Biogas slurry biological fermentation coupling biological flocculation synchronous denitrification and carbon reduction method

Abstract

The invention relates to the technical field of agricultural biomass resource treatment and utilization, in particular to a biogas slurry biological fermentation coupled biological flocculation synchronous denitrification and carbon reduction method which comprises the following steps: step A, performing intermittent aerobic aeration fermentation on biogas slurry for 7-15 days through a compound fermentation inoculant; step B, preparing a polyaluminum chloride solution with the mass fraction of 5%-20% and a biological flocculant solution with the mass fraction of 0.05%-0.3%; step C, slowly adding the polyaluminum chloride solution obtained in the step B into a biogas slurry tank while stirring, continuously stirring, and standing; and step D, slowly adding a biological flocculant solution into the stood biogas slurry, continuously stirring, and then standing. According to the method, after the biogas slurry obtained after anaerobic fermentation solid-liquid separation is subjected to intermittent aeration fermentation, different flocculant solutions are added in stages for primary flocculation and secondary flocculation, suspended solids, COD and ammonia nitrogen in the biogas slurry are synchronously removed, and the method has important significance and practical application value for maintaining sustainable development of large-scale biogas projects.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural biomass resource processing and utilization, and in particular to a method for synchronous denitrification and carbon reduction of biogas slurry by coupling biological fermentation with biological flocculation. Background Art

[0003] Chinese patent CN 103524176 B discloses a method for producing liquid compound fertilizer using biogas slurry. The method prepares compound liquid fertilizer by pretreating the biogas slurry, adjusting the acidity and alkali, and compounding humic acid and nutrient elements. The biogas slurry nutrient recovery and fertilizer technology can significantly improve the economic value of the biogas slurry. However, for large-scale biogas projects, the biogas slurry fertilizer technology can only use a small amount of biogas slurry, and cannot solve the problem of large-scale biogas slurry concentration in large-scale biogas projects. Summary of the invention

[0004] The object of the present invention is to provide a method for synchronous denitrification and carbon reduction by coupling biogas slurry biological fermentation with biological flocculation, which can solve the above-mentioned technical problems.

[0005] The present invention provides a method for synchronously removing nitrogen and reducing carbon by coupling biogas slurry biological fermentation with biological flocculation, comprising the following steps:

[0006] Step A, intermittent aeration fermentation of biogas slurry: intermittent aerobic aeration fermentation of biogas slurry by composite fermentation bacteria for 7-15 days;

[0007] Step B, preparation of flocculant solution: preparing a polyaluminium chloride (PAC) solution with a mass fraction of 5%-20% and a bioflocculant solution with a mass fraction of 0.05%-0.3%;

[0008] Step C, primary flocculation of biogas slurry: slowly adding the polyaluminium chloride solution obtained in step B into the biogas slurry pool while stirring, continuously stirring, and then allowing to stand;

[0009] Step D, secondary flocculation of biogas slurry: slowly add the bioflocculant solution to the biogas slurry after standing, continue stirring, and then stand. The order of the above steps C and D should not be reversed.

[0010] Preferably, the microorganisms in the composite fermentation agent in step A include Bacillus, yeast, lactic acid bacteria, and Bacillus thuringiensis. The above strains are all biological materials that can be purchased through commercial channels.

[0011] Preferably, the effective viable count of microorganisms in the biogas slurry in step A is 3-16×10 8 cfu / L.

[0012] Preferably, the effective viable count of microorganisms in the biogas slurry in step A is 5-8×10 8cfu / L.

[0013] Preferably, the fermentation temperature of the biogas slurry fermentation process in step A is 5-40°C.

[0014] Preferably, in step A, intermittent aeration is used to control the redox potential of the fermentation process to be -100 mV-100 mV.

[0015] Preferably, in step B, the mass fraction of the polyaluminium chloride solution is 10%, and the mass fraction of the bioflocculant solution is 0.1%.

[0016] Preferably, in step C, the polyaluminium chloride solution accounts for 0.8wt%-1.6wt% of the biogas slurry.

[0017] Preferably, in step D, the bioflocculant solution accounts for 0.008wt%-0.012wt% of the biogas slurry.

[0018] Preferably, the stirring time in steps C and D is 5-10 min.

[0019] Beneficial effects:

[0020] The present invention performs intermittent aeration fermentation on the biogas slurry with solid-liquid separation by anaerobic fermentation, and then adds different flocculant solutions in stages to perform primary flocculation and secondary flocculation according to the physical and chemical properties of the biogas slurry, and clarifies different addition amounts and flocculation sequences to achieve simultaneous removal of suspended matter, COD and ammonia nitrogen in the biogas slurry. The technology is suitable for the centralized treatment of large amounts of biogas slurry in large-scale biogas projects, and is of great significance and practical application value for maintaining the sustainable development of large-scale biogas projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 The present invention is a process flow chart of the method for synchronous denitrification and carbon reduction of biogas slurry biological fermentation coupled with biological flocculation. DETAILED DESCRIPTION

[0023] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0025] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. In addition, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0026] Example 1

