Rapid structure characterization of bacterial aggregates

While the structure of bacterial aggregates formed in wastewater treatment is recognized to be an important determinant of the efficiency of various p rocesses including sedimentation, thickening, and sludge dewatering, very f ew methods exist for rapidly quantifying this structure. In this paper, lig ht scattering over small angles of scatter (0.03-6.25 degrees) is sh own to produce results typical of fractal structures. Neither polydispersity effe cts nor multiple scattering appear to induce major problems in analysis of light scattering data for such assemblages with deviation from Rayleigh-Gan s-Debye scattering behavior apparently insignificant as a result of both th e low refractive index of the primary scatterers and the small angles of sc atter being used. Addition of polymer results in production of larger aggre gates that do exhibit effects suggestive of multiple scattering at low angl es of scatter. Power law scattering is observed for such systems at larger scattering angles with a relatively ordered decrease in flee compactness wi th increased polymer dose (fractal dimensions reducing from around 2.2 in t he absence of polymer to 1.7-1.8 in the presence of 1 wt % (dry solids) of cationic polymer). These results are supportive of the use of small-angle s tatic light scattering for rapid determination of biosolids flee structure provided that due consideration is given to the limitations of the techniqu e.