A strain-piezoelectric material synergistic denitrification system and its application

Abstract

This invention belongs to the field of water treatment denitrification technology, specifically relating to a strain-piezoelectric material synergistic denitrification system and its application. This strain-piezoelectric material synergistic denitrification system includes *Streptomyces* denitrifying bacteria and barium strontium titanate, with the barium strontium titanate loaded on the surface of the *Streptomyces* denitrifying bacteria. This invention induces a piezoelectric effect in the barium strontium titanate through mechanical feeding, providing an electron donor for the *Streptomyces* denitrifying bacteria, thus improving electron transfer efficiency and consequently increasing denitrification efficiency. Experiments show that under optimal conditions of 0.5 g / L barium strontium titanate concentration and 400 r / min stirring speed, the total nitrogen and nitrate nitrogen removal rates of this system are higher than those of strain DD alone, while the total organic carbon removal rate is also significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of water treatment denitrification technology, specifically relating to a denitrification system with synergistic effects of bacterial strain and piezoelectric material and its application. Background Technology

[0002] With the development of industry and agriculture, large amounts of nitrogen-containing wastewater are discharged into water bodies, leading to excessive nitrogen accumulation and severe eutrophication. Biological denitrification is the core method for removing total nitrogen and nitrate nitrogen from wastewater, but its efficiency is often limited by insufficient electron donors, slow transfer rates, and the metabolic activity of microorganisms. Traditional biological denitrification requires the addition of organic carbon sources, which not only increases treatment costs but may also lead to secondary pollution; while autotrophic denitrification suffers from a slow rate bottleneck, making it difficult to meet the nitrogen removal needs of water bodies.

[0003] Piezoelectric catalysis is an emerging technology that converts mechanical energy into electrical energy. Piezoelectric materials use the electronic energy generated from mechanical energy to support the metabolism of denitrifying microorganisms. Strontium barium titanate, as a typical perovskite-type piezoelectric material, possesses excellent piezoelectric properties and strong chemical stability, making it potentially valuable in water treatment applications. Streptomyces are a type of actinomycetes with strong denitrification capabilities and high environmental adaptability; however, when used alone, they still suffer from slow nitrate removal rates and long reaction cycles, making it difficult to meet practical treatment needs. Summary of the Invention

[0004] To address the problems of slow nitrate removal rates and long reaction cycles in existing technologies that rely solely on Streptomyces microorganisms, making it difficult to meet practical treatment needs, this invention aims to develop a novel strategy that utilizes environmental mechanical energy to directly enhance the metabolic functions of microorganisms. It provides a strain-piezoelectric material synergistic denitrification system and its application. To achieve the above objectives, this invention adopts the following technical solution.

[0005] This invention provides a strain-piezoelectric material synergistic denitrification system, the denitrification system comprising Streptomyces denitrifying bacteria and barium strontium titanate.

[0006] The barium strontium titanate is loaded onto the surface of the Streptomyces denitrifying bacteria to form a composite system. The composite system uses mechanical energy to induce a piezoelectric effect in the barium strontium titanate, thereby providing an electron donor for the denitrification process of the Streptomyces denitrifying bacteria.

[0007] Among them, barium strontium titanate can be prepared by hydrothermal synthesis or sol-gel method to ensure good piezoelectric properties.

[0008] The denitrification system provided by this invention effectively reduces the concentration of total nitrogen and nitrate nitrogen in nitrogen-containing wastewater, breaks through the bottleneck of traditional denitrification technology, meets the needs of deep treatment of slightly polluted water bodies, and avoids the risk of secondary pollution and increased costs caused by the addition of additional organic carbon sources, thus achieving a highly efficient and stable denitrification process.

[0009] Preferably, the piezoelectric coefficient, dielectric constant, and other parameters of barium strontium titanate can be controlled by adjusting the barium / strontium doping ratio. When the strontium doping content reaches 6%, the piezoelectric coefficient of barium strontium titanate will increase, providing an important way to optimize denitrification performance. However, excessive doping will lead to performance degradation, and the doping ratio needs to be controlled within the optimal range.

[0010] Preferably, the *Streptomyces* denitrifying bacteria include *Streptomyces DD*, a Gram-positive bacterium currently deposited at the China Center for Type Culture Collection (CCTCC), located at Wuhan University, No. 299 Bayi Road, Wuchang District, Wuhan, with accession number CCTCC NO: M 20251374 and deposit date of June 12, 2025. *Streptomyces* denitrifying bacteria possess unique aerobic denitrification capabilities, metabolic diversity, and environmental adaptability, exhibiting significant advantages in scenarios such as low C / N ratio wastewater and slightly polluted water bodies. However, when used alone, they still suffer from relatively low nitrogen removal rates.

[0011] The present invention also provides the application of the strain-piezoelectric material synergistic denitrification system in water treatment.

[0012] Preferably, the denitrification system is used for denitrification treatment of nitrogen-containing wastewater; wherein the nitrogen-containing wastewater is wastewater with a low carbon-to-nitrogen ratio, polluted water body, and / or industrial nitrate wastewater.

[0013] Preferably, the denitrification treatment refers to reducing the content of total nitrogen, nitrate nitrogen and total organic carbon in the nitrogen-containing wastewater.

[0014] Preferably, the method for denitrifying nitrogen-containing wastewater using the denitrification system includes the following steps:

[0015] The activated Streptomyces denitrifying bacteria were inoculated and cultured. After culture, the bacteria were centrifuged, the supernatant was discarded, the bacterial precipitate was collected, and the precipitate was prepared into a microbial suspension.

