Method for enhancing biological treatment of acidic organic wastewater by using compatible solute

Abstract

The invention discloses a method for enhancing biological treatment of acidic organic wastewater by using a compatible solute. According to the method, under the acidic condition, a compatible solute is added into a biological treatment system, microorganisms uptake the compatible solute, metabolism of the compatible solute is utilized, secretion of extracellular polymeric substances of the microorganisms is promoted, the activity of the microorganisms is improved, cells are protected from being damaged by acid stress, and the acid resistance of sludge is enhanced; finally, the biological treatment of acidic organic wastewater is enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of industrial wastewater treatment, and relates to a method for enhancing the biological treatment of acidic organic wastewater by using compatible solutes. Background Art

[0002] In recent years, acidic organic wastewater has attracted increasing attention due to its serious threats to the environment, such as corroding buildings, hindering the growth and production of animals and plants, and endangering human health. A large amount of acidic organic wastewater is generated in industrial processes, which mainly comes from the wastewater discharged by enterprises such as metallurgy, metal processing, petrochemical, chemical fiber, and electroplating, such as the waste liquid flow in the metal industry, the drainage in the mining industry, the wastewater in the pulp and paper industry, and the acidic pickling wastewater in the steel industry. When acidic organic wastewater enters the water body, it will destroy the natural neutralization effect, change the pH value of the water body, affect the normal growth of aquatic organisms, and reduce the self-purification function of the water body. When acidic organic wastewater seeps into the soil, it will destroy the physical and chemical properties of the soil, cause soil acidification, and affect the normal growth of crops. The acidification of the water body will also damage ships, bridges and other water-based buildings. Therefore, acidic organic wastewater must meet the standards of discharge regulations under controlled conditions before it can be discharged into the environment. And this kind of acidic organic wastewater has the characteristics of low pH value, complex composition, high organic matter concentration, and poor biodegradability, which brings difficulties to the treatment of wastewater.

[0003] Currently, the commonly used methods for treating acidic organic wastewater mainly include physical methods, chemical methods, and biological methods. Physical methods usually use extraction, adsorption and other methods to remove the refractory organic matter in acidic wastewater. However, the low pH value of acidic wastewater will affect the extraction effect, cause corrosion to adsorbents and shorten the service life of adsorbents, and may cause secondary pollution. Chemical methods usually use neutralization and precipitation methods to pre-treat wastewater. After adding alkaline substances to neutralize the pH value of the wastewater, subsequent treatment is carried out. However, the quality of industrial wastewater fluctuates greatly, and in actual applications, it is necessary to frequently monitor and adjust the pH value, which increases the complexity and difficulty of operation. The biological method is a method that can replace the physical and chemical methods to treat the organic matter in acidic wastewater to a certain extent. It uses the adsorption and metabolism functions of microorganisms or plants themselves to convert pollutants into harmless substances, so as to achieve the degradation effect. Compared with the physical and chemical methods, the biological method has the advantages of high shock load resistance, low energy consumption, low cost, and environmental friendliness. Exploring the biological treatment of acidic organic wastewater is of great significance for the construction of a resource-saving and environment-friendly society.

[0004] However, the low pH value characteristic of acidic organic wastewater will severely inhibit the microbial activity and even lead to cell decomposition and death. Therefore, for the biological treatment of acidic organic wastewater, how to enable microorganisms to survive and play their effectiveness in an acidic environment is the key. In view of the current situation of microbial acid stress, industrial practices often adopt some bioaugmentation measures to treat acidic wastewater, such as using limited acidophilic microorganisms and domesticating non-acidophilic acid-tolerant microorganisms. Although acid-tolerant bacteria can maintain good physiological morphology and cell activity under acidic conditions, most acid-tolerant bacteria do not have the ability to degrade organic matter, and screening a strain of obligate degrading acid-tolerant bacteria requires a huge time cost and economic cost. In addition, gradually domesticating microorganisms not only requires a huge time cost and economic cost, but also the quality of industrial wastewater fluctuates greatly, which may lead to unstable treatment efficiency and unqualified wastewater discharge.

