Method for improving sludge dewatering and resource utilization of dewatering product and application

Abstract

The invention discloses a method for improving sludge dewatering and resource utilization of dewatering products, which comprises the following steps: heating sludge to about 65 DEG C, keeping the constant temperature, adding a ferrous sulfate heptahydrate solution and a calcium hypochlorite solution, fully reacting, and performing vacuum filtration and dewatering. The dehydrated cement cake is prepared into iron-rich biochar which is applied to wastewater treatment. The calcium hypochlorite is activated through low-temperature heating in cooperation with ferrous iron to generate a large number of active substances (. OH), and tightly combined extracellular polymeric substances and hydrophilic organic matters in cells are effectively degraded, so that the water binding capacity of sludge flocs is remarkably reduced, and the sludge dewatering performance is improved. In order to reduce iron sludge accumulation and improve the utilization value of dewatered sludge cakes, the dewatered sludge cakes are pyrolyzed in a nitrogen atmosphere to prepare iron-rich sludge biochar which is used for wastewater treatment. According to the method, the sludge dewatering performance is improved, the resource utilization value of the sludge cake is enhanced, and a novel and complete technical path is provided for sludge treatment and disposal.

Description

Technical Field

[0001] The invention belongs to the technical field of sludge treatment, and particularly relates to a method for improving sludge dehydration and resource utilization of dehydration products and an application thereof. Background Art

[0002] Excess sludge originates from domestic sewage treatment processes and is characterized by high moisture content and organic matter content. Due to its strong hydrophilicity and difficulty in dewatering, excess sludge is challenging to treat. Sludge dewatering is a key technology for addressing the high sludge production at the end of sewage treatment plants. Its dewatering effectiveness significantly impacts sludge resource utilization and treatment costs. Waste activated sludge contains a large amount of organic matter and has excellent resource utilization potential. However, extracellular polymeric substances (EPPs), composed of large hydrophilic molecules such as proteins and polysaccharides, possess a stable colloidal structure and are a major barrier to dehydration. This is a challenge that traditional mechanical dewatering technologies struggle to address.

[0003] Advanced oxidation technologies (AOTs) have attracted widespread attention for their ability to effectively destroy extracellular polymeric substances (ECPs) and degrade hydrophilic organic matter in sludge. The choice of oxidant and its activation method are key factors in determining the efficiency of AOTs. Common oxidants, such as hydrogen peroxide, calcium peroxide, and persulfates, still face challenges in terms of safety and affordability. Calcium hypochlorite, due to its rapid onset and outstanding bleaching properties, has long been used as a bleaching agent and disinfectant. In recent years, as a strong oxidant, calcium hypochlorite has been increasingly used in water pollution control and sludge treatment and disposal. Patent CN201510091619 utilizes a combination of calcium hypochlorite and pulverized coal to produce a non-toxic and non-toxic sludge deodorizer that rapidly removes odors from sludge. Previous studies have shown that calcium hypochlorite can also enhance sludge dissolution, hydrolysis, and acidification, promoting fermentation. Patent CN202111352913 utilizes calcium hypochlorite to promote the release of organic matter from sludge, providing more substrate for methane production during anaerobic digestion, significantly increasing methane production during anaerobic digestion. However, the ability of oxidants alone to act on wastewater treatment and sludge disposal is limited and requires catalytic activation to improve performance.

[0004] Thermal treatment technologies, particularly high-temperature hydrothermal technology, have been widely researched for their potential to improve reaction efficiency. However, this technology requires high temperatures (>120°C), resulting in high energy consumption and demanding equipment, which limits its widespread application. Therefore, the development of low-temperature thermal treatment technologies operating below 100°C has become a new research direction. Previous studies have shown that while low-temperature treatment can disrupt sludge flocs and cell structures, excessive floc fragmentation can lead to dewatering performance degradation.

