Method for improving methane yield of high-concentration acid organic wastewater by anaerobic enhanced treatment

Abstract

The application discloses a method for improving the methane yield of high-concentration acid organic wastewater by anaerobic enhanced treatment, which comprises the following steps: (1) selecting anaerobic sludge in a stably operated anaerobic biological treatment system as inoculated sludge; (2) preparing chitosan-modified ferroferric oxide (Cs-Fe3O4) microspheres by using chitosan to modify ferroferric oxide; and (3) adding the Cs-Fe3O4 microsphere composite material in an acid high-concentration organic wastewater anaerobic methane production reactor, wherein the adding amount of the Cs-Fe3O4 microsphere composite material is 0.1-2.0% (mass percent), and the methane production rate of the anaerobic reactor is increased by 40-140%. The method can improve the reactor stability and accelerate the methane production when acidification occurs in the anaerobic biological reactor or acid wastewater is treated. The method for improving the anaerobic methane production of high-concentration acid organic wastewater by using the Cs-Fe3O4 microsphere composite material disclosed by the application has the characteristics of simple operation, economy, high efficiency and stability, and has the advantages of easy engineering popularization, and has a wide application prospect in the anaerobic biological treatment of high-concentration organic wastewater.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of anaerobic digestion methane production, and particularly relates to a method for improving methane production rate by anaerobic intensified treatment of high-concentration acid organic wastewater. BACKGROUND

[0002] In recent years, sewage energyization and resourceization is the development trend in the field of water treatment at home and abroad. Because anaerobic digestion technology can realize the treatment of pollutants and the recovery of energy materials at the same time, the anaerobic digestion technology has been widely applied to the treatment of high-concentration organic waste. However, when the anaerobic digestion technology is applied to the high-concentration organic waste with good biodegradability, acidification is prone to occur. The accumulation of volatile fatty acids will cause the pH of the system to decrease. The methanogenic functional bacteria are sensitive to pH, and their growth and metabolic rate are slow under adverse environmental conditions, which further causes the accumulation of fatty acids, the acidification of the system, and even the collapse of the anaerobic system in severe cases. In the traditional method, the pH of the system is usually controlled by adding alkaline substances to maintain the stability of the anaerobic system. However, when these chemicals are consumed, acidification in the anaerobic system may occur again. Severe acid shock will cause serious damage to the functional microorganisms in the anaerobic digestion, and it will take a long time to restore the stability of the system. Therefore, it is crucial to improve the acid shock resistance of the system and promote the conversion of fatty acids to methane during the anaerobic digestion of high-concentration organic wastewater.

[0003] It is reported that direct electron transfer process can accelerate acid conversion to methane as an efficient electron transfer form, and thus can be used as an effective means to solve the low acid conversion efficiency in anaerobic digestion process. A large number of studies have proved that iron-based conductive materials are more conducive to accelerating the metabolism of fatty acids than carbon-based materials. On the one hand, they can act as electron conductors to connect acid-producing bacteria and methanogenic bacteria, promote the formation of direct electron transfer process between the two bacteria, and ultimately improve the rapid conversion of acid and increase the maximum methanogenic rate. On the other hand, iron ions can participate in microbial metabolism as trace elements to improve the activity of functional microorganisms and enzymes. Considering sustainability and recycling, magnetite (Fe3O4) has attracted a lot of attention at present, but in practical application, Fe3O4 has problems such as easy agglomeration, instability under long-term running conditions, and difficulty in contacting with microorganisms. Among them, a large amount of iron ions in Fe3O4 will be lost under acid impact, which on the one hand will reduce the effect of Fe3O4, and on the other hand a large amount of dissolved iron ions will inhibit the activity of microorganisms. In addition, Fe3O4 is not conducive to the adhesion of microorganisms, thereby reducing the electron transfer efficiency between microorganisms. The existence of the above defects limits the wide application of Fe3O4 in anaerobic digestion system, so that the effect of using Fe3O4 to improve the anaerobic biological treatment performance of high-concentration organic wastewater under acid impact is not ideal. Therefore, the present application uses chitosan (Cs) with high biological affinity to modify Fe3O4 to prepare a composite material Cs-Fe3O4, thereby improving the stability and biological affinity of Fe3O4, and applying it to the anaerobic digestion system is more conducive to the conversion of fatty acids in the acidification system or the anaerobic digestion process of acid high-concentration organic wastewater, thereby accelerating the recovery of the anaerobic digestion system and realizing efficient degradation of organic matter while recycling biological energy. SUMMARY

