A method for producing biogas by anaerobic fermentation treatment of high-concentration organic wastewater

Abstract

The present invention provides a method for producing biogas by anaerobic fermentation treatment of high-concentration organic wastewater, which relates to the field of waste liquid treatment. The method comprises: mixing and adsorbing modified biochar with a particle size of 5 mm with high-concentration organic wastewater to obtain low-concentration organic wastewater and adsorbed biochar; mixing low-concentration organic wastewater with modified biochar with a particle size of 10 to 20 mm and anaerobic sludge, and anaerobically fermenting to obtain biogas liquid; desorbing the adsorbed biochar with the biogas liquid to obtain waste liquid; mixing the waste liquid with biochar with a particle size of 10 to 20 mm and anaerobic granular sludge, and anaerobically fermenting to achieve the treatment of high-concentration organic wastewater. By adopting the method provided by the present invention, the wastewater treatment efficiency is above 85%, and the biogas yield is 0.45 Nm 3 / kg COD or above, of which the methane content is above 65%.

Description

Technical Field

[0001] The present invention relates to the field of waste liquid treatment, in particular to a method for producing biogas by treating high-concentration organic waste water with anaerobic fermentation. Background Art

[0002] Crop straw is one of the main agricultural wastes. According to statistics, my country produced 865 million tons of straw in 2021. With the continuous development of agricultural production and the gradual improvement of the structure of energy consumption in life, the problem of straw utilization has become increasingly prominent and has become a new source of rural non-point source pollution. Biochar, as a biocompatible conductive porous adsorption material, is conducive to the reproduction and habitat of anaerobic fermentation functional microorganisms, which can increase the number and activity of microorganisms. At the same time, because it has a large number of oxygen-containing functional groups such as quinone and hydroquinone, it can act as an electron shuttle and promote direct interspecies electron transfer of microorganisms. Therefore, the use of straw to prepare biochar is an important way to achieve its high value utilization.

[0003] Anaerobic microbial treatment is only effective in treating medium- and low-concentration organic wastewater, but its ability to withstand the impact of pollutants in high-concentration wastewater is relatively weak. Treatment of high-concentration wastewater, such as thermochemical byproduct wastewater, industrial wastewater, fine chemical wastewater, pesticide wastewater, pharmaceutical wastewater, and slaughterhouse wastewater, typically requires pretreatment such as absorption and dilution. Furthermore, anaerobic microorganisms grow and reproduce relatively slowly, resulting in a long reactor startup time, reduced reactor treatment efficiency, and increased costs. Therefore, it is crucial to utilize multiple technologies in a coupled manner to achieve efficient, cascaded treatment of high-concentration organic wastewater. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a method for producing biogas by anaerobic fermentation treatment of high-concentration organic wastewater. The present invention makes full use of the physical and chemical properties of biochar and anaerobic fermentation technology to achieve efficient step-by-step deep treatment of high-concentration organic wastewater.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a method for producing biogas by treating high-concentration organic wastewater through anaerobic fermentation, comprising the following steps:

[0007] 1) Mixing and adsorbing modified biochar with a particle size of 5 mm with high-concentration organic wastewater to obtain low-concentration organic wastewater and adsorbed biochar;

[0008] 2) mixing the low-concentration organic wastewater obtained in step 1) with modified biochar having a particle size of 10 to 20 mm and anaerobic sludge, and obtaining biogas slurry after anaerobic fermentation;

[0009] 3) desorbing the adsorbed biochar obtained in step 1) with the biogas slurry obtained in step 2) to obtain waste liquid;

[0010] 4) The waste liquid obtained in step 3) is mixed with modified biochar with a particle size of 10 to 20 mm and anaerobic sludge, and subjected to anaerobic fermentation to achieve the treatment of high-concentration organic wastewater.

[0011] Preferably, the preparation methods of modified biochar in step 1), step 2) and step 4) all include:

[0012] Carbonizing crop straw to obtain biochar;

[0013] The biochar is activated and modified to obtain modified biochar.

[0014] Preferably, the crop straw includes one or more of wheat straw, corn straw, rice straw, peanut straw and cotton straw.

[0015] Preferably, the carbonization treatment includes hydrothermal carbonization treatment or pyrolytic carbonization treatment;

[0016] The conditions of the hydrothermal carbonization treatment include: temperature of 180-300°C and time of 1-3h;

[0017] The conditions of the pyrolysis carbonization treatment include: a temperature of 300 to 1000° C. and a time of 0.5 to 2 hours.

[0018] Preferably, the activation modification includes chemical impregnation and / or physical ball milling.

[0019] Preferably, the amount of modified biochar added in step 1), step 2) and step 4) is 5 to 15 g / L.

