Method for enhancing release-conversion of phosphorus in anaerobic fermentation of excess sludge by humus

Abstract

The invention discloses a method for enhancing release-conversion of phosphorus in anaerobic fermentation of excess sludge by humus. In order to relieve the current situation of phosphorus resource shortage and depletion at present, the invention aims to improve the residual sludge fermentation phosphorus release performance by adding humus exogenous to the anaerobic fermentation process. The method comprises the following steps: 1, pretreating the excess sludge with low-temperature heat and acid to strengthen the disintegration and lysing efficiency of extracellular polymeric substances of the excess sludge, so as to provide sufficient substrates for subsequent anaerobic fermentation acid production and improve the release efficiency of phosphorus; 2, the pretreated sludge is subjected to anaerobic fermentation, humus is added to improve the solubility of Fe-P (Fe < 3 + > is reduced into Fe < 2 + >), and the humus and metal ions are competitively complexed to improve the release efficiency of soluble phosphorus. Compared with the method for reinforcing the release-conversion of the phosphorus in the excess sludge by the humus, the method has the advantages of low cost, no secondary pollution risk and the like, can achieve an ideal phosphorus release-conversion effect, and has important significance for realizing the recovery and recycling of phosphorus resources in the sludge.

Description

Technical Field

[0001] The invention relates to a method for releasing and transforming phosphorus by anaerobic fermentation of excess sludge using humus, and belongs to the field of waste treatment and resource recycling. Background Art

[0002] In recent years, the production of excess activated sludge, as the main by-product of the sewage treatment process, has gradually increased and is expected to reach more than 9,000 tons by 2025. It contains high-rich organic matter and nutrients and has the potential for energy and resource utilization. During the sewage treatment process, about 90% of the phosphorus is enriched in the sludge, making the sludge an important secondary phosphorus resource. After recycling, it can meet 12-15% of the total phosphorus demand. Although traditional anaerobic fermentation technology can partially release phosphorus resources in sludge, it is limited by the low efficiency of organic phosphorus hydrolysis and the re-fixation of metal ions (such as Fe 3+ With PO4 3+ Phosphorus release rates are generally less than 30% due to the semi-rigid structure of sludge cells. To release the large amounts of organic matter and phosphorus within the cells and improve anaerobic fermentation efficiency, efficient pretreatment methods are crucial. Currently, technologies for enhancing phosphorus release through anaerobic digestion primarily focus on anaerobic co-fermentation and the addition of chemical agents. Co-fermentation with organic waste suffers from drawbacks such as over-acidification, which can lead to system breakdown and odor generation, while chelating agents such as EDTA are environmentally toxic. Humic substances (HS), as natural organic macromolecules that can also be produced endogenously, are rich in reactive groups such as carboxyl and phenolic hydroxyl groups. They can disrupt phosphorus binding sites by complexing metal ions (such as Fe⁺ and Al⁺), promoting phosphorus release. They also act as electron shuttles, accelerating the activity of extracellular hydrolases and enhancing organophosphate mineralization. However, existing research has primarily focused on the effects of humic substances on organic matter transformation, and their mechanisms of action in regulating phosphorus release and transformation and inhibiting refixation remain unclear. Summary of the Invention

[0003] The present invention aims to solve the current problems of low phosphorus release efficiency and unclear phosphorus form transformation in sludge, and provides a method for humus-enhanced phosphorus release-transformation in anaerobic fermentation of excess sludge.

[0004] The method for releasing and converting phosphorus by anaerobic fermentation of excess sludge using humus-enhanced methods of the present invention is specifically carried out in the following steps: 1. The residual sludge was taken from the secondary sedimentation tank of the sewage treatment plant, filtered through a 40-mesh filter and allowed to settle naturally at 4°C. After settling for 20-28 hours, the supernatant was discarded to obtain the sludge sample, which was then placed in an anaerobic reactor. 2. Adjust the pH in the anaerobic reactor to 2-5, and place the mixture in the anaerobic reactor in a water bath heating pot for pretreatment; 3. The pretreated sludge in step 2 and the fresh residual sludge are inoculated according to the volume ratio, and humic acid or fulvic acid is added respectively. Then the anaerobic reactor is placed in a constant temperature oscillator, the speed of the constant temperature oscillator is controlled to be 100~120rpm, the fermentation temperature is 30~35℃, and the fermentation time is 4~10 days to carry out anaerobic fermentation of the sludge.

