A method for promoting sludge thermal hydrolysis by catalytic oxidation of in-situ quinone compounds

Abstract

The present application relates to a method for promoting sludge thermal hydrolysis by exciting in-situ quinone compound catalytic oxidation, and belongs to the field of organic waste treatment. In the method, humic acid and other quinone compounds generated in the process of sludge high-temperature thermal hydrolysis are used as in-situ organic catalysts, and the catalytic oxidation function of the quinone compounds is excited to improve the effect of sludge thermal hydrolysis. On the premise of not affecting the effect of sludge hydrolysis, the hydrolysis temperature is reduced, the Maillard product is effectively reduced, and the quality of carbon source released by sludge hydrolysis is improved. Under the same sludge thermal hydrolysis conditions, the soluble COD concentration can be increased from 17.1 g / L to 24.3 g / L by exciting the catalytic oxidation of in-situ quinone compounds, and the increase rate is 42.1%. The method does not need to add additional catalyst, and the exciting agent is cheap metal such as ferrous ion, so the cost is low and the efficiency is high. It is a new method and new idea for improving the effect of sludge thermal hydrolysis and improving the biodegradability of hydrolyzed sludge carbon source, and it integrates sludge reduction and resource utilization, which has high application value.

Description

TECHNICAL FIELD

[0001] The application relates to a method for promoting sludge thermal hydrolysis by catalytic oxidation of in-situ quinone compounds and belongs to the field of organic waste treatment. BACKGROUND

[0002] With the development of economy, the process of urbanization is accelerating, and the scale and treatment capacity of municipal sewage treatment plants are also increasing. As a by-product of biological treatment process, the amount of residual sludge in sewage treatment plants increases year by year. In 2022, the production of residual sludge in China will exceed 6500 tons (water content 80%), becoming a serious burden for sewage plants. Anaerobic digestion as a new sludge disposal method can well realize the reduction, harmlessness and resource utilization of sludge, and also provides a feasible method for sewage treatment plants to achieve "carbon neutralization". However, the low conversion rate of sludge anaerobic digestion products is the main reason restricting its development and application. The thermal hydrolysis process can break the sludge zooglea, break the microbial cell wall and decompose the organic matter, and then promote the release of intracellular proteins, polysaccharides and other organic matter into the supernatant, which is beneficial to the subsequent sludge anaerobic digestion. However, when the sludge hydrolysis temperature exceeds 140℃, the Maillard reaction will be intensified, producing a large amount of refractory organic matter; and when the hydrolysis temperature is lower than 160℃, the sludge organic matter is not released completely, which seriously affects the hydrolysis effect of sludge.

[0003] Combining oxidation technology with high-temperature thermal water is an effective method to reduce the temperature of thermal hydrolysis, alleviate the Maillard reaction and reduce the generation of refractory organic matter without affecting the hydrolysis effect of sludge. Traditionally, stoichiometric KMnO4, HNO3 and the like are used as oxidizing agents; but the substances reduced by such oxidizing agents will pollute the environment; with the proposal of "green chemistry", green oxidation with molecular oxygen and H2O2 as clean oxygen source has received widespread attention; the by-products generated by these oxidizing agents in the reaction are generally water, which does not pollute the environment. However, they also have some shortcomings, such as that molecular oxygen is difficult to directly react with hydrocarbons, so it is necessary to find suitable catalysts to activate the oxidizing agent or the substrate. For the selective oxidation of hydrocarbons, metal-containing catalysts are currently used; such catalysts have the advantages of high activity, relatively mild reaction conditions and the like. However, the catalytic process of most metal catalysts is easily affected by factors such as water, and the use conditions are harsh; and the price is expensive or toxic, which may pollute the environment. Therefore, finding an effective new method for catalytic oxidation of hydrocarbons is a subject of great significance and strategy.

[0004] As an important organic catalytic material, quinone compounds can widely participate in reversible hydrogenation and dehydrogenation reaction, and play an important role in electron and proton transfer in the oxidation process of organic matter. Organic catalysis is a completely different field from metal catalysis, and is developing continuously. Organic catalysis is to use small organic molecules without metal atoms as catalysts to catalyze organic chemical reactions. It has the advantages of environmental friendliness, low price and convenient use, so the use of environmentally friendly non-metallic catalytic system to catalyze the oxidation of hydrocarbon compounds has attracted widespread attention. In the process of sludge thermal hydrolysis, a large amount of quinone substances are generated, and the catalytic oxidation of these quinone substances is stimulated, so that the hydrolysis effect of sludge can be improved.

