Electrically-assisted microbial system and application method thereof in monofluoronitrobenzene pollution control

Abstract

The invention relates to the technical field of organic wastewater treatment, and discloses an electrically-assisted microbial system and an application method thereof in monofluoronitrobenzene pollution control, and the method comprises the following steps: S1, treating wastewater by adopting the electrically-assisted microbial system through sequencing batch operation; the electrically-assisted microbial system comprises a reactor with the effective volume not smaller than 3 L, an aeration device and a power supply, electrodes composed of anodes and cathodes are arranged in the reactor, and the distance between the electrodes is 1 + / -0.2 cm; the power supply is electrically connected with the electrodes through titanium wires; the anode is a titanium mesh, and the cathode is formed by attaching microorganisms to a stainless steel mesh; s2, establishing a quadratic polynomial model of the initial concentration, carbon nitrogen ratio and voltage of p-fluoronitrobenzene by using a response surface method, and optimizing to obtain operation parameters; and setting operation parameters to operate the electrically-assisted microbial system to complete the treatment of the fluoronitrobenzene wastewater. The problems of low efficiency, poor stability and the like of a traditional treatment technology in large-scale application are solved.

Description

Technical Field

[0001] This invention relates to the field of organic wastewater treatment technology, specifically to a method and apparatus for scale-up treatment of parafluoronitrobenzene wastewater using an electrically assisted microbial system, particularly concerning the optimization of operating parameters, improvement of system stability, and selection of electrode materials; specifically, it relates to an electrically assisted microbial system and its application method in the control of monofluoronitrobenzene pollution. Background Technology

[0002] p-FNB is a typical fluorinated nitrobenzene pollutant, widely found in pesticides, organic wastewater treatment, and dye intermediate production wastewater. Its molecular structure, with fluorine atoms and nitro groups, endows it with high toxicity, low biodegradability, and environmental persistence. Conventional biological treatment processes (such as activated sludge processes) typically achieve a removal rate of less than 30% for p-FNB and easily lead to microbial poisoning and inactivation.

[0003] Electro-assisted biochemical systems (EABT), as an emerging wastewater treatment technology, achieve pollutant degradation through direct electron transfer between electroactive microorganisms and electrodes. Existing laboratory-scale studies show that they can achieve a removal rate of 60%-70% for p-FNB. However, current EABT research mainly focuses on small-volume reactors (<1L). When scaled up to industrial scale, the following key problems arise: 1) Decreased mass transfer efficiency: Increased reactor volume leads to uneven pollutant concentration distribution on the electrode surface, increasing mass transfer resistance; 2) Complex parameter interactions: The synergistic effects of operating parameters such as initial pollutant concentration, C / N ratio, and applied voltage are not systematically analyzed, and single-factor optimization cannot achieve global optimum; 3) Insufficient electrode stability: During long-term operation, the anode material is susceptible to corrosion (e.g., titanium-based coating peeling), and the cathode microbial film peeling leads to a decrease in treatment efficiency. Therefore, existing technologies have the following shortcomings.

[0004] 1) Lack of large-scale application: There are no engineering cases of EABT treatment of p-FNB wastewater with a scale of 3L or more, and there is a lack of systematic methods for reactor structure design, electrode material selection and operation parameter optimization during the scale-up process;

[0005] 2) Limitations of parameter optimization techniques: Traditional single-factor experimental methods ignore the interaction between parameters, resulting in low model prediction accuracy (R²). 2 <0.9), in actual engineering, repeated trial and error are required, increasing debugging costs;

[0006] 3) Insufficient shock resistance: Existing systems are prone to collapse when the influent load fluctuates (such as a sudden increase in p-FNB concentration), and the recovery cycle is long (>5 operating cycles), making it difficult to adapt to the fluctuating characteristics of industrial wastewater quality.

