Micro-Bubble Flotation of Freshwater Algae: A Comparative Study of Differing Shapes and Sizes

This study investigates the effects of the morphology (shape and size) of differing algae species on the removal efficiency by the dissolved air flotation (DAF) process. Three selected shapes in this research are spherical (Microcystis sp.), oval (Chlamydomonas angulosa), and filamentous algae (Phormidium sp.), cultured in the laboratory under certain cultivated conditions. Physical properties of three differing algae were understood as morphology, size distribution, and zeta potential in various pHs. Under pH conditions of 4.5˜7, all algae species showed negative charges: −10 mV for filamentous shape, ˜ −20 mV for oval shape, and ˜ −40 mV for spherical shape. The size of these shapes ordered increasingly as spherical < oval < filamentous algae. In order to separate algae from water, positively charged bubbles were generated by adding a coagulant (as Al3+) and were applied at 10%, 20%, and 30% recycling ratio. Assessment of algae removal efficiency was shown by the number of the cells, total organic carbon (TOC), dissolved organic carbon (DOC), and the morphological changes (i.e., shape or size distribution). In terms of the number of cell, filamentous algae showed the greatest removal, i.e., 86% removal at 30% recycling ratio and 5 mg/L of Al3+ addition. For TOC and DOC removal perspectives, spherical algae showed the greatest removal above 80%. These results, therefore, confirm that the shapes and sizes of algae affect the removal process of bubble technology.