A method for recovering substances in microbial anaerobic digestion process

Abstract

The present invention discloses a material recovery method in the process of microbial anaerobic digestion, and belongs to the technical field of resource utilization of organic solid waste and residual sludge. It includes zeolite modification: modifying zeolite with an iron-containing solution to obtain iron oxide modified zeolite; inoculum: selecting sludge that has undergone anaerobic fermentation as seed sludge, washing, sieving and storing at low temperature, and awakening it with glucose as substrate when it is taken; sludge anaerobic digestion: taking another part of the sludge as substrate, contacting and mixing the seed sludge with the substrate at a ratio of volatile solid VS of (1-2): (2-1) to digest the material; then adding iron oxide modified zeolite to the digested material, reacting in an oxygen-deficient, sealed environment; during the reaction, collecting gas.

Description

Technical Field

[0001] The invention relates to the technical field of resource utilization of organic solid waste-residual sludge, and more specifically, to a material recovery method in a microbial anaerobic digestion process. Background Art

[0002] At present, the technical maturity and implementation of residual sludge treatment in my country are still gradually improving. Anaerobic digestion is currently the main way to make residual sludge harmless and resourceful. The volatile fatty acids (VFAs) produced by anaerobic digestion of residual sludge can be used as a carbon source for biological denitrification and phosphorus removal, and are also important chemical raw materials; the calorific value of biogas produced by the anaerobic process is about 13~21 MJ / kg, which is equivalent to the calorific value of lignite. However, the current anaerobic digestion process of residual sludge has the disadvantages of low methane production rate and no recovery of nitrogen and phosphorus resources. In addition, it is also difficult to recover nitrogen and phosphorus in residual sludge. Summary of the invention

[0003] 1. Problem to be solved

[0004] In view of the problem that the existing surplus sludge is still difficult to be utilized as a resource even after anaerobic digestion treatment, the present invention provides a material recovery method in the process of microbial anaerobic digestion.

[0005] 2. Technical solution

[0006] In order to solve the above problems, the technical solution adopted by the present invention is as follows:

[0007] A method for recovering substances in a microbial anaerobic digestion process comprises the following steps:

[0008] Zeolite modification: Zeolite is modified to obtain iron oxide modified zeolite;

[0009] Inoculum: The sludge after anaerobic fermentation is selected as the seed sludge, which is washed and sieved.

[0010] Afterwards, it is stored at low temperature and awakened with glucose as substrate when it is used;

[0011] Anaerobic digestion of sludge: Take another part of the sludge as substrate, and mix the seed sludge and substrate in a VS ratio of (1~2):(2~1) to mix and digest the material;

[0012] Then, iron oxide-modified zeolite is added to the digestate to react in an oxygen-deficient, sealed environment;

[0013] During the reaction, gas collection was performed.

[0014] Furthermore, the modification method of the zeolite is as follows:

[0015] Stage 1: contacting the zeolite with the iron-containing solution several times, maintaining each contact time T1 not less than 12 hours, preferably 12 to 24 hours;

[0016] Stage 2: contacting the zeolite with the iron-containing solution again, maintaining the contact time T2 for not less than 12 hours, preferably 12 to 24 hours; then adding alkali, and maintaining the contact state for a time T3 of not less than 24 hours, preferably 24 to 28 hours;

[0017] It should be noted here that dividing the contact between zeolite and iron into several times can, on the one hand, increase the iron loading amount; on the other hand, it can improve the iron loading stability; on the other hand, it can gradually change the original morphological structure of the zeolite, so that the zeolite, which originally had a plate-like shape and a plate-like surface with pores but was relatively smooth, will have a porous (small pore) and rough membrane-like surface after modification, thereby increasing the specific surface area of ​​the zeolite several times.

[0018] Furthermore, in stage one, the concentration of iron ions in the iron-containing solution is 0.1-0.6 M, and the liquid-to-solid ratio of the iron-containing solution to the zeolite is 5-15 mL / g.