[0005] Therefore, it is necessary to develop a sewage treatment method based on in-situ catalysis to solve the problem of poor sludge hydrolysis effect in the prior art. SUMMARY

[0006] The problem to be solved by the present application is that when the temperature of the excess sludge thermal hydrolysis exceeds 140 DEG C, the Maillard reaction will be intensified, and a large amount of refractory organic matter will be produced; and when the hydrolysis temperature is lower than 160 DEG C, the sludge organic matter is not released completely, which seriously affects the hydrolysis effect of the sludge.

[0007] The present application uses quinone compounds generated in the process of sludge thermal hydrolysis as an in-situ catalyst, and through the action of an excitation agent, the oxidation of the quinone compounds is strengthened, and the hydrolysis and release of sludge organic matter are promoted.

[0008] The present application provides a method for promoting sludge thermal hydrolysis by exciting in-situ quinone compound catalytic oxidation, which comprises the following steps:

[0009] S1, after adjusting the moisture content of the municipal sludge, an excitation agent is added, and the pH is adjusted;

[0010] S2, the sludge liquid obtained in step S1 is added to a reactor, and the dissolution and release of sludge organic matter are promoted under high temperature and high pressure; compounds containing quinone groups are generated, which catalytically degrade macromolecular organic matter in the sludge, and realize the deep decomposition and dissolution of macromolecular organic matter. In this step, a large amount of humic acid and other compounds containing quinone groups are generated, and in-situ quinone compounds generate free radicals, unstable metals and the like under the action of the excitation agent, which catalytically promote the deep decomposition and dissolution of macromolecular organic matter in the sludge.

[0011] Further, the excitation agent is a soluble salt or salt solution of an inorganic electron activator.

[0012] In some preferred embodiments, after adjusting the pH in step S1, the step of adding an electron oxidant is further included.

[0013] The in-situ quinone compound produced in step S2 plays an electron transfer role. The excitation agent generates high-valence metal-based active groups under high temperature and high pressure conditions, selectively catalyzes the oxidation of refractory organic matter, obtains electrons, and transfers the electrons to the quinone compound to form hydroquinone, which further transfers the electrons to the oxidizing agent. Ultimately, the deep decomposition and dissolution of macromolecular organic matter in the sludge are achieved.

[0014] In some preferred embodiments, the water content of the sludge in step S1 is adjusted to ≥80%; when the water content of the sludge is adjusted to more than 80%, the flowability of the sludge is better, which is more conducive to the reaction.

[0015] Further, in step S1, the pH value is 5.0-8.0. Under this condition, the reaction condition is mild, which can reduce the corrosion of the reaction equipment.

[0016] In some preferred embodiments, the excitation agent is selected from Fe(0), Fe(II), Mn(II), Zn(II), Co(II), and Ni(II) and other electron activators.

[0017] Further, the concentration of the excitation agent is 0.2-2.0 g / L.

[0018] In a preferred embodiment, the excitation agent used is ferrous ion, and the pH value is 5.0-8.0. Under this pH condition, the ferrous ion can form high-valence iron ion Fe(IV)-based active components, greatly reducing or avoiding the formation of hydroxyl radicals (·OH), realizing the selective catalytic degradation of special groups of refractory organic matter, and reducing the loss of the biodegradable part of sludge organic matter, ensuring the quality of the released organic matter in the sludge hydrolysis process.

[0019] In a preferred embodiment, the excitation agent added is a soluble Fe(II) salt or a salt solution. Since the ferrous ion plays a dual role of catalytic oxidation (beneficial to the release of organic matter) and chemical flocculation (unfavorable to the release of organic matter) in the hydrolysis process, the Fe(II) concentration needs to be controlled at 0.2-2.0 g / L for the best.

[0020] In some preferred embodiments, the reaction temperature of step S2 is 100-220°C.

[0021] Further, the reaction time of step S2 is 30-240 minutes.

