A method for simultaneous nitrogen and phosphorus treatment in a sludge alkaline fermentation directional acetic acid production process

Abstract

The application provides a sludge alkaline fermentation directional acetic acid production process synchronous nitrogen and phosphorus treatment method, which comprises the following steps: adding a pH regulator to sludge mixed solution to make the mixed solution alkaline, and adding NaCl to obtain an alkaline fermentation solution; adding Na2SO4 to the alkaline fermentation solution to perform anaerobic fermentation; during the fermentation process, inserting an iron plate electrode, and performing electric enhanced coupling treatment by electrification; after several days of reaction, adding MgSO4; during the anaerobic fermentation process, adjusting the pH value of the alkaline fermentation solution by using a pH regulator at regular intervals or irregular intervals to make the solution alkaline; soaking zeolite in a NaCl solution to obtain modified zeolite by drying, and putting the modified zeolite into the fermentation solution on the 18th-20th day of fermentation. The technical scheme of the application improves the acetic acid production ratio and acetic acid production amount of ordinary fermentation; and the addition of NaCl modified zeolite and the combination of electric enhancement realize synchronous nitrogen and phosphorus removal, and improve the hydrolysis efficiency.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology, and in particular to a method for simultaneous nitrogen and phosphorus treatment in a directional acetic acid production process using alkaline fermentation of sludge. Background Technology

[0002] To address the insufficient carbon source for nitrogen and phosphorus removal in wastewater treatment plants, volatile fatty acids (VFAs) are typically produced through sludge fermentation. VFAs have a complex composition, with acetic acid being a relatively high-quality carbon source. Various methods exist to enhance sludge acid production. Alkaline fermentation, compared to other methods (pre-oxidation, surfactant pretreatment, etc.), is a relatively mature and cost-effective method. However, alkaline fermentation still suffers from low acetic acid yield and proportion, and high nitrogen and phosphorus release. Therefore, it is necessary to find methods to increase the acetic acid yield and proportion in the VFAs of alkaline fermentation and reduce the nitrogen and phosphorus concentrations in the sludge fermentation broth. Persulfate pre-oxidation of sludge can effectively increase the total VFA yield and acetic acid proportion in both conventional and alkaline fermentation. However, the dosage of persulfate is large, resulting in high reagent costs, and it does not solve the problem of high nitrogen and phosphorus concentrations in the sludge fermentation broth. Summary of the Invention

[0003] To address the above technical problems, this invention discloses a method for simultaneous nitrogen and phosphorus treatment in the directional acetic acid production process of sludge alkaline fermentation, which increases acetic acid production and reduces nitrogen and phosphorus concentrations.

[0004] The technical solution adopted by this invention is as follows:

[0005] A method for simultaneous nitrogen and phosphorus treatment in a sludge alkaline fermentation process for directional acetic acid production includes the following steps:

[0006] Step S1: Add a pH adjuster to the sludge mixture to make it alkaline, and add NaCl to obtain an alkaline fermentation solution.

[0007] Step S2: Add Na2SO4 to the alkaline fermentation solution to carry out anaerobic fermentation; during the fermentation process, insert an iron plate electrode and apply electricity to perform electro-enhanced coupling treatment; after the reaction has been going on for a few days, add MgSO4.

[0008] Step S3: During the anaerobic fermentation process, the pH value of the alkaline fermentation solution is adjusted by a pH adjuster at regular or irregular intervals to make the solution alkaline.

[0009] Step S4: The zeolite is soaked in NaCl solution and dried to obtain modified zeolite. The modified zeolite is then added to the fermentation solution on day 18-20 of fermentation.

[0010] It is generally believed that using persulfate can increase the yield of total VFAs and the proportion of acetic acid in both conventional and alkaline fermentation. The technical solution of this invention uses sulfate, which also increases the proportion of acetic acid in conventional fermentation and promotes the targeted production of acetic acid in alkaline fermentation of sludge. Addressing the issue of high nitrogen and phosphorus release during alkaline fermentation, the technical solution of this invention uses iron and magnesium sulfates to achieve simultaneous phosphorus removal, at a cost far lower than persulfate. Furthermore, during anaerobic fermentation, voltage is applied for electro-enhancing. The electro-effect causes iron ions to dissolve from the electrode iron plate, promoting phosphorus flocculation and precipitation. The electro-process forms chlorination with NaCl, promoting the conversion of ammonia nitrogen. In the later stages of fermentation, NaCl-modified zeolite is added, which, under electro-effect, forms interfacial chlorination, further improving the conversion of ammonia nitrogen adsorbed at the interface. Simultaneously, electro-driven directional transfer of small molecule acids and ammonia nitrogen enhances the removal effect. Moreover, the osmotic pressure of NaCl on cells and the electro-induced chlorination promote cell rupture, increasing hydrolysis efficiency.

