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Environmental Engineering and Management Journal September 2014, Vol.13, No. 9, 2337-2342
"Gheorghe Asachi" Technical University of Iasi, Romania
DECONTAMINATION OF SYNTHETIC WASTEWATER CONTAINING
PHARMACEUTICAL CONTAMINANTS BY ANODIC OXIDATION
WITH BORON- DOPED DIAMNOND (BDD) ELECTRODE
Carmen Ionela Brînzilă1,2, Maria Jose Pacheco2, Lurdes Ciríaco2,
Romeo Cristian Ciobanu1, Ana Lopes2
1"Gheorghe Asachi" Technical University of Iasi,Faculty of Electrical Engineering, Energetic and Applied Informatics, RO-700050, Iasi, Romania 2University of Beira Interior, Department of Chemistry, 6201-001 Covilhã, Portugal
Abstract

Tetracycline (TC) are used as bacteriostatic agents, inhibits the synthesis of bacterial proteins, with activity against a wide variety
of organisms with application in human and veterinary medicine. The presence of TC in the environment constitutes a serious
problem, being weakly metabolized or absorbed into the human or animal body con. TC residues even in low concentration may
produce serious toxic and other effects on humans and living organism. In this study are presented the applications of
electrochemical advanced oxidation processes (EAOPs) for degradation of TC using de BDD electrode. The influence of
experimental parameters (COD, TOC, nitrogen (total Kjeldhal, organic and inorganic), HPLC and UV-Vis spectrophotometry) on
electrochemical degradation is evaluated. A pseudo-first kinetic order is obtained for electrochemical reactions with BDD. Model
TC solutions is used and different experimental conditions, namely, initial concentration, initial pH, applied current density, type
and concentration of the electrolyte, is also tested. To study the influence of the experimental conditions on the degradation of the
antibiotic, assays was been running at experimental conditions that allow kinetic and/or diffusive control, in order to determine
medium mass transfer coefficients that help to predict degradation rates at experimental conditions other than those tested.
Key words: anodic oxidation, BDD, pharmaceutical compounds
Received: March, 2014; Revised final: August, 2014; Accepted: September, 2014

1. Introduction
widely prescribed due to its characteristics as broad spectrum antibiotic. Due to its large use, residues of Part of the ingested antibiotics goes directly tetracycline have already been detected in surface to the environment, excreted in the urine, faces and waters that received discharges from municipal manure, as parent compounds or by-products. wastewater treatment plants and agricultural drained Leftover feed supplemented with antibiotics can also (Brinzila et al., 2012; Kümmerer, 2009). go directly to the soil and ground water of the Tetracycline was considered the second surrounding environment. most common antimicrobial, with applications in The presence of those antibiotics in the human therapy, veterinary medicine and aquaculture environment can lead to hazardous events, since their (Hirsch et al., 1999, 2002; Jeong et al., 2010). presence in streams, lakes and water supplies may Detectable levels of tetracycline was obtained in lead to the growth of multi-resistant bacteria in the several rivers and streams from many parts of the animals themselves, in humans and in wildlife. U.S. (Kolpin et al., 2002), proving that their sorption Among veterinary antibiotics, tetracycline family is in solids is not irreversible, thus favoring their  Author to whom all correspondence should be addressed: [email protected] Brinzila et al./Environmental Engineering and Management Journal 13 (2014), 9, 2337-2342
mobility in the environment. Residues of tetracycline used. Thus, in the present study, it is proposed the were already detected in surface waters that received degradation of tetracycline using a boron-doped discharges from municipal wastewater treatment diamond (BDD) electrode, a non-active anode plants and agricultural drained (Boxall et al., 2003; (Ciriaco et al., 2009; Panizza et al., 2009; Sires et al., Hirch et al., 1999; Kolpin et al., 2002). For these 2013) on whose surface hydroxyl radicals are formed reasons, the elimination of antibiotics from the from water discharged, being the main species terrestrial and aqueous resources is an emergent goal responsible for the oxidation of the pollutants. and, in the last years, several studies on the degradation of tetracycline, using different 2. Experimental
technologies, were conducted (Hirsch et al., 2002). Decontamination of waters containing The tetracycline used (C22H24N2O8.xH2O)
