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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/273147251

Photocatalytic degradation of pharmaceuticalwastes by alginate supported TiO2nanoparticles in packed bed photo reactor

(PBPR)

 Article  in  Ecotoxicology and Environmental Safety · March 2015

Impact Factor: 2.76 · DOI: 10.1016/j.ecoenv.2015.02.035 · Source: PubMed

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Santanu Sarkar

Tata Steel, India

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Sudip Chakraborty

Università della Calabria

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Chiranjib Bhattacharjee

Jadavpur University

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Photocatalytic degradation of pharmaceutical wastes by alginatesupported TiO2 nanoparticles in packed bed photo reactor (PBPR)

Santanu Sarkar a, Sudip Chakraborty b, Chiranjib Bhattacharjee a,n

a Department of Chemical Engineering, Jadavpur University, Kolkata 700032, Indiab Department of Informatics, Modeling, Electronics and Systems Engineering (D.I.M.E.S.), University of Calabria, Via-P. Bucci, Cubo 42a, 87036 Rende (CS),

Italy

a r t i c l e i n f o

 Article history:Received 29 November 2014Received in revised form19 February 2015Accepted 24 February 2015Available online 3 March 2015

Keywords:

PhotocatalysisAlginate beadsPharmaceutical compoundsPacked bed photo reactor

a b s t r a c t

In recent years deposal of pharmaceutical wastes has become a major problem globally. Therefore, it isnecessary to removes pharmaceutical waste from the municipal as well as industrial ef uents before itsdischarge. The convectional wastewater and biological treatments are generally failed to separate dif-ferent drugs from wastewater streams. Thus, heterogeneous photocatalysis process becomes lucrativemethod for reduction of detrimental effects of pharmaceutical compounds. The main disadvantage of theprocess is the reuse or recycle of photocatalysis is a tedious job. In this work, the degradation of aqueoussolution of chlorhexidine digluconate (CHD), an antibiotic drug, by heterogeneous photocatalysis wasstudy using supported TiO2 nanoparticle. The major concern of this study is to bring down the limitationsof suspension mode heterogeneous photocatalysis by implementation of immobilized TiO2 with help of calcium alginate beads. The alginate supported catalyst beads was characterized by scanning electronmicroscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDAX) as well as the characteristiccrystalline forms of TiO2   nanoparticle was conrmed by XRD. The degradation ef ciency of TiO2   im-pregnated alginate beads (TIAB) was compared with the performance of free TiO2 suspension. Although,the degradation ef ciency was reduced considerably using TIAB but the recycle and reuse of catalyst wasincreased quite appreciably. The kinetic parameters related to this work have also been measure.Moreover, to study the susceptibility of the present system photocatalysis of other three drugs ibuprofen(IBP), atenolol (ATL) and carbamazepine (CBZ) has been carried out using immobilized TiO2. The con-tinuous mode operation in PBPR has ensured the applicability of alginate beads along with TiO 2   inwastewater treatment. The variation of residence time has signicant impact on the performance of PBPR.

& 2015 Elsevier Inc. All rights reserved.

1. Introduction

Wastewaters from pharmaceutical industries and from house-holds contain lots of drugs especially antibiotics are vigorouslyentering to water environment. Therefore, threats due to phar-maceutical drugs to the aquatic life as well as all living element

become major concern of research work (Carballa et al., 2004;Hirsch et al., 1998;  Ternes, 1998;  Kidd et al., 2007;   Lange et al.,2001;   Oaks et al., 2004). For remediation of a disease pharma-ceutical drugs are frequently used and thereafter without alter-nation major part of those medicines enters to the environmentthrough municipal sewage system. Moreover, sometime medicinesare thrown into environment directly and pharmaceutical wastes

from the respective industries directly disposed off to the waterbodies (Hirsch et al., 1998; Ternes, 1998; Kidd et al., 2007; Halling-Sørensen et al., 1998). As a result a gradual growth pharmaceuticalcomponent is observed in water environment. However, it is im-possible to separate pharmaceutical compounds i.e. antibiotics,hormones, steroids, etc. through wastewater treatment and cannot

be degraded by means of biological treatment (Daughton andTernes, 1999; Zwiener and Frimmel, 2000). Several groups of re-searcher have adopted photocatalysis in presence of nanoparticle,one of the main categories of advanced oxidation process (AOP) toeliminate detrimental effects of pharmaceutical compounds (Kla-varioti et al., 2009).

