CN117447038A - Method for promoting anaerobic methane production of excess sludge by using iron-calcium combined pretreatment - Google Patents

Abstract

The invention discloses a method for promoting anaerobic methane production of excess sludge by using iron and calcium combined pretreatment, which comprises the following steps: s1, obtaining excess sludge, carrying out pretreatment on S2 and iron calcium in a combined way, and carrying out anaerobic fermentation treatment S3; according to the method for promoting anaerobic methanogenesis of the excess sludge by adopting the combined pretreatment of the potassium ferrate and the calcium peroxide, the sludge cracking efficiency based on advanced oxidation is enhanced by the potassium ferrate, the stability of the potassium ferrate is improved by the alkaline environment created by the calcium peroxide, the extracellular polymer and the cell wall are jointly acted to improve the cracking, the dissolution of intracellular organic matters is promoted, and the anaerobic methanogenesis efficiency of the excess sludge is further improved.

Description

A method for promoting anaerobic methane production from residual sludge using combined iron and calcium pretreatment

Technical field

The present invention relates to the technical field of sludge treatment, and specifically relates to a method for promoting anaerobic methane production from remaining sludge using combined iron and calcium pretreatment.

Background technique

During the sewage treatment process, microorganisms use organic matter for anabolism to produce a large amount of residual sludge, which becomes the main by-product of the sewage treatment plant. Effective treatment of it has become a serious environmental problem. Among the many residual sludge treatment processes, anaerobic biological treatment has attracted much attention due to its green, low-cost, and energy-generating characteristics, and has actual and potential practical and research value. In fact, the remaining sludge has distinct pollution characteristics, but also has the potential to be used as a resource to "turn waste into treasure". Because it contains a large amount of carbon and nutrients, it can produce volatile fatty acids, methane, hydrogen, etc. after anaerobic digestion. Clean resources are conducive to the utilization of remaining sludge resources, reducing the burning of fossil fuels, greatly reducing treatment costs and saving energy.

Anaerobic digestion is usually based on hydrolysis, acidification and methanogenesis, that is, organic matter is first hydrolyzed and then fermented to produce single-chain fatty acids and hydrogen, which are ultimately utilized by heterotrophic bacteria and methanogens. Generally speaking, the remaining sludge hydrolysis stage is the rate-limiting step of anaerobic digestion, because the protection of dense extracellular polymers and cell walls makes it difficult for organic matter to be released in the water, resulting in a lack of necessary activity for subsequent microbial life activities and methane production. Material basis. Therefore, it is undoubtedly of great significance to use appropriate pretreatment methods to promote the dissolution and hydrolysis of organic matter and realize the resource utilization of remaining sludge.

The pretreatment of excess sludge includes acid, alkali, mechanical and heating methods. Among them, advanced oxidation technology is widely used for wall breaking and hydrolysis of excess sludge due to its simplicity and high efficiency. Potassium ferrate (PF) is a new green, environmentally friendly strong oxidant that can efficiently oxidize organic matter under acid and alkali conditions without producing harmful by-products. It produces Fe ³⁺ or Fe ( OH) ₃ , which can be used as an exogenous electron acceptor in the subsequent anaerobic digestion process to enrich iron-reducing bacteria and further hydrolyze and acidify the released refractory organic matter. It can also be used as an excellent floc for most pollutants. Therefore, the use of potassium ferrate for pretreatment can effectively destroy the sludge floc structure, release intracellular organic matter, promote sludge reduction, and facilitate subsequent anaerobic digestion. Generally, potassium ferrate is extremely oxidizing under acidic conditions, but it is extremely unstable and easy to decompose. However, the stability can be greatly improved under alkaline conditions. Its oxidation characteristics under acidic and alkaline conditions are as follows:

FeO ₄ ^2- +8H ⁺ +3e ^- →Fe ³⁺ +4H ₂ O, E ⁰ =+2.20V

FeO ₄ ^2- +4H ₂ O +3e ^- →Fe ³⁺ +5OH ^- , E ⁰ =+0.72V

Calcium peroxide (CaO ₂ ) is a thermally stable, environmentally friendly inorganic peroxide that can slowly release hydrogen peroxide and calcium hydroxide at a "controlled" rate when in contact with an aqueous medium. _2O2 has a higher utilization efficiency and is considered _the solid form _{of H2O2} . In addition, the released H ₂ O ₂ further generates free radicals, including ·OH, HO ₂ · and ·O ₂ ^- . The release process is as follows:

CaO ₂ +2H ₂ O→Ca(OH) ₂ +H ₂ O ₂

CaO ₂ +2H ₂ O→Ca(OH) ₂ +O ₂

H ₂ O ₂ +e ^- →·OH+OH ^-

·OH+ H ₂ O ₂ →H ₂ O+ HO ₂ ·

HO ₂ ·→· O ₂ ^- +H ⁺

The products H ₂ O ₂ and Ca(OH) ₂ in the above reaction equation both have the function of destroying the extracellular polymers and cell walls of sludge and promoting the dissolution of sludge. In addition, the slow release of calcium peroxide is beneficial to providing the needs for microbial growth. The oxygen, microaerobic environment promotes further hydrolysis of dissolved organic matter.