[0022] Further, in step S2, the high-temperature and high-pressure hydrolysis is carried out in a closed reactor, and the pressure changes with the temperature and does not need to be adjusted. The quinone compound required for the reaction is spontaneously generated in the high-temperature and high-pressure reaction process and does not need to be added additionally.

[0023] Further, the concentration of the quinone compound in step S2 is 0.2-10 g / L. The quinone compound required for the reaction is spontaneously generated in the high-temperature and high-pressure reaction process and does not need to be additionally added. However, since oxygen cannot directly contact the organic group to be oxidized, the quinone compound and ferric ions are needed as a composite electron transfer agent and play a crucial role. The concentration of the quinone compound should be controlled within 0.2-10 g / L for the best results. Therefore, in the process of high-temperature thermal hydrolysis of sludge, the release amount of the quinone compound needs to be regulated according to the concentration and hydrolysis temperature of the hydrolyzed sludge, otherwise it needs to be additionally added.

[0024] In some preferred embodiments, the electron oxidizing agent comprises one or a combination of air, H2O2, and oxygen.

[0025] In one embodiment of the present application, the added oxidizing agent includes, but is not limited to, air, H2O2, oxygen, and other weak oxidizing agents to prevent the loss of excessive oxidation of organic matter.

[0026] In some preferred embodiments, the method of promoting sludge thermal hydrolysis by exciting in-situ quinone compound catalytic oxidation further comprises step S3, a step of recovering the exciting agent. The hydrolyzed sludge obtained in step S2 is cooled and the exciting agent is recovered. After the hydrolyzed sludge is cooled and cooled, solid-liquid separation is performed, and the liquid phase is a sludge hydrolysate which can be further utilized as a resource, such as being used for anaerobic fermentation to produce acid.

[0027] In one embodiment, the exciting agent is iron, which is recovered by rotary centrifugal precipitation separation.

[0028] Further, the selection of the operating parameters in step S1 and step S2 is based on the increase of the concentration of the soluble biodegradable carbon source and the total soluble organic matter. Unlike the conventional advanced oxidation process which aims to remove pollutants (such as COD), the purpose of sludge thermal hydrolysis is to release as much organic matter as possible with good biodegradability. Therefore, the selection of various operating parameters needs to take into account the increase of the concentration of the soluble biodegradable carbon source (BOD) and the improvement of the dewatering performance of the hydrolyzed sludge-total soluble organic matter (SCOD).

[0029] The second aspect of the present application also provides the use of the method of promoting sludge thermal hydrolysis by exciting in-situ quinone compound catalytic oxidation described above in the field of organic solid waste treatment.

[0030] Advantages:

[0031] (1) The technical scheme of the present application stimulates the catalytic oxidation function of in-situ quinone compounds, enhances the total organic matter release effect of sludge thermal hydrolysis, and can effectively reduce Maillard products and improve the quality of sludge hydrolysis carbon source release by reducing the hydrolysis temperature without affecting the sludge hydrolysis effect. It is a new method and new idea to improve the effect of sludge thermal hydrolysis and improve the biodegradability of hydrolyzed sludge carbon source, and integrates sludge reduction and resource utilization, which has high application value.

[0032] (2) In the process of sludge thermal hydrolysis, a large amount of quinone substances are produced, and the catalytic oxidation of these quinone substances can improve the effect of sludge hydrolysis. And this kind of compound has the advantages of high activity, mild reaction condition, environmental friendliness, etc. This kind of in-situ catalyst is produced in the process of sludge high-temperature thermal hydrolysis, and does not need to be added extra, which is low in cost and high in efficiency.

[0033] (3) The sludge thermal hydrolysis in-situ quinone compound catalytic oxidation activator used in the present application is the core of the whole reaction, which plays the role of catalytic oxidation initiator. The quinone compound produced in the process of sludge thermal hydrolysis has complex composition and insufficient catalytic ability, and must be pre-activated and excited. The activator is a cheap metal such as ferrous ion, which is low in cost and high in efficiency. In order to solve the problem that the sludge hydrolysis temperature exceeds 140℃, the Maillard reaction will be intensified, and a large amount of refractory organic matter will be produced; and when the hydrolysis temperature is lower than 160℃, the sludge organic matter is not released completely, which seriously affects the effect of sludge hydrolysis. The present application provides a new solution. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 Organic matter release situation (a) and humic acid (quinone compound) release situation (b) under different thermal hydrolysis temperatures in Example 1;