[0005] Ferrous iron is often used to activate oxidants to increase the production of reactive species. However, its ability to activate calcium hypochlorite is relatively low, requiring large doses to significantly enhance dewatering efficiency. This not only increases the amount of iron-containing sludge produced but also poses environmental risks. Therefore, there is an urgent need to develop a new technology to improve sludge dewatering, reduce chemical usage, and improve treatment efficiency.

[0006] Regulations on sludge disposal are becoming increasingly stringent around the world, prioritizing resource utilization over landfill or simple storage that can cause secondary pollution. In this context, the subsequent utilization of sludge cake has become a key issue in sludge treatment and disposal systems. Dewatered sludge cake, rich in organic matter and iron, can be produced through pyrolysis into sludge biochar. This biochar, with its rich functional groups and porous structure, serves as an excellent catalyst. Applying this biochar to wastewater treatment can achieve waste resource utilization, forming a complete sludge waste-to-wealth technology pipeline and creating greater social and economic value. Summary of the Invention

[0007] In response to the problems existing in the prior art, the purpose of the present invention is to provide a method and application for improving sludge dehydration and resource utilization of dehydration products. Low temperature combined with ferrous iron to activate calcium hypochlorite is used to improve sludge dehydration. The dehydration product is iron-rich sludge biochar, which is used as an efficient catalyst to activate periodate to degrade organic pollutants in wastewater.

[0008] Specifically, low-temperature heat is used to destroy the extracellular polymer structure of the sludge and increase the reaction rate. Ferrous iron is used as an activator, combined with heat-activated strong oxidant calcium hypochlorite, to produce a large number of hydroxyl radicals, which further attack the extracellular polymers and intracellular substances of the sludge, degrade hydrophilic organic matter, expose hydrophobic sites, and thus convert bound water into free water. In addition, cations (Fe 3+ , Ca 2+ The addition of ) causes the fine flocs to reflocculate and squeeze out free water, further improving the sludge dewatering capacity. The dehydrated product is then pyrolyzed under a nitrogen atmosphere to produce iron-rich sludge biochar, which is used to catalyze the activation of sodium periodate to degrade sulfamethoxazole in wastewater.

[0009] To achieve the above purpose, this method is implemented through the following technical solutions:

[0010] A method for improving sludge dehydration and resource utilization of dehydration products comprises the following steps:

[0011] S1: The remaining sludge to be treated is screened and gravity concentrated, and the pretreated sludge is subjected to low-temperature heat treatment;

[0012] S2: While maintaining the low-temperature heating condition of step S1, add the ferrous sulfate heptahydrate solution and stir rapidly to mix evenly, then immediately add the calcium hypochlorite solution and stir rapidly to mix thoroughly to obtain a mixture, then continue the reaction with slow stirring;

[0013] S3: After the reaction in step S2 is completed, the resulting mixture is subjected to solid-liquid separation to obtain a dehydrated wet filter cake;

[0014] S4: drying and grinding the wet filter cake from step S3, and pyrolyzing the cake at high temperature in a tubular furnace under a nitrogen atmosphere to obtain iron-rich sludge biochar.

[0015] Furthermore, in step S1, the residual sludge is passed through a 0.8-1.2 mm sieve to remove stones and impurities, and is concentrated to a solid content concentration of 15-16 g / L, a moisture content of more than 98%, and a pH of 6.5-7.0.

[0016] Furthermore, in step S1, the mixture is heated to 60-65° C. and kept at a constant temperature, and the stirring speed is 250-400 rpm.

[0017] Furthermore, in step S2, the amount of ferrous sulfate heptahydrate used is 150-200 mg / g sludge dry weight, and the amount of calcium hypochlorite used is 4%-6% of the sludge dry weight.

[0018] Furthermore, in step S2, the stirring speed of the rapid stirring is 250-400 rpm, the stirring speed of the slow stirring is 150-200 rpm, and the stirring reaction time is 25-30 min.

[0019] Furthermore, in step S4, the high temperature pyrolysis temperature is 450-550° C., and the pyrolysis time is 0.5-2 h.

