Coagulation and flocculation processes are often used to eliminate colloidal particles during water treatment. Aggregate properties are influenced by both physicochemical conditions (type and dose of coagulant, pH, alkalinity and temperature) and hydrodynamics (magnitude and distribution of the shear rate), primarily given by the geometry of the mixing tank and the stirrer shape and speed. Aggregate properties significantly influence their subsequent separation. E.g. relatively small and dense aggregates can improve the sand filtration efficiency by their strong adhesion to the sand surface. On the other hand, large, dense and strong (resistant to breakage) aggregates are suitable for separation by sedimentation. Nevertheless, if the sand filtration is used for separation of the latter suspension, the large aggregates form the undesirable layer on the filter surface that prevents the other aggregates from penetration to the filter bed. To optimize the aggregate formation, it is therefore important to understand the aggregation mechanisms and evolution of aggregate properties in dependence on mentioned physicochemical and hydrodynamic conditions.
Research activities
- Clarification of effect of physical-chemical parameters (dose and type of coagulation reagent, concentration and composition of impurities, pH, alkalinity, temperature) on coagulation and flocculation
- Measurement and description of properties (size, structure, porosity, shape) of aggregates formed during water treatment
- Research on influence of hydrodynamic conditions (magnitude and distribution of velocity gradient, mixing time) on aggregate properties in mixing devices with different geometry
- Description of effect of aggregate properties on their subsequent separation by sand filtration and/or sedimentation
- Aggregation kinetics modelling
- Optimisation of aggregation processes in laboratory, pilot-plant and operation conditions
- Design of water treatment technologies for formation and separation of aggregates