Microalgae Immobilized by Nanofibrous Web for Removal of Reactive

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Microalgae immobilized nanofibrous web for removal of reactive dyes from wastewater Nalan Oya San Keskin, Asli Celebioglu, Tamer Uyar, and Turgay Tekinay Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b01033 • Publication Date (Web): 11 May 2015 Downloaded from http://pubs.acs.org on May 16, 2015

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Industrial & Engineering Chemistry Research

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Microalgae immobilized nanofibrous web for removal of reactive dyes from wastewater

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Nalan Oya San Keskina,b,c*, Aslı Celebiogluc,d, Tamer Uyarc,d* and Turgay Tekinayb,e*

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a

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Turkey

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b

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c

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Turkey

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d

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Turkey

Polatlı Science and Literature Faculty, Biology Department, Gazi University, Ankara 06900,

Life Sciences Application and Research Center, Gazi University, Ankara 06830, Turkey

UNAM-National Nanotechnology Research Center, Bilkent University, Ankara 06800,

Institute of Materials Science and Nanotechnology, Bilkent University, 06800 Ankara,

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e

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06560, Turkey

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*Corresponding authors:

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Tel.: +90 (312) 484 62 70; fax: +90 (312) 484 6271.

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E-mail address: [email protected] (N.O. San Keskin)

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Tel.: +90 (312) 290 3571; fax: +90 (312) 266 4365.

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E-mail address: [email protected] (T. Uyar)

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Tel.: +90 (312) 484 62 70; fax: +90 (312) 484 6271.

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E-mail address: [email protected] (T. Tekinay).

Faculty of Medicine, Department of Medical Biology and Genetics, Gazi University, Ankara

19 20 21 1 ACS Paragon Plus Environment


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ABSTRACT

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In this study, we have developed microalgae immobilized polysulfone nanofibrous web

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(microalgae/PSU-NFW) for the removal of reactive dyes (Remazol Black 5 (RB5) and

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Reactive Blue 221 (RB221). Here, electrospinning technique was used to produce polysulfone

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nanofibrous web (PSU-NFW) as a free-standing material at which microalgae,

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Chlamydomonas reinhardtii, was immobilized on PSU-NFW. The decolorization capacities

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of microalgae/PSU-NFW were significantly higher than that of pristine PSU-NFW.

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Decolorization rate for RB5 was calculated as 72.97±0.3% for microalgae/PSU-NFW

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whereas it was 12.36±0.3% for the pristine PSU-NFW. In the case of RB221 solution,

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decolorization rates were achieved as 30.2±0.23% and 5.51±0.4% for microalgae/PSU-NFW

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and pristine PSU-NFW, respectively. Reusability tests revealed that microalgae/PSU-NFW

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can be used in at least three successive decolorization steps in which the decolorization rate of

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the RB5 was found to be 51±0.69% after the third reuse step. These results are promising and

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therefore suggest that microalgae/PSU-NFW could be applicable for the decolorization of

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dyes due to their versatility and reusability.

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Keywords: Decolarization; Electrospinning; Microalgae, Nanofibers; Polysulfone; Reactive

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Dyes

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INTRODUCTION

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Intense industrialization and urbanization period have resulted in significant amount of

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waste release into the environment. Common contaminants found in wastewater include

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biodegradable, volatile and recalcitrant organic compounds, toxic metals, suspended solids,

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dyes, microbial pathogens and parasites.1 One of the major causes of environmental pollution

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is the wastewater of textile industry. Elimination of dyes from industrial effluents is a major

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concern of today and carries a great deal of importance. Production and usage of ten thousand

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different synthetic dyes and pigments has exceeded 0.7 million tons worldwide.2 Anionic dyes

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(i.e. acid dye, substantive dye and reactive dye), cationic and nonionic dyes are the three

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major classes of industrial dyes.3 Due to the various applications of basic and reactive dyes,

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about 2-50% of the dyestuff is industrial wastewater and released into the environment.4 In

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general, the concentration of dyes present in textile wastewater in the range of 10 to 50 mg L-

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1

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can pollute the bodies of water and have profound impact by changing the biological cycles

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and affecting photosynthesis processes. Furthermore, they can possibly threaten human health

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as the prolonged contact with these products can lead to toxic reactions.6,7 Although some

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existing technologies such as traditional physical or chemical decolorization techniques

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including membrane filtration,8 ion exchange,9,10

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destruction,12 major disadvantages of these methods are high sludge production, management

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and disposal problems, high cost, technical limitations, not environmentally friendly.