[0005] Compared with domesticating non-acidophilic acid-tolerant microorganisms and using limited acidophilic organisms, enhancing the pH tolerance of microorganisms by adding exogenous additives is a faster and more economical method. Compatible solutes refer to a class of polar, highly soluble and uncharged (or widely manifested as zwitterions at physiological pH values) within the physiological pH range, and can accumulate at high concentrations (>1 mol kg -1) small molecule organic compounds. In many extremophiles, the accumulation of this low molecular weight compound can not only cope with high salt environments, but also has a positive effect on other environmental changes such as temperature stress. Studies have shown that trehalose (Trehalose, a-D-glucopyranosyl-Q-D-glucopyranoside) is a sugar substance with the unique ability to protect biomolecules from environmental stress and is present in many bacteria, fungi, and some desiccation-tolerant higher plants. Wang et al. found that adding an appropriate amount of trehalose can enhance the resistance of L. plantarum LIP-1 to spray drying and freeze-drying treatments by improving the integrity of cell membranes and DNA. (Ruixue Wang, Jingjing E, Ying Yang, et al. Trehalose enhances the resistance of Lactiplantibacillus plantarum LIP-1 to spray-and freeze-drying treatments by regulating amino acid metabolism[J]. Food Bioscience, 2024, 104256(60): 2212-4292.). Zeidler et al. found that the concentration of trehalose in Acinetobacter baumannii accumulates with an increase in NaCl concentration to rapidly adapt to changes in osmotic pressure. (Zeidler S, Hubloher J, Schabacker K, et al., a temperature-and salt-induced solute with implications in pathobiology of Acinetobacter baumannii[J]. Environmental Microbiology, 2017, 19(12): 5088-5099.) A composite protective agent composed of trehalose and mannitol protects the structural integrity of IgY (immunoglobulin Y), thereby reducing the aggregation between IgYs during freeze-drying.(Zhe Wang, Wenchao Liu, Xu Duan, et al. Effects of freezing and drying programs on IgY aggregation and activity during microwave freeze-drying: Protective effects and interactions of trehalose and mannitol[J]. International Journal of Biological Macromolecules, 2024, 129448(160): 0141-8130.)。At present, there is no literature report on the application of compatible solutes in the biological treatment of acidic organic wastewater. Summary of the Invention

[0006] The object of the present invention is to provide a method for strengthening the biological treatment of acidic organic wastewater by using compatible solutes. This method adds compatible solutes to the biological treatment system under acidic conditions. Microorganisms take up the compatible solutes, utilize the compatible solutes for metabolism, promote the secretion of microbial extracellular polymers, improve the activity of microorganisms, protect cells from acid stress, enhance the acid tolerance of sludge, and ultimately strengthen the biological treatment of acidic organic wastewater.

[0007] The technical solution for achieving the object of the present invention is as follows:

[0008] A method for strengthening the biological treatment of acidic organic wastewater by using compatible solutes, comprising the following steps:

[0009] Step 1: Add biological sludge to acidic wastewater containing organic pollutants, and the pH value of the acidic wastewater ≤ 7;

[0010] Step 2: Add compatible solutes to the mud-water mixture formed in Step 1. After uniform mixing, biologically degrade the organic matter in the wastewater. The compatible solutes are one or more of trehalose and mannitol.

[0011] Further, in Step 1, the biological sludge is the sludge commonly used in the biological treatment of organic wastewater, such as anaerobic sludge, aerobic sludge, anaerobic ammonium oxidation sludge, etc. In the specific embodiment of the present invention, anaerobic sludge is taken as an example.

[0012] Further, in Step 1, the organic pollutants are the common organic pollutants in the biological treatment of organic wastewater, such as glucose, nitrobenzene, pyridine, N-methylpyrrolidone, etc. In the specific embodiment of the present invention, nitrobenzene is taken as an example.

[0013] Further, in Step 1, the pH value of the acidic wastewater is 4 - 6.

[0014] Further, in Step 1, the sludge concentration is 3 g VSS / L -1 (VSS: Volatile Suspended Solids).