Heterogeneous photocatalysis in presence of nanoparticlemainly TiO2   has become a promising pathway for separation of several micropollutants form wastewater streams (Devipriya andYesodharan, 2005; Woo et al., 2009; Zayani et al., 2009; Hsu et al.,2008; Calza et al., 2006; Sakkas et al., 2007; Zhang et al., 2010; Anet al., 2011; Sarkar et al., 2014a,b). Small size nanoparticle provides

Contents lists available at ScienceDirect

journal homepage:   www.elsevier.com/locate/ecoenv

Ecotoxicology and Environmental Safety

http://dx.doi.org/10.1016/j.ecoenv.2015.02.0350147-6513/& 2015 Elsevier Inc. All rights reserved.

n Corresponding author.E-mail addresses: cbhattacharyya@chemical.jdvu.ac.in,

c.bhatta@gmail.com (C. Bhattacharjee).

Ecotoxicology and Environmental Safety 121 (2015) 263–270

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higher surface to volume ratio thus it offers better surface reaction.Titanium oxide nanoparticle is used frequently due to its strongoxidizing power, higher photo stability and non-toxic nature(Gupta and Tripathi, 2011). Many researchers have highlightedmany advantageous sides of photocatalysis in presence of TiO2nanoparticle although the scale up of heterogeneous photo-catalysis process is the main challenging task. The recovery andreuse of TiO2 nanoparticle at the end of photocatalysis process is

the main obligation of photocatalysis process and eventually it isvery tedious job in practice.The problem related to the larger scale implementation of 

heterogeneous photocatalysis is cumbersome separation and re-cycling of photo catalyst during the wastewater treatment. Thisproblem can be obliterated by implementation of immobilizationof TiO2  on solid support. The immobilization is very simple andeasy to execute for immobilization of cells and enzyme ( Santoset al., 2008). However, mentioned method by Santos et al. (2008)can be adopted to entrap TiO2  nanoparticle. Moreover, it is ne-cessary to develop a cost effective and environment friendly en-trapment method so that it can be easily adopted by researchfraternity. Harikumar et al. (2011) described that calcium alginatewas nontoxic, biodegradable, non-immunogenic, water insolubleand thermally irreversible type of polymer matrix which couldprovide better support for immobilization of nanoparticle. There-fore, calcium alginate beads can be used for environment friendlyimmobilization of TiO2 nanoparticle and those photo active beadsshould be used in wastewater treatment in large scale.

The main goal of this current research work is to develop animmobilized photocatalytic system to remove pharmaceuticalcomponents from the wastewater. The current research group hasalready established that photocatalysis in presence of TiO2  nano-particle is very much effective in removal of anti-biotic likechlorhexidine digluconate (CHD) (Das et al., 2014,   Sarkar et al.,2014a,b). Although, the last successful attempt of photocatalyticdegradation of CHD has been done using suspension of photocatalyst (Das et al., 2014, Sarkar et al., 2014a,b) but it prevails somelimitations which have been described earlier. As per literature

survey, this research work has made the   rst attempt to imple-ment immobilized TiO2  using alginate in the  eld of pharmaceu-tical wastewater treatment and at the same time elimination of disadvantages of suspension mode has been tried so far. Further-more, a new concept of packed bed photo reactor (PBPR) has beenintroduced here in which nanoparticle impregnated alginate beadshave been used as packing material. Introduction of PBPR has beenmade to eliminate the major limitation of batch mode duringtreatment of large volume of wastewater as PBPR has been oper-ated in continuous mode. Moreover, to ascertain the applicabilityof immobilized system as well as PBPR, the present research workhas tried to carry out photocatalytic degradation of different drugsin continuous mode. Other three pharmaceutical drugs i.e. ibu-profen (IBP), atenolol (ATL) and carbamazepine (CBZ) which have

also some other detrimental effects on environment (Hapeshiet al., 2010,   Georgaki et al., 2014), were also treated with im-mobilized TiO2 system to check the viability of present treatmentmethod using PBPR.

2. Experimental

 2.1. Chemical and reagents

Titanium dioxide photocatalyst nanopowder AeroxidesP25(mixture of rutile and anatase, 718467) of particle size 21 nm withsurface area (BET) 35–65 m2 g1 from Sigma-Aldrich, were used asphoto catalysis. Chlorhexidine digluconate solution (20% w/v),

Ibuprofen (CH3H18O2, purityZ99%), atenolol and carbamazepine

(C15H12N2O) were purchased from Sigma-Aldrich to prepare thesimulated solutions for experimental purpose. All experimentswere carried out with ultrapure water from Ariums Pro VF (Sar-torius Stedim Biotech) of 18.2 MΩ cm resistivity. All other che-micals i.e. sodium alginate, calcium chloride (di-hydrate) werepurchased from Sigma Aldrich Chemical Co., USA.

