Method for obtaining high-quality carbon source from sludge

Abstract

The invention relates to the technical field of solid waste recycling and sewage treatment, in particular to a method for obtaining a high-quality carbon source from sludge. The method comprises the following steps: obtaining a sludge raw material; taking a part of the sludge raw material, adjusting the water content of the sludge raw material to be greater than 90%, adding a hydrogen peroxide solution into the sludge raw material, uniformly mixing to form a mixed solution, and heating the mixed solution to dissolve organic matters in the sludge raw material; adjusting the pH value of the heated mixed solution to 7.5-8.5, and cooling and precipitating to obtain supernate containing organic matters; inoculating a sludge raw material in the supernate as an anaerobic microorganism source, adding biochar loaded with zero-valent iron, mixing, adjusting the pH value to 6-7, and reacting for 6-96 hours under an anaerobic constant-temperature condition to obtain a solution which is the high-quality carbon source. By improving the biodegradability of organic components, an internal driving circulation system is formed, and the extraction efficiency of the high-quality carbon source in the sludge is improved.

Description

Technical Field

[0001] This invention relates to the fields of solid waste resource utilization and wastewater treatment technology, specifically to a method for obtaining high-quality carbon sources from sludge. Background Technology

[0002] With the continuous advancement of urbanization in my country, the scale of urban wastewater treatment plants is increasing daily. Finding a reasonable, effective, and cost-efficient method for sludge resource utilization is of great significance. Furthermore, excessive fertilizer use, nutrient surplus, and industrial development have led to a gradual increase in nitrogen and phosphorus emissions, resulting in a continuously rising proportion of nitrogen and phosphorus in urban wastewater and a lower proportion of COD, i.e., a reduced C / N ratio. Currently, nitrogen removal in wastewater in my country still relies primarily on traditional biological denitrification. Low C / N ratios in domestic wastewater cannot meet the carbon source requirements for biological denitrification, easily leading to substandard ammonia nitrogen levels in wastewater treatment plant effluents. To address the problem of insufficient carbon source in wastewater treatment plants, most domestic wastewater treatment plants adopt external carbon source addition to increase the C / N ratio. However, the large-scale addition of carbon sources results in the generation of large amounts of sludge and high operating costs.

[0003] Therefore, developing a new technology for preparing high-quality carbon sources from waste sludge will enable the resource utilization of waste sludge and has significant application value. Summary of the Invention

[0004] This invention addresses the problem of low efficiency in carbon source extraction from sludge digestion. It proposes using zero-valent iron and biochar as carriers to attach anaerobic microorganisms, forming active particles. The fatty acids produced by the anaerobic microorganisms create a weakly acidic environment, driving the zero-valent iron and biochar to form a redox-like system similar to an iron-carbon micro-battery. This promotes the decomposition of organic components in the sludge, improves their biodegradability, and further promotes the anaerobic decomposition of short-chain fatty acids by microorganisms, forming a benign internal driving cycle system and improving the extraction efficiency of high-quality carbon sources from sludge.

[0005] The technical solution adopted by this invention to solve the technical problem is:

[0006] A method for obtaining a high-quality carbon source from sludge includes the following steps:

[0007] Step 1, Obtain sludge raw material;

[0008] Step 2: Take a portion of the sludge raw material, adjust the moisture content of the sludge raw material to be greater than 90%, add hydrogen peroxide solution to the sludge raw material and mix evenly to form a mixed solution, and heat the mixed solution to dissolve the organic matter in the sludge raw material;

[0009] Step 3: Adjust the pH of the heated mixed solution to 7.5-8.5, and after cooling and precipitation, obtain the supernatant containing organic matter;

[0010] Step 4: Inoculate the sludge raw material from Step 1 into the supernatant as an anaerobic microbial source, and add biochar loaded with zero-valent iron. Mix and adjust the pH value to 6-7, and react under anaerobic constant temperature conditions for 6-96 hours. The solution after the reaction is a high-quality carbon source.

[0011] In the above method, in step 2, the concentration of the hydrogen peroxide solution is 20% to 40%, and the mass percentage of the sludge raw material to the hydrogen peroxide solution is 10:1 to 20:1.