[0015] Further, in Step 2, the dosing concentration of the compatible solute is 0 - 400 mg / L -1 but not 0, and more preferably 100 - 400 mg / L -1 .

[0016] Further, in Step 2, the operating temperature of the biodegradation system is 25°C - 35°C.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] The present invention alleviates the impact of the acidic environment on microorganisms by adding a compatible solute, efficiently treats acidic organic wastewater, and can effectively reduce the process investment cost and operating cost. Taking trehalose, which is cheap, easily available, and has a low cost, as an additive, microorganisms take in trehalose, utilize trehalose metabolism, promote the secretion of bacterial extracellular polymers, improve the acid tolerance of sludge, and are used for the degradation of toxic pollutants nitrobenzene in acidic wastewater. For example, when the pH = 4 and the nitrobenzene content is 100 mg / L, in the experimental group with a trehalose addition amount of 300 mg / L, the nitrobenzene degradation rate is increased from 70.60 ± 0.66% in the group without trehalose addition to 100%, achieving the efficient biological treatment of acidic organic wastewater by microorganisms. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is the nitrobenzene degradation efficiency graph (a) and aniline production efficiency graph (b) in the nitrobenzene degradation system of anaerobic sludge with or without trehalose addition at different pH values.

[0020] Figure 2 It is the nitrobenzene degradation efficiency graph (a) and aniline production efficiency graph (b) in the nitrobenzene degradation system of anaerobic sludge with different concentrations of trehalose added under the condition of pH = 4.

[0021] Figure 3 It is the content change graph of SMPs (a), TB (b), and LB (c) in EPS secreted by anaerobic microorganisms in the nitrobenzene degradation system of anaerobic sludge with or without trehalose addition at different pH values.

[0022] Figure 4 It is the nitrobenzene degradation efficiency graph (a) and aniline production efficiency graph (b) in the nitrobenzene degradation system of anaerobic sludge with 1 mM different compatible solutes added under the condition of pH = 4. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be further described below in conjunction with embodiments and the accompanying drawings.

[0024] The target pollutant in the following embodiments is nitrobenzene. Due to the electron-withdrawing property of -NO2, the electron cloud density on the benzene ring decreases, which hinders the electrophilic attack of oxidase and makes the aerobic degradation of nitrobenzene difficult to proceed. The nucleophilic reaction of -NO2 is easier. Under anaerobic conditions, nitrobenzene can be reduced to aniline through a series of electron gains and losses and protonations. Aniline can be further degraded under aerobic conditions, which can overcome the disadvantages of aerobic degradation of nitrobenzene. Therefore, the biological treatment of nitrobenzene usually uses anaerobic conditions to degrade nitrobenzene.

[0025] Example 1

[0026] (1) The anaerobic sludge used in this batch experiment was taken from a sewage treatment plant of a chemical factory. The taken anaerobic activated sludge had a high concentration and strong activity, and its physical form was black and viscous. The sludge was rinsed three times with a buffer salt solution to remove the excess ash and physical impurities in the sludge. Then it was loaded into an anaerobic bioreactor with a volume of 10 L, and the sludge concentration was controlled at 3 g VSSL -1 . The nitrobenzene simulated wastewater was reconfigured for the reactor every 3 days to cultivate the sludge and maintain the sludge activity. Among them, the composition of the nitrobenzene simulated wastewater was: 100 mg L -1 nitrobenzene, 1.02 g L -1 NH4Cl, 0.252 g L -1 NaH2PO4·2H2O, 1.5 g L -1 NaHCO3, 400 mg L -1 glucose.

[0027] (2) The refractory organic pollutant targeted in this embodiment is nitrobenzene. The batch experiment for nitrobenzene degradation was carried out in 100 mL serum bottles. During the experiment, each serum bottle under each condition contained 80 mL of simulated wastewater. The same volume of anaerobic sludge acclimated with nitrobenzene was added to each serum bottle, and the sludge concentration in the serum bottle was controlled at 3 g VSS L -1 . The serum bottles were placed in a constant-temperature shaking incubator at a constant speed of 180 r min -1 , and the reaction was carried out under the constant temperature condition of 35 °C.

