The settling and bioflocculation of two strains of algae were investigated in the laboratory to provide insights to help improve algae settling in large-scale, algae-based wastewater treatment systems with simultaneous algae biofuel production. Energyefficient algae harvesting is a requirement for cost effective production of biofuels from algae, but algae harvesting usually requires energy-intensive methods such as centrifugation, filtration or dissolved air flotation. Bioflocculation using bacteriallyderived exudates is promising, but its use in high-rate algae pond (HRAP) wastewater systems has not yielded consistently reliable settling. To improve our understanding of the complex interactions between mixed cultures of algae and bacteria, the settling of the algae Scenedesmus sp. and Chlorella vulgaris were observed with and without bioflocculation by the bacterium Burkholderia cepacia. Scenedesmus and Chlorella responded in opposite ways to changes in operating conditions such as culture age and bioflocculation. Scenedesmus settled better in later growth stages, while Chlorella settled better in its early growth phase. Scenedesmus settling was improved by bioflocculation during early and late growth stages, but not in mid-growth. Scenedesmus responded better to B. cepacia cells plus filtrate than to filtrate alone. In contrast, Chlorella settling was not improved by bioflocculation with either B. cepacia cells nor filtrate at any growth stage. Longer contact time between the algae cells and bioflocculants improved the settling of Scenedesmus, but not Chlorella. The widely different settling behavior of the two species of algae used in this research may explain the varied results often observed with mixed cultures in algae wastewater ponds.
- wastewater treatment,
Available at: http://works.bepress.com/ynelson/31/