CN114455691B - Composite sewage denitrification process device and operation parameter optimization method - Google Patents
Composite sewage denitrification process device and operation parameter optimization method Download PDFInfo
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Abstract
The invention discloses a composite sewage denitrification process device and an operation parameter optimization method, wherein in the composite sewage denitrification process device with an electrode biological carrier, a Box-Behnken model is adopted to design an orthogonal experiment, the carbon-nitrogen ratio, the hydraulic retention time and the sludge volume fraction are selected as influencing factors, the nitrate-nitrogen removal rate, the COD removal efficiency and the denitrification contribution ratio of an electrode carrier area are selected as response variables, the orthogonal experiment result is analyzed by using a response surface method, and a mathematical model between the influencing factors and the response variables is established. The invention obtains the optimized regulation and control scheme of the process operation condition by utilizing the response surface method, can predict the efficiency of the process under different operation conditions, and has the advantages of reducing the experimental workload and shortening the process operation time.
Description
Technical Field
The invention relates to the technical field of sewage treatment, in particular to a composite sewage denitrification process device and an operation parameter optimization method.
Background
The composite process of the biological carrier with the built-in electrode is a newly developed sewage treatment process in recent years. The process couples a bioelectrochemical system with the traditional anaerobic technology, and the bioelectrochemical module is used as a subsequent processing unit of the anaerobic biological process, so that the removal of pollutants which are difficult to degrade and pollutants with low concentration and the denitrification under the condition of low carbon-nitrogen ratio can be enhanced, the problems of high energy consumption, poor economy and the like of the bioelectrochemical system are solved, the defects of long starting time, low reaction speed and the like of the traditional biological treatment process are overcome, the impact load resistance of the process is higher, and the pollutant removal efficiency is higher.
Aiming at sewage denitrification treatment, the traditional biological denitrification process converts nitrogen in water into nitrogen for removal through ammoniation, nitrification and denitrification processes, wherein the denitrification process needs sufficient electron donors (usually organic carbon), but most of the organic carbon is consumed in an aerobic zone, so that the electron donors are insufficient in the denitrification process, and the effluent nitrate nitrogen is remained, so that increasingly strict sewage discharge standards are difficult to meet. Therefore, when the traditional sewage denitrification process is used for treating sewage with a low carbon-nitrogen ratio, an additional carbon source needs to be added, so that the cost of sewage treatment is increased, and the quality of effluent water is also influenced by residual organic carbon. When a bioelectrochemical system is used for denitrification, the cathode is used as an electron donor through directional potential regulation, so that autotrophic denitrification of nitrate and nitrogen at the cathode is realized, and the demand on an organic carbon source is greatly reduced. On the basis, a bioelectrochemical system is coupled with a traditional anaerobic process to construct a composite sewage denitrification process with a built-in electrode biological carrier, so that the denitrification process can be further strengthened, namely heterotrophic denitrification is realized by utilizing an anaerobic biological region, in a rear electrode biological carrier region, the defect of an electron donor is supplemented by utilizing bioelectrochemical reaction, the denitrification process is further strengthened, and further the efficient denitrification of sewage with low carbon-nitrogen ratio is realized.
In the composite sewage denitrification process, the control of proper hydraulic retention time, sludge volume fraction and carbon-nitrogen ratio is the key for stable operation of the process, and meanwhile, the sewage denitrification efficiency, the Chemical Oxygen Demand (COD) removal rate and the contribution of electrode biological carriers are all important indexes for evaluating the process efficiency, but the research on the optimization regulation strategy and the key index efficiency of the composite sewage denitrification process is deficient.
Disclosure of Invention
The invention aims to provide a composite sewage denitrification process device and an operation parameter optimization method, which utilize a response surface method to obtain an optimized regulation and control scheme of process operation conditions, can predict the efficiency of processes under different operation conditions, and have the advantages of reducing the experimental workload and shortening the process operation time.