 2.2. Immobilization of TiO 2   in calcium alginate beads

The titanium dioxide impregnated beads were prepared byentrapping TiO2 nanoparticles in the calcium alginate beads. About100 mL of casting solution was prepared by mixing 4.0 g (4%) of sodium alginate powder and 1.0–4.0 g of TiO2  nanoparticle in ul-trapure water and stirring until a homogenous solution wasachieved. First, TiO2 nanoparticle was added to 100 ml water andstirred for 30 min to form homogeneous suspension and thensodium alginate was introduced in that solution. The mixture(100 mL) was injected drop wise into 400 mL CaCl2   solution(0.5 M) using a syringe (10 mL) with a needle (0.8 mm in diameter,38 mm in length) to form TiO2 impregnated alginate beads (TIAB).The TIAB were cured in the CaCl2  solution for overnight at roomtemperature and then rinsed with ultrapure water for several

times. Prepared TIAB stored in ultrapure water and kept in 4°

 C forfuture use. Blank beads were also prepared by above mentionedmethod but without TiO2 addition.

 2.3. Adsorption and photocatalysis

The photocatalytic degradation using suspension mode of TiO2was carried out under articial UV source in a quartz reactor in thebatch mode. The experimental details have been already describedby Das et al. (2014) and Sarkar et al. (2014a) in suspension mode.The batch study using TIAB was carried out maintaining the fa-vorable conditions similar to the batch study in suspension mode.The pH and the temperature were maintained at 10.5 and 30 ° Cand substrate to catalyst ratio (S/C) was  xed at 2.5. The irradiationtime for both systems maintained for 1 h. With certain intervalaliquot solution was piped out from the reaction broth to measurethe concentration of antibiotic, CHD. For the adsorption process,same type of experimental study was carried out as mentionedabove but without UV irradiation. To increase the ef cacy of TIABand to eliminate the limitations of batch mode operation, thephotocatalysis has been carried out in continuous mode usingPacked Bed Photo Reactor (PBPR). The present mode of operationhas been illustrated schematically in Fig. 1. The residence time (τ )and all other physical parameters were selected according to thebest removal condition achieved in batch mode. To maintainconstant temperature during the photocatalysis reaction the re-actor is jacketed for the circulation of coolant and to protect UV 

Fig. 1.   Schematic representation of PBPR.

S. Sarkar et al. / Ecotoxicology and Environmental Safety 121 (2015) 263– 270264

https://www.researchgate.net/publication/227220603_A_review_of_TiO2_nanoparticles?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==http://-/?-https://www.researchgate.net/publication/222673866_Use_of_sugarcane_bagasse_as_biomaterial_for_cell_immobilization_for_xylitol_production?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/222673866_Use_of_sugarcane_bagasse_as_biomaterial_for_cell_immobilization_for_xylitol_production?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/222673866_Use_of_sugarcane_bagasse_as_biomaterial_for_cell_immobilization_for_xylitol_production?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==http://-/?-https://www.researchgate.net/publication/261721215_Remediation_of_Antiseptic_Components_in_Wastewater_by_Photocatalysis_Using_TiO2_Nanoparticles?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/261948808_Application_of_ANFIS_model_to_optimise_the_photocatalytic_degradation_of_chlorhexidine_digluconate?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/261948808_Application_of_ANFIS_model_to_optimise_the_photocatalytic_degradation_of_chlorhexidine_digluconate?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/261948808_Application_of_ANFIS_model_to_optimise_the_photocatalytic_degradation_of_chlorhexidine_digluconate?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==http://-/?-http://-/?-https://www.researchgate.net/publication/261721215_Remediation_of_Antiseptic_Components_in_Wastewater_by_Photocatalysis_Using_TiO2_Nanoparticles?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/261948808_Application_of_ANFIS_model_to_optimise_the_photocatalytic_degradation_of_chlorhexidine_digluconate?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/261948808_Application_of_ANFIS_model_to_optimise_the_photocatalytic_degradation_of_chlorhexidine_digluconate?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==http://-/?-https://www.researchgate.net/publication/40766679_Drugs_degrading_photocatalytically_kinetics_and_mechanisms_of_ofloxacin_and_atenolol_removal_on_titania_suspensions_Water_Res?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/40766679_Drugs_degrading_photocatalytically_kinetics_and_mechanisms_of_ofloxacin_and_atenolol_removal_on_titania_suspensions_Water_Res?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/276496078_A_Study_on_the_Degradation_of_Carbamazepine_and_Ibuprofen_by_TiO2_ZnO_Photocatalysis_upon_UVVisible-Light_Irradiation?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/276496078_A_Study_on_the_Degradation_of_Carbamazepine_and_Ibuprofen_by_TiO2_ZnO_Photocatalysis_upon_UVVisible-Light_Irradiation?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/261721215_Remediation_of_Antiseptic_Components_in_Wastewater_by_Photocatalysis_Using_TiO2_Nanoparticles?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/261721215_Remediation_of_Antiseptic_Components_in_Wastewater_by_Photocatalysis_Using_TiO2_Nanoparticles?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE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light, it is covered with quartz glass so that the wavelength of UV irradiation is unaltered. An articial UVA tube having 365 nmwavelengths has been used as a source of UV illumination and theintensity of UV are  xed for PBPR. The void fraction of PBPR is 0.37under fully loaded with TIAB and according to that the   ow ratewas kept constant using peristaltic pump to ascertain a  xed re-sidence time. The residence time was varied with change of pharmaceutical drugs and the residence time was a variable