[0012] In the above method, in step 2, the heating temperature is 80~100℃, and the heating time is not less than 1 hour.

[0013] In the above method, in step 4, the volume ratio of the supernatant to the inoculated sludge is 9:1;

[0014] In the above method, in step 4, 40-60g of the biochar loaded with zero-valent iron is added to each liter of the supernatant.

[0015] In the above method, in step 4, the temperature of the anaerobic isothermal condition is 25℃~40℃, the reaction is an anaerobic microbial catalytic-driven iron-carbon micro-battery redox reaction, the time of the anaerobic microbial catalytic-driven iron-carbon micro-battery redox reaction is 24~48 hours, and the anaerobic microbial catalytic-driven iron-carbon micro-battery redox reaction causes the organic matter to decompose and produce small molecule fatty acids.

[0016] In the above method, in step 4, the pH is controlled to be no lower than 5.0 and the redox potential is controlled between -300 and 100mV during the reaction process.

[0017] In the above method, the preparation method of the biochar loaded with zero-valent iron is as follows: biochar is added to ferrous sulfate solution and shaken for at least 10 hours to allow iron ions to enter the biochar pores and be fully loaded to form a mixture. Then, 0.1 mol / L sodium borohydride solution is slowly added dropwise to the above mixture until no bubbles are generated. After centrifugation and drying, a composite material in which nano-zero-valent iron is fully loaded and coupled in the biochar pores is formed.

[0018] In the above method, the concentration of the ferrous sulfate solution is 0.1 mol / L, and 200-300g of biochar is added to each liter of ferrous sulfate solution. The ferrous sulfate solution can completely submerge the biochar, and the biochar is biochar particles with a particle size of <5mm obtained by sieving.

[0019] In the above method, NaCl and KCl are added during the preparation of the biochar, and the amount added is 1~5g of NaCl and KCl per 100g of biochar.

[0020] By employing the above technical solution, the present invention has at least the following advantages:

[0021] 1) This invention utilizes the slightly acidic environment formed by the self-generated anaerobic environment of microorganisms to drive an iron-carbon micro-battery-like redox system, which can serve as a microbial carrier to promote the degradation of sludge, facilitate the growth of microorganisms, and improve the degradation activity of the cells.

[0022] 2) The microbial anaerobic process can initiate the operation of the iron-carbon micro-battery-like redox system, thereby promoting the decomposition of organic components in the sludge, improving biodegradability, enhancing the efficiency of the microbial anaerobic process, and further promoting the stable and continuous operation of the iron-carbon micro-battery-like redox system, ultimately forming a virtuous cycle of internally driven active particle system, effectively improving the extraction of high-quality carbon sources.

[0023] 3) Using nano-zero-valent iron and biochar composite material as microbial carrier, and taking advantage of the sensitivity of nano-zero-valent iron and the naturally occurring trace metal elements Na and K in biochar, this invention can catalytically drive iron-carbon micro-battery-like redox systems in anaerobic micro-acid systems compared to conventional iron-carbon materials.

[0024] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0025] Figure 1 This is a comparison graph showing the effect of adding different high-quality carbon sources to the anaerobic isothermal reaction stage of this invention on the yield.

[0026] Figure 2 This is a line graph showing the effect of adding different substances to pH during the anaerobic isothermal reaction stage of this invention.

[0027] Figure 3 These are the XRD patterns of the original biochar of this invention before and after loading with zero-valent iron;

[0028] Figure 4 This is a comparison chart showing the effect of adding Na and K elements on the yield of high-quality carbon source during the loading of zero-valent iron in the original biochar of this invention. Detailed Implementation

[0029] To further illustrate the technical means and effects of the present invention in achieving the intended purpose, the following detailed description of the specific implementation methods, structures, features and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0030] Example 1

[0031] This embodiment provides a method for obtaining a high-quality carbon source from sludge, the method including the following steps: Step 1, obtaining sludge raw material, wherein the sludge raw material is residual sludge after filter pressing taken from a sewage treatment plant in Jinhua;

[0032] Step 2: Take a portion of the sludge raw material and pretreat it. The specific method is as follows: First, adjust the moisture content of the sludge raw material to be greater than 90%. Then, add hydrogen peroxide solution to the sludge raw material and mix evenly to form a mixed solution to dissolve the organic matter (mainly the cell sap of bacteria) in the sludge raw material. Heat the mixed solution to dissolve the macromolecular organic matter in the sludge raw material into the mixed solution. During this process, hydrogen peroxide (H2O2) will generate hydroxyl radicals (·OH), thereby improving the ability to decompose organic matter.

