WO2015006882A1

WO2015006882A1 - Method for implementing zero emission biogas slurry in pure straw anaerobic digestion

Info

Publication number: WO2015006882A1
Application number: PCT/CN2013/000856
Authority: WO
Inventors: 李秀金; 胡赟; 邹德勋; 袁海荣; 朱保宁; 刘研萍
Original assignee: 北京化工大学
Priority date: 2013-07-17
Filing date: 2013-07-17
Publication date: 2015-01-22
Also published as: CN104662157A

Abstract

Disclosed in the present invention is a method for implementing zero emission biogas slurry in pure straw anaerobic digestion, comprising (1) pretreating a pure straw feedstock; (2) adjusting the C/N of the pretreated straw, and feeding; (3) discharging fermentation residues from the anaerobic digestion reactor, and isolating biogas slurry therefrom; (4) performing an aerobic nitrification treatment on the biogas slurry outside the anaerobic digestion reactor; (5) refluxing 100% of the biogas slurry in the straw feeding process, after the aerobic treatment, to the anaerobic digestion system, and performing a denitrification treatment on the biogas slurry in the anaerobic digestion reactor. The method of the present invention combines the in vitro aerobic nitrification and in vivo denitrification of the biogas slurry, thereby effectively reducing the COD and ammonia nitrogen concentration of the biogas slurry, no additional carbon source needs to be added in the denitrification process, and the inhibitory effect of reusing the biogas slurry on the system is eliminated, thereby achieveing zero emission biogas slurry and 100% reuse, and avoiding secondary pollution; at the same time, completely replacing the straw with biogas slurry for feeding regulates water, thereby achieving significant water conservation, reducing operating costs and being capable of maintaining the long-term stable operation of the anaerobic digestion reactor.

Description

Method for realizing zero discharge of pure straw anaerobic digestion biogas slurry

The invention belongs to the technical field of solid waste treatment, and particularly relates to a method for realizing zero discharge of pure straw anaerobic digestion biogas slurry. Background technique

China is a traditional agricultural country with abundant straw resources. Except for a small amount of effective use, open burning is still the main disposal method, which wastes a lot of resources when causing air pollution. Straw wet anaerobic digestion technology has been widely used in recent years due to its low energy consumption and high productivity. However, the disposal of biogas slurry after digestion has become one of the main problems hindering the development of anaerobic digestion technology of orange stalk. . The traditional biogas project is equipped with a biogas slurry and biogas residue storage tank. It has a large area, high investment cost and difficult subsequent processing. A large amount of biogas slurry is often discharged disorderly, resulting in serious secondary pollution.

At present, the treatment of biogas slurry is mainly concentrated on irrigation or foliar spraying as organic liquid fertilizer, extracting nutrients from it and adding other nutrients to make high-efficiency bacterial fertilizer and microbial agents, and discharging them after physical and biological treatment. Or return the biogas directly to the anaerobic digestion system. Among them, the reflux of biogas slurry can significantly reduce the discharge of biogas slurry and reduce the cost of treatment and disposal. However, direct recirculation easily leads to the accumulation of COD, ammonia nitrogen and other inhibitory substances in the reactor, which makes the system unable to operate stably for a long time, and is boring with pure orange stalk as raw material. Related research on oxygen digestion reactors is still very limited.

Patent CN102586333 proposes a method of recycling part of biogas slurry to straw anaerobic digestion system to reduce biogas discharge, but the direct reuse of biogas slurry may cause the increase of system organic load and the accumulation of some anaerobic reaction inhibitors (such as ammonia nitrogen). The system can not be operated stably for a long time, and the complete reduction of biogas slurry can not be achieved. Patent CN102503019 proposes to carry out micro-oxidation and decolorization treatment of waste liquid produced in traditional industries such as sucrose and alcohol by biological fermentation, and then return to the original anaerobic. The oxygen digestion reactor relieves the impact of the direct reflux of the biogas slurry on the system, but the aerobic treatment process is complicated and is aimed at the alcohol fermentation industry.

The invention proposes to combine the aerobic nitrification of the biogas liquid with the denitrification in the body to realize zero discharge and 100% reuse of the pure straw anaerobic fermentation biogas slurry. At present, the research on the similar treatment of pure straw anaerobic digestion biogas slurry has not been reported. Summary of the invention

The invention aims to provide a method for realizing zero discharge and 100% reuse of pure straw anaerobic digestion biogas slurry by combining aerobic nitrification of biogas liquid with denitrification in vivo. The purpose is to achieve zero discharge and 100% reuse of biogas slurry, avoid secondary pollution; completely replace the regulating water in the straw feeding process, significantly save water consumption and reduce operating cost; and maintain anaerobic digestion reactor Long-term stable operation and improved production efficiency.

