Removal of ciprofloxacin from hospital wastewater using electrocoagulation technique by aluminum electrode: Optimization and modelling through response surface methodology

https://doi.org/10.1016/j.psep.2017.04.026Get rights and content

Highlights

  • Hospital wastewater were used for real sample analysis in the current work.

  • Removal of CIP was successfully optimized using response surface methodology.

  • Electrical energy consumption at optimum operating conditions was 0.613 kWh m−3.

Abstract

Pharmaceuticals as severe contaminants of surface and ground water around the manufacturing communities and residential zones received growing attention recently. Since, there is no report on ciprofloxacin (CIP) removal using electrocoagulation (EC) process by aluminum electrodes, the present work deals with efficient removal of CIP from hospital wastewater using mentioned method. Response surface methodology (RSM) was used to evaluate the main effects of parameters, their simultaneous interactions and quadratic effect to achieve the optimum condition for EC process. According to the obtained results from regression analysis, it was found that the experimental data are best fitted to the second-order polynomial model with coefficient of determination (R2) value of 0.9086, adjust correlation coefficient (Adj. R2) value of 0.8796 and predicted correlation coefficient (pred. R2) value of 0.7834. EC process was applied successfully with removal efficiency of 88.57% under optimal operating condition of pH 7.78, inter-electrode distance 1 cm, reaction time 20 min, current density 12.5 mA cm−2 and electrolyte dose of 0.07 M NaCl with the initial CIP concentration of 32.5 mg L−1. The experimental efficiency was in satisfactory agreement with the predicted efficiency of 90.34%. The obtained results revealed that, sweep flocculation as a determinant mechanism controlled the adsorption of CIP molecules on aluminum hydroxide precipitates. Electrode consumption and electrical energy consumption were found to be 66.80 g m−3 and 0.613 kWh m−3, respectively. The obtained results from real sample analysis revealed that the initial CIP concentration of 154 ± 6 μg L−1 of hospital wastewater were found to reached to zero after applying optimal condition of EC process.

Graphical abstract

Major pathways of antibiotics release into the environment which cause antibiotic resistance for human.

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Introduction

The 1960s was a decade that for the first times the presence of pharmaceuticals and personal care products (PPCPs) were diagnosed in surface waters in United States and Europe. Antibiotics as one of the most widely used PPCPs are approximately 90% excreted in urine and up to 75% in animal excrement, entering to the wastewater system as their parent forms (El-Shafey et al., 2012). Ciprofloxacin (CIP) as a synthetic antibiotic has been widely used for treatment of bacterial infectious disease in humans and animals. It is noteworthy to mention that drug manufacturers and hospitals are the most important sources of contaminated wastewaters. Inappropriate disposal of unused or expired CIP and its incomplete metabolization severely results in its increasing contamination in surface water during the last decade (Dewitte et al., 2008, El-Shafey et al., 2012). According to the statistics presented by the health communities, the amount of CIP contamination discerned in surface water and underground water were within the concentration range of 1˂ μg L−1, respectively. However, the detected amount of CIP in the wastewater of hospitals and drug manufacturers is much higher up to 150 μg L−1 and 50 mg L−1, respectively, which is extremely harmful to the health of the human beings (El-Shafey et al., 2012). Most of the conventional treatments such as activated sludge and trickling filter applied in wastewater treatment plants were unsuccessful which results in releasing them in environment and consequently contamination of surface water, soil and ground water. It is reported that the presence of CIP in daily drinking water may cause nervousness, nausea, vomiting, headaches, diarrhea and tremors. Higher concentrations may cause serious adverse effects including thrombocytopenia, acute renal failure, and elevation of liver enzymes, eosinophilia and leucopenia. On the other hand, the presence of CIP in water sources results in development of bacteria resistant to antibiotics which seriously emerging threat to public health and requires action across all government sectors and societies (Bajpai et al., 2012, Wang et al., 2010, Wu et al., 2010, Zaidi et al., 2016). The treatments of resistant bacteria are difficult, costly and toxic which require alternative medications or higher doses (Somayajula et al., 2012, Vasudevan, 2014, Vasudevan et al., 2011a, Vasudevan et al., 2011b) (Fig. 1).