[0033] Step 3: Adjust the pH of the mixed solution after heating reaction to 7.5~8.5 (in this embodiment, sodium hydroxide is used to adjust the pH value), and after cooling and precipitation, obtain the supernatant containing macromolecular organic matter.

[0034] Step 4: Inoculate the sludge raw material from Step 1 into the supernatant as an anaerobic microbial source (mainly acid-producing bacteria), and add biochar loaded with zero-valent iron. Specifically, the volume ratio of the supernatant to the inoculated sludge is 9:1. Add 50g of the biochar loaded with zero-valent iron to each liter of the supernatant, mix the supernatant, inoculated sludge raw material, and biochar evenly, and adjust the initial pH to 6-7. React under anaerobic isothermal conditions for 12-96 hours. The resulting solution is a high-quality carbon source. The high-quality carbon source formed by this invention can be used as a carbon source in the denitrification stage of biological nitrogen and phosphorus removal and the phosphorus release / uptake stage of biological phosphorus removal in wastewater treatment.

[0035] The method for obtaining high-quality carbon sources from sludge in this embodiment includes two steps: 1) In the first step, residual sludge containing a large amount of organic components is used as raw material for anaerobic acidification by anaerobic microorganisms. Under the action of acid-producing bacteria, the organic components (small molecule organic matter, as large molecule organic matter is difficult to decompose in this step) are gradually decomposed into small molecule organic acids, hydrogen, and carbon dioxide, thereby providing and maintaining a slightly acidic environment; 2) In the second step, the redox reaction of the iron-carbon micro-battery, due to the presence of nano-zero valent iron, can drive the Fe-C redox system under slightly acidic conditions. Nano-zero valent iron acts as the anode, and the oxidation reaction formula is: Biochar is used as the cathode. ↑, Anode reaction generates The cathode produces nascent [H] atoms, which are highly chemically active. Through redox reactions, they cause organic matter to undergo chain breaking and ring opening, thereby decomposing organic matter, enhancing the degradation of macromolecular organic matter into small molecule organic matter (which can be decomposed by anaerobic microorganisms), and promoting anaerobic acidification to produce small molecule organic acids.

[0036] In this invention, the high-quality carbon source includes at least the following two parts: 1) small molecule organic acids produced by anaerobic acidification of anaerobic microorganisms, such as formic acid, acetic acid, propionic acid, etc.; 2) small molecule organic compounds generated by the degradation of macromolecular organic compounds in the redox reaction of iron-carbon micro batteries.

[0037] This invention utilizes the anaerobic acidification reaction of anaerobic microorganisms to continuously generate small-molecule organic acids, thereby driving and maintaining the acidic operating conditions of the Fe-C redox system. The anaerobic acidification reaction of anaerobic microorganisms is often inefficient due to the recalcitrant nature of large organic molecules. However, the redox reaction within the Fe-C redox system degrades large organic molecules into smaller ones. Anaerobic microorganisms can efficiently break down these smaller organic molecules into small-molecule organic acids, thus accelerating the anaerobic acidification process and further providing a continuous slightly acidic environment for the Fe-C redox system. Therefore, the microbial membrane and the Fe-C system can be coupled and work synergistically.

