Method for detecting VFA (Volatile Fatty Acid) of anaerobic jar in dry anaerobic system

Abstract

The invention discloses a method for detecting VFA (Volatile Fatty Acid) of an anaerobic jar in a dry anaerobic system, which comprises the following steps: taking a material in the dry anaerobic jar, filtering out impurities in the material, and then centrifuging to take supernate; adding the supernate into a distillation flask, adding pure water into the distillation flask, then adding phosphoric acid, and adding pure water into a conical flask for absorbing distilled gas; placing the distillation flask and the conical flask on a distillation instrument, starting a condensation pipe of the distillation instrument for water circulation, and then starting distillation; after distillation is finished, the liquid in the conical flask is placed on a distillation instrument to be heated to a boiling state, a phenolphthalein color developing agent is added, a sodium hydroxide solution is used for titration until the liquid becomes light red, and the volume of consumed sodium hydroxide is recorded and used for calculating the VFA of the anaerobic jar. A part of water sample can be obtained from the sludge treated by the method and can be directly used for detecting VFA (Volatile Fatty Acid).

Description

Technical Field

[0001] The invention relates to the field of anaerobic fermentation, and in particular to a method for detecting VFA of an anaerobic tank in a dry anaerobic system. Background Art

[0002] Kitchen waste refers to the waste generated in residents' daily life, food processing, catering services, and corporate catering activities, including discarded vegetable leaves, leftovers, leftover rice, fruit peels, eggshells, tea dregs, bones, fish bones, etc. Its main sources are family kitchens, restaurants, hotels, canteens, markets, and other industries related to food processing. Kitchen waste contains extremely high moisture and organic matter, and is easily rotten and produces a foul odor.

[0003] Kitchen waste can be transformed into new resources after proper treatment and processing. Its high organic content allows it to be used as fertilizer and feed after strict treatment. It can also produce biogas for fuel or power generation, and the oil and fat part can be used to prepare biofuel. However, if kitchen waste cannot be disposed of in a timely and effective manner, it will inevitably have a huge impact and harm on human health and the social environment. Most projects treat kitchen waste as a resource, among which anaerobic digestion technology is widely used. Dry anaerobic is a high-solid anaerobic process with the advantages of low energy consumption, less sewage to be treated, high feed organic load (OLR), and lax pretreatment requirements. It has become the mainstream method for treating kitchen waste.

[0004] Dry anaerobic fermentation is a biogas fermentation technology with a feed TS content (dry matter content) greater than or equal to 20%. It produces less biogas slurry and biogas residue, and has a strong load resistance. Therefore, the TS content in the dry anaerobic tank is about 20%, and generally not less than 16%. The feed of the dry anaerobic system is the material obtained by pre-treatment of kitchen waste by screening, crushing, extrusion, etc., with a solid content of about 30%. After entering the dry anaerobic tank, there will be a residence time of about 40 days. The sample in the dry anaerobic tank is mixed with impurities and sludge, resulting in no way to accurately detect its VFA (volatile fatty acids). The anaerobic tank needs to monitor its VFA daily to achieve the purpose of determining the state of the tank. Summary of the invention

[0005] The object of the present invention is to provide a method for detecting VFA in an anaerobic tank in a dry anaerobic system, wherein part of the water sample can be obtained from the treated sludge and can be directly used to detect VFA.

[0006] In one aspect of the present invention, the present invention provides a method for detecting VFA in an anaerobic tank in a dry anaerobic system. According to an embodiment of the present invention, the method comprises the following steps:

[0007] (1) Take the material in the dry anaerobic tank, filter out the impurities in the material, and then centrifuge to obtain the supernatant;

[0008] (2) adding the supernatant to a distillation flask, adding pure water to the distillation flask, and then adding phosphoric acid, and adding pure water to a conical flask to absorb the distilled gas;

[0009] (3) Place the distillation flask and conical flask on the distiller, start the water circulation of the distiller's condenser, and then start distillation;

[0010] (4) After the distillation is completed, place the liquid in the conical flask on a distiller and heat it to boiling. Add phenolphthalein color developer and titrate with sodium hydroxide solution until the liquid turns light red. Record the volume of sodium hydroxide consumed for calculating the VFA of the anaerobic tank.

[0011] In addition, the method for detecting VFA in an anaerobic tank in a dry anaerobic system according to the above embodiment of the present invention may also have the following additional technical features:

[0012] In some embodiments of the present invention, in step (1), filtering is performed using a mesh screen.

[0013] In some embodiments of the present invention, in step (1), the centrifugal speed is 10000 rpm and the centrifugal time is 18-30 min.

[0014] In some embodiments of the present invention, in step (2), the volume ratio of the supernatant, pure water and phosphoric acid in the distillation flask is 20:50:1.