[0035] Figure 2 Sludge high-temperature thermal hydrolysis organic matter release effect when ferrous ion is used as an activator in Example 2;

[0036] Figure 3 Sludge high-temperature thermal hydrolysis organic matter release effect when ferrous ion is coupled with hydrogen peroxide in Example 3;

[0037] Figure 4 Sludge high-temperature thermal hydrolysis organic matter release effect of ferrous activator at different temperatures in Example 4;

[0038] Figure 5 Catalytic oxidation principle of quinone compounds in Example 3. DETAILED DESCRIPTION

[0039] The application will be further described and concretely explained with the following examples. The application can be better understood according to the following examples. However, it is easy for those skilled in the art to understand that the specific material ratio, process conditions and results described in the examples are only used to illustrate the application, and should not and will not limit the application described in detail in the claims.

[0040] The experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials described are all commercially available unless otherwise specified.

[0041] The dewatered sludge from Wuxi Shuofang Municipal Sewage Treatment Plant was selected as the urban sludge, and FeCl2·4H2O was purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0042] In the following examples, the measurement method of humic acid (quinone compound) is as follows:

[0043] Dissolved humic acid in thermally hydrolyzed sludge was extracted and purified according to the method provided by the International Humic Substances Society (IHSS), and all the extracted and purified dissolved humic acid samples were freeze-dried into powder and stored under dry conditions at room temperature and in the dark for later use. The specific steps are as follows: first, the sludge sample powder was obtained by grinding the freeze-dried supernatant of the thermally hydrolyzed sludge through a 200-mesh sieve, and then the sludge sample was acidified to pH = 1.0 using 6 mol / L HCl. After oscillating the acidified solution for 1 h, the supernatant containing fulvic acid was discarded, and the solid phase was collected. Then, the remaining solid was dissolved using 6 mol / L NaOH during nitrogen blowing, and then the mixed solution was oscillated for 15 h and centrifuged. The supernatant was collected for extracting humic acid. Next, the first step was repeated to pH = 1.0 ± 0.2 to separate humic acid and fulvic acid. The humic acid extract was completely dissolved with prepared 0.1 mol / L KOH, and the potassium ion concentration was maintained at about 0.3 mol / L with a potassium chloride solution, and then the alkaline solution was centrifuged to remove suspended solids. The solution was acidified to pH = 1.0 ± 0.2 and centrifuged. The precipitate was further acidified with a mixed solution of 0.1 mol / L HCl and 0.3 mol / L HF (volume ratio = 1:1) and oscillated for 12 hours. Finally, the supernatant was discarded, and the precipitate was washed with ultrapure water to remove Cl - - ​The humic acid samples were finally freeze-dried into solid powder using vacuum freeze-drying technique. The raw sludge and thermally hydrolyzed humic acids at 140, 160, 170, 180, and 200 °C were labeled as 140 °C HAs, 160 °C HAs, 170 °C HAs, 180 °C HAs, and 200 °C HAs, respectively. The humic acid content after thermal hydrolysis was determined by gravimetric quantification. All index determinations were repeated three times.

[0044] The SCOD dissolution rate can represent the overall sludge hydrolysis effect.

[0045] The formula of sludge disintegration degree (DD):

[0046]

[0047] Example 1 High-temperature thermal hydrolysis experiment of conventional sludge

[0048] The municipal sludge was adjusted to a water content of about 95% and a pH of 7, and after stirring for 1 h, a sludge-water mixture was obtained, which was stored at 4 °C for use. When used, 500 mL of the mixed sludge-water mixture was taken and directly injected into the sludge thermal hydrolysis reactor, which was heated to 140, 160, 170, 180, and 200 °C using electric heating. After 30 min of reaction, the heating was stopped, and when the temperature dropped to about 50 °C, the thermally hydrolyzed sludge was taken out and centrifuged at a speed of 8000 rad / min for 10 min for solid-liquid separation. Finally, the supernatant after centrifugation was collected and stored at 4 °C in the dark for subsequent determination of various indexes.