parameter during photocatalysis of individual drug. The experi-mental study was continued till the outlet concentration of phar-maceutical drug became constant. To study the reusability of TIABmultiple experimental runs were carried out using same beads.

In case of other three drugs, the photocatalytic degradation wascarried in continuous mode only. The variable process parametersof the best   t were taken from the earlier batch studies, carriedout by other research groups (Hapeshi et al., 2010; Georgaki et al.,2014) using TiO2 suspension.

 2.4. Analytical methods

 2.4.1. Characterization of immobilized photo catalyst 

The physical appearance of TIAB was white color sphericalparticles with average diameter of 3.33 mm. The surfacemorphologies of the entrapped catalysts inside alginate matrixwere evaluated by using scanning electron microscopy (SEM) incombination with energy dispersive X-ray analysis (EDAX). TheX-ray powder diffraction (XRD) pattern for the TIAB was recordedusing Shimadzu XRD-6000 diffractometer using Cu Kα   radiation(l¼1.54 Å) operating at 40 kV, 20 mA and scanning rate of 2° min1. The BET specic surface areas of the TIAB was de-termined by the N2 adsorption–desorption method.

 2.4.2. Measurement of degradation

The concentration of chlorhexidine digluconate concentration

in the reaction mixtures was determined using spectrophotometerat 275 nm. The details of identication have been elaborately de-scribed in the recent publication by the same research group (Daset al., 2014;   Sarkar et al., 2014a). To validate the concentrationmeasurements and for the identication of product pattern, RP-HPLC system (Cyber Lab, Millbury, USA) with Zorbax SB Phenylcolumn (4.8250 mm2, 5  mm, Agilent, USA) was used. The detailsof HPLC analysis and the chromatogram from HPLC were described

earlier (Das et al., 2014) and chromatogram ensured the genera-tion of by-product. To characterize the degraded by-products fromCHD, the mass spectra analysis was done in Quadrapole-TOF Mi-cromass Spectrometer (Waters Co., USA). The details of chroma-togram and mass spectroscopy had been indicated in the experi-mental research work by the present research group (Das et al.,2014).

The residue of other three drugs and identication & mea-surement of degraded by-products from ATL, IBP and CBZ werecarried out according to the principles that described by Hapeshiet al. (2010)  and Georgaki et al. (2014)  respectively. In all threecases HPLC (Perkin Elmer, Series 200) was used with essential C18column for IBP and ATL and Hypersil BDS C8 column for CBZ

(250 mm4 mm5 μm).The removal percentage of pharmaceutical components has

been calculated during the whole study using Eq. (1).

⎛

⎝⎜

⎞

⎠⎟

C 

C % Removal of pharmaceutical component 1 100%

(1)

t

0

= − ×

where, C t is the concentration of any drug at any time  t  and  C 0 iscorresponding value at  t ¼0.

Fig. 2.  (a) Photograph of TIAB and (b) and (C) SEM images at different magni cations, (d) EDXA spectra of a single TIAB congaing 4% alginate beads and 2% TiO 2 nanoparticles

by weight.

