An anaerobic digestion method for sludge reduction

Abstract

The present application relates to the technical field of sludge anaerobic digestion, and discloses an anaerobic digestion method for sludge reduction, comprising the following steps: (1) adding calcium peroxide into dewatered sludge to carry out hydrolysis acidification reaction, and obtaining pretreated sludge; (2) carrying out anaerobic digestion on the pretreated sludge, taking 24h as a cycle, and when 3-5 cycles after feeding sludge, carrying out heat exchange treatment on the obtained inoculated sludge; (3) adding sodium persulfate into the inoculated sludge, stirring first and then ultrasonicating, and obtaining mixed sludge; (4) carrying out anaerobic digestion on the mixed sludge. The dewatered sludge is pretreated by adding calcium peroxide, and after a period of anaerobic digestion, sodium persulfate is added, so that the oxidation of the refractory organic matter is enhanced, the influence of the generated free radicals on the sludge flocculation body is strengthened, the interaction is promoted, the organic matter in the sludge particles is further degraded, and the biogas production in the subsequent anaerobic digestion process is obviously increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sludge anaerobic digestion, in particular to a sludge reduction anaerobic digestion method. BACKGROUND

[0002] Anaerobic digestion is mainly under anaerobic conditions, by facultative anaerobic bacteria and obligate anaerobic bacteria to degrade organic matter, and convert organic matter into carbon dioxide and methane. Anaerobic digestion can directly handle wet sludge, and the treatment efficiency is relatively high. In this process, harmful substances in sludge are decomposed, and easily perishable and odorous substances in sludge are degraded into low molecular organic matter, the total amount of sludge is reduced and energy gases such as hydrogen and methane are obtained, and at the same time, pathogenic bacteria are reduced and odor is eliminated, so that the sludge is reduced, stabilized and harmless, and the sludge is realized resource utilization while realizing sludge stabilization.

[0003] At present, although the sludge anaerobic digestion technology has been applied to a certain extent, the overall operation efficiency is still low, and the sludge organic matter degradation rate of many anaerobic digestion facilities is only 30-35%, and the biogas production is also low. The main problem is that the sludge quality is poor, and the operation and management level of the treatment plant is low, which leads to the fact that the stability of the anaerobic digestion equipment and the biogas production rate and other indicators are generally low. However, with the continuous progress of technology and the accumulation of experience, domestic sludge has begun to be pretreated by methods such as alkali dissolution, heat treatment, ultrasonic treatment and microwave treatment to improve the sludge hydrolysis rate and anaerobic digestion performance.

[0004] However, most of the sludge pretreatment methods have high energy consumption and are difficult to be popularized on a large scale, and the use of methods such as biochar, activated carbon, olivine and quicklime can greatly increase the methane content in biogas, but the release of intracellular organic matter in bacteria in sludge is slow, and the anaerobic digestion efficiency is still low. Therefore, if a kind of anaerobic digestion method which can improve the anaerobic digestion efficiency of sludge and realize sludge reduction can be developed, it will have important practical value for promoting the development of anaerobic digestion technology. SUMMARY

[0005] In order to solve the above technical problems, the present application provides a sludge reduction anaerobic digestion method, which pretreats the dewatered sludge by adding calcium peroxide to improve the biodegradability of the sludge, and after a period of anaerobic digestion, sodium persulfate is added to form a double oxidation system, which can enhance the oxidation of refractory organic matter and strengthen the influence on sludge flocculation, so that the organic matter in the sludge particles is further degraded, the biogas production in the subsequent anaerobic digestion process is significantly increased, and the sludge reduction is realized, and the anaerobic digestion efficiency is significantly improved.

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] The present application provides a sludge reduction anaerobic digestion method, comprising the following steps:

[0008] (1) adding calcium peroxide into the dewatered sludge to perform hydrolysis acidification reaction, to obtain pretreated sludge;

[0009] (2) performing anaerobic digestion on the pretreated sludge, taking 24h as a cycle, when 3-5 cycles after feeding sludge, performing heat exchange treatment on the obtained inoculated sludge;

[0010] (3) adding sodium persulfate into the inoculated sludge, stirring first and then ultrasonic, to obtain mixed sludge;

[0011] (4) performing anaerobic digestion on the mixed sludge.