[0020] The present invention also discloses the use of the iron-rich sludge biochar in catalytically activating sodium periodate to degrade organic wastewater, wherein the organic pollutants in the organic wastewater include sulfamethoxazole, the dosage of sodium periodate in the organic wastewater is 0.1-1.0 mmol / L, preferably 0.5-1.0 mmol / L, and the dosage of the iron-rich sludge biochar is 0.3-1.0 g / L, preferably 0.6-0.8 g / L.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The low-temperature heat treatment used in the present invention destroys the structure of sludge cells and extracellular polymers, while simultaneously synergizing ferrous iron to activate calcium hypochlorite to produce more active substances, effectively attacking hydrophilic organic matter, exposing hydrophobic sites, and releasing bound water in extracellular polymers. The introduction of cations promotes reflocculation of fine particles, further squeezing out interstitial water, thereby improving sludge dewatering efficiency. The dewatered sludge cake is recycled into iron-rich biochar catalyzed by sodium periodate for the removal of sulfamethoxazole from wastewater.

[0023] (2) This method uses low-temperature heat combined with ferrous iron to activate calcium hypochlorite, allowing oxidation reactions to proceed directly under neutral pH conditions in the original sludge. Unlike traditional Fenton technology, this method does not require the use of acid, thus overcoming the limitation of operating within a narrow pH range.

[0024] (3) Ferrous activation of calcium hypochlorite requires a large amount of ferrous iron, and low-temperature heat treatment alone can worsen the sludge filtration rate. This method combines low-temperature heat treatment with ferrous activation of calcium hypochlorite, reducing the use of chemical agents. At the same time, the generation of active substances and cations effectively increases the sludge filtration rate. The present invention achieves excellent dehydration efficiency under conditions of lower temperature and less chemical addition, not only saving energy and reducing costs, but also reducing environmental risks, providing a highly efficient solution for the treatment and disposal of excess sludge.

[0025] (4) To prevent the accumulation of iron-containing mud cakes and avoid secondary pollution, this method uses pyrolysis of the iron-containing mud cakes as the dehydration product to prepare iron-rich sludge biochar. No additional iron source is required. The biochar has rich functional groups and a porous structure, and can be used as an adsorbent and a good catalyst for wastewater treatment. Utilizing "waste" to manage "waste" can improve social and economic benefits.

[0026] Other features and advantages of the present invention will be set forth in the following description, and in part will be apparent from the description, or may be learned by practicing the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The figure shows the effect of different dosages of ferrous sulfate heptahydrate on the sludge dewatering performance in Example 1.

[0028] Figure 2 The figure shows the effect of different calcium hypochlorite dosages on sludge dewatering performance in Example 2.

[0029] Figure 3 This is the effect of different temperatures on sludge dewatering performance in Example 3.

[0030] Figure 4 The dehydration effect of this method in Example 4 is compared with that of different advanced oxidation technologies. DETAILED DESCRIPTION

[0031] To make the objectives, technical solutions, and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. It is apparent that the embodiments described are only a portion of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other implementations obtained by those of ordinary skill in the art without inventive effort are within the scope of protection of the present invention.

[0032] In the following examples, the test sludge used was from the secondary sedimentation tank of a sewage treatment plant in Deqing County, Huzhou City, Zhejiang Province. After passing through a 1 mm sieve to remove stones and impurities and then undergoing gravity concentration, the basic parameters of the sludge are shown in Table 1:

[0033] Table 1 Basic properties of raw sludge

[0034]

[0035] DS stands for dry sludge.

