Method for promoting sludge dewatering

Abstract

The invention discloses a method for promoting sludge dewatering. According to the method, low-temperature heating and iron-rich sludge biochar (Fe (at) SBC) are cooperated to activate potassium peroxymonosulfate composite salt (PMS) to promote sludge dewatering. According to the invention, low-temperature heating is cooperated with Fe-coated SBC to activate PMS so as to form a composite conditioning agent, so that deeper dehydration of activated sludge is realized; the sludge does not need to be subjected to original acid regulation treatment; the activated sludge is used as a raw material for preparing the biochar, so that the treatment cost and waste utilization are saved; compared with high-temperature heating, low-temperature heating can reduce more cost. The method disclosed by the invention can be widely applied to treatment and disposal of residual activated sludge in a sewage treatment plant, and has obvious social and environmental benefits.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sludge dewatering, and particularly relates to a method for promoting sludge dewatering. BACKGROUND

[0002] With the rapid development of industrialization and urbanization, the production of wastewater is continuously increasing. A large amount of sludge is inevitably produced in the operation process of the sewage treatment process based on the activated sludge method. As an inevitable by-product of biological treatment of wastewater, sludge has the characteristics of high water content and complex components. The colloidal structure of sludge is mainly composed of extracellular polymeric substances (EPS), and the structure significantly inhibits the dewatering efficiency through hydrogen bonding and high zeta potential, thereby causing significant challenges to sludge treatment and disposal. Although mechanical dewatering can reduce the water content to 80-85%, the residual bound water still makes the sludge volume large, and the subsequent disposal faces high transportation cost and secondary pollution risk. Sludge dewatering is a key link to realize the reduction and resource utilization of sludge.

[0003] Chemical conditioning releases bound water by destroying the EPS structure, and is a core technology for improving the dewatering performance of sludge. The advanced oxidation process (AOPs) represented by Fenton oxidation can attack biological macromolecules such as proteins (PN) and polysaccharides (PS) through hydroxyl radicals (·OH), and improve the dewatering performance of sludge. However, traditional AOPs have the bottlenecks of iron ion leaching, narrow pH adaptation range, and low utilization rate of oxidants. In recent years, AOPs based on persulfate have attracted widespread attention because they can generate various active oxygen species such as sulfate radicals (SO4 •- ) and ·OH. Potassium peroxymonosulfate composite salt (PMS) can be activated by heating, ultraviolet light, electricity, ozone, alkali metals or transition metals (such as Fe2S) to generate a large amount of strong oxidizing SO4 •- , which can effectively destroy the EPS and sludge structure, promote the release of EPS bound water, and thus improve the dewatering performance of sludge.

[0004] Thermal treatment can destroy the sludge flocculation structure and accelerate the reaction. Studies have shown that when the temperature exceeds 150℃, the dewatering capacity of sludge will be enhanced. However, too high a temperature will cause the release of refractory substances into the filtrate, complicating the subsequent water treatment. At the same time, high temperature also increases the cost of sludge dewatering. Low-temperature thermal treatment has the advantages of low cost and non-toxicity, and can destroy the sludge flocculation structure. However, due to the limited ability to degrade organic matter, low-temperature thermal treatment alone will worsen the dewatering performance of sludge. Studies have shown that thermal treatment combined with oxidants can significantly improve the dewatering efficiency, for example, calcium peroxide combined with low temperature can reduce the water content from 79.9% to 69.2%. However, single activation mode (heat, transition metal or biochar) is often limited by insufficient free radical yield or catalyst deactivation.

[0005] In addition, the wide application of biochar in environmental protection makes it a frontier hotspot in the research of environmental functional materials. In the field of sludge dewatering, the addition of biochar can improve the permeability and porosity of sludge to release the internal bound water. At the same time, biochar has good adsorption and catalytic degradation performance, which can reduce the content of pollutants in the dewatering liquid. In recent years, many studies have tried to use sludge as raw material to produce biochar and use it for dewatering. However, the unprocessed sludge biochar has certain limitations in improving the dewatering performance of sludge, and the modification of sludge biochar is the key to improve the catalytic effect. Iron-rich sludge biochar not only acts as a carrier for Fe(II) to further catalyze PMS to produce reactive oxygen species, but also enhances the skeleton to improve the dewatering performance of sludge.