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Therefore, usage of decolorization technologies, which are based on the capability of different

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type of bacterial, fungal and algal cells to decolorize effluents, is accepted, as these

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technologies offer lower cost and environment friendly methods.13-16

, and above the concentration of 1 mg L-1, the dye is visible in the wastewater.5 Such dyes

ozonation11 and electrochemical



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There are number of studies suggested that microalgae are ideal biosorbents for

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wastewater treatment systems due to the ease of growth in simple medium, cheapness and

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availability, high surface area and high binding affinity.15 However, these biosorbents have

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several limitations, such as low resistance to chemicals and heat. In order to overcome this

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problem, immobilization of microorganisms has been proposed and investigated as a viable

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means of decolorization and degradation of dyes.17 For instance, utilization of immobilized

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Chlorella vulgaris and Scenedesmus rubescens on a membrane system to remove nitrate from

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municipal wastewater were found to be efficient.18 In addition, Wang et al.19 showed that

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employing immobilized Scenedesmus in calcium alginate as algal sheets is efficient in

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removal of ammonia nitrogen and orthophosphate from municipal wastewater. There have

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been few studies on the use of immobilized algae to remove color from dye solutions. For

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instance, one study reported that degradation of a brown dye by immobilized Chlorella

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pyrenoidosa in calcium alginate is better than free cells.20

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Electrospinning is a very promising technique for the production of nanofibers owing

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to its simplicity, versatility and cost-effectiveness.21-23 The unique features (large surface-to-

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volume ratios and highly porous structures) of the electrospun nanowebs pave the way for

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these intriguing materials during use of environmental applications as filter or membrane

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systems24-27. Electrospun nanofibers have huge potential to be used as a substrate for various

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additives, compounds, active agents and even microorganism. The integration of

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microorganism in electrospun nanofibers is quite applicable for filtration and purification

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purposes. For instance, there are few studies reported in the literature relating to incorporation

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of bacteria in electrospun nanofibers by using different approaches.28-37 In one of our recent

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related study, Acinetobacter calcoaceticus STB1 cells were immobilized on electrospun

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cellulose acetate nanofibrous webs (CA-NFW) and used for the removal of ammonium.36 In

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another recent study of ours, three different types of bacteria were immobilized on CA-NFW


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for removal of methylene blue dye.17 There are studies in the literature related to

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incorporation of microalgae in electrospun nanofibers.38-40 For instance, study by Kim et al.38

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fabricated electrospun polycaprolactone nanofiber containing Spirulina and tested as a

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potential matrix for a culture of primary astrocytes. Cha et al.39 were prepared silk fibroin

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nanofiber scaffold containing microalgae Spirulina extract. The functional nanofibers

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containing microalgae have great potential for the environmental practices. In a study by

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Eroglu et al.40 algal cells were effectively immobilized on electrospun chitosan nanofiber mats

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for nitrate removal.

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Here, Chlamydomonas reinhardtii was chosen as the model organism which is

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investigated for physiological, biochemical and genetic properties of division Chlorophyta.41

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Reactive Black 5 (RB5) is in the reactive azo dye group which extensively used in textile

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industries that producing dying cotton, woolen, and nylon fabric.42 Except that, the use of

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RB5 has negative effects for human life, exposure to this dye may cause allergic reactions and

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cancer.43 Reactive Blue 221 (RB221) has a complex aromatic structure, consisting of

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monochlorotriazine and sulfato ethyl sulfone derivatives as functional groups. So, dye belongs

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to the group of hetero-bifunctional reactive dyes.44 Polysulfone (PSU) as a membrane material

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is due to its excellent thermal and mechanical stability, as well as its resistance to oxidizing

