1. A method for anaerobic digestion of excess sludge is characterized in that the excess sludge is dried and crushed to obtain dry sludge, water is added into the dry sludge to be uniformly mixed for hydrothermal reaction, then the mixture is cooled and centrifuged, solids are dried to obtain pretreated sludge, and the pretreated sludge is mixed with inoculated sludge for anaerobic digestion.

2. The method of anaerobic digestion of excess sludge according to claim 1, wherein the drying temperature of the excess sludge is 50-70 ℃; the mixing mass ratio of the dry sludge to the water is 1: 8-10.

3. The method for anaerobic digestion of excess sludge according to claim 1, characterized in that the hydrothermal reaction temperature is 140 ℃ and 200 ℃, and the hydrothermal reaction time is 20-30 min; the centrifugal speed is 5000r/min, and the centrifugal time is 15 min.

4. The method of anaerobic digestion of excess sludge according to claim 1, characterized in that the mass mixing ratio of the pretreated sludge to the inoculated sludge is 1: 1; the anaerobic digestion temperature is 32-38 ℃, and the anaerobic digestion time is 15-25 days.

5. The method for anaerobic digestion of excess sludge according to claim 1, characterized in that the excess sludge is pretreated before being dried and crushed: standing for 24-48h to remove supernatant, adding persulfate into the lower-layer sludge, and mixing, wherein the mixing mass ratio of the persulfate to the lower-layer sludge is (1-5): (500-2000).

6. The method for anaerobic digestion of excess sludge as claimed in claim 5, wherein the hydrothermal reaction is carried out under ultrasonic conditions with ultrasonic frequency of 20-50kHz, power of 100-150W, hydrothermal reaction temperature of 100-140 ℃ and hydrothermal reaction time of 5-20 min.

7. The method for anaerobic digestion of excess sludge according to claim 5, wherein the hydrothermal reaction is carried out under ultraviolet ultrasonic conditions with an ultraviolet wavelength of 200-300nm, a hydrothermal reaction temperature of 50-100 ℃, and a hydrothermal reaction time of 5-10 min.

8. The method for anaerobic digestion of excess sludge according to claim 7, characterized in that quicklime is added into the mixed solution during the hydrothermal reaction, the addition amount of quicklime being 3-5% of the total mass of the materials.

Background

Sewage treatment plants produce more than 4000 million tons of sludge per year, with a water content of 80%, but the efficiency of sludge treatment is only 20%. The residual sludge is used as a byproduct of biological treatment of a sewage treatment plant, is a solid-liquid mixture with complex components, and the solid phase of the solid-liquid mixture mainly comprises four parts, namely active microorganisms (such as bacteria, fungi, parasites and the like), microorganism autooxidation residues, organic matters (such as nitrogen-containing compounds such as proteins and humus and the like, polysaccharide substances, polychlorinated biphenyl, dioxin and other non-degradable toxic and harmful substances) and inorganic matters (such as heavy metals such as copper, zinc, chromium and the like and inorganic salts), wherein the organic matters are adsorbed on the surface of the sludge and are not degraded or are difficult to degrade. Improper disposal can cause significant environmental hygiene problems. Sludge treatment has become a problem to be regarded as important.

The anaerobic digestion of the sludge can kill pathogenic bacteria and other microorganisms in the sludge, decompose organic matters, generate methane which can be recycled, realize the stabilization of the sludge, improve the sanitary quality of the sludge, and simultaneously realize the requirements of reduction, harmlessness and recycling of sludge treatment, thereby being an environment-friendly technology. In addition, according to the notice of the best feasible technical guideline (trial) for pollution control in sludge treatment and disposal in urban sewage treatment plants issued by the ministry of environmental protection in 2010, the mesophilic anaerobic digestion process of sludge is determined as one of the best feasible processes for sludge treatment, and is preferably selected by large and medium-sized water plants. But the traditional anaerobic sludge digestion method has low digestion rate, long retention time and large volume of a digestion tank. Hydrolysis has been studied as a major step in limiting the rate of anaerobic digestion of sludge, which greatly limits the progress of anaerobic digestion.

Therefore, in order to overcome the technical limitation problem faced by anaerobic digestion, it is urgently needed to develop a method for pretreating sludge to facilitate hydrolysis and anaerobic digestion thereof.

Disclosure of Invention

In order to solve the technical problems, the invention provides the method for anaerobic digestion of the excess sludge, which improves the dissolution of organic matters in the sludge, improves the hydrolysis limit and promotes the anaerobic digestion of the excess sludge through the hydrothermal reaction after drying the excess sludge.