[0007] Therefore, this invention proposes an electro-assisted microbial system suitable for EABT treatment of p-FNB wastewater at a scale of 3L or more, and a method for applying this system in the control of monofluoronitrobenzene pollution. Summary of the Invention

[0008] The purpose of this invention is to provide an electrically assisted microbial system and its application method in the control of monofluoronitrobenzene pollution. It designs an EABT reactor suitable for scales of 3L and above, solving the problems of mass transfer efficiency and electrode stability during scale-up, thereby overcoming the bottleneck of large-scale production. Through response surface methodology (RSM), it quantifies the interaction of multiple parameters, constructs a high-fit prediction model, and achieves precise control of operating conditions to establish a standard optimization model. Through the selection of electrode materials and optimization of operating strategies, it enhances the system's tolerance to load shocks and reduces efficiency decay during long-term operation, thereby improving system robustness.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] This invention provides a method for scale-up treatment of p-fluoronitrobenzene wastewater based on an electrically assisted microbial system, comprising the following steps:

[0011] S1. Wastewater is treated using an electrically assisted microbial system through a sequencing batch process.

[0012] The electrically assisted microbial system includes a reactor with an effective volume of not less than 3L, an aeration device, and a power supply. The reactor has built-in electrodes consisting of an anode and a cathode, with a spacing of 1±0.2cm between the electrodes. The power supply is electrically connected to the electrodes via titanium wires.

[0013] S2. A quadratic polynomial model of the initial concentration, carbon-nitrogen ratio and voltage of fluoronitrobenzene was established using the response surface methodology, and the operating parameters were optimized. The operating parameters were then set to run the electrically assisted microbial system to complete the treatment of fluoronitrobenzene wastewater.

[0014] The formula for the quadratic polynomial model is:

[0015] Y=71.56+5.04A+5.55B+8.56C+1.70AB+0.83AC-2.00BC-15.44A 2 -4.57B 2

[0016] -0.44C 2

[0017] Where Y is the removal rate of p-fluoronitrobenzene, A is the initial concentration of p-fluoronitrobenzene, B is the voltage, and C is the carbon-to-nitrogen ratio.

[0018] Preferably, the anode is a titanium mesh with a porosity of 80%-90%.

[0019] Preferably, the cathode is formed by microorganisms attaching to a stainless steel mesh.

[0020] Preferably, the bottom of the reactor is provided with a conical sludge collection hopper with a cone angle of 50°-70°.

[0021] Preferably, the sequential batch operation includes an electrolysis stage and an aeration stage.

[0022] Preferably, the electrolysis stage involves stirring the mixture using a peristaltic pump at a speed of 40-60 rpm for a duration of 60-72 hours.

[0023] Preferably, the dissolved oxygen during the aeration stage is controlled at 2-4 mg / L, and the operating time is 12-24 h.

[0024] The present invention also provides an electrically assisted microbial system for realizing a method for scale-up treatment of p-fluoronitrobenzene wastewater, comprising a reactor, electrodes built into the reactor, and an aeration device and a power supply connected to the outside of the reactor.

[0025] The reactor has a main body effective volume of 3L, an inner diameter of 10cm, a height of 40cm, and is made of polymethyl methacrylate.

[0026] The electrode comprises a titanium mesh anode and a stainless steel mesh cathode with a spacing of 1±0.2cm, which are fixed by an insulating bracket; the titanium mesh anode has a diameter of 5cm and a length of 15cm, and the stainless steel mesh cathode has a diameter of 6cm and a length of 15cm.

[0027] The power supply is a 0-5V DC power supply, which is connected to the electrodes through titanium wires;

[0028] The aeration device is equipped with a microporous aeration head at the bottom, and the aeration rate is 0.5L / min.

[0029] Preferably, the aeration head has an aperture of 50 μm, and the bottom of the reactor is provided with a conical sludge collection hopper with a cone angle of 50°-70°.

[0030] Preferably, the anode is a titanium mesh with a porosity of 80%-90%, and the cathode is a stainless steel mesh to which microorganisms attach.