[0004] In view of the problems in the prior art, the present application provides a method for improving methane production rate in anaerobic enhanced treatment of high-concentration acid organic wastewater, which promotes electron transfer between microorganisms by adding more stable composite material Cs-Fe3O4 in the acid high-concentration organic wastewater anaerobic methanation system, thereby accelerating the degradation of fatty acids and the generation of methane, and greatly improving the stability and recovery speed of the anaerobic reactor under acid impact. At the same time, the composite material Cs-Fe3O4 can buffer the pH of the system and reduce the large dissolution of iron ions, thereby reducing the inhibition of anaerobic methanogenic bacteria.

[0005] To solve the above technical problems, the technical scheme adopted by the present application is:

[0006] A method for improving anaerobic degradation and methane production of high-concentration organic wastewater under acid impact, comprising the following steps:

[0007] Step 1) Obtaining and culturing sludge, selecting anaerobic sludge from a municipal wastewater treatment plant, and culturing using brewery wastewater as a substrate to obtain inoculated sludge;

[0008] Step 2) Preparation of chitosan-modified magnetic ferroferric oxide (Cs-Fe3O4) microsphere composite material;

[0009] Step 3) Application of Cs-Fe3O4 microsphere composite material in methanogenesis in anaerobic biological treatment of high-concentration acidic organic wastewater. Acidic distillery wastewater was used as the substrate, and inoculated sludge obtained in Step 1 and the composite material Cs-Fe3O4 obtained in Step 2 were added to the anaerobic reactor, and then the anaerobic methanogenesis reaction was carried out.

[0010] Preferably, the sludge in Step 1 is derived from the anaerobic treatment system of a municipal wastewater treatment plant, and the sludge is sieved to remove large-particle impurities and concentrated by sedimentation to a sludge concentration of 30-40 g / L. The obtained anaerobic sludge is added to the anaerobic reactor under the conditions of a temperature of 30-40°C and a pH of 6.5-7.5, and distillery wastewater is used as the influent of the anaerobic reactor with a hydraulic retention time of 1-4 days. When the COD removal rate in the anaerobic reactor is 80%-95% and the methane content in biogas is 40%-70%, the inoculated sludge is obtained.

[0011] Preferably, the preparation method of the chitosan-modified magnetic ferroferric oxide (Cs-Fe3O4) microsphere composite material in Step 2 is as follows: a mixed solution of 20-80 mM Fe 3+ and 10-40 mM Fe 2+ is prepared, 3-12% w / v chitosan is added to the prepared mixed solution and stirred uniformly, 0.5-2.0% v / v acetic acid is added to the above uniformly stirred mixed solution, and the mixture is stirred thoroughly for 0.5-2 h until the chitosan is completely dissolved. The mixed solution is added dropwise to a 1-3 M sodium hydroxide solution, followed by standing for 6-12 h, filtering and washing to neutral, and vacuum drying for 18-24 h to obtain the Cs-Fe3O4 microsphere composite material.

[0012] Preferably, the high-concentration acidic organic wastewater in Step 3 has the following main characteristics: a pH of 4.0-6.0 and a COD concentration of 6000-10000 mg / L.

[0013] Preferably, the dosage of the Cs-Fe3O4 microsphere composite material in Step 3 is 0.1-2.0 wt% microsphere composite material per volatile suspended solid content of the inoculated sludge.

[0014] Further preferably, the dosage of the chitosan-modified magnetic ferroferric oxide (Cs-Fe3O4) microsphere composite material in Step 3 is 0.5 wt% microsphere composite material.

[0015] Preferably, the organic wastewater in step 1) and step 3) is brewing wastewater, and the brewing wastewater is pretreated by filtration to remove suspended substances such as chaff, wheat bran and broken grain particles in the brewing wastewater before the anaerobic methanogenesis reaction.

[0016] Compared with the prior art, the present application has the following beneficial effects:

[0017] (1) In the present application, the composite material Cs-Fe3O4 microspheres are applied to the anaerobic digestion of acidic brewing wastewater, the composite material Cs-Fe3O4 microspheres are beneficial to the adhesion of microorganisms, Fe3O4 can promote the electron transfer between acid-producing bacteria and methanogenic bacteria, thereby accelerating the conversion of fatty acids in the brewing wastewater and increasing the pH of the reactor, in addition, chitosan has a certain buffering effect on pH. Therefore, Cs-Fe3O4 can reduce the harm of low pH to methanogenic bacteria through multiple pathways and improve the performance of anaerobic digestion of high-concentration organic wastewater under acidic shock.

