Assessment of Effective Operational Parameters on Removal of Amoxicillin from Synthetic Wastewater Using Electrocoagulation Process

In this study, efficiency of electrocoagulation (EC) process with aluminum electrodes for treatment of Amoxicillin (AMO) from synthetic solution has been studied and concluded. This experiment was conducted in a batch system with a volume of 1 L that had been equipped with four aluminum electrodes. The effect of operating parameters, such as voltage, time of reaction, initial AMO concentration, KCl concentration and pH on the AMO removal efficiency was investigated. In optimum condition (pH 7, voltage 60 V, electrolysis time 75 min, KCl concentration 3 g/L), electrocoagulation method was able to remove 98.8% of AMO antibiotics from synthetic solution. In addition, it is found that an increase in the applied voltage the speed of the treatment significantly. However, simultaneous increase of electrode and energy consumption was observed. The method was found to be highly efficient and relatively fast compared to conventional existing techniques and also, it can be concluded that the electrocoagulation process has the potential to be utilized for the cost-effective removal of AMO from water and wastewater. Original Research Article Balarak et al.; JPRI, 29(1): 1-8, 2019; Article no.JPRI.50457 2


INTRODUCTION
Pollution of water resources by different pollutants is nowadays a global environmental issue [1]. Traditionally, the impact of chemical pollution has focused almost exclusively on the conventional priority pollutants [2]. However, the growing use of pharmaceuticals worldwide, classified as the so-called emerging pollutants, has become a new environmental problem, which has raised great concern among scientists in the last few years [3,4].
Most of these pharmaceuticals commonly in use are antibiotics which are defined as chemical compounds with antibacterial properties [5,6]. In recent years, the undue use of these antibiotics in human and veterinary medicine are widespread and consequently, the possibility of environmental matrices contamination with these compounds increased [7,8]. Therefore, the use of antibiotics and growth hormones has a significant effect on the quality of surface and groundwater [9]. Amoxicillin (AMO) is a drug belonging to the class of semi-synthetic b-lactam antibiotic that has a broad spectrum against both Gramnegative and Gram-positive bacteria [10]. AMO is one of the top-priority human and veterinary pharmaceuticals, and should receive greater attention in the management of environmental systems in Iran due to its high consumption [11]. AMO belongs to a group of drugs that are predominantly excreted in an unmetabolized form, and some investigations have reported that AMO might present a possible chronic risk in the aquatic environment [12,13].
Even low concentrations of pharmaceuticals released from the environmental matrix into water can pose serious environmental damages. Thus, it is of great importance to develop some efficient and cost-effective treatment technologies to remove such compounds [14,15].
Various techniques such as ozonation, photo-Fenton process, photo electro-catalytic degradation, ion exchange and adsorption have been employed for the removal of antibiotics from aqueous solution and Pharmaceutical wastewater [16][17][18].
Electrocoagulation (EC) process is an alternative of the conventional coagulation process in which coagulant agents are generated in situ through the dissolution of a sacrificial anode by applying current between the anode-cathode electrodes [19,20]. The electrocoagulation process has several advantages that make it attractive for treating various contaminated streams [21,22]. In the past decades electrocoagulation has been applied for the treatment of many kinds of wastewater [23]. The pollutant is coagulated by aluminum hydrates or hydroxides produced from the sacrificial anode [24].
An examination of the chemical reactions occurring in the EC process shows that the main reactions occurring at the aluminum electrodes are [25]: The present work was carried out to study the removal of AMO by EC with aluminum electrodes from synthetic wastewater. Wastewater parameters, such as reaction time, high salt concentration, voltage, initial concentration of AMO, and pH, were also investigated to examine their effects on the AMO.

MATERIALS AND METHODS
At present study all chemicals including AMO, sodium hydroxide (NaOH), concentrated sulfuric acid (H2SO4) and potassium chloride (KCl) were used as analytical grade. Analytical grade AMO was obtained from Sigma Aldrich Co. The chemical structure of AMO (CAS number: 26787-78-0, molecular weight: 365.4 g/mol, Molecular Formula C16H19N3O5S, Solubility in water: 3430 mg/L at 20°C and Henry's law constant: 27.3 L.atm/mol at 20°C) is shown in Fig. 1. A stock AMO solution was obtained by dissolving 1 g of AMO, (99%), in deionized distilled water and dilute to 1000 mL.
Desired concentrations of AMO solutions (10, 25, 50 and 100 mg/L) were prepared by diluting proper amount of stock solution with deionized water. In order to survey the effect of electrical conductivity of the solution on AMO removal efficiency, the experiments was performed at various voltage (10, 20, 40, 60 V) with adding proper amount of potassium chloride before injecting solution into the EC reactor. The chloride salt added to the solution can also prevent the formation of the oxide layer on the anode and therefore reduce the passivation problem of the electrodes. Also, the pH of influent solution was adjusted to a desired value [3,5,7 and 9] using H 2 SO 4 and NaOH solutions (0.1 M).

