Method for promoting sludge dewatering by utilizing low-temperature heating in cooperation with POM (polyoxymethylene) under acidic condition

Abstract

The invention discloses a method for promoting sludge dewatering by utilizing low-temperature heating under an acidic condition in cooperation with POM (polyoxymethylene), which comprises the following steps: firstly, heating activated sludge to be treated to a set temperature, adding phosphomolybdic acid into the activated sludge under a stirring condition, then adding dilute sulphuric acid to adjust the pH value to 2.0-7.0, and reacting under the stirring condition, according to the method disclosed by the invention, phosphomolybdic acid and low-temperature heat are used for cooperatively treating the sludge, and through the synergistic effect of acidic catalysis and thermally induced structure relaxation, the oxidative cracking of an extracellular polymeric substance (EPS) and the dissolution of organic matters in sludge floc are synchronously realized; the technical bottlenecks that the reaction path is limited and the energy utilization efficiency is low in the traditional single chemical oxidation or thermal conditioning process are broken through.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sludge dewatering, and particularly relates to a method for promoting sludge dewatering by low-temperature heating under acidic conditions in cooperation with POM. BACKGROUND

[0002] With the deepening of industrialization and urbanization, the residual activated sludge (WAS) generated in the wastewater treatment process has become a major challenge in the field of environmental governance. According to the statistics of the Ministry of Housing and Urban-Rural Development of the People's Republic of China, the dry basis sludge production and disposal capacity doubled from 2014 to 2023, with the production increasing from 7.115 million tons to 15.054 million tons and the disposal capacity increasing from 6.813 million tons to 14.937 million tons. The sludge not only has a high water content (initially up to 95%-99%) and poor dewatering performance, but also contains a large amount of extracellular polymeric substances (EPS) in its gel-like structure, which are firmly bound by the stable action of multiple layers (such as TB-EPS, LB-EPS and S-EPS), seriously hindering deep dewatering. In addition, the physical properties of high water content and large volume not only occupy a large amount of space, but also result in high transportation, treatment and disposal costs, accounting for more than 50% of the total operating cost of the sewage treatment plant. Therefore, developing efficient and environmentally friendly conditioning technology to simultaneously improve sludge dewatering performance and reduce pollutant load has become an urgent need in the industry.

[0003] Chemical conditioning is a key technology for improving sludge dewatering performance, and its core mechanism lies in effectively destroying the EPS structure and releasing the water molecules firmly bound therein. As a class of inorganic metal-oxo cluster anions composed of molybdenum (Mo), tungsten (W) and other early transition metals, polyoxometalates (POMs) exhibit significant potential in advanced oxidation processes due to their flexible adjustable acidity and rapid reversible multi-electron redox properties. Under acidic conditions, phosphomolybdic acid can synergistically play the roles of protonation and catalytic oxidation, on the one hand, by providing protons to neutralize the negative charge on the surface of EPS and destroy its stability, and on the other hand, by oxidizing key hydrophilic components such as proteins and polysaccharides in EPS, thereby efficiently releasing the internal bound water.

[0004] However, the single phosphomolybdic acid treatment system still has certain limitations in practical application, mainly manifested as a relatively slow reaction rate, and excessive oxidation leading to excessive dispersion of sludge floc structure, which is not conducive to subsequent solid-liquid separation. In order to strengthen the reaction process, heat treatment is introduced as an auxiliary means. Studies have shown that high temperature conditions (> 150℃) can effectively destroy the sludge floc structure and improve the dewatering performance, but excessively high temperature not only promotes the dissolution of refractory organic matter, increasing the treatment load of the filtrate, but also significantly increases the operating cost. In contrast, low-temperature heat treatment has economic and environmental friendliness, but its degradation ability of organic matter is limited, and even the use alone may worsen the dewatering effect. The combination of heat treatment and chemical oxidation can effectively overcome the shortcomings of a single method. For example, it has been reported that low-temperature calcium peroxide treatment can reduce the sludge moisture content from 79.9% to 69.2%, showing a significant synergistic effect.

[0005] Therefore, the present application proposes an efficient sludge dewatering strategy of heat treatment under acidic conditions in combination with POM, which finds an environmentally friendly and efficient new way for residual sludge dewatering, 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 residual sludge in sewage treatment plants. SUMMARY

[0006] In view of the problems existing in the prior art, the purpose of the present application is to provide a method for promoting sludge dewatering by low-temperature heating under acidic conditions in combination with POM, which overcomes the problems of low utilization efficiency of oxidizing agent and easy over-damage of floc structure in the sludge dewatering process in the prior art.

