Method for enhancing biological treatment of acidic organic wastewater using compatible solutes

Abstract

The application discloses a method for strengthening biological treatment of acid organic wastewater by using compatible solutes. The method adds compatible solutes to a biological treatment system under acid conditions, and microorganisms take in the compatible solutes, metabolize the compatible solutes, promote secretion of extracellular polymers of the microorganisms, improve activity of the microorganisms, protect cells from acid stress, enhance acid resistance of sludge, and finally strengthen biological treatment of the acid organic wastewater.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater treatment technology, and relates to a method for enhancing the biological treatment of acidic organic wastewater using compatible solutes. Background Technology

[0002] In recent years, acidic organic wastewater has attracted increasing attention due to its serious environmental threats, such as corroding buildings, hindering plant and animal growth and production, and harming human health. Industrial processes generate large amounts of acidic organic wastewater, primarily originating from wastewater discharged by metallurgical, metal processing, petrochemical, chemical fiber, and electroplating enterprises. Examples include wastewater from the metal industry, drainage from mining, wastewater from the pulp and paper industry, and acidic pickling wastewater from the steel industry. When acidic organic wastewater enters water bodies, it disrupts natural neutralization, altering the pH level, affecting the normal growth of aquatic organisms, and reducing the self-purification function of water bodies. Acidic organic wastewater seeping into the soil damages its physical and chemical properties, causing soil acidification and affecting the normal growth of crops. Water body acidification can also damage ships, bridges, and other water-based structures. Therefore, acidic organic wastewater must be discharged into the environment under controlled conditions and in compliance with emission regulations. This type of acidic organic wastewater is characterized by low pH, complex composition, high organic matter concentration, and poor biodegradability, which makes wastewater treatment difficult.

[0003] Currently, commonly used methods for treating acidic organic wastewater mainly include physical, chemical, and biological methods. Physical methods typically employ extraction and adsorption to remove recalcitrant organic matter from acidic wastewater. However, the low pH of acidic wastewater can affect extraction efficiency, corrode adsorbents, shorten their lifespan, and potentially cause secondary pollution. Chemical methods usually involve pretreatment of the wastewater using neutralization and precipitation, adding alkaline substances to neutralize the pH before further treatment. However, industrial wastewater quality fluctuates significantly, requiring frequent pH monitoring and adjustments in practical applications, increasing operational complexity and difficulty. Biological methods can, to some extent, replace physical and chemical methods for treating organic matter in acidic wastewater. They utilize the adsorption and metabolic functions of microorganisms or plants to convert pollutants into harmless substances, thereby achieving degradation. Compared to physical and chemical methods, biological methods offer advantages such as resistance to shock loads, low energy consumption, low cost, and environmental friendliness. Exploring biological methods for treating acidic organic wastewater is of great significance for building a resource-saving and environmentally friendly society.

[0004] However, the low pH of acidic organic wastewater severely inhibits microbial activity and can even lead to cell decomposition and death. Therefore, for the biological treatment of acidic organic wastewater, the key is to enable microorganisms to survive and exert their effectiveness in an acidic environment. In response to the current situation of microbial acid stress, industries often adopt bioaugmentation measures to treat acidic wastewater, such as utilizing a limited number of 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 lack the ability to degrade organic matter, and screening for a specific acid-tolerant bacterium requires significant time and economic costs. Furthermore, gradually domesticating microorganisms not only requires substantial time and economic investment, but also results in significant fluctuations in industrial wastewater quality, potentially leading to unstable treatment efficiency and failure to meet discharge standards.

[0005] Compared to domesticating non-acidophilic acid-tolerant microorganisms and utilizing limited acidophilic organisms, enhancing microbial pH tolerance through the addition of exogenous additives is a faster and more economical method. Compatible solutes refer to a class of polar, readily soluble, and uncharged (or widely exhibiting amphoteric behavior at physiological pH) solutes that can accumulate at high concentrations (>1 mol kg) within cells under physiological pH conditions. -1Small molecular weight organic compounds. In many extremophiles, the accumulation of these low molecular weight compounds not only helps them cope with high-salt environments, but also has a positive effect on other environmental changes such as temperature stress. Studies have shown that trehalose (aD-glucopyranosyl-QD-glucopyranoside) is a sugar that has the unique ability to protect biomolecules from environmental stress and is found in many bacteria, fungi and some drought-resistant 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-andfreeze-drying treatments by regulating amino acid metabolism[J].FoodBioscience,2024,104256(60):2212-4292.) Zeidler et al. found that the concentration of trehalose in Acinetobacter baumannii increases with the increase of NaCl concentration, thus rapidly adapting 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].EnvironmentalMicrobiology,2017,19(12):5088-5099.) The composite protectant composed of trehalose and mannitol protects the structural integrity of IgY (immunoglobulin Y), thereby reducing the aggregation of IgY 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.). Currently, there are no literature reports on the application of compatible solutes in the biological treatment of acidic organic wastewater. Summary of the Invention

[0006] The purpose of this invention is to provide a method for enhancing the biological treatment of acidic organic wastewater using compatible solutes. This method involves adding compatible solutes to a biological treatment system under acidic conditions. Microorganisms absorb and utilize these compatible solutes for metabolism, promoting the secretion of extracellular polymers, increasing microbial activity, protecting cells from acid stress, and enhancing the acid resistance of the sludge, ultimately thus enhancing the biological treatment of acidic organic wastewater.

