Method for improving sludge dewatering performance by combining sludge biochar with advanced oxidation process

Abstract

The invention provides a method for improving sludge dewatering performance by combining sludge biochar with an advanced oxidation process, which comprises the following steps: activating municipal sludge by using an activator, dewatering the activated sludge to obtain activated sludge powder, and pyrolyzing the activated sludge powder to obtain the sludge biochar. According to the method, activated sludge biochar is obtained, the sludge biochar has multiple effects of filtration aiding, catalysis, flocculation, adsorption and the like, and finally, the sludge dewatering performance is improved through the method that the sludge biochar cooperates with ferrous sulfate heptahydrate to activate sodium hypochlorite. The positive influence on the current sludge sustainable treatment and disposal is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of municipal sludge treatment, and particularly relates to a method for improving the sludge dewatering performance by combining sludge biochar with advanced oxidation process. Background Art

[0002] With the continuous increase in the output of municipal sludge, the regulations on sludge treatment and disposal management have become gradually strict. Sludge is a colloidal system composed of small particles stably suspended in water, with poor sedimentation performance. In addition, extracellular polymeric substances (EPS) in sludge are an important part that makes it difficult to separate sludge from water. EPS has strong hydrophilicity, making water molecules tightly bound to sludge flocs. Therefore, sludge dewatering is a technical problem in sludge treatment.

[0003] In sludge treatment, although a single pretreatment conditioning method can destroy EPS and microbial cell walls, it often causes problems such as an increase in sludge viscosity, floc breakage, and clogging of filter presses, resulting in the still difficult discharge of the released free water and bound water. Therefore, although a single pretreatment can improve the dewatering performance of sludge, it is difficult to achieve deep dewatering of sludge.

[0004] To promote the deep dewatering of sludge, it is necessary to increase the porosity of the filter cake and reduce the compressibility of the filter cake. Using a physical conditioner as a skeleton material can achieve these goals. Modifying the skeleton material can expand its chemical properties, enabling it to have both physical effects and the functions of a chemical conditioner, thus promising to achieve the deep dewatering of sludge through the integrated conditioning of a multifunctional skeleton material.

[0005] To further improve the effect of sludge dewatering, the combined conditioning of chemical agents and skeleton materials can reduce the dosage of a single chemical agent. The activation of persulfate technology based on SO4-· is one of the current popular sludge pretreatment methods, which has the characteristics of being fast, efficient, thorough, highly versatile, and having a mild reaction. However, the price of persulfate is relatively high, which will limit its practical application and promotion.

[0006] In summary, it is necessary to find a conditioner with strong oxidizing properties that can be used to destroy the EPS structure of sludge, has a low cost, and is easy to store for sludge conditioning. It is also necessary to find an economically effective carbon raw material to be converted into biochar with a large specific surface area, excellent adsorption performance, and rich active sites, and try to use it as a coagulant aid, filter aid, and adsorbent for the synergistic conditioning of activated sludge. Selecting appropriate activation methods and catalysts can improve its efficiency, but some technical and economic challenges also need to be overcome. Summary of the Invention

[0007] In response to the above improvement requirements, the present invention provides a sludge biochar combined with activated sodium hypochlorite Fenton-like technology, which is based on the strong oxidizing properties of ·OH and ·Cl, can effectively destroy sludge EPS and release bound water, and can provide multiple functions such as filter aid, catalysis, flocculation, and adsorption. The present invention combines sludge reduction and sludge resource utilization into an integrated solution, which has a positive impact on the current sustainable treatment and disposal of sludge.

[0008] To achieve the above object, the present invention provides a method for improving the dehydration performance of sludge by combining sludge biochar with advanced oxidation process. The specific technical solution is as follows:

[0009] An activator is added to the original municipal sludge for mixed activation treatment to obtain activated sludge; the activated sludge is dehydrated to obtain activated sludge powder; the sludge powder is pyrolyzed to obtain activated sludge biochar; wherein, zinc chloride is selected as the activator.

[0010] The conditioning method of the present invention uses ferrous sulfate heptahydrate as a catalyst. The ·OH and ·Cl generated by activating sodium hypochlorite can oxidize and break down the sludge, causing the sludge to decompose into smaller sludge flocs, so that the bound water is smoothly released from the solid-phase sludge into the liquid phase; on the other hand, Fe 2+ is in-situ generated Fe 3+ , providing a flocculation effect, causing many fine colloidal particles to connect; the sludge biochar provides a skeleton effect on the one hand, and on the other hand, its surface is rich in metal elements and has a good flocculation effect within a reasonable range.