[0012] The present application performs pretreatment on the dewatered sludge by adding calcium peroxide, which can slowly dissolve in water to generate hydrogen peroxide, oxygen and hydroxyl radicals, all of which have strong oxidizing property, can oxidize and decompose sludge, break down microbial cells, increase soluble COD (SCOD), and improve the biodegradability of sludge. However, due to the slow process of calcium peroxide releasing hydrogen peroxide, the efficiency of sludge pretreatment will be reduced. And in the process of anaerobic digestion, with the passage of time, the soluble easily degradable organic matter is gradually consumed, part of the organic matter remaining in the dead microorganisms and anaerobic sludge flocs is difficult to be utilized, the degradation rate begins to decrease, i.e. the gas production per unit time begins to decrease, which will further result in low final methane production.

[0013] Therefore, after a period of anaerobic digestion, the present application adjusts the pH by adding acid sodium persulfate, which is beneficial to improve the activity of acid-producing bacteria, can promote the hydrolysis and acid production of sludge, and further improve the methane production efficiency of sludge. In addition, the added sodium persulfate can be activated by the hydrogen peroxide generated by calcium peroxide to generate sulfate radicals and form a double oxidation system, which can enhance the oxidizability of refractory organic matter. However, since the reaction is an exothermic reaction, the inoculated sludge needs to be heat exchanged first to maintain a suitable temperature, and stirring can promote the reaction, and ultrasonic can strengthen the influence of generated free radicals on sludge flocs, promote interaction, and further degrade the organic matter inside the sludge particles, so that the biogas production in the subsequent anaerobic digestion process is significantly increased.

[0014] Preferably, in step (1), the water content of the dewatered sludge is 70-80%.

[0015] Preferably, in step (1), the hydrolysis acidification reaction controls the temperature to be 33-36℃, the rotation speed to be 200-300rpm, and the residence time to be 10-20h.

[0016] As preferred, in step (1), the mass ratio of the added amount of calcium peroxide to the dewatered sludge is 0.5-0.6:1.

[0017] As preferred, in step (1), the stirring speed is 150-200 rpm for 10-20 min.

[0018] As preferred, in step (2), the moisture content of the pretreated sludge is adjusted to 80-90% by adding distilled water; and the temperature of the anaerobic digestion is 32-38℃.

[0019] As preferred, in step (2), the temperature of the inoculated sludge after heat exchange is controlled to 15-25℃.

[0020] As preferred, in step (2), the inoculated sludge is subjected to heat exchange with the dewatered sludge, and if the temperature of the inoculated sludge still does not reach the required temperature, the inoculated sludge is subjected to heat exchange with a cold medium.

[0021] The heat exchange of the inoculated sludge with the dewatered sludge can save energy, and the dewatered sludge after warming can better perform hydrolysis and acidification.

[0022] As preferred, in step (3), the added amount of sodium persulfate is 0.6-0.8% of the mass of the inoculated sludge.

[0023] As preferred, in step (3), after adding the sodium persulfate, an acidic substance is added to adjust the pH to 5.5-6.5; the acidic substance is one or more of acetic acid, oxalic acid, succinic acid, citric acid, malic acid and tartaric acid.

[0024] The addition of sodium persulfate can promote sludge lysis and hydrolysis and acid production, greatly improve the anaerobic acid production rate of sludge, and further improve the efficiency of sludge anaerobic digestion. The introduction of calcium ions in the system can also alleviate the impact of acid on the activity of methanogenic bacteria.

[0025] The acidic substance can not only adjust the pH, but also be an organic acid, thereby effectively improving the C / N ratio, enhancing the metabolic activity of microorganisms in the anaerobic digestion system, and also serving as a raw material for methane synthesis, which can improve the biogas yield and methane content of subsequent sludge anaerobic digestion.

[0026] As preferred, in step (3), the stirring speed is 150-200 rpm for 40-60 min; the ultrasonic frequency is 20-35 kHz, the power is 100-150 W, and the time is 20-30 min.

[0027] Preferably, in step (4), the moisture content of the mixed sludge is adjusted to 80-90% by adding distilled water, and the pH is adjusted to 6.75-7.25; the temperature of the anaerobic digestion is 32-38℃, and the time is 10-20 days.