[0018] (2) In the present application, the surface of Fe3O4 is modified by chitosan (Cs) to obtain Cs-Fe3O4 composite material, and the obtained Cs-Fe3O4 composite material does not destroy the magnetism of the original Fe3O4, and is also convenient for recycling and utilization.

[0019] (3) The chitosan-modified magnetic Fe3O4 (Cs-Fe3O4) microsphere composite material prepared in the present application is more stable, chitosan has low toxicity, low cost, good biocompatibility, good metal ion stability, can reduce the loss of iron ions under acidic shock, and avoids the inhibition of a large amount of iron ions to anaerobic microorganisms.

[0020] (4) The present application is simple to operate, more economical and stable than the method of adding chemical reagents to restore the stability of the anaerobic reactor, and can reduce the repeated addition of chemical reagents. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be described clearly and completely below in combination with the drawings of the embodiments of the present application.

[0022] Figure 1 Figure 1 is a graph of the maximum methanogenic rate of the anaerobic digestion process of acidic high-concentration organic wastewater in Example 3 and Example 4 of the present application when the composite material Cs-Fe3O4 microspheres are added.

[0023] Figure 2 Figure 2 is a graph of the change of volatile fatty acids in the anaerobic digestion process of acidic high-concentration organic wastewater in Example 3 of the present application.

[0024] Figure 3Figure of methane production of the acidification system with addition of composite material Cs-Fe3O4 microspheres in Example 5 of the present application.

[0025] Figure 4 Flow chart of the method of the present application. DETAILED DESCRIPTION

[0026] In order to have a clearer understanding of the technical features, objectives and effects of the present application, the present application is further illustrated by the following examples.

[0027] Example 1

[0028] The anaerobic digestion performance of different pH distillery wastewater was investigated. The steps were as follows: first, inoculated sludge was added into the anaerobic bottle, then distillery wastewater with pH of 4.0-7.0 was used as the substrate, a certain amount of ultrapure water was added, the ratio of sludge concentration to COD concentration in the anaerobic system was controlled to be 1:1, nitrogen gas was used to blow off the oxygen in the reactor to make the microorganisms in the anaerobic bottle in an anaerobic environment, then the anaerobic bottle was placed in a constant temperature shaker with a temperature of 35±5℃ and a rotation speed of 120 rpm to carry out the anaerobic methane production experiment. The methane production, COD and volatile fatty acid of the system were detected. After the reaction, the COD removal and methane production of the distillery wastewater under the impact of different acidic pH were compared. The results showed that when the acidic impact pH was 5 or lower, the anaerobic system showed obvious inhibition, the COD removal rate of the system decreased by 6.82-30.38% compared with the normal operation condition, the methane production decreased by 11.62-46.07%, and the volatile fatty acid degradation efficiency in the system was low.

[0029] In the present example, the characteristics of the inoculated sludge were as follows: pH was 7.0±0.2, volatile suspended solid particles VSS was 32.0±1.09 g / L, and the inoculated sludge was obtained by domesticating the sludge from the anaerobic tank of the municipal wastewater treatment plant through the following steps:

[0030] 1) obtaining active sludge from the anaerobic tank of the municipal wastewater treatment plant;

[0031] 2) adding the sludge in step 1) into the anaerobic reactor, then adding distillery wastewater, adjusting the pH of the system in the reactor to be 6.5-7.5, blowing off the oxygen in the reactor with nitrogen gas to make the microorganisms in the reactor in an anaerobic environment, then controlling the temperature of the reactor to be 35±5℃ and the rotation speed to be 100-120 rpm;

[0032] 3) taking a fixed amount of waste liquid from the reactor every day and adding the same amount of fresh waste liquid; when the organic matter degradation rate and the methane production rate in the reactor were basically stable, i.e. the COD removal rate was stable at about 80%-95%, the sludge in the reactor could be used as the inoculated sludge for anaerobic methane production.

