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In this paper, a new ferric chloride(polyvinylpyrrolidonegraftedpolyacrylamide) hybrid copolymer was successfully synthesized by free radical polymerization in solution using ceric ammonium nitrate as redox initiator. The hybrid copolymer was characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Response surface methodology (RSM), involving central composite design (CCD) matrix with two of the most important operating variables in the flocculation process; hybrid copolymer dosage and pH were utilized for the study and for the optimization of the wastewater treatment process. Response surface analyses showed that the experimental data could be adequately fitted to quadratic polynomial models. Under the optimum conditions, the turbidity and chemical oxygen demand (COD) removal efficiencies were 96.4% and 83.5% according to RSM optimization, whereas the optimum removals based on the genetic algorithm (GA) were 96.56% and 83.54% for the turbidity and COD removal models. Based on these results, wastewater treatment using this novel hybrid copolymer has proved to be an effective alternative in the overseeing of turbidity and COD problems of municipal wastewater.
Coagulationflocculation is one of the chemical treatment processes commonly used for water and wastewater. It has a wide range of application in water and wastewater facilities because it is efficient and simple to operate [
The addition of inorganic salts to organic flocculants was suggested as the main method of preparing hybridflocculants [
The traditional method of experimentation involves changing one factor at a time. This conventional method of experimentation requires many experiments, which are not only timeconsuming, but also lead to low efficiency of optimization. To find a solution to this problem, design of experiment (DOE) has been employed to study the effect of variables and their responses using a minimum number of experiments. Response surface methodology (RSM) is a collection of statistical and mathematical methods which are useful for developing, improving, and optimizing processes [
Genetic algorithm (GA) is defined as a search technique used in computing to find out the exact or estimated solution in order to optimize and investigate the problem. GAbased optimization is a stochastic search method that involves random generation of positional design solutions which it systematically evaluates and refines until a stopping criterion is met [
In this research, the hybrid copolymer ferric chloride(polyvinylpyrrolidonegraftedpolyacrylamide) (FeCl_{3}(PVPgPAM)) was successfully synthesized by free radical polymerization and characterization of the novel hybrid copolymer was carried out using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Moreover, the possible effectiveness of utilizing the hybrid copolymer was investigated as an alternative flocculent in wastewater treatment to remove turbidity and chemical oxygen demand (COD) from that water. This paper also targeted the use of a genetic algorithm with RSM to find the optimal parameters and to investigate the promoted effectiveness of predication for removal of pollutants from wastewater.
Acrylamide (AM) was purchased from Amresco (Solon, OH, USA). Ferric chloride (FeCl_{3}) was provided by Shanghai Chemicals Reagent Corp. (Shanghai, China). Polyvinylpyrrolidone (PVP) was obtained from Shanghai Zhanyun Chemical Co., Ltd (Shanghai, China). Ammonium cerium (IV) nitrate (CAN) was supplied by Sinopharm Chemicals Reagent Co. Ltd (Beijing, China). Acetone used was of analytical regent grade.
The hybrid copolymer was synthesized by a ceric ioninduced redox initiation method according to the following steps: One gram of polyvinylpyrrolidone (PVP) was dissolved in 100 mL of distilled water at ambient temperature in a 500 mL threenecked flask, stirred with a mechanical stirrer and equipped with a thermostatic water bath, nitrogen line, a reflex condenser, and a rubber septum gap. After that, the system was purged with nitrogen for 30 min to remove the dissolved oxygen from the solution. Then, 0.1 mol of acrylamide and 0.55 mmol of ammonium cerium (IV) nitrate were added to the polymerization system under atmospheric nitrogen. The polymerization reaction was carried out for 2 h at 60 °C. To this, a solution, 1 M of ferric chloride (prepared in 50 mL of distilled water) was added to the polymerization flask at 60 °C and mixed with constant stirring under a nitrogen atmosphere for 3 h. Finally, the produced gel was cooled to ambient temperature, precipitated in acetone, and dried in a vacuum oven at 60 °C to constant weight.
The Fourier transform infrared (FTIR) spectra were measured on a Nexus FTIR spectrophotometer (Thermo Fisher Scientific Inc., Waltham, MA, USA) using the KBr pellet method. The IR spectra were recorded within the range of 4000–400 cm^{−1}. The morphology of the hybrid copolymer surface was investigated using scanning electron microscope (SEM) images with different magnification obtained from a QUANTA 200 scanning electron microscope (FEI Company, Hillsboro, OR, USA).
The samples of wastewater in this study were collected from the sewer system network in the east campus at the China University of Geosciences (Wuhan). The wastewater samples were transported to the laboratory within 20 min and then characterized there for turbidity, COD and pH. The measured values of the wastewater sample for the flocculation experiments were as follows: Turbidity 305 NTU, COD 368 mg/L, and pH 7.4.
The jar test used in our experiments was a programmable apparatus (TA6, Wuhan, China). It consisted of six paddles on a bench. The paddles were connected to each other by a gear mechanism, and all of these paddles were simultaneously rotated by the same motor at a controlled speed and time.
Wastewater samples of 1000 mL each, were transferred to the jars and then pH adjusted using 0.5 M HCl or 0.5 M NaOH solutions. The required dose of FeCl_{3}(PVPgPAM) hybrid copolymer was added to each beaker. Directly after the addition of the hybrid copolymer dosage, the wastewater sample in the jar was stirred rapidly at a paddle speed of 120 rpm for 2 min then stirred slowly at a paddle speed of 30 rpm for 20 min, and finally, the treated wastewater was allowed to settle for 30 min.
The removal of the pollutants (COD and turbidity) was calculated according to the following formula:
Response surface methodology is a statistical method frequently used in designing experimental, building models, for evaluating the effects of several factors and to find the optimum conditions for desirable responses as well as to reduce the number of experiments [
The independent variables (factors) were hybrid copolymer dosage (denoted by
Experimental factor levels for independent variables.
Variables (Factors)  Symbol  Real values of coded levels  

