Sludge acidification conditioning dehydration method

Abstract

The invention belongs to the technical field of sludge dewatering, and particularly relates to a sludge acidification conditioning dewatering method. Comprising the following steps: adjusting the pH value of the sludge to 2-4, then adding a nitrite solution, uniformly mixing, standing for reaction so as to generate free nitrous acid in the system, and carrying out selective oxidative degradation, moisture release, filtration and dehydration on extracellular polymeric substances of the sludge through the free nitrous acid, thereby obtaining the dewatered sludge. According to the method, free nitrous acid with a certain concentration is generated in a sludge system under the combined action of an acidification environment and nitrite, and the free nitrous acid is used for breaking sludge extracellular polymeric substances and releasing water adsorbed and wrapped by sludge flocs, so that the dehydration performance of the sludge is remarkably improved, and the dehydration efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of sludge dehydration, and particularly relates to a sludge acidification conditioning and dehydration method. Background Art

[0002] With the acceleration of urbanization, excess sludge generated during sewage treatment has become a prominent issue hindering environmental sustainability. The current mainstream technology transfers pollutants into sludge through microbial metabolism and physicochemical methods. However, since the solid matter in sludge is primarily humus, composed of hydrophilic, negatively charged colloidal particles with a strong affinity for water, the sludge moisture content is generally as high as 95% to 99%, and its dewatering performance is poor, making direct mechanical dewatering very difficult. Therefore, in practical projects, sludge is generally conditioned before dewatering to improve its dewatering performance.

[0003] Although traditional sludge dewatering processes can reduce moisture content, they rely on high pretreatment costs, resulting in sludge treatment costs accounting for 50% to 60% of the total operating costs of sewage treatment plants, seriously restricting technical and economic feasibility.

[0004] To improve sludge dewatering performance, various dewatering conditioning methods have been developed, including physical, chemical, and biological conditioning. Physical conditioning uses physical fields such as ultrasound and microwaves to disrupt the sludge floc structure and release bound water. Chemical conditioning uses alkaline agents or oxidation to dissolve extracellular polymers, improving sludge dewatering performance. Biological conditioning utilizes enzymatic hydrolysis or microbial metabolic activity to decompose organic matter in sludge, enhancing its degradation capacity.

[0005] Although the above-mentioned sludge conditioning technologies can improve dehydration efficiency by destroying the sludge floc structure and promoting the degradation of extracellular polymers, physical methods such as ultrasound and microwaves have high energy consumption, while alkaline conditioning consumes a large amount of chemicals and has high treatment costs. Biological methods such as bioleaching are time-consuming and difficult to achieve efficient and low-cost targeted degradation of extracellular polymers. Summary of the Invention

[0006] In order to solve the technical problems of high treatment cost and difficulty in achieving efficient and low-consumption degradation in existing sludge conditioning technologies, the present invention provides a sludge acidification conditioning and dehydration method.

[0007] The present invention creates an acidic environment to activate the oxidative efficiency of nitrite, thereby achieving efficient breakdown of sludge extracellular polymers and release of bound water. The combined action of the acidified environment and nitrite can simultaneously achieve sludge floc destruction and cell lysis, significantly improving sludge dewatering performance while avoiding the destruction of resource components by strong alkaline conditions. This solves the technical problems of existing sludge conditioning technologies, such as high treatment costs and difficulty in achieving efficient and low-cost degradation.

[0008] The present invention controls the pH value of the sludge to 2-4 by acidifying the sludge, destroying the surface charge balance of the sludge flocs and weakening the binding effect of the sludge extracellular polymers on water. At the same time, nitrite is introduced under acidic conditions, and the free nitrous acid generated by the nitrite under acidic conditions is used to selectively oxidize and degrade the extracellular polymers in the sludge, thereby further releasing interstitial and intracellular water.