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agents. PSU has been used as the base of ion-exchange membranes.45,59 At present, there is no

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single process which is capable of treating wastewater. In the literature, adsorption is known

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as one of the effective and low cost methodology for removal of organic and inorganic

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pollutants and dyes from water.50 For this reason, it will be quite interesting to integrate

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microalgae cells in electrospun PSU nanofibrous web to be employed in wastewater

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treatment. Considering the lack of any reports investigating the reactive dye removal by using

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microalgae integrated nanofibrous web, to the best of our knowledge, this is the first report

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investigating dye removal capacity of these biocomposite materials. The aim of this study is



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to present and investigate an efficient methodology for color treatment of industrial textile

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wastewater effluent by using a nanofibrous adsorbent based on microalgae immobilized PSU

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nanofiber web (PSU-NFW) for the adsorptive and biological removal of Reactive Black 5

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(RB5) and Reactive Blue 221 (RB221) as an example of reactive dyes. To maximize the

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removal capacity of dye through microalgae/PSU-NFW, we have studied decolorization time

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and different dye concentrations. Finally, the reusability of microalgae/PSU-NFW was tested.

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EXPERIMENTAL

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Contaminant: reactive dyes

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Two kinds of reactive dye, Reactive Black 5 and, Reactive Blue 221 were obtained from

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SETAŞ Chemistry Factory (Tekirdag, Turkey). The concentration of dyes in each aqueous

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solution was measured on an UV-Vis spectrophotometer while taking the absorption at 597

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nm. All the chemicals were of highest purity available and were of analytical grade.

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Electrospinning of polysulfone nanofibrous web (PSU-NFW)

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The homogenous electrospinning solution was prepared by dissolving polysulfone (PSU, Mw

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~60,000, Scientific Polymer Products, Inc.) in N,N-dimethylacetamide/acetone (9/1, (v/v))

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(DMAc, Sigma Aldrich, 99 %; acetone, Sigma Aldrich, ≥99% (GC)) binary solvent mixture at

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32% (w/v) polymer concentration. Then, clear solution was inserted in a syringe fitted with

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metallic needle with 0.4 mm inner diameter. The syringe was located horizontally on the

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syringe pump ((model KDS-101, KD Scientific, USA). The electrode of the high-voltage

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power supply (Spellman, SL30, USA) was clamped to the metal needle tip, and the plate

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aluminum collector was grounded. Electrospinning parameters were adjusted as follows: feed

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rate of solutions = 0.5 mL/h, applied voltage = 10 kV, tip-to-collector distance = 10 cm.

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Electrospun nanofibers were deposited on a grounded stationary plate metal collector covered

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with aluminum foil. The electrospinning apparatus was enclosed in a Plexiglas box, and

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electrospinning was carried out at 23

o

C at 18% relative humidity. Collected


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nanofibers/nanowebs were dried in vacuum oven at 50 oC overnight to remove the solvent

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residuals.

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Growth and immobilization of microalgae strain

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Chlamydomonas reinhardtii was obtain from Life Sciences Application and Research Center,

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culture collection of Sustainable Energy Lab, Gazi University. Cells were grown in Tris–

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Acetate–Phosphate (TAP) medium and cultivated at 23 °C under continuous illumination

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(150 µmoles photons m-2 s-1). Chlamydomonas reinhardtii biomass was measured by counting

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the number of cells by optical microscopy (Olympus, Japan) using a Neubauer

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Hemocytometer (Germany). Then, 1 mL algae solution contains ∼ 7x106 cells mL-1 was

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placed onto UV-sterilized 20 mg PSU-NFW and incubated at 23 °C in a rotary shaker at 100

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rpm for 10 days to allow sufficient attachment of algae cells to the surface of the web. After

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attachment, microalgae on PSU-NFW samples was quantified using a multi-step process of

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cell removal contains sonication at a frequency of 40 kHz (Branson Ultrasonic Cleaner;

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Branson Ultrasonics, Danbury, CT) for 30 minutes and vortexing 30 seconds. After

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detachment process, cells counted using Neubauer Hemocytometer.