Potassium ferrate and calcium peroxide have application potential in anaerobic fermentation. The present invention proposes to use potassium ferrate and calcium peroxide in combination to pretreat remaining sludge to promote the hydrolysis of intracellular substances and simultaneously reconcile the environment required for subsequent anaerobic fermentation. Under the conditions, the remaining sludge after wall breaking is further used as the substrate for anaerobic fermentation to produce methane. At present, there is no research or technical invention on combining potassium ferrate and calcium peroxide to enhance the hydrolysis of residual sludge to produce methane. Based on this, the present invention proposes a method for promoting anaerobic methane production from residual sludge using a combination of iron and calcium.

Contents of the invention

In order to solve the above technical problems, the present invention provides a method for promoting anaerobic methane production from residual sludge using a combination of iron and calcium.

The technical solution of the present invention is: a method for promoting anaerobic methane production from residual sludge using combined iron and calcium pretreatment, which includes the following steps:

S1. Obtain remaining sludge

The activated sludge obtained from the secondary sedimentation tank of the sewage treatment plant is sieved and then gravity settled for 23 to 25 hours. After discarding the supernatant, the remaining sludge is obtained as a fermentation substrate; and the contents of TSS and VSS in the fermentation substrate are detected. The content of TSS (total suspended solids) in the fermentation substrate is 31.5~32.5g/L, and the content of VSS (volatile suspended solids) is 18.5~19.5g/L;

S2, combined iron and calcium pretreatment

Measure 135~145mL of fermentation substrate and place it in a serum bottle. Use 0.28~0.32g/g VSS calcium peroxide and 0.2~1g/g VSS potassium ferrate to pretreat the fermentation substrate in sequence to obtain the pretreated product. fermentation substrate;

S3. Anaerobic fermentation treatment

Measure 95~105mL of pretreated fermentation substrate and place it in an anaerobic fermentation bottle, then add hydrochloric acid with a molar concentration of 4~6mol/L, adjust the pH of the pretreated fermentation substrate to 6.5~7.5, and then follow the predetermined steps. The volume ratio of the treated fermentation substrate: the inoculated anaerobic digestion sludge is 1:0.98~1.02. Add the inoculated anaerobic digestion sludge, aerate for 18~22 minutes, seal, and then transfer to 36~38°C with constant temperature shaking. The bed performs anaerobic fermentation, and collects gas during the anaerobic fermentation process to obtain methane;

Note: Using 0.28~0.32g/g VSS calcium peroxide and 0.2~1g/g VSS potassium ferrate to pretreat the fermentation substrate in sequence can make potassium ferrate and calcium peroxide act on the sludge efficiently, further Improve the cracking of extracellular polymers and cell walls, thereby improving the dissolution efficiency of intracellular organic matter; and using the above range of calcium peroxide and potassium ferrate has a better pretreatment effect on volatile suspended solids, thereby further improving the remaining sludge The purpose of methane production efficiency; it can be seen from the example data that when the content of potassium ferrate is 1g/g VSS, it has an inhibitory effect on the yield of methane in the early stage, the lag period of methane production is significantly increased, and excessive addition of potassium ferrate may cause Some refractory organic matter such as humic acid and cellulose are removed, which has an inhibitory effect on methanogenic bacteria, and the economic cost is also slightly higher; when the content of potassium ferrate is less than 0.2g/g VSS, the SCOD, protein and Polysaccharides were significantly reduced, resulting in a significant reduction in methane production.

Further, in step S1, the sieving method is: sieving using a sieve with a hole diameter of 1 to 3 mm;

Note: The use of screens with the above pore sizes can effectively remove insoluble impurities in activated sludge, thereby improving the purity of activated sludge and further improving the anaerobic methane production efficiency of remaining sludge.

Further, in step S2, the pretreatment method is: first place the serum bottle on a magnetic stirrer, and then stir the fermentation substrate at a speed of 250~300r/min, the stirring time is 10~20min, and Add 0.28~0.32g/g VSS calcium peroxide to the above fermentation substrate and stir for 5~7min, then add 0.2~1g/g VSS potassium ferrate and stir for 3~5min, and finally in a constant temperature oscillating shaker Shake for 22 to 24 hours to obtain the pretreated fermentation substrate;

Note: The above pretreatment method uses a combination of potassium ferrate and calcium peroxide to treat the remaining sludge. Potassium ferrate strengthens the sludge cracking efficiency based on advanced oxidation. The alkaline environment created by calcium peroxide improves the stability of potassium ferrate. The two work together to improve the cracking of extracellular polymers and cell walls, promote the dissolution of intracellular organic matter, and can effectively improve the methane production efficiency of the fermentation substrate, namely activated sludge.

Further, the oscillation processing parameters are: oscillation temperature is 36~38°C, oscillation speed is 145~155rpm;

Explanation: The oscillation treatment effect under the above parameters is better, and can fully act on the remaining sludge, improve the dissolution of intracellular organic matter, and further improve the anaerobic methane production effect of the remaining sludge.