[0011] As a further improvement of the present invention, in step S2, the dosage of Na2SO4 is 0.15-0.85 g / gVS, and the dosage of MgSO4 is 0.1-0.4 g / gVS.

[0012] As a further improvement of the present invention, in step S1, the pH value of the mixture is 8.5-9.5, and NaCl is added to make the concentration of NaCl in the solution 0.5-4 mol / L; in step S3, the pH value of the solution is 8.5-9.5.

[0013] As a further improvement of the present invention, in step S1, the pH value of the mixture is 9; in step S3, the pH value of the solution is 9.

[0014] As a further improvement of the present invention, in step S3, the pH value of the solution is adjusted every 24 hours.

[0015] As a further improvement of the present invention, in step S4, the particle size of the zeolite is 80-120 mesh, the concentration of the NaCl solution used for soaking is 1-3 mol / L, and the soaking time is 6-24 h; the dosage of the modified zeolite is 100-300 g / L. Further, the dosage of the modified zeolite is 200 g / L. Further, the soaking time is 6-12 h.

[0016] As a further improvement of the present invention, in step S4, the concentration of the NaCl solution used for soaking is 2 mol / L.

[0017] As a further improvement of the present invention, in step S2, the voltage applied for the electro-enhanced coupling process is 1mV-10mV.

[0018] As a further improvement of the present invention, in step S2, the current is set to be a staged current adjustment during the electro-enhanced coupling treatment. A voltage of 5-10mV is used in the first 2 hours of fermentation, and a voltage of 1-4mV is used to continuously enhance the electro-enhanced effect after 2 hours. The electrode plate spacing is 3-5cm.

[0019] As a further improvement of the present invention, in step S2, anaerobic fermentation is carried out in a constant temperature shaking incubator. The temperature of the anaerobic fermentation is 35°C, the shaking speed is 120 r / min, and the fermentation cycle is 20 days.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] The technical solution of this invention uses sulfates to increase the proportion of acetic acid produced by ordinary fermentation, promotes the targeted production of acetic acid by alkaline fermentation of sludge, and increases the amount of acetic acid produced; moreover, it uses iron, magnesium and other sulfates, adds NaCl to modify zeolite, and combines the effect of electrical enhancement to achieve the effect of simultaneous nitrogen and phosphorus removal, improves hydrolysis efficiency, and greatly reduces costs. Detailed Implementation

[0022] The preferred embodiments of the present invention will be described in further detail below.

[0023] A method for treating sludge by targeted alkaline fermentation to produce acetic acid and simultaneous nitrogen and phosphorus includes the following steps:

[0024] (1) Fermentation system setup:

[0025] The sludge mixture is added to the reaction. First, the pH of the mixture in the reactor is adjusted to 9 using 2 mol / L hydrochloric acid and 2 mol / L NaOH solution to make the mixture alkaline. Then, NaCl is added, and the concentration of NaCl in the mixture is 0.5-4 mol / L.

[0026] After conditioning, the reactor was purged with nitrogen to remove air and ensure a strictly anaerobic environment. The reactor was then placed in a constant-temperature shaking incubator for anaerobic fermentation at 35°C and a shaking speed of 120 r / min for a fermentation period of 20 days.

[0027] (2) Stage addition of reagents: Add Na2SO4 and MgSO4 to the alkaline fermentation system for anaerobic fermentation. Specifically, in the early stage of establishing the fermentation system, add Na2SO4 at a dosage of 0.15-0.85 g / gVS; on the 8th day of the reaction, add MgSO4 at a dosage of 0.1-0.4 g / gVS.

[0028] During the anaerobic fermentation process, the pH value of the solution in the reactor is adjusted regularly with 2 mol / L hydrochloric acid or 2 mol / L NaOH solution to make the pH = 9, and the solution in the reactor is alkaline. The adjustment frequency is once every 24 hours.

[0029] Further preferably, during fermentation, a voltage of 1mV-10mV is applied to the fermentation system for electro-enhancement. Specifically, iron plates are used as electrodes, and the current is adjusted in stages: 5-10mV is used for the first 2 hours of fermentation, followed by a continuous voltage of 1-4mV after 2 hours, with an electrode spacing of 3-5cm. After each fermentation, the electrode plates are soaked in 2mol / L hydrochloric acid for 24 hours, then deionized and reused.

[0030] (3) Modification and addition of zeolite: 80-120 mesh zeolite was soaked in 2 mol / L NaCl solution for 6-24 h for modification. The modified zeolite was not deionized and was directly dried to obtain modified zeolite. Modified zeolite was added on day 19 of the fermentation reaction at a dosage of 100-300 g / L.

