A method for simultaneously removing nitrogen and carbon by coupling biogas slurry biological fermentation with bioflocculation

Abstract

The present application relates to the technical field of agricultural biomass resource processing and utilization, and particularly relates to a method for simultaneously removing nitrogen and reducing carbon by biologic fermentation coupling bio-flocculation of biogas slurry, which comprises the following steps: step A, intermittently aerating and fermenting the biogas slurry by using a composite fermentation agent for 7-15 days; step B, preparing a polyaluminum chloride solution with a mass fraction of 5%-20% and a bio-flocculant solution with a mass fraction of 0.05%-0.3%; step C, slowly adding the polyaluminum chloride solution obtained in step B to the biogas slurry in a biogas slurry tank while stirring, continuously stirring, and then standing; and step D, slowly adding the bio-flocculant solution to the biogas slurry after standing, continuously stirring, and then standing. After the biogas slurry obtained by solid-liquid separation of anaerobic fermentation is intermittently aerated and fermented, different flocculant solutions are added in stages to realize primary flocculation and secondary flocculation, so that the suspended solids, COD and ammonia nitrogen in the biogas slurry are simultaneously removed, which is of great significance and practical application value for maintaining the sustainable development of large-scale biogas engineering.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of agricultural biomass resource processing and utilization technology, and in particular to a method for simultaneous denitrification and carbon reduction of biogas slurry by biological fermentation and flocculation coupling. BACKGROUND

[0002] A method for producing liquid compound fertilizer by using biogas slurry is disclosed in Chinese patent CN 103524176 B. The method processes and prepares compound liquid fertilizer by pretreating, acid-base adjusting, humic acid and nutrient element compounding, etc. of the biogas slurry. The biogas slurry nutrient recovery and fertilizer technology can significantly improve the economic value of the biogas slurry. However, for large-scale biogas engineering, the biogas slurry fertilizer technology can only utilize a small amount of biogas slurry, and cannot solve the problem of large amount of biogas slurry concentrated in large-scale biogas engineering. SUMMARY

[0003] The present application aims to provide a method for simultaneous denitrification and carbon reduction of biogas slurry by biological fermentation and flocculation coupling, which can solve the above technical problems.

[0004] The present application provides a method for simultaneous denitrification and carbon reduction of biogas slurry by biological fermentation and flocculation coupling, comprising the following steps:

[0005] Step A, intermittent aeration fermentation of biogas slurry: the biogas slurry is subjected to intermittent aerobic aeration fermentation by a composite fermentation agent for 7-15 days;

[0006] Step B, preparation of flocculant solution: a polyaluminum chloride (PAC) solution with a mass fraction of 5%-20% and a biological flocculant solution with a mass fraction of 0.05%-0.3% are prepared;

[0007] Step C, primary flocculation of biogas slurry: the polyaluminum chloride solution obtained in step B is slowly added to the biogas slurry tank while stirring, and then the stirring is continued and then the tank is left to stand;

[0008] Step D, secondary flocculation of biogas slurry: the biological flocculant solution is slowly added to the biogas slurry left to stand, and then the stirring is continued and then the tank is left to stand. The order of steps C and D should not be reversed.

[0009] Preferably, the microorganisms in the composite fermentation agent in step A include Bacillus group, yeast group, lactic acid bacteria group, and Bacillus thuringiensis. The above-mentioned bacterial species are biological materials that can be purchased through commercial channels.

[0010] Preferably, the effective viable count of microorganisms in the biogas slurry in step A is 3-16 x 10 8 cfu / L.

[0011] Preferably, the effective viable count of microorganisms in the biogas slurry in step A is 5-8 x 10 8 cfu / L.

[0012] Preferably, the fermentation temperature of the biogas slurry fermentation process in step A is 5-40℃.

[0013] Preferably, the redox potential of the fermentation process in step A is controlled to be -100mV-100mV by intermittent aeration.

[0014] Preferably, the mass fraction of the polyaluminum chloride solution in step B is 10%, and the mass fraction of the bioflocculant solution is 0.1%.

[0015] Preferably, the polyaluminum chloride solution in step C accounts for 0.8wt%-1.6wt% of the biogas slurry.

[0016] Preferably, the bioflocculant solution in step D accounts for 0.008wt%-0.012wt% of the biogas slurry.

[0017] Preferably, the time of continuous stirring in steps C and D is 5-10min.