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] (1) The dewatered sludge is pretreated by adding calcium peroxide, which slowly dissolves in water to generate hydrogen peroxide, oxygen and hydroxyl radicals, all of which have strong oxidizing properties and can oxidize and decompose the sludge, break down microbial cells, increase soluble COD, and improve the biodegradability of the sludge;

[0030] (2) After a period of anaerobic digestion, sodium persulfate is added, which can be activated by the hydrogen peroxide generated by calcium peroxide to generate sulfate radicals and form a dual oxidation system, which can enhance the oxidizing properties of the system on refractory organic matter. Ultrasound can enhance the influence of the generated free radicals on the sludge floc, promote interaction, and further degrade the organic matter inside the sludge particles, significantly increasing the biogas production during subsequent anaerobic digestion.

[0031] (3) Adjusting the pH to be acidic is beneficial to improving the activity of acid-producing bacteria, promoting sludge hydrolysis and acidification, and thus improving the methane production efficiency of the sludge. Moreover, the added acidic substance is organic acid, which can also be used as a raw material for methane synthesis, thereby increasing the biogas production and methane content during subsequent anaerobic digestion of the sludge. DETAILED DESCRIPTION

[0032] The technical solutions of the present application are illustrated by specific examples below, but the scope of protection of the present application is not limited thereto.

[0033] An anaerobic digestion method for sludge reduction includes the following steps:

[0034] (1) Calcium peroxide is added to the dewatered sludge for hydrolysis and acidification, and the mass ratio of the added calcium peroxide to the dewatered sludge is 0.5-0.6:1. The hydrolysis and acidification is controlled at a temperature of 33-36℃ and a rotation speed of 200-300 rpm, and the residence time is 10-20 h, to obtain pretreated sludge;

[0035] (2) The pretreated sludge is subjected to anaerobic digestion at a temperature of 32-38℃, and 24 h is taken as one cycle. When the sludge is fed for 3-5 cycles, the obtained inoculated sludge is subjected to heat exchange treatment, and the temperature of the inoculated sludge after treatment is controlled at 15-25℃;

[0036] (3) adding sodium persulfate in an amount of 0.6-0.8% of the mass of the inoculated sludge to the inoculated sludge, adding an acidic substance to adjust the pH to 5.5-6.5 after adding the sodium persulfate, then stirring at a rotation speed of 150-200 rpm for 40-60 min, and then ultrasonicating under conditions of a frequency of 20-35 kHz and a power of 100-150 W for 20-30 min to obtain mixed sludge;

[0037] (4) anaerobically digesting the mixed sludge, the temperature of the anaerobic digestion being 32-38℃ and the time being 10-20 days.

[0038] In a specific embodiment of the present application, the dewatered sludge has a water content of 70-80%.

[0039] In a specific embodiment of the present application, in step (2), the water content of the pretreated sludge is adjusted to 80-90% by adding distilled water.

[0040] In a specific embodiment of the present application, in step (3), the acidic substance is one or more of acetic acid, oxalic acid, succinic acid, citric acid, malic acid, and tartaric acid.

[0041] In a specific embodiment of the present application, in step (4), the water content of the mixed sludge is adjusted to 80-90% by adding distilled water, and the pH is adjusted to 6.75-7.25 (which can be adjusted by adding an alkaline substance, the alkaline substance being NaOH and / or KOH).

[0042] Example 1

[0043] (1) adding calcium peroxide to dewatered sludge (water content: 78%, organic matter content: 46% (mass fraction of organic matter in dry solid of the sludge)) to perform hydrolysis acidification reaction, the amount of calcium peroxide added being 0.5:1 by mass ratio of dewatered sludge, the control temperature of the hydrolysis acidification being 35±1℃, the rotation speed being 250 rpm, and the residence time being 15 h to obtain pretreated sludge.

[0044] (2) adjusting the water content of the pretreated sludge to 88% by adding distilled water, and anaerobically digesting the pretreated sludge at a temperature of 35±1℃, with a cycle of 24 h, and when 3 cycles have passed after the sludge is fed, performing heat exchange treatment of the obtained inoculated sludge with dewatered sludge and a cold medium, and controlling the temperature of the inoculated sludge after the treatment to be 17℃.