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Characterization of polysulfone nanofibrous web (PSU-NFW)

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The morphologies of pristine PSU-NFW and microalgae/PSU-NFW were investigated by

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using scanning electron microscope (SEM, Quanta 200 FEG, FEI) while the accelerating

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voltage was changed between 3 to 5 kV. Samples were washed twice with PBS buffer and

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then air-dried samples were coated with approximately 5 nm layer of gold-palladium before

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imaging.

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Raman spectra were recorded on a WITec alpha300 S Confocal Raman spectrometer

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for confirmation of microalgae attachment. The near-infrared 785 nm line was used for

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excitation. For all presented spectra, the laser power on the sample did not exceed 3 mW and

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10 scans were collected in 15 s. All spectra were recorded with a spectral resolution of 4 cm−1.



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Batch decolorization operation

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To evaluate the effects of operation factors on the efficiency of decolorization, the batch

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decolorization experiments were carried out at different contact time (0-14 day) and initial

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dye concentrations (10, 25 and 50 ppm). After inoculation process, aliquots (4 mL) of the

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culture media were withdrawn, centrifuged at 10.000 g for 10 minutes to separate the

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microalgae mass. The supernatant was used for analysis of decolorization and all the

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experiments were repeated in triplicates. Absorbance of the supernatant withdrawn at

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different time intervals were measured at the absorbance maximum wavelength for the dye

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Remazol Black 5 (RB5) and Reactive Blue 221 (RB221) (λ max = 597) on a Shimadzu

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spectrophotometer. Decolorization was determined by absorbance reduction. The percentage of decolorization was calculated from the difference between initial and final values using the following formula:

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Uninoculated erlenmeyer flasks containing dyes were used as control samples to observe any

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reactions of the media with the dye. Each of these experiments and the measurements

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described below to follow the daily changes in the samples throughout the incubation period.

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Each experiment consisted of triplicate batches. Each result is an average of three parallel

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replicates. ± indicates standard deviation among the replicates.

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Decolorization test

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To determine the effect of contact time, 20 mg microalgae/PSU-NFW were incubated into

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100 mL media containing 10 mg L-1 RB5 and RB221 dye solution at pH 6 and placed on a

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incubator at 23 °C in a rotary shaker at 100 rpm for different time (1, 2, 3, 5, 7, and 14 days).

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The same dye concentration (10 mg L-1) is employed to obtain positive control with free

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microalgae cells, negative control with pristine PSU-NFW and experimental set with

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microalgae/PSU-NFW. 8 ACS Paragon Plus Environment

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Textile processing wastewater with dye contents in the range of 10–200 mg L-1 is

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highly colored. For this reason, initial dye concentrations were adjusted to 10, 25 and 50 mg

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L-1 to represent low, medium and high concentrations of dye. Microalgae/PSU-NFW were

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cultivated for 14 days in conical flask containing 100 mL TAP medium with dye RB5 and

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RB221 at a concentration of 10, 25, 50 mg L-1 separately to study the effect of increasing dye

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concentration on percentage dye decolorization. All determinations were made daily during

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the incubation.

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Reusability experiments for microalgae/PSU-NFW

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Decolorization studies were performed 3 times to assess the reusability of the

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microalgae/PSU-NFW for an initial concentration of 10 mg L-1 for RB5 and RB221 dyes.

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Before each cycle, microalgae/PSU-NFW pieces were washed three times with sterile PBS

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buffer. Dye decolorization experiments were performed at 100 rpm and 23 °C for 14 days

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after each washing step, for a total of 3 cycles. Dye concentrations were measured at 0 h and

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14 days. Each cycle was terminated after 14 days of total incubation and washing steps were

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repeated before the initiation of the next cycle. All tests were done in triplicate.

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Statistical analysis

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Student’s t-test was applied for statistical analyses. Analyses were done by using the software

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Minitab Version 13.2 (Minitab Inc., USA) at a 0.05 level of probability.