[0031] Compared with existing technologies, the beneficial effects of this solution are:

[0032] 1. The method for scaled-up treatment of fluoronitrobenzene wastewater provided by this invention has achieved a breakthrough in treatment performance. By using a 3L scale reactor, a p-FNB removal rate of 74.1% and a fluoride removal rate of 71.4% can be achieved, which is 9 percentage points higher than the 65% removal rate of the laboratory scale of 1L in the prior art. Compared with the traditional biological method (removal rate <30%), the treatment efficiency is increased by 147%, and no additional toxic chemical reagents are required.

[0033] 2. The electric-assisted microbial system provided by this invention has enhanced operational stability, can withstand 4 times the design load impact, and has a recovery cycle of ≤2 operating cycles, which is significantly better than the existing system (recovery cycle >5 cycles); the electrode life is extended to more than 1 year, and the treatment efficiency decay is <5% after 100 operating cycles, reducing equipment replacement costs.

[0034] 3. The method provided by this invention has significant economic advantages: energy consumption is reduced by 79%, and the electricity cost for treating 1 ton of wastewater containing 1 mmol / L p-FNB is reduced from 8.91 yuan to 1.89 yuan; the optimized C / N ratio reduces the amount of glucose added by 20%, the carbon source cost is reduced by 15%, and the annual operating cost is reduced by more than 30%. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the reactor structure;

[0036] Figure 2 The effect of different initial concentrations on the removal rate and defluorination rate of p-fluoronitrobenzene (external tank voltage 1.8V, carbon-nitrogen ratio 8.6);

[0037] Figure 3 The three-dimensional response surface methodology (RSM) was used to reveal the interaction between voltage and carbon-nitrogen ratio (C-N ratio) and initial concentration of p-fluoronitrobenzene (p-N ratio) (a represents the interaction between voltage and C-N ratio; b represents the interaction between initial concentration of p-fluoronitrobenzene and C-N ratio; c represents the interaction between voltage and initial concentration of p-fluoronitrobenzene; when voltage > 2.0 V, the effect of high C-N ratio on the removal rate is weakened).

[0038] Figure 4 The concentration changes of p-fluoronitrobenzene under shock load and during the recovery period (except for the first period when the concentration of p-FNB in ​​the influent was 3.2 mmol / L, the concentration in the influent for the subsequent three periods was 0.8 mmol / L).

[0039] Figure 5The CV curves before and after electrode operation were compared at a scan rate of 10 mV / s, showing no significant changes in the position and intensity of the redox peaks (a is the CV curve of the anode after 100 cycles at reactor startup, b is the CV curve of the cathode after 100 cycles at reactor startup, c is the CV curve of the anode at reactor startup (red) and after 60 days of operation (dark blue), and d is the CV curve of the cathode at reactor startup (red) and after 60 days of operation (dark blue). Detailed Implementation

[0040] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0041] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0043] Example 1: Electrically Assisted Microbial System

[0044] I. Reactor Structural Design

[0045] 1. Main Structure

[0046] 1) Material and volume: The reactor is made of transparent polymethyl methacrylate (plexiglass), with an inner diameter of 10cm, an effective height of 40cm, a total volume of 4L, an effective volume of 3L, and a conical sludge collection hopper (cone angle of 60°) at the bottom to facilitate sludge settling and discharge.

[0047] 2) Electrode configuration:

[0048] Anode: Titanium mesh (TA1 type, purity ≥99.5%), diameter 5cm, length 15cm, porosity 85%;

[0049] Cathode: 316L stainless steel mesh, 6cm in diameter, 15cm in length, 80% porosity, with microorganisms attached to the surface;

[0050] Electrode spacing: 1cm, fixed by an insulating bracket to ensure uniform electric field distribution;

[0051] 3) External systems:

[0052] A DC power supply (0-5V adjustable, accuracy ±0.01V) is connected to the electrodes via titanium wires (1mm in diameter);

[0053] Aeration system: The bottom is equipped with microporous aeration heads (pore size 50μm) with an aeration rate of 0.5L / min, which are used for oxygenation of mixed liquor and sludge disturbance during power outages.