Furthermore, in step S2, before the pretreatment, the fermentation substrate is pretreated; the method of pretreatment is:

S2-1. Take 100~120g of straw, soak it in distilled water for 20~30min, naturally dry it at 26~28℃ for 3~5h, and grind it in a grinder for 20~25min to obtain powdered straw;

S2-2. Take 1/2 of the powdered straw and measure the peroxide with a mass concentration of 8~10U/m L according to the weight and volume ratio of powdered straw:catalase solution: 40~50g:95~100mL. Hydrogenase solution, and spray the catalase solution on the surface of the powdered straw at a rate of 5 to 7 mL/min until the spraying is completed, stir and mix and compress it into a block with a size of 1cm×1cm×1cm using a press. A mixture is called a compound;

S2-3. Perform microwave irradiation treatment on the fermentation substrate in the serum bottle. The microwave irradiation intensity is 10~300W and the microwave irradiation time is 10~12min. During the microwave irradiation period, add in sequence to the serum bottle The remaining 1/2 of the powdered straw and the compound obtained in step S2-2 are mixed evenly;

Description: The compound obtained by mixing powdered straw and catalase is used in conjunction with microwave irradiation to pretreat the fermentation substrate, which can effectively increase the stability of catalase and reduce the impact of microwave radiation on the catalase solution. The influence of activity, using catalase to catalyze the decomposition of calcium peroxide, makes calcium peroxide better act on sludge. Calcium peroxide can promote the degradation of humus and lignocellulose in sludge, making it easily degradable. of organic matter, thereby promoting the production of methane; at the same time, calcium peroxide has oxidizing properties. As an oxidant, it can release hydroxyl radicals, promote the decomposition of the remaining sludge EPS floc through chemical oxidation, and microwave treatment can promote the interaction between the complex and the fermentation substrate. contact to further improve the subsequent catalytic efficiency of calcium peroxide on sludge; preparing the complex into blocks can effectively increase the contact area for microwave action, thereby increasing methane production.

Further, in step S2-3, the microwave irradiation intensity is modulated during the microwave irradiation period, which is divided into the following two stages:

The first stage: The microwave irradiation intensity is initially adjusted to 250~300W, the microwave irradiation time is 3~5min, and then the microwave irradiation intensity is decreased at a rate of 25~30W/min, and the microwave irradiation intensity is adjusted at a rate of 1.8~3.5g/min. Add the remaining 1/2 of the powdered straw until the microwave irradiation intensity is adjusted to 70~80W;

The second stage: The microwave irradiation intensity continues to decrease at a rate of 13~15W/min, and the microwave irradiation is processed for 2~4 minutes, then the microwave irradiation intensity is kept unchanged, and the amount of microwave irradiation is added to the serum bottle at a rate of 2~4 pieces/min. Add the compound and mix well, continue the microwave irradiation treatment for 2 to 4 minutes until the compound is added;

Description: Adding a portion of powdered straw to the fermentation substrate can provide the carbon source and energy required by anaerobic microorganisms, reduce the viscosity of the remaining sludge and improve its air permeability, and further promote the growth and metabolism of anaerobic microorganisms. Thus, the efficiency of anaerobic methane production from sludge can be improved. The second stage treatment after the microwave irradiation intensity is reduced to 70~80W can on the one hand reduce the impact of microwave irradiation treatment on the activity of the composite as much as possible, and on the other hand, Adjusting the microwave irradiation intensity in a decreasing manner under lower irradiation intensity can gradually weaken the effect of microwave irradiation intensity on catalase activity, thereby enhancing the methane production effect of sludge.

Further, in step S2, the purity of the calcium peroxide is 68~72%;

Note: Calcium peroxide at the above purity can effectively promote the decomposition and transformation of organic matter in sludge, further improving the efficiency of methane production from sludge.

Further, in step S3, nitrogen with a purity of 99.99~99.999% is used in the aeration process;

Note: The use of high-purity nitrogen can maintain a relatively stable anaerobic environment in the anaerobic reactor, which is conducive to the growth and reproduction of methanogens. At the same time, it can inhibit the growth and reproduction of ammonia-oxidizing bacteria, thereby preventing ammonia-oxidizing bacteria from harming methanogens. Competitive inhibition.

Further, in step S3, the inoculated anaerobic digestion sludge is collected from the sludge anaerobic digestion tank, and the content of VSS in the inoculated anaerobic digestion sludge is 19~21g/L;

Note: Excessive concentration of volatile suspended solids in the inoculated anaerobic digestion sludge may cause the viscosity of the sludge to increase, which is not conducive to the anaerobic digestion process. High concentrations of volatile suspended solids may hinder the gas from sludge. escape, resulting in reduced digestion gas production. In addition, too high a concentration of volatile suspended solids may also lead to a decrease in the activity of microorganisms in the reactor, further affecting the efficiency of methane production from sludge. If the concentration of volatile suspended solids is too small, the number of microorganisms in the sludge may be insufficient, and there may be insufficient microorganisms to decompose and transform organic matter, thus affecting the methane production effect of the sludge. In addition, too low a concentration of volatile suspended solids may make it difficult to maintain stable parameters such as temperature and pH value in the reactor, which is not conducive to the growth and reproduction of methanogens.