tetracycline was studied using activated sludge from Sigma Aldrich (purity 99%) and it was used processes and the obtained results strongly suggest without further purification. Experimental conditions that tetracycline was mainly removed due to a of degradation assays: reactor- up-flow reactor, bach sorption mechanism, being the biodegradation mode with recirculation, anode – BDD, 20 cm2, process of minor relevance (Boxall et al., 2003). cathode – stainless steel 20 cm2, distance between Thus, due to tetracycline biorefractory nature there electrode 1 cm, current density – 30 mA/cm2, are a few studies reported in the literature using Tetracycline concentration – 100 ppm, supporting advanced oxidation processes, as an alternative to electrolyte – 0.035 M Na2SO4 , volume of solutions – conventional biological treatment, for the 200 mL, at room temperature. A Concessus type degradation of these compounds. The application of pump was used for recirculation of the solution that allowed the use of different flow rates, varying from 2 nanopore arrays electrode in the degradation of tetracycline was studied by Liu et al. (2003) using 75 to 100 L h-1. High performance liquid three different processes: electrochemical, chromatography (HPLC) was performed using a photochemical and photo-electrochemical, obtained Merck-Hitachi LaChrom Elite HPLC system, at the the best results for the photo-electrochemical experimental conditions tested and selected combined process. Palominos et al. (2009) use the wavelength was 360 nm. UV-Visible measurements made between 200 and 800 nm, using a Shimatzu 2 and ZnO aqueous suspensions in the photo catalytic oxidation of tetracycline, under simulated UV-1800 spectrophotometer. solar light. They found that the ZnO presents a For measurements of pH, a Mettler-Toledo slightly higher oxidation rate than TiO pH-meter was used and H2SO4 and NaOH optimized conditions. Wang et al. (2011) found that concentrated solutions were used for pH adjustment. the photo catalytic degradation was more efficient, Conductivity was measured using a conductivity achieving 80% of total organic carbon removal after meter Mettler Toledo type (Seven Easy S30K). 3 h assay, under slightly alkaline pH condition and 3. Results and discussions
solar irradiation. Electrochemical process as anodic oxidation Monitorization methods used in degradation was used for the degradation of tetracycline's (Rossi of tetracycline was: chemical oxygen demand – et al., 2009; Vandenyapina et al., 2008; Zhang et al., COD, total organic carbon- TOC, total nitrogen – 2009). In the majority of the studies previously TN, total Kjeldhal nitrogen - TKN, high performance referred, no significant levels of mineralization were liquid chromatography – HPLC, UV-Visible achieved with the active anodes used e.g. Pt plates, absorption spectrophotometry, pH and conductivity and applying low current densities (Vendenyapina et (Table 1). The evolution of the electrochemical al., 2008), Ti/RuO2 used in the electro degradation of degradation assays with time was followed by an oxytetracycline hydrochloride (Rossi et al., 2009), UV/Vis spectroscopy, through measurements of Ti/RuO2–IrO2 anode (Zhang et al., 2009), where the chemical oxygen demand, total organic carbon and degradation rate of tetracycline increased with by HPLC. Moreover, for some selected samples the current density and decreased with the increasing in identification and characterization of the analytes, the initial concentration. namely degradation products, was achieved by Miyata et al. (2011) indicated that anodic oxidation using a Ti/IrO2 and a Ti/PbO2 anode was In order to study the influence of the effective for the degradation of tetracycline. These experimental conditions on the mineralization degree authors also evaluated the applicability of the electro of the antibiotic pollutant, the ratio COD/TOC will oxidation using a Ti/IrO2 anode on the treatment of a be determined for the different experimental livestock wastewater spiked with oxytetracycline and conditions tested and combustion efficiencies was results obtained in the oxytetracycline aqueous solutions, suggest that this method may be suitable The influence of the initial concentration for the degradation of this compound in livestock and the hydrodynamics inside the electrochemical cell on the rate of electro degradation and However, in the majority of the studies mineralization of TC using a BDD anode will also be previously referred no significant levels of assessed. To study of the influence of experimental mineralization were achieved with the active anodes conditions on the degradation of the antibiotic, assays Decontamination of synthetic wastewater containing pharmaceutical contaminants by anodic oxidation were running at experimental conditions that allow flow rate, probably due to a decrease in the width of kinetic and/or diffusive control, in order to determine the diffusion layer that favors the mass transfer medium mass transfer coefficients to predict process. During the electro degradation assay the degradation rates at experimental conditions other organic nitrogen is mainly converted to ammonium, than those tested. nitrate and nitrite. At different [TC]0 tetracycline initial Corresponding to different recirculation concentration (100 and 150 mg L-1) was made four flow rate: FR1 = 37 L