Anaerobic digestion method for sludge reduction

Abstract

The invention relates to the technical field of sludge anaerobic digestion, and discloses a sludge reduction anaerobic digestion method, which comprises: (1) adding calcium peroxide into dewatered sludge, and carrying out a hydrolytic acidification reaction to obtain pretreated sludge; (2) carrying out anaerobic digestion on the pretreated sludge, taking 24 hours as a cycle, and carrying out heat exchange treatment on the obtained inoculated sludge 3-5 cycles after sludge feeding; (3) adding sodium persulfate into the inoculated sludge, stirring and then carrying out ultrasonic treatment to obtain mixed sludge; and (4) carrying out anaerobic digestion on the mixed sludge. According to the invention, calcium peroxide is added to pretreat dewatered sludge, and sodium persulfate is added after anaerobic digestion is carried out for a period of time, so that the oxidability of refractory organic matters can be enhanced, the influence of generated free radicals on sludge floccules is enhanced, interaction is promoted, and the treatment effect is improved. Organic matters in the sludge particles are further degraded, and the biogas yield is obviously increased in the subsequent anaerobic digestion process.

Description

Technical Field

[0001] The invention relates to the technical field of anaerobic digestion of sludge, in particular to an anaerobic digestion method for reducing sludge. Background Art

[0002] Anaerobic digestion mainly involves the degradation of organic matter by facultative anaerobes and obligate anaerobes under anaerobic conditions, and the conversion of organic matter into carbon dioxide and methane. Anaerobic digestion can directly treat wet sludge, and the treatment efficiency is relatively high. In this process, harmful substances in the sludge are decomposed, and the easily corruptible and smelly substances in the sludge are degraded and converted into low-molecular organic matter. The total amount of sludge is reduced and energy gases such as hydrogen and methane are obtained. At the same time, pathogens can be reduced, odors can be eliminated, and the sludge can be reduced, stabilized and harmless, and the sludge can be utilized as a resource while achieving sludge stabilization.

[0003] Although anaerobic sludge digestion technology has been applied to a certain extent, the overall operating efficiency is still low. The degradation rate of sludge organic matter in many anaerobic digestion facilities is only 30-35%, and the amount of biogas produced 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, resulting in generally low indicators such as the stability of anaerobic digestion equipment and biogas production rate. However, with the continuous advancement of technology and the accumulation of experience, China has begun to use alkaline hydrolysis, heat treatment, ultrasonic treatment, microwave treatment and other methods to pre-treat sludge in order to improve the sludge hydrolysis rate and anaerobic digestion performance.

[0004] However, most sludge pretreatment methods have high energy consumption and are difficult to promote on a large scale. Although the use of biochar, activated carbon, olivine, quicklime and other methods can significantly increase the methane content in biogas, the release of bacterial intracellular organic matter in the sludge is relatively slow, and the anaerobic digestion efficiency is still low. Therefore, if an anaerobic digestion method can be developed that can both improve the anaerobic digestion efficiency of sludge and achieve sludge reduction, it will have important practical value for promoting the development of anaerobic digestion technology. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides an anaerobic digestion method for sludge reduction, by adding calcium peroxide to pre-treat the dewatered sludge to improve the biodegradability of the sludge, and after a period of anaerobic digestion, by adding sodium persulfate to form a dual oxidation system, the oxidizability of difficult-to-degrade organic matter can be enhanced, the influence on sludge flocs can be strengthened, the organic matter inside the sludge particles can be further degraded, and the biogas production in the subsequent anaerobic digestion process is significantly increased, thereby achieving sludge reduction and significantly improving the anaerobic digestion efficiency.

[0006] The purpose of the present invention is achieved through the following technical solutions: The present invention provides an anaerobic digestion method for sludge reduction, comprising the following steps: (1) adding calcium peroxide to dewatered sludge to perform a hydrolysis and acidification reaction to obtain pretreated sludge; (2) subjecting the pretreated sludge to anaerobic digestion with a cycle of 24 hours, and subjecting the obtained inoculated sludge to heat exchange treatment after 3-5 cycles; (3) adding sodium persulfate to the inoculated sludge, stirring first and then ultrasonicating to obtain mixed sludge; (4) Anaerobic digestion of the mixed sludge.

