Low-carbon dehydration treatment method for high-organic-matter sludge

Abstract

The invention provides a low-carbon dehydration treatment method for high-organic-matter sludge, and belongs to the technical field of sludge treatment. A low-carbon dehydration treatment method for high-organic-matter sludge comprises the following steps that food wastewater sludge is fed into a conditioning tank, a ferric chloride solution is added, the mass of FeCl3 accounts for 3.3%-7.0% of the mass of absolute dry sludge, and a mud cake is obtained after stirring, standing and filter pressing are conducted. According to the method, concentration is canceled, lime and PAM are not added, sludge self-flocculation is used in cooperation with low-dosage ferric chloride conditioning, the treatment time is shortened to 2.5 hours from 4 hours or above, the dosage of ferric chloride is reduced by about 50%, the efficiency is remarkably improved, the cost is reduced, and meanwhile the treatment cost is reduced. The problems that the pH value of a mud cake is too high, the calorific value is reduced, and the follow-up disposal approach is limited due to addition of lime are thoroughly avoided, and efficient, low-carbon and low-cost collaborative optimization of sludge dewatering and recycling is achieved.

Description

Technical Field

[0001] This invention belongs to the field of sludge treatment technology, specifically relating to a low-carbon dewatering treatment method for high organic matter sludge. Background Technology

[0002] With the rapid development of my country's food and agricultural product processing industries, the large amount of residual sludge generated after the biochemical treatment of their production wastewater has become a challenge for environmental governance. This type of sludge originates from processes such as beer, starch, brewing, dairy, and meat processing. Its core characteristics are extremely high organic content (volatile solids typically account for over 60% on a dry basis), fine sludge particles, and strong colloidal stability, resulting in extremely poor dewatering performance. Specifically, it exhibits huge specific resistance and a long capillary time to water absorption (CST) (>100 seconds), classifying it as typical difficult-to-dewater sludge.

[0003] Currently, for this type of high-organic-matter sludge, the industry generally uses a three-stage traditional process of "concentration + chemical conditioning + mechanical dewatering". First, the sludge moisture content is reduced from approximately 98% to 92%-95% through gravity thickening or mechanical thickening (such as a screw press), while polyacrylamide (PAM) is added to promote solid-liquid separation. Then, a large amount of chemical conditioning agent, usually a compound of ferric chloride and lime, is added during the conditioning stage to disrupt the sludge's colloidal structure and improve dewatering performance. Finally, the sludge is pressed and dewatered using equipment such as a plate and frame filter press.

[0004] However, this traditional process suffers from a series of significant drawbacks when treating high-organic-matter sludge due to mechanistic mismatch: The process is lengthy and inefficient; multiple stages in series result in single-batch processing times often exceeding 4 hours, leading to low equipment utilization. It also consumes large quantities of chemicals, resulting in high costs: it relies on PAM for front-end concentration and requires the addition of large doses of ferric chloride (typically 8%-15% of the oven-dry sludge weight) and lime (8%-15% of the dry sludge weight) for double conditioning, keeping chemical costs high.

[0005] The addition of lime causes serious secondary problems. Lime leads to an excessively high pH value (>11) in the sludge cake, which not only reduces its calorific value, hindering its energy utilization through incineration, but also corrodes incinerator equipment. Simultaneously, the high alkalinity severely limits the safe disposal of sludge in agricultural land use and building material production. Lime itself, as an inert additive, does not participate in the dehydration reaction; instead, it significantly increases the yield of oven-dry sludge cake, increasing the load and costs of subsequent transportation and disposal. Continuous operation of multiple units results in high cumulative power consumption, and particulate matter such as lime exacerbates the wear and tear on pumps, valves, and pipelines.