[0033] Example 2

[0034] The effect of different concentrations of composite material Cs-Fe3O4 on anaerobic digestion of brewery wastewater was investigated. The steps were as follows: first, inoculated sludge was added to the anaerobic bottle, then a certain amount of ultrapure water and brewery wastewater was added, the ratio of sludge concentration to COD concentration in the anaerobic system was controlled at 1:1, and finally different concentrations of composite material Cs-Fe3O4 were added. After blowing off the oxygen in the reactor with nitrogen to make the microorganisms in the reactor in an anaerobic environment, the anaerobic methane production reaction was carried out in a constant temperature shaker at 35±5℃ and a rotation speed of 120 rpm. The methane accumulation in the reaction bottle at different times during the reaction was detected. After the reaction, the effect of different concentrations of composite material Cs-Fe3O4 on the methane production performance of anaerobic digestion of brewery wastewater was investigated. The results showed that after fitting the change of methane accumulation with time by Gompertz equation, the promotion effect of 0.5wt% Cs-Fe3O4 on the brewery wastewater methane production process was the most obvious, and the cumulative methane production was increased by 11.4%.

[0035] In this embodiment, the preparation steps of the chitosan modified magnetic ferroferric oxide (Cs-Fe3O4) microsphere composite material are as follows: a mixed solution of 20-80mM Fe 3+ and 10-40mM Fe 2+ was prepared, 3-12% w / v chitosan was added to the mixed solution, stirred uniformly, 0.5-2.0% v / v acetic acid was added, and the mixed solution was stirred for 0.5-2h until the chitosan was completely dissolved. The mixed solution was added dropwise into a 1-3M sodium hydroxide solution, and was left to stand for 6-12h. After filtration and washing to neutral, the composite material Cs-Fe3O4 microspheres were obtained after vacuum drying for 18-24h.

[0036] Example 3

[0037] A method for improving methane production rate in anaerobic enhanced treatment of high-concentration acidic organic wastewater, the steps are as follows: first, inoculated sludge was added to the anaerobic bottle, then brewery wastewater with pH of 5.0±0.1 was added, and finally composite material Cs-Fe3O4 was added. After blowing off the oxygen in the reactor with nitrogen to make the microorganisms in the reactor in an anaerobic environment, the anaerobic methane production reaction was carried out in a constant temperature shaker at 35±1℃ and a rotation speed of 120 rpm. The volatile fatty acid content and methane accumulation in the reaction bottle at different times during the reaction were detected.

[0038] In this embodiment, the effect of composite material Cs-Fe3O4 on the methane production performance of anaerobic digestion of brewery wastewater under acid shock was investigated. The results showed that after fitting the change of methane accumulation with time by Gompertz equation, the methane production rate of the control group was 0.0189h-1, and the methane production rate of the group with 0.5wt% Cs-Fe3O4 was 0.0208h-1, which was increased by 10.6%. Figure 1The maximum methane production rate was 173.52 mL / g COD / d, and the methane production lag phase was 0.48 d. Compared with the blank experiment group, the methane production lag phase of the anaerobic digestion of the wine wastewater under acid shock was shortened by 30.43%, and the maximum methane production rate was increased by 49.77%. In addition, it was found that Figure 3 It can be seen that the degradation rate of volatile fatty acids in the anaerobic reactor with the addition of composite material Cs-Fe3O4 is faster, and all the volatile fatty acids in the anaerobic system are completely degraded at 72 h.

[0039] Example 4

[0040] A method for improving the methane production rate of high-concentration acid organic wastewater by anaerobic enhanced treatment, which adopts the same method as example 3, the only difference is that this is the second acid shock experiment. The results show that the change of methane accumulation with time after fitting by Gompertz equation is Figure 1 The maximum methane production rate was 173.52 mL / g COD / d, and the methane production lag phase was 0.48 d. Compared with the blank experiment group, the methane production lag phase of the anaerobic digestion of the wine wastewater under acid shock was shortened by 30.43%, and the maximum methane production rate was increased by 49.77%. In addition, it was found that

[0041] Example 5

[0042] Under acidic conditions, the effect of composite material Cs-Fe3O4 microspheres on the anaerobic biological treatment performance of wine wastewater, steps: first, add inoculated sludge to the anaerobic bottle, then add a certain amount of ultrapure water and wine wastewater, adjust the pH of the anaerobic system to 5.0, then add composite material Cs-Fe3O4, blow off the oxygen in the reactor with nitrogen to make the microorganisms in the reactor in an anaerobic environment, and then carry out the anaerobic methane production reaction in a constant temperature shaker at 35±1℃ and a rotation speed of 120 rpm. The volatile fatty acid content and methane accumulation in the reaction bottle at different times during the reaction were detected. The results show that the anaerobic digestion process of wine wastewater under acidic conditions is severely inhibited, and the control group anaerobic reactor almost collapsed, and the pH of the system was basically 4.4-5.0. While the anaerobic reactor with the addition of composite material Cs-Fe3O4 runs stably, the pH of the anaerobic reactor recovers to about 6.0 on the second day, the reaction is basically completed on the 10th day, and the methane production is 12.18 times that of the control group.