[0007] To achieve the above-mentioned purpose, the technical solutions of the present application are as follows: A method for promoting sludge dewatering by low-temperature heating under acidic conditions in combination with POM, comprising the following steps: First, the activated sludge to be treated is heated to a set temperature, and under stirring, phosphomolybdic acid is added to the activated sludge, then dilute sulfuric acid is added to adjust the pH value to 2.0-7.0, and then the reaction is carried out under stirring, and after the reaction is completed, the sludge dewatering is completed.

[0008] Further, the concentration of the activated sludge to be treated is 16 g / L, and the stirring speed is 200 r / min.

[0009] Further, the set temperature is 25-85℃.

[0010] Further, the dosage of phosphomolybdic acid is 100-600 mg / g DS.

[0011] Further, the method further comprises evaluating the dewatering effect of the treated activated sludge, and the evaluation is carried out by using a conventional Buchner funnel method.

[0012] Compared with the prior art, the present application has the following advantages: 1) The present application utilizes low-temperature heating under acidic conditions in combination with phosphomolybdic acid to achieve deeper dewatering of activated sludge; phosphomolybdic acid has strong catalytic activity and high stability under acidic conditions, providing an efficient and renewable solution for sludge dewatering; low-temperature heating can reduce more costs compared to high-temperature heating. The method of the present application can be widely applied to the treatment and disposal of excess activated sludge in sewage treatment plants, having obvious social and environmental benefits; 2) The present application uses phosphomolybdic acid and low-temperature heat to treat sludge, through the synergistic effect of acidic catalysis and heat-induced structural relaxation, simultaneously achieving the oxidation and disintegration of extracellular polymeric substances (EPS) and the dissolution of organic matter in sludge flocs, breaking through the technical bottleneck of limited reaction path and low energy utilization efficiency in traditional single chemical oxidation or thermal conditioning process; 3) The preparation method of the present application is simple to operate, can significantly improve the dewatering performance of sludge, and also provides an effective and harmless new way for the environmental reuse of activated sludge; 4) The method of the present application has high dewatering performance: significantly improves the dewatering efficiency of sludge, reduces the water content of sludge, reduces the water content from more than 95% initially to less than 70%, realizes sludge reduction, reduces the volume of sludge, and is convenient for subsequent treatment and disposal; Cost-effective: reduces the use of traditional chemical conditioning agents, reduces sludge treatment costs, and reduces transportation energy consumption by 30%~50%, which is more competitive in economy; Environmentally friendly: phosphomolybdic acid as an environmentally friendly material can reduce potential harm to the environment, and also avoids the secondary pollution that may be caused by traditional oxidizing agents; Strong pollutant removal capacity: can effectively degrade organic pollutants in sludge, including refractory organic compounds, achieving deep removal of harmful substances in sludge and improving the environmental safety of sludge; Strong adaptability: suitable for sludge of different properties, including municipal sludge and industrial sludge, and can maintain good dewatering effect under different operating conditions, having strong universality and adaptability; Easy to operate: simple process operation, 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. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 Effect of different reaction temperatures on sludge dewatering performance; Figure 2 Effect of different doses of phosphomolybdic acid on sludge dewatering performance; Figure 3Effect of different reaction pH on sludge dewatering performance Figure 4 Effect of different conditioning system on sludge dewatering performance DETAILED DESCRIPTION

[0014] The application will be further described in conjunction with the accompanying drawings, but the scope of protection of the application is not limited to the scope described.

[0015] Example 1: Source and characteristic parameters of activated sludge 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 value is 6.6 ± 0.1; total solid content (DS, g / L) is 16.0 ± 0.08; sludge specific resistance (SRF, ×10 13 m / kg) is 3.3 ± 0.16; water content (%) is 98.4 ± 0.1.

[0016] Example 2: Effect of different reaction temperatures on sludge dewatering performance 100 mL of activated sludge solution with a solid content of 16 g / L was measured and placed in a 250 mL beaker, and the sludge temperature was heated to different temperatures under the action of a magnetic heating stirrer with a stirring speed of 200 r / min. Then 500 mg / g DS of phosphomolybdic acid was added to the sludge solution, followed by the addition of dilute sulfuric acid to adjust the pH value to 2.0, and the stirring reaction was carried out for 30 min with a stirring speed of 200 r / min. Finally, the sludge specific resistance (SRF) and sludge water content were determined by the conventional Buchner funnel test to evaluate the sludge dewatering efficiency. The reaction temperatures were 25, 40, 55, 70 and 85℃, respectively.