[0049] As shown in Figure 1 (a), the release effect of organic matter in the sludge increased first and then decreased with the increase of the thermal hydrolysis temperature, and the SCOD was the highest at 170 °C. As shown in Figure 1 (b), a large amount of humic acid (quinone compounds) was released at different thermal hydrolysis temperatures, and reached the peak value at 180 °C.

[0050] Example 2 High-temperature thermal hydrolysis of sludge under different concentrations of ferrous iron activators

[0051] The municipal sludge was adjusted to a moisture content of about 95%, and the slurry mixture was stored at 4°C for 1 hour. When used, 500 mL of the mixed slurry was first taken, and 0, 0.5, 1.5, 2.5, 3.5, 4.5 and 6 mL of 20% FeCl2·4H2O aqueous solution was added to control the concentration of ferrous ion Fe(II) at 0, 1, 3, 5, 7, 9 and 12 mM / L, respectively. After stirring, the pH was adjusted to 6. Then, the slurry was injected into the hot hydrolysis reactor, and heated to 170°C by electric heating. After 30 minutes of reaction, the heating was stopped, and when the temperature dropped to about 50°C, the hot hydrolysis sludge was taken out, centrifuged at a speed of 8000 rad / min for 10 min, and then solid-liquid separation was performed. Finally, the supernatant after centrifugation was collected and stored at 4°C in the dark for subsequent determination of various indicators.

[0052] Table 1

[0053] Sample name Raw sludge 0 mM 1 mM 3 mM 5 mM 7 mM 9 mM 12 mM SCOD (mg / L) 150 17067 14400 10667 21867 23733 24267 20152 Sludge disintegration degree (%) / 25.4％ 21.4％ 15.8％ 32.7％ 35.5％ 36.3％ 30.1％

[0054] As shown in Table 1 and Figure 2 , when the concentration of ferrous ion Fe(II) is greater than 3 mM, the concentration of SCOD is greatly improved, and when the concentration of Fe(II) is 5, 7 and 9 mM, the slurry hydrolysis effect is enhanced by 7.22%, 10.02% and 10.83% compared with the slurry without Fe(II). The sludge disintegration degree can reach 36.3%, and the SCOD concentration can be increased from 17.1 g / L to 24.3 g / L, with an increase rate of 42.1%. It is proved that the addition of appropriate amount of Fe(II) as an excitation agent can promote the hydrolysis effect of sludge.

[0055] Example 3 Sludge high-temperature thermal hydrolysis under the coupling of ferrous excitation agent and different concentrations of hydrogen peroxide

[0056] The municipal sludge was adjusted to a moisture content of about 95%, and the slurry mixture was stored at 4°C for 1 hour. When used, 500 mL of the mixed slurry was first taken, and 0, 0.5, 1.5, 2.5, 3.5, 4.5 and 6 mL of 20% FeCl2·4H2O aqueous solution was added to control the concentration of ferrous ion Fe(II) at 0, 1, 3, 5, 7, 9 and 12 mM / L, respectively. After stirring, the pH was adjusted to 6. Then, the slurry was injected into the hot hydrolysis reactor, and heated to 170°C by electric heating. After 30 minutes of reaction, the heating was stopped, and when the temperature dropped to about 50°C, the hot hydrolysis sludge was taken out, centrifuged at a speed of 8000 rad / min for 10 min, and then solid-liquid separation was performed. Finally, the supernatant after centrifugation was collected and stored at 4°C in the dark for subsequent determination of various indicators.

[0057] Table 2

[0058] Sample name 0 mM 2.5 mM 5 mM 7.5 mM 10 mM SCOD (mg / L) 24267 23932 26673 24868 19052 Sludge disintegration degree (%) 36.3％ 35.8％ 39.9％ 37.2％ 28.4％

[0059] As shown in Table 2 andFigure 3 As shown, after the introduction of an appropriate amount of electronic oxidant, the sludge disintegration degree can be further improved to 39.9%; the catalytic oxidation decomposition effect of sludge organic matter can be improved; however, the presence of excessive oxidant can cause excessive decomposition of organic matter, forming CO2, resulting in a decrease in soluble SCOD. The concentration of H2O2 exceeding 7.5 mM has a certain inhibitory effect on the dissolution of organic matter.