S. Sarkar et al. / Ecotoxicology and Environmental Safety 121 (2015) 263– 270   265

https://www.researchgate.net/publication/40766679_Drugs_degrading_photocatalytically_kinetics_and_mechanisms_of_ofloxacin_and_atenolol_removal_on_titania_suspensions_Water_Res?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/40766679_Drugs_degrading_photocatalytically_kinetics_and_mechanisms_of_ofloxacin_and_atenolol_removal_on_titania_suspensions_Water_Res?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/276496078_A_Study_on_the_Degradation_of_Carbamazepine_and_Ibuprofen_by_TiO2_ZnO_Photocatalysis_upon_UVVisible-Light_Irradiation?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/276496078_A_Study_on_the_Degradation_of_Carbamazepine_and_Ibuprofen_by_TiO2_ZnO_Photocatalysis_upon_UVVisible-Light_Irradiation?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/261721215_Remediation_of_Antiseptic_Components_in_Wastewater_by_Photocatalysis_Using_TiO2_Nanoparticles?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/261721215_Remediation_of_Antiseptic_Components_in_Wastewater_by_Photocatalysis_Using_TiO2_Nanoparticles?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/261721215_Remediation_of_Antiseptic_Components_in_Wastewater_by_Photocatalysis_Using_TiO2_Nanoparticles?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/261948808_Application_of_ANFIS_model_to_optimise_the_photocatalytic_degradation_of_chlorhexidine_digluconate?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==http://-/?-https://www.researchgate.net/publication/261721215_Remediation_of_Antiseptic_Components_in_Wastewater_by_Photocatalysis_Using_TiO2_Nanoparticles?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/261721215_Remediation_of_Antiseptic_Components_in_Wastewater_by_Photocatalysis_Using_TiO2_Nanoparticles?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/261721215_Remediation_of_Antiseptic_Components_in_Wastewater_by_Photocatalysis_Using_TiO2_Nanoparticles?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==http://-/?-https://www.researchgate.net/publication/40766679_Drugs_degrading_photocatalytically_kinetics_and_mechanisms_of_ofloxacin_and_atenolol_removal_on_titania_suspensions_Water_Res?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/40766679_Drugs_degrading_photocatalytically_kinetics_and_mechanisms_of_ofloxacin_and_atenolol_removal_on_titania_suspensions_Water_Res?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/40766679_Drugs_degrading_photocatalytically_kinetics_and_mechanisms_of_ofloxacin_and_atenolol_removal_on_titania_suspensions_Water_Res?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/276496078_A_Study_on_the_Degradation_of_Carbamazepine_and_Ibuprofen_by_TiO2_ZnO_Photocatalysis_upon_UVVisible-Light_Irradiation?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==http://-/?-https://www.researchgate.net/publication/261721215_Remediation_of_Antiseptic_Components_in_Wastewater_by_Photocatalysis_Using_TiO2_Nanoparticles?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/261721215_Remediation_of_Antiseptic_Components_in_Wastewater_by_Photocatalysis_Using_TiO2_Nanoparticles?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/261721215_Remediation_of_Antiseptic_Components_in_Wastewater_by_Photocatalysis_Using_TiO2_Nanoparticles?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/261721215_Remediation_of_Antiseptic_Components_in_Wastewater_by_Photocatalysis_Using_TiO2_Nanoparticles?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/261721215_Remediation_of_Antiseptic_Components_in_Wastewater_by_Photocatalysis_Using_TiO2_Nanoparticles?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/261948808_Application_of_ANFIS_model_to_optimise_the_photocatalytic_degradation_of_chlorhexidine_digluconate?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/40766679_Drugs_degrading_photocatalytically_kinetics_and_mechanisms_of_ofloxacin_and_atenolol_removal_on_titania_suspensions_Water_Res?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/40766679_Drugs_degrading_photocatalytically_kinetics_and_mechanisms_of_ofloxacin_and_atenolol_removal_on_titania_suspensions_Water_Res?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/40766679_Drugs_degrading_photocatalytically_kinetics_and_mechanisms_of_ofloxacin_and_atenolol_removal_on_titania_suspensions_Water_Res?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/276496078_A_Study_on_the_Degradation_of_Carbamazepine_and_Ibuprofen_by_TiO2_ZnO_Photocatalysis_upon_UVVisible-Light_Irradiation?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/276496078_A_Study_on_the_Degradation_of_Carbamazepine_and_Ibuprofen_by_TiO2_ZnO_Photocatalysis_upon_UVVisible-Light_Irradiation?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==https://www.researchgate.net/publication/276496078_A_Study_on_the_Degradation_of_Carbamazepine_and_Ibuprofen_by_TiO2_ZnO_Photocatalysis_upon_UVVisible-Light_Irradiation?el=1_x_8&enrichId=rgreq-db32d860-9f74-4a2b-b95c-00cf73087347&enrichSource=Y292ZXJQYWdlOzI3MzE0NzI1MTtBUzoyOTE0MTY0NTU1NjUzMTJAMTQ0NjQ5MDUwNTM1NQ==http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-