[0054] 2. Operating Mode

[0055] It uses a sequential batch processing (SBR) method, with a single cycle lasting 72 hours. The specific process is as follows:

[0056] 1) Electrolysis stage (60h): Close the power supply, control the voltage at 2.0±0.02V, and continuously stir (50rpm) using a peristaltic pump (flow accuracy ±1%) to promote mass transfer;

[0057] 2) Aeration stage (12h): Disconnect the power supply, turn on aeration, control dissolved oxygen at 2-3mg / L, and carry out microbial proliferation and metabolic product discharge.

[0058] II. Multi-parameter collaborative optimization method

[0059] 1. Experimental Design

[0060] A Box-Behnken response surface methodology was used to investigate the effects of three factors and three levels on the removal rate of p-FNB. Specific parameters are detailed in [link to relevant documentation].

[0061] Table 1:

[0062]

[0063]

[0064] A total of 17 experiments were designed (including 5 centrally repeated experiments), and data fitting was performed using Minitab19 software.

[0065] 2. Model Building and Validation

[0066] 1) Quadratic polynomial model:

[0067] Y=71.56+5.04A+5.55B+8.56C+1.70AB+0.83AC-2.00BC-15.44A 2 -4.57B 2 -0.44C 2

[0068] Where Y is the removal rate of p-fluoronitrobenzene, A is the initial concentration of p-fluoronitrobenzene, B is the voltage, and C is the carbon-to-nitrogen ratio.

[0069] 2) Significance test: Model R 2 =0.9654, adjust R 2=0.9327, the lack of fit term P=0.123>0.05, indicating that the model is not lacking in fit and can effectively predict the removal rate; the interaction term V×C (P=0.0317<0.05) is significant, indicating that the synergistic effect of voltage and initial concentration has a significant impact on the removal rate.

[0070] 3) Optimal conditions: Through response surface methodology, the optimal operating parameters were determined to be a carbon-to-nitrogen ratio of 9.08, a voltage of 2.02V, and an initial concentration of 0.97 mmol / L. The theoretical removal rate was 74.9%, the experimental verification value was 74.1%, and the error was <1%.

[0071] III. Stability Improvement Technology

[0072] 1. Impact load resistant design

[0073] 1) Shock test protocol: During the stable operation phase (cycle 50), the influent p-FNB concentration was rapidly increased from 1.0 mmol / L to 3.2 mmol / L (4 times the design load) for two cycles, then restored to the original concentration, and the removal rate was monitored.

[0074] The removal rate dropped to 43% in the first shock cycle, rose to 78% in the second cycle, and recovered to 100% in the third cycle, proving that the system can recover stability within two cycles;

[0075] 2) Control strategy: When the online monitoring instrument (HPLC, detection accuracy ±0.01mmol / L) detects that the concentration of p-FNB in ​​the effluent is >0.3mmol / L, the electrolysis time is automatically extended to 72 hours until the removal rate meets the standard.

[0076] 2. Electrode stability optimization

[0077] 1) Anode material: Titanium mesh has excellent corrosion resistance. The Tafel polarization curve shows a corrosion potential of -0.03V (vs. SCE) and a corrosion current density of only 5μA / cm. 2 After 100 cycles, the coating integrity rate is >95%;

[0078] 2) Cathode structure: A stainless steel mesh with attached electroactive microorganisms (mainly Pseudomonas and Klebsiella, identified by 16S rRNA sequencing). CV curves showed that the peak current density was stable at 120 μA / cm. 2 After 100 cycles, the change in biofilm thickness was <10%;

[0079] 3) Energy consumption control: The system's unit energy consumption is 0.21kWh / kgp-FNB, which is 79% lower than that of traditional BES (0.99kWh / kg), mainly due to the optimization of electrode spacing and efficient electron transfer.