[0045] (3) adding sodium persulfate in an amount of 0.8% of the mass of the inoculated sludge to the inoculated sludge, adding an acidic substance (acetic acid) to adjust the pH to 6.0-6.5 after adding the sodium persulfate, then stirring at a rotation speed of 150 rpm for 60 min, and then ultrasonicating under conditions of a frequency of 20 kHz and a power of 100 W for 20 min to obtain mixed sludge.

[0046] (4) Adjust the moisture content of the mixed sludge to 89% by adding distilled water, and add an alkaline substance (KOH) to adjust the pH to 6.75-7.25. Perform anaerobic digestion of the mixed sludge, with the temperature of the anaerobic digestion being 35±1℃, and the residence time being 20 days.

[0047] Example 2

[0048] (1) Add calcium peroxide to the dewatered sludge (moisture content of 78%, organic matter content of 46% (referring to the mass fraction of organic matter in the dry solid of the sludge)) to perform a hydrolysis acidification reaction, with the mass ratio of the added calcium peroxide to the dewatered sludge being 0.55:1. The control temperature of the hydrolysis acidification is 35±1℃, the rotation speed is 250 rpm, and the residence time is 16 h, to obtain pretreated sludge.

[0049] (2) Adjust the moisture content of the pretreated sludge to 88% by adding distilled water, and perform anaerobic digestion of the pretreated sludge at a temperature of 35±1℃. Take the obtained inoculated sludge and the dewatered sludge to perform heat exchange treatment when 3 cycles have passed since the sludge was fed, and control the temperature of the inoculated sludge after the treatment to be 20℃.

[0050] (3) Add sodium persulfate to the inoculated sludge, with the mass of the added sodium persulfate being 0.7% of the mass of the inoculated sludge. After adding the sodium persulfate, add an acidic substance (acetic acid) to adjust the pH to 5.5-6.0, and then stir at a rotation speed of 200 rpm for 50 min, and then perform ultrasonic treatment for 20 min under the condition of a frequency of 20 kHz and a power of 100 W, to obtain mixed sludge.

[0051] (4) Adjust the moisture content of the mixed sludge to 89% by adding distilled water, and add an alkaline substance (KOH) to adjust the pH to 6.75-7.25. Perform anaerobic digestion of the mixed sludge, with the temperature of the anaerobic digestion being 35±1℃, and the residence time being 15 days.

[0052] Example 3

[0053] (1) Add calcium peroxide to the dewatered sludge (moisture content of 78%, organic matter content of 46% (referring to the mass fraction of organic matter in the dry solid of the sludge)) to perform a hydrolysis acidification reaction, with the mass ratio of the added calcium peroxide to the dewatered sludge being 0.6:1. The control temperature of the hydrolysis acidification is 35±1℃, the rotation speed is 250 rpm, and the residence time is 18 h, to obtain pretreated sludge.

[0054] (2) The moisture content of the pretreated sludge was adjusted to 88% by adding distilled water, and the pretreated sludge was subjected to anaerobic digestion at a temperature of 35±1℃, with 24h as a cycle. When 4 cycles after the sludge was fed, the obtained inoculated sludge was subjected to heat exchange treatment with the dewatered sludge, and the temperature of the inoculated sludge after the treatment was controlled to be 20℃.

[0055] (3) Sodium persulfate was added to the inoculated sludge at a mass ratio of 0.6% of the inoculated sludge, and then an acidic substance (acetic acid) was added to adjust the pH to 5.5-6.0. After that, the mixture was stirred at a speed of 150 rpm for 50 min, and then was subjected to ultrasonic treatment under the conditions of a frequency of 20 kHz and a power of 100 W for 20 min, to obtain the mixed sludge.

[0056] (4) The moisture content of the mixed sludge was adjusted to 89% by adding distilled water, and an alkaline substance (KOH) was added to adjust the pH to 6.75-7.25. The mixed sludge was subjected to anaerobic digestion at a temperature of 35±1℃, with a residence time of 15 days.