[0009] It should be noted that free nitrous acid (FNA), short for free nitrous acid, is a low-cost, highly efficient, and renewable chemical. It is a protonated product of nitrite and is present in anaerobic digestion wastewater. It has strong oxidizing properties and can effectively disrupt cell structures. FNA is widely used to disrupt cells and enhance the release of organic matter, serving as a pretreatment method to enhance organic wastewater treatment. FNA can also break down extracellular polymeric substances (ECPs) on the cell surfaces of sludge microorganisms, which play a crucial role in influencing various sludge properties. pH is also a key factor influencing FNA formation. Leveraging FNA's ability to disrupt the structure and composition of ECPs, a nitrite solution is introduced after sludge acidification. Under acidic conditions, the free nitrous acid generated in the sludge system by the addition of nitrite selectively oxidizes and degrades sludge microorganisms and their ECPs, further releasing intracellular and interstitial water. The combined action of acidification and nitrite simultaneously achieves sludge floc disruption and cell lysis, improving sludge dewatering performance.

[0010] The present invention provides a sludge acidification conditioning and dehydration method, comprising the following steps: The pH of the sludge is adjusted to 2-4, and then a nitrite solution is added. After mixing, the mixture is allowed to stand for reaction to generate free nitrous acid in the system. The free nitrous acid selectively oxidizes and degrades the extracellular polymers in the sludge to release water. After filtration and dehydration, dehydrated sludge is obtained.

[0011] Preferably, the nitrite solution is a sodium nitrite solution.

[0012] Preferably, the nitrite solution is obtained by dissolving nitrite in water; the concentration of the nitrite solution is 15 g / L to 100 g / L.

[0013] Preferably, the mass of nitrite is 1% to 6% of the dry weight of the sludge.

[0014] Preferably, the acid used for pH adjustment is sulfuric acid or hydrochloric acid, and the concentration of the acid is 20 wt % to 50 wt %.

[0015] Preferably, the reaction time is 6 h to 24 h.

[0016] Preferably, the moisture content of the sludge is 97.8%~99.5%.

[0017] Compared with the prior art, the present invention has the following technical effects: The present invention adjusts the pH value of sludge to 2-4, then adds a nitrite solution, mixes well and then allows the mixture to stand for reaction. Nitrite is added to the acidified sludge to generate free nitrous acid, a strong oxidizing substance, thereby constructing an acidic environment for the sludge to activate the oxidizing efficiency of the nitrite, achieving efficient breakdown of sludge extracellular polymers and release of bound water. Sludge floc breakdown and cell lysis are achieved through the combined action of the acidified environment and nitrite. The present invention can adapt to the improvement of the dewatering performance of sludge with different moisture contents, has a stable treatment effect, and avoids the destruction of resource components by strong alkaline conditions. The present invention solves the technical problems of high treatment cost and difficulty in achieving efficient and low-cost degradation of existing sludge conditioning technologies. DETAILED DESCRIPTION

[0018] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below with reference to specific embodiments.

[0019] In the description of the present invention, unless otherwise specified, all reagents used are commercially available and all methods used are conventional techniques in the art.

[0020] Example 1 A sludge acidification conditioning and dehydration method comprises the following steps: 150 mL of residual sludge from a sewage treatment plant with a water content of 98.5% was taken, and the pH value of the sludge was adjusted to 2.5 with 20 wt % sulfuric acid. Then, 2.3 mL of a 15 g / L sodium nitrite solution was added to the acidified sludge, mixed thoroughly, and allowed to react for 24 h to obtain pretreated sludge; the mass of sodium nitrite was 1.3% of the dry weight of the sludge.

[0021] The pretreated sludge liquid is transported to a 0.30 MPa vacuum filtration and dehydration device for filtration and dehydration to obtain dehydrated sludge.

[0022] Example 2 A sludge acidification conditioning and dehydration method comprises the following steps: 150 mL of residual sludge from a sewage treatment plant with a water content of 98.5% was taken, and the pH value of the sludge was adjusted to 3 with 20 wt % sulfuric acid. Then, 2.9 mL of a 15 g / L sodium nitrite solution was added to the acidified sludge, mixed thoroughly, and allowed to react for 24 h to obtain pretreated sludge; the mass of sodium nitrite was 1.6% of the dry weight of the sludge.