[0020] Preferably, the anaerobic sludge in step 2) and step 4) both include anaerobic granular sludge;

[0021] The addition amount of the anaerobic sludge is 15%-25%, which is the volume percentage.

[0022] Preferably, the conditions for the anaerobic fermentation in step 2) and step 4) include: a fermentation temperature of 35-38° C., a fermentation time of 30-35 days, and a stirring speed of 100-120 rpm.

[0023] The present invention uses crop straw as raw material, crushes it into different particle sizes, and adopts hydrothermal or pyrolysis process to prepare powdered biochar and granular biochar, and modifies and activates the biochar to improve its quality. First, powdered biochar is used as an adsorbent to adsorb high-concentration organic wastewater, and the high-concentration organic wastewater is converted into low-concentration organic wastewater after adsorption, and then anaerobically fermented to produce biogas. In addition, granular biochar is used as a carrier material for UASB. At the same time, granular biochar is used as a fermentation enhancer to increase biogas production and also increase the methane content in biogas. After anaerobic fermentation, the biogas liquid can be used as a water source in the desorption stage of powdered biochar, and the powdered biochar after desorption can be recycled and used in the adsorption stage to achieve recycling. The low-concentration organic wastewater after desorption enters the UASB fermentation tank again for treatment.

[0024] The beneficial effects of the present invention are:

[0025] The method provided by the present invention has a treatment efficiency of more than 83% and a biogas yield of 0.45 Nm 3 / kg COD or above, of which the methane content is above 65%. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments are briefly introduced below.

[0027] Figure 1 The present invention is a flow chart of the anaerobic fermentation treatment of high-concentration organic wastewater to produce biogas. DETAILED DESCRIPTION

[0028] The present invention provides a method for producing biogas by treating high-concentration organic wastewater through anaerobic fermentation, comprising the following steps:

[0029] 1) Mixing and adsorbing modified biochar with a particle size of 5 mm with high-concentration organic wastewater to obtain low-concentration organic wastewater and adsorbed biochar;

[0030] 2) mixing the low-concentration organic wastewater obtained in step 1) with modified biochar having a particle size of 10 to 20 mm and anaerobic sludge, and obtaining biogas slurry after anaerobic fermentation;

[0031] 3) desorbing the adsorbed biochar obtained in step 1) with the biogas slurry obtained in step 2) to obtain waste liquid;

[0032] 4) The waste liquid obtained in step 3) is mixed with modified biochar with a particle size of 10 to 20 mm and anaerobic sludge, and subjected to anaerobic fermentation to achieve the treatment of high-concentration organic wastewater.

[0033] The present invention mixes and adsorbs biochar with a particle size of 5 mm with high-concentration organic wastewater to obtain low-concentration organic wastewater and adsorbed biochar.

[0034] In the present invention, the addition amount of the modified biochar is preferably 5 to 15 g / L. In the present invention, the adsorption conditions preferably include a stirring speed of 80 to 120 rpm and an adsorption time of 0.5 to 3.0 h.

[0035] In the present invention, the method for preparing the modified biochar preferably comprises: carbonizing crop straw to obtain biochar; and activating and modifying the biochar to obtain modified biochar.

[0036] In the present invention, the crop straw preferably includes one or more of wheat straw, corn straw, rice straw, peanut straw and cotton straw.

[0037] In the present invention, the carbonization treatment preferably includes hydrothermal carbonization or pyrolytic carbonization. In the present invention, the conditions for the hydrothermal carbonization treatment preferably include: a temperature of 180-300°C for 1-3 hours. In the present invention, the conditions for the pyrolytic carbonization treatment preferably include: a temperature of 300-1000°C for 0.5-2 hours.

[0038] In the present invention, the activation modification preferably includes chemical impregnation and / or physical ball milling. In the present invention, the chemical impregnation preferably includes acid impregnation and / or alkaline impregnation. The present invention does not specifically limit the conditions of the acid impregnation method and the alkaline impregnation method, and those skilled in the art can operate according to the existing technology, such as "Hou Qixiong. Research on the removal of zero-valent mercury from coal-fired flue gas by impregnating activated carbon with succinic acid, North University of China, 2016, Master's thesis", "Wang Xu et al. Optimization of conditions for laccase treatment of poplar alkali impregnation wastewater based on response surface, Industrial Water Treatment, 2021, 41 (10) 67-72". The present invention does not specifically limit the physical ball milling method, and those skilled in the art can operate according to the conventional existing technology, such as "Song Jun et al. Study on phase evolution and cycle performance of Si@Cu composite materials prepared by ball milling, New Chemical Materials, 2023, 11".