[0057] Example 4

[0058] (1) Calcium peroxide was added to the dewatered sludge (moisture content: 78%, organic matter content: 46% (mass fraction of organic matter in the dry solid of the sludge)) to perform hydrolysis acidification reaction, and the mass ratio of the added calcium peroxide to the dewatered sludge was 0.6:1. The hydrolysis acidification was controlled at a temperature of 36±1℃ and a speed of 300 rpm, with a residence time of 15h, to obtain pretreated sludge.

[0059] (2) The moisture content of the pretreated sludge was adjusted to 88% by adding distilled water, and the pretreated sludge was subjected to anaerobic digestion at a temperature of 35±1℃, with 24h as a cycle. When 4 cycles after the sludge was fed, the obtained inoculated sludge was subjected to heat exchange treatment with the dewatered sludge, and the temperature of the inoculated sludge after the treatment was controlled to be 20℃.

[0060] (3) Sodium persulfate was added to the inoculated sludge at a mass ratio of 0.7% of the inoculated sludge, and then an acidic substance (acetic acid) was added to adjust the pH to 6.0-6.5. After that, the mixture was stirred at a speed of 150 rpm for 50 min, and then was subjected to ultrasonic treatment under the conditions of a frequency of 25 kHz and a power of 150 W for 20 min, to obtain the mixed sludge.

[0061] (4) The moisture content of the mixed sludge was adjusted to 89% by adding distilled water, and an alkaline substance (KOH) was added to adjust the pH to 6.75-7.25. The mixed sludge was subjected to anaerobic digestion at a temperature of 35±1℃, with a residence time of 15 days.

[0062] Comparative Example 1

[0063] The difference from Example 3 is that sodium persulfate is not added.

[0064] (1) Calcium peroxide was added to the dewatered sludge (moisture content: 78%, organic matter content: 46% (mass fraction of organic matter in dry solid of sludge)) to perform hydrolysis acidification reaction, the mass ratio of the added amount of calcium peroxide to the dewatered sludge was 0.6:1, the control temperature of the hydrolysis acidification was 35±1°C, the rotation speed was 250 rpm, and the residence time was 18 h to obtain pretreated sludge.

[0065] (2) The moisture content of the pretreated sludge was adjusted to 89% by adding distilled water, and an acidic substance (acetic acid) was added to adjust the pH to 6.75-7.25, and the pretreated sludge was subjected to anaerobic digestion, the temperature of the anaerobic digestion was 35±1°C, and the residence time was 20 days.

[0066] Comparative Example 2

[0067] The difference from Example 3 is that sodium persulfate is added in step (1).

[0068] (1) Calcium peroxide and sodium persulfate were added to the dewatered sludge (moisture content: 78%, organic matter content: 46% (mass fraction of organic matter in dry solid of sludge)) to perform hydrolysis acidification reaction, the mass ratio of the added amount of calcium peroxide to the dewatered sludge was 0.6:1, the mass ratio of the added amount of sodium persulfate to the dewatered sludge was 0.6%, the control temperature of the hydrolysis acidification was 35±1°C, the rotation speed was 250 rpm, and the residence time was 18 h to obtain pretreated sludge.

[0069] (2) The moisture content of the pretreated sludge was adjusted to 89% by adding distilled water, and an acidic substance (acetic acid) was added to adjust the pH to 6.75-7.25, and the pretreated sludge was subjected to anaerobic digestion, the temperature of the anaerobic digestion was 35±1°C, and the residence time was 20 days.

[0070] Comparative Example 3

[0071] The difference from Example 3 is that the timing of adding sodium persulfate is different.

[0072] (1) Calcium peroxide was added to the dewatered sludge (moisture content: 78%, organic matter content: 46% (mass fraction of organic matter in dry solid of sludge)) to perform hydrolysis acidification reaction, the mass ratio of the added amount of calcium peroxide to the dewatered sludge was 0.6:1, the control temperature of the hydrolysis acidification was 35±1°C, the rotation speed was 250 rpm, and the residence time was 18 h to obtain pretreated sludge.

[0073] (2) The moisture content of the pretreated sludge was adjusted to 88% by adding distilled water, and the pretreated sludge was subjected to anaerobic digestion at a temperature of 35±1℃, with 24h as a cycle. When 3 cycles had elapsed after the sludge was fed, the obtained inoculated sludge was subjected to heat exchange treatment with the dewatered sludge, and the temperature of the inoculated sludge after the treatment was controlled to 20℃.