[0006] Chinese patent CN110204174A discloses a method for conditioning sludge dewatering, which uses sludge carbon-based divalent iron material and sludge carbon-based zero-valent iron material as catalysts for sludge enhanced dewatering treatment, but the sludge to be dewatered needs to be adjusted in pH before the reaction can be carried out, and the sludge dewatering step is relatively complicated and the efficiency is low. SUMMARY

[0007] To overcome the defects of the sludge dewatering step being relatively complicated and the efficiency being low in the prior art, the present application provides a method for promoting sludge dewatering, which uses low-temperature heating in combination with iron-rich sludge biochar (Fe@SBC) to activate peroxymonosulfate (PMS), wherein the iron-rich sludge biochar catalyst has a wide pH range and can efficiently catalyze the PMS oxidation reaction. The present application can simultaneously achieve extracellular polymeric substance oxidation and sludge thermal porosity expansion, breaking through the technical limitations of traditional single oxidation or thermal conditioning. It provides a new way for the dewatering of excess sludge, which is environmentally friendly and efficient, has obvious social and environmental benefits, provides a valuable reference for the future development of sludge dewatering, and provides a new idea for the resource utilization of excess sludge in sewage treatment plants.

[0008] The present application is realized by the following technical solutions: A method for promoting sludge dewatering, which uses low-temperature heating in combination with iron-rich sludge biochar (Fe@SBC) to activate peroxymonosulfate (PMS) to promote sludge dewatering, the specific steps comprising: 1) Take the activated sludge to be treated, heat the activated sludge to 25-85℃, and stir; 2) Add 100-500 mg / g DS of peroxymonosulfate to the sludge solution of step 1); 3) Add 50-350 mg / g DS of iron-rich sludge biochar to the sludge solution of step 2), stir for 30-40 min, and complete the sludge dewatering process.

[0009] Further, the potassium peroxymonosulfate composite salt includes potassium bisulfate, potassium peroxymonosulfate, and potassium sulfate.

[0010] Further, the concentration of the activated sludge is 16 g / L, and the stirring speed is 200 r / min.

[0011] Further, the stirring reaction temperature is 70 DEG C.

[0012] Further, the dosage of the potassium peroxymonosulfate composite salt is 400 mg / g DS.

[0013] Further, the dosage of the iron-rich sludge biochar is 300 mg / g DS.

[0014] Further, the iron-rich sludge biochar catalyst is prepared by the following method: after drying and pyrolysis of activated sludge, mixing with FeCl3, ultrasonic, drying, and finally programmed temperature pyrolysis carbonization, Fe@SBC is obtained.

[0015] Advantages of the present application: (1) High efficiency of dewatering: significantly improve the efficiency of sludge dewatering, reduce the water content of sludge, reduce the water content from more than 95% to less than 70%, realize sludge reduction, reduce the volume of sludge, and facilitate subsequent treatment and disposal.

[0016] (2) Significant cost-effectiveness: reduce the use of traditional chemical conditioning agents, reduce sludge treatment cost, and reduce transportation energy consumption by 30%~50%, which is more competitive in economy.

[0017] (3) Environmental friendliness: iron-rich biochar as an environmentally friendly material can efficiently remove harmful substances in sludge, reduce potential harm to the environment, and avoid secondary pollution caused by traditional oxidants.

[0018] (4) Strong pollutant removal capacity: can effectively degrade organic pollutants in sludge, including refractory organic compounds, achieve deep removal of harmful substances in sludge, and improve the environmental safety of sludge.

[0019] (5) Synergistic effect: low-temperature heating and iron-rich biochar catalyze PMS to produce synergistic effect, enhance the generation and utilization efficiency of active oxygen, and improve the removal effect of organic matter and nutrients in sludge.

[0020] (6) Strong adaptability: suitable for different types of sludge, including municipal sludge and industrial sludge, and can maintain good dewatering effect under different operating conditions, with strong universality and adaptability.

[0021] (7) Simple operation: the process operation is simple, easy to control and manage, suitable for large-scale continuous production, and can be directly applied to existing sludge treatment facilities without large-scale modification.

