Algal Bioflocculation for SolidLiquid Separation

A key requirement for microalgae biofuels production is a very low cost harvesting technology. Commercially available solidliquid separation technologies applicable to microalgae, such as chemical coagulation, membrane separations and centrifugation, are too costly for biofuels production or other lowcost microalgae processes, such as wastewater treatment. A low cost harvesting process is bio flocculation, in which the algal cells spontaneously aggregate into larger colonies or bioflocs and settle rapidly when removed from mixed raceway cultivation ponds. Algal bio flocculation is well known and commonly observed in algal cultures, particularly in wastewater treatment ponds, but it is neither reliable nor effective enough for practical, commercial, applications. The goal of this project is to improve bio flocculation harvesting to achieve a 95% recovery of algal biomass using a simple sedimentation process. Phase I demonstrated that through a simple biomass recycle process natural algal cultures can be converted from settleable to nonsettleable and back again. Biomass recycle thus provides a relatively simple and straightforward approach to controlling the bio flocculation properties of microalgal cultures. This allows for an initial about 40fold concentration, to roughly 2% solids slurry that could be further concentrated to 20% solids with commercially available technologies, such as centrifugation or membranes. A nearterm application of such a process would be in a combined algal wastewater treatmentbiofuels production. In Phase II, bio flocculation harvesting of microalgae cultivated on wastewaters, both settled raw and treated (high and low organics, respectively) will be demonstrated for over a year of continuous operation at two different California locations. The first location will be the San Luis Obispo Water Resource Reclamation Facility, where six 33 m2 raceway ponds will be operated. The second location is the City of Delhi wastewater treatment plant, where nine 3.5 m2 ponds will be operated. Technoeconomic analysis and life cycle assessments will be used to document the commercial viability of this technology in municipal wastewater treatment with biofuel coproducts. Alternative biofuel options including compressed biogas for vehicles will be examined. Depending on the Phase II results, Phase III would carry out a largerscale demonstration of this technology at the Delhi site and develop a market analysis and marketing effort to apply algal waste water treatment with coproduction of biofuels. A potential market of a thousand such systems maybe possible in the US, though only a fraction of these would likely be implemented in the next decade. Such systems could be a starting point for a US microalgae biofuels industry. Key Words – Algal biofuels, Algae harvesting, Bio flocculation, Strain selection, Biofuels