High performance ozone nanobubbles based advanced oxidation processes (AOPs) for degradation of organic pollutants...

Advanced Oxidation Processes (AOPs) have proven to be an effective solution for chemical wastewater treatment, particularly for degradation of organic pollutants, especially dyes. Ozonation is recognized as one of the most prevalent AOPs. Nevertheless, some cases show a lowered efficiency of O₃ utilization which is attributed to its inadequate distribution in the treated water causing low residence time, low mass transfer coefficient as well as shorter half-life. This study demonstrates the application of ozone nanobubbles to enhance the degradation of organics under high pollution load conditions. We propose an integrated method that utilizes bulk nanobubbles to enhance the reactivity of ozone for the degradation of organics. We examined the degradation of organic pollutants under parameters such as varying pH levels, ozone concentrations and presence of salts and surfactants. The degradation of the organic pollutant by ozone nanobubbles (0.177 L mg^-1min^-1) demonstrated a threefold increase in reaction rate constants compared to microbubbles (0.025 L mg^-1min^-1). The plausible reason for these findings is (i) higher mass transfer coefficient (ii) higher ozone solubility (iii) NBs may act as a surface for chemical reaction (iv) NBs may increase the half-life of ozone. The presence of reactive oxygen species was verified using scavenging tests. This part of the studies revealed contribution of reactive oxygen species (ROSs) such as hydroxyl radical (^•OH), superoxide radical anion (O₂^•-) and singlet oxygen (¹O₂) in the degradation process. The conditions that provide total degradation of 100% in 300 s for both organic pollutants (Green rit and methylene blue dye) are: 5 LPM (Litre per minute) ozone flow rate, acidic pH, monovalent salts (NaCl, 2 mM) and lower concentration of surfactants (CTAB and SDS, 0.3 CMC). A degradation mechanism has been outlined based on intermediates identified by LC-MS. This work presents a new method that combines AOPs with nanobubbles, which should lead to increased environmental sustainability and efficiency.