[0074] (3) Sodium persulfate was added to the inoculated sludge at a rate of 0.6% of the mass of the inoculated sludge, and an acidic substance (acetic acid) was added to adjust the pH to 5.5-6.0 after the addition of the sodium persulfate. Then, the mixture was stirred at a speed of 150 rpm for 50 min, and was subjected to ultrasonic treatment for 20 min under the conditions of a frequency of 20 kHz and a power of 100 W, to obtain a mixed sludge.

[0075] (4) The moisture content of the mixed sludge was adjusted to 89% by adding distilled water, and an alkaline substance (KOH) was added to adjust the pH to 6.75-7.25. The mixed sludge was subjected to anaerobic digestion at a temperature of 35±1℃, with a residence time of 15 days.

[0076] Comparative Example 4

[0077] The difference from Example 3 is that the sodium persulfate was added in excess.

[0078] (1) Calcium peroxide was added to the dewatered sludge (moisture content: 78%, organic matter content: 46% (mass fraction of organic matter in the dry solid of the sludge)) to perform hydrolytic acidification, with the addition amount of the calcium peroxide being 0.6:1 relative to the mass of the dewatered sludge. The hydrolytic acidification was controlled at a temperature of 35±1℃ and a rotation speed of 250 rpm, with a residence time of 18h, to obtain pretreated sludge.

[0079] (2) The moisture content of the pretreated sludge was adjusted to 88% by adding distilled water, and the pretreated sludge was subjected to anaerobic digestion at a temperature of 35±1℃, with 24h as a cycle. When 3 cycles had elapsed after the sludge was fed, the obtained inoculated sludge was subjected to heat exchange treatment with the dewatered sludge, and the temperature of the inoculated sludge after the treatment was controlled to 20℃.

[0080] (3) Sodium persulfate was added to the inoculated sludge at a rate of 1.0% of the mass of the inoculated sludge, and an acidic substance (acetic acid) was added to adjust the pH to 5.5-6.0 after the addition of the sodium persulfate. Then, the mixture was stirred at a speed of 150 rpm for 80 min, and was subjected to ultrasonic treatment for 20 min under the conditions of a frequency of 20 kHz and a power of 100 W, to obtain a mixed sludge.

[0081] (4) The moisture content of the mixed sludge was adjusted to 89% by adding distilled water, and an alkaline substance (KOH) was added to adjust the pH to 6.75-7.25. The mixed sludge was subjected to anaerobic digestion at a temperature of 35±1℃, with a residence time of 15 days.

[0082] Comparative Example 5

[0083] The difference from Example 3 is that no acid substance is added after the addition of sodium persulfate.

[0084] (1) Calcium peroxide was added to the dewatered sludge (water content of 78%, organic matter content of 46% (meaning that the mass fraction of organic matter in the dry solid of the sludge)) to perform a hydrolysis acidification reaction, the mass ratio of the added amount of calcium peroxide to the dewatered sludge was 0.6:1, the control temperature of the hydrolysis acidification was 35±1°C, the rotation speed was 250 rpm, and the residence time was 18 h, to obtain pretreated sludge.

[0085] (2) The water content of the pretreated sludge was adjusted to 88% by adding distilled water, and the pretreated sludge was subjected to anaerobic digestion at a temperature of 35±1°C, with 24 h as one cycle. When the sludge was fed for 3 cycles, the obtained inoculated sludge was subjected to heat exchange treatment with the dewatered sludge, and the temperature of the inoculated sludge after the treatment was controlled to be 20°C.

[0086] (3) Sodium persulfate was added to the inoculated sludge in an amount of 0.6% of the mass of the inoculated sludge, followed by stirring at a rotation speed of 150 rpm for 50 min, and then ultrasonic treatment for 20 min under the conditions of a frequency of 20 kHz and a power of 100 W, to obtain mixed sludge.

[0087] (4) The water content of the mixed sludge was adjusted to 89% by adding distilled water, and an alkaline substance (KOH) was added to adjust the pH to 6.75-7.25, and the mixed sludge was subjected to anaerobic digestion, with the temperature of the anaerobic digestion being 35±1°C and the residence time being 15 days.