In order to achieve the purpose, the invention provides the following scheme:
a composite sewage denitrification process device comprises: the sampling valve is arranged in the middle of each section of cylindrical pipe; a water inlet pipe is arranged on the side wall of the fifth cylindrical pipe, one end of the water inlet pipe penetrates through the side wall of the fifth cylindrical pipe and extends downwards to the inside of the conical pipe, the other end of the water inlet pipe is connected with simulated wastewater, the third cylindrical pipe and the fourth cylindrical pipe form a bioelectrode carrier area, the sixth cylindrical pipe and the conical pipe form an anaerobic sludge area, a cathode module is arranged at the central position inside the third cylindrical pipe, an anode module is arranged at the central position inside the fourth cylindrical pipe, the cathode module and the anode module are connected with an external circuit arranged outside in series to form a loop, a three-phase separator and an overflow weir are arranged at the position of the first cylindrical pipe, and a water outlet pipe is communicated with the bottom of the overflow weir; the water inlet pipe is used for sending simulated wastewater, the simulated wastewater is fed into the anaerobic sludge area, returns and rises after being filled in the anaerobic sludge area, flows into the overflow weir through the first cylindrical pipe after passing through the biological electrode carrier area, and is discharged through the water outlet pipe.
Optionally, the height of the first cylindrical pipe is 15cm, and the inner diameter of the first cylindrical pipe is 12cm; the heights of the second cylindrical pipe, the third cylindrical pipe, the fourth cylindrical pipe, the fifth cylindrical pipe and the sixth cylindrical pipe are all 20cm, and the inner diameters of the second cylindrical pipe, the third cylindrical pipe, the fourth cylindrical pipe, the fifth cylindrical pipe and the sixth cylindrical pipe are all 12cm; the height of the conical pipe is 20cm, the inner diameter of the top of the conical pipe is 12cm, and the inner diameter of the bottom of the conical pipe is 6cm; the distance between one end of the water inlet pipe and the bottom of the conical pipe is 9cm.
Optionally, the cathode module, the anode module and the external circuit are connected in series by titanium wires to form a loop.
Optionally, the cathode module and the anode module are formed by connecting nine carbon fiber brushes in series, and the external circuit is formed by connecting a power supply and a resistor in series.
Optionally, the carbon fiber brushes are 2.5cm in diameter and 16cm in height.
Optionally, peristaltic pumps are arranged at the water inlet pipe and the water outlet pipe.
A composite sewage denitrification process operation parameter optimization method applies the composite sewage denitrification process device and comprises the following steps:
s1) designing an orthogonal experiment: selecting a Box-Behnke model in Design Expert software, selecting HRT (hydraulic retention time), vs (sludge volume fraction) and C/N (carbon-nitrogen ratio) as influence variables, selecting NR (nitrogen removal efficiency), CR (chemical oxygen demand) removal efficiency and ER (electrode carrier nitrogen removal contribution ratio) as response variables, and obtaining more than 10 groups of orthogonal experimental schemes;
s2) collecting experimental data: based on an orthogonal experimental scheme, feeding simulated wastewater into a water inlet pipe, setting hydraulic retention time HRT by adjusting the pump speed of a peristaltic pump, setting sludge volume fraction Vs by adjusting the sludge inoculation amount, and setting carbon-nitrogen ratio C/N by adjusting the concentration of the fed simulated wastewater, then respectively taking water samples at the positions of a water outlet and an electrode carrier region, measuring the concentration of nitrate nitrogen and COD of the water samples, and calculating to obtain denitrification efficiency NR, COD removal efficiency CR and electrode carrier denitrification contribution ratio ER so as to obtain experimental data of response variables in different orthogonal experimental schemes;
s3) response surface model building: performing mathematical analysis on the experimental data of the response variables, and fitting a quadratic polynomial regression equation by a least square method to obtain a response surface model between the influence factors and the response variables:
wherein: y is a response variable, b is a constant coefficient, and x is an influence variable;
s4) fitting coefficient analysis: performing variance analysis and significance analysis on the quadratic polynomial regression equation and the regression coefficient by using Design Expert software;
s5) determining the optimal process parameters of the model: and obtaining the optimal operating parameters of the influencing variables by optimizing by using Design Expert software and taking the response variables as comprehensive target values.
Optionally, after step S5), the method further includes:
s6) verifying the validity of the model: and under the condition of the optimal operation parameters, verifying by using the composite sewage denitrification process device to obtain the actual response variable value, and calculating the model prediction deviation.
