[Influence of microbubble and its generation process on mixed liquor properties of activated sludge].

Microbubble aeration is supposed to be able to provide potential advantage for aerobic biological wastewater treatment due to enhancement of oxygen mass transfer. On the other hand, microbubble and its generation methods might affect mixed liquor properties of activated sludge. Then SPG membrane microbubble generation system was used to investigate mixed liquor properties of activated sludge in microbubble aeration. The results indicated that sludge floatation happened in microbubble aeration due to attachment of microbubbles to sludge flocs, resulting in a decrease in mixed liquor suspended solid (MLSS) concentration in the bioreactor and poor sludge settleability. The strong shear stress caused by liquid recycling pump (centrifugal type) during microbubble generation led to sludge broken. As a result, sludge floc size decreased significantly and sludge EPS released. The release of sludge EPS was considered to be responsible for increased turbidity and organic carbon (especially colloidal organic carbon) concentration in the supernatant. The re-flocculation ability of sludge flocs also almost lost due to sludge EPS release. In addition, the mixed liquor viscosity increased along with sludge broken and sludge EPS release, but the surface tension of mixed liquor remained constant.