Method for pretreating sludge by activating sulfite with iron sulfide

Abstract

The invention provides a method for pretreating sludge by activating sulfite with iron sulfide, and belongs to the technical field of sludge treatment. The method comprises the following steps: firstly, naturally settling sludge to obtain a sludge sample, and then adding iron sulfide and sulfite into the sludge sample for pretreatment. The method for pretreating the sludge by activating the sulfite with the iron sulfide has the advantages that the raw materials are easy to obtain, secondary pollution is avoided and the like, an ideal sludge wall breaking effect can be achieved, more organic substances of intracellular and extracellular polymers in the sludge pretreated by activating the sulfite with the iron sulfide are released and enter a liquid phase, and the sludge can be recycled. Therefore, the overall hydrolytic acidification rate of the sludge is increased, and the purpose of maximizing resource and energy recovery is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of sludge treatment, and in particular to a method for pretreating sludge by activating sulfite with iron sulfide. Background Art

[0002] At present, the demand for sewage treatment plants is increasing year by year with population growth and industrial development. By the end of 2022, the daily treatment capacity of urban sewage treatment plants will reach 220 million tons. The main biological treatment process of sewage plants is the activated sludge method, but the anabolism of functional microorganisms in this method will produce a large amount of sludge. Considering that sludge contains a large amount of renewable organic matter, it is regarded as a sustainable resource with economic potential. It also contains toxic substances such as pathogens and persistent organic pollutants. This characteristic makes the treatment and disposal of sludge very important. If it is not properly handled, it may cause secondary pollution to the environment and seriously threaten the ecosystem. Anaerobic fermentation of sludge can produce organic volatile acids with wide applicability. These volatile acids can be used as a supplementary carbon source or for biological denitrification and phosphorus removal, and can also be used in food, medicine and cosmetics industries. The generation cycle of hydrolytic acidifying microorganisms is shorter than that of methanogens, and they have strong adaptability to the environment. They can degrade macromolecular organic matter into short-chain fatty acids. Therefore, anaerobic fermentation is an efficient and applicable method for treating sludge with complex components.

[0003] However, the complex floc structure of sludge composed of microbial cell walls limits the dissolution of sludge, resulting in a low hydrolysis rate that limits sludge fermentation. Therefore, it is of great significance to study a method for pretreating sludge by activating sulfite with iron sulfide, which can destroy the floc structure and enhance the hydrolysis process, thereby improving the biodegradability of the substrate. Summary of the invention

[0004] The purpose of the present invention is to provide a method for pretreating sludge by activating sulfite with iron sulfide, so as to solve the problems of long sludge anaerobic fermentation cycle, difficulty in breaking the sludge microorganism wall and low organic matter release rate in the prior art.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for pretreating sludge by activating sulfite with iron sulfide, comprising the following steps:

[0007] (1) allowing the sludge to settle naturally to obtain a sludge sample;

[0008] (2) Add iron sulfide and sulfite to the sludge sample for pretreatment.

[0009] Preferably, in step (1), the temperature of natural sedimentation is 1 to 6° C., and the time of natural sedimentation is 20 to 28 hours.

[0010] Preferably, in step (1), the pH value of the sludge sample is 6.5-7.5, the concentration of TSS is 10-20 g / L, and the concentration of VSS is 8-10 g / L.

[0011] Preferably, in step (2), the amount of iron sulfide added is 0.1 to 0.6 mmol / g VSS; SO3 2- The molar ratio of iron to iron sulfide is 1:1 to 3.

[0012] Preferably, in step (2), after iron sulfide and sulfite are added to the sludge sample, the pH value is adjusted to 5-7.

[0013] Preferably, the iron sulfide is Fe3S4, Fe7S8 or FeS2; and the sulfite comprises calcium sulfite or sodium sulfite.

[0014] Preferably, in step (2), the pretreatment rotation speed is 120-150 rpm, the pretreatment temperature is 30-35° C., and the pretreatment time is 20-28 h.

[0015] Beneficial effects of the present invention:

[0016] (1) The present invention uses iron sulfide to activate sulfite to pretreat the sludge, which contains transition metal active sites and is easy to obtain. The residual sulfite is easily oxidized by oxygen to non-toxic SO4 2- , and also produces peroxysulfate free radicals (SO5 - ·) and sulfite radicals (SO3 - ·) and other active substances, which can not only effectively destroy the semi-rigid cell wall structure, but also destroy the specific functional groups and polymer main chain bonds in the sludge flocs.