[0036] Example 1: Effect of different ferrous iron dosages on sludge dewatering performance

[0037] Step 1: Prepare the sludge: adjust the moisture content of the sludge to 98.4%;

[0038] Step 2: Preheat the sludge: Take 6 portions of 100 mL of sludge in a 250 mL beaker and preheat to 65°C at a stirring rate of 300 r / min;

[0039] Step 3: Adding chemical agents: Maintaining the heating temperature conditions of the second step unchanged, add ferrous sulfate heptahydrate at a constant temperature (65°C) and rapid stirring (300 r / min) to achieve concentrations of 0 mg / g, 50 mg / g, 100 mg / g, 150 mg / g, 200 mg / g, and 250 mg / g DS in the sludge, respectively. Stir rapidly to uniformity. Then, add calcium hypochlorite to maintain a final concentration of 40 mg / g DS in the sludge. Stir rapidly to uniformity. Then, stir slowly at 200 r / min and continue the reaction for 30 minutes.

[0040] Step 4: Dehydration: The mixed sludge is filtered through a circulating water vacuum pump connected to a Buchner funnel at a pressure of 0.06 MPa for 30 minutes to obtain a wet mud cake, and the sludge specific resistance is measured at the same time.

[0041] Step 5: Drying: Weigh the wet mud cake and dry it in an oven at 105°C for 4 hours. Measure the difference in mass before and after drying to calculate the moisture content of the wet mud cake obtained in step 4.

[0042] The effects of different ferrous sulfate heptahydrate dosages on the moisture content and sludge specific resistance (SRF) of the wet mud cake in Example 1 are shown in FIG. Figure 1 .like Figure 1 As shown in the figure, with the increase of ferrous sulfate heptahydrate dosage, the moisture content and SRF of the wet mud cake showed a downward trend. When the dosage of ferrous sulfate heptahydrate increased from 0 mg / g DS to 200 mg / g DS, the sludge moisture content decreased from 77.1% to the lowest value of 71.7%, and the sludge specific resistance decreased by 66.4%. 2+As an activator, it can activate hypochlorite and produce more active substances under thermal conditions. Therefore, the hydrophilic organic matter that binds water in the sludge is oxidized and degraded by the active substances, the hydrophobic sites are exposed, the water channels are increased, and water is released, thereby improving the dewatering performance of the sludge. At the same time, Fe 2+ Converted to Fe 3+ It has a flocculating effect and can accelerate the sludge filtration rate. However, when the dosage of ferrous sulfate heptahydrate increases to 250mg / g DS, the moisture content and sludge specific resistance show a deteriorating trend, indicating that the optimal dosage of ferrous sulfate heptahydrate is 200mg / g DS.

[0043] Example 2: Effect of different calcium hypochlorite dosages on sludge dewatering performance

[0044] The method and steps of Example 2 are the same as those of Example 1, except that "in the third step, the dosage of ferrous sulfate heptahydrate is fixed at 200 mg / g DS, and the dosage of calcium hypochlorite is adjusted to 0 mg / g, 20 mg / g, 40 mg / g, 60 mg / g, 80 mg / g, and 100 mg / g DS, respectively." The other conditions remain unchanged, and the conditioning is completed and the corresponding indicators are tested.

[0045] The effects of different calcium hypochlorite dosages on the moisture content and SRF of the wet mud cake in Example 2 are shown in FIG. Figure 2 .like Figure 2 As shown in the figure, Ca(ClO)2 acts as the oxidant of the system and is the source of active substances. Its dosage plays a crucial role in the sludge dewatering performance. When the Ca(ClO)2 dosage is increased to 40 mg / g DS, the best dewatering effect appears for the first time, the sludge moisture content is reduced to 71.7%, and the sludge specific resistance is 1.1×10 13 m / kg. As the dosage increases further, the moisture content and sludge specific resistance begin to fluctuate. At 100mg / g DS Ca(ClO)2, the moisture content does not decrease significantly. This may be because calcium hypochlorite is a strong oxidant. Excessive amounts will break up the sludge flocs, block the filtration channels, and prevent water from being released. At the same time, calcium hypochlorite is alkaline when dissolved in water. As the dosage increases, the Fe 2+ The excess Ca(ClO)2 is consumed, and the hydrolysis of the excess Ca(ClO)2 produces more hydroxide ions, which gradually increases the pH of the system and is not conducive to the dehydration of the system. Taking into account cost and efficiency, the optimal dosage of Ca(ClO)2 is set at 40mg / gDS.