[0023] The pretreated sludge liquid is transported to a 0.30 MPa vacuum filtration and dehydration device for filtration and dehydration to obtain dehydrated sludge.

[0024] Example 3 A sludge acidification conditioning and dehydration method comprises the following steps: 150 mL of residual sludge from a sewage treatment plant with a water content of 98.5% was taken, and the pH value of the sludge was adjusted to 2 with 20 wt % sulfuric acid. Then, 2.1 mL of a 15 g / L sodium nitrite solution was added to the acidified sludge, mixed thoroughly, and allowed to react for 24 h to obtain pretreated sludge; the mass of sodium nitrite was 1.2% of the dry weight of the sludge.

[0025] The pretreated sludge liquid is transported to a 0.30 MPa vacuum filtration and dehydration device for filtration and dehydration to obtain dehydrated sludge.

[0026] Example 4 A sludge acidification conditioning and dehydration method comprises the following steps: 150 mL of residual sludge from a sewage treatment plant with a water content of 98.5% was taken, and the pH value of the sludge was adjusted to 3.5 with 20 wt % sulfuric acid. Then, 4.8 mL of a 15 g / L sodium nitrite solution was added to the acidified sludge, mixed thoroughly, and allowed to react for 24 h to obtain pretreated sludge; the mass of sodium nitrite was 2.7% of the dry weight of the sludge.

[0027] The pretreated sludge liquid is transported to a 0.30 MPa vacuum filtration and dehydration device for filtration and dehydration to obtain dehydrated sludge.

[0028] Example 5 A sludge acidification conditioning and dehydration method comprises the following steps: 150 mL of residual sludge from a sewage treatment plant with a water content of 98.5% was taken, and the pH value of the sludge was adjusted to 4 with 20 wt % sulfuric acid. Then, 4.6 mL of a 35 g / L sodium nitrite solution was added to the acidified sludge, mixed thoroughly, and allowed to react for 24 h to obtain pretreated sludge; the mass of sodium nitrite was 6% of the dry weight of the sludge.

[0029] The pretreated sludge liquid is transported to a 0.30 MPa vacuum filtration and dehydration device for filtration and dehydration to obtain dehydrated sludge.

[0030] Example 6 A sludge acidification conditioning and dehydration method comprises the following steps: 150 mL of residual sludge from a sewage treatment plant with a water content of 97.8% was taken and the pH value of the sludge was adjusted to 3 with 20 wt % sulfuric acid. Then, 4.9 mL of a 16 g / L sodium nitrite solution was added to the acidified sludge, mixed thoroughly, and allowed to react for 8 h to obtain pretreated sludge; the mass of sodium nitrite was 3.5% of the dry weight of the sludge.

[0031] The pretreated sludge liquid is transported to a 0.30 MPa vacuum filtration and dehydration device for filtration and dehydration to obtain dehydrated sludge.

[0032] Comparative Example 1 A sludge acidification conditioning and dehydration method comprises the following steps: 150 mL of residual sludge from a sewage treatment plant with a water content of 98.5% was taken, and the pH value of the sludge was adjusted to 2.5 with 20 wt % sulfuric acid. The sludge was fully mixed and allowed to react for 24 h to obtain pretreated sludge.

[0033] The pretreated sludge liquid is transported to a 0.30 MPa vacuum filtration and dehydration device for filtration and dehydration to obtain dehydrated sludge.

[0034] The difference between Comparative Example 1 and Example 1 is that no sodium nitrite solution was added.

[0035] Comparative Example 2 A sludge acidification conditioning and dehydration method comprises the following steps: 150 mL of residual sludge from a sewage treatment plant with a water content of 98.5% was taken, and the pH value of the sludge was adjusted to 3 with 20 wt % sulfuric acid. The mixture was thoroughly mixed and allowed to stand for 24 h to obtain pretreated sludge.

[0036] The pretreated sludge liquid is transported to a 0.30 MPa vacuum filtration and dehydration device for filtration and dehydration to obtain dehydrated sludge.

