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