The textile industry is one of the longest and most complicated industrial chains in manufacturing industry and still among the largest qindustries in the world regarding production rates and numbers of labour. Each step in the textile manufacturing process generates some kind of solid, liquid or gaseous waste. The textile industries as well as the waste streams generated by textile processing activities are generally characterized by the different preparation (desizing, scouring, mercerising and bleaching), dyeing and finishing activities
A large amount of refractory COD is caused by high molecular synthetic textile auxiliaries and dyes that are mainly colored and/or toxic compounds. In some cases, textile dyes contain high adsorbable organically bound halogens (AOX) and heavy metal concentrations in their chemical structures. In particular, because particularly pigments are highly structured, complex polymers and toxic to microorganisms, biological treatment of these effluents that is the most common way of textile wastewater treatment, cannot remove all organic substances sufficiently.
Generally, there are several types of wet processing stages, fabric production profiles and hence fluctuations in effluent flow rates and compositions involved. Liquid wastes are the main contributors to waste emissions, whereas solid wastes mainly originate from fabric rejects, and air emissions are related to volatile organic compounds (VOCs). Waste emissions are typically hot, alkaline, with an apparent smell and colour due to the consumption of dyes and auxiliaries in the dyeing process. Textile effluent discharge into natural water bodies hence may lower the dissolved oxygen levels and deteriorate the aesthetic value of water sources owing to their strong colour and foaming nature.
Ozone is known to effectively decolourise textile dyes in aqueous solution and in real/simulated dyehouse effluent at mass-transfer limited rates. Ozonation pretreatment of textile industry wastewater is an important step in terms of improving wastewater biodegradability as well as reducing acute toxicity, which should be removed completely via sequential biological treatment. Also, various Fenton Processes and AOP combinations are found to increase COD and color removal efficiencies