Low level (−1)  Center level (0)  High level (+1)  
Dose (mg/L) 

50  100  150 
pH 

5  7  9 
The second order polynomial equation is used to prove the relationship between the factors (
The IR spectra of the hybrid copolymer are shown in
Fourier transform infrared spectroscopy (FTIR) spectra of the ferric chloride(polyvinylpyrrolidonegraftedpolyacrylamide)(FeCl_{3}(PVPgPAM)) hybrid copolymer.
The technique used for studying the surface morphology of the polymers is scanning electron microscopy (SEM). The SEM images obtained for the FeCl_{3}(PVPgPAM) hybrid copolymer as shown in
Scanning electron microscopy (SEM) images for FeCl_{3}(PVPgPAM) at different magnification.
Response surface methodology was used to determine the relationship between the flocculation process responses (turbidity and COD removals) with the most important variables (hybrid copolymer dosage and wastewater pH). A total of ten experiments was carried out as mentioned before and their results are shown in
Experimental variables and results for wastewater flocculation.
Run No.  Coded variables  Real variables  Results  

Dose  pH  Dose (mg/L)  pH  Turbidity Removal (%)  COD Removal (%)  
1  1  −1  150  5  91  72 
2  −1  1  50  9  78  50 
3  0  0  100  7  93  83 
4  −1  −1  50  5  83  54 
5  0  −1  100  5  89  70 
6  1  0  150  7  97  84 
7  1  1  150  9  86  63 
8  0  1  100  9  85  62 
9  −1  0  50  7  88  60 
10  0  0  100  7  95  80 
Analysis of variance (ANOVA) with an alpha (
Analysis of variance (ANOVA) results showing the terms in each response quadratic model.
Response  Source  Sum of Squares  df  Remark  

Turbidity removal 

104.17  1  128.68  0.0003  significant 

32.67  1  40.35  0.0031  significant  

0.000  1  0.00  1.0000  not significant  

10.01  1  12.37  0.0245  significant  

133.76  1  165.24  0.0002  significant  
COD removal 

504.17  1  57.02  0.0016  significant 

73.50  1  8.31  0.0449  significant  

6.25  1  0.71  0.4478  not significant  

136.30  1  15.41  0.0172  significant  

434.30  1  49.12  0.0022  significant 
Notes:
To evaluate the quality of the model developed, the coefficient of determination (
As shown in
ANOVA results for response models.
Response  Probability 