[0005] The present invention optimizes the humus addition strategy and explores its phosphorus release-conversion performance during anaerobic fermentation, providing a new method for the efficient release-conversion of sludge phosphorus resources. In step 2, the pretreatment temperature and heating time are controlled to perform pretreatment, enhance the efficiency of extracellular polymer decomposition and lysis of residual sludge, improve the release of organic matter and phosphorus in the cell content, and provide sufficient substrate for subsequent anaerobic fermentation. In step 3, the mixture is placed in a constant temperature oscillator, and the rotation speed, temperature and time are controlled to perform anaerobic fermentation of sludge. Under the action of hydrolytic bacteria and acid-producing bacteria, large molecular organic matter is converted into small molecular volatile acids, and under the competitive complexation, adsorption and electron shuttle of polyphosphate bacteria and humus, orthophosphate is released from the solid phase to the liquid phase.

[0006] The technical solution further defined in the present invention is: In the aforementioned method for humus-enhanced anaerobic fermentation of excess sludge for phosphorus release and conversion, in step 1, the pH of the sludge sample is 6.6-7.5, the TSS concentration is 15-30 g / L, and the VSS concentration is 10-15 g / L.

[0007] In the aforementioned method for humus-enhanced anaerobic fermentation of excess sludge for phosphorus release and conversion, in step 2, HCl and / or NaOH are used to adjust the pH inside the anaerobic reactor to 3.0±0.1, and the temperature of the water bath heating pot is controlled at 80~100°C for 0.5~1.5 hours.

[0008] In the aforementioned method for humus-enhanced anaerobic fermentation of excess sludge for phosphorus release and conversion, the inoculum volume ratio of the pretreated sludge to the fresh sludge in step three is 9:1.

[0009] In the aforementioned method for humus-enhanced anaerobic fermentation of excess sludge for phosphorus release and conversion, the amounts of humic acid and fulvic acid in step three are 0.8-1.2 g / L and 1.3-1.8 g / L, respectively, based on the volume of sludge in the anaerobic reactor.

[0010] The above parameters effectively ensure the technical effects of pretreatment and anaerobic fermentation.

[0011] Principle of the present invention: The present invention proposes a method for enhancing phosphorus release and conversion in anaerobic fermentation of excess sludge by using humus, with the aim of maximizing the release of phosphorus in excess sludge. The low temperature heat and pH 3 conditions in step 2 can effectively break the cell wall of microorganisms, allowing the organic matter and phosphorus in the cell contents to be released into the liquid phase, providing favorable conditions for subsequent anaerobic fermentation acid production and further release of phosphorus. Humus is added during the anaerobic fermentation process, and humus can enhance the release of Fe as an electron shuttle. 3+ Reduction to Fe 2+ , increasing the solubility of Fe-P. At the same time, it provides more binding sites for metal ions, avoids the re-combination of metal ions and phosphates, and improves the release efficiency of phosphorus.