[0007] The technical solution for achieving the objective of this invention is as follows:

[0008] A method for enhancing the biological treatment of acidic organic wastewater using compatible solutes includes the following steps:

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

[0010] Step 2: Add a compatible solute to the mud-water mixture formed in Step 1, mix evenly, and then biodegrade the organic matter in the wastewater. The compatible solute is one or more of trehalose and mannitol.

[0011] Furthermore, in step 1, the biological sludge is the sludge conventionally used in the biological treatment of organic wastewater, such as anaerobic sludge, aerobic sludge, anaerobic ammonia oxidation sludge, etc. In a specific embodiment of the present invention, anaerobic sludge is used as an example.

[0012] Furthermore, in step 1, the organic pollutants are common organic pollutants found in biologically treated organic wastewater, such as glucose, nitrobenzene, pyridine, and N-methylpyrrolidone. In a specific embodiment of the present invention, nitrobenzene is used as an example.

[0013] Furthermore, in step 1, the pH value of the acidic wastewater is 4 to 6.

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

[0015] Furthermore, in step 2, the concentration of the compatible solute added is 0–400 mg / L. -1 But not 0, more preferably 100–400 mg / L. -1 .

[0016] Furthermore, in step 2, the operating temperature of the biodegradation system is 25℃~35℃.

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

[0018] This invention mitigates the impact of acidic environments on microorganisms by adding compatible solutes, thus efficiently treating acidic organic wastewater and effectively reducing process investment and operating costs. Taking inexpensive and readily available trehalose as an additive as an example, microorganisms ingest trehalose, utilize its metabolism, and promote the secretion of extracellular polymers, thereby improving the acid resistance of sludge and contributing to the degradation of toxic pollutants like nitrobenzene in acidic wastewater. For instance, in an experimental group with pH=4 and nitrobenzene content of 100 mg / L, the trehalose addition of 300 mg / L increased the nitrobenzene degradation rate from 70.60 ± 0.66% to 100% compared to the group without trehalose, achieving highly efficient biological treatment of acidic organic wastewater. Attached Figure Description

[0019] Figure 1 The degradation efficiency of nitrobenzene and the formation efficiency of aniline are shown in Figure (a) and Figure (b) of nitrobenzene degradation system with or without trehalose at different pH values.

[0020] Figure 2 The graph shows the degradation efficiency of nitrobenzene and the formation efficiency of aniline in an anaerobic sludge system with different concentrations of trehalose added at pH=4.

[0021] Figure 3 The graph shows the changes in the contents of SMPs(a), TB(b), and LB(c) in EPS secreted by anaerobic microorganisms in anaerobic sludge degradation systems of nitrobenzene with or without the addition of trehalose at different pH values.

[0022] Figure 4 The graph shows the degradation efficiency of nitrobenzene and the formation efficiency of aniline in an anaerobic sludge system with 1 mM of different compatible solutes added at pH=4. Detailed Implementation

[0023] The present invention will be further described below with reference to embodiments and accompanying drawings.

[0024] The following examples target nitrobenzene as a pollutant. Due to the electron-withdrawing property of -NO2, the electron cloud density on the benzene ring decreases, thus hindering the electrophilic attack of oxidases and making aerobic degradation of nitrobenzene difficult. The nucleophilic reaction of -NO2 is more readily achieved. Under anaerobic conditions, nitrobenzene can be reduced to aniline through a series of electron gains, losses, and protonation. Aniline can then be further degraded under aerobic conditions, overcoming the drawbacks of aerobic degradation of nitrobenzene. Therefore, the biological treatment of nitrobenzene typically employs anaerobic degradation.

[0025] Example 1

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

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

[0028] (3) Anaerobic sludge was introduced into nitrobenzene acidic wastewater with pH values ​​of 4, 5, 6, and 7, respectively, and 0 and 300 mg L of nitrobenzene were added to the system at the same time. -1 Trehalose was used to biodegrade nitrobenzene. Sequencing batch experiments were conducted to investigate the role of trehalose in alleviating acid stress and enhancing nitrobenzene degradation. Results are as follows: Figure 1 As shown, the specific results are analyzed below:

[0029] 1) Under pH=4 conditions, the nitrobenzene in the experimental group with added trehalose was completely degraded at 48h; however, the nitrobenzene in the component without added trehalose had a degradation efficiency of 70.60±0.66% after 35h, and the nitrobenzene basically did not degrade further, while the aniline formation efficiency was 62.53±2.07%.