[0007] The present invention pre-treats the dewatered sludge by adding calcium peroxide. Calcium peroxide will slowly dissolve in water to generate hydrogen peroxide, oxygen and hydroxyl radicals, all of which have strong oxidizing properties and can oxidatively decompose the sludge, crack the microbial cells, increase the soluble COD (SCOD), and improve the biodegradability of the sludge. However, since the process of calcium peroxide releasing hydrogen peroxide is relatively slow, the efficiency of sludge pretreatment will be reduced. In addition, during the anaerobic digestion process, as time goes by, the soluble and easily degradable organic matter is gradually consumed, and some of the organic matter remaining in the dead microorganisms and anaerobic sludge flocs is difficult to be utilized, and the degradation rate begins to decrease, that is, the gas production per unit time begins to decrease, which will lead to a lower final methane gas production.

[0008] Therefore, after the anaerobic digestion is carried out for a period of time, the present invention adjusts the pH by adding acidic sodium persulfate, so that it is conducive to improving the activity of acid-producing bacteria, which can promote the hydrolysis and acidification of sludge, and then 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 dual oxidation system, which can enhance the oxidizability of difficult-to-degrade 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. Ultrasound can promote the generated free radicals to strengthen the effect on the sludge flocs, promote interaction, and further degrade the organic matter inside the sludge particles. In the subsequent anaerobic digestion process, the biogas production is significantly recovered.

[0009] Preferably, in step (1), the moisture content of the dewatered sludge is 70-80%.

[0010] Preferably, in step (1), the hydrolysis and acidification reaction is controlled at a temperature of 33-36°C, a rotation speed of 200-300 rpm, and a residence time of 10-20 h.

[0011] Preferably, in step (1), the mass ratio of the added amount of calcium peroxide to the dewatered sludge is 0.5-0.6:1.

[0012] Preferably, in step (1), the stirring speed is 150-200 rpm and the time is 10-20 min.

[0013] Preferably, in step (2), the water content of the pretreated sludge is adjusted to 80-90% by adding distilled water; and the temperature of the anaerobic digestion is 32-38°C.

[0014] Preferably, in step (2), the temperature of the inoculated sludge after heat exchange is controlled to be 15-25°C.

[0015] Preferably, in step (2), heat exchange is performed between the inoculated sludge and the dewatered sludge. If the temperature of the inoculated sludge still does not reach the required temperature, the inoculated sludge is then heat exchanged with the cold medium.

[0016] Heat exchange between inoculated sludge and dewatered sludge can save energy, and the dewatered sludge after heating can be better hydrolyzed and acidified.

[0017] Preferably, in step (3), the amount of sodium persulfate added is 0.6-0.8% of the mass of the inoculated sludge.

[0018] Preferably, in step (3), after adding 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.

[0019] By adding sodium persulfate, sludge lysis and hydrolysis acid production are promoted at the same time, which greatly increases the anaerobic acid production rate of sludge, and thus improves the anaerobic digestion efficiency of sludge. The introduction of calcium ions into the system can also alleviate the effect of acid on the activity of methanogens.

[0020] Acidic substances can not only adjust pH, but also, as they are organic acids, they can effectively increase the C:N ratio and enhance the metabolic activity of microorganisms in the anaerobic digestion system. They can also be used as raw materials for methane synthesis, thereby increasing the amount of biogas and methane content in subsequent sludge anaerobic digestion.

[0021] Preferably, in step (3), the stirring speed is 150-200 rpm, the time is 40-60 min; the ultrasonic frequency is 20-35 kHz, the power is 100-150 W, and the time is 20-30 min.

[0022] Preferably, 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; the temperature of the anaerobic digestion is 32-38°C, and the time is 10-20 days.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) Pretreatment of 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 sludge, break down microbial cells, increase soluble COD, and improve the biodegradability of sludge; (2) After a period of anaerobic digestion, sodium persulfate is added, which can be activated by hydrogen peroxide generated by calcium peroxide to generate sulfate free radicals and form a dual oxidation system, which can enhance the oxidizability of difficult-to-degrade organic matter. Ultrasound can promote the effect of the generated free radicals on sludge flocs, promote interaction, and further degrade the organic matter inside the sludge particles. In the subsequent anaerobic digestion process, the biogas production is significantly restored.

