water Article Brine Recycling from Industrial Textile Wastewater Treated by Ozone. By-Products Accumulation. Part 1: Multi Recycling Loop Lucyna Bili ´nska 1,*, Kazimierz Blus 1, Marta Gmurek 2 and Stanisław Ledakowicz 2 1 Textile Company Bilinski, Mickiewicza 29, 95-050 Konstantynow Lodzki, Poland; [email protected] 2 Faculty of Process & Environmental Engineering, Lodz University of Technology, Wolczanska 213, 90-924 Lodz, Poland; [email protected] (M.G.); [email protected] (S.L.) * Correspondence: [email protected]; Tel.: +48-42-211-05-02; Fax: +48-42-211-05-06 Received: 8 January 2019; Accepted: 28 February 2019; Published: 5 March 2019 Abstract: The “reactive” dyeing of textiles requires an application of low-molecular-weight salts (LMWS), such as NaCl or Na2SO4, as necessary auxiliary agents. LMWS acts only as a remediation factor and remains in the dyeing effluents constitute brine. The main goal of the presented study was to investigate the application of ozone technology for industrial textile wastewater highly polluted by LMWS. The study was divided into two parts. In Part 1, by-products accumulated during multi-recycling of the same wastewater was investigated. While Part 2 was devoted to the scaling up of ozonation process, Part 1 concerns the efficiency of textile wastewater ozonation carried out as a repeatable process. The sequence of wastewater treatment and textile dyeing was repeated four times in a closed loop using the same process water. Although the wastewater decolorization was efficient in the subsequent ozonation cycles, some adverse effects, such as an increase in chemical oxygen demand (COD) and self-buffering at pH 9.5–10.0, were suggested the accumulation of by-products. The preliminary detection of by-products by thin layer chromatography (TLC) revealed phenol and naphthol derivatives as the transformation products (TPs) of ozonation. Dyeing of cotton using purified wastewater (brine) resulted in very good DECMC color matching parameters (under 1.16), but only in the first recycling loop, and then the TPs affected the process. Keywords: ozone treatment; industrial textile wastewater; wastewater recycling; brine production from wastewater; by-products of ozonation 1. Introduction About 97% of the world’s water resources are salty, which makes the water undrinkable, and less than 1% water is potable. Unfortunately, the volume of the potable water used in industry and farming is still increasing, and numerous regions on our planet suffer from a water deficit [1]. Moreover, many industrial branches produce salty wastewater that contains a huge concentration of low-molecular-weight salt (LMWS), like NaCl and Na2SO4. Therefore, a large amount of LMWS is emitted into the environment, which disturbs living conditions in the biosphere [2,3]. As far as salty wastewater is concerned, the textile industry is one of the greatest polluters. LMWSs are commonly used in dyeing processes as auxiliaries—even 1.5 kg of LMWS per 1 kg of textiles can be used in these operations [4–7]. It should be kept in mind that during industrial dyeing by reactive dyes, the application of LMWS is inherent. LMWSs are remediating agents, which increase a dye distribution from the dyebath into the textile material by changing the equilibrium conditions of the dyeing liquor [8]. Therefore, LMWS cannot be eliminated from a typical exhaustion-fixation dyeing process. Consequently, thousands of tons of LMWS are used daily by textile manufacturers [2]. Water 2019, 11, 460; doi:10.3390/w11030460 www.mdpi.com/journal/water Water 2019, 11, 460 2 of 12 The regions of huge areas, like the Panjab region in India, have been polluted by the emission of textile wastewater released into the environment, without any previous purification, which increases general salinity of surface water [3]. It is difficult to find an efficient and inexpensive treatment method that could be used to clean wastewater polluted by LMWS. Especially, biological treatment, which is the most commonly used method, could be severely affected by a high concentration of LMWS. The use of membrane filtration methods could be an option to deal with salinity; however, among them, reverse osmosis (RO) is the only method that can eliminate LMWS from wastewater. On the other hand, RO is not suitable for COD removal from wastewater because of fouling. The use of microfiltration (MF) or ultrafiltration (UF) as a pretreatment step before nanofiltration (NF) and RO is possible, but this solution cannot eliminate the fouling problem entirely. Another problem is the huge volume of highly contaminated concentrate and backwashes. At present, the operating cost of membrane filtration is still high when industrial wastewater treatment is concerned [9]. An application of ozone as a non-discharge treatment method can be an alternative for the purification of textile wastewater contaminated by LMWS. In contrast to membrane filtration, ozonation cannot remove LMWS but can serve as a technique for brine recovery from wastewater. Ozone