Method for enhancing anaerobic digestion of excess sludge by using nonionic surfactant

Abstract

The invention belongs to the field of organic solid waste treatment, and provides a method for enhancing anaerobic digestion of excess sludge by using a nonionic surfactant, which comprises the following steps of: pretreating the excess sludge by using the nonionic surfactant before anaerobic digestion; the method comprises the steps of preparation of a nonionic surfactant stock solution, stirring pretreatment of residual sludge and a nonionic surfactant, anaerobic digestion reaction and the like. Compared with the traditional anaerobic digestion technology, the method has the advantages that the micro stable structure of the residual sludge is destabilized by adopting the nonionic surfactant, the problem of low biodegradability caused by the micro stable structure of the residual sludge is solved in a targeted manner, and the bioaccessibility of organic components in the sludge is improved, so that the anaerobic digestion methane production rate of the residual sludge is improved. Compared with the existing anaerobic digestion synergistic technology, the method has the advantages that hazardous chemicals are not used, the energy investment is greatly reduced, the construction, operation and maintenance cost is low, and the applicability is relatively high.

Description

Technical Field

[0001] The present invention belongs to the field of solid waste treatment, and particularly relates to a method for enhancing the anaerobic digestion of excess sludge by using non-ionic surfactants. Background Art

[0002] The activated sludge process is the main treatment technology for urban domestic wastewater, and excess sludge is an inevitable by-product of the activated sludge process. As a complex of microbial cell residues and their extracellular polymeric substances, excess sludge contains a large amount of biological proteins, carbohydrates and humus, and has extremely high resource conversion potential; at the same time, it also contains various pathogenic bacteria and harmful heavy metal elements, and also has significant pollution attributes.

[0003] Anaerobic digestion technology has become the preferred technology for excess sludge treatment because it can improve sludge dewatering performance, inactivate pathogenic microorganisms, enhance sludge fertilizer efficiency, especially convert organic matter into biogas, an alternative to fossil energy. However, the multiple protection systems formed by microbial extracellular polymeric substances and cell membranes in excess sludge seriously limit its anaerobic digestion efficiency. Moreover, various organic substances and metal elements in excess sludge form stable macromolecular mixtures through bridging and complexation through different molecular interactions, further reducing the bioaccessibility of its substrate. Specifically, in terms of the microbial cell structure, the main components of the organic matter in excess sludge are aerobic active microorganisms and their extracellular polymeric substances, and these microbial structures also form a barrier to the dissolution of organic matter during the anaerobic digestion process. In terms of material properties, the wrapping effect of hydrophobic proteins in the sludge results in poor hydrophilicity of its micro-surface interface, with self-aggregation characteristics and the ability to capture enzymes related to anaerobic digestion. More notably, the aromatic structure in humic acid will further strengthen the hydrophobicity of the system through π-π electron interaction with proteins. This strong stability formed by the interaction of hydrophobic substances seriously restricts the mass transfer efficiency in the microbial metabolism process. To break through this limitation, the key lies in dissociating the material interactions in microbial EPS and destroying the colloidal stable structure formed by hydrophobic substances. One effective strategy is to modify the hydrophobic functional groups on the solid surface of the sludge to enhance hydrophilicity and achieve the destabilization of the sludge micro-structure.

[0004] Existing pretreatment methods for excess sludge (including acid-base pretreatment, ultrasound, high pressure, and hydrothermal hydrolysis, etc.) destroy the sludge floc structure through violent reaction methods, thereby facilitating microorganisms to uptake organic matter from excess sludge. However, there are still problems such as excessive energy consumption, high cost, and large demand for hazardous chemicals. Therefore, it is urgent to seek an effective, environmentally friendly, and economical pretreatment method for excess sludge. The non-ionic surfactant pretreatment technology aims to modify the micro surface interface of excess sludge, destabilize its colloidal-like stable structure, and improve the bioaccessibility of organic matter therein, thereby effectively improving the resource conversion efficiency and rate of anaerobic digestion of excess sludge. The expansion and application of the relevant content of the present invention have important practical significance for optimizing the anaerobic digestion technology of excess sludge. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a method for enhancing the anaerobic digestion of excess sludge using a non-ionic surfactant to solve the problems in the prior art. The technical solution adopted by the present invention is as follows:

[0006] A method for enhancing the anaerobic digestion of excess sludge using a non-ionic surfactant. This method uses a non-ionic surfactant as a conditioner for excess sludge and performs conditioning treatment on the excess sludge before anaerobic digestion, including the following steps:

[0007] Step 1, adding a non-ionic surfactant to the excess sludge and stirring evenly;

[0008] Step 2, adding the evenly stirred mixture as a substrate into an anaerobic digestion reactor.