Optionally, the adjusting range of the hydraulic retention time HRT in the step S1) is 2-8, the adjusting range of the sludge volume fraction Vs is 0.2-0.3, and the adjusting range of the carbon-nitrogen ratio C/N is 1-5.
Optionally, the response surface model in step S3) is expressed as:
NR＝68.5+36.24A+1.63B+0.8125C-0.75AB-0.525AC-6.94A 2 -4.11B 2 -1.99C 2
ER＝8-6.5A-5.2B-0.9C+0.5AB+0.45BC+2.58A 2 +3.93B 2 +4.93C 2
CR＝91.62-0.5A+1.69B+2.06C
wherein: a is hydraulic retention time, B is sludge volume fraction, and C is carbon-nitrogen ratio.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects: the invention provides a composite sewage denitrification process device and an operation parameter optimization method.A composite device with an electrode biological carrier arranged inside is constructed, a response surface method design experiment is adopted, the carbon-nitrogen ratio, the hydraulic retention time and the sludge volume fraction are taken as key operation parameters, and a relation model between the key operation parameters and the response variables is established by analyzing three response variables of denitrification efficiency, COD removal efficiency and electrode carrier denitrification contribution ratio to obtain an optimal operation regulation and control scheme; compared with a single-factor optimization method, the method can simultaneously optimize and regulate a plurality of factors, reduce the experiment time and reduce the experiment cost; compared with other optimization methods, the method provided by the invention optimizes the sludge volume fraction of the composite process, and compares the integral performance of the process and the denitrification contribution ratio of the electrode area under different sludge volume fraction conditions; according to the invention, the denitrification contribution ratio of the electrode carrier is taken as the response variable, so that the positive influence of electrode carrier embedding on the process performance can be quantified, and the optimal condition is determined; in a word, the invention can optimize and regulate the operation condition of the composite process, and accelerate the application of the composite process with the built-in electrode biological carrier to the actual sewage treatment process.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a schematic structural view of a composite sewage denitrification apparatus according to an embodiment of the present invention;
FIG. 2 is a flow chart of a method for optimizing operation parameters of a composite sewage denitrification process according to an embodiment of the invention;
FIG. 3 shows nitrate Nitrogen (NO) in an embodiment of the present invention 3 — N) contour plot of the removal rate as a function of C/N and HRT (at 25% sludge volume fraction);
FIG. 4 is a contour plot of COD removal efficiency as a function of C/N and HRT (at 25% sludge volume fraction) for the example of the present invention;
FIG. 5 is a line contour plot of electrode contribution ratio as a function of C/N and HRT (at 25% sludge volume fraction) for an example of the present invention;
fig. 6 is a comparison graph of the predicted value and the actual value of the performance under the condition of the optimal operating parameter according to the embodiment of the present invention.
Description of the reference numerals: 1. a water inlet pipe; 2. an anaerobic sludge zone; 3. an electrode carrier region; 4. an external circuit; 5. a three-phase separator; 6. a water outlet pipe; 7. a first cylindrical tube; 8. a second cylindrical tube; 9. a third cylindrical tube; 10. a fourth cylindrical tube; 11. a fifth cylindrical pipe; 12. a sixth cylindrical tube; 13. a conical tube; 14. and an overflow weir.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
The invention aims to provide a composite sewage denitrification process device and an operation parameter optimization method, which utilize a response surface method to obtain an optimized regulation and control scheme of process operation conditions, can predict the efficiency of processes under different operation conditions, and have the advantages of reducing the experimental workload and shortening the process operation time.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