[0011] The above technical solutions proposed by the concept of the present invention can obtain the following beneficial effects:

[0012] (1) The present invention can achieve the best dehydration effect at pH = 6, and can improve the sludge dehydration performance within the weak alkaline and strong alkaline ranges (pH = 4 - 8). Considering the comprehensive dehydration performance and economic cost, the initial pH value does not need to be adjusted in actual application. Compared with the traditional Fenton process that needs to be adjusted to acidic conditions, the cost is low and the operation is convenient.

[0013] (2) Compared with the traditional Fenton process, biochar has a good skeleton construction function in sludge dehydration, providing a drainage channel for sludge dehydration. The surface of the sludge biochar is rich in metal elements and has a good flocculation effect. On the other hand, the adsorption effect of the sludge biochar can weaken the quenching effect of excessive Fe 2+ , making the dehydration performance of the system more stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is the schematic diagram of the combined treatment of sludge biochar to improve the dehydration performance of sludge in the embodiment of the present invention, and is the microscopic morphology of the sludge biochar.

[0015] Figure 2 are the capillary suction time, sludge specific resistance, and moisture content of the sludge cake of the sludge treated under different dosages of the sludge biochar of the present invention.

[0016] Figure 3 are the capillary suction time, sludge specific resistance, and moisture content of the sludge cake of the sludge treated under different dosages of ferrous sulfate heptahydrate of the present invention.

[0017] Figure 4 are the capillary suction time, sludge specific resistance, and moisture content of the sludge cake of the sludge treated under different dosages of sodium hypochlorite of the present invention.

[0018] Figure 5 are the capillary suction time, sludge specific resistance, and moisture content of the sludge cake of the sludge treated under different initial pH values of the present invention. Detailed implementation manners

[0019] The present invention will be further explained in detail below in conjunction with the accompanying drawings and embodiments, so that the objectives, technical solutions, and advantages of the present invention are clearer. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] A method for improving the sludge dewatering performance by combined treatment of sludge biochar, which adopts the method of synergistically activating sodium hypochlorite with sludge biochar and ferrous sulfate heptahydrate, specifically includes the following steps: (1) Prepare sludge biochar; (2) Pour an appropriate amount of sludge into 6 500 mL beakers for each experiment, each beaker containing 300 mL of sludge, set the stirring speed to 100 r / min and stir for 3 min, and 150 r / min and stir for 20 min; (3) The dosing sequence for each experiment is sodium hypochlorite, ferrous sulfate heptahydrate, and sludge biochar; immediately after each experiment, measure the capillary suction time (CST) and sludge specific resistance (SRF) of the sludge, and dry the sludge cake after suction filtration in an oven at 105 °C to measure the moisture content (Mc) of the sludge cake.

[0021] The sludge biochar in this experiment is prepared from municipal sludge: the sludge is placed in an oven at 105 °C and dried, then crushed in a pulverizer, and then passed through an 80-mesh sieve to obtain the original sludge powder. Take 20 g of the sludge powder and soak it in an appropriate amount of 3 mol / L zinc chloride solution, stir and soak for 12 h, then filter by suction, dry at 105 °C, crush and pass through a 100-mesh sieve, and then put it into a tubular furnace and heat it to 650 °C at a heating rate of 5 °C / min for pyrolysis, keep it warm for 2 h, and after cooling, wash it successively with (1 + 9) hydrochloric acid and deionized water and then dry it. (See Appendix Figure 1 )

[0022] Example 1: Source and basic properties of municipal sludge The sludge in this experiment was from the New Area Wastewater Treatment Plant in Handan City. The sludge moisture content was 98.53 ± 0.10%, the sludge capillary suction time was 40.1 ± 2.19 s, the sludge specific resistance was 19.36 ± 2.15×10 12 m / kg, the moisture content of the sludge cake was 79.48 ± 0.79%, and the sludge VSS was 7.60 ± 0.13 g / L.

[0022] Example 2: Influence of different dosages of sludge biochar on sludge dewatering performance Under room temperature conditions, without adjusting the pH of the original sludge, fixing the dosage of ferrous sulfate heptahydrate at 1.2 mmol / gVSS and the dosage of sodium hypochlorite at 1.2 mmol / gVSS, different dosages of sludge biochar (0.06, 0.08, 0.1, 0.12, 0.14, 0.16 g / gVSS) were added. Immediately after the experiment, the sludge dewatering performance was measured. When the dosage of sludge biochar was 0.12 g / gVSS, the sludge CST, SRF and Mc were 22.60 s, 4.8×10 12 m / kg and 71.53% respectively. The above results prove the feasibility of the combination of sludge biochar and activated sodium hypochlorite in the present invention. (See Appendix Figure 2 )

