The activated sludge wastewater treatment process depends upon the formation of biological floc for effective liquid-solids separation, nutrient stabilization and sludge dewatering. Continued research into floc formation, intrafloc interactions and floc hydrodynamics is necessary for improved understanding of the activated sludge process.The overall goal of this research program was to investigate laser-based methods for characterizing biological flocs. The research objectives included the selection of laser-based methods which are applicable to the wastewater treatment plant environment, design and development of laser-based instrument configurations, measurement of particles with known characteristics, measurement of activated sludge samples and determination of the factors affecting laser-based instrument operation. / Master of Science

X-rays have been widely exploited to unravel the structure of matter since their discovery in 1895. Nowadays, with the emergence of new X-ray sources with higher intensity and very short pulse duration, notably X-ray Free Electron Lasers, the number of experiments that may be considered in the X-ray regime has increased dramatically, making the characterization of gas phase atoms and molecules in space and time possible. This thesis explores in the theoretical analysis and calculation of X-ray scattering atoms and molecules, far beyond the independent atom model. Amethod to calculate inelastic X-ray scattering from atoms and molecules is presented. The method utilizes electronic wavefunctions calculated using ab-initio electronic structure methods. Wavefunctions expressed in Gaussian type orbitals allow for efficient calculations based on analytical Fourier transforms of the electron density and overlap integrals. The method is validated by extensive calculations of inelastic cross-sections in H, He+, He, Ne, C, Na and N2. The calculated cross-sections are compared to cross-sections from inelastic X-ray scattering experiments, electron energy-loss spectroscopy, and theoretical reference values. We then begin to account for the effect of nuclear motion, in the first instance by predicting elastic X-ray scattering from state-selected molecules. We find strong signatures corresponding to the specific vibrational and rotational state of (polyatomic) molecules. The ultimate goal of this thesis is to study atomic and molecular wavepackets using time-resolved X-ray scattering. We present a theoretical framework based on quantum electrodynamics and explore various elastic and inelastic limits of the scattering expressions. We then explore X-ray scattering from electronic wavepackets, following on from work by other groups, and finally examine the time-resolved X-ray scattering from non-adiabatic electronic-nuclear wavepackets in the H2 molecule, demonstrating the importance of accounting for the inelastic effects.