Activated sludge characteristics affecting sludge filterability in municipal and industrial MBRs: Unraveling correlations using multi-component regression analysis

In the field of membrane bioreactors (MBRs) many membrane fouling related questions still remain unanswered. The goal of this research is to unveil some of the black-box features of activated sludge filterability by correlating the results from activated sludge filterability measurements following the Delft Filtration Characterization method (DFCm) with a large set of activated sludge characteristics. Ten different MBRs in Belgium and the Netherlands were sampled in both winter and summer. All samples were subjected to the DFCm, automated image analysis and an extensive set of standardized measurements. No clear correlation could be found between a single sludge parameter and activated sludge filterability. However, a combination of sludge morphology and relative hydrophobicity (RH) allows for a clear classification of activated sludge into two classes, i.e., bad and poor to good, implying that deflocculation and a low RH have a negative impact on activated sludge filterability. Furthermore, for sludge samples having poor to good filterability, accurate estimations of sludge filterability can be made when including more parameters. The main conclusion is that filterability can be predicted by analyzing the bioflocculation state of the activated sludge.

► Activated sludge (AS) samples were taken from ten different membrane bioreactors.
► Correlations with AS filterability and AS characteristics were assessed.
► AS filterability cannot be attributed to a single activated sludge parameter.
► Deflocculation and low hydrophobicity negatively impact sludge filterability.
► Bioflocculation state is a major indicator for activated sludge filterability.