A method for the pretreatment of sludge with ferrous sulphide activated sulphite

Abstract

The application provides a method for pretreating sludge by using iron sulfide to activate sulfite, and belongs to the technical field of sludge treatment. First, sludge is naturally settled to obtain a sludge sample, then iron sulfide and sulfite are added to the sludge sample for pretreatment. The method for pretreating sludge by using iron sulfide to activate sulfite has the advantages of easy availability of raw materials, no secondary pollution, and the like, and can achieve an ideal sludge wall breaking effect. After the sludge is pretreated by using iron sulfide to activate sulfite, more intracellular and extracellular polymeric substance organic matters in the sludge are released into a liquid phase, so that the overall hydrolysis acidification rate of the sludge is improved, and the purpose of maximizing resource and energy recovery is achieved.

Description

Technical Field

[0001] This invention relates to the field of sludge treatment technology, and in particular to a method for pretreating sludge using ferric sulfide to activate sulfite. Background Technology

[0002] Currently, the demand for wastewater treatment is increasing year by year with population growth and industrial development. By the end of 2022, the daily treatment capacity of urban wastewater treatment plants reached 220 million tons. The main biological treatment process in wastewater treatment plants is the activated sludge process. However, the biosynthesis and metabolism of functional microorganisms in this process produce a large amount of sludge. Considering that sludge contains a large amount of renewable organic matter, it is considered a sustainable resource with economic potential. However, it also contains toxic substances such as pathogens and persistent organic pollutants. This characteristic makes the treatment and disposal of sludge extremely important. Improper treatment may cause secondary pollution to the environment and seriously threaten the ecosystem. Anaerobic fermentation of sludge can produce widely applicable volatile organic acids. These volatile acids can be used as a supplementary carbon source or for biological nitrogen and phosphorus removal, and can also be applied in industries such as food, pharmaceuticals, and cosmetics. Furthermore, hydrolytic acidifying microorganisms have a shorter generation cycle than methanogens and are more adaptable to the environment. They can degrade large organic molecules into short-chain fatty acids. Therefore, anaerobic fermentation is an efficient and applicable method for treating sludge with complex compositions.

[0003] However, the complex flocculent structure of sludge, composed of microbial cell walls, restricts sludge dissolution, resulting in a low hydrolysis rate and limiting sludge fermentation. Therefore, it is of great significance to study a method for pretreating sludge with ferric sulfide-activated sulfite, which can disrupt the flocculent structure, enhance the hydrolysis process, and thus improve the biodegradability of the substrate. Summary of the Invention

[0004] The purpose of this invention is to provide a method for pretreating sludge using ferric sulfide-activated sulfite, in order to solve the problems of long anaerobic fermentation cycle, difficulty in breaking down sludge microorganisms, and low organic matter release rate in the prior art.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for pretreating sludge using ferric sulfide to activate sulfite, comprising the following steps:

[0007] (1) Allow 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 settling is 1 to 6°C and the time of natural settling is 20 to 28 hours.

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

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

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

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

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

[0015] The beneficial effects of this invention are:

[0016] (1) This invention uses iron sulfide to activate sulfite for pretreatment of sludge. It contains transition metal active sites and is easy to obtain. The residual sulfite is easily oxidized by oxygen to non-toxic SO4. 2- It also produces persulfate free radicals (SO5). - ·) and sulfite radicals (SO3) - Active substances such as · can not only effectively destroy the semi-rigid cell wall structure, but also destroy specific functional groups and polymer backbone bonds in sludge flocs.

[0017] (2) This invention verifies that, with the extension of the sludge pretreatment time using iron sulfide-activated sulfite, the trend of soluble protein changes is first an increase followed by a decrease, while soluble carbohydrates continuously increase. This indicates that ferric sulfide-activated sulfite pretreatment of sludge can disrupt the cell structure of sludge microorganisms, which is beneficial for the dissolution of intracellular organic matter. Compared with other forms of ferric sulfide-activated sulfite pretreatment for sludge, Fe3S4-activated sulfite pretreatment has a significant effect on the release of soluble proteins, while the release of soluble carbohydrates is basically the same as that of Fe7S8, but higher than that of FeS2. This shows that the Fe3S4-activated sulfite pretreatment method for sludge has significant advantages.

[0018] (3) The method of activating sulfite with iron sulfide to pretreat sludge provided by the present invention has the advantages of readily available raw materials and no secondary pollution, and can achieve the ideal sludge cell breaking effect. After the sludge is pretreated with Fe3S4 activated sulfite, more organic matter in the intracellular and extracellular polymers is released into the liquid phase, which increases the overall hydrolysis and acidification rate of the sludge, promotes the generation of short-chain fatty acids, and achieves the goal of maximizing resource and energy recovery. Attached Figure Description

[0019] Figure 1 This is a comparison chart showing the changes in the concentrations of soluble protein and soluble carbohydrate in the pretreated sludge samples of Example 1 and Comparative Examples 1-2 over the pretreatment time.