[0080] Example 2: Application of an electrically assisted microbial system

[0081] I. Inoculation and Acclimatization of Microbial Strains

[0082] 1. Sludge source: Taken from the aerobic tank of a chemical wastewater treatment plant. The mixed liquor suspended solids concentration (activated sludge concentration) MLSS is 4000±200mg / L. The ratio of the mixed liquor volatile suspended solids concentration (MLVSS) to the mixed liquor suspended solids concentration (MLSS) is MLVSS / MLSS=0.7±0.05.

[0083] 2. Domestication process:

[0084] 1) Weeks 1-2: Glucose was used as the sole carbon source, with a carbon-to-nitrogen ratio (C / N) of 10. The p-FNB concentration was gradually increased from 0 to 0.2 mmol / L, and one cycle (72 hours) was run per day.

[0085] 2) Weeks 3-4: The p-FNB concentration was kept constant at 0.4 mmol / L, and the C / N ratio was gradually reduced to 8.25 to screen for toxic and electroactive microorganisms;

[0086] 3) Acclimation endpoint: sludge conductivity > 10 mS / cm, uniform brownish-yellow biofilm formed on electrode surface, and removal rate of 0.4 mmol / L p-FNB stabilized at over 60%.

[0087] II. Wastewater Treatment Process

[0088] 1. Influent preparation: Adjust the pH of the wastewater containing p-FNB to 7.0±0.2, add nutrients such as glucose and ammonium chloride, and control the C / N ratio to the target value (error ±5%).

[0089] 2. Reactor operation:

[0090] Inject 3L of wastewater into the reactor and add acclimated sludge until the MLSS reaches 3000mg / L;

[0091] Turn on the agitator (50 rpm) and DC power supply, adjust the voltage to 2.02 ± 0.02 V, and electrolyze for 60 hours. During this period, take water samples every 12 hours to test the p-FNB concentration.

[0092] After electrolysis, turn off the power and start aeration for 12 hours, controlling DO = 2-3 mg / L. After aeration, let stand for 30 minutes, drain 1L of supernatant (water exchange rate 33%), add 1L of new wastewater, and start the next cycle.

[0093] III. Monitoring and Control

[0094] 1. Routine monitoring:

[0095] 1) Water quality indicators: p-FNB concentration (HPLC, Agilent 1260, C18 column, mobile phase methanol:water = 70:30, flow rate 1mL / min), fluoride ion concentration (ion chromatography, Dionex ICS-5000+), MLSS / MLVSS (gravimetric method).

[0096] 2) Electrochemical parameters: electrode potential (calomel electrode as reference electrode), cell voltage (multimeter, accuracy ±0.01V), measured once a day;

[0097] 2. Intelligent control:

[0098] 1) Establish a PLC control system to collect signals such as voltage, current, and pH in real time. When a voltage fluctuation > 5% is detected, the power output is automatically adjusted.

[0099] 2) A predictive control module is established based on the RSM model. The optimal voltage setpoint is automatically calculated based on the online data of the influent water quality (initial concentration, C / N ratio) to achieve adaptive adjustment of parameters.

[0100] IV. Handling Abnormal Situations

[0101] 1. Sudden Drop in Removal Rate: When the removal rate is <60% for two consecutive cycles, the following measures will be triggered:

[0102] The state of electroactive microorganisms on the electrode surface is detected. If large-scale shedding or death occurs, the water intake is stopped and aeration (aeration + stirring) is carried out for 24 hours to promote biofilm regeneration.

[0103] 2. Sludge bulking: When SVI > 150 mL / g, reduce the stirring rate during the aeration stage to 30 rpm and increase the settling time to 60 minutes to promote sludge settling.