[0046] Example 3: Effect of different temperatures on sludge dewatering performance

[0047] The method and steps of Example 3 are the same as those of Example 1, except that "the sludge preheating temperature in the second step is adjusted to 5° C., 25° C., 45° C., 65° C., and 85° C., respectively; the constant temperature in the third step is the same as the heating temperature in the second step; and the dosage of ferrous sulfate heptahydrate and calcium hypochlorite in the third step is fixed at 200 mg / g DS and 40 mg / g DS respectively." The remaining conditions remain unchanged, and the conditioning is completed and the corresponding indicators are tested.

[0048] The results of the effects of different temperatures on sludge dewatering performance in Example 3 are as follows: Figure 3 As shown in Figure 2, with the increase of temperature, the sludge moisture content first decreases and then increases. When the temperature is 65℃, the moisture content and SRF are the optimal values, which are 71.7% and 1.1×10 13 m / kg. This indicates that 65°C is an appropriate temperature threshold for promoting sludge dewatering in this system. At 85°C, the sludge moisture content decreases, but the filtration rate deteriorates. This may be because the higher temperature causes excessive fragmentation of sludge flocs, resulting in excessive release of intracellular substances that cannot be fully degraded, insufficient reflocculation capacity, and continued water binding. Higher temperatures increase energy consumption. Therefore, 65°C is selected as the optimal temperature for this system.

[0049] Example 4: Comparison of dehydration effects between this method and different advanced oxidation technologies

[0050] The waste activated sludge was respectively subjected to the optimal conditions (Heat+Fe 2+ +Ca(ClO)2) and common advanced oxidation systems (Fenton, Fe 2+ +SPS, Fe 2+ +Ca(ClO)2) treatment, and the sludge specific resistance, moisture content and post-reaction pH of the sludge under these treatment conditions were measured respectively.

[0051] Heat+Fe 2+ The operation steps for adding Ca(ClO)2 were the same as those in Example 1, except that in the third step, the dosage of ferrous sulfate heptahydrate was fixed at 200 mg / g DS and the dosage of calcium hypochlorite was fixed at 40 mg / g DS. The other conditions remained unchanged.

[0052] The Fenton treatment steps are as follows: first, adjust the pH of the prepared sludge to 3.0, add 110 mg / g DS ferrous sulfate heptahydrate and 88 mg / g DS H2O2 at room temperature (25°C), stir rapidly and evenly, and then stir slowly at 200 r / min and continue the reaction for 30 minutes.

[0053] Fe 2+The +SPS treatment step is to add 167 mg / g DS ferrous sulfate heptahydrate and 143 mg / g DS sodium persulfate to the prepared sludge (pH 6.5-7.0, no pH adjustment required), quickly stir until uniform, and then slowly stir at 200 r / min for 30 minutes.

[0054] Fe 2+ +Ca(ClO)2 treatment steps are the same as Heat+Fe 2+ +Ca(ClO)2, the only difference is that it maintains room temperature conditions and does not require heating.

[0055] The results of the effects of different treatment methods on sludge characteristics are shown in Figure 4 According to the moisture content, Heat+Fe 2+ +Ca(ClO)2 system is superior to the three common systems, and its water content is reduced to 71.7%. 2+ The dehydration performance of the +Ca(ClO)2 system is lower than that of the classic Fenton system, which is probably caused by the low dosage of the reagent. However, under the same chemical dosage, combined with low temperature, the dehydration performance of Heat+Fe 2+ The sludge dewatering capacity of the +Ca(ClO)2 system is significantly stronger than that of the classic Fenton system. The pH value after the system reaction not only affects the treatment effect, but is also the main factor determining the subsequent treatment cost. The Fenton system is limited to a narrow pH range, and the pH of the system after the reaction is about 2.7; Fe 2+ +SPS system is acidic because SPS is acidic when dissolved in water. The pH of the system after reaction is also 2.7, which is strongly acidic. In contrast, Ca(ClO)2 dissolves in water and produces hypochlorous acid, but it is also accompanied by a large amount of OH - After the reaction, the pH of the system is about 4.6, and the weakly acidic environment is more conducive to the treatment of the filtrate and the secondary utilization of the mud cake.