Fig. 1. Chemical structure of the used AMO
Experiments were performed in a bipolar batch reactor (Fig. 2), with aluminum electrode installed parallel to each other. Only the outer electrodes were connected to the power source, and anodic and cathodic reactions occurred on each surface of the inner electrode when the current passed through the electrodes. The Plexiglas cell as electrolytic reactor having dimensions of 12.5 cm×12.5 cm×15 cm with a working volume of about 1 L was used to conduct the experiments, and a magnetic stirrer was applied for mixing (100 rpm). Aluminum sheets with the dimensions of 0.12 m× 0.12 m × 0.0025 m were also used as electrodes.
Between two tests, electrolytic cell (including the electrodes) was cleaned with 15% (W/V) hydrochloric acid solution. The gap between the anode and cathode was 2.5 cm. A Single-output Adjustable DC Power Supply (MPS-3005D) was used as the power supplier. Retention time, pH, voltage, and initial AMO, KCl concentrations were selected as parameters. At different time intervals, the samples were taken from the reactor and centrifuged for 10 min at 3600 rpm before analysis. The concentration of AMO in a solution was measured using an HPLC (C18 ODS column) with a UV detector 2006 at a wavelength of 190 nm. The mobile phase was a mixture of buffer phosphate with pH= 4.8 and acetonitrile with a volumetric ratio of 60/40 with an injection flow rate of 1 mL/min. The equation used to calculate the AMO percent recovery in the treatment experiment was [26]: Where: C o and C e are initial and equilibrium concentration respectively in (mg/L). Electric energy consumption was also calculated using the commonly used equation [27]: E= Where E is the energy consumption (KWh/m 3 ), U is the applied voltage (V), I is the current intensity (A), T is the EC time (h), and V is the volume of the treated wastewater (L).  Fig. 3 the relation between the percentage removal of AMO and initial solution concentration. The percentage removal was gradually decreased from 98.82 to 74.3% as the AMO concentration increased from 10 to 100 mg/L. This may be attributed to the fact that at a constant current density the same amount of aluminum ions passes to the solution at different AMO concentrations [28]. Consequently, the formed amount of complex aluminum hydroxide was insufficient to coagulate the greater number of AMO molecules at higher AMO concentrations [29]. On the other hand, the decrease in removal efficiency with increasing initial AMO concentration may be attributed to requiring more coagulant when increasing levels of pollutant [30].

RESULTS AND DISCUSSION
The EC time is a significant parameter which has a vital importance and influence on the performance of EC process [28]. In this experiment the effect of time was studied at constant distance 2.5 cm. Fig. 3 illustrates the effect of retention time on the removal of AMO at neutral pH. In this process, EC involves two stages which are destabilization and aggregation. The first stage is usually short, whereas the second stage is relatively long. Results show that the efficiency start to be significant at the treatment time of 60 minutes but the maximum efficiency was obtained at a treatment time of 90 minutes. EC time has significant improvement in removal efficiency. It is assumed that the more time consumed, the more production rate of hydroxyl and AMO ions on the electrodes [31].
In all electrochemical processes, the applied voltage is one of the important parameters to control reaction rate in electrochemical reactors. As shown in Fig. 4, removal efficiencies of the studied AMO improved with an increase in voltage. In fact, at low voltages, less aluminum hydroxides were produced, thus the lower removal efficiencies; however, production of aluminum hydroxides improved as the voltage increased, which raised the removal efficiencies It has been established that the pH has a considerable influence on the performance of EC process. Therefore, pH [3,5,7 and 9] was examined as one of the main variables affecting removal of AMO from synthetic solutions. The results are shown in Fig. 7; the efficiency of AMO removal was low either at low pH or at high pH. The average AMO removal increased from 76.2.0% to 98.2.0% when the pH was increased from 3 to 7. Further increasing the pH to 9 resulted in a reduction of AMO removal efficiency to 79.4%. This behavior was attributed to the amphoteric character of aluminum hydroxide which does not precipitate at very low pH [24]. Moreover, high pH leads to the formation of Al(OH) 4 , which is soluble and useless for adsorption of AMO [25]. Therefore, further increase of the influent pH would decrease the AMO removal efficiency.

CONCLUSION
In this research, the removal efficiency of EC process by means of aluminum electrodes for Removal of AMO in batch system was studied.
The results showed that the highest AMO removal efficiency was 98.8%, at the optimized conditions of pH of 7, initial AMO concentration of 10 mg/L, voltage of 60 V, electrolysis time of 75 min and distance of approximately 2.5 cm.
The removal efficiency increased with the increase in KCl concentration. It can be concluded that the EC process by aluminum electrodes is an efficient method for reactive AMO removal from colored solutions.

CONSENT
It is not applicable.

ETHICAL APPROVAL
It is not applicable.