Molecular Origins of Higher Harmonics in Large- Amplitudeoscillatory Shear Flow: Shear Stress Response

Biofilm sloughing is an integral aspect, and a dynamic activity of biofilm development. This study focused on biofilm sloughing on carriers in integrated fixed-film activated sludge (IFAS) systems in both laboratory (LS; synthetic feed) and full-scale (FS; municipal) systems. During biofilm development in the LS system the relative hydrophobicity of flocs and biofilm increased with an increase in carrier bound biomass. There was a decline in relative hydrophobicity of the flocs and attached biomass upon sloughing. The protein to polysaccharide ratio in the extracted EPS of the suspended biomass (flocs and sloughed biomass) and biofilms decreased and increased, respectively, which corresponds to confocal imaging showing that micro-colonies with polysaccharide rich content sloughing from the biofilms. Sloughed biomass rapidly associated with flocs to form large and compact structures that led to a decrease in SVI from 60-70 ml/L to 34 ml/L. The α and β diversities determined by 16S rRNA gene sequencing (Illumina) of FS samples revealed greater diversity of the biofilm community compared to flocs. The α diversity of biofilms and suspended solids decreased and increased, respectively, during sloughing. The shift in community structure was in part due to the loss of Comamonadacae from the biofilm.. At the class level, after biofilm sloughing, Alphaproteobacteria, Gammaproteobacteria, Flavobacteria, and Acidobacteria-6 dominated on the remaining biofilm. The relative abundance of Rhodocyclacae decreased in biofilms and flocs, after biofilm sloughing. Live-dead staining revealed areas of the biofilm where viability of biomass is an additional factor in sloughing.