[0019] Furthermore, in stage 1, each time the zeolite is brought into contact with the iron-containing solution, the temperature is maintained at 70±5°C (preferably 70±2°C). After the contact is completed, the surface of the zeolite is cleaned until the cleaning solution is neutral and the Cl- residual amount is less than 1wt% after detection, and then dried; this contact is repeated.

[0020] Furthermore, in stage 2, the concentration of iron ions in the iron-containing solution is 0.5-1.5 M, and the liquid-to-solid ratio of the iron-containing solution to the zeolite is 5-10 mL / g;

[0021] The amount of base added is such that the molar ratio of the iron ions to the hydroxide ions is (1-2):(2-1).

[0022] Furthermore, in stage 2, the alkali is prepared into an alkali solution, and after the alkali solution is added, the liquid-to-solid ratio of the total amount of solution (calculated as the sum of the initial addition amounts of various solutions) to the zeolite is no more than 15 mL / g.

[0023] Furthermore, the inoculum is selected from anaerobic fermented sludge as seed sludge, which is washed and sieved. If the seed sludge is stored at a low temperature (about 0-8°C) after sieving, an awakening step is required when it is used;

[0024] Furthermore, the seed sludge TS=8~15%, VS=7~12%, VS / TS=0.70~0.90; and the anaerobic sludge load reaches 0.3~0.5gCOD CH4 / (gVSS·d).

[0025] Furthermore, the sludge is anaerobically digested, and another part of the sludge is taken and diluted as an anaerobic digestion substrate, and the seed sludge and the substrate are mixed at a VS ratio of (1~2):(2~1) to obtain a digestion material; then, iron oxide-modified zeolite is added to the digestion material, and deoxygenation can be carried out by means such as nitrogen stripping, and then the material is sealed and an anaerobic digestion reaction is carried out at a certain temperature. During the reaction, gas is collected.

[0026] Furthermore, the modified zeolite is added into the mixed digested material at 8-12 g / L, preferably 10 g / L, and the mixture is stripped with nitrogen. The bottle mouth is sealed and anaerobic digestion is performed at 32-38°C to produce biogas.

[0027] Furthermore, the iron oxide modified zeolite obtained after modification, the iron oxide is one or more of ferroferric oxide, ferric oxide or ferrous oxide; preferably ferric oxide.

[0028] Furthermore, during the anaerobic digestion of the sludge, a shaking mixing treatment is required.

[0029] 3. Beneficial effects

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The material recovery method in the process of microbial anaerobic digestion provided by the present invention utilizes the modified iron oxide modified zeolite to promote the simultaneous hydrolysis and methanogenesis steps, thereby realizing the simultaneous recovery of carbon, nitrogen and phosphorus in the anaerobic digestion process of sludge; the addition of the modified iron oxide modified zeolite can not only have a good adsorption effect on nitrogen and phosphorus in the sludge fermentation liquid, but also provide a carrier for microorganisms, thereby facilitating the enrichment of fermentation bacteria, accelerating the electron transfer between fermentation bacteria, and enhancing gas production. Specifically:

[0032] On the one hand, zeolite is a cheap porous material with good microbial adhesion, and the iron oxide-modified zeolite has a stronger ability to simultaneously adsorb nitrogen and phosphorus;

[0033] On the other hand, the modified iron oxide-modified zeolite, due to the addition of iron element, further enhances the electron conduction between microorganisms, improves the systemicity of the entire anaerobic reaction process, and enhances the methane production efficiency of anaerobic digestion.