[0028] (3) The anaerobic sludge was respectively introduced into nitrobenzene acidic wastewater with pH = 4, 5, 6, 7, and at the same time, 0, 300 mg L -1 trehalose was respectively added to the system to carry out the biodegradation of nitrobenzene and conduct batch experiments to study the effect of trehalose on alleviating acid stress and strengthening nitrobenzene degradation. The results are as Figure 1 shown, and the specific result analysis is as follows:

[0029] 1) Under the condition of pH = 4, in the experimental group with the addition of trehalose, nitrobenzene was completely degraded at the 48th hour; however, in the component without the addition of trehalose, after 35 hours, the degradation efficiency of nitrobenzene was 70.60 ± 0.66%, and subsequently, nitrobenzene basically stopped degrading, and the production efficiency of aniline was 62.53 ± 2.07%.

[0030] 2) Under the condition of pH = 5, in the experimental group with the addition of trehalose, nitrobenzene was completely degraded at the 45th hour; however, in the component without the addition of trehalose, after 45 hours, the degradation efficiency of nitrobenzene was 86.76 ± 1.72%, and subsequently, nitrobenzene stopped degrading, and the production efficiency of aniline was 79.95 ± 2.84%.

[0031] 3) Under the conditions of pH = 6 and 7, 100 mg / L of nitrobenzene in the experimental group with the addition of trehalose and the control group without the addition of trehalose was completely degraded within 35 hours, and the aniline production rate was 87.00 ± 2.00% in both cases. -1 The above results show that under acid stress, the ability of microorganisms to degrade nitrobenzene is significantly reduced, and after a period of time, the nitrobenzene concentration no longer degrades, which may be due to the decrease in sludge activity under acid stress and the loss of the ability to degrade nitrobenzene in an acidic environment. In the experimental group with the addition of trehalose under acidic conditions, the degradation efficiency of nitrobenzene and the production efficiency of aniline are higher than those without the addition of trehalose. The addition of trehalose can significantly increase the anaerobic biodegradation rate of nitrobenzene in an acidic environment. The difference in the degradation efficiency of nitrobenzene and aniline indicates that under acidic conditions, the addition of trehalose effectively alleviates the impact of acid stress on microorganisms. Under the conditions of pH = 6 and 7, the degradation efficiency of the experimental group with the addition of trehalose is slightly higher than that of the control group with the addition of trehalose, indicating that the addition of trehalose can also improve the efficiency of microorganisms to degrade nitrobenzene under neutral conditions.

[0032] Example 2

[0033] Anaerobic sludge was introduced into the acidic simulated nitrobenzene wastewater with pH = 4, and at the same time, trehalose was added to the system. The dosing concentrations of trehalose were 100, 200, 300, and 400 mg / L respectively, and nitrobenzene was biodegraded. Sequential batch experiments were carried out under the same sequential batch conditions regulated in Example 1, and a control group without the addition of trehalose was set up to study the effect of trehalose concentration on alleviating microbial acid stress and enhancing nitrobenzene degradation under acidic conditions. The results are as

[0034] shown, and the specific result analysis is as follows: -1 It can be seen from Figure (a) in Figure 2 that at pH = 4, under anaerobic conditions, the addition of different concentrations of trehalose can accelerate the reduction of nitrobenzene to varying degrees. Different concentrations of seaweed (100, 200, 300, 400 mg / L) were added to the system Figure 2

[0035] (1) Figure 2 ​-1 ) At the 46th hour, nitrobenzene was completely degraded. The degradation efficiency of nitrobenzene in the control group was 73.78 ± 0.67%.

[0036] (2) As can be seen from Figure (b) in Figure 2 , the formation pattern of aniline is similar to the degradation pattern of nitrobenzene. With the increase in the concentration of trehalose, the formation efficiency of aniline continuously increases.

