between 97.5% and 98.5%. This significantly increased the sludge treatment capacity and the solids throughput of the screw press.

[0084] Table 7. Effect of different influent sludge moisture contents on effluent sludge moisture contents

[0085]

[0086]

[0087] Verification Example of Inflow and Outflow Water Control Mode

[0088] 1. Principle of Inlet and Outlet Water Flow Control System

[0089] During sludge dewatering, the mass of its solids is conserved. Based on this principle, the following derivation can be made: Sludge dewatering rate calculation: (Weight of sludge before dewatering - Weight of sludge after dewatering) / Weight of sludge before dewatering. By controlling the effluent / sludge output, the target sludge moisture content can be achieved.

[0090] 2. Application of inlet and outlet water volume control system

[0091] The sludge from the wastewater treatment plant in this project typically has a moisture content of 99.2%, which can reach 98% after thickening. After treatment with a screw press sludge dewatering machine, the moisture content is generally around 86%. The dewatering outflow rate is 3.5 m³ / h. 3 Under the condition of / h, the influent flow rate is controlled at 3.7m 3 / h, 3.8m 3 / h, 3.9m 3 / h, 4.0m 3 / h, the moisture content of the dewatered sludge was 85.2%, 89.8%, 92.2%, and 93.6%, as shown in Table 8 and Figure 7 As shown.

[0092] Table 8. Effects of different influent volumes on sludge moisture content.

[0093] serial number Original moisture content <![CDATA[Dehydration flow rate (m 3 / h)]]> <![CDATA[Inflow rate (m 3 / h)]]> Moisture content after dehydration 1 99.2％ 3.5 3.7 85.2％ 2 99.2％ 3.5 3.8 89.8％ 3 99.2％ 3.5 3.9 92.2％ 4 99.2％ 3.5 4.0 93.6％

[0094] As can be seen from the table above, by controlling the influent flow rate, the moisture content of the dewatered sludge can be effectively controlled within the range of 85% to 95%.

[0095] 3. Verification of the inlet and outlet water flow control system

[0096] To verify the accuracy and precision of the theoretical formula calculations, on-site calibration was performed according to the method for determining sludge moisture content in CJ / T 221-2005. Dewatered sludge obtained under different inflow conditions was measured and calculated according to the aforementioned national standard to obtain the actual moisture content of the dewatered sludge, which was then compared with the results calculated by the theoretical formula, as shown in Table 9. Figure 8 As shown:

[0097] Table 9 Comparison of theoretical moisture content of sludge discharged from the control system with the moisture content measured according to national standards.

[0098]

[0099] The data comparison above shows that the sludge moisture content calculated by the theoretical formula is basically consistent with the actual measured sludge moisture content, and the error is within the allowable range. This indicates that, under the condition of a certain dewatering outflow rate, controlling the inflow rate through an automatic control system to ensure that the sludge moisture content is within the range of 85% to 95% is an effective and feasible technical means to meet the requirements of various subsequent treatments.

[0100] Frequency Domain Reflection Analysis (FDR) Control Mode Verification Example

[0101] 1. Frequency Domain Reflectance Analysis (FDR) Control Mode Principle

[0102] Sludge moisture sensing technology based on frequency domain reflectance analysis is a novel method for rapidly measuring sludge moisture content by utilizing the dielectric properties of sludge. This method outperforms other measurement methods in terms of real-time performance and accuracy, making it suitable for real-time measurement of sludge moisture content.

[0103] FDR technology has been widely used in the rapid measurement of soil and food moisture, and can also be applied to the rapid measurement of sludge moisture content. The FDR method mainly utilizes the oscillation of LC capacitors and inductors to measure the dielectric constant of different types of sludge by measuring the change in electromagnetic wave oscillation frequency, and then uses the relationship between dielectric constant and moisture content to inversely determine the moisture content of the sludge.

[0104] In a gas-liquid-solid three-phase system, the dielectric constant of water (εw = 80, 20℃) is much greater than that of sludge solids (εs = 3-4, 20℃) and air (εa = 1, 20℃). Therefore, the dielectric constant of sludge mainly depends on the water content, and thus the water content of sludge can be indirectly obtained from the dielectric constant.

[0105] The principle of FDR sludge moisture content monitoring is as follows: Figure 9 As shown, this monitoring device utilizes the oscillation of an LC circuit to determine the dielectric constant of a medium based on the change in the oscillation frequency of electromagnetic waves in different media. Furthermore, it infers the sludge moisture content through a specific correlation. The frequency F of the LC oscillation circuit is expressed as:

[0106]

[0107] In the formula: L — inductance;

[0108] C — Capacitor.

