Flocculation Treatment of an Industrial Effluent: Performance Assessment by Laser Diffraction Spectroscopy

Flocculation processes are extensively used as separation methods to remove suspended and dissolved solids, colloids, and organic substances in effluents. As flocculation performance affects the economy of many industrial processes, it is important to understand the underlying mechanisms, as well as the predominant flocculant properties influencing the final results. In the present study, a strategy based on the use of laser diffraction spectroscopy was developed to screen different flocculants performance in an industrial potato crisps manufacturing effluent, using anionic polyelectrolytes as flocculants. The flocculation process was monitored over time, and information on floc average size and structure was obtained. The effect of flocculants properties, including their hydrophobic content and concentration, on the flocculation process and on flocs density was investigated. With this methodology for continuous monitoring of the flocculation process in real effluents, it is possible to obtain simultaneously information about the kinetics of floc size evolution and also about the evolution of floc structure with time. This is an important proof of concept, since it will allow in the future to perform prescreening of polymers to be used in the flocculation treatment of a specific effluent, minimizing in this way pilot trials. The highest polyelectrolyte concentration studied leads to the largest flocs obtained, which were, however, very sensitive to the turbulent environment. This agrees with the low scattering exponent values obtained for all the flocs, which indicate an open and porous floc structure. Characteristics of the polymers used proved to have an important role in the floc size. Higher zeta potential, hydrodynamic diameter, and molecular weight of the flocculant resulted in larger flocs. The presence of hydrophobicity in the polyelectrolyte also was showed to influence the floc properties, although an optimum content could be identified above which flocculation was hindered.