[0056] Example 5: Degradation performance of iron-rich sludge biochar activated with sodium periodate

[0057] The dehydrated cake was ground into fine particles and pyrolyzed in a tube furnace to obtain iron-rich sludge biochar. To 100 mL of a mixed solution containing 10 μmol / L sulfamethoxazole, the pH of the solution was adjusted to 3.0-11.0 using 4.8 mol / L dilute sulfuric acid or sodium hydroxide. Subsequently, 0.0-1.0 g / L of iron-rich biochar was added for adsorption. After adsorption equilibrium, 0.0-1.5 mmol / L sodium periodate solution was added to the beaker to initiate the oxidation reaction for 30 minutes. Samples were taken at different time points to determine the concentration of sulfamethoxazole and calculate the removal efficiency.

[0058] In Table 2, the effects of different iron-rich sludge biochar dosages on sulfamethoxazole degradation were investigated, maintaining a constant sulfamethoxazole concentration of 10 μmol / L, pH of 3.0, and sodium periodate at 1 mmol / L. As the iron-rich sludge biochar dosage increased, its ability to adsorb sulfamethoxazole improved. Increasing the iron-rich sludge biochar dosage from 0.1 g / L to 0.8 g / L, with the addition of an oxidant, increased sulfamethoxazole removal from 39.7% to 98.9% within 30 minutes. This may be due to the increased catalyst dosage providing more active sites, thereby improving degradation efficiency. The optimal iron-rich biochar dosage was 0.8 g / L.

[0059] In Table 3, the effects of varying sodium periodate concentrations on sulfamethoxazole degradation were investigated, maintaining a sulfamethoxazole concentration of 10 μmol / L, a pH of 3.0, and an iron-rich biochar concentration of 0.8 g / L. When the sodium periodate dosage was 0.0 mmol / L, sulfamethoxazole degradation was primarily due to adsorption by the iron-rich sludge biochar, which only adsorbed 33.6% of the sulfamethoxazole. Increasing the sodium periodate concentration from 0.1 mmol / L to 1.0 mmol / L increased the sulfamethoxazole removal efficiency from 70.8% to 98.9%. However, further increases in sodium periodate concentration did not affect the removal efficiency, likely due to the limited catalytic sites that could not activate the excess sodium periodate. Therefore, 1 mmol / L sodium periodate was the optimal dosage.

[0060] In Table 4, the effect of initial pH on the degradation rate of sulfamethoxazole was investigated by maintaining a constant sulfamethoxazole concentration of 10 μmol / L, an iron-rich biochar concentration of 0.8 g / L, and a sodium periodate concentration of 1 mmol / L. The initial pH not only affected the catalytic oxidative degradation phase but also the adsorption efficiency of the iron-rich sludge biochar. A pH of 5.0 favored sulfamethoxazole adsorption by the iron-rich sludge biochar, while a pH of 3.0 favored catalytic degradation of sulfamethoxazole, with degradation rates of 84.8% and 98.9% after 30 minutes of reaction, respectively. The optimal pH for the system was 3.0.

[0061] Table 5 studies the treatment of organic wastewater at a pH of 3.0 using sodium periodate alone (1 mmol / L), iron-rich sludge biochar alone (0.8 g / L), and a combination of iron-rich sludge biochar and sodium periodate. The removal efficiency of sulfamethoxazole using sodium periodate alone was 8.1%, indicating that sodium periodate's ability to degrade sulfamethoxazole without a catalyst was insufficient. Iron-rich sludge biochar alone adsorbed 33.6% of sulfamethoxazole. However, when iron-rich sludge biochar was introduced into the sodium periodate system, the degradation efficiency of sulfamethoxazole reached 89.9% within 30 seconds, and the removal rate reached 98.9% within 30 minutes. This suggests that the addition of iron-rich sludge biochar enhanced the system's oxidative capacity, thereby improving the degradation efficiency of sulfamethoxazole.