[0038] In practical implementation, to further demonstrate the extraction efficiency of the high-quality carbon source of the present invention, this embodiment designed a comparative experiment to conduct a comparative experiment on the different substances added in step 4 and the carbon source extraction yield at different times. Specifically, this included the method of obtaining high-quality carbon source of the present invention (adding biochar loaded with zero valent iron in step 4), and Comparative Examples 1 and 2), which differ from the method of obtaining high-quality carbon source of this embodiment in that Comparative Example 1) did not add biochar loaded with zero valent iron in step 4 (traditional anaerobic sludge group); Comparative Example 2) added original biochar in step 4 (original biochar group), wherein the original biochar is biochar without zero valent iron loading. The method of obtaining high-quality carbon source of the present invention, Comparative Example 1), and Comparative Example 2) were all sampled at 6 hours, 12 hours, 24 hours, 48 ​​hours, 72 hours, and 96 hours to test the VFA content (specifically, the VFA content was determined by gas chromatography-mass spectrometry). The results are shown in […]. Figure 1 .pass Figure 1The VFA content results show that the extraction effect of the present invention for obtaining high-quality carbon source (VFA) is significantly higher than that of Comparative Example 1) and Comparative Example 2). Specifically, the VFA content measured at 6 hours, 12 hours, 24 hours, 48 ​​hours, 72 hours, and 96 hours in Comparative Example 1) was 313.17 mg / L, 1655.08 mg / L, 1276.81 mg / L, 1267.66 mg / L, 965.03 mg / L, and 653.99 mg / L, respectively. Comparative Example 2) obtained a higher VFA content of 313.17 mg / L, 1655.08 mg / L, 1276.81 mg / L, 1267.66 mg / L, 965.03 mg / L, and 653.99 mg / L, respectively. The VFA content measured by the method at 6 hours, 12 hours, 24 hours, 48 ​​hours, 72 hours, and 96 hours were 819.14 mg / L, 3766.79 mg / L, 3084.66 mg / L, 2828.18 mg / L, 1904.03 mg / L, and 1854.02 mg / L, respectively; the VFA content measured by the method of the present invention at 6 hours, 12 hours, 24 hours, 48 ​​hours, 72 hours, and 96 hours were 505.44 mg / L, 4164.43 mg / L, 4549.64 mg / L, 4673.77 mg / L, 4099.45 mg / L, and 4006.96 mg / L, respectively. The method for obtaining high-quality carbon sources in this invention exhibits the highest VFA extraction capacity at 48 hours. Similarly, when sampling at 48 hours, the VFA content of this invention is approximately 1.8 times that of Comparative Example 2) and 3.7 times that of Comparative Example 1). After 48 hours, as the anaerobic biochemical process gradually enters the methanogenesis stage, VFA is gradually decomposed, leading to a decrease in its yield. However, the decreasing trend of the anaerobic active particle extraction method of this invention is relatively gentle, indicating that the VFA accumulation capacity is better than other methods.

[0039] This invention utilizes a slightly acidic environment created by the anaerobic acidification reaction of anaerobic microorganisms to drive an iron-carbon micro-battery-like redox system. The invention also measured the pH value during system operation and included a comparative example (3). In comparative example 3), only biochar loaded with zero-valent iron was added in step 4, without inoculating with sludge raw materials. An anaerobic isothermal reaction was then performed, and pH values ​​were measured every few minutes. The results are as follows: Figure 2 As shown: When the system of the present invention is started, the pH gradually decreases from the neutral range and stabilizes at around 5.0-5.3. In Comparative Example 3), the use of zero-valent iron-loaded biochar particles alone cannot acidify the pH. On the contrary, due to the oxidation of nano-zero-valent iron, which consumes hydrogen ions in the water, the pH tends to rise slightly. In the present invention, due to the action of anaerobic bacteria, a slightly acidic environment is formed through the anaerobic acidification process, maintaining the pH value of the system between 5.0 and 5.3 throughout the entire anaerobic isothermal reaction process, thereby activating the micro-battery reaction function.

[0040] The microbial anaerobic process of this invention can initiate the operation of an iron-carbon micro-battery-like redox system, thereby promoting the decomposition of organic components in sludge, improving the biodegradability of macromolecular organic matter, enhancing the efficiency of the microbial anaerobic process, and further promoting the stable and continuous operation of the iron-carbon micro-battery-like redox system, ultimately forming a virtuous cycle of internally driven active particle system, effectively improving the extraction of high-quality carbon sources.