[0017] Figure 1 Effect of reaction temperature on sludge dewatering performance. As can be seen from Figure 1 , two parameters representing sludge dewatering efficiency: with the increase of temperature, the dewatering performance of sludge is gradually optimized, the water content decreases from 76.1% to 67.2% at 70℃, and the sludge specific resistance decreases from 3.3 × 10 13 m / kg to 0.9 × 10 13 m / kg. When the temperature rises to 85℃, the water content increases, which may be due to the increase of fine sludge particles caused by the high temperature, resulting in the deterioration of water content. Considering the cost, 70℃ is selected as the final reaction temperature.

[0018] Example 3: Effect of different doses of phosphomolybdic acid on sludge dewatering performance Example 3: Effect of different dosages of phosphomolybdic acid on sludge dewatering performance

[0019] Figure 2 The effect of different dosages of phosphomolybdic acid on sludge dewatering performance can be seen in Table 3. Figure 2 As can be seen in Table 3, the moisture content decreased and then increased with increasing dosage of phosphomolybdic acid, and the SRF increased with increasing dosage of phosphomolybdic acid. The best results were obtained at a dosage of 500 mg / g DS, with a moisture content of 67.2% and an SRF of 0.9 x 10 13 m / kg. At a dosage of 600 mg / g DS, the moisture content deteriorated and the SRF did not change significantly. Based on a comprehensive consideration, the best results for dewatering of activated sludge were obtained at a dosage of 500 mg / g DS of phosphomolybdic acid.

[0020] Example 4: Effect of different reaction pH values on sludge dewatering performance Example 4: Effect of different reaction pH values on sludge dewatering performance

[0021] Figure 3 The effect of different reaction pH values on sludge dewatering performance can be seen in Table 4. Figure 3 As can be seen in Table 4, both the moisture content and the SRF increased with increasing reaction pH value. When the pH value reached 2.0, the SRF and the moisture content of the sludge were 3.3 x 10 13m / kg and 76.1% down to 0.9 x 10 13 m / kg and 67.2%. In summary, 2.0 was chosen as the optimal reaction pH value.

[0022] Example 5: Optimal conditions for dewatering of activated sludge A 100 mL activated sludge solution with a solid content of 16 g / L was placed in a 250 mL beaker and stirred under the action of a magnetic heating stirrer at a stirring speed of 200 r / min. After heating the sludge temperature to 70°C, 500 mg / g DS of phosphomolybdic acid was added to the sludge solution, and dilute sulfuric acid was added to adjust the pH value to 2.0. The stirring reaction was carried out for 30 min at a stirring speed of 200 r / min. Finally, the sludge specific resistance (SRF) and sludge moisture content were determined by a conventional Buchner funnel test to evaluate the sludge dewatering efficiency.

[0023] Figure 4 The effects of different treatments on the dewatering performance of sludge. At a pH value of 2.0, a reaction temperature of 70°C, and a phosphomolybdic acid addition amount of 500 mg / g DS, the moisture content and sludge specific resistance of the sludge were 67.2% and 0.9 x 10 13 m / kg, respectively, both of which were the lowest. Therefore, this condition was determined as the optimal condition for dewatering of activated sludge.

Claims

1. A method for dewatering sludge using low temperature heating under acidic conditions in conjunction with POM promotion, characterized by It comprises the following steps: First, the activated sludge to be treated is heated to a set temperature, and phosphomolybdic acid is added to the activated sludge under stirring, then dilute sulfuric acid is added to adjust the pH value to 2.0-7.0, and then the reaction is carried out under stirring, and the sludge dewatering is completed after the reaction is completed.

2. The method for sludge dewatering by low temperature heating under acidic condition in combination with POM promotion according to claim 1, characterized in that The concentration of the activated sludge to be treated is 16 g / L, and the stirring speed is 200 r / min.

3. The method for sludge dewatering by low temperature heating under acidic condition in combination with POM promotion according to claim 1, characterized in that The set temperature is 25-85℃.

4. The method for sludge dewatering by low temperature heating under acidic condition in conjunction with POM promotion according to claim 1, characterized in that The dosage of the phosphomolybdic acid is 100-600 mg / g DS.

5. The method for sludge dewatering by low temperature heating under acidic condition in conjunction with POM promotion according to claim 1, characterized in that The method further comprises evaluation of the dewatering effect of the treated activated sludge, which is carried out by using a conventional Buchner funnel method.

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