[0006] In recent years, although some studies have attempted to optimize conditioning agents or improve equipment, most have remained within the established mindset of "pre-concentration" and "lime dependence." CN113415975A discloses a method for treating sludge, which involves concentrating sludge to obtain concentrated sludge, then mixing the concentrated sludge with biochar and a conditioning agent before feeding it to a plate and frame filter press for dewatering. The dewatered sludge obtained by this method has low specific resistance and low compressibility, achieving sludge volume reduction. However, the efficiency and cost of sludge treatment equipment still need improvement. CN109987816A discloses a method for dewatering and concentrating industrial sludge, which involves adding a dewatering agent to the sludge and sequentially processing it through a first mixing tank, a second mixing tank, a third mixing tank, and then a filter press. This method can extend the service life of the filter cloth in the filter press, shorten the working cycle to 1.5-2 hours, and allow the sludge cake to dry completely in 2-3 days naturally. However, this method still needs further optimization in terms of the range and optimal dosage of dehydrating agents to improve dehydration effect and shorten processing time.

[0007] Therefore, for sludge with high organic matter and high specific resistance, there is an urgent need to develop a new dewatering method and system that can completely eliminate the pre-concentration step, completely avoid lime addition, and significantly reduce the amount of iron salt used. This would fundamentally solve a series of problems existing in current technologies, such as long process, high chemical consumption, high cost, serious secondary pollution, and limited subsequent disposal methods, and achieve low-carbon, efficient, and resource-based treatment of sludge. Summary of the Invention

[0008] In view of this, the present invention provides a low-carbon dewatering treatment method for high organic matter sludge, in order to solve the technical problems of long process, high chemical consumption, high cost and serious secondary pollution in the treatment of high organic matter sludge in the prior art.

[0009] To achieve the above-mentioned objective, this invention provides a low-carbon dewatering treatment method for high-organic-matter sludge, comprising the following steps: S1, with a moisture content of 97.3%-98% and a specific resistance of 5-10×10⁻⁶. 13 Food wastewater sludge at a concentration of m / kg is fed into the conditioning tank; S2. Add ferric chloride solution, wherein the mass of FeCl3 is 3.3%-7.0% of the oven-dry sludge mass; S3. After stirring and settling, conditioned sludge is obtained; S4. Pump the conditioned sludge into a plate and frame filter press for feeding and pressing to obtain sludge cake.

[0010] Preferably, the food wastewater sludge is residual sludge from a soy sauce processing plant or residual sludge from a malt processing plant.

[0011] Preferably, the mass concentration of the ferric chloride solution in S2 is 30-35%.

[0012] Preferably, the stirring speed in S3 is 150-250 r / min.

[0013] Preferably, the stirring time in S3 is 3.5-4.5 minutes.

[0014] Preferably, the standing time mentioned in S3 is a standing reaction at room temperature and pressure for 30-35 minutes.

[0015] Preferably, the pressing pressure in S4 is 1.5-2.0 MPa, and the pressing time is 30-40 minutes.

[0016] Preferably, the moisture content of the mud cake in S4 is 70-73%.

[0017] This invention achieves effective activation of the self-flocculation potential of food wastewater sludge and efficient synergy with chemical conditioning through precise control of conditioning process parameters. The self-flocculation effect of this type of sludge is most significant when its moisture content is 97.3%-98%. This invention eliminates pre-concentration, directly treating the sludge in this state, and employs a stirring intensity of 150-250 r / min and a stirring time of 3.5-4.5 min. This provides sufficient energy to promote the release of extracellular polymeric substances (EPS) from the sludge, enhance particle collision and flocculation, while avoiding excessive shearing that could lead to floc destruction. Based on this, a small amount of ferric chloride (FeCl3 accounting for 3.3%-7.0% of the dry sludge mass) is added in combination. The positive charge generated by its hydrolysis can efficiently neutralize the negative charge on the surface of the sludge colloid, further compress the double layer and reduce the Zeta potential. This produces a "charge neutralization-bridging" synergistic effect with the biofloc skeleton formed by self-flocculation, thereby forming a dense and hydrophobic floc structure in a very short time. This significantly improves the dewatering performance and filtration rate of the sludge. Ultimately, it achieves the beneficial effect of obtaining low moisture content sludge cake and improving treatment efficiency while eliminating the addition of lime and PAM and significantly reducing the amount of iron salt.

