Method for promoting short-chain fatty acid production by anaerobic fermentation of excess sludge

Abstract

This invention discloses a method for promoting the production of short-chain fatty acids through anaerobic fermentation of waste sludge, relating to the field of solid waste treatment technology. The method includes the following steps: before anaerobic fermentation, biochar and persulfate are added to the waste sludge for pretreatment. This invention utilizes biochar to activate the SO4· ... ‑ ·OH and 1 O2 and other reactive oxygen species disrupt the structure of sludge cells, causing them to release large amounts of organic matter, increasing the rate of hydrolysis, and enhancing the metabolism of acid-producing microorganisms, thereby promoting the generation of high-quality recyclable short-chain fatty acids. This achieves the reduction, stabilization, and resource recovery of excess sludge, not only treating waste with waste but also avoiding the introduction of new pollutants. Compared with existing technologies, this invention has advantages such as low cost, short anaerobic digestion time, no secondary pollution, and ease of implementation. It solves the problems of large volume of excess sludge, high hazard, and difficulty in resource recovery.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment technology, and in particular to a method for promoting the anaerobic fermentation of residual sludge to produce short-chain fatty acids. Background Technology

[0002] Activated sludge-based biological wastewater treatment is currently the most widely used biological wastewater treatment technology. However, this method has always suffered from the drawback of generating large amounts of excess sludge. Furthermore, the excess sludge has a complex composition, consisting of a mixture of inorganic and organic matter, cells, and colloidal substances, and contains recalcitrant organic matter, heavy metals, and small amounts of pathogenic microorganisms (pathogens, parasites, harmful insect eggs). If left untreated and disposed of improperly, it will not only occupy a large amount of land resources, but also easily ferment, producing leachate that pollutes soil, groundwater, and surface water bodies such as rivers and lakes, causing serious secondary pollution to the environment.

[0003] Anaerobic digestion technology is widely used to effectively reduce and utilize sludge. Reusing the short-chain fatty acids produced by anaerobic fermentation of excess sludge in wastewater treatment processes is an effective way to supplement influent carbon sources on-site. However, because most organic matter in sludge is contained within microbial cells, the hydrolysis stage of anaerobic digestion is slow, becoming a major limiting factor and ultimately resulting in insignificant solubilization and reduction effects on sludge. Therefore, seeking efficient sludge lysis technology to promote the anaerobic fermentation of excess sludge to produce short-chain fatty acids is of significant practical importance. Summary of the Invention

[0004] The purpose of this invention is to provide a method for promoting the anaerobic fermentation of waste sludge to produce short-chain fatty acids, so as to solve the problems existing in the prior art, improve the anaerobic digestion efficiency of sludge, shorten the digestion time, and increase the accumulation of short-chain fatty acids.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] One of the technical solutions of this invention is a method for promoting the anaerobic fermentation of waste sludge to produce short-chain fatty acids, comprising the following steps:

[0007] Before anaerobic fermentation, biochar and persulfate are added to the remaining sludge for pretreatment.

[0008] Furthermore, the biochar is biochar prepared using residual sludge as biomass material.

[0009] Furthermore, the method for preparing the biochar includes the following steps:

[0010] The remaining sludge was dried and then pyrolyzed before being ground and sieved to obtain the biochar.

[0011] Furthermore, the drying process specifically involves drying at 60-105℃ for 2-12 hours; the pyrolysis treatment specifically involves pyrolysis at 500-600℃ for 3-5 hours under an inert atmosphere.

[0012] Furthermore, the persulfate is potassium persulfate or sodium persulfate.

[0013] Furthermore, the dosage of biochar is 0.1-0.5 g / gVSS (volatile suspended solids); the dosage of persulfate is 0.2-1 g / gVSS.

[0014] Furthermore, the pretreatment time is 30-120 minutes.

[0015] The second technical solution of the present invention is a method for shortening the digestion time in the process of producing short-chain fatty acids from anaerobic fermentation of waste sludge, which adopts the above-mentioned method for promoting the production of short-chain fatty acids from anaerobic fermentation of waste sludge.

[0016] The third technical solution of the present invention is a method for increasing the accumulation of short-chain fatty acids during the anaerobic fermentation of waste sludge to produce short-chain fatty acids, which adopts the above-mentioned method for promoting the anaerobic fermentation of waste sludge to produce short-chain fatty acids.