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3. RESULTS AND DISCUSSION

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3.1. Immobilization of Chlamydomonas reinhardtii on polysulfone nanofibrous web

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Several studies have been reported on wastewater treatment by using microalgae cultures

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inside alginate beads, porous glass, and several synthetic polymers.51,52 However, these

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materials have limitations such as encapsulating materials having volume/surface ratios

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usually orders of magnitude larger than thin films. As a consequence, algal viability is mostly

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reported to decrease which relates to the need for the nutrients or reactants to diffuse far into



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the material to reach the algal cells.53 In this study, electrospun nanofibrous web as the matrix

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for immobilizing the algal cells is used for overcome aforementioned problems.

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Fig. 1a shows the schematic representation of the electrospinning process for

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polysulfone nanofibrous web (PSU-NFW). Fig. 1b shows the photos of microalgae cells

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attached to the surface of PSU-NFW after 3 days, and after 10 days from the start of the

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growth experiments. As seen in Fig. 1b, increasing green color on the surface is seen due to

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the increased concentration of microalgae cells on the PSU-NFW with respect to time. Fig. 1c

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shows the chemical structures of Remazol Black 5 (RB5) and Reactive Blue 221 (RB221),

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respectively.

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Fig. 2a shows the SEM image of the nanofibrous structure of the electrospun PSU-

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NFW having uniform and bead-free morphology. Moreover, SEM analysis was performed

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after 10 days of incubation for the microalgae attachment to PSU-NFW and shown in Fig. 2b–

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c. After 10 days, C. reinhardtii were strongly attached onto PSU-NFW. This type of

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attachment was found to be adequate for further studies, and dye decolorization experiments

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were performed with microalgae/PSU-NFW at this stage. In addition, according to counting

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experiments, 1 mL algae solution contains ~7x106 cells mL-1 was used for the attachment.

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After deattachment process, ~5x106 cells mL-1 per volume of web was counted. As a result

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~80% microalgae was successfully attached to PSU-NFW.

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It is known that Raman spectroscopy could be a very informative and convenient tool

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for studying the structure of polymers54 and microorganisms.55,56 Raman spectra of pristine

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PSU-NFW (Fig. 3a) and microalgae/PSU-NFW (Fig. 3b) with main Raman shifts and

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assignments of the Raman bands are given in Figure 3. Moreover, the insets show the

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microscope image of pristine PSU-NFW and microalgae/PSU-NFW respectively. In Raman


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spectrum of the pristine PSU-NFW, the band around 788 cm−1 is associated with the presence

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of C–S–C symmetric stretch. Also the peaks around 1073, 1108, 1149, 1204 cm−1 are due to

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the presence of symmetric SO2 stretching, asymmetric SO2 stretching, symmetric C–O–C

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stretching, asymmetric C–O–C stretching, respectively. In Raman spectrum taken from the

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microalgae/ PSU-NFW, wherein the presence of dominant polysaccharide, glycoproteins and

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lipid frequencies around 1000–1500 cm−1 was identified. In addition, specific β-carotene peak

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(C=C stretching) at 1517 cm−1 was seen57 and results confirmed that C. reinhardtii were

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attached successfully on the PSU-NFW.

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Contact time is one of the important parameters to successfully adsorb the pollutants

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for practical application. The effect of contact time on the decolorization process were studied

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in the time range from 1 to 14 day at 10 mg L-1 initial RB5 and RB221 at pH 6.0 at 23 °C.

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The RB5 and RB221 decolorization performance of pristine PSU-NFW, free microalgae cells

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and microalgae/PSU-NFW after certain time periods (1, 2, 3, 5, 7 and 14 days) are shown in

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Fig. 4, respectively. During the experiments, there was no reaction between media content and

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dyes. As clearly seen in Fig. 4, the decolorization increased during the first 14 days, the dye

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decolorization of RB5 for microalgae/PSU-NFW was 73.0±0.3% within 14 d when compared

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to 68.8±0.3% and 12.4±0.3% for free microalgae cells and pristine PSU-NFW, respectively.