[0034] (2) The material recovery method in the process of microbial anaerobic digestion provided by the present invention, the modified iron oxide modified zeolite, on the one hand, has a porous and rough surface and a large specific surface area, which greatly enhances its effect on promoting the growth and aggregation of microorganisms, especially hydrolytic bacteria and methanogens in the anaerobic digestion process; at the same time, it has excellent adsorption effect on nitrogen and phosphorus;

[0035] On the other hand, a higher iron loading can promote the hydrolysis of sludge, enhance the interspecies electron transfer of methanogens, increase methane production, and avoid ammonia inhibition during anaerobic digestion, thereby improving the stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The iron oxide modified zeolite (FeO-molecular sieve) in Example 1 of the present invention;

[0037] Figure 2 The iron oxide modified zeolite (D-FeO-molecular sieve) in Comparative Example 1 of the present invention;

[0038] Figure 3 Infrared spectra of the iron oxide modified zeolite before and after anaerobic digestion according to Example 1 of the present invention;

[0039] Among them, FeO-zeolite is iron oxide-modified zeolite before anaerobic digestion;

[0040] FeO-zeolite' is iron oxide modified zeolite after anaerobic digestion. DETAILED DESCRIPTION

[0041] The present invention is further described below with reference to specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art;

[0042] The essential features and remarkable effects of the present invention can be reflected in the following embodiments. The described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Therefore, they do not limit the present invention in any way. Those skilled in the art may make some non-essential improvements and adjustments based on the contents of the present invention, which all fall within the scope of protection of the present invention.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs; the terms used herein and / or include any and all combinations of one or more of the associated listed items.

[0044] Herein, the term “not less than” or “not higher than” a certain value should be understood to include the value. For example, “the time is not less than 12 hours” should be understood to mean “the time can be 12 hours, or longer than 12 hours”.

[0045] Herein, “TS” means: total solid content of sludge, %;

[0046] “VS” means: volatile solid content of sludge, %;

[0047] “VS / TS” means: total solid content of sludge / volatile solid content.

[0048] In the present invention, the awakening method of the seed mud can be a general awakening method without any additional special requirements. As an example, the awakening (acclimation) conditions in the following embodiments can be:

[0049] When used, a nutrient solution of COD:N:P=200:5:1 was prepared with glucose as the carbon source, NH4Cl as the nitrogen source, and KH2PO4 as the phosphorus source. The seed mud was awakened under the condition of 2500 mg-COD / g-VS, and 1 ml / L of trace element mother solution was added. The composition of the trace element mother solution is as follows (per 1 L): EDTA 0.01 g, MnSO4▪H2O 0.5 g, NaCl 1.0 g, FeSO4▪H2O 0.1 g, NiCl2·6H2O 0.04 g, CoCl2▪6H2O 0.1 g, ZnSO4▪7H2O 0.1 g, CaCl20.1 g, CuSO4▪5H2O0.01 g, AlK(SO4)2▪12H2O 0.01 g, H3BO30.01 g, NaMoO4▪2H2O 0.025 g.

[0050] The present invention is further described below in conjunction with specific embodiments.

[0051] Example 1

[0052] This embodiment provides a method for modifying zeolite to obtain iron oxide modified zeolite (FeO-molecular sieve). The specific steps are as follows:

[0053] 1. Add zeolite with a particle size of 3-5 mm to the iron-containing solution for full contact, and keep the contact time for 12 hours, during which the temperature is kept at 70±2°C; after the contact is completed, use ultrapure water to repeatedly wash the surface of the zeolite until the washing solution is approximately neutral and no chloride ions are detected, and then dry it. The product is named Fe-molecular sieve; wherein,

[0054] The liquid-to-solid ratio of the iron-containing solution to the zeolite was 10 mL / g;

[0055] The iron-containing solution is prepared from ferric chloride, wherein the concentration of iron ions is 0.1 M.

[0056] 2. Add zeolite to the iron-containing solution again for full contact, and keep the contact time for 12 hours, during which the temperature is kept at 70±2℃;

[0057] Then add the alkali solution and keep the contact state for another 24 hours, during which the temperature is maintained at 70±2°C.

[0058] After completion, it is repeatedly washed with ultrapure water until the washing solution is approximately neutral and no chloride ions are detected, and then dried. The product is named FeO-molecular sieve; wherein,

[0059] The liquid-to-solid ratio of the iron-containing solution to the zeolite is 10 mL / g; after the addition of the alkali solution, the liquid-to-solid ratio of the total amount of the solution (calculated as the sum of the initial addition amounts of various solutions) to the zeolite is 15 mL / g; the iron-containing solution is prepared by ferric chloride, in which the concentration of iron ions is 0.1 M, and the molar ratio of iron ions to hydroxide ions is 1:2.