As shown in fig. 1, a composite sewage denitrification process apparatus provided by an embodiment of the present invention includes: the sampling valve comprises a first cylindrical pipe 7, a second cylindrical pipe 8, a third cylindrical pipe 9, a fourth cylindrical pipe 10, a fifth cylindrical pipe 11, a sixth cylindrical pipe 12 and a conical pipe 13 which are sequentially connected through flanges from top to bottom, wherein the flanges are arranged at the joints between the cylindrical pipes and between the sixth cylindrical pipe 12 and the conical pipe 13, silica gel gaskets are arranged at the flanges and are fixedly connected through screws so as to keep internal sealing, and a sampling valve is arranged in the middle of each section of cylindrical pipe; a water inlet pipe 1 is arranged on the side wall of the fifth cylindrical pipe 11, one end of the water inlet pipe 1 penetrates through the side wall of the fifth cylindrical pipe 11 and extends downwards to the inside of the conical pipe 12, simulated wastewater is introduced into the other end of the water inlet pipe 1 (the device is inoculated by granular sludge of a common sewage treatment plant, the inlet water of the device is simulated wastewater configured by tap water, glucose is used as a carbon source, potassium nitrate is used as a nitrogen source, and trace elements required by growth of other microorganisms are also included), the third cylindrical pipe 9 and the fourth cylindrical pipe 10 form a bioelectrode carrier area 3, the sixth cylindrical pipe 12 and the conical pipe 13 form an anaerobic sludge area 2, a cathode module is arranged at the center inside the third cylindrical pipe 9, an anode module is arranged at the center inside the fourth cylindrical pipe 10, the cathode module, the anode module and an external circuit 4 arranged outside are connected in series to form a loop, a three-phase separator 5 and an overflow weir 14 are arranged at the first cylindrical pipe 7, and the bottom of the overflow weir 14 is communicated with a water outlet pipe 6; when the device is operated, simulated wastewater is fed into the water inlet pipe 1 through a peristaltic pump, is fully filled in the anaerobic sludge area 2, returns and rises, flows into the overflow weir 14 through the first cylindrical pipe 7 after passing through the bioelectrode carrier area 3, and is discharged through the water outlet pipe 6; the sludge inoculation amount, the influent water concentration and the peristaltic pump rotation speed are changed by following orthogonal experimental condition settings.
Wherein the height of the first cylindrical pipe 7 is 15cm, and the inner diameter is 12cm; the heights of the second cylindrical pipe 8, the third cylindrical pipe 9, the fourth cylindrical pipe 10, the fifth cylindrical pipe 11 and the sixth cylindrical pipe 12 are all 20cm, and the inner diameters are all 12cm; the height of the conical tube 13 is 20cm, the inner diameter of the top is 12cm, and the inner diameter of the bottom is 6cm; the distance between one end of the water inlet pipe 1 and the bottom of the conical pipe 13 is 9cm; the cathode module, the anode module and the external circuit 4 are connected in series by adopting titanium wires to form a loop; the cathode module and the anode module are formed by connecting nine carbon fiber brushes in series, and the external circuit 4 is formed by connecting a power supply and a resistor in series; the diameter of each carbon fiber brush is 2.5cm, and the height of each carbon fiber brush is 16cm; peristaltic pumps are arranged at the water inlet pipe 1 and the water outlet pipe 6.
The response surface method is a set of statistical design and numerical optimization techniques, is very effective in problem modeling and analysis in which output or response is affected by a plurality of factors, can analyze the relationship between a plurality of relevant variables and response values, and finally optimizes the response values. The main advantage is that it allows the evaluation of independent variables and their interaction with dependent variables with a reduced number of runs.