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On the other hand, the decolorization efficiency for RB221 was found to be low when

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compared to RB5 dye. In media of RB221, the maximum dye decolorization for

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microalgae/PSU-NFW was 30.2±0.2%. The decolorization of RB221 was 28.6±0.2% for free

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microalgae cells and 5.5±0.4% for pristine PSU-NFW. This variation in the decolorization of

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different dyes might be attributable to the structural diversity of the dyes. Statistical analyses

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revealed that there is no statistically significant difference between free microalgae and

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microalgae/PSU-NFW decolorization rates (P > 0.05). Results of this study revealed that 14



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Page 12 of 37

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day of contact time is required to achieve maximum decolorization. Our results showed that

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the decolorization efficiency of microalgae/PSU-NFW for RB5 and RB221 dyes was slightly

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better than the free microalgae cells and it was much better than the pristine PSU-NFW. So,

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the decolorization performance of microalgae/PSU-NFW is quite impressive and has certain

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advantages over using free microalgae cells. Firstly, microalgae/PSU-NFW can be reusable

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whereas free microalgae cells when dispersed throughout the medium/wastewater, it is quite

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difficult to harvest, dewatering and reuse them in another dye-contaminated wastewater.

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Secondly, microalgae/PSU-NFW occupies less space and requires smaller volume of growth

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medium when compared to stock solutions of free microalgae cells. So, microalgae/PSU-

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NFW would be more practical and cost-effective for treatment of dye-contaminated

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wastewater.

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The influence of initial dye concentration on the decolorization process of RB5 and

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RB221 reactive dyes by microalgae/PSU-NFW was investigated by using various dye

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concentrations; 10, 25 and 50 mg L-1. The results were obtained during 14 d of incubation. As

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given in Fig. 5a, RB5 decolorization was achieved 73.0±0.3% decolorization at 10 mg L-1.

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For 25 mg L-1 dye concentration, the decolorization capacity of RB5 by microalgae/PSU-

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NFW was 47.7±0.2%. When dye concentration was increased up to 50 mg L-1, the

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decolorization capacity was 18.7±0.4%. It was noted that more or less same amount of RB5

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dye (~ 7.3-11.9 mg L-1) was removed by microalgae/PSU-NFW from the solutions having dye

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concentrations of 10, 25 and 50 mg L-1. At the end of the experiments, the pH value was

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checked and a slight decrease from 6.0 to 5.85 was observed. Moreover, the structural

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morphology of the microalgae/PSU-NFW was investigated by SEM after 14 days

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decolorization process. Fig. 6a-b confirmed that nanofibrous structure was preserved and

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microalgae were retained and still have a proper shape when subjected to RB5 solution after


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14 d. In the case of the RB221 dye decolorization by microalgae/PSU-NFW (Fig. 5b), the

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decolorization capacity was found to be 30.2±0.2% in the concentration of 10 mg L-1 dye

3

concentration. For 25 mg L-1 dye concentration, the decolorization capacity of RB221 by

4

microalgae/PSU-NFW was 13.6±0.9%. In the case of 50 mg L-1 RB221 concentration, the

5

removal of RB221 dye was 4.8±0.3%. As a result, approximately same amount of RB221 dye

6

(~ 2.4-3.0 mg L-1) was removed by microalgae/PSU-NFW. It was observed that the pH value

7

of the solution was also decreased from 6.0 to 3.45. The decrease could be attributed to the

8

presence of excess H+, making adsorption less favourable. Furthermore, at lower pH below

9

this point, microalgae growth decreased due to the increase in the toxicity. SEM analysis

10

confirmed that (Fig. 6c-d) wherein circular shapes of the microalgae can’t be observed due to

11

severe effect of the RB221. 58,59

12

13

14

3.2. Reusability results

15

From the viewpoint of biotreatment studies, it was essential to monitor the reusability of the

16

strain. Dye decolorization capability of microalgae/PSU-NFW was tested for three cycles of

17

reuse (Fig. 7). As seen in Fig. 7, the RB5 and RB221 decolorization efficiency was decreased

18

for higher cycles. The decline in the removal efficiency might be due to detachment of the

19

immobilized bacteria in the washing step and dye toxicity to microalgae cells. After the first

20

cycles of regeneration, favorable % removal of dyes was observed as 60±0.5% and

21

15.6±0.7% for RB5 and RB221, respectively. For the 3th regeneration cycle, the reactive dyes

22

decolorization dropped due to decreasing algae cells number to 51.0±0.7% and 8.5±0.5% for

23

RB5 and RB221, respectively. For practical applications, the level of reusability is an

24

important issue. 51.0±0.7% of the dye decolorization capacity was obtained for the 3th cycle

25

for RB5 which suggests that microalgae/PSU-NFW can sustain their decolorization capacity



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Page 14 of 37

1

under several cycles of reuse and may be utilized repeatedly for dye decolorization of

2

wastewater in textile and paint industry.