[0037] The difference between Comparative Example 2 and Example 2 is that no sodium nitrite solution was added.

[0038] Comparative Example 3 A sludge acidification conditioning and dehydration method comprises the following steps: 150 mL of residual sludge from a sewage treatment plant with a water content of 98.5% was taken, and the pH value of the sludge was adjusted to 2 with 20 wt % sulfuric acid. The mixture was thoroughly mixed and allowed to react for 24 h to obtain pretreated sludge.

[0039] The pretreated sludge liquid is transported to a 0.30 MPa vacuum filtration and dehydration device for filtration and dehydration to obtain dehydrated sludge.

[0040] The difference between Comparative Example 3 and Example 3 is that no sodium nitrite solution was added.

[0041] Comparative Example 4 A sludge acidification conditioning and dehydration method comprises the following steps: 150 mL of residual sludge from a sewage treatment plant with a water content of 98.5% was taken, and the pH value of the sludge was adjusted to 3.5 with 20 wt % sulfuric acid. The sludge was fully mixed and allowed to react for 24 h to obtain pretreated sludge.

[0042] The pretreated sludge liquid is transported to a 0.30 MPa vacuum filtration and dehydration device for filtration and dehydration to obtain dehydrated sludge.

[0043] The difference between Comparative Example 3 and Example 4 is that no sodium nitrite solution was added.

[0044] Comparative Example 5 A sludge acidification conditioning and dehydration method comprises the following steps: 150 mL of residual sludge from a sewage treatment plant with a water content of 98.5% was taken, and the pH value of the sludge was adjusted to 4 with 20 wt % sulfuric acid. The mixture was thoroughly mixed and allowed to react for 24 h to obtain pretreated sludge.

[0045] The pretreated sludge liquid is transported to a 0.30 MPa vacuum filtration and dehydration device for filtration and dehydration to obtain dehydrated sludge.

[0046] The difference between Comparative Example 5 and Example 5 is that no sodium nitrite solution was added.

[0047] Comparative Example 6 A sludge acidification conditioning and dehydration method comprises the following steps: 150 mL of residual sludge from the sewage treatment plant was taken, with a water content of 97.8%. The pH value of the sludge was adjusted to 3 with 20 wt % sulfuric acid, and the mixture was thoroughly mixed and allowed to react for 8 h to obtain pretreated sludge.

[0048] The pretreated sludge liquid is transported to a 0.30 MPa vacuum filtration and dehydration device for filtration and dehydration to obtain dehydrated sludge.

[0049] The difference between Comparative Example 6 and Example 6 is that no sodium nitrite solution was added.

[0050] Experimental test: In the embodiment of the present invention, multiple sampling and measurement of the basic properties of sludge from a municipal sewage treatment plant were carried out, and the obtained results are shown in Table 1.

[0051] Table 1 Basic physical and chemical properties of sludge As shown in Table 1, the sludge is neutral, has a high water content, a high organic content, and poor sedimentation performance. Sludge specific resistance is a comprehensive evaluation index of sludge filtration performance, which can reflect the difficulty of sludge dewatering. The full name of sludge specific resistance in English is Specific Resistance to Filtration, abbreviated as SRF. SRF represents the resistance generated by the filtration of unit mass of sludge on a unit filtration area under a certain pressure. The larger the SRF, the more difficult it is to filter and the worse the dewatering performance. It is generally believed that a sludge specific resistance greater than 1 10 13m·kg -1 It is difficult to filter sludge; therefore, the sludge used in this embodiment is difficult to filter sludge.