[0088] Comparative Example 6

[0089] The difference from Example 3 is that the amount of calcium peroxide added is too small and the residence time of the hydrolysis acidification is too short.

[0090] (1) Calcium peroxide was added to the dewatered sludge (water content of 78%, organic matter content of 46% (meaning that the mass fraction of organic matter in the dry solid of the sludge)) to perform a hydrolysis acidification reaction, the mass ratio of the added amount of calcium peroxide to the dewatered sludge was 0.3:1, the control temperature of the hydrolysis acidification was 35±1°C, the rotation speed was 250 rpm, and the residence time was 5 h, to obtain pretreated sludge.

[0091] (2) The water content of the pretreated sludge was adjusted to 88% by adding distilled water, and the pretreated sludge was subjected to anaerobic digestion at a temperature of 35±1°C, with 24 h as one cycle. When the sludge was fed for 3 cycles, the obtained inoculated sludge was subjected to heat exchange treatment with the dewatered sludge, and the temperature of the inoculated sludge after the treatment was controlled to be 20°C.

[0092] (3) Add sodium persulfate in an amount of 0.6% of the inoculated sludge to the inoculated sludge, add an acidic substance (acetic acid) to adjust the pH to 5.5-6.0 after adding the sodium persulfate, then stir at a rotation speed of 150 rpm for 50 min, and then perform ultrasonic treatment at a frequency of 20 kHz and a power of 100 W for 20 min to obtain mixed sludge.

[0093] (4) Adjust the water content of the mixed sludge to 89% by adding distilled water, and add an alkaline substance (KOH) to adjust the pH to 6.75-7.25, and then perform anaerobic digestion of the mixed sludge, with the temperature of the anaerobic digestion being 35±1℃ and the residence time being 15 days.

[0094] Table 1

[0095] Methane production (ml / g VS) Organic matter degradation (%) Example 1 467.8 46.3 Example 2 459.3 44.5 Example 3 431.4 40.8 Example 4 448.2 43.6 Comparative Example 1 264.1 24.7 Comparative Example 2 315.9 30.2 Comparative Example 3 362.3 33.8 Comparative Example 4 398.7 37.0 Comparative Example 5 376.5 35.9 Comparative Example 6 365.8 34.2

[0096] Note: VS is volatile solids; the organic matter degradation rate is the ratio of the mass of organic matter in the sludge after treatment to the mass of organic matter in the sludge before treatment.

[0097] As shown in Table 1, the present application performs pretreatment on the dewatered sludge by adding calcium peroxide, which slowly dissolves in water to generate hydrogen peroxide, oxygen and hydroxyl radicals, all of which have strong oxidizing properties and can oxidize and decompose the sludge, break down microbial cells, increase soluble COD, and improve the biodegradability of the sludge. However, the process of releasing hydrogen peroxide from calcium peroxide is relatively slow, which will lead to a decrease in the efficiency of sludge pretreatment, and pretreatment by only adding calcium peroxide cannot solve the problem of a gradual decrease in the degradation rate over time during anaerobic digestion, and the organic matter remaining in dead microorganisms and anaerobic sludge flocs is still difficult to utilize, so the methane production and the organic matter degradation rate of Comparative Example 1 relative to Example 3 both decrease significantly.

[0098] Therefore, after anaerobic digestion for a period of time, by adding sodium persulfate and process improvement, the sodium persulfate can be activated by hydrogen peroxide generated by calcium peroxide, to generate sulfate radicals, and form a dual oxidation system, which can enhance the oxidation of refractory organic matter, and the added acidic substances can also be used as raw materials for methane synthesis, which can improve the biogas yield and methane content of subsequent sludge anaerobic digestion. In addition, the effects of stirring and ultrasonic waves can further degrade the organic matter inside the sludge particles, and the biogas production in the subsequent anaerobic digestion process is significantly increased. The comparative example 2 can improve the pretreatment efficiency of the sludge by adding sodium persulfate in the pretreatment process, but it cannot solve the problem that the organic matter remaining in the dead microorganisms and anaerobic sludge flocs is still difficult to utilize during the anaerobic digestion process. The comparative example 3 adds sodium persulfate too early in the anaerobic digestion stage, and since the release rate of hydrogen peroxide by calcium peroxide is relatively slow, it needs sufficient time for hydrogen peroxide to exert an oxidative cracking effect on microbial cells, and after a period of anaerobic digestion, the organic matter is gradually consumed. At this time, the addition of sodium persulfate can exert a better oxidative cracking effect on the refractory organic matter and sludge flocculation, and thus the methane production will be affected.