[0016] The microbial suspension and the barium strontium titanate are added to the nitrogen-containing wastewater to form a mixed reaction system, and the concentration of the barium strontium titanate in the nitrogen-containing wastewater is controlled to be 0.25 g / L to 2.5 g / L.

[0017] The mixed reaction system is stirred to stimulate the piezoelectric effect of barium strontium titanate, providing an electron donor for the denitrifying bacteria of the genus Streptomyces, thereby improving the electron transfer efficiency and enhancing the denitrification process, thus achieving the removal of total nitrogen and nitrate nitrogen from the nitrogen-containing wastewater.

[0018] In the mixed reaction system, barium strontium titanate and Streptomyces denitrifying bacteria combine through interfacial interactions. The Streptomyces denitrifying bacteria form a biofilm on the surface of barium strontium titanate. Scanning electron microscopy shows that the barium strontium titanate particles are tightly attached to the Streptomyces denitrifying bacteria. EDS detection shows that titanium, strontium, and bismuth elements are present on the surface of barium strontium titanate and are uniformly dispersed within the field of view.

[0019] Preferably, the initial total nitrogen concentration of the nitrogen-containing wastewater is 0~10 mg / L, the initial nitrate nitrogen concentration is 0~10 mg / L, and the initial total organic carbon concentration is ≤15 mg / L.

[0020] Preferably, the barium strontium titanate is in powder form with a particle size of 50 nm to 100 nm and a purity of 99.5%. The barium strontium titanate is placed in anhydrous ethanol and ultrasonically cleaned three times at 300 W for 15 minutes each time to remove residual impurities from the surface. The cleaned barium strontium titanate is then vacuum-dried for later use. The powdered barium strontium titanate is referred to as barium strontium titanate powder.

[0021] Preferably, the stirring speed is 200 r / min to 500 r / min. More preferably, the stirring speed is 400 r / min. During the stirring process, mechanical vibration acts on the barium strontium titanate, stimulating its piezoelectric effect to generate a potential difference, promoting electron transfer on the surface of Streptomyces cells, enhancing nitrate reductase activity, and simultaneously increasing dissolved oxygen in the water to meet the metabolic needs of Streptomyces.

[0022] Preferably, the bacterial cell concentration of the microbial suspension is 10. 7 CFU / mL.

[0023] Preferably, the Streptomyces denitrifying bacteria form a biofilm on the surface of barium strontium titanate.

[0024] Preferably, the method for activating Streptomyces denitrifying bacteria is as follows:

[0025] The Streptomyces denitrifying bacteria were inoculated onto LB solid medium and cultured at 30°C and 180–200 rpm for 48–72 h. The LB solid medium contained 10 g / L tryptone, 5 g / L yeast extract, 10 g / L sodium chloride, 10 g / L agar, and had a pH of 7.0.

[0026] Preferably, the activated Streptomyces denitrifying bacteria are inoculated into LB liquid medium for culture.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. This invention provides a strain-piezoelectric material synergistic denitrification system. The strain-piezoelectric material synergistic denitrification system provided by this invention includes *Streptomyces* denitrifying bacteria and barium strontium titanate; barium strontium titanate is loaded on the surface of the *Streptomyces* denitrifying bacteria. The *Streptomyces* denitrifying bacteria are Gram-positive bacteria and possess aerobic denitrification capabilities.

[0029] In existing technologies, while Streptomyces denitrifying bacteria possess the ability to remove nitrates and nitrogen, their single-system approach relies on the oxidation of organic substrates for energy, resulting in low electron transfer efficiency. This leads to slow processing rates and long reaction cycles, typically requiring 48 hours to achieve near-complete removal. This invention constructs a mechanically driven synergistic denitrification system by loading barium strontium titanate piezoelectric material onto the surface of Streptomyces denitrifying bacteria. Under mechanical stirring, barium strontium titanate continuously generates piezoelectric electrons, which are directly transferred to the Streptomyces electron transport chain. This overcomes the energy supply bottleneck of traditional systems, achieving continuous and efficient electron supply, significantly improving the nitrate and nitrogen removal rate, and shortening the reaction cycle. This effectively addresses the shortcomings of existing technologies in meeting practical treatment needs.

[0030] 2. The denitrification system with strain-piezoelectric material synergy provided by this invention also includes a mechanical stirring device and a biofilm structure. The mechanical stirring device provides mechanical stimulation to activate the piezoelectric effect of barium strontium titanate. The stirring speed needs to be controlled between 200 r / min and 500 r / min, with the optimal speed being 400 r / min. Simultaneously, it increases dissolved oxygen in the water to meet the metabolic needs of Streptomyces. The biofilm structure is due to the formation of a biofilm on the surface of barium strontium titanate by Streptomyces, achieving close adhesion between the strain and the piezoelectric material through interfacial interactions, thus enhancing electron transfer efficiency. Therefore, the denitrification system has the advantages of high efficiency, low cost, no secondary pollution, and wide applicability, solving the problems of insufficient electron donors in biological denitrification and incomplete single piezoelectric denitrification reactions in existing technologies.

[0031] 3. The synergistic piezoelectric denitrification system of barium strontium titanate and Streptomyces DD provided by this invention achieves a total nitrogen removal rate of ≥80% and a nitrate nitrogen removal rate of ≥85% under optimal conditions of 400 r / min and 0.5 g / L barium strontium titanate, which is about 40% higher than that of a single strain group. Moreover, there is no accumulation of nitrous oxide, which solves the problem of secondary pollution in traditional biological denitrification and greatly improves the denitrification efficiency.