[0018] Compared with the prior art, the present invention has the following beneficial effects; This invention innovatively skips the mechanical thickening step and utilizes the self-flocculation potential of high-organic-matter sludge, combined with precisely optimized ferric chloride dosage (only 3.3%-7.0% of the oven-dry sludge mass), achieving highly efficient conditioning of high-resistivity sludge without the addition of lime or PAM. This process significantly shortens the traditional three-stage "thickening + conditioning + dewatering" process, which takes over 4 hours, to approximately 2.5 hours, significantly improving treatment efficiency and equipment utilization. Regarding reagent costs, it completely eliminates the purchase and addition costs of lime and PAM, and reduces the high proportion of ferric chloride dosage (typically 8%-15%) in traditional processes by about 50%, achieving extreme simplification of reagent consumption from the source. Simultaneously, the absence of lime fundamentally solves a series of secondary problems caused by excessively high pH values ​​(>11) in the sludge cake: it maintains the calorific value of the sludge cake, facilitating subsequent energy incineration without corroding equipment, and eliminates the risk of soil alkalization, opening up avenues for the agricultural and building material resource utilization of sludge. The resulting sludge cake has a stable moisture content of around 70% and a dense and uniform structure. Furthermore, the entire system has lower energy consumption, reduced equipment wear, and enhanced operational reliability due to the simplified process. This achieves synergistic optimization of efficiency, cost, environmental protection, and resource utilization in the dewatering treatment of high organic matter sludge. Attached Figure Description

[0019] Figure 1 This is a photograph of the mud cake prepared in Example 1. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] Example 1 In this embodiment, the food wastewater sludge to be treated is residual sludge from a malt processing plant, with a moisture content of 98% and a specific resistance of 10 × 10⁻⁶. 13 m / kg, higher than the specific resistance range of easily dewatered sludge. The sludge particles are fine and unevenly distributed.

[0022] This embodiment provides a low-carbon dewatering treatment method for high-organic-matter sludge, comprising the following steps: S1. Feed the food wastewater sludge into the conditioning tank; S2. Add ferric chloride solution, wherein the mass of FeCl3 is 3.3% of the dry sludge mass, and the mass concentration of the ferric chloride solution is 30%. S3. Stir at 150 r / min for 4.5 minutes, and let stand at room temperature and pressure for 30 minutes to obtain conditioned sludge; S4. Pump the conditioned sludge into a plate and frame filter press for feeding and pressing. The pressing pressure is 1.5 MPa, and the pressing time is 40 minutes. The time for a single batch is about 2.5 hours, yielding a sludge cake with a moisture content of 73%. A picture of the cake is shown below. Figure 1 The pH of the mud cake is approximately 6.2.

[0023] Example 2 In this embodiment, the food wastewater sludge to be treated is residual sludge from a malt processing plant, with a moisture content of 97.3% and a specific resistance of 5 × 10⁻⁶. 13 m / kg, higher than the specific resistance range of easily dewatered sludge. The sludge particles are fine and unevenly distributed.

[0024] This embodiment provides a low-carbon dewatering treatment method for high-organic-matter sludge, comprising the following steps: S1. Feed the food wastewater sludge into the conditioning tank; S2. Add ferric chloride solution, wherein the mass of FeCl3 is 7.0% of the dry sludge mass, and the mass concentration of the ferric chloride solution is 35%. S3. Stir at 250 r / min for 3.5 minutes, and let stand at room temperature and pressure for 35 minutes to obtain conditioned sludge; S4. Pump the conditioned sludge into a plate and frame filter press for feeding and pressing. The pressing pressure is 2.0 MPa and the pressing time is 30 minutes to obtain a sludge cake with a moisture content of 70%.

[0025] Example 3 In this embodiment, the food wastewater sludge to be treated is residual sludge from a malt processing plant, with a moisture content of 97.5% and a specific resistance of 8 × 10⁻⁶. 13 m / kg, higher than the specific resistance range of easily dewatered sludge. The sludge particles are fine and unevenly distributed.