[0099] The comparative examples 3-4 show that the addition amount of sodium persulfate and acidic substances will affect the metabolic activity of microorganisms, and excessive sodium persulfate will be detrimental to the survival of microorganisms, and the acidic substances can also be used as raw materials for methane synthesis, and the absence of acidic substances will also lead to a decrease in methane production. The comparative examples 5-6 show that the addition amount of calcium peroxide and the hydrolysis acidification time will affect the subsequent anaerobic digestion process, since the release of hydrogen peroxide by calcium peroxide is relatively slow, and the addition of too little calcium peroxide and too short hydrolysis acidification time will result in less hydrogen peroxide generated by calcium peroxide, poor pretreatment effect on the sludge, and the inability to form a good dual oxidation system with the subsequently added sodium persulfate, leading to a decrease in methane production.

[0100] The above are only preferred embodiments of the present application, and do not limit the patent scope of the present application, and any equivalent structure or equivalent process transformation made by the present application specification, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. An anaerobic digestion method for sludge reduction, characterized by, The method comprises the following steps: (1) adding calcium peroxide into the dewatered sludge to perform a hydrolytic acidification reaction, the mass ratio of the added calcium peroxide to the dewatered sludge being 0.5-0.6:1, to obtain pretreated sludge; (2) performing anaerobic digestion on the pretreated sludge, taking 24 hours as one cycle, and when 3-5 cycles after feeding sludge, performing heat exchange treatment on the obtained inoculated sludge; (3) adding sodium persulfate into the inoculated sludge, the added amount of the sodium persulfate being 0.6-0.8% of the mass of the inoculated sludge, adding an acidic substance to adjust the pH to 5.5-6.5 after adding the sodium persulfate, the acidic substance being an organic acid, stirring first and then ultrasonicating, to obtain mixed sludge; (4) performing anaerobic digestion on the mixed sludge.

2. The sludge-reducing anaerobic digestion method according to claim 1, characterized by, In step (1), the dewatered sludge has a water content of 70-80%.

3. The sludge-reducing anaerobic digestion method according to claim 1, characterized by, In step (1), the hydrolytic acidification reaction is controlled at a temperature of 33-36℃, a rotation speed of 200-300 rpm, and a residence time of 10-20 hours.

4. The sludge-reducing anaerobic digestion method according to claim 1, characterized by, In step (2), the water content of the pretreated sludge is adjusted to 80-90% by adding distilled water; and the anaerobic digestion is performed at a temperature of 32-38℃.

5. The sludge-reducing anaerobic digestion method according to claim 1 or 4, characterized by, In step (2), the temperature of the inoculated sludge after heat exchange is controlled to be 15-25℃.

6. The sludge-reducing anaerobic digestion method according to claim 1, characterized by, In step (3), the acidic substance is one or more of acetic acid, oxalic acid, succinic acid, citric acid, malic acid and tartaric acid.

7. The sludge-reducing anaerobic digestion method according to claim 1, characterized by, In step (3), the stirring is performed at a rotation speed of 150-200 rpm for 40-60 minutes; and the ultrasonicating is performed at a frequency of 20-35 kHz and a power of 100-150 W for 20-30 minutes.

8. The sludge-reducing anaerobic digestion method according to claim 1, characterized by, In step (4), the water content of the mixed sludge is adjusted to 80-90% by adding distilled water, and the pH is adjusted to 6.75-7.25; and the anaerobic digestion is performed at a temperature of 32-38℃ for 10-20 days.

9. The sludge-reducing anaerobic digestion method according to claim 8, characterized by, In step (4), the pH of the mixed sludge is adjusted to 6.75-7.25 by adding an alkaline substance.

10. The sludge-reducing anaerobic digestion method according to claim 9, characterized by, In step (4), the alkaline substance is NaOH and / or KOH.