[0032] The synergistic piezoelectric denitrification system of barium strontium titanate and Streptomyces DD provided by this invention is simple to construct. It only requires placing the piezoelectric material barium strontium titanate and Streptomyces DD together in a reactor and stirring, making it easy to implement. Furthermore, the deep coupling between the two achieves a synergistic enhancement effect greater than the sum of its parts (1+1>2), and electron transfer within the system is also relatively active. In addition, the piezoelectric effect is activated solely through mechanical stirring, requiring no external power supply, aeration, or other additional energy consumption, making it energy-saving, environmentally friendly, and easy to operate. Attached Figure Description

[0033] Figure 1 The graph shows the effects of barium strontium titanate at different concentrations and 400 r / min on enhancing total nitrogen and nitrate nitrogen levels in Streptomyces DD, as described in this invention.

[0034] (a) shows the changes in total nitrogen and nitrate nitrogen under the condition of 0.25 g / L barium strontium titanate + DD;

[0035] (b) shows the changes in total nitrogen and nitrate nitrogen under the condition of 0.5 g / L barium strontium titanate + DD;

[0036] (c) shows the changes in total nitrogen and nitrate nitrogen under the condition of 1.5 g / L barium strontium titanate + DD;

[0037] (d) shows the changes in total nitrogen and nitrate nitrogen under the condition of 2.5 g / L barium strontium titanate + DD;

[0038] The horizontal axis represents the reaction time, ranging from 0 to 72 hours; the vertical axis represents nitrogen concentration on the left and nitrogen removal rate on the right; DD stands for Streptomyces DD.

[0039] Figure 2 The graph shows the enhanced total nitrogen and nitrate nitrogen effects of 0.5 g / L barium strontium titanate on Streptomyces DD at different rotation speeds in this invention.

[0040] (a) shows the variation curves of total nitrogen and nitrate nitrogen under the condition of 200 r / min;

[0041] (b) shows the variation curves of total nitrogen and nitrate nitrogen under the condition of 300 r / min;

[0042] (c) shows the variation curves of total nitrogen and nitrate nitrogen under the condition of 400 r / min;

[0043] (d) shows the variation curves of total nitrogen and nitrate nitrogen under the condition of 500 r / min;

[0044] The horizontal axis represents the reaction time, ranging from 0 to 72 hours; the vertical axis represents nitrogen concentration on the left and nitrogen removal rate on the right.

[0045] Figure 3 The graph shows the nitrogen removal efficiency of single Streptomyces DD and Streptomyces DD + barium strontium titanate under the optimal conditions of 400 r / min and 0.5 g / L barium strontium titanate in this invention.

[0046] (a) shows the variation curves of total nitrogen and nitrate nitrogen under single Streptomyces DD conditions;

[0047] (b) shows the changes in total nitrogen and nitrate nitrogen under the conditions of Streptomyces DD + barium strontium titanate;

[0048] The horizontal axis represents the reaction time, ranging from 0 to 72 hours; the vertical axis represents nitrogen concentration on the left and nitrogen removal rate on the right; BST stands for barium strontium titanate, and DD stands for Streptomyces DD.

[0049] Figure 4 The graph shows the total organic carbon removal efficiency of Streptomyces DD alone and Streptomyces DD + barium strontium titanate under the optimal conditions of 400 r / min and 0.5 g / L barium strontium titanate in this invention. The horizontal axis represents the reaction time, ranging from 0 to 72 h; the left axis of the vertical axis represents the dissolved organic carbon concentration, and the right axis represents the dissolved organic carbon removal rate.

[0050] Streptomyces sp.DD refers to Streptomyces DD.

[0051] Figure 5 This is a microscopic characterization diagram of Streptomyces DD+ barium strontium titanate in this invention; wherein:

[0052] (a) is a scanning electron microscope image of Streptomyces DD+ barium strontium titanate, wherein the scanning electron microscope image within the box is Streptomyces DD and barium strontium titanate;

[0053] (b) shows scanning electron microscope images and corresponding energy dispersive spectra of titanium, strontium and bismuth, where (b1) is a scanning electron microscope image of strontium, bismuth and titanium, (b2) is an energy dispersive spectrum of strontium, (b3) is an energy dispersive spectrum of bismuth and (b4) is an energy dispersive spectrum of titanium.

[0054] Figure 6 This is a diagram showing the impedance changes during the reaction process in this invention; wherein:

[0055] (a) shows the impedance changes at 1d, 2d and 3d under the Streptomyces DD condition;

[0056] (b) shows the impedance changes of Streptomyces DD + barium strontium titanate reaction at 1d, 2d and 3d;

[0057] The horizontal axis Z' represents the real part of the impedance, ranging from 0 to 2800 ohms; the vertical axis Z'' represents the imaginary part of the impedance.

[0058] Figure 7 This is the differential pulse voltammetry curve of the reaction on the 3rd day in this invention; where the horizontal axis is the potential, ranging from -1.0 to -0.8V; and the vertical axis is the current. Detailed Implementation

[0059] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments, but this should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art, and the materials, reagents, etc. used in the following embodiments are commercially available unless otherwise specified.

[0060] In the following embodiments, the piezoelectric material, barium strontium titanate, was purchased from Aladdin Reagent (Shanghai) Co., Ltd., using a powder with a particle size of 50 nm and a purity of 99.5%. Before use, it was washed three times with deionized water to remove surface impurities. The washed barium strontium titanate powder was then vacuum-dried for later use. Hereinafter, barium strontium titanate is referred to as barium strontium titanate powder, abbreviated as BST.

[0061] Streptomyces ( Streptomyces sp.)DD is deposited at the China Center for Type Culture Collection, located at Wuhan University, No. 299 Bayi Road, Wuchang District, Wuhan, with accession number CCTCC NO: M 20251374 and deposit date of June 12, 2025.