[0024] (3) By adjusting the pH to an acidic state, the activity of acid-producing bacteria can be enhanced, which can promote the hydrolysis and acid production of sludge, thereby improving the methane production efficiency of the sludge. Moreover, the added acidic substance is an organic acid, which can also be used as a raw material for methane synthesis, thereby increasing the amount of biogas and methane content in the subsequent anaerobic digestion of sludge. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is described below with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0026] An anaerobic digestion method for sludge reduction comprises the following steps: (1) adding calcium peroxide to the dewatered sludge for hydrolysis and acidification reaction, wherein the mass ratio of the added amount of calcium peroxide to the dewatered sludge is 0.5-0.6:1, the controlled temperature of the hydrolysis and acidification is 33-36°C, the rotation speed is 200-300 rpm, and the residence time is 10-20 hours to obtain pretreated sludge; (2) The pretreated sludge is subjected to anaerobic digestion at a temperature of 32-38°C, with a cycle of 24 hours. After 3-5 cycles of sludge entry, the obtained seeding sludge is subjected to heat exchange treatment, and the temperature of the seeding sludge after treatment is controlled to be 15-25°C; (3) adding sodium persulfate in an amount of 0.6-0.8% by mass of the inoculum sludge to the inoculum sludge, and then adding an acidic substance to adjust the pH to 5.5-6.5, stirring at a speed of 150-200 rpm for 40-60 min, and then ultrasonicating at a frequency of 20-35 kHz and a power of 100-150 W for 20-30 min to obtain mixed sludge; (4) The mixed sludge is subjected to anaerobic digestion at a temperature of 32-38° C. for 10-20 days.

[0027] In a specific embodiment of the present invention, the moisture content of the dewatered sludge is 70-80%.

[0028] In a specific embodiment of the present invention, in step (2), the water content of the pretreated sludge is adjusted to 80-90% by adding distilled water.

[0029] In a specific embodiment of the present invention, in step (3), the acidic substance is one or more of acetic acid, oxalic acid, succinic acid, citric acid, malic acid and tartaric acid.

[0030] In a specific embodiment of the present invention, 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 (it can be adjusted by adding alkaline substances, the alkaline substances are NaOH and / or KOH).

[0031] Example 1 (1) Calcium peroxide is added to dewatered sludge (water content of 78%, organic matter content of 46% (referring to the mass fraction of organic matter in sludge dry solids)) for hydrolysis and acidification reaction, the mass ratio of calcium peroxide added to dewatered sludge is 0.5:1, the control temperature of hydrolysis and acidification is 35±1°C, the rotation speed is 250rpm, and the residence time is 15h to obtain pretreated sludge.

[0032] (2) The water content of the pretreated sludge was adjusted to 88% by adding distilled water, and the pretreated sludge was anaerobically digested at a temperature of 35±1°C, with a cycle of 24 hours. After 3 cycles of sludge entry, the obtained inoculum sludge was heat exchanged with the dewatered sludge and the cold medium, and the temperature of the inoculum sludge after treatment was controlled to 17°C.

[0033] (3) Sodium persulfate in an amount of 0.8% by mass of the inoculum sludge was added to the inoculum sludge, and then an acidic substance (acetic acid) was added to adjust the pH to 6.0-6.5, followed by stirring at a speed of 150 rpm for 60 min, and then ultrasonicating at a frequency of 20 kHz and a power of 100 W for 20 min to obtain mixed sludge.

[0034] (4) The water content of the mixed sludge was adjusted to 89% by adding distilled water, and the pH was adjusted to 6.75-7.25 by adding alkaline substances (KOH), and the mixed sludge was anaerobically digested at a temperature of 35±1°C and a residence time of 20 days.

[0035] Example 2 (1) Calcium peroxide was added to dewatered sludge (water content of 78%, organic matter content of 46% (referring to the mass fraction of organic matter in sludge dry solids)) for hydrolysis and acidification reaction, the mass ratio of calcium peroxide added to dewatered sludge was 0.55:1, the control temperature of hydrolysis and acidification was 35±1°C, the rotation speed was 250rpm, and the residence time was 16h to obtain pretreated sludge.

