Successful application of Shirasu porous glass (SPG) membrane system for microbubble aeration in a biofilm reactor treating synthetic wastewater

Abstract Microbubble aeration is supposed to be able to provide potential advantage for aerobic biological wastewater treatment due to enhancement of oxygen mass transfer. Then SPG membrane microbubble generation system was used to aerate a biofilm reactor treating a synthetic wastewater. Successfully long-term operation of the experimental system demonstrated the application feasibility of microbubble aeration in aerobic biological wastewater treatment. The air permeation of SPG membrane depended on its surface property and pore size, rather than membrane fouling which influenced microbubble generation and subsequent oxygen transfer. Stable and efficient COD removal was achieved but the ammonia removal became inefficient at high organic loading rate due to DO limitation. The suitable SPG membrane area-based COD removal capacity should be controlled around 6.69 kgCOD/(m 2  d), considering the stable DO concentration and efficient contaminant removal. Microbubble floatation also provided contribution to suspending and colloidal contaminant removal. The oxygen utilization was estimated as high as almost close to 100% under certain conditions based on contaminant removal, but the energy consumption of this microbubble aeration system was also very high. To use hydrophobic SPG membranes and increase their air supply capacity could contribute to energy-saving.