Filterability and Floc size in ­Membrane Bioreactors: European Scale Assessment

Filterability is a recognized parameter to evaluate membrane bioreactor (MBR) sludge quality. A link was established between filterability and submicron particles, i.e. sludge with worse filterability has a higher amount of submicron particles. In this research, the relation between filterability and suspended particles, measured through particle counting in the range 2-100 µm, was investigated to evaluate whether suspended material can be a source of submicron particles, causing the aforementioned filterability decrease. The research was performed at 4 pilot-scale MBRs, complementing previous research performed at 4 full-scale MBRs. Results showed that MBR activated sludge filterability improves with increasing sludge floc size, supporting the initial hypothesis. Nevertheless, in one single MBR installation varitions in the membrane tank floc size are likely to be limited.