[0062] Streptomyces DD was cultured using LB solid medium, which is based on the following formula: 10.0 g / L peptone, 5.0 g / L yeast extract, 10 g / L sodium chloride, and 10.0 g / L agar; the initial pH was 7.0.

[0063] Preparation of Streptomyces DD bacterial suspension: Streptomyces DD was activated by culturing at 30℃ for 48 h. The activated colonies were inoculated into LB liquid medium and cultured at 30℃ with shaking at 180 rpm for 48 h until the strain entered the logarithmic growth phase. The bacterial suspension in the logarithmic growth phase was centrifuged at 5000 rpm for 10 min, the bacterial cells were collected, resuspended in sterile physiological saline, and the bacterial concentration was adjusted to 10. 7 The concentration of CFU / mL was used to obtain Streptomyces DD bacterial solution, which was then set aside for later use. This Streptomyces DD bacterial solution is also known as Streptomyces DD bacterial solution.

[0064] The formula for the simulated nitrogen-containing wastewater was: 10 mg / L potassium nitrate, 0.5 g / L potassium dihydrogen phosphate, 0.2 g / L magnesium sulfate heptahydrate, and 0.1 g / L calcium chloride. The solution was diluted with deionized water, and the pH was adjusted to 7.0 using 0.1 mol / L hydrochloric acid or sodium hydroxide. The initial total nitrogen concentration of the simulated water was measured to be approximately 7.5 mg / L.

[0065] Example 1: Experiment on the effect of different barium strontium titanate concentrations on synergistic piezoelectric denitrification effect at a constant stirring speed.

[0066] Four parallel experiments were set up. In each group, 500 mL of simulated nitrogen-containing wastewater was placed in a 1000 mL Erlenmeyer flask, and barium strontium titanate powder was added to achieve concentrations of 0.25 g / L, 0.5 g / L, 1.5 g / L, and 2.5 g / L, respectively. 10 mL of a 10% concentration of barium strontium titanate was added to each group. 7Streptomyces DD bacterial culture (CFU / mL) was prepared by placing conical flasks in a constant-temperature shaker at 30℃ and 400 rpm for 72 h. Samples (10 mL each time) were taken at 0 h, 12 h, 24 h, 36 h, 48 h, 60 h, and 72 h after reaction. The samples were filtered through a 0.45 μm filter, and the total nitrogen concentration was determined by UV spectrophotometry, while the nitrate concentration was determined by ion chromatography.

[0067] The specific method for determining total nitrogen concentration using ultraviolet spectrophotometry is as follows:

[0068] 1) Sample preparation:

[0069] Samples were taken at 0h, 12h, 24h, 36h, 48h, 60h, and 72h of the reaction, with 10mL taken each time. The obtained samples were filtered through a 0.45μm filter membrane to remove suspended barium strontium titanate powder and Streptomyces DD bacterial precipitate from the system, yielding the filtered samples.

[0070] 2) Dissolution and transformation:

[0071] Take 5 mL of the filtered sample and place it into a 10 mL colorimetric tube. Add 5 mL of 40 g / L alkaline potassium persulfate solution, seal the tube stopper, tighten it, and place it in an autoclave. Digest at 120 °C and 0.1 MPa for 30 minutes. After digestion, allow it to cool naturally to room temperature, add 1 mL of hydrochloric acid solution to neutralize the alkalinity, and dilute to the 10 mL mark with deionized water. Shake well and set aside to obtain the sample solution.

[0072] 3) Plot the standard curve:

[0073] Take six 10mL colorimetric tubes and add 0.00, 0.10mL, 0.20mL, 0.50mL, 1.00mL, and 2.00mL of nitrate nitrogen standard stock solution, respectively. Make up to 5mL with deionized water, and then proceed with the sample processing, digestion, and conversion steps described above for digestion, neutralization, and volume adjustment to obtain a series of nitrate nitrogen standard solutions. The final concentrations of nitrate nitrogen in the series of nitrate nitrogen standard solutions are 0.00, 1.00mg / L, 2.00mg / L, 5.00mg / L, 10.00mg / L, and 20.00mg / L, respectively. Using deionized water as a blank control group, measure the absorbance of each standard solution at 220nm and 275nm using a UV spectrophotometer, and record them as A. 220 and A 275 .

[0074] Calculate the corrected absorbance using the following formula:

[0075] A （校） =A 220 - 2×A 275 ;

[0076] In the above formula, A （校） 2 is an empirical correction value for absorbance correction.

[0077] With the corrected absorbance as the ordinate (y) and the nitrate nitrogen concentration as the abscissa (x), and k as the ratio of the change in corrected absorbance to the change in nitrate nitrogen concentration, a linear regression method was used to fit the standard curve, resulting in the standard curve regression equation: y = kx + b.

[0078] 4) Determine the total nitrogen concentration of the sample.

[0079] Absorbance Measurement: Take the sample solutions obtained after sample processing in step 1) and digestion and conversion in step 2), respectively, and pour them into 1cm quartz cuvettes. Measure the absorbance at wavelengths of 220nm and 275nm, and record them as A. 200（样） and A 275（样） Simultaneously, the absorbance of the blank control group was remeasured to ensure instrument stability.

[0080] Calculate the concentration:

[0081] Calculate the corrected absorbance of the sample using the following formula:

[0082] A （样校） =A 200（样） -2×A 275（样） ;

[0083] In the above formula, A （样校） 2 is the absorbance for sample correction, and 2 is the empirical correction value.

[0084] A （样校） Substituting into the regression equation of the standard curve above, the nitrate nitrogen concentration in the sample solution is obtained, which is the total nitrogen concentration in the original reaction solution.