[0023] Example 3: Influence of different dosages of ferrous sulfate heptahydrate on sludge dewatering performance Under room temperature conditions, without adjusting the pH of the original sludge, fixing the dosage of sludge biochar at the optimal dosage and the dosage of sodium hypochlorite at 1.0 mmol / gVSS, different dosages of ferrous sulfate heptahydrate (1.5, 1.8, 2.1, 2.4, 2.7, 3.0 mmol / gVSS) were added. When the dosage of ferrous sulfate heptahydrate was 2.40 mmol / gVSS, the sludge CST was 17.73 s, the SRF was 2.33×10 12 m / kg, and the Mc was 73.49%. The appropriate addition of Fe 2+ has an enhancing effect on the conditioning of sludge dewatering in this system. With the increase of the dosage of Fe 2+ , a part of Fe 2+ will quench ·OH in the reaction system, resulting in a decrease in sludge dewatering performance. (See Appendix Figure 3 )

[0024] Example 4: Influence of different dosages of sodium hypochlorite on sludge dewatering performance At room temperature, without adjusting the pH of the raw sludge, fixing the dosage of sludge biochar and ferrous sulfate heptahydrate at the optimal dosage, adding different dosages of sodium hypochlorite (0.6, 0.9, 1.2, 1.5, 1.8, 2.1 mmol / gVSS). When the dosage of sodium hypochlorite reaches 1.5 mmol / g VSS, the CST decreases to 18.00 s, and the CST reduction rate reaches 67.20%. As the dosage of sodium hypochlorite continues to increase, the sludge dewatering performance deteriorates. However, during the experiment, Mc shows a trend of first increasing slightly and then decreasing. This is because the HClO decomposed from excessive sodium hypochlorite has strong oxidizing properties and further decomposes the organic substances in the sludge, resulting in the destruction of the sludge structure. (See appendix Figure 4 )

[0025] Example 5: Influence of different initial pH values on sludge dewatering performance At room temperature, fixing the dosages of sludge biochar, ferrous sulfate heptahydrate, and sodium hypochlorite at the optimal dosages, using 1 mol / L hydrochloric acid and 1 mol / L sodium hydroxide to adjust the pH of the sludge (2, 4, 6, raw sludge pH, 8, 10) respectively. In the range of pH = 4 - 8, the sludge dewatering performance reaches good results. When pH = 6, the sludge CST and SRF reach the lowest values of 20.53 s and 2.49×10 12 m / kg, and their reduction rates reach 67.60% and 80.96% respectively; the improvement effect of Mc in the range of pH = 4 - 8 is similar, and it decreases significantly at pH = 2 and 10. The present invention can improve the sludge dewatering performance in the range from weak acid to weak base, and the effect of conditioning the sludge dewatering in the weak acidic condition is better. (See appendix Figure 5 ).

Claims

1. A method for improving the sludge dewatering performance by combining sludge biochar with advanced oxidation process, characterized in that A method for improving the sludge dewatering performance by using biochar prepared from municipal sludge to synergistically activate sodium hypochlorite with ferrous sulfate heptahydrate, and it is a method of oxidative flocculation - framework construction - adsorption for sludge.

2. The method for improving the sludge dewatering performance by using a sludge biochar combined with an advanced oxidation process according to claim 1, characterized in that: The source of the sludge biochar is the product of pyrolysis after activation of municipal sludge.

3. A method for improving the sludge dewatering performance by a combined process of sludge biochar and advanced oxidation according to claim 2, characterized in that: The biochar activator is zinc chloride.

4. A method for improving the sludge dewatering performance by a combined process of sludge biochar and advanced oxidation according to any one of claims 1-3, characterized in that: The concentration of zinc chloride is 3 mol / L.

5. A method for improving the sludge dewatering performance by a combined process of sludge biochar and advanced oxidation according to any one of claims 1-4, characterized in that: The activated sludge is pyrolyzed at 650 °C for 2 h.

6. The method for improving the sludge dewatering performance by using the sludge biochar combined with the advanced oxidation process according to claim 1, wherein: The catalyst is ferrous sulfate heptahydrate.

7. A method for improving the sludge dewatering performance by a combined process of sludge biochar and advanced oxidation according to any one of claims 1, 2, and 6, characterized in that: The addition amount of the sludge biochar is 0.12 g / g VSS of the original sludge, the addition amount of ferrous sulfate heptahydrate is 2.4 mmol / g VSS, and the addition amount of sodium hypochlorite is 1.5 mmol / g VSS.

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