[0027] A method for synchronous nitrogen removal and carbon reduction by coupling biogas slurry biological fermentation with biological flocculation

[0028] Biogas slurry biological fermentation: after solid-liquid separation, a composite fermentation agent (accounting for 6% of the weight of the biogas slurry) was added to the biogas slurry for intermittent aerobic aeration fermentation for 10 days; the composite fermentation agent included bacillus group, yeast group, lactic acid bacteria group and Bacillus thuringiensis, among which the bacillus group accounted for 18%, the yeast group accounted for 38%, the lactic acid bacteria accounted for 29%, and the Bacillus thuringiensis accounted for 15%; the effective viable bacteria count of microorganisms in the biogas slurry was 8×10 8 cfu / L; the fermentation temperature was 20±5℃, and the redox potential of the fermentation process was controlled to be -100mV-100mV through intermittent aeration.

[0029] Biogas slurry graded flocculation: The biogas slurry after biological fermentation is introduced into the flocculation sedimentation tank, and a 10% PAC solution is slowly added, accounting for 0.8wt% of the biogas slurry, and slowly stirred for 5-10min for primary flocculation; 24h later, a 0.1% bioflocculant solution is gradually added, accounting for 0.012wt% of the biogas slurry, and slowly stirred for 5-10min for secondary flocculation. After biological fermentation and secondary flocculation, the COD and ammonia nitrogen removal rates in the biogas slurry are 72.6% and 89.6% respectively, and the turbidity is reduced from 700NTU to 80NTU.

[0030] Example 2

[0031] The intermittent aeration biological fermentation method of the biogas slurry in this embodiment is the same as that in Example 1, with the only difference that: the addition amount of the PAC solution with a mass fraction of 10% in the primary flocculation process of the biogas slurry after biological fermentation accounts for 1.2wt% of the biogas slurry, and the addition amount of the secondary flocculation biological flocculant solution is consistent with that in Example 1. After biological fermentation and secondary flocculation, the COD and ammonia nitrogen removal rates in the biogas slurry are 78.6% and 72.7% respectively, and the turbidity decreases from 700NTU to 5.9NTU.

[0032] Example 3

[0033] The intermittent aeration biological fermentation method of the biogas slurry in this embodiment is the same as that in Example 1. The addition amount of the PAC solution with a mass fraction of 10% in the primary flocculation process of the biogas slurry after biological fermentation is the same as that in Example 2. The only difference is that the addition amount of the biological flocculant solution with a mass fraction of 0.1% in the secondary flocculation process accounts for 0.010wt% of the biogas slurry. After biological fermentation and secondary flocculation, the COD and ammonia nitrogen removal rates in the biogas slurry are 74.1% and 65.6% respectively, and the turbidity decreases from 700NTU to 64.5NTU.

[0034] Example 4

[0035] The intermittent aeration biological fermentation method of the biogas slurry in this embodiment is the same as that in Example 1, the only difference is that: the addition amount of 10% PAC in the primary flocculation process of the biogas slurry after biological fermentation accounts for 1.6wt% of the biogas slurry, and the addition amount of 0.1% bioflocculant solution in the secondary flocculation process accounts for 0.008wt% of the biogas slurry. After biological fermentation and secondary flocculation, the COD and ammonia nitrogen removal rates in the biogas slurry are 77.3% and 79.9% respectively, and the turbidity decreases from 700NTU to 2.4NTU.

[0036] Example 5

[0037] The intermittent aeration biological fermentation method of the biogas slurry in this embodiment is the same as that in Example 1, the only difference is that: the addition amount of the PAC solution with a mass fraction of 10% in the first flocculation process of the biogas slurry after biological fermentation is 1.6wt% of the biogas slurry, and the addition amount of the bioflocculant solution with a mass fraction of 0.1% in the secondary flocculation process is 0.012wt% of the biogas slurry. After biological fermentation and secondary flocculation, the COD and ammonia nitrogen removal rates in the biogas slurry are 78.9% and 80.5% respectively, and the turbidity is reduced from 700NTU to 2.2NTU.

[0038] Comparative Example 1

[0039] In this comparative example, the biogas slurry was not subjected to biological fermentation but directly subjected to flocculation treatment, and the flocculation method was the same as that in Example 1. The results showed that the turbidity decreased slowly during the direct flocculation process without biological fermentation, only from 700NTU to 400NTU, and the COD and ammonia nitrogen removal rates were 35.8% and 27.1%, respectively.

[0040] Comparative Example 2

[0041] The difference between this comparative example and Example 1 is that the order of biological flocculation and PAC flocculation is adjusted during the flocculation process, that is, after the biological fermentation of the biogas slurry, biological flocculation is first carried out and then PAC is added for secondary flocculation. The results show that the turbidity is reduced from 700NTU to 210NTU, and the COD and ammonia nitrogen removal rates are 56.4% and 67.1% respectively; the denitrification and carbon reduction effects are significantly lower than those in Example 1, indicating that the order of primary and secondary flocculation directly affects the effect of the technology.

