Nitrogen balances and impacts on the algae cultivation-extraction-digestion-cultivation process

Anaerobic digestion of lipid extracted algae is a method for recycling nutrients to a cultivation system. Growth of algae on recycled nitrogen from these systems has been demonstrated. This study focuses on how the initial nitrogen concentration impacts each stage of an integrated cultivation-extraction-digestion-cultivation process; and how the nitrogen is distributed in each step. The entire process was performed at five different initial nitrogen concentrations, ranging from nutrient deplete to excess. Algae production and lipid content were measured to evaluate the impact of initial nitrogen concentration. A thorough nitrogen mass balance for every step of the process was completed. The results show that initial nitrogen concentration had significant impacts on the whole process. The nitrogen recoveries through the nutrient recycle process were all approximately 65% regardless of initial nitrogen concentration. All nitrogen balances closed within experimental error. The largest losses of nitrogen occurred in the extraction and cultivation steps.