Sequencing coagulation–photodegradation treatment of Malachite Green dye and textile wastewater through ZnO micro/nanoflowers

ABSTRACT

Sequencing coagulation–photodegradation over ZnO micro/nanoflowers was assessed for Malachite Green (MG) dye removal and followed by the MG-containing textile wastewater treatment. The ZnO micro/nanoflowers were prepared using a facile reflux route and analyzed by various characterization techniques. The flower-like morphological structures of ZnO were witnessed through microscopy analyses. X-ray diffraction findings showed that the prepared ZnO samples were highly crystalline with hexagonal wurtzite structure. The operational parameters including type of coagulant, coagulant dosage, solution pH, photocatalyst dosage and light power exerted their individual influences on the removal of MG dye. The CaCO₃ was the best coagulant among the three coagulants tested due to its high formation of precipitates and adsorption of cationic dye molecules. Using CaCO₃ as a coagulant, 88.3% MG removal was obtained at coagulant dosage of 160 mg and solution pH of 9.0. Complete removal of MG was found with 0.5 g L⁻¹ ZnO micro/nanoflowers and 105 W light power. The kinetic analysis showed that a Langmuir−Hinshelwood model was in good agreement with dye removal data. Moreover, a complete removal of MG dye and 80.0% of chemical oxygen demand removal over sequencing coagulation–photodegradation were observed for MG-containing textile wastewater treatment. The sequencing coagulation–photodegradation process using ZnO micro/nanoflowers indicated much promise to be an attractive method for textile effluent treatment applications.

KEYWORDS:

• Coagulation
• dye
• flower-like
• photocatalysis
• textile wastewater
• ZnO

Additional information

Funding

This work was supported by the Universiti Tunku Abdul Rahman (UTARRF/2016–C2/S03 and UTARRF/2017-C1/L02) and Ministry of Higher Education of Malaysia (FRGS/1/2015/TK02/UTAR/02/2 and FRGS/1/2016/TK02/UTAR/02/1).