[0041] Preferably, in step 2, the concentration of the hydrogen peroxide solution is 30%, and the mass percentage of the sludge raw material to the hydrogen peroxide solution is 15:1.

[0042] As a possible implementation, the concentration of the hydrogen peroxide solution can be any value between 20% and 40%; the mass percentage of the sludge raw material to the hydrogen peroxide solution can be any value between 10:1 and 20:1.

[0043] As a possible implementation, the amount of biochar loaded with zero-valent iron added can be any value between 40 and 60 g per liter of the supernatant.

[0044] Furthermore, to prevent the reaction from entering the methanogenesis stage under anaerobic isothermal oxidation, the pH is controlled to be no lower than 5.0 and the redox potential is controlled between -300 and 100 mV during the reaction.

[0045] In this embodiment, the anaerobic microbial sources include, but are not limited to: lactic acid bacteria (such as lactic acid streptococcus, acidophilic lactobacillus), bifidobacteria and clostridium (such as butyric acid clostridium, acetone butanol clostridium).

[0046] Furthermore, in order to ensure the organic matter is fully dissolved, in step 2, the heating temperature is 80~100℃, and the heating time is no less than 1 hour. Specifically, in this embodiment, the heating conditions are heating at 80~100℃ for 90 minutes.

[0047] The anaerobic isothermal conditions are maintained at a temperature of 25°C to 40°C. The reaction is an anaerobic microbial-catalyzed iron-carbon micro-battery-like redox reaction. The duration of the anaerobic microbial-catalyzed iron-carbon micro-battery-like redox reaction is 6 to 96 hours. The anaerobic microbial-catalyzed iron-carbon micro-battery-like redox reaction causes the organic matter to decompose and produce small molecule fatty acids.

[0048] Preferably, to prevent the reaction from entering the methanogenesis stage under anaerobic isothermal conditions, the reaction time under anaerobic isothermal conditions is 12-48 hours.

[0049] More preferably, in order to ensure VFA yield, the reaction time under anaerobic isothermal conditions is 24-48 hours.

[0050] Example 2

[0051] This embodiment further specifies the preparation method of the biochar loaded with zero-valent iron. Specifically, the preparation method is as follows: biochar is added to a 0.1 mol / L ferrous sulfate solution, with 200-300 g of biochar added per liter of ferrous sulfate solution, ensuring the ferrous sulfate solution completely submerges the biochar. The biochar is sieved to obtain particles with a diameter <5 mm. The mixture is shaken for at least 10 hours to allow iron ions to fully load and form a mixture within the biochar pores. Then, a 0.1 mol / L sodium borohydride solution is slowly added dropwise to the mixture until no more bubbles are generated. After centrifugation and drying (at a drying temperature of 40-60°C), a composite material is formed where nano-zero-valent iron is fully loaded and coupled within the biochar pores, which is the biochar loaded with zero-valent iron [see XRD pattern for details]. Figure 3 Biochar loaded with zero-valent iron exhibits characteristic diffraction peaks for C (PDF#50-1363) and Fe (PDF#85-1410), while pristine biochar only exhibits characteristic diffraction peaks for C (PDF#50-1363).

[0052] In the preparation method of this embodiment, the biochar used can be purchased directly or prepared by the user. Specifically, in this embodiment, NaCl and KCl are added during the preparation of the biochar, with an addition amount of 1-5g of NaCl and KCl per 100g of biochar. Na and K elements can not only increase the porosity of biochar, thereby enabling it to load more zero-valent iron, but these inorganic ions can also enhance the electron transfer efficiency in the subsequent iron-carbon micro-battery redox system, improving its redox effect. Regarding the impact of Na and K on VFA yield, this invention provides two examples, specifically differing in the addition of zero-valent iron-loaded biochar in step 4 of the method for obtaining high-quality carbon source from sludge. Example 1) involves not adding Na and K elements during the preparation of zero-valent iron-loaded biochar, while Example 2) involves adding Na and K elements during the preparation of zero-valent iron-loaded biochar. The results show that adding Na and K can significantly increase the yield of VFA. Specifically, the VFA content measured at 6 hours, 12 hours, 24 hours, 48 ​​hours, 72 hours, and 96 hours using the method of obtaining a high-quality carbon source in Example 1 was 467.56 mg / L, 3362.25 mg / L, 3988.48 mg / L, 3587.12 mg / L, 3106.78 mg / L, and 2990.98 mg / L, respectively; the VFA content measured at 6 hours, 12 hours, 24 hours, 48 ​​hours, 72 hours, and 96 hours using the method of obtaining a high-quality carbon source in Example 2 was 512.56 mg / L, 4012.38 mg / L, 4501.32 mg / L, 4755.23 mg / L, 4178.02 mg / L, and 4003.29 mg / L, respectively.