[0036] (2) The water content of the pretreated sludge was adjusted to 88% by adding distilled water, and the pretreated sludge was anaerobically digested at a temperature of 35±1°C, with a cycle of 24 hours. After 3 cycles of sludge entry, the obtained inoculum sludge was heat exchanged with the dewatered sludge, and the temperature of the inoculum sludge after treatment was controlled to 20°C.

[0037] (3) Sodium persulfate in an amount of 0.7% by mass of the inoculum sludge was added to the inoculum sludge, and then an acidic substance (acetic acid) was added to adjust the pH to 5.5-6.0, followed by stirring at a speed of 200 rpm for 50 min, and then ultrasonicating at a frequency of 20 kHz and a power of 100 W for 20 min to obtain mixed sludge.

[0038] (4) The water content of the mixed sludge was adjusted to 89% by adding distilled water, and the pH was adjusted to 6.75-7.25 by adding alkaline substances (KOH), and the mixed sludge was anaerobically digested at a temperature of 35±1°C and a residence time of 15 days.

[0039] Example 3 (1) Calcium peroxide is added to dewatered sludge (water content of 78%, organic matter content of 46% (referring to the mass fraction of organic matter in sludge dry solids)) for hydrolysis and acidification reaction, the mass ratio of calcium peroxide added to dewatered sludge is 0.6:1, the control temperature of hydrolysis and acidification is 35±1°C, the rotation speed is 250rpm, and the residence time is 18h to obtain pretreated sludge.

[0040] (2) The water content of the pretreated sludge was adjusted to 88% by adding distilled water, and the pretreated sludge was anaerobically digested at a temperature of 35±1°C, with a cycle of 24 hours. After 3 cycles of sludge entry, the obtained inoculum sludge was heat exchanged with the dewatered sludge, and the temperature of the inoculum sludge after treatment was controlled to 20°C.

[0041] (3) Sodium persulfate in an amount of 0.6% by mass of the inoculum sludge was added to the inoculum sludge, and then an acidic substance (acetic acid) was added to adjust the pH to 5.5-6.0, followed by stirring at a speed of 150 rpm for 50 min, and then ultrasonicating at a frequency of 20 kHz and a power of 100 W for 20 min to obtain mixed sludge.

[0042] (4) The water content of the mixed sludge was adjusted to 89% by adding distilled water, and the pH was adjusted to 6.75-7.25 by adding alkaline substances (KOH), and the mixed sludge was anaerobically digested at a temperature of 35±1°C and a residence time of 15 days.

[0043] Example 4 (1) Calcium peroxide was added to dewatered sludge (water content of 78%, organic matter content of 46% (referring to the mass fraction of organic matter in sludge dry solids)) for hydrolysis and acidification reaction, the mass ratio of calcium peroxide added to dewatered sludge was 0.6:1, the control temperature of hydrolysis and acidification was 36±1°C, the rotation speed was 300rpm, and the residence time was 15h to obtain pretreated sludge.

[0044] (2) The water content of the pretreated sludge was adjusted to 88% by adding distilled water, and the pretreated sludge was anaerobically digested at a temperature of 35±1°C, with a cycle of 24 hours. After 4 cycles of sludge entry, the obtained inoculum sludge was heat exchanged with the dewatered sludge, and the temperature of the inoculum sludge after treatment was controlled to 20°C.

[0045] (3) Sodium persulfate in an amount of 0.7% by mass of the inoculum sludge was added to the inoculum sludge, and then an acidic substance (acetic acid) was added to adjust the pH to 6.0-6.5, followed by stirring at a speed of 150 rpm for 50 min, and then ultrasonicating at a frequency of 25 kHz and a power of 150 W for 20 min to obtain mixed sludge.

[0046] (4) The water content of the mixed sludge was adjusted to 89% by adding distilled water, and the pH was adjusted to 6.75-7.25 by adding alkaline substances (KOH), and the mixed sludge was anaerobically digested at a temperature of 35±1°C and a residence time of 15 days.

[0047] Comparative Example 1 The difference from Example 3 is that no sodium persulfate is added.