The beneficial effects of the present invention are:

(1) The present invention uses potassium ferrate and calcium peroxide to pretreat remaining sludge. Potassium ferrate strengthens the sludge cracking efficiency based on advanced oxidation. The alkaline environment created by calcium peroxide improves the stability of potassium ferrate. , the two work together to improve the cracking of extracellular polymers and cell walls, and promote the dissolution of intracellular organic matter. The SCOD released is 10.3 times that of calcium peroxide alone and 3.2 times that of potassium ferrate alone. Supernatant protein The concentration of polysaccharide is 12.4 times and 14.4 times that of calcium peroxide alone, and 2.0 times and 10.0 times that of potassium ferrate alone.

(2) Calcium peroxide of the present invention slowly releases oxygen to provide a microaerobic environment and improve the activity of facultative bacteria. Under the alkaline conditions created by calcium peroxide, Fe(OH) ₃ , the reduction product of potassium ferrate, is enriched as an electron acceptor. Iron-reducing bacteria, the two work together to further strengthen the hydrolysis and acidification of refractory organic matter and provide high-quality substrates for methanogens. It is worth noting that compared with the use of potassium ferrate alone, the slowly released oxygen from calcium peroxide can oxidize Fe (II) produced by the reduction of dissimilated iron, promote iron circulation and achieve the regeneration of Fe (III). The combined effect of the two increases the methane production rate by 112.0% compared to using calcium peroxide alone, and 133.8% compared to using potassium ferrate alone.

(3) The operating conditions of the present invention are simple, the operating cost is low, the ferrate and calcium peroxide used are easily available and environmentally friendly, and there is no secondary pollution.

Description of the drawings

Figure 1 is a flow chart of the method of the present invention;

Figure 2 is a bar graph of the concentration of intracellular substances released after pretreatment in Example 1, Example 6, Example 7, and Comparative Examples 1 to 3 of the present invention;

Figure 3 is a line chart of anaerobic methane production within 0 to 12 days of residual sludge pretreatment in Example 1, Example 6, Example 7, and Comparative Examples 1 to 3 of the present invention.

Detailed ways

The present invention will be described in further detail below in conjunction with specific embodiments to better reflect the advantages of the present invention.

Example 1: A method for strengthening anaerobic methane production from residual sludge using combined iron and calcium pretreatment, including the following steps:

S1. Obtain remaining sludge

The activated sludge obtained from the secondary sedimentation tank of the sewage treatment plant was sieved through a sieve with a pore size of 2 mm and then settled by gravity for 24 hours. After discarding the supernatant, the remaining sludge was obtained as a fermentation substrate; and the TSS and TSS in the fermentation substrate were detected. VSS content; the measured TSS content in the fermentation substrate was 32g/L, and the VSS content was 19g/L;

S2, combined iron and calcium pretreatment

Measure 140 mL of fermentation substrate and place it in a 300 mL serum bottle. Use 0.3 g/g VSS calcium peroxide and 0.6 g/g VSS potassium ferrate to pretreat the fermentation substrate in sequence to obtain the pretreated fermentation substrate;

The pretreatment method is: first place the serum bottle on the magnetic stirrer, then stir the fermentation substrate at a speed of 275r/min, the stirring time is 15min, and add 0.3g/g VSS to the fermentation substrate with a purity of 70 % calcium peroxide and stir for 6 minutes, then add 0.5g/g VSS potassium ferrate and stir for 4 minutes, and finally shake for 23 hours in a constant-temperature oscillating shaker with a shaking temperature of 37°C and a shaking speed of 150 rpm to obtain the predetermined Treated fermentation substrate;

Before pretreatment, the fermentation substrate is pretreated; the pretreatment method is:

S2-1. Take 110g of straw, soak it in distilled water for 25 minutes, dry it naturally at 27°C for 4 hours, and grind it in a grinder for 23 minutes to obtain powdered straw;

S2-2. Take 1/2 of the powdered straw, and measure the catalase solution with a mass concentration of 9U/mL according to the weight-volume ratio of powdered straw:catalase solution of 45g:98mL, and add the The catalase solution is sprayed on the surface of the powdered straw at a rate of 6mL/min until the spraying is completed, stir and mix well and compress it into a block mixture with a size of 1cm×1cm×1cm, which is the composite;

S2-3. Perform microwave irradiation treatment on the fermentation substrate in the serum bottle. The microwave irradiation intensity is 150W and the microwave irradiation time is 11 minutes. During the microwave irradiation period, add the remaining powdered straw to the serum bottle and step S2. -2 obtained complex and mix well;

S3. Anaerobic fermentation treatment

Measure 100mL of the pretreated fermentation substrate and place it in a 300mL anaerobic fermentation bottle, then add hydrochloric acid with a molar concentration of 5mol/L, adjust the pH of the pretreated fermentation substrate to 7, and then follow the pretreated fermentation substrate The volume ratio of material: inoculated anaerobic digestion sludge is 1:1. Add the inoculated anaerobic digestion sludge, aerate it with nitrogen with a purity of 99.995% for 20 minutes, seal it, and then transfer it to a 37°C constant temperature oscillating shaker for anaerobic testing. Fermentation, and collecting gas during anaerobic fermentation to obtain methane;

The inoculated anaerobic digestion sludge was collected from the sludge anaerobic digestion tank, and the VSS content in the inoculated anaerobic digestion sludge was 20g/L.