[0015] In some embodiments of the present invention, in step (3), the distillation process is carried out in two stages. During the first stage of distillation, seven tenths of the liquid in the distillation flask is evaporated into the conical flask and then the process is stopped. The liquid is the VFA test liquid. After the temperature is slightly lowered, pure water is added to the distillation flask to four fifths of the initial liquid volume of the distillation flask, and the second stage of distillation is continued. Seven tenths of the liquid in the distillation flask is evaporated into the conical flask and then the process is stopped.

[0016] In some embodiments of the present invention, in step (4), the concentration calculation formula of VFA in the anaerobic tank is as follows:

[0017] formula:

[0018] In the formula, ρ is the concentration of VFA, in mg / L; c is the concentration of the prepared sodium hydroxide solution, in mol / L; V2 is the volume of sodium hydroxide consumed, in ml; M is the molar mass of acetic acid; V1 is the volume sampled from the conical flask, in ml.

[0019] In some embodiments of the present invention, in step (4), the concentration of the sodium hydroxide solution is 0.1 mol / L to 0.5 mol / L.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention can firstly solve the problem that the material in the dry anaerobic tank is in a mixed state of impurities and sludge, and extract a liquid that can be used for experiments; secondly, the liquid can also be used to detect other indicators, such as cod, ammonia nitrogen, total nitrogen, etc., not only VFA; finally, a method for stably detecting VFA in a dry anaerobic tank is provided, so that the staff can more intuitively determine the activity state of the current bacteria in the tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a flow chart of a method for detecting VFA of an anaerobic tank in a dry anaerobic system in an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not 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] The following instruments and reagents are required for the following examples: mesh screen, centrifuge tube, high-speed centrifuge, beaker, phosphoric acid, distillation flask, conical flask, distiller, phenolphthalein reagent, basic burette, sodium hydroxide solution.

[0025] The distillation flask and conical flask in the above instruments are both distiller and can be used separately. The distiller is a heating device. The distillation flask is placed on the heating plate. The distillation flask itself is connected to the conical flask through a condenser. At the beginning of distillation, the condenser must ensure that tap water flows to achieve the purpose of cooling the distilled gas into liquid, and then all falls into the conical flask.

[0026] Example 1

[0027] A method for detecting VFA in an anaerobic tank in a dry anaerobic system comprises the following steps:

[0028] 1) Use a 20-mesh sieve to remove impurities from the dry anaerobic tank material and take out only the sludge. Put the sludge into 50ml centrifuge tubes (even number), put them symmetrically into a high-speed centrifuge, select a speed of 10000rpm, centrifuge for 20 minutes, then take out the centrifuge tube, take out only the supernatant and put it into a pre-prepared beaker, and remove the suspended impurities when taking it out.

[0029] 2) Take 10 ml of the upper clear liquid after removing impurities and add it to the distillation flask, add 100 ml of pure water to the distillation flask, and then add 2 ml of phosphoric acid to change the environment inside the flask, and add 30 ml of pure water to the conical flask of the receiving device of the distiller to absorb the distilled gas.

[0030] 3) Start the distillation operation, place the distillation flask and the conical flask on the distiller, start the water circulation of the distiller's condenser, and then start the distillation. The obtained water vapor will enter the conical flask. The first wave will stop after 70ml of liquid is distilled from the distillation flask to the conical flask. When the temperature drops slightly, add 50ml of pure water to the distillation flask and continue the second wave of distillation. Stop after 50ml of liquid is distilled into the conical flask.

[0031] 4) Place the liquid in the conical flask on a distiller and heat it to boiling, add phenolphthalein color developer, and titrate with sodium hydroxide solution (concentration of 0.173 mol / L) until the liquid turns light red. Record the volume of sodium hydroxide consumed for calculating the VFA of the dry anaerobic tank.

[0032] Since 1.1 ml of sodium hydroxide solution is consumed, the following is obtained according to the calculation formula:

[0033] The result showed that VFA was 1633 mg / L.

[0034] Example 2

[0035] A method for detecting VFA in an anaerobic tank in a dry anaerobic system. The difference between this embodiment and embodiment 1 is that the sampling time from the dry anaerobic tank is different, and the sodium hydroxide solution in step 4) is different. In this embodiment, the sodium hydroxide solution is 0.178 mol / L, and 2.4 ml of sodium hydroxide solution is consumed. According to the formula The test result was 3665 mg / L.

[0036] Example 3

[0037] The difference between this embodiment and embodiment 1 is that: this embodiment takes samples from the dry anaerobic tank for 7 consecutive days, and samples are taken from the front sampling port, the middle sampling port, and the rear sampling port of the anaerobic tank every day to perform VFA concentration detection. The experimental data obtained by the detection are shown in the following table:

[0038] Table 1 VFA concentration test results of Example 3 for 7 consecutive days

[0039]

[0040] This food waste treatment plant has been using this detection method for more than two years, with daily testing. According to the test data, the dry anaerobic tank is running stably without any crash. VFA will increase significantly when the feed rate of the anaerobic tank is suddenly increased. After a period of continuous high feed rate operation, VFA has reached 17,000 (this data is the highest data reached when our plant tested the anaerobic tank's bearing capacity, and the material has become partially acidified). After running stably for about a year and without acidification and collapse of the anaerobic tank, there is a complete cognitive system for the data detected by this method, which can be used to guide production and stabilize operation. The VFA data of the front, middle and back ends (suitable for horizontal anaerobic tanks) have relatively clear specified ranges. The front end VFA is controlled below 8,000 to ensure the stable operation of the anaerobic tank.

