Microalgae have been regarded as a pollutant causing algal blooms in lakes or reservoirs but have recently been considered as a useful source of biomass to produce biofuel or feed for livestock. For the algae particle separation process, carbon dioxide (CO2), one of the main greenhouse gases, is dissolved into a body of water rather than being emitted into atmosphere. This study aims at determining the feasibility of CO2 bubbles as an algae particle separation collector in a flotation process and providing useful information for effective algae harvesting by describing optimal operating conditions of dissolved carbon dioxide flotation or dissolved air flotation. The first step is to develop a flotation model for bi-functional activity, algae control and algae harvesting at the same time. A series of model simulations is run to investigate algae particle separation possibilities such as an initial collision-attachment efficiency that depends upon separation characteristics due to an algae life cycle, including: pH, size distribution, zeta potential, cell surface charge, density, electric double layer, alkalinity, and so on. Based on the separation characteristics, conditions required to form flocculation are predicted in order to obtain the optimal flotation efficiency.