[0037] The above results indicate that low-concentration trehalose (400 mg / L -1 ) can significantly improve the anaerobic biodegradation rate of nitrobenzene at low pH (pH = 4). The difference in the concentrations of nitrobenzene and aniline shows that under acidic conditions, the addition of trehalose enhances the biodegradation of nitrobenzene by microorganisms and the formation of aniline.

[0038] Example 3

[0039] Extracellular Polymeric Substances (EPS) are secreted by microbial cells and are viscous substances containing different proportions of polysaccharides, proteins, nucleic acids, humic-like substances, etc. They play an important role in enhancing the resistance of microorganisms to toxic substances and maintaining cell viability. EPS is mainly composed of protein (PN) and polysaccharide (PS), and can be further divided into total EPS (T-EPS), soluble microbial products (SMP), loosely bound EPS (LB-EPS), and tightly bound EPS (TB-EPS) according to the structure.

[0040] In this example, the effect of trehalose addition on EPS secretion under acidic conditions was measured, and the results are as Figure 3 shown. The specific result analysis is as follows:

[0041] SMPs are soluble cell components secreted by cells and contain a large number of negatively charged substances. As Figure 3 shown in (a), the content of SMPs in the experimental group with trehalose addition was significantly higher than that in the control group. As the pH decreased from 7 to 4, the contents of SMPs increased by 18.04 ± 6.40 mg / gVSS -1 , 41.02 ± 1.81 mg / gVSS -1 and 22.47 ± 6.30 mg / gVSS -1 , and its main component is PN. Since low pH weakens the adsorption bridging effect between EPS, leading to the decomposition of flocs and causing more EPS to be released from the sludge flocs into the surrounding environment, this result indicates that trehalose promotes the secretion of PN and increases the possibility of binding with positively charged H + to relieve acid stress.

[0042] LB-EPS loosely wraps around microbial cells to resist the influence of adverse external environments. As Figure 3 (b) shows, when pH = 7 - 4, the contents of LB-EPS in the experimental groups with the addition of trehalose increased by 8.48 ± 2.90 mg gVSS -1 , 10.37 ± 2.26 mg gVSS -1 and 5.74 ± 1.50 mg gVSS -1 compared with the control group. Overall, the LB-EPS in the experimental groups showed a downward trend, but the PN / PS values in the experimental groups were always higher than those in the control group. This indicates that the addition of trehalose mainly promotes the secretion of PN in LB-EPS. A lower PN / PS value means a higher hydroxyl concentration, which leads to the destruction of hydrogen bonds in PN, resulting in the formation of a relatively loose PN structure. At the same time, the loose PN structure exposes more hydrophobic groups, which is beneficial to the aggregation of sludge, thereby improving the flocculation and sedimentation properties of sludge.

[0043] Compared with SMPs and LB-EPS, TB-EPS plays a more important role in sludge aggregation. As Figure 3 (c) shows, when pH = 7 - 5, the contents of TB-EPS in the experimental groups with the addition of trehalose increased by 4.32 ± 0.05 mg gVSS -1 , 14.89 ± 1.71 mg gVSS -1 and 2.99 ± 0.58 mg gVSS -1 compared with the control group. Overall, the TB-EPS in the experimental groups showed a sharp upward trend, indicating that low pH has a serious negative impact on sludge aggregation, and trehalose can mitigate the damage to flocs caused by acid stress. When pH = 4, the overall TB-EPS decreased, and the PN / PS values in the experimental groups were lower than those in the control group, which may be related to the fact that the microorganisms were severely inhibited at too low a pH value and could not secrete more TB-EPS. In addition, the decrease in PN in TB-EPS is related to the reduction of microbial metabolic activity, indicating that an acidic environment will inhibit the metabolic activity of microorganisms, and the addition of trehalose can alleviate this inhibitory effect.

[0044] The above results show that low pH can significantly inhibit microbial activity. Under acid stress, the ability of microorganisms to degrade nitrobenzene is significantly reduced, and even after 35 h, nitrobenzene is no longer degraded. However, the added trehalose can significantly resist the stress of low pH on microorganisms, improve the degradation efficiency of microorganisms on nitrobenzene, and nitrobenzene is completely degraded at 47 h. In addition, the addition of trehalose can stimulate microorganisms to secrete EPS, promote the aggregation of sludge cells to form large particles, protect cells from the influence of the external environment, quickly adapt to the acidic environment, improve the acid resistance of sludge, and thus improve the biodegradation efficiency of microorganisms on pollutants.