Embodiment 2: Different from Embodiment 1, in step S1,

The activated sludge obtained from the secondary sedimentation tank of the sewage treatment plant was sieved through a sieve with a pore size of 1 mm and then settled by gravity for 23 hours. After discarding the supernatant, the remaining sludge was obtained as a fermentation substrate; and the TSS and TSS in the fermentation substrate were detected. The content of VSS; the content of TSS and VSS in the fermentation substrate were measured to be 31.5g/L and 18.5g/L.

Embodiment 3: Different from Embodiment 1, in step S1,

The activated sludge obtained from the secondary sedimentation tank of the sewage treatment plant was sieved through a sieve with a pore size of 3 mm and then settled by gravity for 25 hours. After discarding the supernatant, the remaining sludge was obtained as a fermentation substrate; and the TSS and TSS in the fermentation substrate were detected. The content of VSS; the content of TSS and VSS in the fermentation substrate were measured to be 32.5g/L and 19.5g/L.

Embodiment 4: Different from Embodiment 1, in step S2,

Measure 140 mL of fermentation substrate and place it in a 300 mL serum bottle. Use 0.3 g/g VSS calcium peroxide and 0.2 g/g VSS potassium ferrate to pretreat the fermentation substrate in sequence to obtain the pretreated fermentation substrate.

Embodiment 5: Different from Embodiment 1, in step S2,

Measure 140 mL of fermentation substrate and place it in a 300 mL serum bottle. Use 0.3 g/g VSS calcium peroxide and 1 g/g VSS potassium ferrate to pretreat the fermentation substrate in sequence to obtain the pretreated fermentation substrate.

Embodiment 6: Different from Embodiment 1, in step S2,

The pretreatment method is: first place the serum bottle on the magnetic stirrer, then stir the fermentation substrate at a speed of 250r/min, the stirring time is 20min, and add 0.28g/g VSS purity to the fermentation substrate. The purity is 68 % calcium peroxide and stir for 7 minutes, then add 0.2g/g VSS potassium ferrate and stir for 5 minutes, and finally shake for 24 hours in a constant-temperature oscillating shaker with a shaking temperature of 36°C and a shaking speed of 145 rpm to obtain the predetermined Treated fermentation substrate.

Embodiment 7: Different from Embodiment 1, in step S2,

The pretreatment method is: first place the serum bottle on the magnetic stirrer, then stir the fermentation substrate at a speed of 300r/min, the stirring time is 10min, and add 0.32g/g VSS purity to the fermentation substrate. The purity is 72 % calcium peroxide and stir for 5 minutes, then add 1g/g VSS potassium ferrate and stir for 3 minutes, and finally shake for 22 hours in a constant temperature oscillating shaker with a shaking temperature of 38°C and a shaking speed of 155 rpm to obtain pretreatment The final fermentation substrate.

Embodiment 8: Different from Embodiment 1, in the pretreatment method,

S2-1. Take 100g of straw, soak it in distilled water for 20 minutes, dry it naturally at 26°C for 5 hours, and grind it in a grinder for 20 minutes to obtain powdered straw.

Embodiment 9: Different from Embodiment 1, in the pretreatment method,

S2-1. Take 120g of straw, soak it in distilled water for 30 minutes, dry it naturally at 28°C for 3 hours, and grind it in a grinder for 25 minutes to obtain powdered straw.

Embodiment 10: Different from Embodiment 1, in the pretreatment method,

S2-2. Take 1/2 of the powdered straw, and measure the catalase solution with a mass concentration of 8U/m L according to the weight-volume ratio of powdered straw:catalase solution of 40g:95mL, and add The catalase solution was sprayed on the surface of the powdered straw at a rate of 5 mL/min until the spraying was completed, stirred, mixed and compressed into a block mixture with a size of 1 cm × 1 cm × 1 cm, which is the composite.

Embodiment 11: Different from Embodiment 1, in the pretreatment method,

S2-2. Take 1/2 of the powdered straw, and measure the catalase solution with a mass concentration of 10U/mL according to the weight-volume ratio of powdered straw:catalase solution of 50g:100mL, and add The catalase solution is sprayed on the surface of the powdered straw at a rate of 7 mL/min until the spray is completed, stir and mix well and compress it into a block mixture with a size of 1 cm × 1 cm × 1 cm, which is the composite.

Embodiment 12: Different from Embodiment 1, in the pretreatment method,

S2-3. Perform microwave irradiation treatment on the fermentation substrate in the serum bottle. The microwave irradiation intensity is 10W and the microwave irradiation time is 10 minutes. During the microwave irradiation period, add the remaining 1/2 of the powdered straw to the serum bottle. and the complex obtained in step S2-2, and mix well.

Embodiment 13: Different from Embodiment 1, in the pretreatment method,

S2-3. Perform microwave irradiation treatment on the fermentation substrate in the serum bottle. The microwave irradiation intensity is 300W and the microwave irradiation time is 12 minutes. During the microwave irradiation period, add the remaining 1/2 of the powdered straw to the serum bottle. and the complex obtained in step S2-2, and mix well.

