Phenolic compounds are considered as one of the most hazardous organic pollutants in wastewater owing to their high toxicity even at very low concentrations. They pose serious problems to human health and the environment due to their low biodegradability and high biotoxicity. Combined ozonation with adsorption has recently emerged as a popular technology for the removal of phenolic compounds from aqueous effluents because of their high efficiency, low cost, and simple application. Ozone (O3) is an effective oxidizing agent (E0 = 2.07 V) that may directly oxidize phenolic compounds or indirectly oxidizing them with hydroxyl radical. Mineralization of phenolic compounds by ozonation alone is more difficult because these generate recalcitrant intermediates such as catechol, hydroquinone/benzoquinone, oxalic, and formic acids. These compounds still remain in the aqueous solution, thereby contributing to the Chemical Oxygen Demand (COD). However, including adsorption in the treatment process will enable the mopping up the intermediates so that synergy in the treatment may be achieved. Research work that have been reported in the literature on the intermediates analysis, degradation pathways, and reaction mechanisms for the phenol degradation using combined ozonation with adsorption in the batch reactor will be summarized.
Batch studies are important to understand reaction pathways, equilibrium limits, and kinetics of removal, but continuous studies are essential for large scale application of the technology in industrial applications. Combined adsorption with ozonation in a fluidized bed column is proposed as an effective treatment technology for large scale process owing to high heat and mass transfer rates, uniform mixing of solids, good contact between particles and fluid, low energy requirements, cost-effectiveness, and, the constant pressure drop across the bed within the range of operating flowrate. Hydrodynamic studies in fluidized bed column are carried out and the hydrodynamic parameters viz. minimum fluidization velocity, terminal velocity of particles, pressure drop across the bed, and bed voidage are presented. Preliminary work on adsorption kinetics, and isotherms will be presented.
Keywords: Ozonation, Adsorption