[0020] Figure 2 This is a comparison chart showing the yield of soluble protein and soluble carbohydrates after sludge pretreatment in Examples 1, 4-5, and Comparative Example 2. Detailed Implementation

[0021] This invention provides a method for pretreating sludge using ferric sulfide to activate sulfite, comprising the following steps:

[0022] (1) Allow 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 this invention, in step (1), the temperature of natural settling is 1-6°C, preferably 2-5°C, more preferably 3-4°C, and the time of natural settling is 20-28h, preferably 22-26h, more preferably 24h.

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

[0026] In this invention, in step (2), the dosage of iron sulfide 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; the SO3 in the sulfite 2- The molar ratio of iron to iron in iron sulfide is 1:1 to 3, preferably 1:1 to 2, and more preferably 1:1.

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

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

[0029] In this invention, nitrogen purging is not required before pretreatment in step (2).

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

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

[0032] The sludge used in the embodiments and comparative examples of this 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 allowed to settle naturally at 4°C for 24 hours. The supernatant was then drained and concentrated. After concentration, the sludge was passed through a 40-mesh sieve to remove impurities, resulting in a sludge sample with a pH of 6.85, a TSS concentration of 15.6 g / L, and a VSS concentration of 8.0 g / L.

[0035] 100 mL of sludge sample was transferred to an Erlenmeyer flask, and Fe3S4 and CaSO3 were added according to VSS, with Fe3S4 added at 0.4 mmol / g VSS and CaSO3 added at 1.2 mmol / g VSS. The pH was then adjusted to 6, and the flask was placed in a constant temperature incubator for pretreatment at 135 rpm and 32°C for 24 h. During the pretreatment, the concentration of dissolved organic matter in the sludge was measured.

[0036] Example 2

[0037] The sludge was allowed to settle naturally at 4°C for 24 hours. The supernatant was then drained and concentrated. After concentration, the sludge was passed through a 40-mesh sieve to remove impurities, resulting in a sludge sample with a pH of 6.85, a TSS concentration of 15.6 g / L, and a VSS concentration of 8.0 g / L.

[0038] 100 mL of sludge sample was transferred to an Erlenmeyer flask, and Fe3S4 and CaSO3 were added according to VSS, with Fe3S4 added at 0.6 mmol / g VSS and CaSO3 added at 1.8 mmol / g VSS. The pH was then adjusted to 6, and the flask was placed in a constant temperature incubator for pretreatment at 150 rpm and 35°C for 20 h. During the pretreatment, the concentration of dissolved organic matter in the sludge was measured.

[0039] Example 3

[0040] The sludge was allowed to settle naturally at 4°C for 24 hours. The supernatant was then drained and concentrated. After concentration, the sludge was passed through a 40-mesh sieve to remove impurities, resulting in a sludge sample with a pH of 6.85, a TSS concentration of 15.6 g / L, and a VSS concentration of 8.0 g / L.

[0041] 100 mL of sludge sample was transferred to an Erlenmeyer flask, and Fe3S4 and CaSO3 were added according to VSS, with Fe3S4 added at 0.1 mmol / g VSS and CaSO3 added at 0.3 mmol / g VSS. The pH was then adjusted to 6, and the flask was placed in a constant temperature incubator for pretreatment at 120 rpm and 30°C for 28 h. During the pretreatment, the concentration of dissolved organic matter in the sludge was measured.

[0042] Example 4

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

[0044] Example 5

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

[0046] Comparative Example 1

[0047] The difference from Example 1 is that only CaSO3 was added to the sludge sample at a dosage of 1.2 mmol / g VSS, and Fe3S4 was not added, while all other conditions were the same.

[0048] Comparative Example 2

[0049] The sludge was allowed to settle naturally at 4°C for 24 hours. The supernatant was then drained and concentrated. After concentration, the sludge was passed through a 40-mesh sieve to remove impurities, resulting in a sludge sample with a pH of 6.85, a TSS concentration of 15.6 g / L, and a VSS concentration of 8.0 g / L.

[0050] 100 mL of sludge sample was transferred to an Erlenmeyer flask, and the pH was adjusted to 6. The flask was then placed in a constant temperature incubator for pretreatment at a speed of 135 rpm and a temperature of 32°C for 24 hours. During the pretreatment, the concentration of dissolved organic matter in the sludge was measured.