A method for anaerobic digestion of excess sludge comprises drying and crushing excess sludge to obtain dry sludge, adding water, mixing, performing hydrothermal reaction, cooling, centrifuging, drying solids to obtain pretreated sludge, and mixing with inoculated sludge for anaerobic digestion.

Further, the drying temperature of the residual sludge is 50-70 ℃; the mixing mass ratio of the dry sludge to the water is 1: 8-10.

Further, the hydrothermal reaction temperature is 140-; the centrifugal speed is 5000r/min, and the centrifugal time is 15 min.

Further, the mass mixing ratio of the pretreated sludge to the inoculated sludge is 1: 1; the anaerobic digestion temperature is 32-38 ℃, and the anaerobic digestion time is 15-25 days.

Further, the residual sludge is pretreated by the following steps before being dried and crushed: standing for 24-48h to remove supernatant, adding persulfate into the lower-layer sludge, and mixing, wherein the mixing mass ratio of the persulfate to the lower-layer sludge is (1-5): (500-2000).

Further, the hydrothermal reaction is carried out under the ultrasonic condition, the ultrasonic frequency is 20-50kHz, the power is 100-.

Excess sludge carries out above-mentioned processing before drying and smashing, help promoting the efficiency of follow-up stoving step on the one hand, the energy saving, on the other hand, through throwing the persulfate in to lower floor's mud, at the stoving in-process, the persulfate produces the sulfate radical free radical and exerts its extremely strong oxidizing function, carry out the pre-oxidation treatment to excess sludge along with the evaporation to dryness in-process that volatilizees of moisture to effectively destroy microorganism cell wall and sludge flocculating constituent in the excess sludge, improve the efficiency of follow-up heating hydrolysis.

The pretreated excess sludge is further destroyed based on huge energy released by cavitation effect of ultrasonic waves under the ultrasonic-assisted action, so that the hydrolysis rate of the sludge is more rapid and efficient, and the hydrolysis process can be completed within 5-20min at the temperature of 140 ℃ under the condition of 100 ℃ plus materials, thereby realizing the efficient and rapid hydrolysis of the excess sludge. The ultrasonic treatment can also homogenize the O-O bonds in the unreacted persulfate in the sludge, thereby generating sulfate radicals, and further strengthening the hydrolysis process of the residual sludge.

Further, the hydrothermal reaction is carried out under the ultraviolet ultrasonic condition, the ultraviolet wavelength is 200 and 300nm, the hydrothermal reaction temperature is 50-100 ℃, and the hydrothermal reaction time is 5-10 min.

The ultraviolet wavelength irradiation can promote the structural variation of organic matters which are difficult to degrade, such as protein, and the like, and promote the denaturation and inactivation of the protein, the treatment under the ultrasonic condition can promote the enhancement of the influence of the ultraviolet environment on the organic matters, the mutual action of the organic matters and the protein, and the like, which are difficult to degrade, can convert the organic matters into micromolecule substance components which are easy to decompose, the hydrolysis efficiency and quality are improved, and the hydrolysis reaction of the residual sludge can be completed at a lower temperature.

Furthermore, in the hydrothermal reaction process, adding quicklime into the mixed solution, wherein the adding amount of the quicklime is 3-5% of the total mass of the materials.

The quick lime contacts with the water in the mixture and can initiate hydrolysis reaction rapidly and generate the extremely strong calcium hydroxide of basicity, and this process is exothermic reaction simultaneously, and the temperature that makes the mixture that can be rapid promotes, and quick lime's addition also gives the mixture alkaline environment simultaneously to accelerate hydrolysis reaction's emergence rate.

Compared with the prior art, the invention has the beneficial effects that:

(1) microbial flocs in the sludge are dissolved, and complex biomolecules are decomposed and converted into bio-oil, water-soluble products, hydrocarbons and gases. Organic macromolecules are hydrolyzed into organic micromolecular substances, such as proteins, carbohydrates and the like, which are released from cells, wherein a part of organic substances are further hydrolyzed into amino acids, long-chain fatty acids and the like. The total solids entering anaerobic digestion are increased by 70%, and the biodegradation performance of the sludge is also improved.

(2) The water retention property of extracellular polymeric substances is reduced, so that the bound water in cells is released, and the dehydration property of the sludge is improved.

(3) The diversity of related microbial communities is increased, the abundance of genes related to denitrification is increased, and the anaerobic digestion is facilitated.

(4) Compared with various pretreatment methods of other sludge, the method has the advantages of simplicity, high efficiency and energy conservation.

Detailed Description

Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention.

It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Further, for numerical ranges in this disclosure, it is understood that each intervening value, between the upper and lower limit of that range, is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in a stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference herein for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.

It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification. The specification and examples are exemplary only.