[0018] Beneficial effects:

[0019] The present application realizes the simultaneous removal of suspended solids, COD and ammonia nitrogen in the biogas slurry by intermittent aeration fermentation of the biogas slurry after anaerobic fermentation solid-liquid separation, adding different flocculant solutions for primary flocculation and secondary flocculation according to the physicochemical properties of the biogas slurry, and determining the different addition amounts and flocculation sequences. The technology is suitable for centralized treatment of large amounts of biogas slurry in large-scale biogas engineering, and has important significance and practical application value for maintaining the sustainable development of large-scale biogas engineering. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the specific embodiments or prior art of the present application, the drawings needed in the specific embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0021] Figure 1 Process flow chart of the method of biogas slurry biological fermentation coupled with biological flocculation simultaneous denitrification and decarburization. DETAILED DESCRIPTION

[0022] The technical solutions of the present application will be described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0023] In the description of the present application, it is to be understood by those skilled in the art that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0024] In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise specifically limited. In addition, the terms "mounting", "connecting", "connecting" should be broadly understood, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the communication between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0025] Example 1

[0026] A method for simultaneous denitrification and decarburization by coupling biologic fermentation of biogas slurry with bio-flocculation

[0027] Biologic fermentation of biogas slurry: After solid-liquid separation, a composite fermentation agent (6% of the weight of the biogas slurry) is added to the biogas slurry for intermittent aerobic aeration fermentation for 10 days; the composite fermentation agent includes Bacillus group, yeast group, lactic acid bacteria group, and Bacillus thuringiensis, wherein the Bacillus group accounts for 18% of the composite fermentation agent, the yeast group accounts for 38%, the lactic acid bacteria group accounts for 29%, and Bacillus thuringiensis accounts for 15%; the effective viable count of microorganisms in the biogas slurry is 8x10 8 cfu / L; the fermentation temperature is 20±5℃, and the oxidation-reduction potential during the fermentation process is controlled at-100mV-100mV through intermittent aeration.

[0028] Biological fermentation of biogas slurry: the biogas slurry after biological fermentation was introduced into the flocculation sedimentation tank, 10% PAC solution was slowly added, accounting for 0.8wt% of the biogas slurry, and slowly stirred for 5-10 minutes for primary flocculation; 0.1% biological flocculant solution was gradually added after 24 hours, accounting for 0.012wt% of the biogas slurry, and slowly stirred for 5-10 minutes for secondary flocculation. After biological fermentation and secondary flocculation, the removal rates of COD and ammonia nitrogen in the biogas slurry were 72.6% and 89.6% respectively, and the turbidity decreased from 700 NTU to 80 NTU.

[0029] Example 2

[0030] In this example, the intermittent aeration biological fermentation of biogas slurry was the same as that in Example 1, the difference was that the addition amount of 10% PAC solution in the primary flocculation process after biological fermentation accounted for 1.2wt% of the biogas slurry, and the addition amount of the biological flocculant solution in the secondary flocculation process was the same as that in Example 1. After biological fermentation and secondary flocculation, the removal rates of COD and ammonia nitrogen in the biogas slurry were 78.6% and 72.7% respectively, and the turbidity decreased from 700 NTU to 5.9 NTU.

[0031] Example 3

[0032] In this example, the intermittent aeration biological fermentation of biogas slurry was the same as that in Example 1, the addition amount of 10% PAC solution in the primary flocculation process after biological fermentation was the same as that in Example 2, the difference was that the addition amount of 0.1% biological flocculant solution in the secondary flocculation process accounted for 0.010wt% of the biogas slurry. After biological fermentation and secondary flocculation, the removal rates of COD and ammonia nitrogen in the biogas slurry were 74.1% and 65.6% respectively, and the turbidity decreased from 700 NTU to 64.5 NTU.

[0033] Example 4

[0034] In this example, the intermittent aeration biological fermentation of biogas slurry was the same as that in Example 1, the difference was that the addition amount of 10% PAC in the primary flocculation process after biological fermentation accounted for 1.6wt% of the biogas slurry, and the addition amount of 0.1% biological flocculant solution in the secondary flocculation process accounted for 0.008wt% of the biogas slurry. After biological fermentation and secondary flocculation, the removal rates of COD and ammonia nitrogen in the biogas slurry were 77.3% and 79.9% respectively, and the turbidity decreased from 700 NTU to 2.4 NTU.

[0035] Example 5

[0036] The intermittent aeration biological fermentation of biogas slurry in this example is the same as that in Example 1, the difference is only that the addition amount of 10% PAC solution in the primary flocculation process after biological fermentation is 1.6wt% of the biogas slurry, the addition amount of 0.1% biological flocculant solution in the secondary flocculation process is 0.012wt% of the biogas slurry, after biological fermentation and secondary flocculation, the removal rates of COD and ammonia nitrogen in the biogas slurry are 78.9% and 80.5% respectively, and the turbidity is reduced from 700NTU to 2.2NTU.

[0037] Comparative Example 1

[0038] In this comparative example, the biogas slurry is not subjected to biological fermentation, but is directly subjected to flocculation treatment, and the flocculation method is the same as that in Example 1. The results show that the turbidity decreases slowly in the direct flocculation process without biological fermentation, and is only reduced from 700NTU to 400NTU, and the removal rates of COD and ammonia nitrogen are 35.8% and 27.1% respectively.