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3. Results and discussions

 3.1. Characterization of TIAB

The formation of nano-TiO2   impregnated bead (Fig. 2a) wasconrmed by SEM with EDXA and XRD patterns. TiO2   nano-particles were entrapped in a polymeric matrix to study its activitytowards the photo catalytic degradation of antibiotic drugs. Cal-

cium alginate was used as the solid support in this research topic.Calcium alginate beads in diluted acidic and alkaline solutionswere mechanically stable. SEM analysis was carried out to conrmthe presence of nanoparticles, and its distribution pattern inpolymeric matrix. A representative SEM image (Fig. 2b and c)shows that most of the particles are well distributed. The quanti-tative compositional analysis of the TiO2   nanoparticle entrappedbeads was carried out using EDXA spectroscopy measurements.The spectra conrm the presence of TiO2   in the structure. Thespectra were recorded from a single bead which was producedfrom casting solution containing 4% alginate and 2% TiO2   nano-particles by weight. From the measurements, it was ensured thatthe each bead consisted of an average 6.21% Ti, 18.14% O2, 15.43%Ca, 9.83% Na and 47.28% Cl2  and the EDXA spectrum has been

shown in Fig. 2(d). EDXA analysis showed minimum level of im-purities were present inside the alginate beads. The characteriza-tion by XRD evidenced the amorphous nature of the TIAB.Therefore, it was dif cult to identify the crystalline phases of TiO2.Under reduce scanning velocity two phases of TiO2, anatase andrutile phases were observed. The BET surface area of the sameTIAB was measured to be 21.43 m2 g1.

 3.2. Effect of alginate to catalyst (A/C) ratio

The main process parameter of the current system is alginate tocatalyst ratio as all other parameters are kept same with theparametric values from the earlier study (Das et al., 2014). It refersthat at S/C ratio (substrate to catalyst ratio) 2.5, pH of 10.5, tem-

perature of 30° C and UV intensity of 80 μW/cm

2

the removalpercentage of CHD reached its steady state value after 1 h. To studythe effect of alginate to catalyst (A/C) ratio, it was varied in fourdifferent ways from ratio 0.5 to 4.0 and the effect has been clearlyindicated in  Fig. 3 though so many trial experiments were con-ducted with the variation of A/C ratio.   Fig. 3   reveals that withdecrease of A/C ratio adsorption ef ciency of the system decreasesfor the current system. With increase of A/C ratio concentration of nanoparticle inside alginate matrix was decreased, therefore more

porous vacant sites were available on outer surface of beads toadsorb the substrate molecules. Thus, higher adsorption was ob-served for lower catalyst concentration. TiO2   nanoparticles wereentrapped inside porous matrix of beads therefore; during pho-tocatalysis a different observation was identied. Both at lowerand higher value of A/C ratio photocatalytic activity were reduced.Lower value of A/C ratio refers higher catalyst concentration andhigher catalyst concentration causes problem for UV penetration

(Das et al., 2014; Sarkar et al., 2014a). As a result at lower value of A/C ratio photocatalytic degradation of CHD was reduced. But athigher A/C ratio, available active site on alginate beads for pho-tocatalytic reaction was not suf cient. Moreover, at similar situa-tion TiO2  distribution on surface of the alginate beads was in-adequate which referred poor amount of active sites was availablefor photocatalysis. Larger value of A/C refers higher concentrationof alginate present in TIAB and as a result the opacity of the al-ginate beads increases which causes lower UV penetrationthrough alginate surface to reach the active site of the TiO2  na-noparticle. Therefore, at that particular ratio it was impossible todegrade CHD completely by photocatalysis. On the contrary theresidual amount of CHD after adsorption process could be de-graded completely by photocatalysis using alginate beads with A/Cratio of 2. However, for this type of reaction A/C ratio played themajor role for percentage removal of pharmaceutical componentand it should be optimized to achieve better removal of the pol-lutants from the system.

Minute observation on Fig. 3 could reveal that at lower value of A/C ratio during the photocatalysis same percentage of CHD wasremoved. This was due to at lower value of such ratio the dis-tributions of TiO2 on the upper surface of TIAB was similar and atsame time the dif culty of UV penetration through alginate beadsreduced to some extent.

From the above discussion, it may be concluded that A/C ratioshould be maintained in such way that both the stability and thecatalytic activity of TIBA can reach their optimum value. Then onlyTIBA can be reused several times without losing catalytic activityin photocatalytic wastewater treatment.

