Evaluation of the Feasibility of the Algae Cultivation-Extraction-Digestion-Recultivation Process to Recycle Nutrients and Determine the Nitrogen Balances and Impacts in the Process

Abstract

Nutrient supply is one of the critical obstacles limiting algal biofuel industrialization. It has been demonstrated that anaerobic digestion is an effective method to release nitrogen and phosphorus from algal biomass, but the nutrient recycle system of cultivation-extraction-digestion-recultivation has not been completely evaluated. In this dissertation, algae were cultivated on nutrients released from anaerobic digestion of lipid extracted algae. Algae recovery was calculated to demonstrate the feasibility of the nutrient recycle process. The quality of recultivated algae for algal biofuel was validated and the limiting nutrient was analyzed. Initial nitrogen concentration was shown to have significant impact on the entire process including algae and lipid productivity, as well as lipid and nitrogen content of the biomass. The nitrogen balance for each step of the entire process was closed within experimental error. Total nitrogen recoveries throughout the whole process were all approximately 65% regardless of the different initial nitrogen concentration. The biggest nitrogen losses occurred in lipid extraction and algae cultivation steps. The work described in this dissertation demonstrates the effectiveness of this nutrient recycle system, and therefore provides a promising method to significantly lower nutrient cost for algal biofuel production. Nitrogen analysis validates the experimental and analytical methods in this dissertation and provides points of future work to further optimize this recycle process.