[0026] This embodiment provides a low-carbon dewatering treatment method for high-organic-matter sludge, comprising the following steps: S1. Feed the food wastewater sludge into the conditioning tank; S2. Add ferric chloride solution, wherein the mass of FeCl3 is 5.2% of the dry sludge mass, and the mass concentration of the ferric chloride solution is 32%. S3. Stir at 200 r / min for 4 minutes, and let stand at room temperature and pressure for 32 minutes to obtain conditioned sludge; S4. The conditioned sludge is pumped into a plate and frame filter press for feeding and pressing. The pressing pressure is 1.8 MPa and the pressing time is 35 minutes. The time for a single batch is 2.5 hours, and a sludge cake with a moisture content of 72% and a pH of about 6.5 is obtained.

[0027] Comparative Example 1 This comparative example is the same as the example, except that the mass of FeCl3 in S2 in this comparative example is 2.0% of the dry sludge mass. The moisture content of the sludge cake is 80%.

[0028] Comparative Example 2 This comparative example is the same as the example, except that the mass of FeCl3 in S2 in this comparative example is 8.0% of the dry sludge mass. The moisture content of the sludge cake is 73%.

[0029] Comparative Example 3 This comparative example is the same as the previous example, except that the stirring speed in S3 of this comparative example is 100 r / min. The moisture content of the mud cake is 79%.

[0030] Comparative Example 4 This comparative example is the same as the example, except that the stirring speed in S3 of this comparative example is 300 r / min. The moisture content of the mud cake is 76%.

[0031] The dewatering performance of sludge is determined by the particle aggregation state, surface charge, and water removal resistance. Sludge particle size reflects floc size; larger particle size usually means denser floc structure, providing a smoother channel for water outflow and facilitating dewatering. Zeta potential characterizes the charge stability of colloidal particle surface; the closer its absolute value is to zero, the weaker the electrostatic repulsion between particles, making it easier to destabilize and aggregate into large flocs, thus improving dewatering performance. Capillary absorption time (CST) comprehensively reflects the actual ease of water removal from sludge, and it is directly affected by particle size and Zeta potential. When the particle size is too small and the absolute value of Zeta potential is too high, the sludge particles are stable, fine, and have a high bound water content, which leads to a significant increase in CST value, indicating extremely poor dewatering performance.

[0032] Conditioned sludge from Examples 1-3 and Comparative Examples 1-4 was taken, and its sludge particle size, Zeta potential, and capillary absorption time (CST) were measured respectively. The measurement results are shown in the table below.

[0033] Table 1. Statistics of sludge particle size, Zeta potential, and capillary absorption time (CST) for each group. Comparing the test data of Example 1 and Comparative Examples 1 and 2, both excessive and insufficient addition of ferric chloride negatively impacts the dewatering properties of the conditioned sludge. Insufficient ferric chloride dosage fails to adequately neutralize the negative charge on the sludge colloid surface, resulting in strong electrostatic repulsion between particles and hindering effective collision and aggregation to form large, dense flocs. Consequently, numerous fine, dispersed particles easily clog the filter cloth pores during the filter press process, and the resulting filter cake structure is loose and has small pores, making it difficult for bound water to be mechanically expelled. This ultimately leads to low dewatering efficiency and high moisture content in the sludge cake.

[0034] Conversely, when excessive ferric chloride is added, the excess positive charge causes a "charge reversal" on the surface of the colloidal particles, changing them from negative to positive. The particles then re-disperse due to the repulsion of like charges. Simultaneously, the large amount of fine hydroxide colloids generated from the hydrolysis of excess ferric chloride encapsulates and blocks the internal channels of the flocs, increasing sludge viscosity and compressibility. During filter press filtration, this over-conditioned sludge forms a dense but poorly permeable filter cake, making it difficult for external pressure to be effectively transmitted to the interior. This increases resistance to water removal, further deteriorating dewatering performance and unnecessarily increasing reagent costs and sludge dry weight.

