Continuous preparation method for preparing biogas by using dextran wastewater

Abstract

A continuous preparation method for preparing biogas by using dextran wastewater relates to the technical field of biogas preparation, and adopts the technical scheme that the method comprises the following steps: S1, adding anaerobic sludge and clear water or low-concentration wastewater, gradually increasing the temperature of an anaerobic fermentation tank, and starting an internal reflux system; s2, stopping heating when the temperature rises to 30 DEG C; during primary feeding, wastewater is added into the anaerobic fermentation tank according to the starting feeding amount, and primary feeding lasts for multiple days; gradually increasing the wastewater feeding amount of each stage by taking several days as one stage; s3, gradually increasing the temperature in the anaerobic fermentation tank to 50-55 DEG C, and gradually increasing the wastewater feeding amount of each stage by taking several days as one stage. After the medium-temperature fermentation stage operates stably, the temperature is increased to the high-temperature fermentation stage, feeding is performed in a small-amount and multiple-time manner, an internal reflux system is started for assistance, the adaptability of anaerobic microorganisms to high-concentration wastewater and temperature is improved, and the microbial activity, the organic matter removal rate and the gas production rate can be effectively improved through high-temperature fermentation.

Description

Technical Field

[0001] The invention relates to the technical field of biogas preparation, and in particular to a continuous preparation method for biogas by utilizing dextran wastewater. Background Art

[0002] A large amount of wastewater is generated during the production of dextran, the main component of which is ethanol, which has a high potential for methane production. At present, the recycling of ethanol in wastewater usually adopts a medium-temperature fermentation process, that is, anaerobic bacteria are used to ferment wastewater in a medium-temperature environment of about 30°C to produce biogas with methane as the main component. The chemical oxygen demand (COD) concentration of the wastewater that can be treated is required to be no higher than 5000 mg / L, but the COD concentration in dextran wastewater is relatively high, generally around 80,000 mg / L, and a large amount of clean water is required to dilute it to below 5000 mg / L before entering the medium-temperature fermentation process. As a result, there are problems such as low efficiency, low gas production rate, and excessive size of treatment equipment when treating dextran wastewater with the medium-temperature fermentation process. Summary of the invention

[0003] In view of the problems of low efficiency, low gas production rate, large processing equipment volume, etc. when treating dextran wastewater by medium-temperature fermentation process, the present invention provides a continuous preparation method for preparing biogas by using dextran wastewater.

[0004] The present invention provides the following technical solution: a continuous preparation method for biogas using dextran wastewater, comprising the following steps: S1, add screened and domesticated anaerobic sludge into the anaerobic fermentation tank, then add clean water or low-concentration wastewater to fill the anaerobic fermentation tank, then gradually increase the temperature in the anaerobic fermentation tank, and start the internal reflux system.

[0005] The screening and acclimation process of anaerobic sludge is to adapt the anaerobic microorganisms in the sludge to the characteristics of the wastewater to be treated, and to improve the degradation ability of anaerobic microorganisms to the specific organic matter in the dextran wastewater. The anaerobic fermentation tank can refer to the relevant technology, add anaerobic sludge, and then fill it with clean water or low-concentration wastewater. Its function is to discharge most of the air in the anaerobic fermentation tank, create an anaerobic environment, and eliminate the interference of the air in the tank on the calculation of the gas production rate; the low-concentration wastewater refers to dextran wastewater with a COD concentration of less than 5000 mg / L. The anaerobic fermentation tank can be heated by passing steam or electric heating into the steam heating pipeline arranged on the side wall of the tank body; the internal reflux system is a circulation pipeline arranged on the anaerobic fermentation tank, and the material is driven to circulate in the circulation pipeline and the anaerobic fermentation tank by the delivery pump as the power; opening the internal reflux system during the heating process can promote the uniform mixing of wastewater and the uniform distribution of microorganisms, and reduce the number of steam-killed bacteria.

[0006] S2, when the temperature rises to 30~35℃, stop heating, prepare feeding, and carry out medium-temperature fermentation to start anaerobic microorganisms and promote their rapid reproduction; when feeding for the first time, add the wastewater to the anaerobic fermentation tank according to the starting feeding amount, and the initial feeding lasts for several days. Since the COD concentration of the wastewater is high, generally greater than 70,000 mg / L, the wastewater is added to the anaerobic fermentation tank several times a day according to the starting feeding amount, and the internal reflux system is turned on at the same time as the feeding, which helps to improve the adaptability of anaerobic microorganisms to high COD concentration wastewater.

[0007] Then, the wastewater feed rate is gradually increased in each stage over several days to avoid excessive shock load on anaerobic microorganisms and maintain stable operation until the transition feed rate is reached.

