Time-Variations of Transfer Efficiency and Headloss for Fine-Pore Membrane Diffusers in Aeration Systems

Fine-pore diffusers are the most common aeration systems in municipal wastewater treatment. Punched polymeric membranes are often used in fine-pore aeration due to their advantageous initial performance. These membranes are subject to fouling and scaling, resulting in increased headloss and reduced oxygen transfer efficiency, both contributing to increase plant energy costs. This paper describes and discusses the change in material properties for polymeric fine-pore diffusers, comparing new and used membranes. Three different diffuser technologies were tested and sample diffusers from two wastewater treatment facilities were analyzed. The polymeric membranes analyzed in this paper were composed of ethylene-propylene-diene (EPDM), polyurethane, and silicon. Transfer efficiency is consistently lower with longer times in operation, as older, dilated orifices produce larger bubbles, which are unfavorable to mass transfer. At the same time, headloss increases with time in operation, since membranes increase in rigidity and hardness, and fouling and scaling phenomena occur at the orifice opening. Evidence here reported shows the change in polymer properties and our laboratory test results correlate these changes with the decrease of oxygen transfer efficiency.