Embodiment 14: Different from Embodiment 1, in step S2-3, the microwave irradiation intensity is modulated during the microwave irradiation, which is divided into the following two stages:

The first stage: The microwave irradiation intensity is initially adjusted to 250W, the microwave irradiation time is 5 minutes, then the microwave irradiation intensity is decreased at a rate of 25W/min, and the remaining 1/2 of the microwave irradiation is added at an amount of 1.8g/min. Powdered straw until the microwave irradiation intensity is adjusted to 70W;

The second stage: the microwave irradiation intensity continues to decrease at a rate of 13W/min, microwave irradiation is processed for 2 minutes, then the microwave irradiation intensity is kept unchanged, and the complex is added to the serum bottle at a rate of 2 pieces/min and mixed. , continue the microwave irradiation treatment for 4 minutes until the compound is added.

Embodiment 15: Different from Embodiment 1, in step S2-3, the microwave irradiation intensity is modulated during the microwave irradiation, which is divided into the following two stages:

The first stage: The microwave irradiation intensity is initially adjusted to 275W, the microwave irradiation time is 4 minutes, and then the microwave irradiation intensity is adjusted incrementally at a rate of 28W/min, and the remaining 1/2 is added at an amount of 2.6g/min. of powdered straw until the microwave irradiation intensity is adjusted to 75W;

The second stage: Continue to adjust the microwave irradiation intensity to 14W/min in descending order, irradiate for 3 minutes, then keep the microwave irradiation intensity unchanged, add the complex to the serum bottle at 3 pieces/min, mix well, and continue to microwave. Irradiate for 3 minutes until the compound is added;

Embodiment 16: Different from Embodiment 1, in step S2-3, the microwave irradiation intensity is modulated during the microwave irradiation, which is divided into the following two stages:

The first stage: The microwave irradiation intensity is initially adjusted to 300W, the microwave irradiation time is 3 minutes, then the microwave irradiation intensity is decreased at a rate of 30W/min, and the remaining 1/2 of the microwave irradiation is added at an amount of 3.5g/min. Powdered straw until the microwave irradiation intensity is adjusted to 80W;

The second stage: the microwave irradiation intensity continues to decrease at a rate of 15W/min, microwave irradiation is processed for 4 minutes, and then the microwave irradiation intensity is kept unchanged, and the complex is added to the serum bottle at a rate of 4 pieces/min and mixed. , continue the microwave irradiation treatment for 2 minutes until the compound is added.

Embodiment 17: Different from Embodiment 1, in step S3,

Measure 95mL of the pretreated fermentation substrate and place it in a 300mL anaerobic fermentation bottle, then add hydrochloric acid with a molar concentration of 4mol/L, adjust the pH of the pretreated fermentation substrate to 6.5, and then follow the pretreated fermentation substrate The volume ratio of material: inoculated anaerobic digestion sludge is 1:0.98. Add the inoculated anaerobic digestion sludge, aerate it with nitrogen with a purity of 99.99% for 22 minutes, seal it, and then transfer it to a 36°C constant temperature oscillating shaker for anaerobic testing. Fermentation, and gas is collected during anaerobic fermentation to obtain methane.

Embodiment 18: Different from Embodiment 1, in step S3,

Measure 105mL of the pretreated fermentation substrate and place it in a 300mL anaerobic fermentation bottle, then add hydrochloric acid with a molar concentration of 6mol/L, adjust the pH of the pretreated fermentation substrate to 7.5, and then follow the pretreated fermentation substrate. The volume ratio of material: inoculated anaerobic digestion sludge is 1:1.02. Add the inoculated anaerobic digestion sludge, aerate it with nitrogen with a purity of 99.999% for 18 minutes, seal it, and then transfer it to a 38°C constant temperature oscillating shaker for anaerobic testing. Fermentation, and gas is collected during anaerobic fermentation to obtain methane.

Embodiment 19: Different from Embodiment 1, in step S3,

The content of VSS in the inoculated anaerobic digestion sludge was 19g/L.

Embodiment 20: Different from Embodiment 1, in step S3,

The content of VSS in the inoculated anaerobic digestion sludge was 21g/L.

Experimental example: Test the SCOD release amount, supernatant protein concentration, polysaccharide concentration, and methane production during 0 to 12 days after pretreatment in each embodiment. The methane production data in the experimental example table takes the methane at 12 days of reaction. Production, detailed exploration is as follows:

To explore the effect of pretreatment of calcium peroxide and potassium ferrate on anaerobic methane production from residual sludge

Table 1 Effects of Example 1, Examples 4-5 and Comparative Examples 1-3 on anaerobic methane production from residual sludge

Comparative Example 1: Different from Example 1, the fermentation substrate was not treated with calcium peroxide and potassium ferrate, and was used as a blank group.

Comparative Example 2: Different from Example 1, only calcium peroxide was added to the fermentation substrate for treatment.

Comparative Example 3: Different from Example 1, only potassium ferrate was added to the fermentation substrate for treatment.