[0031] In the above technical solution, sulfate promotes the targeted acetic acid production and simultaneous phosphorus removal through alkaline fermentation of sludge: Adding magnesium sulfate under alkaline conditions can achieve targeted acetic acid production and simultaneous phosphorus removal. Under alkaline conditions, sulfate ions can promote the conversion of C3-C5 VFAs into acetic acid, thereby increasing the proportion of acetic acid and promoting the targeted acetic acid production through alkaline fermentation of sludge. Adding magnesium sulfate under alkaline conditions... 2+ It promotes the dissolution of organic matter, especially proteins, thereby further increasing acid production on the basis of alkaline fermentation. Electro-enhanced coupled zeolite can remove ammonia nitrogen and phosphorus from sludge fermentation broth.

[0032] The following detailed description is based on specific embodiments.

[0033] Example 1

[0034] A method for simultaneous nitrogen and phosphorus treatment in a sludge alkaline fermentation process for directional acetic acid production, wherein the suspended solids concentration of the sludge mixed liquor in this embodiment is 28.1 ± 5.0 g / L. The method includes the following steps:

[0035] Step S1: Add a pH adjuster to the sludge mixture to achieve a pH of 9. The pH adjuster includes 2 mol / L hydrochloric acid and 2 mol / L NaOH. Add NaCl to obtain an alkaline fermentation solution with a NaCl concentration of 0.5 mol / L. Purge the reactor with nitrogen to remove air and ensure a strictly anaerobic environment. Place the reactor in a constant-temperature shaking incubator for anaerobic fermentation. Set the incubator temperature to 35℃, the shaking speed to 120 r / min, and the fermentation cycle to 20 days.

[0036] In step S2, Na2SO4 was added to the alkaline fermentation solution at a dosage of 0.15 g / gVS for anaerobic fermentation. During the fermentation process, an iron plate electrode was inserted and a voltage of 5 mV was applied for electro-enhanced coupling. After 8 days of reaction, MgSO4 was added at a dosage of 0.24 g / gVS.

[0037] The current for the electro-enhancing process was set to be adjusted in stages. A voltage of 5mV was used for the first 2 hours of fermentation, and a voltage of 2mV was used for continuous electro-enhancing after 2 hours. The electrode plate spacing was 3-5cm.

[0038] Step S3: During the anaerobic fermentation process, the pH value of the alkaline fermentation solution is adjusted every 24 hours using a pH adjuster to make the pH value of the solution 9; the pH adjuster used includes 2 mol / L hydrochloric acid and 2 mol / L NaOH.

[0039] Step S4: Soak 100-mesh zeolite in 2 mol / L NaCl solution for 6 hours, dry it to obtain modified zeolite, and add the modified zeolite to the fermentation solution on the 19th day of fermentation at a dosage of 200 g / L.

[0040] The treatment results of this embodiment are as follows: total VFA concentration of 4770.4 mg COD / L, loss rate of 9.1%; acetic acid concentration of 3812.3 mg COD / L, loss rate of only 9.9%; ammonia nitrogen concentration of 38.4 mg / L, removal rate of 86.5%; and phosphate concentration of 2.67 mg / L, removal rate of 63.8%.

[0041] Comparative Example 1

[0042] Based on Example 1, this comparative example uses existing technology to add persulfate for alkaline fermentation, and the pH value is adjusted to 9.

[0043] In Example 1, the magnesium sulfate dosage was 0.24 g / gVS, the total VFAs yield was 395.4 mg COD / gVS, the acetic acid yield was 314.5 mg COD / gVS, the acetic acid content was 80.0%, and the phosphate concentration was reduced to 4 mg / L.

[0044] In contrast, the total VFA yield of Comparative Example 1 was 292.7 mg COD / gVS, the acetic acid yield was 149.1 mg COD / gVS, the acetic acid content was 51%, and the phosphate concentration was 7.85 mg / L.

[0045] Compared to Comparative Example 1, Example 1 showed a 35.1% increase in total VFAs production, a 111% increase in acetic acid production, and a 96.3% decrease in phosphate concentration.

[0046] Example 2

[0047] Based on Example 1, the difference in this example is as follows: In step S2, the amount of Na2SO4 added is 0.15 g / gVS; on the 8th day of the reaction, MgSO4 is added at a rate of 0.1 g / gVS. Electro-enhancing is performed by passing a 1 mV voltage through the fermentation system. A 5 mV voltage is used for the first 2 hours of fermentation, followed by a continuous 1 mV voltage thereafter, with an electrode spacing of 3 cm. In step S4, the amount of zeolite added is 80 mesh, at a rate of 100 g / L, otherwise the same as in Example 1.

[0048] The treatment results of this embodiment are as follows: total VFA concentration of 4832.54 mg COD / L, loss rate of 8.5%; acetic acid concentration of 3826.11 mg COD / L, loss rate of only 8.8%; ammonia nitrogen concentration of 75.2 mg / L, removal rate of 78.5%; and phosphate concentration of 5.57 mg / L, removal rate of 42.8%.