As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.

The sludge used in the following examples was obtained from a sewage treatment plant from a high tombstone store in Beijing, which uses A2/O as the primary sewage treatment method. The water content of the sludge was 58%, TS was 37.91%, VS was 45.12%, SCOD was 10.01g/L, TOC was 8.5g/L, and TN was 14.2 g/L.

Example 1

(1) Drying the sludge in a ventilation drying oven at 70 ℃ to constant weight, grinding, sieving with a 60-mesh sieve, and storing for subsequent analysis.

(2) Adding deionized water (5 g and 50g are selected at this time) into the dry sludge obtained in the step (1) according to the mass ratio of the dry sludge to the water of 1: 10, uniformly mixing to prepare 5 samples, respectively placing the samples into a reaction kettle, and heating and hydrolyzing the samples according to the following setting requirements under a closed condition: hydrolyzing at 140 deg.C, 155 deg.C, 170 deg.C, 185 deg.C, and 200 deg.C for 30min to obtain mixed hydrolysate; and (4) cooling the reaction kettle to 50 ℃, taking out the hydrolysis mixed solution, and centrifuging for 15min at 5000 r/min. Separating supernatant from precipitate, drying the sludge at 70 deg.C to constant weight, grinding, and sieving with 60 mesh sieve to obtain sample for storage.

(3) A serum bottle is used for simulating an anaerobic digestion reactor, and anaerobic digestion is carried out in a shaker at 35 +/-3 ℃ and the rotating speed is 1000 rpm. And (3) mixing the sludge reacted in the step (2) and the sludge which is not subjected to thermal hydrolysis with the inoculated sludge taken out from the anaerobic digestion tank according to the mass ratio of 1:1, adding the mixture into a serum bottle, and simulating anaerobic digestion to react. Before the reaction started, the serum bottle was purged with nitrogen for 5 minutes to ensure that it remained anaerobic. The reaction time was 20 days.

(4) The VS measurements were performed after 20 days of reaction and the results are shown in Table 1, where CK is the blank without step (1) and step (2).

(5) The soluble protein content was determined after 20 days of reaction and the results are shown in Table 1, where CK is a blank without treatment in steps (1) and (2).

(6) The amount of methane formed was measured by a portable methane analyzer after 20 days of reaction, and the results are shown in Table 1, CK being a blank control without performing the treatments of step (1) and step (2).

TABLE 1

Example 2

(1) Standing the sludge for 24 hours at normal temperature, removing supernatant, and mixing potassium persulfate and lower-layer sludge according to a mass ratio of 5: 800, drying in a 70 ℃ ventilation drying oven to constant weight, grinding, sieving with a 60-mesh sieve, and storing for subsequent analysis.

(2) Adding deionized water (5 g and 50g are selected at this time) into the dry sludge obtained in the step (1) according to the mass ratio of the dry sludge to the water of 1: 10, uniformly mixing, placing in a reaction kettle, and carrying out heating hydrolysis according to the following setting requirements under a closed condition: hydrolyzing at 100 deg.C, 110 deg.C, 120 deg.C, 130 deg.C, 140 deg.C under ultrasonic condition (ultrasonic frequency 50kHz, power 150W) for 20min to obtain mixed hydrolysate; taking out the hydrolysis mixture, and centrifuging at 5000r/min for 15 min. Separating supernatant from precipitate, drying the sludge at 70 deg.C to constant weight, grinding, and sieving with 60 mesh sieve to obtain sample for storage.

(3) A serum bottle is used for simulating an anaerobic digestion reactor, and anaerobic digestion is carried out in a shaker at 35 +/-3 ℃ and the rotating speed is 1000 rpm. And (3) mixing the sludge reacted in the step (2) and the sludge which is not subjected to thermal hydrolysis with the inoculated sludge taken out from the anaerobic digestion tank according to the mass ratio of 1:1, adding the mixture into a serum bottle, and simulating anaerobic digestion to react. Before the reaction started, the serum bottle was purged with nitrogen for 5 minutes to ensure that it remained anaerobic. The reaction time was 20 days.

(4) The VS measurements were performed after 20 days of reaction and the results are shown in Table 2, where CK is the blank without step (1) and step (2).

(5) The soluble protein content was determined after 20 days of reaction and the results are shown in Table 2, where CK is a blank without treatment in steps (1) and (2).

(6) The amount of methane formed was measured by a portable methane analyzer after 20 days of reaction, and the results are shown in Table 2, CK being a blank control in which the treatments of step (1) and step (2) were not conducted.

