Loughborough University Institutional Repository Micro otation performance for algal separation

The performance of microflotation, dispersed air flotation with microbubble clouds with bubble size about 50 microns, for algae separation using fluidic oscillation for microbubble generation is investigated. This fluidic oscillator converts continuous air supply into oscillatory flow with a regular frequency to generate bubbles of the scale of the exit pore. Bubble characterisation results showed that average bubble size generated under oscillatory air flow state was 86 μm, ~ twice the size of the diffuser pore size of 38 μm. In constrast, continuous air flow at the same rate through the same diffusers yielded an average bubble size of 1059μm, 28 times larger than the pore size. Following microbubble generation, the separation of algal cells under fluidic oscillator generated microbubbles was investigated by varying metallic coagulant types, concentration and pH. Best performances were recorded at the highest coagulant dose (150mg/L) applied under acidic conditions (pH 5). Amongst the three metallic coagulants studied, ferric chloride yielded the overall best result of 99.2% under the optimum conditions followed closely by ferric sulphate (98.1%) and aluminium sulphate with 95.2%. This compares well with conventional dissolved air flotation (DAF) benchmarks which has a highly turbulent flow, whereas microflotation is laminar with several orders of magnitude lower energy density.