Conclusion: From the data in Table 1, it can be seen that the anaerobic methane production ability of the remaining sludge during the preparation process of Comparative Examples 1 to 3 was significantly weakened. From the comparison of the data of Example 1, Example 4, and Example 5 and Figure 2, Figure 3 It can be seen that compared with the dosage of 0.5g/gVSS potassium ferrate in Example 1, the cost of the 1g/g VSS agent in Example 5 has doubled, but the improvement effect of methane production is not significant, and the methane production is seriously increased. During the lag period, although the 1g/g VSS dosage led to the release of a large amount of organic matter such as SCOD, supernatant protein, polysaccharides, etc., the 1g/g VSS dosage also had an inhibitory effect on methane production, which shows that potassium ferrate Excessive addition may produce some refractory organic matter such as humic acid and cellulose, thereby inhibiting methane production. Therefore, considering the economic cost and improvement effect, Example 1 is the best, and Example 7 has been considered Excessive dosing, economic costs and potential secondary pollution are not in line with the original intention of the low-cost, environmentally friendly invention, so further increase is not recommended. Therefore, Example 1 is selected as the optimal solution.

Explore the impact of pre-treatment and pre-treatment processes on anaerobic methane production from residual sludge

Table 2 Final methane yields prepared in Example 1, Examples 8 to 13 and Comparative Examples 6 to 7

Comparative Example 6: Different from Example 1, in the pretreatment method, the straw is not ground.

Comparative Example 7: Different from Example 1, in the pretreatment method, the fermentation substrate is not subjected to microwave irradiation treatment.

Conclusion: From the data in Table 3, it can be seen that the lack of grinding of straw and the microwave irradiation of the fermentation substrate in Comparative Examples 6 and 7 will cause a significant reduction in the final methane production. This is because the use of powdered straw and The compound obtained after mixing catalase can effectively increase the stability of catalase and reduce the impact of microwave radiation on the activity of catalase solution. However, the straw mixed directly with catalase due to the contact area between the two Limited, resulting in a slightly weaker improvement effect of straw on catalase, further causing inactivation of catalase and weakening methane production; while the lack of microwave treatment in Comparative Example 7 limited the contact between the complex and the fermentation substrate, affecting to the final production of methane; based on this, Example 1 was selected as the optimal solution.

Exploring the impact of microwave irradiation treatment methods on the anaerobic methane production of residual sludge

Table 3 Final methane yields prepared in Example 1, Examples 14-16 and Comparative Example 8

Comparative Example 8: Different from Example 15, the microwave irradiation intensity of 33W was directly used to irradiate the sludge for 10 to 15 minutes.

Conclusion: From the data in Table 4, it can be seen from the comparison of the data of Example 1 and Examples 14 to 16 that the amount of methane produced in Examples 14 to 16 is slightly better than that in Example 1. This is because a staged approach is adopted to microwave Modulating the intensity of irradiation can provide the carbon source and energy required by anaerobic microorganisms by first adding a portion of powdered straw, further promoting the growth and metabolism of anaerobic microorganisms, thereby improving the efficiency of anaerobic methane production from sludge; The second stage of treatment after the microwave irradiation intensity is reduced to 70~80W can minimize the impact of microwave irradiation on the activity of the complex and effectively enhance the methane production effect of the sludge; while in Comparative Example 8, 33W microwave radiation is directly used. Although the intensity of illumination for sludge treatment can avoid the impact on catalase, it also results in a significant extension of the methane production time. After 12 days of reaction, only about 30% of the methane production obtained by the method of Example 15 can be achieved. , and it can be seen that Example 15 is the optimal solution.

To explore the effect of solid concentration in inoculated anaerobic digestion sludge on the anaerobic methane production of remaining sludge

Table 4 Final methane production obtained in Example 15, Examples 19-20 and Comparative Examples 9-10

Comparative Example 9: Different from Example 1, in step S3, the content of VSS in the inoculated anaerobic digestion sludge was 17.5g/L.

Comparative Example 10: Different from Example 1, in step S3, the content of VSS in the inoculated anaerobic digestion sludge was 21.5g/L.

Conclusion: From the data in Table 4, it can be seen that the final methane production of the anaerobic digestion sludge inoculated in Comparative Example 9 and Comparative Example 10, which contains volatile suspended solids concentrations lower than or higher than the protection range of the present invention, will significantly decrease. This is because the excessive concentration of volatile suspended solids in the inoculated anaerobic digestion sludge increases the viscosity of the sludge, which is not conducive to the anaerobic digestion process. The high concentration of volatile suspended solids may hinder the gas from sludge. The concentration of volatile suspended solids is too small, resulting in an insufficient number of microorganisms in the sludge. There is a lack of sufficient microorganisms to decompose and transform organic matter, thus affecting the methane production effect of the sludge. Based on this, Embodiment 15 is still the optimal solution.