[0017] The present invention discloses the following technical effects:

[0018] (1) The method of the present invention is simple, easy to operate and easy to implement, and has the advantages of low cost and no secondary pollution.

[0019] (2) Using the method of the present invention, recalcitrant organic pollutants in digested sludge can be removed by chemical oxidation of persulfate activated by sludge-based biochar, which is beneficial to improving the harmlessness level of sludge.

[0020] (3) The method of the present invention improves the efficiency of anaerobic digestion of sludge, shortens the digestion time, and increases the accumulation of short-chain fatty acids.

[0021] (4) This invention does not require the use of traditional methods such as multi-step co-precipitation or impregnation sintering, nor does it require additional carrier loading of transition metals. It only requires pyrolysis of sludge to obtain sludge-based biochar with good activation effect on persulfate.

[0022] (5) This invention utilizes biochar to activate SO4· produced by persulfate. - ·OH and 1O2 and other reactive oxygen species disrupt the structure of sludge cells, causing them to release large amounts of organic matter, increasing the rate of hydrolysis, and enhancing the metabolism of acid-producing microorganisms, thereby promoting the generation of high-quality recyclable short-chain fatty acids. This achieves the reduction, stabilization, and resource recovery of excess sludge, not only treating waste with waste but also avoiding the introduction of new pollutants. Compared with existing technologies, this invention has advantages such as low cost, short anaerobic digestion time, no secondary pollution, and ease of implementation. It solves the problems of large volume of excess sludge, high hazard, and difficulty in resource recovery. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a diagram illustrating the effect of each group in Example 1 on the release of dissolved organic matter by disrupting the sludge cell structure.

[0025] Figure 2 This is a graph showing the release of dissolved organic matter during the anaerobic digestion process in each group in Example 2;

[0026] Figure 3 This is a graph showing the accumulation of short-chain fatty acids during the anaerobic digestion process in each group in Example 2. Detailed Implementation

[0027] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0028] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0029] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0030] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0031] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0032] This invention provides a method for promoting the anaerobic fermentation of waste sludge to produce short-chain fatty acids, comprising the following steps:

[0033] Before anaerobic fermentation, biochar and persulfate are added to the remaining sludge for pretreatment.

[0034] The pretreatment process can disrupt the cell structure of the remaining sludge and promote the release of organic matter.

[0035] In this invention, the biochar is prepared using waste sludge as biomass material. The preparation method of the biochar includes the following steps: drying the waste sludge and then subjecting it to pyrolysis, followed by grinding and sieving to obtain the biochar. In a preferred embodiment of this invention, the drying is specifically performed at 60-105℃ for 2-12 hours. The above-mentioned drying temperature and time ensure the drying effect while saving time. A drying temperature higher than the above-mentioned range will cause excessive removal of water from the sludge, resulting in energy waste and affecting the quality of the subsequent sludge-based biochar. A drying temperature lower than the above-mentioned range will result in an excessively low sludge dewatering rate, causing energy waste in the subsequent pyrolysis stage and affecting the formation of surface active groups in the sludge-based biochar prepared by pyrolysis. In a preferred embodiment of this invention, the pyrolysis is specifically performed at 500-600℃ for 3-5 hours at an inert gas flow rate of 0.5-1 L / min. The inert gas is nitrogen or argon. This invention does not have special restrictions on the source of the inert gas; nitrogen or argon, which are well known to those skilled in the art, can be used. The temperature and time of the pyrolysis treatment described above can ensure the quality of sludge-based biochar and the activation effect of persulfate while saving time and energy. However, if the pyrolysis temperature is higher than the range described above, it will cause excessive carbonization of the functional groups on the surface of the sludge-based biochar, affecting the subsequent anaerobic digestion and acid production effect of the sludge; if it is lower than the range described above, the carbonization effect of the sludge-based organic matter will be insufficient, affecting the activation effect of persulfate. The flow rate of the inert gas described above can ensure the quality of sludge-based biochar while saving inert gas consumption. If the flow rate is lower than the specified flow rate, the proportion of oxygen-containing groups on the surface of the sludge-based biochar will increase, affecting its activation effect of persulfate; if the flow rate is higher than the specified flow rate, the proportion of nitrogen-containing groups (such as pyridine rings) on the surface of the sludge-based biochar will be too low, affecting its activation effect of persulfate. In a preferred embodiment of the present invention, the specific surface area of ​​the biochar is not less than 20 m². 2 / g, with a mesh size of not less than 100 mesh. A surface area that is too small will reduce the adsorption performance of sludge-based biochar, result in insufficient activation sites, and reduce the opportunity for contact with persulfate, thus affecting the activation effect; a mesh size that is too small will result in excessively small and fine particle size of the sludge-based biochar and insufficient activation groups on the surface of the sludge-based biochar, also affecting the activation effect.

