Floc Architecture in Wastewater and Natural Riverine Systems

The study of flocs has largely been devoted to the gross (>1 μm) scale so that the behavior of flocs (i.e., transport and settling) can be observed and modeled. With the assistance of a newly developed field kit and correlative microscopy [which includes transmission electron microscopy (TEM), scanning confocal laser microscopy (SCLM), and conventional optical microscopy (COM)], this paper begins to bridge the resolution gap between the gross and fine (submicron) scales in order to better understand the role of floc ultrastructure in outward floc behavior for both natural and engineered systems. Results from both systems have demonstrated that pores which appeared to be devoid of physical structures under the optical microscopic techniques (SCLM and COM) were observed to be composed of complex matrices of polymeric fibrils (4−6 nm diameter) when viewed by high-resolution TEM. These fibrils were found to represent the dominant physical bridging mechanism between organic and inorganic components of the flocs and contributed to the extensive surface area per unit volume of the flocs. In this way, the microbial floc resembles a biofilm and will likely support similar processes with respect to contaminants and the physical−chemical environment.