[0085] The specific method for determining nitrate concentration using ion chromatography is as follows:

[0086] 1) Sample preparation:

[0087] Samples were taken at 0h, 12h, 24h, 36h, 48h, 60h, and 72h of the reaction, with 10mL sample taken each time. The obtained samples were filtered through a 0.45μm filter membrane to remove suspended barium strontium titanate powder and Streptomyces DD bacterial precipitate from the system, yielding the sample to be tested.

[0088] 2) Sample preservation

[0089] The sample to be tested must be injected immediately. If it cannot be tested immediately, the sample must be stored in a refrigerator at 4°C for no more than 24 hours.

[0090] 3) Draw the standard curve

[0091] Start the ion chromatograph and, after the instrument stabilizes, inject a series of nitrate nitrogen standard solutions in ascending order of concentration. The standard solutions are commercially available certified nitrate nitrogen stock solutions, precisely diluted with ultrapure water to concentrations of 0.00, 0.50 mg / L, 1.00 mg / L, 2.00 mg / L, 5.00 mg / L, and 10.00 mg / L. Inject each concentration twice and record the peak area of ​​nitrate nitrogen for each injection. If the relative deviation of the peak area between two parallel injections is >3%, a re-injection is required.

[0092] Using the concentration of the nitrate nitrogen standard series solution as the abscissa x, the corresponding average peak area as the ordinate y, and k as the ratio of the change in the corresponding average peak area to the change in the concentration of the nitrate nitrogen standard series solution, the standard curve is fitted using the linear regression method, and the standard curve regression equation is obtained as: y = kx + b.

[0093] 4) Determine the nitrate concentration in the sample.

[0094] Sample injection: Rinse the injection tubing three times with ultrapure water, then rinse the injection needle three times with the sample to be tested to avoid cross-contamination. Inject 20 μL of the sample and record the peak area of ​​nitrate and nitrogen. After testing every five samples, inject an intermediate concentration standard solution. If the relative deviation between the measured concentration and the theoretical concentration is >5%, the standard curve needs to be redrawn.

[0095] Concentration calculation: Substitute the peak area of ​​nitrate nitrogen in the sample into the regression equation of the standard curve above to calculate the concentration of nitrate nitrogen in the sample to be tested. This concentration is the concentration of nitrate nitrogen in the original reaction solution.

[0096] See results Figure 1 .

[0097] Depend on Figure 1 The experimental results show that different concentrations of barium strontium titanate have a significant impact on the total nitrogen concentration and denitrification efficiency. The bar graph in the figure represents the denitrification efficiency, and the line graph represents the nitrogen concentration. The 0.25 g / L barium strontium titanate group, with its lower concentration and weaker piezoelectric effect, saw the total nitrogen concentration decrease from 7.5 mg / L to 2.0 mg / L after 72 hours, achieving a removal rate of 73%; the nitrate nitrogen concentration decreased from 6.5 mg / L to 2.0 mg / L, achieving a removal rate of 62%. The 0.5 g / L barium strontium titanate group exhibited the best denitrification effect, with the total nitrogen concentration decreasing from 7.5 mg / L to 1.5 mg / L after 72 hours, achieving a removal rate of 80.9%; the nitrate nitrogen concentration decreased from 6.5 mg / L to 1.3 mg / L, achieving a removal rate of 80.0%. The 1.5 g / L and 2.5 g / L barium strontium titanate groups, with higher concentrations, saw the total nitrogen removal rates decrease to 68.3% and 58.1%, respectively, and the nitrate nitrogen removal rates decrease to 61.2% and 55.8%, respectively.

[0098] Therefore, at a constant stirring speed, a 0.25 g / L barium strontium titanate concentration exhibits the best synergistic piezoelectric denitrification effect between barium strontium titanate and Streptomyces DD.

[0099] Example 2: Effect of different stirring speeds on synergistic piezoelectric denitrification effect at a constant concentration of barium strontium titanate.

[0100] Four parallel experiments were set up. In each group, 500 mL of simulated nitrogen-containing wastewater was placed in a 1000 mL Erlenmeyer flask, and barium strontium titanate powder was added to make the concentration of barium strontium titanate in the water 0.5 g / L. 10 mL of a 10% concentration of barium strontium titanate was added to each group. 7 Streptomyces DD bacterial culture (CFU / mL) was prepared by placing conical flasks in a constant-temperature shaker at 30°C with stirring speeds of 200 rpm, 300 rpm, 400 rpm, and 500 rpm for 72 h. Samples (10 mL each) were taken at 0 h, 12 h, 24 h, 36 h, 48 h, 60 h, and 72 h after each reaction. The samples were filtered through a 0.45 μm filter, and the total nitrogen concentration was determined by UV spectrophotometry, while the nitrate nitrogen concentration was determined by ion chromatography.

[0101] The specific methods for determining the total nitrogen concentration using ultraviolet spectrophotometry and the nitrate nitrogen concentration using ion chromatography are the same as in Example 1.

[0102] See results Figure 2 .