[0009] Furthermore, the non-ionic surfactant is a short-chain alkyl glucoside, and its carbon chain length is C8-C10.

[0010] Furthermore, the short-chain alkyl glucoside is prepared by the following method:

[0011] Performing dehydration condensation reaction on short-chain fatty alcohol and glucose at 100-120 °C in the presence of an acidic catalyst. After the reaction, the short-chain alkyl glucoside product is obtained through neutralization, alcohol removal, and purification steps.

[0012] Furthermore, in the dehydration condensation reaction:

[0013] The short-chain fatty alcohol is octanol or decanol, and its molar ratio to glucose is 3:1 to 5:1;

[0014] The acidic catalyst is concentrated sulfuric acid or solid sulfonic acid resin, and its dosage is 0.5%-1.5% of the total mass of the reactants;

[0015] During the reaction process, the generated water is continuously removed through a water separator.

[0016] Further, the dosage of the non-ionic surfactant is 0.025 - 0.10 g / g of the dry sludge mass.

[0017] Further, in step 1, the stirring rate for stirring and mixing is 60 - 90 r / min, and the stirring time is 1 h.

[0018] Further, the non-ionic surfactant is a stock solution of 0.05 g / ml.

[0019] Further, the total solid mass content of the excess sludge is 2.0% - 7.5%, and the mass ratio of the organic solid to the total solid is 42% - 85%.

[0020] Further, in step 2, the hydraulic retention time of the mixed sludge is 20 d - 30 d, and the digestion reaction temperature is 35 - 39 °C.

[0021] Further, in step 1, the non-ionic surfactant is added to the excess sludge in the pretreatment tank and stirred and mixed evenly;

[0022] In step 2, the anaerobic digestion reactor is an anaerobic digestion tank;

[0023] The pretreatment tank is connected to the anaerobic digestion tank through a feed pipeline; a stirring device and a sludge feed port are provided on the pretreatment tank; a biogas outlet and a discharge port are provided on the anaerobic digestion tank; a water bath constant temperature layer is provided on the wall surface of the anaerobic digestion tank; the water bath constant temperature layer is connected to a water pump through a circulation pipeline;

[0024] A stirring device is provided in the pretreatment tank. The stirring device includes a motor and a stirring assembly. The stirring assembly includes a connecting shaft, a temporary storage tank, a hollow shaft, and hollow stirring rods: the top of the connecting shaft is fixedly connected to the output end of the motor, the bottom of the connecting shaft is fixedly connected to the temporary storage tank, the bottom of the temporary storage tank is fixedly connected to the hollow shaft, the top of the hollow shaft communicates with the temporary storage tank, the side of the hollow shaft is connected to a plurality of the hollow stirring rods, a plurality of through holes are provided on the hollow shaft, and the hollow stirring rods communicate with the inside of the hollow shaft through the through holes;

[0025] The temporary storage tank is used to add the non-ionic surfactant.

[0026] The present invention has the following beneficial effects:

[0027] (1) The present invention uses a non-ionic surfactant with biocompatibility to replace hydrochloric acid, sodium hydroxide, etc. added in the acid-base pretreatment technology, reducing the input of hazardous chemicals and lowering the risks in the application process and the potential secondary pollution risks;

[0028] (2) The present invention destroys the microscopic stable structure of the excess sludge by adding a small amount of reagents, which greatly reduces the energy input compared with traditional thermal hydrolysis, ultrasound, high-pressure technology, etc.;

[0029] (3) The present invention adopts a direct adding stirring and mixing method, which has low equipment processing difficulty, simple operation process, and low initial construction cost and later operation and maintenance cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a structural diagram of the device of the present invention;

[0031] Figure 2 It is the experimental data diagram of Experimental Example 1;

[0032] Figure 3 It is the experimental data diagram of Experimental Example 2;

[0033] Figure 4 is a schematic diagram of a stirring assembly;

[0034] In the figure: 1, sludge feed port, 2, pretreatment tank, 3, stirring device, 4, non-ionic surfactant reserve solution, 5, dosing port, 6, screw pump, 7, feed pipeline, 8, water bath constant temperature layer, 9, anaerobic digestion tank, 10, temperature transmitter, 11, biogas outlet, 12, water heater, 13, water pump, 14, circulation pipeline, 15, discharge port, 301, connecting shaft, 302, temporary storage box, 303, hollow shaft, 304, through hole, 305, hollow stirring rod, 306, adjustment sleeve. DETAILED DESCRIPTION