[0041] Comparative Example

[0042] A method for detecting VFA in an anaerobic tank in a dry anaerobic system comprises the following steps:

[0043] 1) Take samples from the three sampling ports (front sampling port, middle sampling port, and rear sampling port) of the anaerobic tank for 5 consecutive days, then add 10g of dry anaerobic material into the distillation flask, add 100ml of pure water into the distillation flask, and then add 2ml of phosphoric acid to change the environment inside the flask, and add 30ml of pure water into the conical flask of the receiving device of the distiller to absorb the distilled gas.

[0044] 2) Start the distillation operation, place the distillation flask and the conical flask on the distiller, start the water circulation of the distiller's condenser, and then start the distillation. The obtained water vapor will enter the conical flask. The first wave will distill 70ml from the distillation flask into the conical flask and then stop. Wait until the temperature drops slightly, add 50ml of pure water to the distillation flask, and continue the second wave of distillation. Stop after 50ml of liquid is distilled into the conical flask.

[0045] 3) Place the liquid in the conical flask on a distiller and heat it to boiling, add phenolphthalein color developer, and titrate with sodium hydroxide solution (concentration of 0.173 mol / L) until the liquid turns light red, and record the volume of sodium hydroxide consumed for calculating the VFA of the dry anaerobic tank.

[0046] The test results of VFA concentration in the anaerobic tank of the 5-day dry anaerobic system are shown in the following table:

[0047] Table 2 Comparative Example Dry Anaerobic System Anaerobic Tank VFA Concentration Test Results

[0048]

[0049] The results obtained at the front-end sampling port of the comparative example were 148, 297, 148, 148, and 297, respectively. The data were detected during the production load increase and feeding stage. The data were low and did not fluctuate at all, and could not provide any reference value for production. Based on the large fluctuations in the feeding conditions of the dry anaerobic tank data after this method was later determined, it was determined that this data had no reference value.

[0050] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A method for detecting VFA in an anaerobic tank in a dry anaerobic system, characterized in that: The following steps are involved: (1) Take the material in the dry anaerobic tank, filter out the impurities in the material, and then centrifuge to obtain the supernatant; (2) adding the supernatant to a distillation flask, adding pure water to the distillation flask, and then adding phosphoric acid, and adding pure water to a conical flask to absorb the distilled gas; (3) Place the distillation flask and conical flask on the distiller, start the water circulation of the distiller's condenser, and then start distillation; (4) After the distillation is completed, take the liquid from the conical flask and place it on the distiller to heat to boiling state, add phenolphthalein color developer, and titrate with sodium hydroxide solution until the liquid turns light red. Record the volume of sodium hydroxide consumed for calculating the VFA of the anaerobic tank.

2. The method for detecting VFA in an anaerobic tank in a dry anaerobic system according to claim 1, characterized in that: In the step (1), filtering is performed using a mesh screen.

3. The method for detecting VFA in an anaerobic tank in a dry anaerobic system according to claim 1, characterized in that: In the step (1), the centrifugal speed is 10000 rpm and the centrifugal time is 18-30 min.

4. The method for detecting VFA in an anaerobic tank in a dry anaerobic system according to claim 1, characterized in that: In the step (2), the volume ratio of the supernatant, pure water and phosphoric acid in the distillation flask is 20:50:

1.

5. The method for detecting VFA in an anaerobic tank in a dry anaerobic system according to claim 1, characterized in that: In the step (3), the distillation process is carried out in two stages. During the first stage of distillation, seven tenths of the liquid in the distillation flask must be distilled into the conical flask before the distillation process is stopped. The liquid is the VFA test liquid. After the temperature is slightly lowered, pure water is added to the distillation flask to four fifths of the initial liquid volume of the distillation flask. The second stage of distillation is continued until seven tenths of the liquid in the distillation flask is distilled into the conical flask before the distillation process is stopped.

6. The method for detecting VFA in an anaerobic tank in a dry anaerobic system according to claim 1, characterized in that: In step (4), the concentration calculation formula of VFA in the anaerobic tank is as follows: official: In the formula, ρ is the concentration of VFA, in mg / L; c is the concentration of the prepared sodium hydroxide solution, in mol / L; V2 is the volume of sodium hydroxide consumed, in ml; M is the molar mass of acetic acid; V1 is the volume sampled from the conical flask, in ml.

7. The method for detecting VFA in an anaerobic tank in a dry anaerobic system according to claim 1, characterized in that: In the step (4), the concentration of the sodium hydroxide solution is 0.1 mol / L to 0.5 mol / L.

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