[0103] Depend on Figure 2 The experimental results show that different stirring speeds have a significant impact on the total nitrogen concentration and denitrification efficiency. The bar chart in the figure represents the denitrification efficiency, and the line graph represents the nitrogen concentration. At stirring speeds of 200 r / min and 300 r / min, due to the lower speeds, the piezoelectric effect of barium strontium titanate was not fully activated, resulting in total nitrogen removal rates of 58.7% and 60.0% after 72 hours, and nitrate removal rates of 55.5% and 60.0%, respectively. The denitrification effect was optimal at a stirring speed of 400 r / min, where the total nitrogen concentration decreased from 7.5 mg / L to 1.4 mg / L after 72 hours (removal rate 81.3%), and the nitrate concentration decreased from 6.5 mg / L to 1.3 mg / L (removal rate 80.0%), which is suitable for the bacterial metabolism. At a stirring speed of 500 r / min, which is too high, the total nitrogen concentration decreased from 7.5 mg / L to 2.0 mg / L after 72 h, with a removal rate of 73.3%, and the nitrate nitrogen concentration decreased from 6.5 mg / L to 1.7 mg / L, with a removal rate of 73.8%.

[0104] Example 3: Comparative experiment on the piezoelectric denitrification effect of a single strain and a synergistic system of *Streptomyces barium titanate* under optimal conditions.

[0105] The experiment was set up in two parallel groups. The first group was a single strain group. 500 mL of simulated nitrogen-containing wastewater was placed in a 1000 mL Erlenmeyer flask, and 10 mL of a 10% concentration of [unspecified ingredient] was added. 7 The first group consisted of a CFU / mL Streptomyces DD bacterial suspension. The conical flask was placed in a constant-temperature shaker at 30℃ and 400 rpm for 72 hours. The second group was a synergistic system of barium strontium titanate and Streptomyces DD. 500 mL of simulated nitrogen-containing wastewater was placed in a 1000 mL conical flask, and 0.25 g of barium strontium titanate powder was added to bring the concentration of barium strontium titanate in the wastewater to 0.5 g / L. Then, 10 mL of a 10% concentration of [missing information - likely a specific concentration] was added. 7 Streptomyces DD bacterial suspension (CFU / mL) was prepared by placing conical flasks in a constant-temperature shaker at 30℃ and 400 rpm for 72 h. Total nitrogen concentration was determined by UV spectrophotometry, nitrate nitrogen concentration by ion chromatography, and changes in total organic carbon concentration in both water bodies were measured using a total organic carbon analyzer. Impedance was measured in both groups using an electrochemical workstation. Differential pulse voltammetry was measured in both groups on day 3 of the reaction, and curves were plotted.

[0106] Among them, the barium strontium titanate and Streptomyces DD synergistic system group is a denitrification system with strain-piezoelectric material synergy.

[0107] The specific methods for determining the total nitrogen concentration using ultraviolet spectrophotometry and the nitrate concentration using ion chromatography are the same as in Example 1.

[0108] The specific method for determining the changes in total organic carbon concentration in the two groups of water bodies using a total organic carbon analyzer is as follows:

[0109] 1) Sample processing

[0110] Samples were taken at 0h, 12h, 24h, 36h, 48h, 60h, and 72h of the reaction, with 10mL of sample taken for each group. The obtained samples were filtered through a 0.45μm filter membrane to remove suspended barium strontium titanate powder and Streptomyces cell precipitate, yielding the filtered sample. If the filtered sample still had slight turbidity, it needed to be further centrifuged to collect the supernatant for later use.

[0111] 2) Acidification to remove inorganic carbon:

[0112] Add one drop of hydrochloric acid solution to the filtered sample, adjust the pH to 3, shake and let stand for 10 minutes to remove dissolved inorganic carbon from the water, and obtain the sample to be tested.

[0113] 3) Sample preservation

[0114] The sample to be tested must be injected for testing immediately. If it cannot be tested immediately, it must be stored in a refrigerator at 4°C for no more than 24 hours.

[0115] 4) Draw the standard curve

[0116] Start the total organic carbon analyzer. After the instrument stabilizes, inject the standard series solutions in ascending order of concentration. The standard series solutions have concentrations of 0.00, 0.50 mg / L, 1.00 mg / L, 5.00 mg / L, and 15.00 mg / L. Inject each concentration twice and record the total organic carbon response value for each injection. If the relative deviation of the response values ​​between two parallel injections is >3%, a re-injection is required. The preparation method of the standard series solutions is as follows:

[0117] First, a total organic carbon standard stock solution with a concentration of 1000 mg / L was prepared using potassium hydrogen phthalate. The total organic carbon standard stock solution was then diluted with ultrapure water specifically for total organic carbon to prepare standard solutions with concentrations of 0.00, 0.50 mg / L, 1.00 mg / L, 5.00 mg / L and 15 mg / L, respectively, thus obtaining the above-mentioned standard series solutions.

[0118] With the total organic carbon standard concentration as the abscissa x, the corresponding average response value as the ordinate y, and k as the ratio of the change in the corresponding average response value to the change in the total organic carbon standard concentration, the standard curve is fitted using the linear regression method, and the standard curve regression equation is obtained as: y=kx+b.

[0119] 5) Measure the total organic carbon concentration in the two water bodies.

[0120] Sample injection: Samples from the single-strain group and the barium strontium titanate and streptomyces DD synergistic system group at the same time point were injected alternately to avoid data deviation caused by instrument drift. The injection needle was rinsed three times with the sample to be tested, and 20 μL was injected each time. The total organic carbon response value of the sample was recorded. For every 5 groups of samples tested, a blank solution was injected once and an intermediate concentration standard solution was injected once. If the total organic carbon in the blank was >0.05 mg / L or the deviation of the standard solution measurement was >5%, the instrument needed to be recalibrated before testing.

[0121] Concentration calculation: Substitute the total organic carbon response value of the sample into the regression equation of the standard curve to calculate the total organic carbon concentration of the sample solution. This concentration is the total organic carbon concentration of the original reaction solution.

