Effective removal of organics from Bayer liquor through combined sonolysis and ozonation: Kinetics and mechanism

[Display omitted] •Combined sonolysis and ozonation (US/O3) treatment for Bayer liquor is proposed.•The types of organics in Bayer liquor and their oxidation mechanism are proposed.•US/O3 is an alternative method for the removal of organics in Bayer liquor.•US/O3 holds the advantages of green efficiently and convenient to remove organics. The presence of organic compounds in the waste liquor is of serious environmental concern that has plagued the development of alumina industry (Bayer Process). The present work attempts to develop a green and efficient process for removal of organics utilizing combined effect of sonolysis and ozonation (US/O3). The effects of reaction duration, ozone concentration and ultrasonic power are assessed for sonolysis (US), ozonation (O3) and combination of sonolysis and ozonation (US/O3). The optimal conditions for US/O3 treatment system is identified to be a reaction duration of 7 h, ozone concentration of 7.65 g/h, and ultrasonic power of 600 W. The total organic carbon (TOC) removal and decolorization are 60.13% and 87.1%, respectively. The process can be scaled-up to industrial scale, which could potentially serve to be a convenient, safe and sustainable alternative to the exisiting treatment technologies. Additionally, the treated waste water can be reused contributing to an improvement in the overall economics.