Adj. 
Pred. 
Adeq. precision  CV% 

0.0005  0.9892  0.9758  0.9466  26.169  1.02  
0.0032  0.9726  0.9383  0.7469  14.859  4.39 
Notes:
The measures of the adequate precision for the response models were 26.169 and 14.859 for the turbidity and COD removal models. These values represent the measures of the signal to noise ratio [
(
(
The 3D surface plots for each model show the responses of experimental variables and these graphs can be used to identify the major interaction between the variables. The 3D surface plot and contour plot for the turbidity removal model (
3D surface plot for (
2D contour plot for (
The common turbidity removal mechanism ensues by neutralizing the negative charge of particles and the positive charge of metal hydrolysis species followed by the aggregation of destabilized particles. There are other mechanisms for turbidity removal that take place by forming flocs composed of metal hydroxide precipitates accompanied or followed by sweep flocculation of colloidal particles [
The 3D surface plot and contour plot for the COD removal model (
The optimal conditions for maximum turbidity and COD removals were determined by the response model obtained from the experimental data. A desirable function was used to find the optimum condition for the two variables, of hybrid copolymer dosage and wastewater pH, in the study of the flocculation process of wastewater. In RSM, the desirability function was set as follows: maximum process removal with the range of hybrid copolymer dosage and within the pH range (5–9). By assay of 39 results of starting points in the optimization of RSM, the best optimum removal efficiency for turbidity and COD removal was 96.4% and 83.5% respectively. This optimum removal was acquired at the desirability function of 0.978 with the design variables as follows: hybrid copolymer dosage of 137 mg/L at wastewater pH 6.68.
Using an optimization technique from the Matlab optimization toolbox, GA was applied to the quadratic equations for turbidity and COD removal models to optimize the variables and responses. The removal optimization can be stated as follows:
Plot of fitness value
To select the best optimum removal efficiency with the lowest cost, a comparison of optimization between the desirable function in RSM and the GA results in terms of variables and the optimum removal efficiency is shown in
The optimized hybrid copolymer dosage of (137 mg/L) for the best predicted turbidity removal can be contributed to a predication of 96.4% for the turbidity removal according to the desirable function in RSM optimization. Whereas, the optimized hybrid copolymer dosage of (130 mg/L) for best predicted COD removal can be contributed to a predication of 83.54% for COD removal based on GA optimization.
Comparison between the desirable function and GA optimization techniques for optimum variables and predication for pollutants removal.
Model  Optimized Technique  Optimal Dose (mg/L)  Optimal pH  Best predicted Removal (%) 


Desirable function  137  6.68  96.40 
Genetic algorithm  150  6.69  96.56  

Desirable function  137  6.68  83.50 
Genetic algorithm  130  6.74  83.54 
Finally, three extra experiments were conducted under the optimum condition to confirm the validity of the statistical experimental strategies. The obtained removal results of these three experiments were close to those estimated by using response surface methodology. These validation experiments proved that the developed models could be considered to be accurate and reliable.
Physicalchemical methods are fast wastewater treatment processes. One such physicalchemical method is flocculation in which many types of commercial and conventional flocculants can be used. In this study, a new hybrid copolymer was synthesized, characterized and employed in wastewater treatment. The novel hybrid copolymer was accomplished by focusing on the influence of two important operating variables: hybrid copolymer dosage and wastewater pH. The experiments of the flocculation process were utilized by RSM. The results were arrived at by applying RSM modeling that had been verified by conducting analysis of variance (ANOVA). The effects of both hybrid copolymer dosage and wastewater pH on the optimal operational conditions are discussed according to the desirable function and GA optimization techniques. Under these optimized conditions, the removal efficiencies according to RSM optimization using the desirable function were 96.4% and 83.5% for turbidity and COD removal models respectively. The optimized desirability function was 0.978. GA optimization established the best prediction of 96.56% for turbidity removal and 83.54% for COD removal.
The financial support for this work from China University of Geosciences (Wuhan, China) is gratefully acknowledged.