[0122] The impedance of the single-strain group and the barium strontium titanate / Streptomyces DD synergistic system group was measured using an electrochemical workstation. Differential pulse voltammetry was measured for both groups on day 3 of the reaction, and curves were plotted. The specific methods are as follows:

[0123] 1) Sample taking:

[0124] EIS Sampling: Samples were taken on reaction days 1, 2 and 3, with 20 ml of reaction solution taken for each group each time. No filtration was required to obtain the test sample for EIS determination.

[0125] DPV sampling: Sampling is only performed on day 3 of the reaction. The sampling amount is the same as that of EIS. The original state of the system is also preserved to obtain the test sample for DPV determination.

[0126] Samples were tested immediately after sampling to ensure that the temperature of the reaction system was stable at 30°C and that the pH of both groups of samples was 7.0 during testing.

[0127] 2) Constructing a three-electrode system:

[0128] The working electrode is a glassy carbon electrode, which is polished to a mirror finish with 0.3μm and 0.05μm alumina powders in sequence before use, rinsed with ultrapure water, and dried with nitrogen. The reference electrode is a saturated calomel electrode, which is checked for salt bridge level before use to ensure there are no air bubbles, and the electrode head is rinsed with ultrapure water. The counter electrode is a platinum wire electrode, which is soaked in concentrated nitric acid for 10 minutes before use and rinsed with ultrapure water. The electrolytic cell is a 50mL glass electrolytic cell: it is soaked in chromic acid cleaning solution for 2 hours before use, rinsed with ultrapure water until neutral, and dried for later use.

[0129] 3) Impedance measurement and curve plotting

[0130] Impedance determination: Insert the three electrodes into 20 mL of the two sets of test samples for impedance determination, ensuring the working electrode surface is completely submerged, and allow to stand for 15 min. In the workstation software, select the impedance spectroscopy module, input the parameters, start the measurement, and record the data. Perform measurements alternately on the test samples from the barium strontium titanate and Streptomyces DD synergistic system group and the single-strain group to ensure data comparability under the same time points and environmental conditions, and to avoid the influence of instrument drift.

[0131] The two sets of test samples used for impedance determination refer to the test samples from the barium strontium titanate and Streptomyces DD synergistic system group and the test samples from the single strain group, respectively. The test samples from the barium strontium titanate and Streptomyces DD synergistic system group were obtained from the reaction system of barium strontium titanate powder, Streptomyces DD, and simulated nitrogen-containing wastewater. The test samples from the single strain group were obtained from the reaction system of Streptomyces DD and simulated nitrogen-containing wastewater.

[0132] Plotting impedance curves: Export the measured impedance data from the workstation software and sort them by frequency from high to low. Plot a scatter plot with Z' as the x-axis and Z'' as the y-axis, and differentiate the curves by time points.

[0133] 4) Measurement of differential pulse voltammetry and curve plotting

[0134] Differential pulse voltammetry determination: Take 20 mL of each of the two groups of test samples used for differential pulse voltammetry determination after 3 days of reaction, pour them into the electrolytic cell, insert the polished and calibrated three electrodes, and let stand for 20 seconds. In the workstation software, select the differential pulse voltammetry module, input the parameters, first determine the test samples of the single strain group used for differential pulse voltammetry determination, and then determine the test samples of the barium strontium titanate and Streptomyces DD synergistic system group used for differential pulse voltammetry determination. Record the differential pulse voltammetry curve data, with the horizontal axis representing potential (V) and the vertical axis representing current (μA).

[0135] Among them, the two groups of test samples used to determine differential pulse voltammetry refer to the test samples of the barium strontium titanate and streptomyces DD synergistic system group and the test samples of the single strain group, respectively; the test samples of the barium strontium titanate and streptomyces DD synergistic system group were taken from the reaction system of barium strontium titanate powder, streptomyces DD and simulated nitrogen-containing wastewater, and the test samples of the single strain group were taken from the reaction system of streptomyces DD and simulated nitrogen-containing wastewater.

[0136] Plotting differential pulse volt-ampere curves: Export the corrected differential pulse volt-ampere data and plot two sets of differential pulse volt-ampere curves with potential on the x-axis and current on the y-axis.

[0137] See results Figures 3-7 .

[0138] Depend on Figure 3 It can be seen that under the optimal conditions of 400 r / min and 0.5 g / L barium strontium titanate, the total nitrogen removal rate of a single strain was 45.8% and the nitrate nitrogen removal rate was 42.5% within 72 h; the total nitrogen removal rate of the barium strontium titanate and Streptomyces DD synergistic system was 80.9% and the nitrate nitrogen removal rate was 86.0% within 72 h.

[0139] Depend on Figure 4 It can be seen that under the optimal conditions of 400 r / min and 0.5 g / L barium strontium titanate, the total organic carbon removal rate of a single strain within 72 h is 61.2%, while the total organic carbon removal rate of the barium strontium titanate and Streptomyces DD synergistic system within 72 h is 85.1%.

[0140] Depend on Figure 6 It can be seen that the peak values ​​of the barium strontium titanate and streptomyces DD synergistic system at various time points are higher, the impedance range is wider, and the impedance value is lower than that of the single system, indicating that the electron transfer efficiency is improved.

[0141] Depend on Figure 7 It can be seen that the reduction peak current of the barium strontium titanate and Streptomyces DD synergistic system is higher than that of the single strain group, proving that the piezoelectric effect promotes electron transfer related to nitrate reduction.