[0012] Beneficial effects of the present invention: After 60 minutes of low-temperature heat plus pH 3 pretreatment, the concentrations of dissolved total phosphorus and orthophosphate in the liquid phase reached peaks of 342.02 mg COD / L and 299.14 mg / L, respectively, 9.0 and 9.6 times those of the untreated group. This indicates that low-temperature heat plus pH 3 pretreatment disrupts the cellular structure of sludge microorganisms, facilitating the dissolution of intracellular organic matter and phosphate. During the subsequent anaerobic fermentation process, the maximum dissolved orthophosphate contents in the pH 3 + HA (humic acid) and pH 3 + FA (fulvic acid) groups reached 562.38 and 542.31 mg / L, respectively, significantly exceeding those in the anaerobic fermentation group without humic substances. This demonstrates the superiority of humic substances in enhancing phosphorus release and conversion in excess sludge. This demonstrates the simplicity and feasibility of this method, the readily available raw materials, and its potential for maximizing resource and energy recovery from excess sludge. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Changes in total dissolved phosphorus content in the liquid phase during anaerobic fermentation; Figure 2 Changes in the content of soluble orthophosphate in the liquid phase during anaerobic fermentation; Figure 3 Changes in various phosphorus contents in the solid phase during anaerobic fermentation (from left to right: 0th, 2nd, 4th, and 10th day); Figure 4 Analysis of solid-liquid phosphorus balance on the 4th day of anaerobic fermentation. DETAILED DESCRIPTION

[0014] The technical solution of the present invention is not limited to the specific implementation methods listed below, but also includes any combination of the specific implementation methods.

[0015] Specific embodiment 1: This embodiment is a method for releasing and converting phosphorus by anaerobic fermentation of excess sludge using humus, which is specifically carried out in accordance with the following steps: 1. The residual sludge was taken from the secondary sedimentation tank of the sewage treatment plant, filtered through a 40-mesh filter and allowed to settle naturally at 4°C. After settling for 24 hours, the supernatant was discarded to obtain a sludge sample, which was then placed in an anaerobic reactor. 2. Use 1.0 M HCl to adjust the pH value inside the anaerobic reactor to 3.0±0.1, place the anaerobic reactor in a water bath heating reaction device, control the pretreatment temperature to 80~100℃, and operate for 30~90 min; 3. After mixing the sludge in step 2 with fresh sludge, add humic acid and fulvic acid at levels of 0.8-1.2 g / L and 1.2-1.8 g / L, respectively, adjust the pH to 6.6-7.5, and then place it in a constant temperature oscillator with a stirring speed of 100-120 rpm, a fermentation temperature of 32-35 °C, and a fermentation time of 5-10 days for anaerobic fermentation of the sludge.

[0016] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the temperature in step 2 is 85° C. and the time is 60 min. Other aspects are the same as specific embodiment 1.

[0017] Specific embodiment three: This embodiment differs from specific embodiments one to two in that in step three, the pretreated sludge and fresh sludge inoculation volume ratio is 9:1, and the rest is the same as specific embodiment one.

[0018] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 2 in that the amounts of humic acid and fulvic acid added in step 3 are 1.0 g / L and 1.5 g / L, respectively. Other aspects are the same as those of specific embodiment 1.

[0019] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 2 in that: in step 3, the stirring speed is 120 rpm, the fermentation temperature is 33-35° C., and the fermentation time is 10 days. Other aspects are the same as specific embodiment 1.

[0020] The following examples and comparative experiments are used to verify the beneficial effects of the present invention:

[0021] Example 1 The method for releasing and converting phosphorus by anaerobic fermentation of excess sludge using humus-enhanced methods is specifically carried out in the following steps: 1. The excess sludge used in this example was collected from the secondary sedimentation tank of the Yangjiabao Wastewater Treatment Plant in Taiyuan City. After filtering through a 40-mesh filter and allowing natural sedimentation at 4°C for 24 hours, the supernatant was discarded to obtain a sludge sample. The TSS concentration of this sludge sample was 18.45 ± 1.21 g / L, and the VSS concentration was 12.76 ± 0.41 g / L. 2. Take three 500 mL anaerobic bottles as reactors and add 360 mL of sludge from step 1 to each. Add 1.0 M HCl and NaOH to adjust the sludge pH to 3.0 ± 0.1. Control the water bath temperature to 85 ± 1°C and treat for 60 minutes. 3. Add 40 mL of sludge from Step 1 to each anaerobic flask in Step 2. Add 1.0 g / L of humic acid and adjust the pH to 7.0 ± 0.1. Then, aerate the anaerobic flask with nitrogen for 10–15 minutes to maintain an anaerobic environment. Ferment at 120 rpm and 35 ± 1°C for 10 days.