[0042] Comparative Example 3

[0043] The difference between this comparative example and Example 1 is that only PAC flocculation is used in the flocculation process, and no biological flocculation treatment is performed, and the amount of PAC added is consistent with that in Example 1. The results show that the turbidity of the biogas slurry is reduced from 700NTU to 150NTU, the COD removal rate is 70.4%, and the ammonia nitrogen removal rate is only about 10%, indicating that it is difficult to achieve the effect of denitrification and carbon reduction by using PAC flocculation alone.

[0044] Comparative Example 4

[0045] In order to compare the effects of biological flocculation and conventional chemical flocculation, the difference between this comparative example and Example 1 is that the biological flocculant solution in the secondary flocculation is replaced by polyacrylamide (PAM) solution, and the addition amount of PAM solution with a mass fraction of 0.1% accounts for 0.016wt% of the biogas slurry. The results show that the turbidity of the biogas slurry decreases from 700NTU to 49.2NTU, and the COD and ammonia nitrogen removal rates are 77.8% and 83.5% respectively; the denitrification and carbon reduction effects are not significantly different from those of Example 1, but the treatment cost is about 1 times higher than that of Example 1, and the sediment after flocculation with PAM is not suitable for reuse considering the difficulty of subsequent degradation, the comprehensive operating cost of the project and the secondary treatment of the sediment.

[0046] The present invention has found, based on a large number of experiments, that the biogas slurry after solid-liquid separation is first subjected to biological fermentation during storage, and then subjected to biological flocculation, so that the turbidity, COD, ammonia nitrogen, etc. of the biogas slurry can be rapidly reduced. In view of the fact that the process adopts the biological flocculation process, the flocculated sludge is pollution-free and can be reused with the biogas sludge, thus avoiding the problem that the flocculated sludge cannot be recycled due to the addition of traditional chemical flocculants. This technology can solve the current situation of large-scale biogas projects with large amounts of biogas slurry and difficult centralized treatment, and provides a new strategy for the disposal and treatment of biogas slurry in large-scale biogas projects and for maintaining the sustainable operation of biogas projects.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for simultaneous denitrification and carbon reduction by biogas slurry biofermentation coupled with bioflocculation, characterized in that: The following steps are involved: Step A, intermittent aeration fermentation of biogas slurry: intermittent aerobic aeration fermentation of biogas slurry by composite fermentation bacteria for 7-15 days; Step B, preparation of flocculant solution: preparing a polyaluminium chloride solution with a mass fraction of 5%-20% and a bioflocculant solution with a mass fraction of 0.05%-0.3%; Step C, primary flocculation of biogas slurry: slowly adding the polyaluminium chloride solution obtained in step B into the biogas slurry pool while stirring, continuously stirring, and then allowing to stand; Step D, secondary flocculation of biogas slurry: slowly add the bioflocculant solution to the biogas slurry after standing, continue stirring, and then stand.

2. The method for simultaneous denitrification and carbon reduction by biogas slurry biofermentation coupled with bioflocculation according to claim 1, characterized in that: The microorganisms in the composite fermentation agent in step A include bacillus group, yeast group, lactic acid bacteria group and bacillus thuringiensis.

3. The method for simultaneous denitrification and carbon reduction by biogas slurry biofermentation coupled with bioflocculation according to claim 1, characterized in that: The effective viable count of microorganisms in the biogas slurry in step A is 3-16×10 8 cfu / L.

4. The method for simultaneous denitrification and carbon reduction by biogas slurry biofermentation coupled with bioflocculation according to claim 3, characterized in that: The effective viable count of microorganisms in the biogas slurry in step A is 5-8×10 8 cfu / L.

5. The method for simultaneous denitrification and carbon reduction by biogas slurry biofermentation coupled with bioflocculation according to claim 1, characterized in that: The fermentation temperature of the biogas slurry fermentation process in step A is 5-40°C.

6. The method for simultaneous denitrification and carbon reduction by biogas slurry biofermentation coupled with bioflocculation according to claim 1, characterized in that: In step A, intermittent aeration is used to control the redox potential of the fermentation process to be -100mV-100mV.

7. The method for simultaneous denitrification and carbon reduction by biogas slurry biofermentation coupled with bioflocculation according to claim 1, characterized in that: In the step B, the mass fraction of the polyaluminium chloride solution is 10%, and the mass fraction of the bioflocculant solution is 0.1%.

8. The method for simultaneous denitrification and carbon reduction by biogas slurry biofermentation coupled with bioflocculation according to claim 1, characterized in that: In step C, the polyaluminium chloride solution accounts for 0.8wt%-1.6wt% of the biogas slurry.

9. The method for simultaneous denitrification and carbon reduction by biogas slurry biofermentation coupled with bioflocculation according to claim 1, characterized in that: In step D, the bioflocculant solution accounts for 0.008wt%-0.012wt% of the biogas slurry.

10. The method for simultaneous denitrification and carbon reduction by biogas slurry biofermentation coupled with bioflocculation according to claim 1, characterized in that: The stirring time in steps C and D is 5-10 minutes.

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