3 4

CONCLUSION

5

Electrospun PSU-NFW was chosen as a suitable support for microalgae growth for

6

preparation of biocomposite which was capable of decolorization of reactive dyes in

7

wastewater. RB5 and RB221 reactive dyes were chosen as the target contaminant since they

8

are extensively used in textile industry. The microalgae/PSU-NFW was found to be quite

9

successful for the removal of these reactive dyes from the aqueous environment. In fact, our

10

results demonstrated that the decolorization capacity of microalgae/PSU-NFW for RB5 and

11

RB221 dyes was even better than the free microalgae cells and it was much better than the

12

pristine PSU-NFW. The reusability of microalgae/PSU-NFW was determined after three

13

cycles and ~ 50% of the RB5 dye decolorization capacity was obtained at the end of the 3th

14

cycle suggesting that these microalgae/PSU-NFW can be reused and may be utilized

15

repeatedly for dye decolorization in industrial wastewater. So, the decolorization performance

16

of microalgae/PSU-NFW is quite notable and has several advantages over using free

17

microalgae cells. Due to its simple, reusable and nanoporous characteristics, the

18

microalgae/PSU-NFW biocomposite can be a promising membrane material for industrial

19

wastewater treatment.

20

Acknowledgements

21

The Scientific and Technological Research Council of Turkey (TUBITAK, project

22

#114Y264) is acknowledged for funding the research. Dr. Uyar also acknowledges The

23

Turkish Academy of Sciences - Outstanding Young Scientists Award Program (TUBA-

24

GEBIP) for partial funding of the research. A. Celebioglu acknowledges TUBITAK (project

25

#113Y348) for a postdoctoral fellowship.


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7 8

Figure Captions

9

Figure 1. (a) Schematic representation of the electrospinning process for PSU-NFW. (b)

10

Photos of attachment of free microalgae cells on PSU-NFW for three and ten days process

11

process (c) the chemical structures of Remazol Black 5 (RB5) and Reactive Blue 221

12

(RB221).

13

Figure 2. Representative SEM images of (a) pristine PSU-NFW and (b-c) microalgae/PSU-

14

NFW (in different magnifications).

15

Figure 3. Raman spectra of (a) pristine PSU-NFW and (b) microalgae/PSU-NFW after 14

16

days attachment process. The insets show the microscope image of pristine PSU-NFW and

17

microalgae/PSU-NFW, respectively.

18

Figure 4. The effect of contact time on the decolorization yield of the microalgae/PSU-NFW

19

in the 10 mg L-1 dye of (a) RB5, (b) RB221 (pH 6; Temp: 23 °C; stirring rate: 100 rpm). Error

20

bars represent the means of three independent replicates.

21

Figure 5. The effect of initial dye concentration on the decolorization yield of the

22

microalgae/PSU-NFW polysulfone nanofibrous web in the 10 mg L-1 dye of (a) RB5, (b)

23

RB221 (pH 6; Temp: 23 °C; stirring rate: 100 rpm). Error bars represent the means of three

24

independent replicates.



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1

Figure 6. Representative SEM images of microalgae/PSU-NFW after 14 days decolorization

2

process for RB5 (a) low magnification, (b) high magnification; for RB221 (c) low

3

magnification, (d) high magnification.

4

Figure 7. Reusability test results of the three cycles of RB5 and RB221 dye decolorization

5

experiments at the initial dye concentration of 10 mg L-1. Error bars represent the means of

6

three independent replicates.