[0022] Example 2 The method for phosphorus release and conversion by anaerobic fermentation of excess sludge using humus-enhanced methods is specifically carried out in the following steps: 1. The excess sludge used in this example was collected from the secondary sedimentation tank of the Yangjiabao Wastewater Treatment Plant in Taiyuan City. After filtering through a 40-mesh filter and allowing natural sedimentation at 4°C for 24 hours, the supernatant was discarded to obtain a sludge sample. The TSS concentration of this sludge sample was 18.45 ± 1.21 g / L, and the VSS concentration was 12.76 ± 0.41 g / L. 2. Take three 500 mL anaerobic bottles as reactors and add 360 mL of sludge from step 1 to each. Add 1.0 M HCl and NaOH to adjust the sludge pH to 3.0 ± 0.1. Control the water bath temperature to 85 ± 1°C and treat for 60 minutes. 3. Add 40 mL of sludge from Step 1 to each anaerobic flask in Step 2. Add 1.5 g / L of fulvic acid (FA) and adjust the pH to 7.0 ± 0.1. Then, aerate the anaerobic flask with nitrogen for 10–15 minutes to maintain an anaerobic environment. Ferment at 120 rpm and 35 ± 1°C for 10 days.

[0023] Comparative experiment 1: The method for releasing and converting phosphorus by anaerobic fermentation of sludge without pretreatment and without adding humus is specifically completed in the following steps: 1. The excess sludge used in this example was collected from the secondary sedimentation tank of the Yangjiabao Wastewater Treatment Plant in Taiyuan City. After filtering through a 40-mesh filter and allowing natural sedimentation at 4°C for 24 hours, the supernatant was discarded to obtain a sludge sample. The TSS concentration of this sludge sample was 18.45 ± 1.21 g / L, and the VSS concentration was 12.76 ± 0.41 g / L. 2. Add 400 mL of the sludge from step 1 to each of three 500 mL anaerobic bottles. Adjust the pH to 7.0 ± 0.1. Then, aerate the anaerobic bottle with nitrogen for 10–15 minutes to maintain an anaerobic environment. Ferment at 120 rpm and 35 ± 1°C for 10 days.

[0024] Comparative test 2: The method for releasing and converting phosphorus by anaerobic fermentation of sludge without adding humus in this embodiment is specifically completed by the following steps: 1. The excess sludge used in this example was collected from the secondary sedimentation tank of the Yangjiabao Wastewater Treatment Plant in Taiyuan City. After filtering through a 40-mesh filter and allowing natural sedimentation at 4°C for 24 hours, the supernatant was discarded to obtain a sludge sample. The TSS concentration of this sludge sample was 18.45 ± 1.21 g / L, and the VSS concentration was 12.76 ± 0.41 g / L. 2. Take three 500 mL anaerobic bottles and add 360 mL of the sludge from step 1 to each. Add 1.0 M HCl and NaOH to adjust the sludge pH to 3.0 ± 0.1. Control the water bath temperature to 85 ± 1°C and treat for 60 min. 3. Add 40 mL of sludge from Step 1 to each anaerobic flask in Step 2. Adjust the pH to 7.0 ± 0.1. Then, aerate nitrogen gas through the anaerobic flask for 10–15 minutes to maintain an anaerobic environment. Ferment at 120 rpm and 35 ± 1°C for 10 days.

[0025] The following is further explained with reference to the accompanying drawings.

[0026] Figure 1 Figure 2 shows the changes in dissolved total phosphorus concentration during fermentation for Examples 1 and 2 and Comparative Experiments 1 and 2. During anaerobic fermentation, dissolved total phosphorus concentration reached a maximum on day 4 and then leveled off. The dissolved total phosphorus content in Example 1 reached a maximum of 753.36 mg / L, 1.07 to 2.88 times that of the other groups.