[0109] The inductance L of the sludge moisture monitoring instrument is constant; therefore, the oscillation frequency F depends only on the capacitance C. The dielectric properties of the sludge primarily affect the capacitance. When the dielectric properties of the sludge change, the capacitance also changes, and so does the frequency. Therefore, there is a certain correlation between the oscillation frequency and the sludge moisture content outside the pipe sleeve. The sludge moisture content can be calculated and deduced from the frequency of the LC oscillation circuit.

[0110] 2. Application of Frequency Domain Reflection Analysis (FDR) Control Mode

[0111] The FDR method can directly determine the moisture content of dewatered sludge without requiring the measurement of the dewatering outflow rate, reducing calculation steps and thus minimizing errors. The moisture content of dewatered sludge under the aforementioned inflow conditions was repeatedly measured using the FDR method, as shown in Table 10. Figure 10 As shown:

[0112] Table 10 Theoretical Moisture Content by FDR Method

[0113] serial number Original moisture content Dewatering flow rate (m³ / h) Inflow rate (m³ / h) FDR determination of moisture content 1 99.2％ 3.5 3.7 85.2％ 2 99.2％ 3.5 3.8 90.1％ 3 99.2％ 3.5 3.9 92.0％ 4 99.2％ 3.5 4.0 94.4％

[0114] Depend on Figure 10 It can be seen that the moisture content of the dewatered sludge obtained by the FDR automatic online measurement method is within the effective range of 85% to 95%.

[0115] Validation of 3-Frequency Domain Reflection Analysis (FDR) Control Mode

[0116] Table 11 Comparison of theoretical moisture content determined by FDR method and national standard method

[0117]

[0118] Comparative analysis of the above data reveals that the moisture content of effluent sludge determined by the FDR automatic online detection method is generally higher than that determined by the national standard gravimetric method, but its error is smaller than that of the theoretically calculated moisture content, thus exhibiting higher accuracy.

[0119] Example of Dehydration System Operating Parameters and Economic Analysis

[0120] After being processed by the sludge treatment unit (12 belt thickeners in the dewatering room), the actual sludge production in recent years has been approximately 500 tons / day (80% moisture content). Due to its low moisture content and poor flowability, the dewatered sludge is difficult to transport via pipeline, leading to frequent plunger pump failures. The remaining sludge is transported by truck to the Jinan Sludge Treatment Plant located northwest of the plant site for disposal, ultimately used for land reclamation. This sludge treatment plant is located north of the Jinan Wastewater Treatment Plant site, 300 meters away. It is adjacent to the biological treatment pond of the wastewater treatment plant to the southeast (across a road) and connected to the dewatering room of the wastewater treatment plant to the southwest (across a road), with the shortest distance being 20 meters. It is separated from the Jinan Wastewater Treatment Plant by a road, with no partition wall between the two plants. The entrance gate of the wastewater treatment plant will be used as the access route for this project. Therefore, it possesses excellent economic and technical conditions for the renovation.

[0121] 1. Parameters of existing belt sludge dewatering units

[0122] The existing dewatering room uses a mechanical thickening and dewatering process. The dewatered sludge is then transported to a sludge treatment plant for digestion, plate and frame dewatering, and drying. Details are shown in Table 12.

[0123] Table 12 Existing Sludge Dewatering Equipment

[0124]

[0125] In actual operation, the moisture content of sludge entering the dewatering machine at a wastewater treatment plant is affected by multiple factors, including operating conditions, influent water quality, and sludge discharge method. Therefore, the optimal sludge moisture content for this model is between 99.2% and 95%. It employs indoor thickening followed by in-depth dewatering and is suitable for residual sludge from biological treatment tanks, primary sludge from primary sedimentation tanks, and chemical sludge from high-density sedimentation tanks. After thickening, dewatering, and mixing, the solids content of the dewatered sludge is greater than 20%.

[0126] The basic parameters of a belt dewatering machine are as follows:

[0127]

[0128] Parameters of 2-Press Screw Type Sludge Dewatering Unit

[0129] The wastewater treatment plant plans to use a screw press dewatering machine to dewater existing sludge. The supporting equipment for the screw press dewatering machine is shown in Table 13. This equipment is a pilot-scale test, but since screw press machines rely on quantity for scale-up, this study already possesses certain conditions and foundations for production-scale testing. Based on this, scaling up parameters can achieve engineering-scale production.