[0035] The following will be combined with the embodiments of the present invention Figures 1-4 , the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0036] A method for strengthening anaerobic digestion of excess sludge using a nonionic surfactant, the method using a nonionic surfactant as an excess sludge conditioner to condition the excess sludge before anaerobic digestion, comprising the following steps:

[0037] Step 1, adding a nonionic surfactant to the excess sludge and stirring to mix;

[0038] Step 2: adding the stirred mixture as a substrate into an anaerobic digestion reactor.

[0039] Further, the non-ionic surfactant is a non-ionic surfactant with biocompatibility and biodegradability, including one or more of alkyl polyglycoside, dodecyl phenol, and glycerol fatty acid ester.

[0040] Further, the dosage of the non-ionic surfactant is 0.025 - 0.10 g / g of the dry sludge mass.

[0041] Further, in step 1, the stirring rate for stirring and mixing evenly is 60 - 90 r / min, and the stirring time is 1 h.

[0042] Further, the non-ionic surfactant is a stock solution of 0.05 g / ml.

[0043] Further, the total solid mass content of the excess sludge is 2.0% - 7.5%, and the mass ratio of the organic solid to the total solid is 42% - 85%.

[0044] Further, in step 2, the hydraulic retention time of the mixed sludge is 20 d - 30 d, and the digestion reaction temperature is 35 - 39 °C.

[0045] Specifically for the non-ionic surfactant of the present invention, the non-ionic surfactant is a short-chain alkyl polyglycoside with a carbon chain length of C8 - C10. The short-chain alkyl polyglycoside is prepared by the following method:

[0046] The short-chain fatty alcohol and glucose are subjected to a dehydration condensation reaction at 100 - 120 °C in the presence of an acidic catalyst, and after the reaction, a short-chain alkyl polyglycoside product is obtained through neutralization, alcohol removal, and purification steps.

[0047] In the dehydration condensation reaction:

[0048] The short-chain fatty alcohol is octanol or decanol, and its molar ratio to glucose is 3:1 to 5:1;

[0049] The acidic catalyst is concentrated sulfuric acid or solid sulfonic acid resin, and the dosage is 0.5% - 1.5% of the total mass of the reactants;

[0050] During the reaction process, the generated water is continuously removed through a water separator.

[0051] Specifically, in step 1 of the present invention, a non-ionic surfactant is added to the excess sludge in the pretreatment tank 2 and stirred and mixed evenly;

[0052] In step 2, the anaerobic digestion reactor is an anaerobic digestion tank 9;

[0053] The pretreatment tank 2 is connected to the anaerobic digestion tank 9 through a feed pipeline 7; a stirring device 3 and a sludge feed port 1 are provided on the pretreatment tank 2; a biogas outlet 11 and a discharge port 15 are provided on the anaerobic digestion tank 9; a water bath constant temperature layer 8 is provided on the wall surface of the anaerobic digestion tank 9; the water bath constant temperature layer 8 is connected to a water pump 13 through a circulation pipeline 14.

[0054] The pretreatment tank 2 is used to put sludge, add a non-ionic surfactant and stir and mix evenly.

[0055] A temperature transmitter 10 is also provided on the anaerobic digestion tank 9.

[0056] A stirring device 3 is provided in the pretreatment tank 2. The stirring device 3 includes a motor and a stirring assembly. The stirring assembly includes a connecting shaft 301, a temporary storage tank 302, a hollow shaft 303 and hollow stirring rods 305: the top of the connecting shaft 301 is fixedly connected to the output end of the motor, the bottom of the connecting shaft 301 is fixedly connected to the temporary storage tank 302, the bottom of the temporary storage tank 302 is fixedly connected to the hollow shaft 303, the top of the hollow shaft 303 communicates with the temporary storage tank 302, the side of the hollow shaft 303 is connected to a plurality of the hollow stirring rods 305, a plurality of through holes 304 are provided on the hollow shaft 303, and the hollow stirring rods 305 communicate with the inside of the hollow shaft 303 through the through holes 304;

[0057] The temporary storage tank 302 is used to add a non-ionic surfactant.