[0039] In the present invention, the organic wastewater preferably includes thermochemical byproduct wastewater, industrial wastewater, fine chemical wastewater, pesticide wastewater, pharmaceutical wastewater or slaughterhouse wastewater.

[0040] The present invention mixes the obtained low-concentration organic wastewater with biochar with a particle size of 10 to 20 mm and anaerobic sludge, and then performs anaerobic fermentation to obtain biogas liquid.

[0041] In the present invention, the preparation of the biochar is the same as above and will not be repeated here. In the present invention, the addition amount of the biochar is preferably 5-15 g / L. In the present invention, the anaerobic sludge preferably includes anaerobic granular sludge. In the present invention, the anaerobic granular sludge is preferably purchased from Beijing Yufeng Agriculture and Forestry Technology Co., Ltd., and the place of production is Suzhou, Anhui. The addition amount of the anaerobic granular sludge is preferably 15%-25% (v / v). In the present invention, the anaerobic granular sludge has a high degree of granulation and good sedimentation performance, an organic matter content VSS greater than 60 g / L; the organic content VSS / TSS of the bacterial sludge is greater than 0.7; the effective sludge particle size is 60%-70%; the sedimentation rate is 30-150 m / h; the particle diameter is 0.5-4.0 mm; the moisture content is 90%; and the sludge methane production activity is greater than 0.31 KgCOD removed / KgVSS·d. In the present invention, the conditions for the anaerobic fermentation preferably include a fermentation temperature of 35 to 38° C., a fermentation time of 30 to 35 days, and a stirring speed of 100 to 120 rpm.

[0042] The invention places the adsorbed biochar in biogas slurry for desorption, wherein the stirring speed is 80-120 rpm and the desorption time is 0.5-3.0 h, thereby obtaining waste liquid.

[0043] The present invention combines the resulting wastewater with biochar (10-20 mm particle size) and anaerobic sludge, and then undergoes anaerobic fermentation to treat high-concentration organic wastewater. The preparation of the biochar is the same as described above and will not be repeated here. The biochar is preferably added in an amount of 5-15 g / L. The anaerobic sludge and anaerobic fermentation conditions are the same as described above and will not be repeated here.

[0044] In order to further illustrate the present invention, the present invention is described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0045] Example 1

[0046] Wheat straw was used as raw material and crushed into particle sizes of 5 mm and 10 mm, respectively. Powdered biochar and granular biochar were prepared by hydrothermal carbonization process. The hydrothermal carbonization temperature was 180℃ and the retention time was 1.0 h. The biochar was modified and activated by acid impregnation method [Hou Qixiong. Research on the removal of zero-valent mercury from coal flue gas by impregnation of activated carbon with succinic acid, North University of China, 2016, Master's thesis] to improve its quality.

[0047] First, powdered biochar was used as an adsorbent to adsorb the thermochemical byproduct wastewater. The powdered biochar was added at a dosage of 5 g / L, the stirring speed was 80 rpm, and the adsorption time was 0.5 h. The thermochemical byproduct wastewater was converted into low-concentration thermochemical byproduct wastewater after adsorption.

[0048] Anaerobic fermentation of the UASB was then performed to produce biogas at a temperature of 35°C, a fermentation time of 30 days, and a stirring speed of 100 rpm. The UASB was inoculated with anaerobic granular sludge at a rate of 15% (v / v). Granular biochar was used as a carrier material in the UASB at a rate of 5 g / L.

[0049] The biogas slurry after anaerobic fermentation can be used as the water source in the desorption stage of powdered biochar, wherein the stirring speed is 80 rpm and the desorption time is 0.5 h. The powdered biochar after desorption can be recycled and continued to be used in the adsorption stage. The low-concentration thermochemical byproduct wastewater after desorption enters the UASB fermentation tank again for treatment, ultimately achieving deep treatment of the thermochemical byproduct wastewater.

[0050] The treatment efficiency of thermochemical byproduct wastewater is 89.76% (calculated based on COD removal rate), and the biogas yield is 0.45Nm 3 / kg COD, of which the methane content is 65.1%.

[0051] Example 2

[0052] Corn straw was used as raw material and crushed into particle sizes of 5 mm and 15 mm respectively. Powdered biochar and granular biochar were prepared by pyrolysis carbonization process. The pyrolysis carbonization temperature was 600 ° C and the retention time was 1.0 h. The biochar was modified and activated by alkaline impregnation method [Wang Xu et al. Optimization of conditions for laccase treatment of poplar alkali impregnation wastewater based on response surface, Industrial Water Treatment, 2021, 41 (10) 67-72] to improve its quality.