[0022] (8) Resource recovery potential: the dewatered sludge can be used as a raw material for resource utilization, such as soil improvement, building materials, etc., realizing the resource utilization of sludge and promoting the development of circular economy. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 the influence of different reaction temperatures on the dewatering performance of sludge; Figure 2 the influence of different doses of peroxymonosulfate composite salt on the dewatering performance of sludge; Figure 3 the influence of different doses of iron-rich sludge biochar on the dewatering performance of sludge; Figure 4 the influence of different conditioning systems on the dewatering performance of sludge. DETAILED DESCRIPTION

[0024] In order to make the technical solutions and advantages of the present application clearer and more apparent, the present application will be further described in detail below with reference to examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0025] Example 1: Source and characteristic parameters of activated sludge and preparation of iron-rich sludge biochar catalyst The original activated sludge solution was taken from the sludge settling tank of Hengfeng Wastewater Treatment Plant in Huzhou, Zhejiang Province, and the sample was stored in a 4℃ refrigerator. The characteristic parameters of the activated sludge are as follows: pH is 6.8 ± 0.1; total solid content (DS, g / L) is 16.0 ± 0.08; sludge specific resistance (SRF, ×10 13 m / kg) is 2.8 ± 0.18; moisture content (%) is 78.9 ± 0.1.

[0026] The iron-rich sludge biochar catalyst used in the examples of the present application is prepared by the following method: after centrifugation and freeze-drying of the activated sludge, pyrolysis is carried out in N2 atmosphere, then mixed with 1 mol / L FeCl3 at 1:10 (W / V), ultrasonic for 2h, then placed in a 105℃ oven for drying, finally placed in a tube furnace, under N2 atmosphere, with a heating rate of 10℃ / min, 500℃ for 1h to obtain Fe@SBC.

[0027] Example 2: Influence of different reaction temperatures on the dewatering performance of sludge Take 100 mL of activated sludge solution with a solid content of 16 g / L into a 250 mL beaker, and stir the reaction under the action of a magnetic heating stirrer, with a stirring speed of 200 r / min. After heating the sludge to different temperatures, add 400 mg / g DS of PMS and 300 mg / g DS of Fe@SBC to the sludge solution, and stir for 30 min at a stirring speed of 200 r / min. Finally, measure the sludge specific resistance (SRF) and sludge moisture content by the conventional Buchner funnel test to evaluate the sludge dewatering performance. The reaction temperatures are 25, 40, 55, 70, and 85°C, respectively.

[0028] Figure 1 The effect of reaction temperature on sludge dewatering performance is shown in Figure 1 It can be seen from the two parameters representing the sludge dewatering performance that as the temperature rises, the sludge dewatering performance is gradually optimized, and at 70°C, the moisture content decreases from 79.0% to 68.6%, and the sludge specific resistance decreases from 2.8 × 10 13 m / kg to 0.6 × 10 13 m / kg. When the temperature rises to 85°C, the sludge specific resistance increases, which may be due to the increase in fine sludge particles at high temperature, which blocks the filter paper and slows down the filtration speed. Considering the cost, 70°C is selected as the final reaction temperature.

[0029] Example 3: Effect of different doses of potassium peroxymonosulfate composite salt on sludge dewatering performance Take 100 mL of activated sludge solution with a solid content of 16 g / L into a 250 mL beaker, and stir the reaction under the action of a magnetic heating stirrer, with a stirring speed of 200 r / min. After heating the sludge to 70°C, add different doses of PMS to the sludge solution, and then add 350 mg / g DS of Fe@SBC, and stir for 30 min at a stirring speed of 200 r / min. Finally, measure the sludge specific resistance (SRF) and sludge moisture content by the conventional Buchner funnel test to evaluate the sludge dewatering performance. The addition amount of potassium peroxymonosulfate composite salt is 0, 100, 200, 300, 400, and 500 mg / g DS, respectively, based on the solid content of the activated sludge.

[0030] Figure 2 The effect of different doses of potassium peroxymonosulfate composite salt on sludge dewatering performance is shown in Figure 2As can be seen from Table 2, both the water content and SRF first decreased and then increased with the increase of the dosage of PMS. The best effect was achieved when the dosage of PMS was 400 mg / g DS, the water content reached 68.6%, and the SRF reached 0.6 x 10 13 m / kg. When the dosage increased to 500 mg / g DS, both the water content and the SRF deteriorated. According to the comprehensive consideration, the dewatering effect of the activated sludge was the best when the dosage of PMS was 400 mg / g DS.