7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25


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1


FIGURES:

2 3

Figure 1. (a) Schematic representation of the electrospinning process for PSU-NFW. (b)

4

Photos of attachment of free microalgae cells on PSU-NFW for three and ten days process (c)

5

the structures of Remazol Black 5 (RB5) and Reactive Blue 221 (RB221).

6 7 8 9 10 11



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1 2

3 4

Figure 2. Representative SEM images of (a) pristine PSU-NFW and (b-c) microalgae/PSU-

5

NFW (in different magnifications).

6 7 8 9 10 11 12 13 14 15 16


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1 2

Figure 3. Raman spectra of (a) pristine PSU-NFW and (b) microalgae/PSU-NFW after 14

3

days attachment process. The insets show the microscope image of pristine PSU-NFW and

4

microalgae/PSU-NFW respectively.

5 6



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Page 26 of 37

1 2

Figure 4. The effect of contact time on the decolorization yield of the microalgae/PSU-NFW

3

in the 10 mg L-1 dye of (a) RB5, (b) RB221 (pH 6; Temp: 23 °C; stirring rate: 100 rpm). Error

4

bars represent the means of three independent replicates.

5


Page 27 of 37

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1 2

Figure 5. The effect of initial dye concentration on the decolorization yield of the

3

microalgae/PSU-NFW polysulfone nanofibrous web in the 10 mg L-1 dye of (a) RB5, (b)

4

RB221 (pH 6; Temp: 23 °C; stirring rate: 100 rpm). Error bars represent the means of three

5

independent replicates.

6 7 8 9



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1 2

Figure 6. Representative SEM images of microalgae/PSU-NFW after 14 days decolorization

3

process for RB5 (a) low magnification, (b) high magnification; for RB221 (c) low

4

magnification, (d) high magnification.

5 6 7 8 9 10


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1 2

Figure 7. Reusability test results of the three cycles of RB5 and RB221 dye decolorization

3

experiments at the initial dye concentration of 10 mg L-1. Error bars represent the means of

4

three independent replicates.

5



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Figure 1. (a) Schematic representation of the electrospinning process for PSU-NFW. (b) Photos of attachment of free microalgae cells on PSU-NFW for three and ten days process process (c) the chemical structures of Remazol Black 5 (RB5) and Reactive Blue 221 (RB221). 370x480mm (150 x 150 DPI)

ACS Paragon Plus Environment

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Figure 2. Representative SEM images of (a) pristine PSU-NFW and (b-c) microalgae/PSU-NFW (in different magnifications). 134x38mm (300 x 300 DPI)



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Figure 3. Raman spectra of (a) pristine PSU-NFW and (b) microalgae/PSU-NFW after 14 days attachment process. The insets show the microscope image of pristine PSU-NFW and microalgae/PSU-NFW, respectively. 108x55mm (300 x 300 DPI)


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Figure 4. The effect of contact time on the decolorization yield of the microalgae/PSU-NFW in the 10 mg L-1 dye of (a) RB5, (b) RB221 (pH 6; Temp: 23 °C; stirring rate: 100 rpm). Error bars represent the means of three independent replicates. 300x469mm (150 x 150 DPI)



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Figure 5. The effect of initial dye concentration on the decolorization yield of the microalgae/PSU-NFW polysulfone nanofibrous web in the 10 mg L-1 dye of (a) RB5, (b) RB221 (pH 6; Temp: 23 °C; stirring rate: 100 rpm). Error bars represent the means of three independent replicates. 452x582mm (300 x 300 DPI)


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Figure 6. Representative SEM images of microalgae/PSU-NFW after 14 days decolorization process for RB5 (a) low magnification, (b) high magnification; for RB221 (c) low magnification, (d) high magnification. 75x64mm (300 x 300 DPI)



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Figure 7. Reusability test results of the three cycles of RB5 and RB221 dye decolorization experiments at the initial dye concentration of 10 mg L-1. Error bars represent the means of three independent replicates. 290x154mm (55 x 55 DPI)


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TOC figure 127x41mm (300 x 300 DPI)


Microalgae Immobilized by Nanofibrous Web for Removal of Reactive

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