[0051] Figure 1 This is a comparison graph showing the changes in the concentrations of soluble protein and soluble carbohydrates in the pretreated sludge samples of Examples 1 and Comparative Examples 1-2 over the pretreatment time. Figure 1 It can be seen that under different pretreatment conditions, the trend of soluble protein is first an increase followed by a decrease, while soluble carbohydrates continuously increase. In Comparative Example 2, soluble protein and carbohydrates reached their highest values ​​at 12 h, at 6.8 ± 0.2 and 8.9 ± 0.3 mg COD / g VSS, respectively. In Comparative Example 1, pretreatment with CaSO3 alone increased the release of soluble carbohydrates and proteins, but not significantly. In Example 1, pretreatment with CaSO3 / Fe3S4 significantly increased the release of soluble organic matter compared to Comparative Example 2 and Comparative Example 1. The contents of soluble protein and soluble carbohydrates reached their highest values ​​at 12 h and 24 h, respectively, at 102.2 ± 5.2 mg COD / g VSS and 28.1 ± 3.1 mg COD / g VSS, which were 14.9 times and 4.3 times that of Comparative Example 1, respectively.

[0052] Figure 2Figure 2 shows a comparison of the yields of soluble proteins and soluble carbohydrates after sludge pretreatment in Examples 1, 4-5, and Comparative Example 2. As can be seen from Figure 2, pretreatment significantly promoted sludge dissolution compared to Comparative Example 2. In Example 1, CaSO3 / Fe3S4 pretreatment significantly promoted the release of soluble proteins from the sludge, reaching 200.7 ± 12.0 mg COD / g VSS, which was 1.8 to 10.7 times higher than that in 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), respectively. In Example 5, the CaSO3 / Fe7S8 pretreatment significantly improved the release of soluble carbohydrates, reaching 23.9 ± 4.6 mg COD / g VSS, which was 5.3 times and 1.3 times higher than Comparative Example 2 and Example 4, respectively, and only slightly higher than Example 1 (23.5 ± 2.0 mg COD / g VSS).

[0053] The above analysis shows that, in Example 1, the CaSO3 / Fe3S4 pretreatment had the best effect on the release of dissolved organic matter. Pretreatment in the early stages of fermentation promoted sludge decomposition, stimulated the conversion of particulate organic compounds in the sludge into soluble organic matter, leading to a surge in dissolved organic matter. This indicates that the method for pretreating sludge using ferric sulfide-activated sulfite provided by this invention is feasible and solves the problems of poor substrate biodegradability and low hydrolysis rate in current anaerobic fermentation of sludge.

[0054] The acid production from the anaerobic fermentation of excess sludge is limited by the hydrolysis stage of large organic molecules encapsulated in cell walls and extracellular polymers. Therefore, pretreatment of sludge with ferric sulfide-activated calcium sulfite improves the efficiency of anaerobic fermentation hydrolysis, relieves hydrolysis limitations, and promotes the formation of short-chain fatty acids. The CaSO3 / Fe3S4 pre-oxidation sludge pretreatment system constructed in this invention demonstrates the feasibility of breaking down sludge floc structure and lysing cells, and clarifies the influence of ferric sulfide morphology on the sludge fermentation efficiency of this pretreatment system. While promoting the disintegration of sludge flocs using CaSO3 / Fe3S4 pretreatment, the system's induction of iron reduction further increases the conversion rate of organic matter to acetic acid, thereby promoting the conversion of energy in the sludge into 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 using ferric sulfide-activated sulfite. The method first involves allowing the sludge to settle naturally to obtain a sludge sample, then adding ferric sulfide and sulfite to the sludge sample for pretreatment. The method for pretreating sludge using ferric sulfide-activated sulfite provided by the present invention has advantages such as readily available raw materials and no secondary pollution, and can achieve ideal sludge cell disruption. After Fe3S4-activated sulfite pretreatment, more organic matter from intracellular and extracellular polymers in the sludge is released into the liquid phase, thereby increasing the overall hydrolysis and acidification rate of the sludge and maximizing resource and energy recovery.

[0056] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for pretreating sludge using ferric sulfide activation of sulfite, characterized in that, Includes the following steps: (1) Allow the sludge to settle naturally to obtain a sludge sample; (2) Add iron sulfide and sulfite to the sludge sample for pretreatment; The iron sulfide is Fe3S4 or Fe7S8; the sulfite contains calcium sulfite or sodium sulfite. In step (2), the pretreatment speed is 120-150 rpm, the pretreatment temperature is 30-35℃, and the pretreatment time is 20-28h. In step (2), the dosage of iron sulfide is 0.1–0.6 mmol / g VSS; the SO3 in the sulfite 2- The molar ratio of iron in ferric sulfide to iron is 1:1 to 3.

2. The method for pretreating sludge using ferric sulfide activation according to claim 1, characterized in that, In step (1), the temperature of natural settling is 1-6℃ and the time of natural settling is 20-28h.

3. The method for pretreating sludge using ferric sulfide activation according to claim 1 or 2, characterized in that, 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.

4. The method for pretreating sludge using ferric sulfide activation according to claim 2, characterized in that, In step (2), after adding iron sulfide and sulfite to the sludge sample, the pH value is adjusted to 5-7.

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