oxidation can give good results when many poorly degradable contaminants, including textile dyes, are taken into consideration [9,10]. It can be concluded that the effectiveness of dye decomposition by ozone treatment has been proven in many papers, and the field seems to be well covered by the literature (Table1). However, it should be noted that only a few authors have dealt with by-products detection [11–15], scaling-up [16], or purified wastewater recycling [17–20]. A publication that includes all these topics has not been found. Table 1. Literature overview of simulated and industrial textile wastewater treatment by ozonation. COD, chemical oxygen demand; TOC, total organic carbon; BOD, biological oxygen demand. Research Goal Textile Wastewater Type References Simulated [17,21–38] Color, COD, TOC or BOD removal Industrial [19,39–47] Kinetic study Simulated [25–27,30,31,33,35,37,48–62] Products, degradation mechanism Simulated [11–15] Salt or alkaline influence Simulated [13,17,31,34] Simulated [27,28] Cost evaluation Industrial [40,43,44] Simulated [17] Recycling Industrial [18–20] Simulated [23,24,27,29,61,63] Toxicity Industrial [44–46,64,65] Scale upgradation Industrial [16] The main objective of the study presented in Part 1 was to investigate the recycling of purified wastewater. For this purpose, a highly contaminated industrial textile wastewater (the bath after the reactive dyeing of cotton, with a residual LMWS concentration equal to 30 g/L) was treated by ozone to remove color and then recycled as a source of ‘ready to use’ brine for the next dyeing. Therefore, the key idea was not to treat the LMWS as a pollutant, but as a resource that can be recycled. Consequently, the challenge was to keep LMWS concentration at a constant level, while the dye residuals were removed. To this end, the same wastewater was recycled four times (five cycles of fabric dyeing and four cycles of ozonation, carried out in a laboratory scale). The additional goal was to analyze the by-products that could have accumulated due to recycling, and their potential influence on the possibility of brine recycling. Water 2019,, 11,, x 460 FOR PEER REVIEW 33 of of 12 12 2. Experimental 2. Experimental 2.1. Materials 2.1. Materials The substances used for textile dyeing and present in the wastewater were dyes and auxiliaries. The substances used for textile dyeing and present in the wastewater were dyes and auxiliaries. The dyes were: Synozol Yellow KHL (C. I. Reactive Yellow145), Synozol Red K3BS150% (C. I. Reactive The dyes were: Synozol Yellow KHL (C. I. Reactive Yellow145), Synozol Red K3BS (C. I. Reactive Red 195), purchased from KISCO (Eksoy Chemical Industries, Adana, Turkey), and150% C. I. Reactive Red 195), purchased from KISCO (Eksoy Chemical Industries, Adana, Turkey), and C. I. Reactive Black 5 (purified dye, Boruta-Zachem (Bydgoszcz, Poland)). The auxiliaries were: an industrial Black 5 (purified dye, Boruta-Zachem (Bydgoszcz, Poland)). The auxiliaries were: an industrial dyeing dyeing assistant—Perigen LDR (SAA—a naphthalene sulfonic acid and carboxylates mixture, assistant—Perigen LDR (SAA—a naphthalene sulfonic acid and carboxylates mixture, Textilchemie Textilchemie Dr. Petry Co. (Reutlingen, Germany)), as well as NaCl, NaOH, and Na2CO3 (technical Dr. Petry Co. (Reutlingen, Germany)), as well as NaCl, NaOH, and Na CO (technical products from products from Tomchem (Łódź, Poland)). 2 3 Tomchem (Łód´z,Poland)). Raw knitted fabric, made of 100% cotton, was obtained from Sontex DK ApS (Ikast, Denmark); Raw knitted fabric, made of 100% cotton, was obtained from Sontex DK ApS (Ikast, Denmark); this fabric was previously bleached by a hydrogen peroxide method. this fabric was previously bleached by a hydrogen peroxide method. 2.2.2.2. Experimental Experimental Procedure Procedure TheThe experiment was carried outout asas aa sequencesequence of of textile textile dyeing dyeing and and ozonation ozonation steps, steps, according according to tothe the scheme scheme presented presented in in Figure Figure1. 1. Figure 1. Scheme of the recycling procedure (5 dyeing cycles and 4 ozonation cycles); blue—dyeing Figurewith C.I. 1. ReactiveScheme Blackof the 5,recycling yellow—dyeing procedure with (5 C. dyeing I. Reactive cycles Yellow145, and 4 ozonation red—dyeing cycles) with; blue C.I.— Reactivedyeing withRed 195.C.I. Reactive Black 5, yellow—dyeing with C. I. Reactive Yellow145, red—dyeing with C.I. Reactive Red 195. Textile dyeing: Cotton dyeing was carried out in a LABOMAT BFA-12 system (laboratory dyeing machineTextile made dyeing by Mathis: Cotton AG, dyeing Oberhasli, was carried Switzerland), out in a LABOM accordingAT BFA to a- standard12 system exhaustion-fixation (laboratory dyeing machineprocedure made at a by temperature Mathis AG of, Oberhasli 60 ◦C (Figure, Switzerland2). The weight), according of each to sample a standard was 10exhaustion g and the-fixation liquor procedureratio was setat a to temperature 1:12. The alkalis, of 60 which°C (Figure were 2) NaOH.