[0036] In this invention, the persulfate is potassium persulfate or sodium persulfate. This invention does not impose any special restrictions on the source of the persulfate; potassium persulfate or sodium persulfate, which are well-known to those skilled in the art, can be used.

[0037] In this invention, the dosage of biochar is 0.1-0.5 g / gVSS; the dosage of persulfate is 0.2-1 g / gVSS. Using the above dosage ensures the best activation effect of persulfate by the sludge-based biochar, which is most beneficial for pre-treated sludge used in subsequent fermentation. Dosage below the above dosage will result in insufficient active sites for the sludge-based biochar to adsorb and activate persulfate to form reactive oxygen species, leading to incomplete persulfate activation. Dosage above the above dosage will cause excessive free radicals generated by persulfate activation to undergo self-quenching reactions, reducing the concentration of reactive oxygen species in the system, thereby affecting the oxidation effect of the system and leading to a decline in the quality of subsequent sludge fermentation.

[0038] In this invention, the pretreatment time is 30-120 minutes. Using this pretreatment time ensures sufficient oxidation and cell dissolution of the sludge while saving time; a pretreatment time shorter than this will reduce the efficiency of sludge cell dissolution and result in incomplete oxidation; a pretreatment time longer than this will waste time and increase the volume of the reaction tank and infrastructure costs.

[0039] In this invention, the residual sludge pretreated with biochar and persulfate (i.e., biochar-activated persulfate-treated sludge) undergoes anaerobic digestion in an anaerobic digester. The organic compounds in the sludge are rapidly utilized by anaerobic and facultative bacteria, increasing the yield of short-chain fatty acids and reducing the volume of residual sludge. The material after anaerobic digestion (unit) is separated into sludge and water by a dewatering device. The supernatant is returned to the aerobic biological treatment tank as an external carbon source, providing carbon for the growth of microorganisms in the aerobic biological treatment tank. The dewatered sludge cake has been stabilized and can be applied to farmland as organic fertilizer.

[0040] The present invention also provides a method for shortening the digestion time in the process of producing short-chain fatty acids from anaerobic fermentation of waste sludge, using the above-mentioned method for promoting the production of short-chain fatty acids from anaerobic fermentation of waste sludge.

[0041] This invention also provides a method for increasing the accumulation of short-chain fatty acids during the anaerobic fermentation of waste sludge to produce short-chain fatty acids, employing the above-described method for promoting the anaerobic fermentation of waste sludge to produce short-chain fatty acids.

[0042] Unless otherwise specified, the raw materials and instruments used in the embodiments of this invention are all conventional raw materials and instruments in the field and can be obtained through commercial channels.

[0043] The residual sludge used in this embodiment of the invention is municipal sludge from a municipal wastewater treatment plant. The basic characteristics of the sludge are: total solids content of 20.6±0.8 g / L, pH value of 7.0±0.3, total suspended solids content of 19.2±0.6 g / L, volatile suspended solids content of 8.86±0.7 g / L, and dissolved chemical oxygen demand of 116±26 mg / L.

[0044] The method for preparing sludge-based biochar used in this embodiment of the invention is as follows:

[0045] The remaining sludge was dried in a 105℃ oven for 2 hours to remove moisture, yielding dry sludge. This dry sludge was then pyrolyzed at 600℃ for 3 hours in an N2 environment (N2 flow rate of 0.8 L / min). After cooling, the sludge was ground and sieved to obtain sludge-based biochar. Its specific surface area was 24.96 m². 2 / g, with an average pore size of 14.29nm.

[0046] The persulfate used in the embodiments of the present invention is specifically sodium persulfate.