[0008] S3, gradually increase the temperature in the anaerobic fermentation tank to 50~55℃ for high-temperature fermentation, and gradually increase the wastewater feed rate in each stage for several days until the designed feed rate is reached and the operation is continued.

[0009] The activity of anaerobic microorganisms is not high during medium-temperature fermentation, so the volatile acid generated when treating high-concentration wastewater cannot be decomposed into methane in time, resulting in the accumulation of volatile acid and acidification of the fermentation liquid. To solve this problem, the present invention increases the temperature in the anaerobic fermentation tank, which helps to improve the activity of microorganisms, the organic matter removal rate and the gas production rate. Compared with the temperature conditions of medium-temperature fermentation, high-temperature fermentation will inhibit the reproduction rate of anaerobic microorganisms, and directly raising the temperature to high-temperature fermentation will kill more microorganisms, resulting in insufficient number of microorganisms to complete the treatment of high-concentration wastewater. Therefore, after the medium-temperature fermentation runs stably for a period of time, it is more helpful to increase the reproduction rate and activity of anaerobic microorganisms; and, heat will be released during the methane generation process. After a period of medium-temperature fermentation, the number of anaerobic microorganisms increases rapidly, and more heat is generated. This part of heat contributes more to raising the fermentation temperature, so as to save the energy consumption required for heating.

[0010] In S2~S3, the wastewater is fed in several times every day, with an interval of several hours each time. During feeding, the COD concentration of the wastewater is greater than 70,000 mg / L, and the pH value is 7.0~7.5. The internal reflux system is opened during the heating and feeding process; the prepared biogas is discharged from the gas outlet.

[0011] Preferably, in S1, the amount of anaerobic sludge added is 30% of the volume of the anaerobic fermentation tank.

[0012] Preferably, in S2, the startup feed amount is 15-20% of the transition feed amount.

[0013] Preferably, in S3, the transition feed amount is 30-35% of the designed feed amount.

[0014] Preferably, in S2-S3, nutrients are added simultaneously each time feeding to promote the growth and metabolic activity of anaerobic microorganisms, and the nutrients include macronutrients and trace nutrients, the macronutrients include ammonia water, superphosphate and ferrous sulfate, and the trace nutrients include zinc, manganese, nickel and cobalt.

[0015] Preferably, in S2-S3, the number of daily feedings increases gradually with the operating time until it reaches the designed number, so as to avoid excessive shock load on the anaerobic microorganisms and maintain stable operation.

[0016] The beneficial effects of the present invention are as follows: the preparation process is divided into a medium temperature fermentation stage and a high temperature fermentation stage, the anaerobic microorganism is started in the medium temperature fermentation stage, and the temperature is raised to the high temperature fermentation stage after the medium temperature fermentation stage runs stably, which can effectively improve the microbial reproduction speed and activity, enhance the treatment capacity of high-concentration wastewater, and improve the organic matter removal rate and gas production rate; directly input dextran wastewater with a COD concentration greater than 70000 mg / L for treatment, complete the feeding of wastewater in a small amount and multiple times, adopt an internal reflux system to circulate the material, improve the adaptability of anaerobic microorganisms to dextran wastewater with extremely high COD concentration, and gradually increase the feed amount and the number of feeds per day to avoid excessive impact load on anaerobic microorganisms. After stable operation, 34.7~55.2 m³ of biogas can be produced per ton of dextran wastewater, and its maximum gas production rate is close to 80% of the theoretical value, and the average gas production rate is increased by 14% compared with the prior art; the organic matter removal rate can reach 95%, which is 12% higher than the prior art. DETAILED DESCRIPTION

[0017] The following is a more detailed description of the embodiments of the present invention so that those skilled in the art can implement the invention after reading this specification. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0018] The present invention provides a continuous preparation method for biogas by using dextran wastewater, comprising the following steps: S1, preparation stage. After the anaerobic fermentation tank and other equipment have been inspected and confirmed to be correct, the effective volume is 1000 m 3 The anaerobic fermentation tank was filled with 300 m3 of anaerobic sludge after screening and domestication. 3 , then add clean water or low-concentration wastewater with a COD concentration of less than 5000 mg / L to fill the anaerobic fermentation tank. Then, use steam to gradually increase the temperature in the anaerobic fermentation tank and turn on the internal reflux system.

[0019] S2, medium temperature fermentation stage. When the temperature in the anaerobic fermentation tank rises to 30-35°C, stop heating and keep the temperature stable, and prepare to feed. Before feeding, adjust the pH value of dextran wastewater with COD concentration greater than 70,000 mg / L to 7.0-7.5.