[0030] 2) Under pH=5 conditions, the nitrobenzene in the experimental group with added trehalose was completely degraded at 45h, but the nitrobenzene degradation efficiency of the component without added trehalose was 86.76±1.72% after 45h, and the nitrobenzene no longer degraded, and the aniline generation efficiency was 79.95±2.84%.

[0031] 3) Under pH conditions of 6 and 7, the experimental group with added trehalose and the control group without added trehalose were compared at a concentration of 100 mg / L. -1 Nitrobenzene was completely degraded within 35 hours, with aniline formation rates of 87.00 ± 2.00%.

[0032] The above results indicate that the ability of microorganisms to degrade nitrobenzene is significantly reduced under acid stress, and the nitrobenzene concentration stops decreasing after a period of time. This may be due to the reduced sludge activity under acid stress, resulting in the loss of the ability to degrade nitrobenzene in an acidic environment. Under acidic conditions, the experimental group with added trehalose showed higher nitrobenzene degradation efficiency and aniline formation efficiency than the group without added trehalose, indicating that adding trehalose significantly improves the anaerobic biodegradation rate of nitrobenzene under acidic conditions. The difference in degradation efficiency between nitrobenzene and aniline suggests that under acidic conditions, the addition of trehalose effectively alleviates the impact of acid stress on microorganisms. At pH 6 and 7, the degradation efficiency of the experimental group with added trehalose was slightly higher than that of the control group with added trehalose, indicating that the addition of trehalose can also improve the efficiency of microbial degradation of nitrobenzene under neutral conditions.

[0033] Example 2

[0034] Anaerobic sludge was introduced into a simulated nitrobenzene acidic wastewater with a pH of 4, while trehalose was added to the system at concentrations of 100, 200, 300, and 400 mg / L. -1 The biodegradation of nitrobenzene was carried out using the same batch conditions as in Example 1, with a control group without trehalose added. The effect of trehalose concentration under acidic conditions on alleviating microbial acid stress and enhancing nitrobenzene degradation was investigated. Results are as follows: Figure 2 As shown, the specific results are analyzed below:

[0035] (1) Figure 2 Figure (a) shows that at pH=4, under anaerobic conditions, adding different concentrations of trehalose can accelerate the reduction of nitrobenzene to varying degrees. Different concentrations of trehalose (100, 200, 300, 400 mg L / L) were added to the system.-1 By 46 hours, all nitrobenzene had completely degraded. In contrast, the degradation efficiency of nitrobenzene in the control group was 73.78 ± 0.67%.

[0036] (2) By Figure 2 As shown in Figure (b), the formation pattern of aniline is similar to that of nitrobenzene degradation. The formation efficiency of aniline continuously increases with increasing trehalose concentration.

[0037] The above results indicate that low concentrations of trehalose (400 mg / L) are effective. -1 Trehalose significantly increased the anaerobic biodegradation rate of nitrobenzene at low pH (pH=4). The difference in nitrobenzene and aniline concentrations indicated that, under acidic conditions, the addition of trehalose enhanced the biodegradation of nitrobenzene and the formation of aniline by microorganisms.

[0038] Example 3

[0039] Extracellular polymeric substances (EPS) are secreted by microbial cells and are viscous substances containing varying proportions of polysaccharides, proteins, nucleic acids, and humic substances. 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 classified according to structure into total EPS (T-EPS), soluble microbial products (SMP), loosely bound EPS (LB-EPS), and tightly bound EPS (TB-EPS).

[0040] This embodiment determined the effect of trehalose dosage on EPS secretion under acidic conditions, and the results are as follows: Figure 3 As shown, the specific results are analyzed below:

[0041] SMPs are soluble cellular components secreted by cells, containing a large number of negatively charged substances. For example... Figure 3 As shown in (a), the SMP content in the trehalose-added experimental group was significantly increased compared to the control group. As the pH increased from 7 to 4, the SMP content increased by 18.04 ± 6.40 mg gVSS. -1 41.02±1.81mg gVSS -1 and 22.47±6.30mg gVSS -1 Furthermore, its main component is PN. Since low pH weakens the adsorption bridging between EPS, leading to floc decomposition and the release of more EPS from the sludge flocs into the surrounding environment, this result indicates that trehalose promotes PN secretion and increases its interaction with positively charged H+. + The possibility of binding, thereby alleviating acid stress.

