33 Advanced technologies THE EFFECT OF ANIONS ON DECOLORIZATION OF TEXTILE AZO DYE REACTIVE ORANGE 16 WITH UV/H 2 O 2 PROCESS Jelena Mitrović * , Miljana Radović Vučić, Miloš Kostić, Nena Velinov, Slobodan Najdanović, Danijela Bojić, Aleksandar Bojić University of Niš, Faculty of Sciences and Mathematics, Niš, Serbia The efects of various organic and inorganic anions on decolorization of textile dye Reactive Orange 16 by means of hydroxyl radicals have been studied. These ani- ons are commonly present in wastewaters from textile industry and include chloride, sulfate, carbonate/bicarbonate, nitrate and acetate anions. The experiments were conducted in the presence of di ferent concentrations of anions and at di ferent ini - tial pH values in a batch photoreactor equipped with UV-C (254 nm) lamps in the presence of hydrogen peroxide. It was obtained that decolorization efciency was signifcantly afected by nature and concentration of the investigated anions. An in- hibitory efect of acetate anions increased with increasing in their concentration and depended on whether protonated or deprotonated forms are favored. Carbonate anion showed specifc, both positive and negative infuence, depending on its con- centration. Infuence of bicarbonate, nitrate and chloride was more prominent at their higher initial concentrations. The presence of sulfate did not have noticeable impact on decolorization of RO16 dye under investigated conditions. Keywords: advanced oxidation process- es, hydroxyl radicals, carbonate/bicarbo- nate anions, acetate anions Introduction Textile dyes are generally small molecules which contain chromophore, responsible for the color and the functional group that allows dye fxation onto fbers. In terms of the chemical structure, azo dyes represent the largest group (around 50%) of all textile dyestuf produced. Azo dyes con- tain one or more azo groups (-N=N-) mostly linked to ben- zene or naphthalene rings [1]. According to their mode of application, textile dyes can be classifed as acid, reactive, metal complex, disperse, vat, mordant, direct, basic, and sul- phur dyes [1]. Today, most commonly used are reactive dyes which form covalent bonds with the fbers and are used for dyeing of cotton, rayon, wool, silk, and nylon. The reactive dye molecule contains specifc functional groups which can undergo the addition or substitution reactions with the -OH, -SH and -NH 2 groups present in the fbers. Due to very good fastness of the substrate, the reactive dyes are one of the most important groups of dyes for dyeing textiles. However, the reactive dye fxation efciency is generally low (up to 50%), which results in a highly colored dye efuent which is unfavorable on environmental grounds [2]. The strong color of discharged dyes, even in very small concentrations, has a huge impact on the aquatic ecosystem caused by their re- duction of light transmittance (turbidity). Therefore, the efu- ents discharged from textile and dyestuf industries have to be treated due to their impact on water bodies and growing public concern over their toxicity and carcinogenicity [3]. Common treatment processes e.g. adsorption on ac- tivate carbon, focculation, coagulation, reverse osmosis and ultrafltration are non-destructive and just transfer con- taminants from one phase to another and form secondary waste [4]. The alternatives to non-destructive water treat- ment are advanced oxidation processes (AOPs), which are characterized by the generation of highly oxidative spe- cies, such as hydroxyl radicals [5]. Among AOPs, UV/H 2 O 2 process has been successfully applied to treat diferent organic pollutants in water, such as pharmaceuticals (me- probamate, carbamazepine, dilantin, atenolol, primidone and trimethoprim) phenol, sunscreen ingredient PBSA, etc. [6-8]. In this process, UV light is absorbed directly by H 2 O 2 and by its photolysis • OH radicals are generated. These radicals are extremely powerful oxidizing agents, capable of oxidizing organic compounds by hydrogen abstraction, electron transfer, and electrophilic addition [5]. It was re- ported that second-order rate constants for the reaction of • OH radicals with organic compounds are in the range of 107 – 1010 M -1 s -1 , depending on the chemical structure of the pollutant [9]. Owing to high reactivity and non-selectivity of • OH radicals, their availability for a reaction towards the target organic pollutants depends on the concentration of scavengers of • OH radicals, either naturally occurring in the surface water or present in the industrial efuent, such as Cl - , SO 4 2- , CO 3 2- , HCO 3 - , NO 3 - and CH 3 COO - . The main objective of this work was the investigation of the efects of various anions either present in textile waste streams or formed through oxidation treatment, such as chloride, sulfate, carbonate, bicarbonate, nitrate and ace- (ORIGINAL SCIENTIFIC PAPER) UDC 677.281:677.027:54-76+546.215 *Author address: Jelena Mitrović, University of Niš, Faculty of Sciences and Mathematics, Višegradska 33, 18000 Niš, Serbia E-mail: jelenam81@gmail.com The manuscript received: March, 03, 2019. Paper accepted: May, 09, 2019. 8(1) (2019) 33-40