[0017] (2) The present invention verifies that as the pretreatment time of sludge with iron sulfide activated sulfite increases, the change trend of soluble protein is to increase first and then decrease, while soluble carbohydrates continue to increase, which indicates that pretreatment of sludge with iron sulfide activated sulfite can destroy the cell structure of sludge microorganisms and is conducive to the dissolution of intracellular organic matter. Compared with other forms of sludge pretreatment methods with iron sulfide activated sulfite, Fe3S4 activated sulfite pretreatment has a significant effect on the release of soluble protein, while the release of soluble carbohydrates is basically the same as Fe7 S8, but higher than FeS2. This shows that the method of Fe3S4 activated sulfite pretreatment of sludge has significant superiority.

[0018] (3) The method of pre-treating sludge by activating sulfite with iron sulfide provided by the present invention has the advantages of easy availability of raw materials and no secondary pollution, and can achieve an ideal sludge wall breaking effect. More organic matter in intracellular and extracellular polymers in the sludge pre-treated with Fe3S4 activated sulfite is released into the liquid phase, thereby improving the overall hydrolysis and acidification rate of the sludge, promoting the generation of short-chain fatty acids, and achieving the purpose of maximizing resource and energy recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a comparison chart of the concentrations of soluble proteins and soluble carbohydrates in the sludge samples pretreated in Example 1 and Comparative Examples 1-2 as the pretreatment time changes;

[0020] Figure 2 It is a comparison chart of the yields of soluble protein and soluble carbohydrates after sludge pretreatment in Example 1, Examples 4-5 and Comparative Example 2. DETAILED DESCRIPTION

[0021] The present invention provides a method for pretreating sludge by activating sulfite with iron sulfide, comprising the following steps:

[0022] (1) allowing the sludge to settle naturally to obtain a sludge sample;

[0023] (2) Add iron sulfide and sulfite to the sludge sample for pretreatment.

[0024] In the present invention, in step (1), the temperature of natural sedimentation is 1 to 6°C, preferably 2 to 5°C, more preferably 3 to 4°C, and the time of natural sedimentation is 20 to 28h, preferably 22 to 26h, more preferably 24h.

[0025] In the present invention, in step (1), the pH value of the sludge sample is 6.5-7.5, preferably 6.8-7.2, and more preferably 7; the concentration of TSS is 10-20 g / L, preferably 12-18 g / L, and more preferably 14-16 g / L; the concentration of VSS is 8-10 g / L, and preferably 9 g / L.

[0026] In the present invention, in step (2), the amount of iron sulfide added is 0.1-0.6 mmol / g VSS, preferably 0.2-0.5 mmol / g VSS, and more preferably 0.3-0.4 mmol / g VSS; SO3 2- The molar ratio of the iron sulfide to the iron element is 1:1 to 3, preferably 1:1 to 2, and more preferably 1:1.

[0027] In the present invention, in the step (2), after iron sulfide and sulfite are added to the sludge sample, the pH value is adjusted to 5 to 7, preferably 5.5 to 6.5, and more preferably 6.

[0028] In the present invention, the iron sulfide is Fe3S4, Fe7S8 or FeS2, preferably Fe3S4 or Fe7S8, and more preferably Fe3S4; the sulfite comprises calcium sulfite or sodium sulfite, preferably calcium sulfite.

[0029] In the present invention, in the step (2), nitrogen filling is not required before pretreatment.

[0030] In the present invention, in step (2), the pretreatment rotation speed is 120-150 rpm, preferably 130-140 rpm, and more preferably 135 rpm; the pretreatment temperature is 30-35°C, preferably 31-34°C, and more preferably 32-33°C; the pretreatment time is 20-28h, preferably 22-26h, and more preferably 24h.

[0031] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0032] The sludge used in the examples and comparative examples of the present invention was taken from the secondary sedimentation tank of Yangjiabao Sewage Treatment Plant in Taiyuan City, Shanxi Province.

[0033] Example 1

[0034] The sludge was naturally settled at 4°C for 24 hours, the supernatant was discharged and concentrated, and after concentration, impurities were removed through a 40-mesh sieve to obtain a sludge sample with a pH value of 6.85, a TSS concentration of 15.6 g / L, and a VSS concentration of 8.0 g / L.

[0035] 100 mL of the sludge sample was transferred to a conical flask, and Fe3S4 and CaSO3 were added according to VSS, where the dosage of Fe3S4 was 0.4 mmol / g VSS and the dosage of CaSO3 was 1.2 mmol / g VSS. The pH value was then adjusted to 6, and then placed in a constant temperature incubator for pretreatment. The rotation speed was 135 rpm, the temperature was 32°C, and the pretreatment time was 24 h. During the pretreatment, samples were taken to detect the concentration of dissolved organic matter in the sludge.