[0058] Specifically, a plurality of adjusting sleeves 306 are sleeved on the hollow shaft 303. Connecting holes are provided on the adjusting sleeves 306. The outer side surface of the adjusting sleeve 306 is fixedly connected to the hollow stirring rod 305. The connecting holes communicate the through holes 304 and the hollow stirring rod 305, so that the hollow stirring rod 305 communicates with the hollow shaft 303. The outer end of the hollow stirring rod 305 is an open structure, the bottom of the hollow shaft 303 is a closed structure, and a plurality of through holes 304 are arranged along the axial and circumferential directions of the hollow shaft 303. The adjusting sleeve 306 can be fixed on the hollow shaft 303 by screws. By adjusting the position of the adjusting sleeve 306, the interval between different adjusting sleeves 306 can be adjusted, so as to adjust the interval between the upper and lower hollow stirring rods 305, and it can adapt to sludges of different volumes.

[0059] A feeding port is provided on the temporary storage tank 302. The non-ionic surfactant is added through the feeding port. A valve can be provided at the top of the hollow shaft 303 to control the flow rate of the non-ionic surfactant in the temporary storage tank 302 flowing into the hollow shaft 303.

[0060] The motor can be fixedly installed on the pretreatment tank 2 through a bracket. When the motor rotates, the hollow shaft 303 rotates. Under the action of centrifugal force, part of the non-ionic surfactant is output outward through the through hole 304, and another part of the non-ionic surfactant is output outward through the hollow stirring rod 305, so as to realize the function of mixing the non-ionic surfactant while stirring, and can make the non-ionic surfactant and the sludge mix evenly.

[0061] During specific implementation:

[0062] In the preparation stage, the anaerobic digestion tank 9 is filled with anaerobic microorganisms. The rotation speed of the stirring device 3 in the anaerobic digestion tank 9 is 30 - 50 r / min. The water bath constant temperature layer 8 controls the temperature in the anaerobic digestion tank to be 35 - 39 °C based on a temperature transmitter, and the internal circulation flow rate is controlled to be 2 times the effective volume of the tank per day.

[0063] The surplus sludge to be treated enters the pretreatment tank 2 through the feed inlet. The non-ionic surfactant stock solution is added to the pretreatment tank 2 through the chemical dosing port 5. The initial dosage of the non-ionic surfactant is calculated according to 0.025 - 0.10 g / g of the sludge dry basis mass. The rotation speed of the stirring device in the pretreatment tank 2 is 50 r / min, and the stirring duration is 1 h.

[0064] The sludge treated with the non-ionic surfactant is sent to the anaerobic digestion tank 9 through the feed pipeline 7 by the screw pump 6. The feed volume and discharge volume of the anaerobic digestion tank 9 are calculated according to the hydraulic retention time of 20 - 30 d.

[0065] Detect the pH in the anaerobic digestion tank 9, the gas production volume of the anaerobic digestion tank 9, the gas methane concentration, and the sludge contact angle, and adjust the dosage of the non-ionic surfactant (within the range of 0.025 - 0.10 g / g) and the hydraulic retention time (within the range of 20 - 30 d) according to the detected parameters.

[0066] Two experimental examples are given below:

[0067] Experimental Example 1:

[0068] Such as Figure 2 , taking the surplus sludge of a certain sewage treatment plant as the treatment object (TS = 3.08%, VS = 1.78%), and selecting alkyl polyglycoside (APG) as the non-ionic surfactant used. The concentration gradients of the APG dosage are set at 0.05, 0.10, and 0.15 g APG / g TS. Anaerobic digestion is carried out on the treated surplus sludge, and the results are as Figure 2As shown, compared with the control group, when the dosages of non-ionic surfactants were 0.05 and 0.10 g APG / g TS respectively, the biogas production from the excess sludge increased by 49.7% and 62.9% respectively. Moreover, when the dosage of non-ionic surfactant was 0.05 g APG / g TS, the time for the excess sludge to reach 80% of the total biogas production was advanced by 4 days, and the biogas production rate was significantly accelerated.

[0069] Experimental Example 2:

[0070] Taking the excess sludge of a sewage treatment plant (TS = 3.08%, VS = 1.78%) as the treatment object, alkyl polyglucoside (APG) was selected as the non-ionic surfactant used. The non-ionic surfactant was added before and after sludge thickening, and the dosage was 0.05 g APG / g TS. Anaerobic digestion was carried out on the excess sludge after treatment and concentrated to a solid content of 10.7%, and the results are as Figure 3 shown. Adding non-ionic surfactants before and after sludge thickening can effectively increase the methane production from the anaerobic digestion of excess sludge. Compared with the control group, adding non-ionic surfactants before and after sludge thickening increased the methane production from the anaerobic digestion of excess sludge by 27.8% and 11.0% respectively on a daily basis.