As shown in FIG. 1 , the present invention relates to a method for realizing zero discharge of pure straw anaerobic digestion biogas slurry, and the specific process thereof comprises The following steps:

h h Pretreatment of pure straw raw materials

The straw is mechanically pulverized, and the pulverized straw has a particle diameter of 3 cm, preferably, a particle diameter of 1 cm; optionally, the pulverized straw is pretreated, and the pretreatment manner includes, but is not limited to, biological, chemical or physical methods, preferably, Soaking with 0.2-0.4% NaOH solution at medium temperature for 12-24h;

Step 2: Adjust the C/N of the pretreated straw and feed it

Adjusting the C N for the pretreated straw, optionally, adding an N source such as urea; adding the biogas slurry and the straw to the semi-continuous or continuous anaerobic digestion reactor with stable operation;

Step 3: The fermentation residue is discharged from the anaerobic digestion reactor, and the biogas slurry is separated therefrom.

In the semi-continuous or continuous feed and discharge system, a corresponding amount of mixed discharge is discharged after daily feeding, and the mixed discharge is subjected to solid-liquid separation to obtain biogas slurry and biogas residue, the biogas residue is separated, and the biogas slurry is subjected to the next treatment. ;

Step 4: The biogas slurry is subjected to aerobic nitrification and COD removal outside the anaerobic digestion reactor.

The separated biogas slurry is sent to an aerobic aeration tank for continuous aeration for 20-24 hours, and the biogas slurry is subjected to in vitro nitrification reaction. In the aerobic aeration process, the ammonia nitrogen is completely converted into nitrite nitrogen and nitrate nitrogen by the nitrifying bacteria, and the ammonia nitrogen removal rate is 100%. The nitrification reaction is as follows:

Nitrous acid bacteria

2NH ₄ + + 0 ₂ ► 2 Ν0 ₂ ' + 4Η ⁺ + 2 Η ₂ 0

Nitric acid bacteria

2 Ν0 ₂ " ► 2 Ν0 ₃ "

At the same time, the aerobic bacteria consume part of the COD in the biogas slurry during the growth process, and the COD removal rate is 50%~60%, which effectively reduces the organic load of the biogas slurry;

Step 5: Denitrification of the biogas slurry in an anaerobic digestion reactor

100% of the aerobic treated biogas slurry is mixed with the orange stalk in step 1 into a semi-continuous or continuous anaerobic digestion reactor with stable operation, and denitrified by a C source dissolved in the biogas slurry after digestion by the straw itself. In the denitrification process, no additional carbon source is needed, and the denitrification reaction in the biogas liquid can be realized, and NH ₄ ⁺ -N is converted into N ₂ , and the denitrification reaction is as follows; nitrate reducing bacteria

NCV + C (in straw) ^ N0 ₂ - + C0 ₂ + H ₂ 0

τ^ . ^ _ί+3:τ ^ _ήΑ , citrate reduction ι ί , _τ ^ 八_{τ τ} ^

Ν0 ₂ + C (in straw) ► Ν ₂ + C0 ₂ + H ₂ 0 Repeat steps 1-5. The number of repetitions can be reasonably selected as needed.

In a preferred embodiment of the present invention, the step 2 includes a step of detecting the biogas slurry TS; preferably, the biogas slurry TS after the solid-liquid separation is 0.5%, and if it is not satisfied, it should be changed. The separation method is such that the separated biogas slurry TS satisfies the above conditions.

In a preferred embodiment of the present invention, in the step 3, the aeration is increased or decreased during the aeration process. Strength control aeration tank DO concentration; further comprising, after continuous aeration, a step of reducing Na ⁺ concentration by dilution; optionally, including detecting a reflux liquid TS, ammonia nitrogen and COD concentration after aeration, preferably, The aeration process and the reflux liquid satisfy DO 2.0 mg/L; biogas slurry TS 0.2%, COD 1500 mg/L, ammonia nitrogen 10 mg/L, Na+ 1000 mg/L; in another preferred embodiment of the present invention, 歩The feed in step 1 only includes refluxing biogas slurry and straw, excluding additional water distribution.

In another preferred embodiment of the present invention, the semi-continuous or continuous feed and discharge system refers to a conventional sequencing batch anaerobic digestion reactor, including but not limited to a CSTR, ASBR reactor, and the size and shape of the reactor do not affect the present invention. Implementation.