h-1; FR2 = 75 L h-1; FR3 = 100 different assays corresponding to different L h-1 at different [TC]0 tetracycline initial recirculation flow rate: FR1 = 37 L h-1; FR2 = 75 L h- concentration (100 and 150 mg L-1) was made four 1; FR3 = 100 L h-1 at constant current density, 300 A different assays at constant current density, 300 A m- m-2, using as electrolyte a sodium sulfate aqueous 2.The duration of the experiments with tetracycline solution, 5 g L-1. The duration of the experiments initial concentration of 100 mg L-1 was 4 h. with tetracycline initial concentration of 100 mg L-1 To ensure that almost complete degradation was 4 h. At initial concentration 150 mg L-1 the of organic matter was achieved, the degradation tests degradation tests was extended to 6 h, to ensure that were extended to 6 h at initial concentration 150 mg almost complete degradation of organic matter was L-1. Results obtained after 4h of electro degradation achieved. Results obtained after 4h of electro of TC with different initial tetracycline degradation of TC with different initial tetracycline concentrations on BDD at a recirculation flow rate concentrations on BDD at a recirculation flow rate FR3 = 100 L h-1, was 99.8% removal rate, with 1.6 % FR3 = 100 L h-1, was 99.8% removal rate, with 1.6 % ACE (average current efficiency) calculated ACE (average current efficiency). At the highest according to Eq. (1): degradation rate tested, 100 L h-1, with an initial tetracycline concentration of 150 mg L-1, after  COD  COD  ACE  100 F V  4h assay, the removals of COD, TOC and absorbance (measured at 276.5 and 360.0 nm) were 93, 87, 99 and 100%, respectively. where F is the Faraday constant, V is the volume of In HPLC analyses the results obtained for the solution in m3, COD this assay indicate that at high current density, the 0 and CODt are the COD values at 0 and 4 h, in mg L-1, I is the applied current main compound and the metabolites that may occur intensity, in A, and t the time, in s. are fast depredated at BDD surface. The removal to After 4 h assay at 100 L h-1 with an initial below the limit of detection of pharmaceuticals (TC) tetracycline concentration of 150 mg L-1, the from ground and surface waters destined for drinking removals of COD, TOC and absorbance (measured at water production is obviously imperative. Since 276.5 and 360.0 nm) were 93, 87, 99 and 100%, conventional drinking water treatments have failed to respectively (Fig.1). Due to the very low values for remove these compounds, it is imperative to develop ACE, showing that diffusion control can be new technologies suitable for water production definitively assumed, average mass transfer plants. Electrode gradation with BDD electrode are coefficients based on COD decay, k promising technologies for electrochemical calculated, using Eq. (2) (Panizza et al., 2001): degradation of TC the high removals of COD show that the metabolites formed during the process are also oxidized, with a high degree of mineralization, since TOC removals are also very high. Average mass transfer coefficients increase with recirculation where A is the electrode geometric area, in m2. Table 1. Degradation of Tetracycline-experimental program
No Ctetracycline
FR
ABDD (cm2) I
(mA) Vsol (mL)
(L h-1)
COD, TOC, Abs, c, pH. T, Nt COD. TOC. Abs. c. pH. TN. Nt COD. TOC. Abs. c. pH. TN. Nt COD. TOC. Abs. c. pH. TN. Nt COD. TOC. Abs. c. pH. TN. Nt COD. TOC. Abs. c. pH. TN. Nt COD. TOC. Abs. c. pH. NNH3. Nt COD. TOC. Abs. c. pH. TN. Nt COD. TOC. Abs. c. pH. TN. Nt COD - Chemical Oxygen Demand, TOC - Total Organic Carbon, Abs - absorbance, C - conductivity, TN - total nitrogen Brinzila et al./Environmental Engineering and Management Journal 13 (2014), 9, 2337-2342
mathematical relationships of the dimensionless numbers of Reynolds (Re), Schmidt (Sc) and Sherwood (Sh) (Rajeshwar et al., 1997), then by calculating Re, Sc and Sh it was possible to determine mass transfer coefficients, km, for the different flow rates (Brinzila at al., 2012). At the highest degradation rate tested, 100 L h-1, with an initial tetracycline concentration of 150 mg L-1, after 4 h assay, the removals of COD, TOC and absorbance (measured at 276.5 and 360.0 nm) were 93, 87, 99 and 100%, respectively. Figure 2 and 3 represents the variation of absorbance with time, respective variation of COD in time, for the assays performed at different initial pH, 100 mg L-1 tetracycline aqueous solutions, and electrolyte sodium sulphate. Fig. 1. Initial UV-Vis absorption spectra for 100 mg L-1
tetracycline aqueous solutions with initial pH between 2 and 12 (with two maxima near 276 and 360 nm) Chemical oxygen demand (COD) and total organic carbon (TOC) measured to determinate removal degree of the organic load, increased with tetracycline initial concentration and recirculation flow rate. The effect of flow rate on the degradation rate of tetracycline diffusion coefficient, D, was calculated using Wilke and Chang equation (3) (Reid et al., 1988): Fig. 3. Variation of COD with time for the assays