[0053] First, powdered biochar was used as an adsorbent to adsorb pharmaceutical wastewater. The powdered biochar was added at a dosage of 5 g / L, the stirring speed was 100 rpm, and the adsorption time was 1.5 h. The pharmaceutical wastewater was converted into low-concentration pharmaceutical wastewater after adsorption.

[0054] Anaerobic fermentation of the UASB was then performed to produce biogas at a temperature of 37°C, a fermentation time of 33 days, and a stirring speed of 110 rpm. The UASB was inoculated with anaerobic granular sludge at an addition rate of 18% (v / v). Granular biochar was used as a carrier material in the UASB at an addition rate of 5 g / L.

[0055] The biogas slurry after anaerobic fermentation can be used as the water source in the desorption stage of powdered biochar. The stirring speed is 100 rpm and the desorption time is 1.5 h. The powdered biochar after desorption can be recycled and used in the adsorption stage. The low-concentration pharmaceutical wastewater after desorption enters the UASB fermentation tank again for treatment, and finally achieves deep treatment of pharmaceutical wastewater.

[0056] The treatment efficiency of pharmaceutical wastewater is 85.2% (calculated based on COD removal rate), and the biogas production rate is 0.54Nm 3 / kgCOD, of which the methane content is 69.2%.

[0057] Example 3

[0058] Rice straw was used as raw material and crushed into particle sizes of 5 mm and 20 mm, respectively. Powdered biochar and granular biochar were prepared by hydrothermal carbonization process. The hydrothermal carbonization temperature was 240 ° C and the retention time was 2.0 h. The biochar was modified and activated by physical ball milling method [Song Jun et al. Preparation of Si@Cu composite materials by ball milling and study on phase evolution and cyclic performance, New Chemical Materials, 2023, 11] to improve its quality.

[0059] Firstly, powdered biochar was used as an adsorbent to treat the slaughterhouse wastewater. The powdered biochar was added at a dosage of 5 g / L, the stirring speed was 120 rpm, and the adsorption time was 3.0 h. The slaughterhouse wastewater was converted into low-concentration slaughterhouse wastewater after adsorption.

[0060] Anaerobic fermentation of the UASB was then performed to produce biogas at a temperature of 38°C, a fermentation time of 35 days, and a stirring speed of 120 rpm. The UASB was inoculated with anaerobic granular sludge at a rate of 20% (v / v). Granular biochar was used as a carrier material in the UASB at a rate of 5 g / L.

[0061] The biogas slurry after anaerobic fermentation can be used as the water source in the desorption stage of powdered biochar. The stirring speed is 120 rpm and the desorption time is 3.0 h. The powdered biochar after desorption can be recycled and used in the adsorption stage. The low-concentration slaughterhouse wastewater after desorption enters the UASB fermentation tank again for treatment, and finally achieves deep treatment of slaughterhouse wastewater.

[0062] The treatment efficiency of slaughterhouse wastewater was 87.9% (calculated based on COD removal rate), and the biogas production rate was 0.61Nm 3 / kgCOD, of which methane content is 73.4% 。

[0063] Table 1 COD changes in various wastewater deep treatment processes

[0064]

[0065] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for treating high-concentration organic wastewater by anaerobic fermentation to produce biogas and increase methane content, characterized in that: For the following steps: 1) Mixing and adsorbing modified biochar with a particle size of 5 mm with high-concentration organic wastewater to obtain low-concentration organic wastewater and adsorbed biochar; 2) mixing the low-concentration organic wastewater obtained in step 1) with modified biochar with a particle size of 20 mm and anaerobic sludge, and obtaining biogas slurry after anaerobic fermentation; 3) desorbing the adsorbed biochar obtained in step 1) with the biogas slurry obtained in step 2) to obtain waste liquid; 4) mixing the waste liquid obtained in step 3) with modified biochar with a particle size of 10 to 20 mm and anaerobic sludge, and performing anaerobic fermentation to achieve the treatment of high-concentration organic wastewater; The preparation methods of modified biochar in steps 1), 2) and 4) all include: Carbonizing crop straw to obtain biochar; activating and modifying the biochar to obtain modified biochar; The crop straw is rice straw; The carbonization treatment is a hydrothermal carbonization treatment; The conditions of the hydrothermal carbonization treatment are: temperature 240°C, time 2h; The activation modification is a physical ball milling method; The amount of modified biochar added in step 1), step 2) and step 4) is 5 g / L; The anaerobic sludge in step 2) and step 4) both include anaerobic granular sludge; The addition amount of the anaerobic sludge is 20%, which is a volume percentage.

2. The method according to claim 1, characterized in that The conditions for the anaerobic fermentation in step 2) and step 4) include: a fermentation temperature of 35-38° C., a fermentation time of 30-35 days, and a stirring speed of 100-120 rpm.

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