Multiphase reacting flow studies of bubble column ozonation reactor for water remediation

Analysis of Ozonation Processes Using Coupled Modeling of Fluid Dynamics, Mass Transfer, and Chemical Reaction Kinetics

The efficacy of oxidation of recalcitrant organic contaminants in municipal and industrial wastewaters by ozonation is influenced by chemical reaction kinetics and hydrodynamics within a reactor. A 3D computational fluid dynamics (CFD) model incorporating both multiphase flow and reaction kinetics describing ozone decay, hydroxyl radical (^•OH) generation, and organic oxidation was developed to simulate the performance of continuous flow ozonation reactors. Formate was selected as the target organic in this study due to its well-understood oxidation pathway. Simulation results revealed that the dissolved ozone concentration in the reactor is controlled by rates of O₃(g) interphase transfer and ozone self-decay. Simulations of the effect of various operating conditions showed that the reaction stoichiometric constraints between formate and ozone were reached; however, complete utilization of gas phase ozone was hard to achieve due to the low ozone interphase mass transfer rate. Increasing the O₃(g) concentration leads to an increase in the formate removal rate by ∼5% due to an enhancement in the rate of O₃(g) interphase mass transfer. The CFD model adequately describes the mass transfer occurring in the two-phase flow system and confirms that O₃(g) interphase mass transfer is the rate-limiting step in contaminant degradation. The model can be used to optimize the ozone reactor design for improved contaminant degradation and ozonation efficiency.

Catalytic ozonation performance and mechanism of Mn-CeOx@γ-Al2O3/O3 in the treatment of sulfate-containing hypersaline antibiotic wastewater

Herein, we attempted to apply an alumina-based bimetallic (Mn-Ce) catalyst as an O₃ activator and explored the feasibility of the treatment of hypersaline organic wastewater. Compared with independent O₃ (35.00 ± 4.20%), mineralization of ciprofloxacin (CIP) under the Mn-CeO_x@γ-Al₂O₃/O₃ (MCAO) process was elevated to 76.04 ± 2.30%. The synergetic corporation among multivalence redox pairs of Mn (III)/Mn (IV), Ce (III)/Ce (IV) promoted the protonation of the surface hydroxyl group (S-OH₂⁺), and subsequently the dominant reactive oxygen species in the MCAO process, OH and O₂^-, were generated rapidly. However, the mineralization of CIP decreased in MCAO/SO₄^2- system due to the formation of SO₄^-, which reacted with CIP more slowly (8.4 × 10⁸ M^-1 s^-1) than OH (4.1 × 10⁹ M^-1 s^-1). In MCAO/SO₄^2-/Cl^- mixture saline conditions, mineralization of CIP was improved at low Cl^- concentration (0.5 wt%) due to the generation of Cl, while inhibited with excessive Cl^- (≥1.5 wt%) owing to the formation of residual chlorides (Cl₂, Cl₂^- and ClO^-). Meanwhile, the MCAO process possessed promising capability to remediate hypersaline wastewater containing dyes, phenol and pesticides, as well as actual salinity-rich wastewater. Based on the above, the present study would provide new insights into hypersaline organic wastewater treatment by the MCAO process.