[0048] (1) Calcium peroxide is added to dewatered sludge (water content of 78%, organic matter content of 46% (referring to the mass fraction of organic matter in sludge dry solids)) for hydrolysis and acidification reaction, the mass ratio of calcium peroxide added to dewatered sludge is 0.6:1, the control temperature of hydrolysis and acidification is 35±1°C, the rotation speed is 250rpm, and the residence time is 18h to obtain pretreated sludge.

[0049] (2) The water content of the pretreated sludge was adjusted to 89% by adding distilled water, and the pH was adjusted to 6.75-7.25 by adding acidic substances (acetic acid). The pretreated sludge was anaerobically digested at a temperature of 35±1°C and a retention time of 20 days.

[0050] Comparative Example 2 The difference from Example 3 is that sodium persulfate is added in step (1).

[0051] (1) Calcium peroxide and sodium persulfate were added to dewatered sludge (water content of 78%, organic matter content of 46% (referring to the mass fraction of organic matter in sludge dry solids)) for hydrolysis and acidification reaction, the mass ratio of calcium peroxide added to dewatered sludge was 0.6:1, the amount of sodium persulfate added was 0.6% of the mass of dewatered sludge, the hydrolysis and acidification control temperature was 35±1°C, the rotation speed was 250rpm, and the residence time was 18h to obtain pretreated sludge.

[0052] (2) The water content of the pretreated sludge was adjusted to 89% by adding distilled water, and the pH was adjusted to 6.75-7.25 by adding acidic substances (acetic acid). The pretreated sludge was anaerobically digested at a temperature of 35±1°C and a retention time of 20 days.

[0053] Comparative Example 3 The difference from Example 3 is that the timing of adding sodium persulfate is different.

[0054] (1) Calcium peroxide is added to dewatered sludge (water content of 78%, organic matter content of 46% (referring to the mass fraction of organic matter in sludge dry solids)) for hydrolysis and acidification reaction, the mass ratio of calcium peroxide added to dewatered sludge is 0.6:1, the control temperature of hydrolysis and acidification is 35±1°C, the rotation speed is 250rpm, and the residence time is 18h to obtain pretreated sludge.

[0055] (2) The water content of the pretreated sludge was adjusted to 88% by adding distilled water, and the pretreated sludge was anaerobically digested at a temperature of 35±1°C, with a cycle of 24 hours. After one cycle of sludge entry, the obtained inoculum sludge was heat exchanged with the dewatered sludge, and the temperature of the inoculum sludge after treatment was controlled to 20°C.

[0056] (3) Sodium persulfate in an amount of 0.6% by mass of the inoculum sludge was added to the inoculum sludge, and then an acidic substance (acetic acid) was added to adjust the pH to 5.5-6.0, followed by stirring at a speed of 150 rpm for 50 min, and then ultrasonicating at a frequency of 20 kHz and a power of 100 W for 20 min to obtain mixed sludge.

[0057] (4) The water content of the mixed sludge was adjusted to 89% by adding distilled water, and the pH was adjusted to 6.75-7.25 by adding alkaline substances (KOH), and the mixed sludge was anaerobically digested at a temperature of 35±1°C and a residence time of 15 days.

[0058] Comparative Example 4 The difference from Example 3 is that too much sodium persulfate is added.

[0059] (1) Calcium peroxide is added to dewatered sludge (water content of 78%, organic matter content of 46% (referring to the mass fraction of organic matter in sludge dry solids)) for hydrolysis and acidification reaction, the mass ratio of calcium peroxide added to dewatered sludge is 0.6:1, the control temperature of hydrolysis and acidification is 35±1°C, the rotation speed is 250rpm, and the residence time is 18h to obtain pretreated sludge.

[0060] (2) The water content of the pretreated sludge was adjusted to 88% by adding distilled water, and the pretreated sludge was anaerobically digested at a temperature of 35±1°C, with a cycle of 24 hours. After 3 cycles of sludge entry, the obtained inoculum sludge was heat exchanged with the dewatered sludge, and the temperature of the inoculum sludge after treatment was controlled to 20°C.

[0061] (3) Sodium persulfate in an amount of 1.0% by mass of the inoculum sludge was added to the inoculum sludge, and then an acidic substance (acetic acid) was added to adjust the pH to 5.5-6.0, followed by stirring at a speed of 150 rpm for 80 min, and then ultrasonicating at a frequency of 20 kHz and a power of 100 W for 20 min to obtain mixed sludge.