[0031] Example 4: Effect of different dosages of Fe-rich sludge biochar on sludge dewatering performance 100 mL of activated sludge solution with a solid content of 16 g / L was weighed into a 250 mL beaker, and was stirred under the action of a magnetic heating stirrer at a stirring speed of 200 r / min. After the temperature of the sludge was heated to 70°C, 400 mg / g DS of PMS was added to the sludge solution, and then different dosages of Fe@SBC were sequentially added. The stirring reaction was carried out for 30 min at a stirring speed of 200 r / min. Finally, the SRF and the water content of the sludge were determined by a conventional Buchner funnel test to evaluate the dewatering performance of the sludge. The addition amount of the Fe-rich sludge biochar was 0, 50, 100, 150, 200, 250, 300, and 350 mg / g DS, respectively, based on the solid content of the activated sludge.

[0032] Figure 3 The effect of different dosages of Fe-rich sludge biochar on sludge dewatering performance. As can be seen from Table 3, Figure 3 As can be seen from Table 3, both the water content and the SRF decreased with the increase of the dosage of Fe@SBC. When the dosage of Fe@SBC reached 300 mg / g DS, the SRF and the water content decreased from 2.8 x 10 13 m / kg and 79.0% of RS to 0.6 x 10 13 m / kg and 68.6%, respectively. When the dosage of Fe@SBC increased to 350 mg / g DS, the water content and the SRF only slightly decreased. Considering the economic benefits, 300 mg / g DS was selected as the optimal dosage of Fe@SBC.

[0033] Example 5: Optimal condition for dewatering of activated sludge 100 mL of activated sludge solution with solid content of 16 g / L was measured and placed in a 250 mL beaker, and stirred under the action of a magnetic heating stirrer, the stirring speed was 200 r / min. Different groups were treated differently, among which the heating temperature was 70℃, the dosage of PMS was 400 mg / g DS, the dosage of Fe@SBC was 300 mg / g DS, the stirring reaction was 30 min, and the stirring speed was 200 r / min. Finally, the sludge specific resistance (SRF) and sludge moisture content were determined by the conventional Buchner funnel test to evaluate the sludge dewatering efficiency.

[0034] Figure 4 The influence of different treatments on the dewatering performance of sludge. It can be seen from Figure 4 that when the sludge temperature is heated to 70℃, PMS and Fe@SBC are added to the sludge solution, the dewatering performance is good. Under this condition, the moisture content of the sludge and the sludge specific resistance are 68.6% and 0.6 × 10 13 m / kg, respectively, and the sludge specific resistance and moisture content reach the minimum value, so this condition is determined as the optimal condition for dewatering of activated sludge.

[0035] The above-described embodiments are only a preferred scheme of the present application, and do not limit the present application in any form, and there are other variants and modifications without exceeding the technical scheme recorded in the claims.

Claims

1. A method of promoting dewatering of sludge, characterized by, The method uses low-temperature heating to activate peroxymonosulfate composite salt (PMS) in cooperation with iron-rich sludge biochar (Fe@SBC) to promote sludge dewatering, and the specific steps include: 1) Take the activated sludge to be treated, heat the activated sludge to 25-85℃, and stir; 2) Add 100-500 mg / g DS of peroxymonosulfate composite salt to the sludge solution of step 1); 3) Add 50-350 mg / g DS of iron-rich sludge biochar to the sludge solution of step 2), stir for 30-40 min, and complete the sludge dewatering process.

2. The method of claim 1, wherein, The peroxymonosulfate composite salt includes potassium bisulfate, potassium persulfate, and potassium sulfate.

3. The method of claim 1, wherein, The concentration of the activated sludge is 16 g / L, and the stirring speed is 200 r / min.

4. The method of claim 1, wherein, The stirring reaction temperature is 70℃.

5. The method of claim 1, wherein, The dosage of the peroxymonosulfate composite salt is 400 mg / g DS.

6. The method of claim 1, wherein, The dosage of the iron-rich sludge biochar is 300 mg / g DS.

7. The method of claim 1, wherein, The iron-rich sludge biochar catalyst is prepared by the following method: after drying and pyrolysis of activated sludge, mixing with FeCl3, ultrasonic, drying, and finally programmed temperature pyrolysis carbonization, Fe@SBC is obtained.

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