[0020] When feeding for the first time, the wastewater is 3 / d of starting feed amount is added to the anaerobic fermentation tank, and is evenly divided into 3 times, each time with an interval of 6 hours. The internal reflux system is opened during each feeding, and nutrients are added at the same time, wherein the nutrients include macronutrients and trace nutrients, wherein the macronutrients include ammonia water, superphosphate and ferrous sulfate, and the trace nutrients include zinc, manganese, nickel and cobalt, and the specific addition amounts are shown in Table 1. The initial feeding stage lasts for 6 days. In other embodiments, urea may also be used instead of ammonia water.

[0021] After feeding, the ethanol in the wastewater is converted into biogas with methane as the main component under the fermentation of anaerobic microorganisms, and discharged from the anaerobic fermentation tank from the gas outlet. The biogas can be used for boiler combustion to replace traditional fossil fuels, achieve energy conservation, emission reduction and resource conservation; the treated wastewater is discharged from the outlet.

[0022]

[0023] Then, gradually increase the wastewater feed volume and daily feed frequency in each stage, taking 3 days as a stage, until reaching 20m 3 / d transition feed rate. As the number of feeds per day increases, the interval between each feed is shortened accordingly. During each feed, the COD concentration of dextran wastewater is greater than 70,000 mg / L, the pH value is 7.0-7.5, and the internal reflux system is turned on and nutrients are added. The amount of nutrients added can be referred to Table 1.

[0024] S3, high temperature fermentation stage. The temperature in the anaerobic fermentation tank is gradually raised to 50-55°C, and the wastewater feed volume and daily feed frequency are gradually increased in each stage for 3 or 2 days until it reaches 60m 3 / d designed feed volume, and then continued to run. As the number of feeds per day increases, the interval between each feed is shortened accordingly. During each feed, the COD concentration of dextran wastewater is greater than 70,000 mg / L, the pH value is 7.0-7.5, and the internal reflux system is turned on and nutrients are added. The amount of nutrients added can be referred to Table 1. The internal reflux system also needs to be turned on during the heating process.

[0025] The feed amount and daily feed frequency of S2~S3 can be found in Table 2.

[0026]

[0027] The continuous operation data within a certain period of time after reaching the designed feed rate can be referred to Table 3. As shown in Table 3, each ton of wastewater can produce 34.7~55.2 m³ of biogas (i.e., gas production rate), and its maximum gas production rate is close to 80% of the theoretical value. The organic matter removal rate is about 95%. After treatment, the effluent COD concentration is less than 5000 mg / L.

[0028]

[0029] The above are one or more embodiments of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A continuous preparation method for biogas using dextran wastewater, characterized in that: The following steps are involved: S1, adding screened and domesticated anaerobic sludge into the anaerobic fermentation tank, adding clean water or low-concentration wastewater to fill the anaerobic fermentation tank, then gradually increasing the temperature in the anaerobic fermentation tank, and starting the internal reflux system; S2, when the temperature rises to 30-35℃, stop heating and prepare for feeding; during the initial feeding, add the wastewater into the anaerobic fermentation tank according to the starting feeding amount, and the initial feeding lasts for several days; then, take several days as a stage, gradually increase the wastewater feeding amount in each stage until the transition feeding amount is reached; S3, gradually raise the temperature in the anaerobic fermentation tank to 50-55°C, and gradually increase the wastewater feed rate in each stage for several days until the designed feed rate is reached and the operation continues; In S2~S3, the wastewater is fed in several times every day, with an interval of several hours each time. During feeding, the COD concentration of the wastewater is greater than 70,000 mg / L, and the pH value is 7.0~7.

5. The internal reflux system is opened during the heating and feeding process; the prepared biogas is discharged from the gas outlet.

2. A continuous preparation method for biogas using dextran wastewater according to claim 1, characterized in that: In S1, the amount of anaerobic sludge added was 30% of the volume of the anaerobic fermentation tank.

3. A continuous preparation method for preparing biogas using dextran wastewater according to claim 1, characterized in that: In S2, the startup feed amount is 15-20% of the transition feed amount.

4. A continuous preparation method for preparing biogas using dextran wastewater according to claim 1, characterized in that: In S3, the transition feed amount is 30-35% of the designed feed amount.

5. A continuous preparation method for biogas using dextran wastewater according to claim 1, characterized in that: In S2-S3, nutrients are added simultaneously each time feeding, and the nutrients include macronutrients and trace nutrients, the macronutrients include ammonia water, superphosphate and ferrous sulfate, and the trace nutrients include zinc, manganese, nickel and cobalt.

6. The method for continuously preparing biogas from dextran wastewater according to claim 1, characterized in that: In S2~S3, the number of feeds per day gradually increases with the operating time.

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