[0130] Table 13. Screw-type dewatering equipment

[0131]

[0132]

[0133] The basic parameters of the screw press dewatering machine are as follows: Processing capacity: 30-50 kgDS / hr; Sludge concentration: 20000 mg / L. Each screw press consists of: screw, shell, inlet, outlet, back pressure plate, water tank, rinsing water mechanism, flocculation mixing tank, electrical control box, and drive unit. The screw press motor and reducer are KG series products, the flocculation mixing tank is an NMRV series product, all parts in contact with water are made of 304L stainless steel, and the rest are made of 304 stainless steel. The electrical control box is made of 316L stainless steel.

[0134] Comparison of dehydration effects between 3-screw dehydrator and existing technologies

[0135] 3.1 Comparison of Moisture Content Control

[0136] Table 14 Comparison of dehydration effects between screw press dehydrator and belt dehydrator

[0137] Sludge dewatering machine categories Screw press sludge dewatering machine Belt sludge dewatering machine Solid content of mud ≥2％ ≥3.5％ Moisture content of mud cake 85％～95％ 80％ Filtrate solids content ≤2000mg / L ≤1000mg / L

[0138] As shown in Table 14, due to the adjustable screw press dewatering machine's features of screw pitch, screw diameter, screw compression ratio, screw speed, and outlet pressure, the sludge moisture content can be adjusted between 85% and 95% to meet the 92% sludge moisture content requirement of the Jinan sludge treatment plant. This is more practical and better suited to the actual needs of the plant compared to the fixed 80% sludge content of belt dewatering machines.

[0139] Table 15 Actual Operating Data of the Screw Press Dehydrator

[0140]

[0141]

[0142] As shown in Table 15, the 22-day continuous monitoring data shows that the screw press has met the stability requirements and can stably meet the required sludge moisture content even when the moisture content is high (above 98%).

[0143] 3.2 Comparison of Flocculant Dosage

[0144] Table 16 Comparison of Flocculant Dosage between Screw Press Dewatering Machine and Belt Dewatering Machine

[0145] Sludge dewatering machine categories Screw press sludge dewatering machine Belt sludge dewatering machine unit flocculant concentration 0.2％ 0.1％ / Total flocculant dosage 0.5～1.5 3～5 kg / t ds

[0146] As shown in Table 16, since the requirements for the target moisture content of sludge in screw press dewatering machines are not as high as those in belt dewatering machines, only a small amount of flocculant is needed to meet the requirements. This saves on operating costs compared to the 3-5 kg / t ds flocculant required for belt dewatering machines.

[0147] Table 17 Flocculant Dosage for Screw Press Dewatering Machine

[0148]

[0149]

[0150] As shown in Table 17, the 22-day continuous monitoring data shows that the screw press has met the stability requirements and the dosage can meet the stability requirements under actual continuous operation.

[0151] 3.3 Comparison of Automatic Control

[0152] Screw press dewatering machines can be controlled via frequency domain reflectance analysis and electrical control cabinet, and linked with chemical stations, sludge pumps, and dosing pumps to achieve 24-hour continuous automatic operation. While belt conveyors offer manual, local PLC automatic control, and remote automatic control modes, they are insufficient for portable control of sludge moisture content. They can only remotely control the start and stop of sludge dewatering, which is far from adequate for wastewater treatment plants to achieve unattended operation and real-time control of sludge effluent volume. After the process control system was upgraded, its stability and processing capacity were greatly improved, and the sludge moisture content and actual processing volume were significantly increased.

[0153] 3.4 Comparison of Operating Costs

[0154] The data in this section are based on the assumption that 90% of the sludge is directly supplied to the sludge plant. After installing six XX404 model units (i.e., a large screw press with a single screw press diameter of 400mm, four units combined into one), and customizing these units according to experimental parameters, this configuration should basically meet the plant's sludge treatment needs. The following is a comparative analysis of operating costs:

[0155] As shown in Table 18, compared to belt dewatering machines, screw press dewatering machines can transport sludge to the sludge plant using a small-power sludge transfer pump, reducing screw power consumption and eliminating the need for two high-power plunger pumps, significantly lowering power consumption (90 kWh / unit) and overall electricity consumption for dewatering. In practical applications, screw press dewatering machines save approximately 1.32 million yuan per year in electricity costs compared to belt dewatering machines. Meanwhile, screw press dewatering machines have very low maintenance costs, while belt dewatering machines require relatively more frequent maintenance, resulting in annual savings of 1.29 million yuan in repair costs. Furthermore, using belt dewatering machines would require manual and vehicle transportation, including labor, transportation, and loading costs, totaling approximately 250,000 yuan.

