A fundamental understanding of biofilm mechanical stability is critical in order to describe detachment and develop biofouling control strategies. It is thus important to characterise the elastic deformation and flow behaviour of the biofilm under different modes of applied force. In this study, the mechanical properties of a mature wastewater biofilm were investigated with methods including macroscale compression and microscale indentation using atomic force microscopy (AFM). The mature biofilm was found to be mechanically isotropic at the macroscale level as its mechanical properties did not depend on the scales and modes of loading. However, the biofilm showed a tendency for mechanical inhomogeneity at the microscale level as indentation progressed deeper into the matrix. Moreover, it was observed that the adhesion force had a significant influence on the elastic properties of the biofilm at the surface, subjected to microscale tensile loading. These results are expected to inform a damage-based model for biofilm detachment.

Detachment is a critically important aspect of biofilm processes; it impacts not only on the characteristics of the biofilm itself but also has general implications for the dissemination of pathogenic bacteria and the operation of biofilm reactors. The mechanisms of biofilm detachment are of fundamental importance in the analysis of biofilm processes. However the complexity of biofilm detachment creates difficulties in performing and analyzing experiments. It is necessary to identify if, under steady conditions, biofilms experiments are reproducible with respect to detachment. In this study mixed culture biofilms were cultivated under low shear conditions over four days in glass flow cells in triplicate under non-recirculation conditions. Detached particles were regularly sampled, were stained, filtered and analyzed using a fluorescence microscope to establish size distributions of detached cells and cell clumps. This study has shown that, despite the existence of a complex particle size distribution, reproducibility is possible in four day old mixed culture biofilms. This has important implications for the study of active or passive detachment in biofilm systems. This study also distinguished between erosion and sloughing following step increases in shear stress.

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