Abstract:

Objective Conventional bubble aeration suffers from low ozone mass transfer efficiency and insufficient ozone utilization, which limits the practical application of ozonation in the advanced treatment of printing and dyeing wastewater. Membrane contactor reactors provide a stable gas-liquid interface for bubbleless ozone transfer and offer a promising strategy to overcome the intrinsic limitations of bubble-based aeration. A polytetrafluoroethylene (PTFE) hollow fiber membrane contactor reactor was constructed to enhance ozone mass transfer, and the mass transfer behavior and wastewater treatment performance of hydrophobic PTFE membrane, hydrophilic PTFE membrane, and conventional aeration were systematically compared.

Method Commercial hydrophobic and hydrophilic PTFE hollow fiber membranes were adopted to construct membrane contactor reactors, while a conventional aerator was used as the control. The surface morphologies of the membranes were characterized by scanning electron microscopy. Ozone mass transfer experiments were carried out under different influent flow rates, inlet gas flow rates, inlet ozone mass concentrations, and initial liquid-phase pH values. The equilibrium dissolved ozone concentration and apparent volumetric mass transfer coefficient (K_La) were calculated based on a pseudo-first-order mass transfer model. Under the optimized operating conditions, the hydrophobic PTFE hollow fiber membrane contactor was further applied to the advanced treatment of actual printing and dyeing wastewater, and its chemical oxygen demand (COD) removal efficiency and ozone utilization efficiency were evaluated.

Results The hydrophobic PTFE hollow fiber membrane exhibited the best ozone mass transfer performance among the three transfer modes under the investigating conditions. Increasing the influent flow rate led to the thinning of the boundary layer and improved the mass transfer coefficient, but excessive flow shortened the gas-liquid contact time and reduced the equilibrium dissolved ozone concentration. The optimal gas flow rate and inlet ozone mass concentration were determined to be 100 mL/min and 67.7 mg/L, respectively. The initial pH value was also found to strongly affect ozone transfer and stability, with pH=7 providing the best balance between mass transfer driving force and ozone decomposition. Under the optimized conditions of influent flow rate of 146.67 mL/min, gas flow rate of 100 mL/min, inlet ozone mass concentration of 67.7 mg/L, and initial pH value of 7, the maximum K_La values of the hydrophobic membrane, hydrophilic membrane, and conventional aerator were 0.623, 0.341, and 0.602 min^-1, respectively. For printing and dyeing wastewater treatment, the COD removal rate achieved by the hydrophobic PTFE membrane reached 60.7%, which was approximately 4 times that of the conventional aerator. The COD removal per unit ozone consumption reached 0.119 mg/mg, about 3.8 times that of conventional aerator.

Conclusion The hydrophobic PTFE hollow fiber membrane contactor effectively enhances ozone mass transfer by maintaining a stable bubbleless gas-liquid interface and reducing liquid-side mass transfer resistance. Compared with hydrophilic membrane contact and conventional bubble aeration, the hydrophobic membrane shows higher mass transfer efficiency, better ozone utilization, and superior COD removal performance in actual printing and dyeing wastewater treatment. This study provides a feasible technical route for improving ozone utilization efficiency and promoting the engineering application of membrane contactor-assisted ozonation in textile wastewater treatment.

Key words: polytetrafluoroethylene, hollow fiber membrane, membrane contactor reactor, ozone oxidation, printing and dyeing wastewater, mass transfer efficiency, wastewater treatment