Literature surveys revealed that developing an efficient and economical procedure for CIP contamination removal from drinking water supply and wastewaters before releasing them into the environment received a great attention, recently. Since CIP is resistant to microbial metabolism, it cannot be efficiently degraded by means of biological treatment processes (Palmisano et al., 2015). Several techniques such as adsorption (Gandhi et al., 2016, Kamaraj et al., 2015, Kamaraj et al., 2014a, Kamaraj et al., 2014b, Kamaraj et al., 2017, Kamaraj and Vasudevan, 2016), advanced oxidation process (Dewitte et al., 2008), have been studied for removal of CIP from the contaminated water. However, among all of them electrochemical techniques such as electrocoagulation (EC) as an advanced, efficient and economical technique received extensive practical applicability by providing satisfactory result for treating various wastewater contaminants such as heavy metals (Kamaraj and Vasudevan, 2015), fluoride (Emamjomeh and Sivakumar, 2009), dyes (Daneshvar et al., 2006), drug (Khandegar and Saroha, 2013a), phenol (Vasudevan, 2014). EC technique included coagulation process in which coagulant agent gets produced in situ through electrochemical reactions of sacrificial anode dissolution (Khandegar and Saroha, 2013b). Electro-synthesized of coagulant provide competitive advantages of producing less sludge thus lowering the sludge disposal cost, removing many species that chemical coagulation cannot remove and the produced sludge is more readily filterable and can be utilized as a soil additive. Other considerable advantages of EC technique including low cost process and maintenance, no harmful substances generation, producing low amount of TDS and secondary pollutants and removing the smallest size of colloidal particles caused its increasingly usage. However, it does not require any chemical storage like adsorption or biological processes. Besides the current studies using electrochemistry, on the other hand, using electrochemical sensors as a device which provides a certain type of response that is directly related to the quantity of a chemical species such as contaminants, showed a rapid growing scientific studies in environmental monitoring field and practiced by the current research group recently (Ahmadzadeh et al., 2015a, Ahmadzadeh et al., 2015c, Fouladgar and Ahmadzadeh, 2016, Kassim et al., 2011, Pardakhty et al., 2016, Rezayi et al., 2014, Soltani et al., 2016).

To the best of our knowledge, there is not any report on CIP removal using EC process by aluminum electrodes. So far only one report based on EC process was found for CIP removal from aqueous solution using iron electrode (Barışçı and Turkay, 2016). However, the reported EC process suffered from low removal efficiency for CIP contaminants in its optimized concentration of 5 mg L−1 in compare to the current work with optimized concentration of 32.5 mg L−1 CIP contaminants. Hence developing of EC process using aluminum electrodes can be regarded as a new and potential research area for CIP contamination removal from hospital and industrial wastewater. Since, most of the reported studies are based on one factor at the time method, in the current study, RSM was used to evaluate the main effects of parameters, their simultaneous interactions and quadratic effect to achieve the optimum condition for EC process. The effects of various operating parameters such as electrolyte type and concentration, inter-electrode distance, initial CIP concentration, pH, current density and reaction time were investigated to achieve the best efficient and CIP contamination remove condition.

Section snippets

Chemicals

CIP (C17H18FN3O3·HCl·H2O, 385.8 mol wt.) purchased from Darou Pakhsh Pharmaceutical Company, Mashhad, Iran. The mobile phase was prepared using HPLC grade acetonitrile and analytical grade hydrochloric acid. Electrolytes including MgSO4, NaCl, KNO3, Na2SO4, and CaCl2 were purchased from Merck Company. Hydrochloric acid and sodium hydroxide from Sigma-Aldrich were used for pH adjustments. Acetic acid and ethanol were obtained from Merck Company. All reagents used are analytical reagent grade with

Preliminary evaluation of electrocoagulation process

The effect of electrolyte type and concentration on the removal efficiency of CIP were investigated. The maximum removal was obtained using NaCl as electrolyte at equilibrium time of 20 min (see Fig. 2). Literature surveys revealed that addition of appropriate electrolyte significantly improved the efficiency of EC process due to increasing the conductivity of the wastewater which affects the Faradic yield, cell voltage and consequently energy consumption of the process.

The presence of NaCl

Conclusions

The current work was aimed to investigate the effect of independent variables on the removal efficiency of CIP from hospital wastewater using response surface methodology. The experimental obtained results revealed that under optimal condition of pH 7.78, inter-electrode distance 1 cm, reaction time 20 min, current density 12.5 mA cm−2 and electrolyte dose of 0.07 M NaCl with the initial CIP concentration of 32.5 mg L−1, the CIP removal efficiency of 88.57% was achieved which is in satisfactory

Acknowledgments

The authors express their appreciation to Neuroscience Research Center and Pharmaceutics Research Center both affiliated to Institute of Neuropharmacology, Kerman University of Medical Sciences, Kerman, Iran.

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