[0071] The above-described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations, variations, modifications, and substitutions made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for enhancing anaerobic digestion of excess sludge by using non-ionic surfactants, characterized in that, This method uses a non-ionic surfactant as a conditioning agent for excess sludge, and conditions the excess sludge before anaerobic digestion, including the following steps: Step 1: Add a non-ionic surfactant to the excess sludge and stir evenly; Step 2: Add the evenly stirred mixture as a substrate into an anaerobic digestion reactor; In Step 1, add a non-ionic surfactant to the excess sludge in a pretreatment tank (2) and stir evenly; In Step 2, the anaerobic digestion reactor is an anaerobic digestion tank (9); The pretreatment tank (2) is connected to the anaerobic digestion tank (9) through a feed pipeline (7); a stirring device (3) and a sludge feed port (1) are provided on the pretreatment tank (2); a biogas outlet (11) and a discharge port (15) are provided on the anaerobic digestion tank (9); a water bath constant temperature layer (8) is provided on the wall surface of the anaerobic digestion tank (9); the water bath constant temperature layer (8) is connected to a water pump (13) through a circulation pipeline (14); A stirring device (3) is provided inside the pretreatment tank (2), and the stirring device (3) includes a motor and a stirring assembly. The stirring assembly includes a connecting shaft (301), a storage tank (302), a hollow shaft (303), and a hollow stirring rod (305): The top of the connecting shaft (301) is fixedly connected to the output end of the motor, the bottom of the connecting shaft (301) is fixedly connected to the storage tank (302), the bottom of the storage tank (302) is fixedly connected to the hollow shaft (303), the top of the hollow shaft (303) communicates with the storage tank (302), the side of the hollow shaft (303) is connected to a plurality of the hollow stirring rods (305), a plurality of through holes (304) are provided on the hollow shaft (303), and the hollow stirring rod (305) communicates with the inside of the hollow shaft (303) through the through hole (304); The non-ionic surfactant is added to the storage tank (302).

2. The method for enhancing anaerobic digestion of excess sludge by using non-ionic surfactants according to claim 1, characterized in that The non-ionic surfactant is a short-chain alkyl glucoside with a carbon chain length of C8-C10.

3. The method for enhancing anaerobic digestion of excess sludge by using non-ionic surfactant according to claim 2, characterized in that, The short-chain alkyl glucoside is prepared by the following method: Perform a dehydration condensation reaction on short-chain fatty alcohol and glucose at 100-120°C in the presence of an acidic catalyst, and obtain a short-chain alkyl glucoside product after neutralization, alcohol removal, and purification steps.

4. The method for enhancing anaerobic digestion of excess sludge by using non-ionic surfactants according to claim 3, wherein In the dehydration condensation reaction: The short-chain fatty alcohol is octanol or decanol, and its molar ratio to glucose is 3:1 to 5:1; The acidic catalyst is concentrated sulfuric acid or solid sulfonic acid resin, and the dosage is 0.5%-1.5% of the total mass of the reactants; During the reaction process, the generated water is continuously removed through a water separator.

5. The method for enhancing anaerobic digestion of excess sludge by using non-ionic surfactants according to claim 1, wherein The dosage of the non-ionic surfactant is 0.025-0.10 g / g of the sludge dry basis mass.

6. The method for enhancing anaerobic digestion of excess sludge by using non-ionic surfactant as claimed in claim 1, wherein In Step 1, the stirring rate for even stirring is 60-90 r / min, and the stirring time is 1 h.

7. The method for enhancing anaerobic digestion of excess sludge by using non-ionic surfactant according to claim 1, characterized in that, The non-ionic surfactant is a stock solution of 0.05 g / ml.

8. The method for enhancing anaerobic digestion of excess sludge by using non-ionic surfactants according to claim 1, characterized in that, The total solid mass content of the excess sludge is 2.0%-7.5%, and the mass ratio of organic solid to total solid is 42%-85%.

9. The method for enhancing anaerobic digestion of excess sludge by using non-ionic surfactant according to claim 1, characterized in that In Step 2, the hydraulic retention time of the mixed sludge is 20 d-30 d, and the digestion reaction temperature is 35-39°C.

Images