[0142] In summary, the synergistic piezoelectric denitrification of barium strontium titanate and Streptomyces DD requires no additional carbon source or external power; the energy comes from mechanical stirring, significantly reducing energy consumption and the risk of secondary pollution, thus meeting green environmental protection requirements. The addition of barium strontium titanate is not a simple physical mixing process, but rather fundamentally activates and enhances the metabolic capacity of Streptomyces, achieving faster and more thorough removal of total nitrogen and nitrate nitrogen. It is suitable for treating wastewater with low carbon-to-nitrogen ratios, slightly polluted water bodies, or industrial nitrate wastewater, demonstrating promising application prospects and practical value.

[0143] The experimental results above show that the strain-piezoelectric material synergistic denitrification system has the advantages of high efficiency, low cost, no secondary pollution, and wide applicability.

[0144] In this denitrification system, barium strontium titanate piezoelectric material is introduced. Mechanical stirring stimulates the piezoelectric effect, creating a potential difference on the surface of barium strontium titanate, directly providing electron donors for Streptomyces DD. Furthermore, the impedance value of the synergistic system is lower than that of the single-strain group, while the reduction peak current is increased, demonstrating a significant optimization of electron transfer efficiency. Streptomyces can obtain sufficient electrons through barium strontium titanate without relying on organic carbon.

[0145] Streptomyces DD forms a biofilm on the surface of barium strontium titanate. Through the interface between barium strontium titanate and the biofilm, the electron transfer pathway from barium strontium titanate to the microbial cell is shortened, while simultaneously activating nitrile reductase activity and accelerating NO3- production. - →NO2 - → The conversion of N2 avoids the accumulation of intermediate products and improves the completeness of the reaction.

[0146] Barium strontium titanate exhibits strong chemical stability, tolerating the complex composition of industrial wastewater. With a particle size of 50 nm and a purity of 99.5%, it disperses uniformly in water. For wastewater with a low C / N ratio, it achieves a total nitrogen removal rate of over 75% without the need for carbon supplementation, meeting municipal effluent requirements. For industrial nitrate wastewater, barium strontium titanate protects Streptomyces from toxic substances, maintaining a stable denitrification efficiency of around 80%, making it suitable for wastewater from chemical and other industries.

[0147] Therefore, this invention can solve the problems of low nitrogen removal efficiency, limited efficiency due to insufficient electron donors, the need for external carbon sources in traditional denitrification, and the tendency to cause secondary pollution when using only Streptomyces microorganisms, thus meeting the actual treatment needs.

[0148] The experimental results above show that in the strain-piezoelectric material synergistic denitrification system, the denitrification effect is optimal when the concentration of barium strontium titanate is controlled at 0.5 g / L and the stirring speed is set at 400 r / min. This system not only efficiently removes total nitrogen, nitrate nitrogen, and total organic carbon from the water, but also avoids secondary pollution such as nitrous oxide. The electron transfer efficiency between the piezoelectric material and microorganisms is also significantly enhanced. Furthermore, the system has a wide adaptability range for barium strontium titanate concentration and stirring speed; it maintains stable denitrification performance even at concentrations between 0.25-2.5 g / L and stirring speeds between 200-500 r / min, making it more flexible and stable to operate in practical wastewater treatment scenarios.

[0149] It should be noted that when numerical ranges are involved in this invention, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. To avoid redundancy, this invention describes preferred embodiments.

[0150] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments, all of which fall within the scope of the invention.

Claims

1. The application of a strain-piezoelectric material synergistic denitrification system in water treatment, characterized in that, The denitrification system includes Streptomyces denitrifying bacteria and barium strontium titanate; The barium strontium titanate is loaded onto the surface of the Streptomyces denitrifying bacteria; The Streptomyces denitrifying bacteria include Streptomyces ( Streptomyces sp.)DD, which is deposited at the China Center for Type Culture Collection, accession number CCTCC NO: M 20251374; The denitrification system is used for the denitrification treatment of nitrogen-containing wastewater; wherein, the nitrogen-containing wastewater is wastewater with a low carbon-to-nitrogen ratio; The denitrification treatment refers to reducing the content of total nitrogen, nitrate nitrogen, and total organic carbon in the nitrogen-containing wastewater; The method for denitrifying nitrogen-containing wastewater using the aforementioned denitrification system includes the following steps: The activated Streptomyces denitrifying bacteria were inoculated and cultured. After culture, the bacteria were centrifuged, the supernatant was discarded, the bacterial precipitate was collected, and it was made into a microbial suspension. The microbial suspension and the barium strontium titanate are added to the nitrogen-containing wastewater to form a mixed reaction system, so that the barium strontium titanate is loaded on the surface of the Streptomyces denitrifying bacteria, and the concentration of the barium strontium titanate in the nitrogen-containing wastewater is controlled to be 0.25 g / L~2.5 g / L; The mixed reaction system is stirred to stimulate the piezoelectric effect of barium strontium titanate, thereby enhancing the denitrification process and achieving the removal of total nitrogen and nitrate nitrogen from the nitrogen-containing wastewater.

2. The application of the strain-piezoelectric material synergistic denitrification system according to claim 1 in water treatment, characterized in that, The initial total nitrogen concentration of the nitrogen-containing wastewater is 0~10 mg / L, the initial nitrate nitrogen concentration is 0~10 mg / L, and the initial total organic carbon concentration is ≤15 mg / L.

3. The application of the strain-piezoelectric material synergistic denitrification system according to claim 1 in water treatment, characterized in that, The barium strontium titanate is in powder form with a particle size of 50 nm to 100 nm.

4. The application of the strain-piezoelectric material synergistic denitrification system according to claim 1 in water treatment, characterized in that, The stirring speed is 200 r / min to 500 r / min.

5. The application of the strain-piezoelectric material synergistic denitrification system according to claim 1 in water treatment, characterized in that, The bacterial cell concentration of the microbial suspension is 10. 7 CFU / mL.

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