[0156] The application of screw press dewatering machines can effectively concentrate and dewater sludge, efficiently control the moisture content of dewatered sludge, and supply it directly to sludge plants through pipelines. This improves the accuracy of sludge dewatering management, reduces energy consumption costs, and saves approximately 2.86 million yuan annually. It also enhances the level of intelligent sludge dewatering, effectively controls labor costs, and has good practical significance. It can be promoted and applied to similar wastewater treatment plants.

[0157] Table 18 Cost Comparison Table

[0158]

[0159]

[0160] 3.5 Comparison of other aspects

[0161] Table 19 Comparison of Sludge Dewatering Machine Performance

[0162] project Belt sludge dewatering machine Screw press sludge dewatering machine Dehydration methods Gravity + Shear floating ring stacked dehydration Direct dewatering of low-concentration sludge Can't Can sludge thickening tank need unnecessary sludge storage tank need unnecessary Space occupied middle Small Continuous operation It's possible, but difficult. Can Environmental hygiene conditions generally good noise big Small Maintenance Management More convenient convenient Rinse water volume Larger Small Electricity consumption Larger Small power consumption Approximately 3 to 5 times that of a stacked spiral. Small Comprehensive cost generally lower

[0163] In addition, compared with belt filter presses, screw presses have the following characteristics: 1. The method of adding flocculants beforehand solves the connection problem of sludge entering the filter press section, improving the concentration effect. It belongs to compression sedimentation, mainly removing the void water between sludge particles. 2. Good phosphorus removal effect, improving the overall operation efficiency of the wastewater treatment plant. 3. Saves investment, reduces the footprint, and can reduce overall costs. Integrated equipment can replace traditional sludge thickening tanks, reducing the footprint of the wastewater treatment plant and lowering construction costs. 4. Adopts low-speed screw extrusion technology, resulting in low power consumption. 5. It has a self-cleaning effect; the strong internal pressure of the filter element prevents sludge blockage, achieving excellent energy-saving and consumption-reducing effects. 6. It achieves small and lightweight equipment, simplifying operation and control.

Claims

1. A sludge dewatering method, using a sludge dewatering device, characterized in that: The sludge dewatering device includes a screw press dewatering machine, a sludge pump, a dosing pump, a stirrer, and a controller. The inlet of the screw press dewatering machine is connected to the outlets of the sludge pump and the dosing pump via pipelines. The outlet of the sludge pump is equipped with a sludge flow meter, the outlet of the dosing pump is equipped with a dosing flow meter, and the filtrate outlet of the screw press dewatering machine is equipped with a filtrate flow meter. The controller is electrically connected to the sludge pump, the dosing pump, the stirrer, the sludge flow meter, the dosing flow meter, and the filtrate flow meter. The screw pitch of the screw press dewatering machine is 3-4 mm, the screw shaft diameter is 40-55 mm, the screw shaft compression ratio is 2-3.5, the screw shaft speed is 3-7 rpm, and the outlet pressure is 0.02-0.04 MPa. The screw press dewatering machine is equipped with a frequency domain reflectance analysis sensor, which is electrically connected to the controller. The sensor senses the moisture content of the sludge entering the screw press dewatering machine, and the controller adjusts the speed of the screw press dewatering machine based on the change in moisture content to achieve the target flow rate of the filtrate. Ensure that the discharged sludge reaches the target moisture content; The formula for controlling the target flow rate of the discharged filtrate is as follows: ； In the formula, To control the target flow rate of the discharged filtrate, The flow rate of sludge entering the screw press dewatering machine is monitored by a sludge flow meter located at the sludge pump outlet. The moisture content of the sludge entering the screw press dewatering machine. The amount of chemical solution entering the screw press dewatering machine is monitored by a flow meter located at the discharge port of the dosing pump. The target moisture content for the sludge discharged from the screw press dewatering machine. +1 The density of suspended solids in the discharged filtrate is expressed in g / L and is a constant value over a certain period of time. The 1 represents the concentration of dissolved suspended solids in the sludge of the municipal wastewater treatment plant, expressed in g / L.

2. The sludge dewatering method according to claim 1, characterized in that: The flocculant dosage of the aforementioned screw press dewatering machine is 0.5-1.5 kg / t ds.

3. The sludge dewatering method according to claim 1, characterized in that: The feed sludge moisture content of the aforementioned screw press dewatering machine is 97.5%-98.5%.

4. The sludge dewatering method according to claim 1, characterized in that: The screw press dewatering machine is also equipped with an online turbidity meter, which is electrically connected to the controller.

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