| The effect of environmental, biological and operational variables on biological flocculation of microalgae grown on anaerobically treated swine waste was investigated in laboratory and field scale systems. Environmental variables considered were season, rainfall, temperature and solar irradiance. The biological variable considered was algal species composition. Operational variables included flow mixing, waste loading, waste pretreatment, algal biofloc and bacterial seeding, pH reduction and carbonate supplementation. Parameters measured consisted of algae removal, settled volume, dehydrogenase activity, optical density, dissolved oxygen concentration, chlorophyl a and pH.;The results indicated that the most important factor affecting bioflocculation was continuous flow mixing. Algal removal and settleable matter production were found to be proportional to flow mixing velocity. Continuous mixing inhibited photosyntheis of Synechocystis sp. This species exhibited the greatest bioflocculation tendency. Waste loading and sludge seeding had moderate effects in the laboratory and slight, a positive effect in the field. Acidification stimulated biological flocculation in laboratory cultures but inhibited it at the field scale. Carbonate supplementation and photosynthetic bacteria seeding had no effect on bioflocculation. Dehydrogenase activity was higher in cultures that were mixed or fast mixed, waste loaded or heavily waste loaded, and algal biofloc or activated sludge seeded. |