[0035] Comparing the test data of Example 1 with Comparative Examples 3 and 4, it can be seen that both excessively fast and excessively low stirring speeds have a negative impact on the dewatering properties of the conditioned sludge. When the stirring speed is too low, the shear force generated is insufficient to break the initial stable system of the sludge colloid, failing to provide enough collision energy for the sludge particles. This results in insufficient release of the extracellular polymers (EPS) abundant in the sludge and low interparticle contact efficiency. Consequently, the sludge's "self-flocculation" potential cannot be effectively activated, making it difficult to form dense flocs with good settling and dewatering properties. Subsequent chemical conditioning (such as Fe) also hinders this process. 3+ Electron neutralization is also difficult to carry out efficiently in a homogeneous system, ultimately leading to poor dehydration performance.

[0036] When the stirring speed is too high, the excessive shear force will mechanically break up and crush the flocs that have already formed or are in the process of forming, destroying their skeletal structure. This not only negates the positive effects of self-flocculation and chemical conditioning, but also produces a large number of fine fragments that are difficult to dewater, increasing the viscosity and specific surface area of ​​the sludge system. These fine particles will severely clog the pores of the filter cloth and form a dense but extremely poorly permeable filter cake layer during pressure filtration, greatly increasing filtration resistance and preventing water from being removed smoothly, thus leading to a significant decrease in dewatering efficiency.

[0037] Comparative Example 5 Approximately 27 cubic meters of residual sludge from the malt processing plant wastewater, with a sludge concentration of 18,000 mg / L, were discharged. 3The sludge is pumped to a screw press thickener and mixed with polyacrylamide (PAM) solution (3.75 kg PAM dosage) to thicken the sludge to a moisture content of 92%. It then enters a conditioning tank where 82.5 kg of 35% ferric chloride solution and 200 kg of lime are added and stirred for approximately 30 minutes. The mixture is then pumped to a plate and frame filter press at a feed pressure of 1.3 MPa, simultaneously squeezing out most of the filtrate. After stopping the feed, the pressing system is started at a pressure of 1.6 MPa to further squeeze out the filtrate. The entire process takes 4 hours, producing 2.24 tons of filter cake with a moisture content of 65%. After removing the lime influence (approximately 25%), the oven-dry sludge yield is 0.58 t / plate.

[0038] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A low-carbon dewatering treatment method for high-organic-matter sludge, characterized in that, Includes the following steps: S1, with a moisture content of 97.3%-98% and a specific resistance of 5-10×10⁻⁶. 13 Food wastewater sludge at a concentration of m / kg is fed into the conditioning tank; S2. Add ferric chloride solution, wherein the mass of FeCl3 is 3.3%-7.0% of the oven-dry sludge mass; S3. After stirring and settling, conditioned sludge is obtained; S4. Pump the conditioned sludge into a plate and frame filter press for feeding and pressing to obtain sludge cake.

2. The low-carbon dewatering treatment method for high-organic-matter sludge according to claim 1, characterized in that, The food wastewater sludge is residual sludge from soy sauce processing plants or malt processing plants.

3. The low-carbon dewatering treatment method for high-organic-matter sludge according to claim 1, characterized in that, The mass concentration of the ferric chloride solution in S2 is 30-35%.

4. The low-carbon dewatering treatment method for high-organic-matter sludge according to claim 1, characterized in that, The stirring speed in S3 is 150-250 r / min.

5. The low-carbon dewatering treatment method for high-organic-matter sludge according to claim 4, characterized in that, The stirring time in S3 is 3.5-4.5 minutes.

6. The low-carbon dewatering treatment method for high-organic-matter sludge according to claim 1, characterized in that, The standing time mentioned in S3 refers to the reaction being allowed to stand at room temperature and pressure for 30-35 minutes.

7. The low-carbon dewatering treatment method for high-organic-matter sludge according to claim 1, characterized in that, The pressing pressure described in S4 is 1.5-2.0 MPa, and the pressing time is 30-40 minutes.

8. The low-carbon dewatering treatment method for high-organic-matter sludge according to claim 1, characterized in that, The mud cake described in S4 has a moisture content of 70-73%.

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