where M is the solvent's molecular weight, y is an performed at different initial pH, 100 mg L-1 association parameter that accounts for hydrogen tetracycline aqueous solutions, electrolyte sodium bonds in the solvent (2.6 for water), T is the absolute temperature, in K,  is the solvent viscosity, in cP, and Vm is the molar volume, in mL m ol-1, obtained Regarding the total Kjeldhal nitrogen with ACD/ChemSketch, 270.3 cm3 mol-1. The elimination, it takes place mainly via transformation calculated value for D was 5.9 x 10-10 m2 s-1. of organic nitrogen into ammonium, nitrate and nitrite. The total nitrogen removal increased with initial tetracycline concentration and showed also a tendency to increase with recirculation flow rate (Brinzila et al., 2012). Fig. 2. Variation of absorbance with time, for the
assays performed at different initial pH, 100 mg L-1 tetracycline aqueous solutions, electrolyte sodium sulphate Fig.4. Variation of pH during the assays run at different
Assuming that mass transport properties of initial pH for 100 mg L-1 tetracycline aqueous solutions, electrochemical processes is described by the electrolyte sodium sulphate Decontamination of synthetic wastewater containing pharmaceutical contaminants by anodic oxidation All the assays whose results are presented in Fig. 6 were run for 4 h and if the removals in COD
and TOC were presented as a function of time it
would be possible to realize that COD removal rate
decreases with current density and TOC removal rate
slightly increases with current density. This means
that the ratio ΔTOC/ΔCOD increases with current
density. This fact must be due to the indirect
oxidation process, since higher hydroxyl radicals
concentration leads to a less specific attack to the
pollutant and by-products and, consequently, to
higher mineralization degree.
4. Conclusions
Fig. 5. Variation of TOC with time, min, for the assays
For the tested conditions, the highest COD performed at different initial pH, 100 mg L-1 tetracycline removal rate was obtained for the assays run at the aqueous solutions, electrolyte sodium sulphate lowest initial pH. For all the initial pH values tested, after 1 h assay the tetracycline concentration, The spectra of TC according to the literature determined by HPLC, was only residual. (Rajeshwar et al., 1997) has two maxima (Fig. 1), pH The highest ratio DTOC/DCOD was has a clear influence in this absorption spectrum due obtained for the assay run at natural pH, meaning that to the various possible protonation states of this for these experimental conditions the mineralization molecule. This influence is expressed as successive is higher. During the assays, the organic nitrogen is increases in the wavelength of the absorption bands mainly converted to ammonia, although the with pH and also in the variation of the relative formation of nitrites and nitrates can also be absorbance of the two main bands, already observed. With the obtained results, in particular those gathered with HPLC technique, it seems UV-Vis absorption spectra for the samples feasible the application of the electrochemical collected during tetracycline degradation assays technology for the degradation of tetracycline. In performed with 100 mg L-1 tetracycline aqueous fact, even for the highest initial tetracycline solutions, at initial pH varying between 2 and 12, concentration tested, 150 mg L-1, after 4 h assay the experimental conditions are described elsewhere presence of the parent compound was not detected. (Brinzila et al., 2012). The increase in current density Besides that, the high removals of COD go to decreases of charge efficiency (for 25, 100, show that the metabolites formed during tetracycline 200, 300 A m2 the value obtained forΔTOC/ΔCOD electrochemical degradation are also oxidized, with a was 0.293, 0.414, 0.484 and 0.544 respectively) for high degree of mineralization, since TOC removals the solution pH 5.6 and with sodium sulphate as are also very high. electrolyte. For 200 and 300 A m-2 applied current densities, the current efficiencies obtained are almost identical, particularly in the results concerning This paper was supported by the project "Development and absorbance measurements, ΔTOC/ΔCOD where support of multidisciplinary postdoctoral programmes in 0.484 (r2=0.97) and 0.424 (r2=0.98) respectively. major technical areas of national strategy of Research - One possible explanation is that for very Development - Innovation" 4D-POSTDOC, contract no. high current densities appear an excess in hydroxyl POSDRU/89/1.5/S/52603, project co-funded by the radicals formed at the anode that has not being used European Social Fund through Sectorial Operational in the degradation of the organic matter still present. Programme Human Resources Development 2007-2013.
The authors also want to thank Fundação para a Ciência e a
Tecnologia, Portugal.

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