[0062] (4) The water content of the mixed sludge was adjusted to 89% by adding distilled water, and the pH was adjusted to 6.75-7.25 by adding alkaline substances (KOH), and the mixed sludge was anaerobically digested at a temperature of 35±1°C and a residence time of 15 days.

[0063] Comparative Example 5 The difference from Example 3 is that no acidic substance is added after adding sodium persulfate.

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

[0065] (2) The water content of the pretreated sludge was adjusted to 88% by adding distilled water, and the pretreated sludge was anaerobically digested at a temperature of 35±1°C, with a cycle of 24 hours. After 3 cycles of sludge entry, the obtained inoculum sludge was heat exchanged with the dewatered sludge, and the temperature of the inoculum sludge after treatment was controlled to 20°C.

[0066] (3) Sodium persulfate in an amount of 0.6% by mass of the inoculum sludge was added to the inoculum sludge, followed by stirring at a rotation speed of 150 rpm for 50 min, and then ultrasonicating at a frequency of 20 kHz and a power of 100 W for 20 min to obtain mixed sludge.

[0067] (4) The water content of the mixed sludge was adjusted to 89% by adding distilled water, and the pH was adjusted to 6.75-7.25 by adding alkaline substances (KOH), and the mixed sludge was anaerobically digested at a temperature of 35±1°C and a residence time of 15 days.

[0068] Comparative Example 6 The difference from Example 3 is that the amount of calcium peroxide added is too small and the residence time of hydrolysis and acidification is too short.

[0069] (1) Calcium peroxide is added to dewatered sludge (water content of 78%, organic matter content of 46% (referring to the mass fraction of organic matter in sludge dry solids)) for hydrolysis and acidification reaction, the mass ratio of calcium peroxide added to dewatered sludge is 0.3:1, the control temperature of hydrolysis and acidification is 35±1°C, the rotation speed is 250rpm, and the residence time is 5h to obtain pretreated sludge.

[0070] (2) The water content of the pretreated sludge was adjusted to 88% by adding distilled water, and the pretreated sludge was anaerobically digested at a temperature of 35±1°C, with a cycle of 24 hours. After 3 cycles of sludge entry, the obtained inoculum sludge was heat exchanged with the dewatered sludge, and the temperature of the inoculum sludge after treatment was controlled to 20°C.

[0071] (3) Sodium persulfate in an amount of 0.6% by mass of the inoculum sludge was added to the inoculum sludge, and then an acidic substance (acetic acid) was added to adjust the pH to 5.5-6.0, followed by stirring at a speed of 150 rpm for 50 min, and then ultrasonicating at a frequency of 20 kHz and a power of 100 W for 20 min to obtain mixed sludge.

[0072] (4) The water content of the mixed sludge was adjusted to 89% by adding distilled water, and the pH was adjusted to 6.75-7.25 by adding alkaline substances (KOH), and the mixed sludge was anaerobically digested at a temperature of 35±1°C and a residence time of 15 days.

[0073] Table 1 Methane production (ml / g VS) Organic matter degradation rate (%) 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 Note: VS is volatile solids; 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.

[0074] As shown in Table 1, the present invention pre-treats 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 oxidatively decompose the sludge, crack the microbial cells, increase the soluble COD, and improve the biodegradability of the sludge. However, the process of calcium peroxide releasing hydrogen peroxide is relatively slow, which will lead to a decrease in the efficiency of sludge pretreatment, and only adding calcium peroxide for pretreatment cannot solve the problem of the gradual decrease in the degradation rate over time during the anaerobic digestion process. The organic matter remaining in the dead microorganisms and anaerobic sludge flocs is still difficult to be utilized. Therefore, the methane gas production and organic matter degradation rate of Comparative Example 1 are significantly reduced relative to those of Example 3.