[0060] like Figure 1 As shown, the FeO-molecular sieve prepared in this embodiment has a porous (small pore) rough membrane surface, which is obviously different from the zeolite which originally presents a plate-like structure and has a relatively smooth pore surface.

[0061] As shown in Table 1, the FeO-molecular sieve prepared in this embodiment has an iron content of up to 36.4%wt and a specific surface area of ​​up to 163.8 m 2 / g.

[0062] Table 1 Element content and specific surface area of ​​FeO-molecular sieve

[0063]

[0064] Comparative Example 1

[0065] This comparative example provides another method for modifying zeolite to obtain iron oxide modified zeolite (D-FeO-molecular sieve). The specific steps are as follows:

[0066] 1. Add 10g of zeolite with a particle size of 3-5mm into 100mL of 2mol / L iron-containing solution, then add 25mL of 1mol / L NaOH solution to fully contact, and let stand at room temperature for 50 hours;

[0067] 2. Then add 25 mL of 10 mol / L NaOH solution to the mixture and react at 70±2℃ for 8 days;

[0068] 3. Finally, the precipitated material is repeatedly washed with ultrapure water until the washing solution is approximately neutral, until no chloride ions are detected, and then dried. The product is named D-FeO-molecular sieve.

[0069] like Figure 2 As shown, the D-FeO-molecular sieve prepared in this comparative example basically presents the original plate-like morphology of zeolite, and the plate-like surface is relatively smooth although it has pores;

[0070] As shown in Table 2, the D-FeO-molecular sieve prepared in this comparative example has an iron content of less than 3%, only 2.148%, and a specific surface area of ​​only 24.18 m 2 / g.

[0071] Table 2 Element content and specific surface area of ​​D-FeO-molecular sieve

[0072]

[0073] Example 2

[0074] Directly carry out anaerobic fermentation of sludge, the specific steps are as follows:

[0075] (1) Inoculum acclimation: The sludge in the anaerobic fermentation tank of the municipal sewage treatment plant was taken as the seed sludge. The seed sludge was washed, sieved and stored. When used, a nutrient solution with COD:N:P=200:5:1 was prepared with glucose as the carbon source, NH4Cl as the nitrogen source and KH2PO4 as the phosphorus source. The seed sludge was awakened under the condition of 2500 mg-COD / g-VS, and 1 ml / L of trace element mother solution was added. The gas produced by the seed sludge was collected and the methane concentration was measured. If the methane concentration reached 4500~5500 ppm, it means that the seed sludge was awakened successfully.

[0076] The composition of the trace element stock solution is as follows (per 1 L): EDTA 0.01 g, MnSO4▪H2O 0.5 g, NaCl 1.0 g, FeSO4▪H2O 0.1 g, NiCl2·6H2O 0.04 g, CoCl2▪6H2O 0.1 g, ZnSO4▪7H2O 0.1 g, CaCl20.1 g, CuSO4▪5H2O 0.01 g, AlK(SO4)2▪12H2O 0.01 g, H3BO30.01 g, NaMoO4▪2H2O0.025 g;

[0077] (2) Take the residual sludge after dehydration from the municipal sewage treatment plant, dilute it with ultrapure water at a mass ratio of 1:4 as the anaerobic digestion substrate, and then mix the seed sludge and substrate at a VS ratio of 1:2;

[0078] (3) The digested material was shaken and nitrogen was blown off for 10 minutes. The bottle mouth was sealed with a rubber stopper, and fermentation was started. The fermentation temperature was controlled at 35° C. During the fermentation process, stirring was performed for 10 minutes every day.

[0079] The fermentation period of Example 1 was 150 days, and the final methane production rate was 96.6 ml / g-VS.

