Algal cells of B. braunii 765 cultivated in the two tested media showed different color behaviors. In BG11 medium, consistent with the algal chlorophyll concentration decline (Fig. 2), the algal cells turned to yellow green from the initial green at the first 2–4 days. Afterward, the alga was adapted to the new culture and became green to dark-green again. However, for the alga cultivated in the wastewater, no obvious such variation was observed.
At the first 2–6 days, the colonies of B. braunii 765 cultivated in the BG11 medium appeared looser structure than those of the inoculums, with a diameter of 15–20 lm vs. 10 lm. Then, the col- ony size gradually recovered and remained stable thereafter. By comparison, the compact degree of algal colonies in the aerated swine lagoon wastewater changed little at first. But after 6 days from inoculation, some clusters (30–50 lm in diameter) formed by 3–5 single colonies appeared in the wastewater and became more and more. The formation of such clusters might be related to an increase of the algal extracellular polysaccharides, whose production would be favored by the high C/N ration of the swine wastewater (Miqueleto et al., 2010). In addition, these bigger colo- nies of B. braunii 765 in the wastewater would make it easier to harvest the alga biomass by auto-flocculation.