As shown in fig. 2, a method for optimizing operation parameters of a composite sewage denitrification process, which applies the composite sewage denitrification process apparatus, comprises the following steps:
s1) designing an orthogonal experiment: selecting a Box-Behnke (BBD) model in Design Expert software, selecting hydraulic retention time HRT, sludge volume fraction Vs and carbon-nitrogen ratio C/N as influence variables, respectively recording the low, medium and high levels of the influence variables as-1 (minimum value), 0 (central value) and +1 (maximum value), corresponding to the adjustment range of the hydraulic retention time HRT of 2-8, the adjustment range of the sludge volume fraction Vs of 0.2-0.3 and the adjustment range of the carbon-nitrogen ratio C/N of 1-5, designing the finally obtained model factor levels as shown in table 1, selecting denitrification efficiency NR, COD removal efficiency CR and electrode carrier denitrification contribution ratio ER as response variables, and obtaining 13 groups of orthogonal experimental schemes;
TABLE 1 design of influence levels
S2) collecting experimental data: based on an orthogonal experimental scheme, more than three sets of composite sewage denitrification process devices are operated, simulated wastewater is fed into a water inlet pipe, hydraulic retention time HRT is set by adjusting the pump speed of a peristaltic pump, sludge volume fraction Vs is set by adjusting the sludge inoculation amount, and carbon-nitrogen ratio C/N is set by adjusting the concentration of the fed simulated wastewater, then water samples are respectively taken at the positions of a water outlet and an electrode carrier region, the concentration of nitrate nitrogen and COD of the water samples is measured, and denitrification efficiency NR, COD removal efficiency CR and electrode carrier denitrification contribution ratio ER are obtained by calculation so as to obtain experimental data of response variables in 13 orthogonal experimental schemes, wherein the experimental data are shown in Table 2;
TABLE 2 orthogonal experimental design and results
The calculation formula of the sludge volume fraction is as follows: the sludge inoculation amount/the total volume of the device is multiplied by 100 percent;
contaminants (COD and NO) 3 — -N) the removal rate comprises: overall COD contaminant removal rate (RE,%) and electrode carrier region NO of the device 3 — -N contaminant removal Rate (RE) e And percent), the calculation formula is as follows:
in the formula: c in The concentration of the inlet water pollutants is mg/L; c ef The concentration of the effluent pollutants is mg/L; c e The concentration of the water inlet pollutant in the electrode carrier area is mg/L;
the electrode area contribution ratio represents the electrode carrier region to NO3 in the device - -N is the ratio of the removal rate to the overall removal rate of the device, and the calculation formula is:
s3) response surface model establishment: importing experimental data of response variables into Design expert software for mathematical analysis, and fitting a quadratic polynomial regression equation by a least square method to obtain a response surface model between the influence factors and the response variables:
wherein: y is a response variable, b is a constant coefficient, and x is an influence variable;
for the denitrification efficiency NR and the electrode carrier denitrification contribution ratio ER, a quadratic model is selected as the most suitable curved surface model modification, and the orthogonal relation between NR, ER and A, B, C is expressed by the following equations respectively:
NR＝68.5+36.24A+1.63B+0.8125C-0.75AB-0.525AC-6.94A 2 -4.11B 2 -1.99C 2
ER＝8-6.5A-5.2B-0.9C+0.5AB+0.45BC+2.58A 2 +3.93B 2 +4.93C 2
for the COD removal efficiency CR, a linear model was chosen as the most suitable curved surface model modification, and the orthogonal relationship between CR and A, B, C is expressed by the equation:
CR＝91.62-0.5A+1.69B+2.06C
wherein: a is hydraulic retention time, B is sludge volume fraction, and C is carbon-nitrogen ratio.
S4) fitting coefficient analysis: using Design Expert software to perform a homogeneity test (F test) of variance and a probability test (P test) on the quadratic polynomial regression equation and the regression coefficient to obtain an analysis of variance result and a significance test result, as shown in table 3;
TABLE 3 analysis of variance
When the Prob > F value of the model analysis result is less than 0.05, the model is shown to be meaningful. From table 3, it can be seen that the model P values of NR and ER are respectively < 0.0001 and 0.0028, both less than 0.05, indicating that the model is significant, and the changes of denitrification efficiency (NR) and electrode carrier denitrification contribution ratio (ER) can be analyzed and predicted more accurately by applying a response curve model. Prob > F values represent important model terms at the same time ((Prob > F) < 0.05), and it can be seen from Table 3 that A, B, A 2 、B 2 、C 2 Is an important model term for NR, A, B, B 2 、C 2 Is an important model term of ER, and can regulate and control the operation parameters according to the influence of each influencing factor on the response value. Model P values for COD removal efficiency (CR) were > 0.0500, indicating that the regression model was not significant, but the linear model fit was higher compared to the P values for the quadratic and cubic models (0.5037 and 0.1655).
FIG. 3 shows NO at 25% sludge volume fraction 3 — Contour plot of N removal at different C/N and HRT, NO 3 — N increases with increasing C/N, and increases and decreases with increasing HRT, optimal NO has been reached around HRT =5h, C/N =4 3 — -N removal 95%. FIG. 4 is a contour plot of COD removal efficiency at different C/N and HRT for 25% sludge volume fraction versus NO 3 — The N removal rate is smaller than the COD removal efficiency, the change range is more than 80%, and the optimal COD removal efficiency of 93% is achieved around HRT =4.6h and C/N = 3. FIG. 5 is a contour diagram of electrode area contribution ratios under different C/N and HRT conditions under the condition that the sludge volume fraction is 25%, wherein the electrode contribution ratio decreases with the increase of C/N and shows a trend of decreasing first and then increasing with the extension of HRT; an optimal electrode contribution of 25% has been reached around HRT =2h, c/N = 2.