[0080] Example 3

[0081] The anaerobic fermentation of sludge using unmodified industrial zeolite is carried out in the following specific steps:

[0082] (1) Inoculum acclimation: The sludge in the anaerobic fermentation tank of the municipal sewage treatment plant is taken as the seed sludge, which is washed, sieved and stored, and awakened when used, in the same manner as in Example 2;

[0083] (2) Take the residual sludge after dehydration from the municipal sewage treatment plant, dilute it with ultrapure water at a mass ratio of 1:4 as the anaerobic digestion substrate, and then mix the seed sludge and substrate evenly at a VS ratio of 1:2;

[0084] (3) 10 g / L of unmodified industrial zeolite was added, the digested material was shaken, nitrogen was blown off for 10 min, the bottle mouth was sealed with a rubber stopper, and fermentation was started, and the fermentation temperature was controlled at 35° C. During the fermentation process, stirring was performed for 10 minutes every day.

[0085] The fermentation period of Example 2 was 150 days, and the final methane yield was 98.1 ml / g-VS.

[0086] Example 4

[0087] The Fe-molecular sieve prepared in step 1 of Example 1 is used for anaerobic fermentation to produce biogas, and the specific steps are as follows:

[0088] (1) Inoculum acclimation: The sludge in the anaerobic fermentation tank of the municipal sewage treatment plant is taken as the seed sludge, which is washed, sieved and stored, and awakened when used, in the same manner as in Example 2;

[0089] (2) Take the residual sludge after dehydration from the municipal sewage treatment plant, dilute it with ultrapure water at a mass ratio of 1:4 as the anaerobic digestion substrate, and then mix the seed sludge and substrate evenly at a VS ratio of 1:2;

[0090] (3) 10 g / L of Fe-zeolite was added, the digested material was shaken, nitrogen was blown off for 10 min, the bottle mouth was sealed with a rubber stopper, and fermentation was started, and the fermentation temperature was controlled at 35° C. During the fermentation process, stirring was performed for 10 minutes every day.

[0091] The fermentation period of Example 3 was 150 days, and the final methane yield was 98.1 ml / g-VS.

[0092] Example 5

[0093] The FeO-molecular sieve prepared in Example 1 is used for anaerobic fermentation of sludge, and the specific steps are as follows:

[0094] (1) Inoculum acclimation: The sludge in the anaerobic fermentation tank of the municipal sewage treatment plant is taken as seed sludge, which is washed, sieved and stored, and awakened when used, in the same manner as in Example 1;

[0095] (2) Take the residual sludge after dehydration from the municipal sewage treatment plant, dilute it with ultrapure water at a mass ratio of 1:4 as the anaerobic digestion substrate, and then mix the seed sludge and substrate evenly at a VS ratio of 1:2;

[0096] (3) 10 g / L of FeO-zeolite was added, the digested material was shaken, nitrogen was blown off for 10 min, the bottle mouth was sealed with a rubber stopper, and fermentation was started, and the fermentation temperature was controlled at 35° C. During the fermentation process, stirring was performed for 10 minutes every day.

[0097] The fermentation period of Example 4 was 150 days, and the final methane yield was 123.0 ml / g-VS.

[0098] Example 6

[0099] Using unmodified zeolite and iron oxide, the sludge is mixed for anaerobic fermentation. The specific steps are as follows:

[0100] (1) Inoculum acclimation: The sludge in the anaerobic fermentation tank of the municipal sewage treatment plant is taken as seed sludge, which is washed, sieved and stored, and awakened when used, in the same manner as in Example 1;

[0101] (2) Take the residual sludge after dehydration from the municipal sewage treatment plant, dilute it with ultrapure water at a mass ratio of 1:4 as the anaerobic digestion substrate, and then mix the seed sludge and substrate evenly at a VS ratio of 1:2;

[0102] (3) 10 g / L of unmodified industrial zeolite and an amount of iron oxide equal to that in Example 1 were added, the digested material was shaken, nitrogen was blown off for 10 min, the bottle mouth was sealed with a rubber stopper, and fermentation was started. The fermentation temperature was controlled at 35° C. During the fermentation process, stirring was performed for 10 minutes every day.