 3.3. Adsorption and photocatalysis of CHD

Simultaneous adsorption and photocatalysis process was car-ried out at 30° C and pH of 10.5 with S/C of 2.5 in batch mode.Those process parameters have been chosen from the previousstudy (Das et al., 2014) carried out using TiO2   suspension toevaluate the comparison between suspension and immobilizedmode of operations. Moreover, at that parametric condition max-imum removal of CHD was possible. After 1 h adsorption process,photocatalysis was carried out for 1 h to  nd out the removal ef-ciency of photocatalysis alone. From Fig. 3 it has been observedthat under same operating condition and maintaining A/C ratio at2, the maximum number of CHD molecules have been adsorbed on

the surface of the TIAB and after that left amount of CHD has beendegraded with help of photocatalysis reaction. This observationcan be justied with help of porous structure of TIAB. As it hasalready been mentioned that TIAB offered higher BET surface areatherefore CHD was adsorbed inside the porous matrix of alginatebeads. As a consequence free molecule of CHD was not availablefor photocatalytic degradation. The main advantage of this processwith the help of TIAB almost all molecules of the pharmaceuticalcomponent (CHD) can be removed within 2 h. Though, in currentprocess adsorption played the major role to remove pharmaceu-tical waste from the system. Therefore, to understand ef cacy of TIAB, the fresh pharmaceutical component was continually fed tothe system for photocatalytic degradation. In later part of thepresent article it would be understandable that the extent of ad-

sorption on photocatalytic degradation using TIAB.

Fig. 3.  Effects of A/C ratio on both adsorptions an photocatalysis process and the

interdependency between adsorption and photocatalysis.

S. Sarkar et al. / Ecotoxicology and Environmental Safety 121 (2015) 263– 270266

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 3.4. Adsorption and reaction kinetics

In the present study two types of kinetics are involved, one isadsorption kinetics and other is reaction kinetics during photo-catalysis. Both are necessary to understand the direction and ex-tent of the removal process. First adsorption of target moleculetakes place on TIAB surface and then photocatalytic degradation of that molecule occurs. Here, CHD was adsorbed on TIAB surface and

simultaneously it was disappeared from the system due photo-catalytic reaction.The phenomenon of adsorption of a substrate on any adsorbent

can be explained through isotherms. For the liquid–solid adsorp-tion the amount of adsorbate absorbs on the solid adsorbent sur-face is the function of concentration of adsorbate at constanttemperature. In the present study TIAB is absorbent and CHD isabsorbate. Though, different types of isotherm have already beendeveloped; among those Langmuir isotherms is quite popular todescribe the adsorption phenomenon on the solid surface. More-over, this was developed considering that adsorbate was inert toactive surface without no phase change and single molecule couldoccupy one active site thus mono layer formation took place. Inthis study, the experimental adsorption data has been well tted

with Langmuir isotherm than all other isotherms, which can beexpressed mathematically using Eq. (2) (Stumn and Morgan, 1996)and in the isotherm study, initial CHD concentration was thevariable parameter, whereas the others were kept constant.

C 

q q K 

C 

q

1

(2)

0

equ max   CHDG

0

max

= +

where,   qequ   is the amount of CHD adsorbed at equilibrium pergram of TIAB,   C 0  initial equilibrium concentration of CHD (maindriving force),  qmax is the maximum amount of CHD adsorbed atequilibrium per gram of TIAB; K CHD adsorption rate constant (g

1).The  tted curve of  C 0 vs  C 0/qequ has linearity with the correlationcoef cient of 0.897 that has been shown in  Fig. 4(a). The valueqmax   and   K CHD   have been obtained as 0.286 and 0.035 g

1

respectively from the same plot.The heterogeneous photocatalysis reactions generally followpseudo   rst order reaction kinetics (Sarkar et al., 2014b). A goodagreement between theoretical pseudo   rst order kinetic modeland experimental observation has been observed and that can beexpressed using Eq. (3).

r   dC

dt  kC

(3)photo   t− = =‵

where,   r photo‵   and   k   is pseudo   st order reaction rate and rateconstant respectively. The above equation can be written afterintegrating with boundary condition

⎛

⎝⎜

⎞

⎠⎟

C 

C   kt ln

(4)

t

0

− =

Initial concentration of pharmaceutical waste (CHD) is re-presented as   C 0. The rate constant values can be calculated fromthe slope of the plot of   ln(C t/C 0) vs time From Fig. 4(b) the valueof rate constant (k) was calculated as 0.0555 min1.

 3.5. Comparison between suspension and entrapment mode

The present research group already observed in suspensionmode maximum 30% CHD was removed due to adsorption and upto 70% removal was possible during photocatalytic degradation(Das et al., 2014) at earlier specied condition. In that case pho-tocatalysis was predominant for removal of CHD. Although at sameparametric condition, in the present study, the adsorption process

on TIAB played the major contribution (79%) for removal of CHD

from the system. Moreover, with combination of both adsorptionand photocatalysis could remove 99% of present antibiotic formthe reaction mixture. Therefore, in batch study adsorption playedthe important role for the removal of pharmaceutical component,CHD from the simulated solution.