[0036] Example 2

[0037] The sludge was naturally settled at 4°C for 24 hours, the supernatant was discharged and concentrated, and after concentration, impurities were removed through a 40-mesh sieve to obtain a sludge sample with a pH value of 6.85, a TSS concentration of 15.6 g / L, and a VSS concentration of 8.0 g / L.

[0038] 100 mL of the sludge sample was transferred to a conical flask, and Fe3S4 and CaSO3 were added according to VSS, where the dosage of Fe3S4 was 0.6 mmol / g VSS and the dosage of CaSO3 was 1.8 mmol / g VSS. The pH value was then adjusted to 6, and then placed in a constant temperature incubator for pretreatment. The rotation speed was 150 rpm, the temperature was 35°C, and the pretreatment time was 20 h. During the pretreatment, samples were taken to detect the concentration of dissolved organic matter in the sludge.

[0039] Example 3

[0040] The sludge was naturally settled at 4°C for 24 hours, the supernatant was discharged and concentrated, and after concentration, impurities were removed through a 40-mesh sieve to obtain a sludge sample with a pH value of 6.85, a TSS concentration of 15.6 g / L, and a VSS concentration of 8.0 g / L.

[0041] 100 mL of the sludge sample was transferred to a conical flask, and Fe3S4 and CaSO3 were added according to VSS, where the dosage of Fe3S4 was 0.1 mmol / gVSS and the dosage of CaSO3 was 0.3 mmol / gVSS. The pH value was then adjusted to 6, and then placed in a constant temperature incubator for pretreatment. The rotation speed was 120 rpm, the temperature was 30°C, and the pretreatment time was 28 h. During the pretreatment, samples were taken to detect the concentration of dissolved organic matter in the sludge.

[0042] Example 4

[0043] The difference from Example 1 is that Fe3S4 in Example 1 is replaced by FeS2, the dosage of FeS2 is 1.2 mmol / gVSS, and other conditions are the same.

[0044] Example 5

[0045] The difference from Example 1 is that Fe3S4 in Example 1 is replaced by Fe7S8, the dosage of Fe7S8 is 1.2 / 7 mmol / gVSS, and other conditions are the same.

[0046] Comparative Example 1

[0047] The difference from Example 1 is that only CaSO3 is added to the sludge sample in an amount of 1.2 mmol / g VSS, and Fe3S4 is not added. Other conditions are the same.

[0048] Comparative Example 2

[0049] The sludge was naturally settled at 4°C for 24 hours, the supernatant was discharged and concentrated, and after concentration, impurities were removed through a 40-mesh sieve to obtain a sludge sample with a pH value of 6.85, a TSS concentration of 15.6 g / L, and a VSS concentration of 8.0 g / L.

[0050] 100 mL of the sludge sample was transferred to a conical flask, and then the pH value was adjusted to 6. It was then placed in a constant temperature incubator for pretreatment. The rotation speed was 135 rpm, the temperature was 32°C, and the pretreatment time was 24 h. During the pretreatment, samples were taken to detect the concentration of dissolved organic matter in the sludge.

[0051] Figure 1 The comparison chart of the concentration of soluble protein and soluble carbohydrate in the sludge samples pretreated in Example 1 and Comparative Examples 1-2 as the pretreatment time changes, from Figure 1 It can be seen that under different pretreatment conditions, the variation trend of soluble protein is to increase first and then decrease, and soluble carbohydrates are continuously increasing. In Comparative Example 2, soluble protein and carbohydrates reach the highest at 12h, which are 6.8±0.2 and 8.9±0.3mg COD / gVSS respectively. In Comparative Example 1, adding CaSO3 alone for pretreatment increases the release of soluble carbohydrates and protein, but not significantly. In Example 1, pretreatment with CaSO3 / Fe3S4 significantly improves the release of soluble organic matter compared with Comparative Example 2 and Comparative Example 1, and the content of soluble protein and soluble carbohydrates reaches the highest value at the 12h and 24h respectively, which is 102.2±5.2mg COD / g VSS and 28.1±3.1mg COD / g VSS, which is 14.9 times and 4.3 times that of Comparative Example 1 respectively.