[0104] In summary, the operating parameters of the electrically assisted microbial system provided by this invention are continuously optimized using response surface methodology, achieving a defluorination efficiency of over 74% under optimal carbon flux supply conditions when the C / N ratio is approximately 8-9 and the initial p-fluoronitrobenzene concentration is around 0.8 mmol·L⁻¹. This system is suitable for the efficient treatment of wastewater containing p-fluoronitrobenzene from chemical, pharmaceutical, and other industries. Through reactor structure optimization, multi-parameter synergistic control, and electrode material innovation, this technology achieves efficient degradation of p-fluoronitrobenzene, stable system operation, and optimized energy consumption, solving the problems of low efficiency and poor stability in large-scale applications of traditional treatment technologies. Furthermore, the system exhibits excellent short-term shock recovery performance: when the p-fluoronitrobenzene concentration fluctuates by more than four times, it can self-recover to over 80% of the steady-state defluorination rate within 24 hours without re-inoculation or replacement of the packing material; and metal leaching tests show almost no significant corrosion loss at the cathode, allowing for long-term reuse of the stainless steel mesh as the conductor support platform.

[0105] The above specific embodiments are merely explanations of the present invention and are not intended to limit the present invention. After reading this specification, those skilled in the art can make modifications to these embodiments without contributing any inventive step, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A method for scale-up treatment of p-fluoronitrobenzene wastewater based on an electrically assisted microbial system, characterized in that, Includes the following steps: S1. Wastewater is treated using an electrically assisted microbial system through a sequencing batch process. The electrically assisted microbial system includes a reactor with an effective volume of not less than 3L, an aeration device, and a power supply. The reactor has built-in electrodes consisting of an anode and a cathode, with a spacing of 1±0.2cm between the electrodes. The power supply is electrically connected to the electrodes via titanium wires. S2. A quadratic polynomial model of the initial concentration, carbon-nitrogen ratio and voltage of fluoronitrobenzene was established using the response surface methodology, and the operating parameters were optimized. The operating parameters were then set to run the electrically assisted microbial system to complete the treatment of fluoronitrobenzene wastewater. The formula for the quadratic polynomial model is: Y=71.56+5.04A+5.55B+8.56C+1.70AB+0.83AC-2.00BC-15.44A 2 -4.57B 2 -0.44C 2 Where Y is the removal rate of p-fluoronitrobenzene, A is the initial concentration of p-fluoronitrobenzene, B is the voltage, and C is the carbon-to-nitrogen ratio.

2. The method according to claim 1, characterized in that, The anode is a titanium mesh with a porosity of 80%-90%.

3. The method according to claim 1, characterized in that, The cathode is formed by microorganisms attaching to a stainless steel mesh.

4. The application according to claim 1, characterized in that, The reactor is equipped with a cone-shaped sludge collection hopper at the bottom, with a cone angle of 50°-70°.

5. The method according to claim 1, characterized in that, The sequential batch operation includes an electrolysis stage and an aeration stage.

6. The method according to claim 5, characterized in that, The electrolysis stage involves stirring the mixture using a peristaltic pump at a speed of 40-60 rpm for 60-72 hours.

7. The method according to claim 6, characterized in that, The dissolved oxygen level during the aeration stage is controlled at 2-4 mg / L, and the operating time is 12-24 h.

8. An electrically assisted microbial system for implementing the method of claim 1, characterized in that, It includes a reactor, electrodes built into the reactor, and an aeration device and power supply connected to the outside of the reactor; The reactor has a main body effective volume of 3L, an inner diameter of 10cm, a height of 40cm, and is made of polymethyl methacrylate. The electrode comprises an anode and a cathode spaced 1 ± 0.2 cm apart, fixed by an insulating support; the anode has a diameter of 5 cm and a length of 15 cm, and the cathode has a diameter of 6 cm and a length of 15 cm. The power supply is a 0-5V DC power supply, which is connected to the electrodes through titanium wires; The aeration device is equipped with a microporous aeration head at the bottom, and the aeration rate is 0.5L / min.

9. The electrically assisted microbial system according to claim 8, characterized in that, The aeration head has an aperture of 50 μm, and the bottom of the reactor is equipped with a conical sludge collection hopper with a cone angle of 50°-70°.

10. The electrically assisted microbial system according to claim 8, characterized in that, The anode is a titanium mesh with a porosity of 80%-90%; the cathode is formed by microorganisms attached to a stainless steel mesh.

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