[0052] Table 2 Sludge specific resistance of dewatered sludge under different treatment conditions As shown in Table 2, it can be seen from Comparative Examples 1 to 6 that only sulfuric acid solution is used to acidify the sludge with a moisture content of 98.5%. Only when the pH value after acidification is 3 and 2.5, the SRF of the dewatered sludge decreases compared with the original sludge. Moreover, when the moisture content of the original sludge to be treated becomes lower, that is, the sludge with a moisture content of 97.8% is treated, even if the pH value is adjusted to 3, the sludge dewatering performance not only does not improve, but even deteriorates. This shows that sulfuric acid acidification alone is not stable in improving the sludge dewatering performance, and the sludge dewatering performance is greatly affected by the moisture content of the sludge itself. Compared with the sulfuric acid acidification treatment of Comparative Examples 1 to 6, the SRF of the dewatered sludge after the combined treatment of sulfuric acid acidification and nitrite in Examples 1 to 6 is lower than the SRF of the sludge treated with sulfuric acid acidification alone, and is lower than the SRF of the original sludge, indicating that the combination of acidification environment and nitrite can effectively reduce the sludge specific resistance, and the formation of free nitrite can effectively improve the dewatering performance of the sludge.

[0053] In Example 1, the sludge specific resistance was changed from 1.36×10 13 m·kg -1 Reduced to 8.1×10 12 m·kg -1 , the specific resistance value decreased by 40%, and the dewatering performance of the sludge was improved; in Example 2, the specific resistance of the sludge was reduced from 1.36×10 13 m·kg -1 Reduced to 9.0×10 12 m·kg -1 The specific resistance value decreased by 34%, which improved the dewatering performance of the sludge. In Example 3, the specific resistance of the sludge decreased from 1.36×10 13 m·kg -1 reduced to 1.02×10 13 m·kg -1 , the specific resistance value decreased by 25%, and the dewatering performance of the sludge was improved; in Example 4, the specific resistance of the sludge was reduced from 1.36×10 13 m·kg -1 reduced to 1.03×10 13 m·kg -1 The specific resistance value decreased by 24%. In Example 5, the specific resistance of the sludge was reduced from 1.36×10 13 m·kg -1 reduced to 1.23×10 13 m·kg-1 , the specific resistance value decreased by 10%; in Example 6, the specific resistance of the sludge was reduced from 1.39×10 13 m·kg -1 Reduced to 8.4×10 12 m·kg -1 , the specific resistance value dropped by 40%. This shows that the combination of acidification and nitrite can effectively reduce the sludge specific resistance, and the formation of free nitrite can effectively improve the dewatering performance of sludge.

[0054] It should be noted that when numerical ranges are mentioned in the present invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints may be selected. Since the steps and methods used are the same as those in the embodiments, the present invention describes preferred embodiments to avoid redundancy. Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they understand the basic inventive concepts, and such changes and modifications fall within the scope of the present invention.

[0055] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. If these modifications and variations of the present invention fall within the scope of the equivalent technology of the present invention, the present invention is also intended to include these modifications and variations.

Claims

1. A sludge acidification conditioning and dehydration method, characterized in that: The following steps are involved: The pH of the sludge is adjusted to 2-4, and then a nitrite solution is added. After mixing, the mixture is allowed to stand for reaction to generate free nitrous acid in the system. The free nitrous acid selectively oxidizes and degrades the extracellular polymers in the sludge to release water. After filtration and dehydration, dehydrated sludge is obtained.

2. The sludge acidification conditioning and dehydration method according to claim 1, characterized in that: The nitrite solution is a sodium nitrite solution.

3. The sludge acidification conditioning and dehydration method according to claim 1, characterized in that: The nitrite solution is obtained by dissolving nitrite in water, and the concentration of the nitrite solution is 15g / L~100g / L.

4. The sludge acidification conditioning and dehydration method according to claim 1, characterized in that: The mass of nitrite is 1%~6% of the dry weight of sludge.

5. The sludge acidification conditioning and dehydration method according to claim 1, characterized in that: The acid used for pH adjustment is sulfuric acid or hydrochloric acid, and the acid concentration is 20wt%~50wt%.

6. The sludge acidification conditioning and dehydration method according to claim 1, characterized in that: The reaction time is 6h~24h.

7. The sludge acidification conditioning and dehydration method according to claim 1, characterized in that: The moisture content of the sludge is 97.8% to 99.5%.

Images