[0062] Table 2 Sulfamethoxazole removal effect under different biochar dosage conditions

[0063]

[0064] Table 3 Sulfamethoxazole removal effect under different periodic acid dosage conditions

[0065]

[0066] Table 4 Sulfamethoxazole removal effect under different initial pH conditions

[0067]

[0068] Table 5 Sulfamethoxazole removal effect in different systems

[0069]

[0070] The optimal conditions in Example 5 are pH = 3.0, the iron-rich biochar dosage is 0.8 g / L, and the sodium periodate concentration is 1 mmol / L.

[0071] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can

[0072] Any changes or substitutions that can be easily imagined within the scope of the present invention should be included in the protection scope of the present invention.

[0073] Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for improving sludge dehydration and resource utilization of dehydration products, characterized in that: The steps include: S1: The remaining sludge to be treated is screened and gravity concentrated, and the pretreated sludge is subjected to low-temperature heat treatment; S2: While maintaining the low-temperature heating condition of step S1, add the ferrous sulfate heptahydrate solution and stir rapidly to mix evenly, then immediately add the calcium hypochlorite solution and stir rapidly to mix thoroughly to obtain a mixture, then continue the reaction with slow stirring; S3: After the reaction in step S2 is completed, the resulting mixture is subjected to solid-liquid separation to obtain a dehydrated wet filter cake; S4: drying and grinding the wet filter cake from step S3, and pyrolyzing the cake at high temperature in a tubular furnace under a nitrogen atmosphere to obtain iron-rich sludge biochar.

2. The method for improving sludge dewatering using a low-temperature combined oxidant according to claim 1, wherein: In step S1, the residual sludge is passed through a 0.8-1.2 mm sieve to remove stones and impurities, and is concentrated to a solid content concentration of 15-16 g / L and a moisture content of more than 98%.

3. The method for improving sludge dehydration and resource utilization of dehydration products according to claim 1, characterized in that: In step S1, the mixture is heated to 60-65° C. and maintained at a constant temperature, and the stirring speed is 250-400 rpm.

4. The method for improving sludge dehydration and resource utilization of dehydration products according to claim 1, characterized in that: In step S2, the amount of ferrous sulfate heptahydrate used is 150-200 mg / g sludge dry weight, and the amount of calcium hypochlorite used is 4%-6% of the sludge dry weight.

5. The method for improving sludge dehydration and resource utilization of dehydration products according to claim 1, characterized in that: In step S2, the stirring speed of the rapid stirring is 250-400 rpm, the stirring speed of the slow stirring is 150-200 rpm, and the stirring reaction time is 25-30 min.

6. The method for improving sludge dehydration and resource utilization of dehydration products according to claim 1, characterized in that: In step S4, the high-temperature pyrolysis temperature is 450-550° C., and the pyrolysis time is 0.5-2 h.

7. The dehydrated iron-rich sludge biochar prepared by the method according to any one of claims 1 to 6.

8. Use of the iron-rich sludge biochar as claimed in claim 7 in catalytic activation of sodium periodate to degrade organic wastewater.

9. The use according to claim 8, characterized in that The organic pollutants in the organic wastewater include sulfamethoxazole, the dosage of sodium periodate in the organic wastewater is 0.1-1.0 mmol / L, and the dosage of iron-rich sludge biochar is 0.3-1.0 g / L.

10. The use according to claim 8, characterized in that The dosage of sodium periodate in organic wastewater is 0.5-1.0 mmol / L, and the dosage of iron-rich sludge biochar is 0.6-0.8 g / L.

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