[0027] Figure 2 Figure 2 shows the changes in soluble orthophosphate (Ortho-P) concentration during fermentation for Examples 1 and 2 and Comparative Experiments 1 and 2. The trend is similar to that of soluble total phosphorus. Example 1 reaches a maximum soluble total phosphorus content of 562.38 mg / L, 1.1 to 2.3 times that of the other groups.

[0028] Figure 3 Figures 2 and 3 show the contents of various phosphorus components on days 0, 2, 4, and 10 of the fermentation process for Examples 1 and 2 and Comparative Experiments 1 and 2. As can be seen, the total phosphorus content in the solid phase was lowest in all groups on day 4, particularly in Example 1, which reached 416.23 mg / L, a decrease of 446.72 mg / L compared to Comparative Experiment 1 and 1.1-2.0 times that of the other groups. Non-apatite inorganic phosphorus (NAIP) was the primary contributor, decreasing by 28.43%, 1.29-2.78 times that of the other groups.

[0029] Figure 4 The following is a solid-liquid phosphorus balance analysis on day 4 of the fermentation process for Examples 1-2 and Comparative Experiments 1-2. As can be seen from the figure, in Comparative Experiment 1, polyphosphate (Poly-P) is the primary source of phosphorus release during anaerobic fermentation. However, the released P binds to metal ions, leading to an increase in the proportion of inorganic phosphorus (IP). NAIP increased by 6.64% in the comparative experiment. The IP contribution values ​​for the other three groups were all positive, reaching a maximum of 352.9 mg / L in Example 1, which is 1.17 and 3.11 times that of the other groups. The final phosphorus release efficiency reached 67.86%, indicating that the addition of humus during anaerobic fermentation significantly improved the efficiency of phosphorus transfer from the solid phase to the liquid phase.

Claims

1. A method for releasing and converting phosphorus by anaerobic fermentation of excess sludge using humus, characterized in that The method proceeds as follows:

1. The residual sludge was taken from the secondary sedimentation tank of the sewage treatment plant, filtered through a 40-mesh filter and allowed to settle naturally at 4°C. After settling for 20-28 hours, the supernatant was discarded to obtain the sludge sample, which was then placed in an anaerobic reactor.

2. Adjust the pH in the anaerobic reactor to 2-5, and place the mixture in the anaerobic reactor in a water bath heating pot for pretreatment; 3. The pretreated sludge and fresh residual sludge in step 2 are inoculated into the anaerobic reactor according to the volume ratio, and humic acid or fulvic acid is added respectively. Then the anaerobic reactor is placed in a constant temperature oscillator, the speed of the constant temperature oscillator is controlled to be 100-120 rpm, the fermentation temperature is 30-35 ° C, and the fermentation time is 4-10 days to carry out anaerobic fermentation of the sludge.

2. The method for releasing and converting phosphorus by anaerobic fermentation of excess sludge using humus-enhanced methods according to claim 1, characterized in that In step 1, the pH of the sludge sample was 6.6–7.5, the TSS concentration was 15–30 g / L, and the VSS concentration was 10–15 g / L.

3. The method for releasing and converting phosphorus by anaerobic fermentation of excess sludge using humus-enhanced methods according to claim 1, characterized in that In step 2, HCl and NaOH are used to adjust the pH inside the anaerobic reactor to 3.0±0.1, and the temperature of the water bath heating pot is controlled at 80~100°C for 0.5~1.5 h.

4. The method for releasing and converting phosphorus by anaerobic fermentation of excess sludge using humus-enhanced methods according to claim 1, wherein: The inoculum volume ratio of the pretreated sludge to the fresh sludge in step 3 was 9:

1.

5. The method for releasing and converting phosphorus by anaerobic fermentation of excess sludge using humus-enhanced methods according to claim 1, characterized in that In step 3, the addition amounts of humic acid and fulvic acid are 0.8-1.2 g / L and 1.3-1.8 g / L, respectively, based on the volume of sludge in the anaerobic reactor.

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