[0042] LB-EPS loosely surrounds microbial cells to protect them from adverse external environments. For example... Figure 3 As shown in (b), at pH = 7-4, the LB-EPS content in the trehalose-added experimental group increased by 8.48 ± 2.90 mg / s² compared to the control group. -1 10.37±2.26mg gVSS -1 and 5.74±1.50 mg gVSS -1 The experimental group showed an overall decreasing trend in LB-EPS, but the PN / PS ratio was consistently higher than that of the control group. This indicates that the addition of trehalose primarily promotes the secretion of PN in LB-EPS. The lower PN / PS ratio signifies a higher hydroxyl concentration, leading to the disruption of hydrogen bonds in the PN and resulting in the formation of a relatively loose PN structure. Simultaneously, the loose PN structure exposes more hydrophobic groups, which is beneficial for sludge aggregation, thereby improving the flocculation and settling properties of the sludge.

[0043] Compared to SMPs and LB-EPS, TB-EPS plays a more important role in sludge aggregation and floc formation. For example... Figure 3 As shown in (c), at pH = 7-5, the TB-EPS content in the trehalose-added experimental group increased by 4.32 ± 0.05 mggVSS compared to the control group. -1 14.89±1.71mg gVSS -1 and 2.99±0.58mg gVSS -1 The experimental group showed a sharp increase in TB-EPS, indicating that low pH has a severe negative impact on sludge aggregation, and trehalose can alleviate the damage of acid stress to flocs. At pH 4, TB-EPS decreased overall, and the PN / PS ratio in the experimental group was lower than that in the control group, which may be related to the severe inhibition of microorganisms due to the low pH, preventing them from secreting more TB-EPS. In addition, the reduction in PN in TB-EPS is related to the decrease in microbial metabolic activity, indicating that an acidic environment inhibits the metabolic activity of microorganisms, and the addition of trehalose can alleviate this inhibitory effect.

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

[0045] Example 4

[0046] Anaerobic sludge was introduced into a simulated acidic wastewater containing nitrobenzene at pH 4. Simultaneously, 1 mM trehalose and mannitol were added to the system to biodegrade nitrobenzene. Sequencing batch experiments were conducted to investigate the effects of different types of compatible solutes on alleviating acid stress and enhancing nitrobenzene degradation. Results are as follows: Figure 4 As shown, the specific results are analyzed below:

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

[0048] 2) Under pH=4 conditions, the nitrobenzene degradation efficiency of the component without added compatible solute was 80.62±1.75% after 35h, and the nitrobenzene basically did not degrade further. The aniline formation efficiency was 69.62±1.55%.

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

[0050] Comparative Example 1

[0051] Anaerobic sludge was passed into simulated nitrobenzene acidic wastewater at pH 4. Simultaneously, 1 mM of proline, thiopurine, and hydroxytetrahydropyrimidine were added to the system to biodegrade nitrobenzene. Sequencing batch experiments were conducted to investigate the effects of different types of compatible solutes on alleviating acid stress and enhancing nitrobenzene degradation. Results are as follows: Figure 4 As shown, the specific results are analyzed below:

[0052] Under pH=4 conditions, the degradation trends of nitrobenzene and the formation of aniline in the components with added 1mM proline, tetrahydropyrimidine, and hydroxytetrahydropyrimidine were similar to those in the components without added compatible solutes, with no significant difference. After 48 h, the degradation efficiencies of nitrobenzene were 90.74±2.36%, 80.94±1.43%, and 80.74±7.06%, respectively, and the formation efficiencies of aniline were 83.02±1.84%, 69.69±2.97%, and 71.59±5.53%, respectively.

[0053] The above results indicate that compatible solutes such as proline, tetrahydropyrimidine, and hydroxytetrahydropyrimidine do not have the effect of alleviating the effects of acid stress on microorganisms.

Claims

1. A method for enhancing the biological treatment of acidic organic wastewater using compatible solutes, characterized in that, Includes the following steps: Step 1: Add biological sludge to acidic wastewater containing organic pollutants, wherein the pH value of the acidic wastewater is 4-5 and the organic pollutant is nitrobenzene; Step 2: Add a compatible solute to the mud-water mixture formed in Step 1, mix evenly, and then anaerobically biodegrade the organic matter in the wastewater. The compatible solute is one or more of trehalose and mannitol.

2. The method according to claim 1, characterized in that, In step 1, the biological sludge is anaerobic sludge or anaerobic ammonia oxidation sludge.

3. The method according to claim 1, characterized in that, In step 1, the sludge concentration is 3 g VSS L. -1 .

4. The method according to claim 1, characterized in that, In step 2, the concentration of the compatible solute added is 0~400 mg / L. -1 But it is not 0.

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

6. The method according to claim 1, characterized in that, In step 2, the operating temperature of the biodegradation system is 25℃~35℃.

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