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 processes including sedimentation, thickening, and sludge dewatering, very few methods exist for rapidly quantifying this structure. In this paper, light scattering over small angles of scatter (0.03-6.25 degrees) is sh own to produce results typical of fractal structures. Neither polydispersity effects nor multiple scattering appear to induce major problems in analysis of light scattering data for such assemblages with deviation from Rayleigh-Gans-Debye scattering behavior apparently insignificant as a result of both the low refractive index of the primary scatterers and the small angles of scatter being used. Addition of polymer results in production of larger aggregates that do exhibit effects suggestive of multiple scattering at low angles of scatter. Power law scattering is observed for such systems at larger scattering angles with a relatively ordered decrease in flee compactness with increased polymer dose (fractal dimensions reducing from around 2.2 in the 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 static light scattering for rapid determination of biosolids flee structure provided that due consideration is given to the limitations of the technique.