In a preferred embodiment of the present invention, the biogas slurry is extracted by solid-liquid separation, and the solid-liquid separation includes, but is not limited to, a combination of one or more of plate and frame filtration, high-speed centrifugation, and filter separation.

In another preferred embodiment of the invention, the experimental material to which the present invention relates is pure crop orange stalks, not mixed with any other fermentation material, including but not limited to corn stalks, wheat straw, straw or combinations thereof.

In another preferred embodiment of the invention, the process of the invention operates continuously for more than 300d, preferably for more than 350d.

Compared with the existing pure straw biogas slurry treatment technology, the invention has the advantages of combining the aerobic nitrification of the biogas liquid with the denitrification in the body, and the specific reaction process is shown in FIG. 2 . During the aerobic aeration process, ammonia nitrogen is converted into nitrite nitrogen and nitrate nitrogen under the action of nitrifying bacteria, and the ammonia nitrogen removal rate is stable at 100% for a long time. Meanwhile, the aerobic bacteria consume the biogas slurry during their own growth. Part of the COD, COD removal rate of 50% to 60%, effectively reduce the organic load of biogas slurry. After the aerobic nitrification, the biogas slurry is 100% reused in the orange stalk feeding process, and the nitrite nitrogen and nitrate nitrogen are converted into a nitrogen discharge system under the action of denitrifying bacteria, and the straw itself can provide sufficient denitrifying bacteria. The carbon source is denitrified without the need to add an additional carbon source. The invention effectively reduces the COD and ammonia nitrogen concentration of the biogas slurry, eliminates the inhibition effect of the biogas slurry 100% reuse system, and maintains the long-term stable operation of the anaerobic digestion reactor while achieving zero discharge of the biogas slurry and 100% reuse; Completely replace the regulated water in the straw feed to achieve significant water savings: In a hydraulic retention time (HRT) of pure straw anaerobic digestion, the unit reactor volume can save more than 50% of water, reducing operating costs. DRAWINGS

Figure 1 is a schematic diagram showing the overall process of a method for realizing zero discharge of pure straw anaerobic digestion biogas slurry.

Figure 2 is a schematic diagram of the principle of aerobic nitrification treatment and denitrification treatment in the biogas liquid. detailed description

The present invention will be further described below in conjunction with specific examples.

The experimental apparatus used in this example was a CSTR anaerobic digestion reactor with a volume of 8 L, an anaerobic fermentation raw material of corn stover, and a loading load of 80 gTS/L (TS is the dry weight of corn stalks). The specific steps are as follows: 1. In a stable semi-continuous anaerobic digestion experiment, 15.05 g of mashed corn stalks with a particle size of 0.3 cm per day were pretreated by immersion in NaOH solution (the amount of NaOH powder and water added was 0.2 dry weight of corn stalk, respectively). % and 600%, NaOH solution concentration is 0.33%), and the treatment time is ld.

2. After the pre-treatment, the orange stalk is adjusted to a C N of 25 and then sent to the CSTR anaerobic digestion reactor, and the discharge of the day is 180mlo.

3. The discharge was centrifuged at 8400 rpm for 10 min in a high-speed centrifuge to obtain about 80 ml of the upper biogas slurry, and the TS was determined to be 0.44%, which satisfies the requirements.

4. Drain the biogas slurry and pour it into a 3L aerobic aeration tank.

5. Monitor the parameters in the aeration tank with DO = 6.7 mg/L. After continuous aeration for 24h, the parameters were TS=0.17%, COD=1250 mg/L _, ammonia nitrogen=21.8mg/L, Na ⁺ =2051 mg/L; Na ⁺ concentration was found to be excessive, so the biogas slurry was diluted. The Na+ concentration meets the requirements.

6. Mix 75 ml of the biogas slurry after aeration with the straw described in 11, without adding water, add to the CSTR anaerobic fermentation system, and discharge the day's discharge.

7. Repeat 3 to 6歩.

This example has been continuously operated for 380 days in the laboratory. There is no phenomenon of straw digestion and gas production inhibition. The pH is stable and the system is operating normally.

The above is only the specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that are not thought of by the creative work are included in the scope of the present invention. Therefore, the scope of the invention should be determined by the scope of the invention as defined by the appended claims.