Claims (9)

1. The method for promoting anaerobic methanogenesis of excess sludge by using the combined pretreatment of iron and calcium is characterized by comprising the following steps of:

s1, obtaining excess sludge

Sieving activated sludge obtained from a secondary sedimentation tank of a sewage treatment plant, and carrying out gravity sedimentation for 23-25 h, and discarding supernatant to obtain residual sludge serving as a fermentation substrate; detecting the contents of TSS and VSS in the fermentation substrate;

s2, iron-calcium combined pretreatment

Weighing 135-145 mL of fermentation substrate, placing the fermentation substrate in a serum bottle, and sequentially preprocessing the fermentation substrate by adopting 0.28-0.32 g/g of calcium peroxide of VSS and 0.2-1 g/g of potassium ferrate of VSS to obtain a preprocessed fermentation substrate;

s3, anaerobic fermentation treatment

Measuring 95-105 mL of pretreated fermentation substrate, placing the fermentation substrate into an anaerobic fermentation bottle, adding hydrochloric acid with the molar concentration of 4-6 mol/L, adjusting the pH of the pretreated fermentation substrate to 6.5-7.5, adding the inoculated anaerobic digestion sludge according to the volume ratio of the pretreated fermentation substrate to the inoculated anaerobic digestion sludge of 1:0.98-1.02, aerating for 18-22 min, sealing, transferring to a constant-temperature oscillating table at 36-38 ℃ for anaerobic fermentation, and collecting gas in the anaerobic fermentation process to obtain methane.

2. A method for promoting anaerobic methanogenesis of excess sludge by combined pretreatment of iron and calcium according to claim 1, wherein in step S1, the sieving method is as follows: sieving by using a screen with the aperture of 1-3 mm.

3. The method for promoting anaerobic methanogenesis of excess sludge by using the combined pretreatment of iron and calcium according to claim 1, wherein in the step S2, the pretreatment method is as follows: firstly placing a serum bottle on a magnetic stirrer, stirring a fermentation substrate at a rotating speed of 250-300 r/min for 10-20 min, adding 0.28-0.32 g/g VSS calcium peroxide into the fermentation substrate, stirring for 5-7 min, adding 0.2-1 g/g VSS potassium ferrate, stirring for 3-5 min, and finally oscillating in a constant-temperature oscillating table for 22-24 h to obtain the pretreated fermentation substrate.

4. A method for promoting anaerobic methanogenesis of excess sludge by combined pretreatment of iron and calcium as recited in claim 3, wherein said oscillation treatment parameters are: the oscillation temperature is 36-38 ℃ and the oscillation speed is 145-155 rpm.

5. A method for promoting anaerobic methanogenesis of excess sludge by combined pretreatment of iron and calcium according to claim 1, wherein in step S2, the fermentation substrate is subjected to pretreatment prior to said pretreatment; the pretreatment method comprises the following steps:

s2-1, taking 100-120 g of straw, soaking the straw in distilled water for 20-30 min, naturally drying the straw at 26-28 ℃ for 3-5 h, and grinding the straw in a grinder for 20-25 min to obtain powdery straw;

s2-2, taking 1/2 of powdery straw, measuring 8-10U/mL of catalase solution according to the weight-volume ratio of 40-50 g to 95-100 mL of the catalase solution, spraying the catalase solution on the surface of the powdery straw at the speed of 5-7 mL/min until the spraying is finished, stirring and mixing uniformly, and compressing the mixture into a block mixture with the size of 1cm multiplied by 1cm, thus obtaining a compound;

s2-3, carrying out microwave irradiation treatment on the fermentation substrate in the serum bottle, wherein the microwave irradiation intensity is 10-300W, the microwave irradiation time is 10-12 min, and sequentially adding the rest 1/2 of powdery straw and the compound obtained in the step S2-2 into the serum bottle during microwave irradiation, and uniformly mixing.

6. The method for promoting anaerobic methanogenesis of excess sludge by combined pretreatment of iron and calcium according to claim 5, wherein in step S2-3, the intensity of microwave irradiation is modulated during the microwave irradiation, and the method is divided into the following two stages:

the first stage: the microwave irradiation intensity is initially adjusted to 250-300W, the microwave irradiation time is 3-5 min, then the microwave irradiation intensity is reduced at the rate of 25-30W/min, and the rest 1/2 of powdery straws are added according to the adding amount of 1.8-3.5 g/min until the microwave irradiation intensity is adjusted to 70-80W;

and a second stage: continuously decreasing the microwave irradiation intensity at the speed of 13-15W/min, performing microwave irradiation treatment for 2-4 min, then keeping the microwave irradiation intensity unchanged, adding the compound into the serum bottle according to 2-4 blocks/min, uniformly mixing, and continuously performing microwave irradiation treatment for 2-4 min until the compound is added.

7. The method for promoting anaerobic methanogenesis of excess sludge by using the combined pretreatment of iron and calcium according to claim 1, wherein in the step S2, the purity of the calcium peroxide is 68-72%.

8. The method for promoting anaerobic methanogenesis of excess sludge by using iron and calcium combined pretreatment as claimed in claim 1, wherein in the step S3, high-purity nitrogen with purity of 99.99-99.999% is adopted in the aeration process.

9. The method for promoting anaerobic methanogenesis of excess sludge by using iron and calcium combined pretreatment according to claim 1, wherein in the step S3, the inoculated anaerobic digestion sludge is obtained by collecting in a sludge anaerobic digestion tank, and the VSS content in the inoculated anaerobic digestion sludge is 19-21 g/L.