(477d) Recovery of Nutrients from Swine Wastewater Using Ultrafiltration: Applications for Microalgae Cultivation in Photobioreactors

Algal biomass has been identified as a promising feedstock that could be used in a number of industrial applications, including biofuel production, aquaculture, and pharmaceutical production.  Through the use of sunlight and CO₂, microalgae species are capable of producing biomass rich in lipids and carbohydrates, which can be extracted from the plant material and used in the production of commodities such as biofuels.  Algae have been shown to have higher rates of productivity and higher lipid contents than traditional bioenergy crops, and do not require high-quality land for cultivation, and would not compete with current agricultural products for space.

While the high productivity and lipid content of microalgae make it a promising feedstock for a number of industrial applications, there are several challenges associated with their cultivation in large-scale production systems.  The production of microalgae can require significant amounts of nitrogen and phosphorus fertilizer.  In order to make the production of microalgae economical, it is important that low cost sources of nitrogen and phosphorus be available to producers.  Considering the relatively high nitrogen content of microalgae (4 to 8 percent), the nitrogen inputs required for microalgae cultivation can be significant.  In addition, the synthesis of nitrogen fertilizer produces around 2 kg of CO₂ kg^-1.  The additional carbon production, if added to the overall lifecycle, undermines the favorable carbon balance for microalgae feedstocks.   

Membrane separations technology constitutes an alternative method for the removal of biological contaminants from the nutrient-rich wastewater prior to use in microalgae cultivation.  A membrane consists of a thin film that separates two phases, and can be used in liquid-liquid separations.  Microfiltration and ultrafiltration involve the use of porous membranes to remove micro- or macro-particles from a solution.  In this study we used ultrafiltration membranes for removing contaminants from swine wastewater for use in algal growth.  Through several trials we have found that the algal wastewater is completely contaminant free and the growth rate of the algae is greater than optimal conditions.