[0045] Example 4

[0046] Anaerobic sludge was separately introduced into nitrobenzene acidic simulated wastewater with pH = 4. Meanwhile, 1 mM of trehalose and mannitol were respectively added into the system to biodegrade nitrobenzene. Sequential batch experiments were carried out to study the effects of different types of compatible solutes on alleviating acid stress and enhancing nitrobenzene degradation. The results are as Figure 4 shown, and the specific result analysis is as follows:

[0047] 1) Under the condition of pH = 4, in the experimental group with trehalose added, nitrobenzene was completely degraded at the 35th h; in the experimental group with mannitol added, nitrobenzene was completely degraded at the 48th h.

[0048] 2) Under the condition of pH = 4, after 35 h in the component without adding compatible solute, the degradation efficiency of nitrobenzene was 80.62 ± 1.75%, and nitrobenzene hardly degraded subsequently, and the production efficiency of aniline was 69.62 ± 1.55%.

[0049] The above results show that mannitol also has the effect of alleviating the impact of acid stress on microorganisms, and can effectively promote the anaerobic biodegradation rate of nitrobenzene and the production rate of aniline under acidic conditions. However, the promoting effect of trehalose is better than that of mannitol.

[0050] Comparative Example 1

[0051] Anaerobic sludge was separately introduced into nitrobenzene acidic simulated wastewater with pH = 4. Meanwhile, 1 mM of proline, thiopurine, and hydroxytetrahydropyrimidine were respectively added into the system to biodegrade nitrobenzene. Sequential batch experiments were carried out to study the effects of different types of compatible solutes on alleviating acid stress and enhancing nitrobenzene degradation. The results are as Figure 4 shown, and the specific result analysis is as follows:

[0052] Under the condition of pH = 4, for the components with 1 mM of proline, thiopurine, and hydroxytetrahydropyrimidine added, the trends of nitrobenzene degradation and aniline production were similar to those of the component without adding compatible solute, with no obvious difference. After 48 h, their nitrobenzene degradation efficiencies were 90.74 ± 2.36%, 80.94 ± 1.43%, and 80.74 ± 7.06% respectively, and the production efficiencies of aniline were 83.02 ± 1.84%, 69.69 ± 2.97%, and 71.59 ± 5.53% respectively.

[0053] The above results show that these compatible solutes such as proline, thiopurine, and hydroxytetrahydropyrimidine do not have the effect of alleviating the impact of acid stress on microorganisms.

Claims

1. A method for strengthening the biological treatment of acidic organic wastewater by using compatible solutes, characterized in that, It includes the following steps: Step 1: Add biological sludge to the acidic wastewater containing organic pollutants, and the pH value of the acidic wastewater is ≤ 7; Step 2: Add compatible solutes to the mud-water mixture formed in Step 1. After uniform mixing, biologically degrade the organic matter in the wastewater. The compatible solutes are one or more of trehalose and mannitol.

2. The method according to claim 1, wherein In Step 1, the biological sludge is anaerobic sludge, aerobic sludge or anammox sludge.

3. The method according to claim 1, wherein In Step 1, the organic pollutants are glucose, nitrobenzene, pyridine or N-methylpyrrolidone.

4. The method according to claim 1, characterized in that, In Step 1, the pH value of the acidic wastewater is 4 - 6.

5. The method according to claim 1, wherein In Step 1, the sludge concentration is 3 g VSS L -1 .

6. The method according to claim 1, wherein In Step 2, the dosing concentration of the compatible solute is 0 to 400 mg / L -1 but not 0.

7. The method according to claim 1, characterized in that In Step 2, the dosing concentration of the compatible solute is 100~400 mg L -1 .

8. The method according to claim 1, wherein In Step 2, the operating temperature of the biological degradation system is 25°C - 35°C.

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