TABLE 2

Example 3

(1) Standing the sludge for 24 hours at normal temperature, removing supernatant, and mixing potassium persulfate and lower-layer sludge according to a mass ratio of 5: 800, drying in a 70 ℃ ventilation drying oven to constant weight, grinding, sieving with a 60-mesh sieve, and storing for subsequent analysis.

(2) Adding deionized water (5 g and 50g are selected at this time) into the dry sludge obtained in the step (1) according to the mass ratio of the dry sludge to the water of 1: 10, uniformly mixing, placing in a reaction kettle, and carrying out heating hydrolysis according to the following setting requirements under a closed condition: hydrolyzing at 50 deg.C, 60 deg.C, 75 deg.C, 85 deg.C, 100 deg.C under ultraviolet ultrasonic condition (ultrasonic frequency 50kHz, power 150W, ultraviolet wavelength 280nm) for 10min to obtain mixed hydrolysate; taking out the hydrolysis mixture, and centrifuging at 5000r/min for 15 min. Separating supernatant from precipitate, drying the sludge at 70 deg.C to constant weight, grinding, and sieving with 60 mesh sieve to obtain sample for storage.

(3) A serum bottle is used for simulating an anaerobic digestion reactor, and anaerobic digestion is carried out in a shaker at 35 +/-3 ℃ and the rotating speed is 1000 rpm. And (3) mixing the sludge reacted in the step (2) and the sludge which is not subjected to thermal hydrolysis with the inoculated sludge taken out from the anaerobic digestion tank according to the mass ratio of 1:1, adding the mixture into a serum bottle, and simulating anaerobic digestion to react. Before the reaction started, the serum bottle was purged with nitrogen for 5 minutes to ensure that it remained anaerobic. The reaction time was 20 days.

(4) The VS measurements were performed after 20 days of reaction and the results are shown in Table 3, where CK is the blank without step (1) and step (2).

(5) The soluble protein content was determined after 20 days of reaction and the results are shown in Table 3, where CK is a blank without treatment in steps (1) and (2).

(6) The amount of methane formed was measured by a portable methane analyzer after 20 days of reaction, and the results are shown in Table 3, CK being a blank control in which the treatments of step (1) and step (2) were not conducted.

TABLE 3

Example 4

(1) Standing the sludge for 24 hours at normal temperature, removing supernatant, and mixing potassium persulfate and lower-layer sludge according to a mass ratio of 5: 800, drying in a 70 ℃ ventilation drying oven to constant weight, grinding, sieving with a 60-mesh sieve, and storing for subsequent analysis.

(2) Adding deionized water (5 g and 50g are selected at this time) into the dry sludge obtained in the step (1) according to the mass ratio of the dry sludge to the water of 1: 10, uniformly mixing, placing in a reaction kettle, adding quicklime accounting for 5% of the total mass of the materials under a closed condition, and performing heating hydrolysis according to the following setting requirements respectively: respectively setting the temperature at 50 ℃ under the ultraviolet ultrasonic condition (ultrasonic frequency of 50kHz, power of 150W and ultraviolet wavelength of 280nm), and hydrolyzing for 10min to obtain mixed hydrolysate; taking out the hydrolysis mixture, and centrifuging at 5000r/min for 15 min. Separating supernatant from precipitate, drying the sludge at 70 deg.C to constant weight, grinding, and sieving with 60 mesh sieve to obtain sample for storage.

(3) A serum bottle is used for simulating an anaerobic digestion reactor, and anaerobic digestion is carried out in a shaker at 35 +/-3 ℃ and the rotating speed is 1000 rpm. And (3) mixing the sludge reacted in the step (2) and the sludge which is not subjected to thermal hydrolysis with the inoculated sludge taken out from the anaerobic digestion tank according to the mass ratio of 1:1, adding the mixture into a serum bottle, and simulating anaerobic digestion to react. Before the reaction started, the serum bottle was purged with nitrogen for 5 minutes to ensure that it remained anaerobic. The reaction time was 20 days.

(4) The VS measurements were performed after 20 days of reaction and the results are shown in Table 4, where CK is the blank without step (1) and step (2).

(5) The soluble protein content was determined after 20 days of reaction and the results are shown in Table 4, where CK is a blank without treatment in steps (1) and (2).

(6) The amount of methane formed was measured by a portable methane analyzer after 20 days of reaction, and the results are shown in Table 4, CK being a blank control without the treatment of step (1) and step (2).

TABLE 4

Comparing the data in tables 1-4, it can be seen that the steps of pre-treating the excess sludge before heating hydrolysis, adding ultraviolet ultrasound in the hydrolysis process, and adding quicklime in the hydrolysis liquid all play a good role in promoting sludge hydrolysis, and all play a good role in promoting methane yield when anaerobic digestion is performed to prepare methane.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included therein.