New developments in mixing, flocculation and flotation for industrial wastewater pretreatment and municipal wastewater treatment

Solid/liquid separations are commonly the first step in any wastewater treatment. Such technologies are mature and new developments are rare. However, in the last decade some significant improvements in separation techniques for industrial waste water pretreatment have been implemented. Advances in the technology include more efficient, faster centrifugal mixing of treatment chemicals and wastewater contaminants, "in situ" continuous flow coagulation and flocculation, implementation of very high molecular weight flocculants and development of more efficient flotation technologies. Recent developments and improvements of commonly used dissolved air flotation units along with development and application of centrifugal flotation units, cavitation air flotation and suspended air flotation will be discussed. Case studies are also described. Hybrid centrifugal - dissolved air flotation technologies provide the best of both systems: efficient continuous flow mixing and in line flocculation with the nucleation and entrainment of fine dissolved air bubbles. This development has resulted in systems with very efficient removal of particulate contaminants, a small footprint, drier sludge, durable long lasting floes, fast response and treatment of the total wastewater stream (norecycling characteristic for DAFs). The design of on-line turbidity driven sensors for automatic control of coagulant and flocculant dosage is also underway. Computational fluid dynamics (CFD) has been used to design better flotation tanks with a vortical flow pattern that results in the formation of a dense air bed inside the tank. Such fine bubble layers prevent sedimentation of already floated heavier particulates, which results in significantly higher flotation rates.