Title: Textile wastewater treatment via ozonation pre-treated with ultrasound cavitation and Fenton-like advanced oxidation processes

Abstract

The Common Effluent Treatment Plant (CETP) at the Kerala Industrial Infrastructure Development Corporation (KINFRA), Kannur, Kerala, India daily treats one lakh liters of textile effluent, containing azo reactive dyes, with the chemical oxygen demand (COD) removal of almost 100%. Nevertheless, large amount (80-100 kg per day) sludge is produced in the stage-1 facility, due to the involvement of chemical and biological processes, which creates handling, storage, transport and reuse issues. Hence, the present work primarily focuses on treating the KINFRA effluent for the maximum COD removal without the generation of any solid sludge. Advanced oxidation processes (AOPs), such as the modified ultrasound (US) cavitation, Fenton-like, and ozonation (O3), have been utilized as stand-alone techniques for this purpose. Moreover, the modified US cavitation and Fenton-like AOPs have also been employed as pre-treatment methods for the post-treatment with the O3 process which has been conducted at the varying O3 flow rate (2-6 g h-1). The US cavitation process has been modified by investigating the effect of various parameters, such as the US power (50-250 W), initial effluent pH (2-10), and O2 flow rate (1-4 L min-1). On the other hand, for the development of Fenton-like AOP, flyash (FA)- Pd composite particles have been synthesized via an electroless process and utilized as activator to activate the various oxidants such as the persulfate (S2O82-) and hydrogen peroxide (H2O2) to generate the radical-ions (●OH and O2●-) for the decomposition of azo reactive dyes present within the textile effluent. The concept of mixed oxidants has also been utilized for the treatment of KINFRA effluent via the Fenton-like method. It has been observed that although the maximum COD removal (93%), without the sludge formation, is obtained by using the Fenton-like process as a pre-treatment and O3 as a post-treatment, the stand-alone O3 process which provides the COD removal of 86-90%, without the sludge formation, appears to be the most superior for the treatment of textile effluent at the commercial level since it can bypass the need to synthesize and use the large amount of FA-Pd based catalyst.