 3.6. Photocatalytic degradation using PBPR

In PBPR, TIAB was used as packing material. In the center of thepacked column UV source was there. The suf cient time wasprovided for photocatalytic degradation. The operating parameterswere chosen from the batch studies which were performed byseveral researchers (Das et al., 2014; Hapeshi et al., 2010; Georgaki

et al., 2014). During all experimental observation A/C ratio of 2 wasmaintained. The photocatalytic degradation of several pharma-ceutical drugs has been carried out using PBPR and experimentalobservation has been represented clearly in the current context.

 3.6.1. Degradation of CHD in PBPR

In the earlier batch study in suspension mode the present re-search group (Das et al., 2014) has revealed that maximum per-centage of CHD can be removed at S/C ratio of 2.5, pH 10.5 andambient temperature (30   °C). In the present case same parametriccondition has been maintained during the photocatalytic de-gradation in PBPR and outlet concentration of CHD has beenmeasured to calculate its removal percentage with time which hasbeen plotted in Fig. 5(a). At the initial stage almost 99% removal

has been observed for 60 min residence time but as the time

Fig. 4 .  Measurement of kinetics parameters for (a) adsorption and(b) photocatalysis of CHD.

S. Sarkar et al. / Ecotoxicology and Environmental Safety 121 (2015) 263– 270   267

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progress the removal percentage has decreased gradually. In the

connection with that it should be noted, the treated simulatedwaste water  rst came out from PBPR after 60 min from the startof removal process. This observation may be explained with thehelp of earlier batch study. According to  Fig. 3 initially maximumremovals of CHD was possible with help of surface adsorption onTIAB but as the time progress active sites present in porous matrixof alginate beads were getting occupied by CHD molecules.Therefore, effective adsorption was reduced after some time and atthat time only photocatalysis became the predominant factor toremove pharmaceutical components. Moreover, the substratemolecules were also available to take part in photocatalysis. It hasalso been observed from Fig. 5(a) that removal percentage of CHDreached to its steady state value after some time. Though, incontinuous mode only 55% steady state removal of CHD was

possible using TIAB in PBPR whereas nearly 70% removal wasachieved (Das et al., 2014) using TiO2  suspension in batch mode.This contradictory behavior was observed as in suspension modeall TiO2 nanoparticles were freely available for photocatalysis butin case of alginate beads catalyst particles were in entrappedcondition. Thus, all nanoparticles could not take part in such re-action. Moreover, lower UV penetration through the alginate sur-face was one of the major drawbacks of the system and beadswere placed around the UV source in multi-layered condition,which also caused lower light penetration through TIABs whichwere far away from UV light.

 3.6.2. Degradation of other drugs

To establish the applicability of PBPR for photocatalytic de-

gradation of pharmaceutical wastes, three other pharmaceutical

components namely ATL, IBP and CBZ were degraded using TIAB in

continuous mode. The removal percentage of those three com-ponents has been shown in  Fig. 5(b)–(d). For all the cases tem-perature, pH and S/C ratio was maintained at 25   °C, 7 and 0.04respectively. The parametric conditions for ATL was taken as de-scribed by Hapeshi et al. (2010) and for other two, it was optedfrom the research work Georgaki et al. (2014). The most interest-ing think is that  Hapeshi et al. (2010)  and Georgaki et al. (2014)was experimented with lower value of substrate concentrationsuch that it could replicate the environmental pollution load dueto those drugs. It has been observed from their studies that atmentioned condition ATL, IBP and CBZ can be removed up to 85%,99% and 99% after 60 min, 20 min and 40 min respectively insuspension mode of operation. For all cases initial concentrationwas kept constant at 10 mg/L. In the current study, the continuous

mode of operation has been preformed considering the residencetime is equal to the time after which the maximum removal per-centage was obtained by Hapeshi et al. (2010) and Georgaki et al.(2014)   in batch mode. In the present system the steady statepercentage of removal was achieved 58%, 85% and 80% for ATL, IBPand CBZ when residence times were 60 min, 20 min and 40 minrespectively and those values were much lesser than suspensionmode. The similar observation was observed in case of CHD.Therefore, similar type of explanation prevails for the removal of ATL, IBP and CBZ using TIAB.

From the above discussion it is clear that TIAB as well as PBPR has failed to achieve maximum percentage of removal of phar-maceutical components from the simulated solution. Though, onething is conrmed that an appreciable amount of drugs can be

removed by such type of continuous mode of photocatalysis

Fig. 5.  Percentage removal of different pharmaceutical drugs using TIAB in PBPR at speci ed conditions.

S. Sarkar et al. / Ecotoxicology and Environmental Safety 121 (2015) 263– 270268

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