Claims

Claim

1. A method for achieving zero discharge of pure straw anaerobic digestion biogas slurry, comprising the following process steps:

(1) pretreating pure straw raw materials;

(2) Adjusting the C/N of the pretreated straw and feeding it;

(3) discharging the fermentation residue from the anaerobic digestion reactor and separating the biogas slurry therefrom;

(4) The biogas slurry is subjected to aerobic nitrification and COD removal outside the anaerobic digestion reactor;

(5) The aerobic treated biogas slurry is refluxed 100% into the anaerobic digestion reactor during the straw feeding process, and the biogas slurry is subjected to denitrification treatment in the anaerobic digestion reactor.

Repeat steps 1-5.

2. A method for realizing zero discharge of pure straw anaerobic digestion biogas slurry, the specific process thereof comprises the following steps: Step 1: pretreating pure straw raw material

The straw is mechanically pulverized, and the stalk has a particle size of 3 cm, preferably, a particle size of 1 cm; optionally, the straw is pretreated by immersing in a 0.2-0.4% NaOH solution at a medium temperature for 12-24 hours;

Step 2: Adjust the C/N of the pretreated orange stalks and feed

Step 3: The fermentation residue is discharged from the anaerobic digestion reactor, and the biogas slurry is separated therefrom

In the semi-continuous or continuous feed and discharge system, a corresponding amount of mixed discharge is discharged after feeding every day, and the mixed discharge is subjected to solid-liquid separation to obtain biogas slurry and biogas residue, the biogas residue is separated, and the biogas slurry is subjected to the next treatment. ;

Nitrous acid bacteria

2NH ₄ ⁺ + 0 ₂ ► 2 Ν0 ₂ ' + 4Η ⁺ + 2 Η ₂ 0 At the same time, aerobic bacteria consume part of the COD in the biogas slurry during their own growth, and the COD removal rate is 50%~60%, effectively reducing the marsh Liquid organic load;

Step 5: The biogas slurry is denitrified in an anaerobic digestion reactor

100% of the aerobic treated biogas slurry is mixed with the straw in the first step into a semi-continuous or continuous anaerobic digestion reactor with stable operation, and the C source dissolved in the biogas slurry is digested by the straw itself. In the denitrification process, no additional carbon source is needed, and the denitrification reaction in the biogas liquid can be realized, and NH-N is converted into N ₂ , and the denitrification reaction formula is as follows; N0 ₃ - ₊ C (in straw) sac ^ N0 ₂ - ₊ C0 _{2 +} H ₂ 0 N ₀₂ - _{+ C} (in straw) sub-salt reduction _{N2 + C} 0 _{2 +} H ₂ 0

Repeat steps 1-5, 2 times or more.

The method for realizing zero discharge of pure straw anaerobic digestion biogas slurry according to claim 2, wherein the step 2 comprises a step of detecting the biogas slurry TS; preferably, the solid-liquid separation After the biogas slurry TS 0.5%, if not satisfied, the separated biogas slurry TS satisfies the above conditions by further separation.

The method for realizing zero discharge of pure straw anaerobic digestion biogas slurry according to claim 2, wherein in the step 3, the aeration tank DO is controlled by increasing or decreasing the aeration intensity during the aeration process. Concentration; further comprising, after continuous aeration, a step of reducing the concentration of Na+ by a dilution method; optionally, including detecting a concentration of reflux TS, ammonia nitrogen and COD after aeration, preferably, said aeration process and reflux The liquid meets DO 2.0 mg/L; biogas slurry TS 0.2%, COD ^ 1500 mg/L ammonia nitrogen 10 mg/L, Na ⁺ ^ 1000 mg/L;

5. A method for achieving zero discharge of pure straw anaerobic digestion biogas slurry according to claim 2, wherein the feeding in step 1 comprises only refluxed biogas slurry and straw, excluding additional water distribution and/or other fermentation materials.

6. A method of achieving zero discharge of pure straw anaerobic digestion biogas slurry according to claim 2, wherein the semi-continuous or continuous feed and discharge system is selected from the group consisting of a CSTR or an ASBR reactor.

7. The method for realizing zero discharge of pure orange stalk anaerobic digestion biogas slurry according to claim 2, wherein the solid-liquid separation is selected from one or more of a plate frame filtration, a centrifugation, and a filter separation method. combination.

8. A method for achieving zero discharge of pure straw anaerobic digestion biogas slurry according to claim 2, wherein the straw is selected from the group consisting of corn orange, wheat straw, straw, and the like, or a combination thereof.

9. A method for achieving zero discharge of pure straw anaerobic digestion biogas slurry according to claim 2, said method being continuously operated for more than 300 days, preferably, continuously operating for more than 350 days.