Influence of design parameters of the zones of flocculation, contact and separation on the formation of floc-bubbles clusters with suitable sizes for separation by flotation within third generation DAF units applied for water treatment

Abstract

Given the severe impairment of water quality of surface water sources, especially regarding the concentration of dissolved organic matter and algae, dissolved air flotation (DAF) have been increasingly used in drinking water treatment due to better performance of this technique compared to conventional systems. The new third generation of DAF system is more compact and capable of operating at higher rates (two or three times higher) with the same efficiency as conventional DAF units and requiring smaller coagulant dosages. However, there remain major gaps regarding the appropriate values of some of its design parameters and their interrelationship. In this project it is proposed to investigate the best conditions for flocculation and supply of air microbubbles with a size range suitable to promote the formation of clusters of flocs and microbubbles that can be efficiently removed at high rates in the zone of separation, enabling the design of efficient low power consumption DAF units, considering its lower air requirements compared to the second generation DAF units. The study of the interdependence of the flocculation, contact and separation zones of these units will be carried out by using appropriate equipment and methods of image analysis to characterize the size of microbubbles and flocs. To characterize the flow structure within the pilot scale DAF unit ultrasound (micro ADV) probes will be used. The influence of surface charge (zeta potential) of flocks and air microbubbles in the performance of flotation it will also be investigated. After finishing the research it is expected to obtain more secure parameters for the design of third generation DAF systems thus contributing not only to the improvement of this technology, but also to improve the mathematical modeling. (AU)