[0049] Example 3

[0050] Based on Example 1, the difference in this example is as follows: In step S2, the amount of Na2SO4 added is 0.85 g / gVS; on the 8th day of the reaction, MgSO4 is added at a rate of 0.4 g / gVS. A 10 mV voltage is applied to the fermentation system for electro-enhancement. The 10 mV voltage is used for the first 2 hours of fermentation, and then a 1 mV voltage is used continuously thereafter, with an electrode spacing of 3 cm. In step S4, the amount of zeolite added is 120 mesh, at a rate of 300 g / L, otherwise the same as in Example 1.

[0051] The treatment results of this embodiment are as follows: total VFA concentration is 4257.65 mg COD / L, with a loss rate of 11.32%; acetic acid concentration is 3758.24 mg COD / L, with a loss rate of only 9.8%; ammonia nitrogen concentration is 31.57 mg / L, with a removal rate of 90.12%; and phosphate concentration is 2.68 mg / L, with a removal rate of 68.24%.

[0052] Example 4 differs from Example 1 in that, in step S4, the zeolite is soaked in a 2 mol / L NaCl solution for 12 hours. All other steps are the same as in Example 1.

[0053] The treatment results of this embodiment are as follows: ammonia nitrogen concentration is 30.54, removal rate is 89.32%; VFAs loss rate is 9.25%.

[0054] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for simultaneous nitrogen and phosphorus treatment in a directional acetic acid production process via alkaline fermentation of sludge, characterized in that: Includes the following steps: Step S1: Add a pH adjuster to the sludge mixture to make it alkaline, and add NaCl to obtain an alkaline fermentation solution. Step S2: Add Na2SO4 to the alkaline fermentation solution for anaerobic fermentation; and during the fermentation process, insert iron plate electrodes and apply current for electro-enhanced coupling treatment; after 5 days of reaction, add MgSO4; in the electro-enhanced coupling treatment, the current is set to be adjusted in stages, with a voltage of 5-10mV used in the first 2 hours of fermentation, and a voltage of 1-4mV used for continuous electro-enhancing after 2 hours, and the electrode plate spacing is 3-5cm; Step S3: During the anaerobic fermentation process, the pH value of the alkaline fermentation solution is adjusted by a pH adjuster at regular or irregular intervals to make the solution alkaline. Step S4: The zeolite is soaked in NaCl solution and dried to obtain modified zeolite. The modified zeolite is then added to the alkaline fermentation solution on the 18th-20th day of fermentation.

2. The method for simultaneous nitrogen and phosphorus treatment in the directional acetic acid production process of sludge alkaline fermentation according to claim 1, characterized in that: In step S2, the dosage of Na2SO4 is 0.15~0.85 g / gVS, and the dosage of MgSO4 is 0.1~0.4 g / gVS.

3. The method for simultaneous nitrogen and phosphorus treatment in the directional acetic acid production process of sludge alkaline fermentation according to claim 1, characterized in that: In step S1, the pH value of the mixture is 8.5-9.5, and NaCl is added to make the NaCl concentration in the solution 0.5-4 mol / L; in step S3, the pH value of the solution is 8.5-9.

5.

4. The method for simultaneous nitrogen and phosphorus treatment in the directional acetic acid production process of sludge alkaline fermentation according to claim 3, characterized in that: In step S1, the pH value of the mixture is 9; in step S3, the pH value of the solution is 9.

5. The method for simultaneous nitrogen and phosphorus treatment in the directional acetic acid production process of sludge alkaline fermentation according to claim 1, characterized in that: In step S3, the pH value of the solution is adjusted every 24 hours.

6. The method for simultaneous nitrogen and phosphorus treatment in the directional acetic acid production process of sludge alkaline fermentation according to claim 1, characterized in that: In step S4, the particle size of the zeolite is 80-120 mesh, the concentration of the NaCl solution used for soaking is 1-3 mol / L, the soaking time is 6-12 h, and the dosage of modified zeolite is 100-300 g / L.

7. The method for simultaneous nitrogen and phosphorus treatment in the directional acetic acid production process of sludge alkaline fermentation according to claim 1, characterized in that: In step S4, the concentration of the NaCl solution used for soaking is 2 mol / L.

8. The method for simultaneous nitrogen and phosphorus treatment in the directional acetic acid production process of sludge alkaline fermentation according to claim 1, characterized in that: In step S2, the voltage applied for the electro-enhanced coupling process is 1mV-10mV.

9. The method for simultaneous nitrogen and phosphorus treatment in the directional acetic acid production process of sludge alkaline fermentation according to any one of claims 1 to 8, characterized in that: In step S2, anaerobic fermentation is carried out in a constant temperature shaking incubator. The anaerobic fermentation temperature is 35℃, the shaking speed is 120r / min, and the fermentation cycle is 20 days.