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.
Highlights
About 97% of the world’s water resources are salty, which makes the water undrinkable, and less than 1% water is potable
low-molecular-weight salt (LMWS) 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]
Based on the presented results, it can be concluded that ozonation is an efficient method for the decolorization of textile wastewater, characterized by high salinity and alkalinity
Summary
About 97% of the world’s water resources are salty, which makes the water undrinkable, and less than 1% water is potable. 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]. Many industrial branches produce salty wastewater that contains a huge concentration of low-molecular-weight salt (LMWS), like NaCl and Na2 SO4. 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]. LMWS cannot be eliminated from a typical exhaustion-fixation dyeing process. Thousands of tons of LMWS are used daily by textile manufacturers [2]
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