[0052] Figure 2The following is a comparison chart of the yield of soluble protein and soluble carbohydrate after the sludge pretreatment in Example 1, Examples 4-5, and Comparative Example 2. As can be seen from Figure 2, compared with Comparative Example 2, the pretreatment significantly promoted the dissolution of the sludge. In Example 1, the CaSO3 / Fe3S4 pretreatment significantly promoted the release of soluble protein in the sludge, which was 200.7±12.0 mg COD / g VSS, which was 1.8 to 10.7 times higher than Comparative Example 2 (18.8±0.5 mg COD / g VSS), Example 4 (34.4±1.6 mg COD / g VSS) and Example 5 (113.6±2.4 mg COD / g VSS). In Example 5, the CaSO3 / Fe7S8 pretreatment had a significant effect on the release of soluble carbohydrates, which was 23.9±4.6 mg COD / g VSS, which was 5.3 times and 1.3 times higher than that of Comparative Example 2 and Example 4, respectively, and only slightly higher than that of Example 1 (23.5±2.0 mg COD / g VSS).

[0053] Through the above analysis, it can be seen that in Example 1, the CaSO3 / Fe3S4 pretreatment has the best effect on the release of soluble organic matter. Pretreatment in the early stage of fermentation promotes the decomposition of sludge, stimulates the conversion of granular organic compounds in the sludge into soluble organic matter, and leads to a surge in soluble organic matter. This shows that the method provided by the present invention for pretreating sludge by activating sulfite with iron sulfide is feasible and solves the problems of poor biodegradability and low hydrolysis rate of substrates in anaerobic fermentation of sludge.

[0054] The acid production of residual sludge by anaerobic fermentation is limited to the release and hydrolysis stage of macromolecular organic matter wrapped in cell walls and extracellular polymers. Therefore, iron sulfide is used to activate calcium sulfite pretreatment sludge to improve the hydrolysis efficiency of anaerobic fermentation, relieve hydrolysis restrictions and promote the generation of short-chain fatty acids. The CaSO3 / Fe3S4 pre-oxidation sludge pretreatment system constructed by the present invention proves the feasibility of the system to break the sludge floc structure and lyse cells, and clarifies the influence of the iron sulfide morphology on the sludge fermentation efficiency of the pretreatment system. While the CaSO3 / Fe3S4 pretreatment promotes the disintegration of sludge flocs, the system's induction of iron reduction will further increase the conversion rate of organic matter to directional acetic acid, thereby promoting the conversion of energy in sludge to high value-added organic matter such as acetic acid.

[0055] As can be seen from the above embodiments, the present invention provides a method for pretreating sludge by activating sulfite with iron sulfide. The present invention first allows the sludge to settle naturally to obtain a sludge sample, and then adds iron sulfide and sulfite to the sludge sample for pretreatment. The method for pretreating sludge by activating sulfite with iron sulfide provided by the present invention has the advantages of easy availability of raw materials and no secondary pollution, and can achieve an ideal sludge wall breaking effect. More organic substances in intracellular and extracellular polymers in the sludge pretreated with Fe3S4 activated sulfite are released into the liquid phase, so that the overall hydrolysis and acidification rate of the sludge is improved, and the purpose of maximizing resource and energy recovery is achieved.

[0056] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for pre-treating sludge by activating sulfite with iron sulfide, characterized in that: The steps include: (1) allowing the sludge to settle naturally to obtain a sludge sample; (2) Add iron sulfide and sulfite to the sludge sample for pretreatment.

2. The method for pretreating sludge by activating sulfite with iron sulfide according to claim 1, characterized in that: In the step (1), the temperature of natural sedimentation is 1 to 6° C., and the time of natural sedimentation is 20 to 28 hours.

3. The method for pretreating sludge by activating sulfite with iron sulfide according to claim 1 or 2, characterized in that: In the step (1), the pH value of the sludge sample is 6.5-7.5, the concentration of TSS is 10-20 g / L, and the concentration of VSS is 8-10 g / L.

4. The method for pretreating sludge by activating sulfite with iron sulfide according to claim 3, characterized in that: In the step (2), the dosage of iron sulfide is 0.1-0.6 mmol / g VSS; SO3 2- The molar ratio of iron to iron sulfide is 1:1 to 3.

5. The method for pretreating sludge by activating sulfite with iron sulfide according to claim 2 or 4, characterized in that: In the step (2), iron sulfide and sulfite are added to the sludge sample and the pH value is adjusted to 5-7.

6. The method for pretreating sludge by activating sulfite with iron sulfide according to claim 5, characterized in that: The iron sulfide is Fe3S4, Fe7S8 or FeS2; the sulfite includes calcium sulfite or sodium sulfite.

7. The method for pretreating sludge by activating sulfite with iron sulfide according to claim 4 or 6, characterized in that: In the step (2), the pretreatment rotation speed is 120-150 rpm, the pretreatment temperature is 30-35° C., and the pretreatment time is 20-28 h.

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