[0043] Comparative example 1

[0044] The same method as in Example 5 was used, except that the composite material Cs-Fe3O4 was replaced by Fe3O4, and the dosage of Fe3O4 was 0.5wt%. The preparation steps of Fe3O4 were as follows: 3.25g of ferric chloride and 1.27g of ferrous chloride were added to a reaction vessel containing 100mL of ultrapure water, and after being stirred thoroughly, 1.5M sodium hydroxide aqueous solution was added to the reaction vessel until the pH of the mixture in the reaction vessel was 11.0±0.2, and the process was carried out under inert gas protection. After the reaction was completed, the black solid obtained by centrifugation, water washing and drying was Fe3O4. The results showed that the anaerobic reactor was also severely inhibited, the pH of the reactor was 4.9-5.6, and the methane production process was severely inhibited. On the 10th day, the cumulative methane production was only 51.86mL.

[0045] As can be seen from the data of the examples and comparative examples, the optimal dosage concentration of the composite material Cs-Fe3O4 is 0.5wt%. In Example 5, the methane production was increased by 110.43% compared with that in Comparative Example 1, and the methane production rate and the degradation efficiency of volatile fatty acids were both greatly improved.

[0046] The above examples are only preferred embodiments of the present application, and the protection scope of the present application is not limited to the above examples. Any technical solutions falling within the concept of the present application shall fall within the protection scope of the present application. It should be pointed out that, for ordinary skilled persons in the technical field, improvements and refinements without departing from the principles of the present application shall also be considered as falling within the protection scope of the present application.

Claims

1. A method for enhancing methane yield through anaerobic treatment of high-concentration acidic organic wastewater, comprising the following steps: Step 1) Obtaining and cultivating sludge: Anaerobic sludge from a municipal wastewater treatment plant was selected and cultured using brewing wastewater as a substrate to obtain inoculated sludge. Step 2) Preparation of chitosan-modified magnetic iron oxide microsphere composite material, wherein the preparation method of the material is as follows: prepare 20-80 mM Fe 3+ With 10-40 mM Fe 2+ The mixture solution was prepared by adding chitosan at a ratio of 3-12% w / v and stirring until homogeneous. Then, acetic acid was added to the homogeneous mixture solution at a ratio of 0.5-2.0% v / v and stirred thoroughly for 0.5-2 h until the chitosan was completely dissolved. The mixture solution after the chitosan was completely dissolved was added dropwise to a 1-3 M sodium hydroxide solution and then allowed to stand for 6-12 h. The mixture was then filtered and washed until neutral and vacuum dried for 18-24 h to obtain the microsphere composite material. Step 3) Application of microsphere composite material in anaerobic biological treatment of high-concentration acidic organic wastewater for methanogenesis. The high-concentration acidic organic wastewater is acidic brewing wastewater. Using acidic brewing wastewater as a substrate, the inoculated sludge obtained in step 1) and the microsphere composite material obtained in step 2) are added to the anaerobic reactor to carry out the anaerobic methanogenesis reaction.

2. The method for enhancing methane yield through anaerobic treatment of high-concentration acidic organic wastewater according to claim 1, characterized in that: After removing large particulate impurities from the sludge by sieving and precipitating in step 1), the sludge is added to the anaerobic reactor at a temperature of 30℃-40℃ and a pH of 6.5-7.

5. Brewing wastewater is used as the influent to the anaerobic reactor, and the hydraulic retention time is 1-4 days. When the COD removal rate in the anaerobic reactor is 80%-95% and the methane content in the biogas is 40%-70%, the inoculum sludge is obtained.

3. The method for enhancing methane yield through anaerobic treatment of high-concentration acidic organic wastewater according to claim 1, characterized in that: The high-concentration acidic organic wastewater described in step 3) has a pH of 4.0-6.0 and a COD concentration of 6000-10000 mg / L.

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