[0103] Example 7

[0104] The D-FeO-molecular sieve prepared in Comparative Example 1 was used to carry out anaerobic fermentation of sludge, and the remaining steps were the same as those in Example 1;

[0105] The final methane yield was 99.5 ml / g-VS.

[0106] Example 8

[0107] The fermentation period was 150 days, and the final methane yield was 104.6 ml / g-VS.

[0108] The test settings, methane yields and nitrogen and phosphorus recovery rates of Examples 2 to 7 are shown in Table 3:

[0109] Table 3. Experimental settings, methane yields, and nitrogen and phosphorus recovery rates of Examples 1 to 5

[0110]

[0111] It can be seen that the iron oxide modified zeolite (FeO-zeolite) has the greatest promotion effect on fermentation gas production and phosphorus recovery. After adding 10g / % of zeolite FeO-zeolite, the gas production increased by 1.27 times, and 59.1% of phosphorus in the fermentation broth could be recovered. Although the apparent recovery rate of nitrogen by FeO-zeolite is very low, Figure 3 As shown in the figure, the infrared characteristic peak of NH4-N was detected on the surface of the used FeO-zeolite, which means that the FeO-zeolite may promote the release of ammonia in the substrate. The unmodified industrial zeolite and Fe-zeolite have high nitrogen recovery, reaching 26.1% and 17.9% respectively, but these two zeolites have little effect on gas production and have no phosphorus recovery function. In addition, there is no significant difference between the ammonia nitrogen concentration in group 5 and the ammonia nitrogen concentration in group 2 without adding any substances (p>0.05), indicating that there is no ammonia inhibition phenomenon in the FeO-zeolite system in group 5, but at the same time, the gas production of FeO-zeolite in group 5 increased by 1.27 times.

Claims

1. A method for recovering substances during anaerobic digestion of sludge, including the recovery of biogas and phosphorus, characterized in that: The following steps are involved: Zeolite modification: zeolite is modified by using an iron-containing solution to obtain iron oxide-modified zeolite; Wherein, the iron oxide is one or more of ferroferric oxide, ferric oxide or ferrous oxide. Inoculum: Select anaerobic fermented sludge as seed sludge, wash, sieve and store at low temperature, and use glucose as substrate to wake it up when using; Anaerobic digestion of sludge: another part of the sludge is taken as substrate, and the seed sludge and substrate are contacted and mixed at a VS ratio of (1~2):(2~1) to obtain digested material; then iron oxide modified zeolite is added to the digested material, and the reaction is carried out in an oxygen-deficient and sealed environment; during the reaction, gas is collected; Wherein, the modification method of the zeolite modification is as follows: Stage 1: contacting the zeolite with the iron-containing solution several times, maintaining the contact time T1 of each time to be not less than 12 hours; in stage 1, the concentration of iron ions in the iron-containing solution is 0.1-0.6 M, and the liquid-to-solid ratio of the iron-containing solution to the zeolite is 5-15 mL / g; Stage 2: the zeolite is contacted with the iron-containing solution again, and the contact time T2 is maintained for not less than 12 hours; then the alkali is added, and the contact state is maintained for a time T3 of not less than 24 hours; in stage 2, the concentration of iron ions in the iron-containing solution is 0.5-1.5M, and the liquid-to-solid ratio of the iron-containing solution to the zeolite is 5-10 mL / g; the amount of alkali added is such that the molar ratio of the iron ions to the hydroxide ions is (1-2):(2-1); The sum of the durations T1, T2, and T3 shall not exceed 80 hours.

2. The method for recovering substances during anaerobic digestion of sludge according to claim 1, characterized in that: The iron oxide modified zeolite is added to the digested material at 8-12 g / L.

3. The method for recovering substances in the anaerobic digestion process of sludge according to claim 1 or 2, characterized in that: Nitrogen stripping is used to create an oxygen-deficient environment, and anaerobic digestion is carried out at 32-38°C to produce biogas.

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