[0060] Example 4 Ferrous ion activator in sludge high-temperature hydrolysis at different temperatures

[0061] The municipal sludge was adjusted to a water content of about 95%, and after stirring for 1 h, the sludge-water mixture was stored at 4°C for standby use. When used, 500 mL of the mixed sludge-water mixture was first taken, the Fe(II) concentration was controlled at 9 mM, and after stirring, the pH was adjusted to 6. Then, the sludge hydrolysis reactor was injected, and the electric heating method was used to heat to 130, 145, 160, 170 and 180°C, respectively. After 30 minutes of reaction, the heating was stopped, and when the temperature dropped to about 50°C, the hydrolyzed sludge was taken out, centrifuged at a speed of 8000 rad / min for 10 min, and then subjected to solid-liquid separation. Finally, the supernatant after centrifugation was collected and stored at 4°C in the dark for subsequent determination of various indicators.

[0062] Table 3

[0063]

[0064] As Figure 1 (a), Figure 4 As shown in Table 3, ferrous ions can promote the dissolution of organic matter at lower hydrolysis temperatures. At 130°C, the addition of ferrous ions can make the sludge disintegration degree reach about 20%; at other temperatures, the addition of ferrous ions can greatly improve the sludge disintegration degree.

[0065] Without the addition of an activator, the release effect of organic matter at a lower temperature (140°C) is not good, and after the addition of an activator, the release rate of organic matter is increased to about 20%, and the release effect is increased by about 76%. Moreover, Figure 4 As shown, ferrous ions can intervene in the polycondensation reaction of complex organic matter at high temperatures of 180°C, reduce the generation of Maillard intermediates under high-temperature hydrolysis conditions, promote the conversion of Maillard intermediates into smaller organic matter, and thus reduce the generation of Maillard products under high-temperature conditions. Promote the release effect of organic matter.

[0066] Although the present application has been disclosed with the above preferred embodiments, it is not intended to limit the present application, and any person skilled in the art can make various modifications and modifications without departing from the spirit and scope of the present application, therefore the protection scope of the present application should be defined by the claims.

Claims

1.A method for promoting sludge thermal hydrolysis by exciting in-situ quinone compound catalytic oxidation, characterized in that, comprising the following steps: S1, adjusting the moisture content of municipal sludge and adding an excitation agent, with a pH value of 5.0-8.0; S2, adding the sludge liquid obtained in step S1 to a reactor to promote the dissolution of sludge organic matter under high temperature and high pressure and release it into the liquid phase; in-situ generated quinone compounds catalyze the degradation of macromolecular organic matter in sludge under the action of the excitation agent, realizing the deep decomposition and dissolution of macromolecular organic matter; In step S1, the excitation agent is a soluble salt or salt solution of inorganic electron activator, and the excitation agent is selected from one or a combination of Fe(0), Fe(II), Mn(II), Zn(II), Co(II) and Ni(II); The reaction temperature of step S2 is 100-220℃; the reaction time is 30-240 minutes; In step S2, the concentration of quinone compounds is adjusted to 0.2-10g / L according to the concentration and hydrolysis temperature of the sludge; The concentration of the excitation agent is 0.2-2.0g / L. 2.The method for promoting sludge thermal hydrolysis by exciting in-situ quinone compound catalytic oxidation according to claim 1, characterized in that, the step S1 further comprises the step of adding an electron oxidizing agent after adjusting the pH value; The electron oxidizing agent is selected from one or a combination of air, H2O2 and oxygen. The moisture content of the sludge in step S1 is adjusted to ≥80%. 4.The method for promoting sludge thermal hydrolysis by exciting in-situ quinone compound catalytic oxidation according to claim 1 or 2, characterized in that, further comprising step S3, 3. The method of claim 1 or 2, wherein the in-situ quinone-based compound catalytic oxidation-promoted sludge thermal hydrolysis is characterized in that, S3, recovering the excitation agent: cooling the hydrolyzed sludge obtained in step S2, solid-liquid separation, and recovering the excitation agent. 5.The application of the method for promoting sludge thermal hydrolysis by exciting in-situ quinone compound catalytic oxidation according to any one of claims 1-4 in the field of organic solid waste treatment. ​ ​ ​

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