[0047] Example 1

[0048] 0.23 g / g VSS of sludge-based biochar and 0.49 g / g VSS of persulfate were added to 500 mL of excess sludge and reacted for 30 min (referred to as the biochar / persulfate group). The treatment was carried out under normal temperature and pressure conditions. Simultaneously, a blank control group, a control group with only persulfate added (omitting the addition of sludge-based biochar compared to the biochar / persulfate group), and a control group with only biochar added (omitting the addition of persulfate compared to the biochar / persulfate group) were set up. After the reaction, the dissolved organic matter in the sludge was measured, and the results are as follows: Figure 1 As shown.

[0049] from Figure 1 As can be seen, under the sole action of persulfate, the sludge cell and extracellular polymer structure were destroyed, and intracellular organic matter was released into the extracellular fluid, increasing the concentration of dissolved organic matter in the sludge. The dissolved organic matter leaching amount was 172 mg / L, which was 1.8 times that of the control group. However, sludge-based biochar activated with persulfate had a better effect on sludge cell lysis, with the dissolved organic matter leaching amount reaching 380 mg / L, which was 4 times that of the control group (95 mg / L). The dissolved organic matter concentration in the biochar-only group was even lower than that in the control group. This is because sludge-based biochar has adsorption capabilities, which can adsorb some of the dissolved organic matter in the sludge, resulting in a lower dissolved organic matter concentration in the biochar-only group compared to the control group.

[0050] Example 2

[0051] 0.23 g / g VSS of biochar and 0.49 g / g VSS of persulfate were added to 1 L of sludge and reacted for 30 min. The reacted sludge was then transferred to an anaerobic digester (referred to as the biochar / persulfate group) for anaerobic digestion. Control groups were set up, including a blank control, a persulfate-only control (omitting the addition of sludge-based biochar compared to the biochar / persulfate group), and a biochar-only control (omitting the addition of persulfate compared to the biochar / persulfate group). The dissolved organic matter during the anaerobic digestion process was measured, and the results are as follows: Figure 2 As shown. The results of detecting short-chain fatty acids during anaerobic digestion are as follows. Figure 3 As shown.

[0052] Depend on Figure 2 It can be seen that the early fermentation stage is the rapid dissolution phase for each experimental group, with dissolved organic matter showing an upward trend. However, due to the different dosages, the timing of each group entering different stages varies. The control group and the biochar-only group showed a significant increase in dissolved organic matter values ​​in the first four days, followed by a slow growth phase. The persulfate-only group showed a slower growth trend starting from day 6. The dissolved organic matter value of the biochar-activated persulfate group peaked at 2660 mg / L on day 10, five times that of the control group (543 mg / L), and then entered a decline phase. This indicates that biochar-activated persulfate treatment of sludge not only increases the dissolution of dissolved organic matter but also advances the time when the dissolved organic matter reaches its peak. The dissolved organic matter concentration in the biochar-only group was lower than that in the control group because sludge-based biochar has adsorption capabilities, adsorbing some of the dissolved organic matter in the sludge, resulting in a lower dissolved organic matter concentration in the biochar-only group compared to the control group.

[0053] Depend on Figure 3 It can be seen that the accumulation of short-chain fatty acids in all anaerobic digestion groups increased with fermentation time. Starting from day 6, the concentration of short-chain fatty acids in the biochar-activated persulfate group significantly exceeded that of the other three groups, reaching a peak of 1773 mg COD / L on day 10. This was 6 times that of the control group (292 mg COD / L), 10 times that of the biochar group (197 mg COD / L), and 2.6 times that of the persulfate group (687 mg COD / L). Biochar-activated persulfate not only greatly promoted acid production but also brought forward the peak value of acid production. The concentration of short-chain fatty acids in the biochar-only group was lower than that in the control group. This is because sludge-based biochar has adsorption capabilities, which can adsorb some of the short-chain fatty acids in the sludge, resulting in a lower concentration of short-chain fatty acids in the supernatant of the biochar-only group compared to the control group.