[0053] As a possible implementation, the biochar can also be prepared by low-temperature pyrolysis of a mixture of sludge and kitchen waste in a dry weight ratio of 3:1 to 5:1. Since the raw material for preparing biochar includes kitchen waste, which contains abundant Na and K elements, using kitchen waste as a raw material can also achieve the effect of increasing VFA production.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for obtaining a high-quality carbon source from sludge, characterized by, The method comprises the following steps: Step 1, obtaining sludge raw material; Step 2, taking part of the sludge raw material, adjusting the water content of the sludge raw material to be greater than 90%, adding hydrogen peroxide solution to the sludge raw material and mixing uniformly to form a mixed solution, and heating the mixed solution to dissolve organic matter in the sludge raw material; Step 3, adjusting the pH value of the heated mixed solution to 7.5-8.5, and after cooling and precipitation, obtaining supernatant containing organic matter; Step 4, inoculating the sludge raw material in step 1 into the supernatant as an anaerobic microbial source, adding biochar loaded with zero-valent iron, mixing and adjusting the pH value to 6-7, and reacting under anaerobic constant temperature conditions for 6-96 hours, and the solution after reaction is a high-quality carbon source.

2. The method of claim 1, wherein in step 2, the concentration of the hydrogen peroxide solution is 20%-40%, and the mass percentage of the sludge raw material to the hydrogen peroxide solution is 10:1-20:

1. In step 2, 3. The method of claim 1, wherein, In step 2, the heating temperature is 80-100℃, and the heating time is not less than 1 hour.

4. The method of claim 1, wherein in step 4, the volume ratio of the supernatant to the inoculated sludge is 9:

1.

5. The method of claim 1, wherein in step 4, 40-60g of the biochar loaded with zero-valent iron is added per liter of the supernatant.

6. The method of claim 1, wherein in step 4, the temperature of the anaerobic constant temperature condition is 25℃-40℃, the reaction is an anaerobic microbial catalytic driven iron-carbon microcell type oxidation-reduction reaction, the time of the anaerobic microbial catalytic driven iron-carbon microcell type oxidation-reduction reaction is 24-48 hours, and the anaerobic microbial catalytic driven iron-carbon microcell type oxidation-reduction reaction decomposes the organic matter to produce small molecule fatty acids.

7. The method of claim 1, wherein in step 4, the pH value is controlled to be not less than 5.0 during the reaction, and the oxidation-reduction potential is controlled to be between-300mv and 100mv.

8. The method of claim 1, wherein the preparation method of the biochar loaded with zero-valent iron is: adding biochar into a ferrous sulfate solution, oscillating for at least 10 hours to make iron ions enter the pore channels of the biochar and fully load to form a mixed solution, then slowly adding 0.1 mol / L sodium borohydride solution to the mixed solution until no bubbles are generated, and centrifuging and drying to form a composite material in which nano zero-valent iron is fully loaded and coupled in the pore channels of the biochar.

9. The method of claim 8, wherein the concentration of the ferrous sulfate solution is 0.1 mol / L, 200-300g of biochar is added per liter of the ferrous sulfate solution, the ferrous sulfate solution can completely immerse the biochar, and the biochar is biochar particles with a particle size of <5mm.

10. The method of claim 8, wherein ​ ​ ​ ​ ​ ​ ​ NaCl and KCl are added in the process of preparing the biochar, and the amount of addition is: 1-5 g of NaCl and KCl are added in every 100 g of biochar.

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