EXPERIMENTELL STUDIE AY FLÖDESSTRUKTUREN I FLOTATION OCH PÅVERKAN AV LUFTINNEHÅLL,| HYDRAULISK BELASTNING OCH KONTAKTZONSGEOMETRI / Experimental study on the flow structure in Dissolved Air Flotation and the influence of air content, hydraulic loading and contact zone geometry
Research on flow dynamics is believed to open ways for increasing the capacity of the Dissolved Air Flotation (DAF) process in water and wastewater treatment. The paper describes a study on the flow dynamics at Lund Institute of Technology in Sweden. By using an Acoustical Doppler Velocimeter (ADV) flow structures were determined in a pilot plant with particle-free water (tap water). Hydraulic loading, air content and contact-zone geometry were examined. The contact zone displayed a split-character with a lower mixed region followed by a higher plug-flow region, which was determined by the contact zone height. Two different flow structures were found in the separation zone. The stratified flow structure, defined by an upper, less dense and horizontally oriented flow layer and a lower, dense and vertically oriented flow layer, was generated for higher air-content and lower hydraulic loading. The short-circuit flow structure, defined as an immediately deviating water trans- port towards the outlet arrangement, was generated for lower air-content and higher hydraulic loading.