[0075] Therefore, the present invention, after carrying out anaerobic digestion for a period of time, by adding sodium persulfate and process improvement, sodium persulfate can be activated by hydrogen peroxide generated by calcium peroxide, generates sulfate radicals, and forms a dual oxidation system, which can enhance the oxidizability of difficult-to-degrade organic matter, and the added acidic substance can also be used as a raw material for methane synthesis, which can improve the subsequent anaerobic digestion of sludge biogas and methane content. Coupled with the effects of stirring, ultrasound, etc., the organic matter inside the sludge particles is further degraded, and the biogas production is significantly recovered in the subsequent anaerobic digestion process. And comparative example 2 adds sodium persulfate during the pretreatment process to improve the pretreatment efficiency of sludge, but it can not solve the problem that the organic matter remaining in dead microorganisms and anaerobic sludge flocs during anaerobic digestion is still difficult to be utilized. In Comparative Example 3, sodium persulfate was added too early in the anaerobic digestion stage. Since calcium peroxide releases hydrogen peroxide at a relatively slow rate, sufficient time is required for hydrogen peroxide to exert an oxidative decomposition effect on microbial cells. After a period of anaerobic digestion, organic matter is gradually consumed. At this time, the addition of sodium persulfate can exert a better oxidative decomposition effect on difficult-to-use organic matter and sludge flocs, thereby affecting the methane production.

[0076] Comparative Examples 3-4 show that the addition 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. Acidic substances can also be used as raw materials for methane synthesis, and no addition of acidic substances will also lead to a decrease in methane gas production. Comparative Examples 5-6 show that the addition of calcium peroxide and the hydrolysis and acidification time will affect the subsequent anaerobic digestion process. Since the release of hydrogen peroxide by calcium peroxide is relatively slow, too little addition and too short hydrolysis and acidification time will lead to less hydrogen peroxide produced by calcium peroxide, poor pretreatment effect on sludge, and failure to form a good dual oxidation system with the subsequently added sodium persulfate, resulting in a decrease in methane gas production.

[0077] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the specification of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. An anaerobic digestion method for sludge reduction, characterized in that: The steps include: (1) adding calcium peroxide to the dewatered sludge for hydrolysis and acidification to obtain pretreated sludge; (2) subjecting the pretreated sludge to anaerobic digestion with a cycle of 24 hours, and subjecting the obtained inoculated sludge to heat exchange treatment after 3-5 cycles; (3) Add sodium persulfate to the inoculated sludge, stir it first and then ultrasonicate it to obtain mixed sludge; (4) Anaerobic digestion of the mixed sludge.

2. The anaerobic digestion method for sludge reduction according to claim 1, characterized in that: In step (1), the moisture content of the dewatered sludge is 70-80%.

3. The anaerobic digestion method for sludge reduction according to claim 1, characterized in that: In step (1), the hydrolysis and acidification reaction is controlled at a temperature of 33-36°C, a rotation speed of 200-300 rpm, and a residence time of 10-20 hours.

4. The anaerobic digestion method for sludge reduction according to any one of claims 1 to 3, characterized in that: In step (1), the mass ratio of the added amount of calcium peroxide to the dewatered sludge is 0.5-0.6:

1.

5. The anaerobic digestion method for sludge reduction according to claim 1, characterized in that: In step (2), the water content of the pretreated sludge is adjusted to 80-90% by adding distilled water; the temperature of the anaerobic digestion is 32-38°C.

6. The anaerobic digestion method for sludge reduction according to claim 1 or 5, characterized in that: In step (2), the temperature of the inoculated sludge after heat exchange is controlled to be 15-25°C.

7. The anaerobic digestion method for sludge reduction according to claim 1, characterized in that: In step (3), the amount of sodium persulfate added is 0.6-0.8% of the mass of the inoculated sludge.

8. The anaerobic digestion method for sludge reduction according to claim 1, characterized in that: In step (3), after adding sodium persulfate, an acidic substance is added to adjust the pH to 5.5-6.

5.

9. The anaerobic digestion method for sludge reduction according to claim 1, 7 or 8, characterized in that: In step (3), the stirring speed is 150-200 rpm, the time is 40-60 min; the ultrasonic frequency is 20-35 kHz, the power is 100-150 W, and the time is 20-30 min.

10. The anaerobic digestion method for sludge reduction according to claim 1, 7 or 8, characterized in that: 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; the temperature of the anaerobic digestion is 32-38°C, and the time is 10-20 days.