S5) determining the optimal process parameters of the model: an Optimization Design module in Design Expert software is used, three response variables are set to be target values, the optimal operation parameter conditions of the composite process are determined to be HRT =6h, C/N =4, and the sludge volume fraction =25%.
After step S5) further comprising:
s6) verifying the validity of the model: under the condition of the optimal operation parameters, verifying by using a composite sewage denitrification process device to obtain an actual response variable value, and calculating the prediction deviation of the model; the composite sewage denitrification process is operated under the condition of the optimal process parameters, the nitric and nitrogen removal rate predicted by responding to the analysis of a curved surface mathematical model is 81.5 percent, the COD removal efficiency is 93.1 percent, and the denitrification contribution ratio of an electrode area is 9.3 percent; the actual results were obtained as: the removal rate of nitric nitrogen is 79.6%, the removal efficiency of COD is 90.1%, and the denitrification contribution ratio of the electrode area is 9.8%. As shown in fig. 6, compared with the actual treatment effect, the predicted values have errors of 2.3%, 3.2% and 5.4%, which are respectively less than the threshold value and within the acceptable range, so that the method for optimally regulating and controlling the operation condition of the composite sewage denitrification process based on the response curve is reliable and effective.
The invention provides a composite sewage denitrification process device and an operation parameter optimization method.A composite device with an electrode biological carrier arranged inside is constructed, a response surface method design experiment is adopted, the carbon-nitrogen ratio, the hydraulic retention time and the sludge volume fraction are taken as key operation parameters, and a relation model between the key operation parameters and the response variables is established by analyzing three response variables of denitrification efficiency, COD removal efficiency and electrode carrier denitrification contribution ratio to obtain an optimal operation regulation and control scheme; compared with a single-factor optimization method, the method can optimize, regulate and control multiple factors simultaneously, reduce the experiment time and reduce the experiment cost; compared with other optimization methods, the method optimizes the sludge volume fraction of the composite process, and compares the integral performance of the process and the denitrification contribution ratio of an electrode area under different sludge volume fraction conditions; according to the invention, the denitrification contribution ratio of the electrode carrier is taken as the response variable, so that the positive influence of electrode carrier embedding on the process performance can be quantified, and the optimal condition is determined; in a word, the invention can optimize and regulate the operation condition of the composite process, and accelerate the application of the composite process with the built-in electrode biological carrier to the actual sewage treatment process.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.
Claims (9)
1. A composite sewage denitrification process device is characterized by comprising: the sampling valve is arranged in the middle of each section of cylindrical pipe; a water inlet pipe is arranged on the side wall of the fifth cylindrical pipe, one end of the water inlet pipe penetrates through the side wall of the fifth cylindrical pipe and extends downwards to the inside of the conical pipe, the other end of the water inlet pipe is connected with simulated wastewater, the third cylindrical pipe and the fourth cylindrical pipe form a bioelectrode carrier area, the sixth cylindrical pipe and the conical pipe form an anaerobic sludge area, a cathode module is arranged at the central position inside the third cylindrical pipe, an anode module is arranged at the central position inside the fourth cylindrical pipe, the cathode module and the anode module are connected with an external circuit arranged outside in series to form a loop, a three-phase separator and an overflow weir are arranged at the position of the first cylindrical pipe, and a water outlet pipe is communicated with the bottom of the overflow weir; the water inlet pipe is used for feeding simulated wastewater, turning back and rising after being filled with the anaerobic sludge area, flowing into the overflow weir in the first cylindrical pipe after passing through the bioelectrode carrier area, and discharging the wastewater through the water outlet pipe;
the composite sewage denitrification process operation parameter optimization method based on the composite sewage denitrification process device comprises the following steps:
s1) designing an orthogonal experiment: selecting a Box-Behnke model in design expert software, selecting HRT (hydraulic retention time), vs (sludge volume fraction) and C/N (carbon-nitrogen ratio) as influence variables, selecting NR (nitrogen removal efficiency), CR (chemical oxygen demand) removal efficiency and ER (electrode carrier nitrogen removal contribution ratio) as response variables, and obtaining more than 10 groups of orthogonal experimental schemes;
s2) collecting experimental data: based on an orthogonal experimental scheme, feeding simulated wastewater into a water inlet pipe, setting hydraulic retention time HRT by adjusting the pump speed of a peristaltic pump, setting sludge volume fraction Vs by adjusting the sludge inoculation amount, and setting carbon-nitrogen ratio C/N by adjusting the concentration of the fed simulated wastewater, then respectively taking water samples at the positions of a water outlet and an electrode carrier region, measuring the concentration of nitrate nitrogen and COD of the water samples, and calculating to obtain denitrification efficiency NR, COD removal efficiency CR and electrode carrier denitrification contribution ratio ER so as to obtain experimental data of response variables in different orthogonal experimental schemes;
s3) response surface model building: performing mathematical analysis on the experimental data of the response variables, and fitting a quadratic polynomial regression equation by a least square method to obtain a response surface model between the influence factors and the response variables:
wherein: y is a response variable, b is a constant coefficient, and x is an influence variable;
s4) fitting coefficient analysis: performing variance analysis and significance analysis on the quadratic polynomial regression equation and the regression coefficient by using DesignExpert software;
s5) determining the optimal process parameters of the model: and obtaining the optimal operating parameters of the influence variables by Optimization by using DesignExpert software and taking the response variables as comprehensive target values.
2. The combined sewage denitrification process device according to claim 1, wherein the first cylindrical pipe has a pipe height of 15cm and an inner diameter of 12cm; the heights of the second cylindrical pipe, the third cylindrical pipe, the fourth cylindrical pipe, the fifth cylindrical pipe and the sixth cylindrical pipe are all 20cm, and the inner diameters of the second cylindrical pipe, the third cylindrical pipe, the fourth cylindrical pipe, the fifth cylindrical pipe and the sixth cylindrical pipe are all 12cm; the height of the conical pipe is 20cm, the inner diameter of the top of the conical pipe is 12cm, and the inner diameter of the bottom of the conical pipe is 6cm; the distance between one end of the water inlet pipe and the bottom of the conical pipe is 9cm.
3. The combined sewage denitrification process unit of claim 1, wherein the cathode module, the anode module and the external circuit are all connected in series by titanium wires to form a loop.
4. The combined sewage denitrification process device according to claim 1 or 3, wherein the cathode module and the anode module are formed by connecting nine carbon fiber brushes in series, and the external circuit is formed by connecting a power supply and a resistor in series.
5. The combined sewage denitrification process device according to claim 4, wherein the carbon fiber brushes are all 2.5cm in diameter and 16cm in height.
6. The combined sewage denitrification process device according to claim 1, wherein peristaltic pumps are arranged at the water inlet pipe and the water outlet pipe.
7. The combined sewage denitrification process apparatus according to claim 1, further comprising, after step S5):
s6) verifying the validity of the model: and under the condition of the optimal operation parameters, verifying by using the composite sewage denitrification process device to obtain the actual response variable value, and calculating the model prediction deviation.
8. The combined sewage denitrification process device according to claim 1, wherein the hydraulic retention time HRT in step S1) is adjusted within a range of 2 to 8, the sludge volume fraction Vs is adjusted within a range of 0.2 to 0.3, and the carbon-nitrogen ratio C/N is adjusted within a range of 1 to 5.
9. The combined sewage denitrification process apparatus according to claim 8, wherein the response surface model in step S3) is expressed as:
NR＝68.5+36.24A+1.63B+0.8125C-0.75AB-0.525AC-6.94A 2 -4.11B 2 -1.99C 2
ER＝8-6.5A-5.2B-0.9C+0.5AB+0.45BC+2.58A 2 +3.93B 2 +4.93C 2
CR＝91.62-0.5A+1.69B+2.06C
wherein: a is hydraulic retention time, B is sludge volume fraction, and C is carbon-nitrogen ratio.
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