[0054] Example 3

[0055] The only difference from the biochar / persulfate group in Example 2 is that the sludge-based biochar was replaced with biochar prepared from plant residue (referred to as the plant residue group), biochar prepared from animal manure (referred to as the animal manure group), and biochar prepared from municipal solid waste (referred to as the municipal solid waste group), respectively. The preparation methods were the same as those for the sludge-based biochar. The dissolved organic matter and short-chain fatty acids during the anaerobic digestion process were tested, and the results are as follows:

[0056] Plant residue group: Dissolved organic matter reached its peak at 150 mg / L on day 23 of anaerobic fermentation; short-chain fatty acids reached their peak at 89 mg COD / L on day 24 of anaerobic fermentation.

[0057] Animal feces group: Dissolved organic matter reached its peak at 274 mg / L on day 8 of anaerobic fermentation; short-chain fatty acids reached their peak at 192 mg COD / L on day 8 of anaerobic fermentation.

[0058] In the municipal solid waste group: dissolved organic matter peaked at 196 mg / L on day 15 of anaerobic fermentation; short-chain fatty acids peaked at 125 mg COD / L on day 15 of anaerobic fermentation.

[0059] Example 4

[0060] 0.23 g / g VSS of biochar and 0.49 g / g VSS of persulfate were added to 1 L of sludge, and then immediately transferred to an anaerobic digester for anaerobic fermentation.

[0061] Results: The dissolved organic matter reached its peak at 1976 mg / L on day 10 of anaerobic fermentation; the short-chain fatty acids reached their peak at 1406 mg COD / L on day 10 of anaerobic fermentation.

[0062] Persulfate can enhance sludge lysis technology, but it requires activation to produce active particles. Biochar, produced by the pyrolysis of biomass under anaerobic conditions, possesses a large specific surface area, abundant pore structure, and oxygen-containing functional groups on its surface. It can act as an electron carrier and transfer medium, utilizing electron redistribution to promote the O2-O2 cleavage of persulfate to generate highly oxidizing SO42-. -This invention enhances the activation performance of carbon-based catalysts for persulfate. Biomass materials suitable for biochar preparation are widely available, including plant residues, animal manure, municipal solid waste, and municipal sludge. Among these, sludge-based biochar prepared from waste sludge has a large specific surface area and contains various non-metallic and metallic elements, exhibiting a metallic phase structure and multiple catalytic active sites, resulting in better activation of persulfate. Furthermore, compared to other biomass materials, waste sludge contains transition metal elements, which also activate persulfate, further improving the activation effect of biochar on persulfate. This invention utilizes biochar prepared from waste sludge to activate persulfate, promoting the anaerobic fermentation of waste sludge to produce short-chain fatty acids, thereby improving the anaerobic digestion efficiency of sludge, shortening digestion time, and increasing the accumulation of short-chain fatty acids.

[0063] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for promoting the anaerobic fermentation of waste sludge to produce short-chain fatty acids, characterized in that, Includes the following steps: Before anaerobic fermentation, biochar and persulfate are added to the remaining sludge for pretreatment. The biochar is prepared using residual sludge as biomass material; The method for preparing the biochar includes the following steps: The remaining sludge was dried and then subjected to pyrolysis, followed by grinding and sieving to obtain the biochar. The drying process specifically involves drying at 60-105 ℃ for 2-12 h; the pyrolysis treatment specifically involves pyrolysis at 500-600 ℃ for 3-5 h under an inert atmosphere.

2. The method for promoting the anaerobic fermentation of excess sludge to produce short-chain fatty acids according to claim 1, characterized in that, The persulfate is potassium persulfate or sodium persulfate.

3. The method for promoting the anaerobic fermentation of excess sludge to produce short-chain fatty acids according to claim 1, characterized in that, The biochar dosage is 0.1-0.5 g / g VSS; the persulfate dosage is 0.2-1 g / g VSS.

4. The method for promoting the anaerobic fermentation of excess sludge to produce short-chain fatty acids according to claim 1, characterized in that, The pretreatment time is 30-120 min.

5. A method for shortening the digestion time during the anaerobic fermentation of waste sludge to produce short-chain fatty acids, characterized in that, The method for promoting the anaerobic fermentation of excess sludge to produce short-chain fatty acids as described in claim 1 is adopted.

6. A method for increasing the accumulation of short-chain fatty acids during the anaerobic fermentation of waste sludge to produce short-chain fatty acids, characterized in that, The method for promoting the anaerobic fermentation of excess sludge to produce short-chain fatty acids as described in claim 1 is adopted.

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