[0039] Comparative Example 2

[0040] The difference between this comparative example and Example 1 is only that the sequence of biological flocculation and PAC flocculation in the flocculation process is adjusted, i.e. the biogas slurry is subjected to biological flocculation first after biological fermentation, and then is subjected to secondary flocculation by adding PAC. The results show that the turbidity is reduced from 700NTU to 210NTU, and the removal rates of COD and ammonia nitrogen are 56.4% and 67.1% respectively. The denitrification and decarburization effect is significantly lower than that of Example 1, indicating that the sequence of primary and secondary flocculation directly affects the effect of the technology.

[0041] Comparative Example 3

[0042] The difference between this comparative example and Example 1 is only that PAC flocculation is used in the flocculation process without biological flocculation treatment, and the addition amount of PAC is the same as that in Example 1. The results show that the turbidity of the biogas slurry is reduced from 700NTU to 150NTU, the removal rate of COD is 70.4%, and the removal rate of ammonia nitrogen is only about 10%, indicating that PAC flocculation alone cannot achieve the effect of denitrification and decarburization.

[0043] Comparative Example 4

[0044] For comparison of the effect of bioflocculation and conventional chemical flocculation, the difference between the comparative example and example 1 is only that the bioflocculant solution in the secondary flocculation is replaced by a polyacrylamide (PAM) solution, and the addition amount of the PAM solution with a mass fraction of 0.1% is 0.016wt% of the biogas slurry. The results show that the turbidity of the biogas slurry is reduced from 700 NTU to 49.2 NTU, the removal rates of COD and ammonia nitrogen are 77.8% and 83.5% respectively; the denitrification and decarburization effects have no significant difference with example 1, but the treatment cost is about 1 times higher than that of example 1, and the sludge after flocculation with PAM is difficult to degrade, considering the comprehensive operation cost of the project and the secondary treatment of the sludge, it is not suitable for reuse.

[0045] The present application is based on a large number of tests, and it is found that the biogas slurry after solid-liquid separation can be rapidly reduced in turbidity, COD, ammonia nitrogen, etc. by biological fermentation during storage and then by bioflocculation. Since the process uses bioflocculation process, the flocculation sludge is pollution-free and can be reused with biogas residue, avoiding the problem that the flocculation sludge cannot be resourceized due to the addition of traditional chemical flocculants. This technology can solve the problem of large amount of biogas slurry in large-scale biogas projects, and provide a new strategy for biogas slurry treatment and disposal in large-scale biogas projects, and maintain the sustainable operation of biogas projects.

[0046] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for simultaneous denitrification and decarburization by coupling biogas slurry biofermentation with bioflocculation, characterized in that, The method comprises the following steps: Step A, intermittent aeration fermentation of biogas slurry: the biogas slurry is subjected to intermittent aerobic aeration fermentation by a composite fermentation inoculant for 7-15 days, the microorganisms in the composite fermentation inoculant include Bacillus group, yeast group, lactic acid bacteria group, Bacillus thuringiensis, and the effective viable count of the microorganisms is 3-16x10 8 cfu / L; the fermentation temperature of the biogas slurry fermentation process is 5-40℃; through intermittent aeration, the oxidation-reduction potential of the fermentation process is controlled to be-100 mV-100 mV; Step B, flocculant solution preparation: preparing a polyaluminum chloride solution with a mass fraction of 5%-20% and a biological flocculant solution with a mass fraction of 0.05%-0.3%; Step C, primary flocculation of biogas slurry: slowly adding the polyaluminum chloride solution obtained in step B to the biogas slurry pool while stirring, continuously stirring, and then standing, with a primary flocculation residence time of 24 h; Step D, secondary flocculation of biogas slurry: slowly adding the biological flocculant solution to the biogas slurry after standing, continuously stirring, and then standing.

2. The method according to claim 1, wherein, The effective viable cell number of microorganisms in the step A biogas slurry is 5-8 x 10 8 cfu / L.

3. The method according to claim 1, wherein, In step B, the mass fraction of the polyaluminum chloride solution is 10%, and the mass fraction of the biological flocculant solution is 0.1%.

4. The method according to claim 1, wherein, In step C, the polyaluminum chloride solution accounts for 0.8wt%-1.6wt% of the biogas slurry.

5. The method according to claim 1, wherein, In step D, the biological flocculant solution accounts for 0.008wt%-0.012wt% of the biogas slurry.

6. The method according to claim 1, wherein, In steps C and D, the time for continuous stirring is 5-10 min. In step B, the mass fraction of the polyaluminum chloride solution is 10%, and the mass fraction of the biological flocculant solution is 0.1%. In step C, the polyaluminum chloride solution accounts for 0.8wt%-1.6wt% of the biogas slurry. In step D, the biological flocculant solution accounts for 0.008wt%-0.012wt% of the biogas slurry. In steps C and D, the time for continuous stirring is 5-10 min.

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