Lipid Productivity of Algae Grown on Dairy Wastewater as a Possible Feedstock for Biodiesel

Lipid Productivity of Algae Grown on Dairy Wastewater as a Possible Feedstock for Biodiesel Ian Woertz The objective of this thesis is to develop a biological wastewater treatment system that utilizes algal growth to simultaneously create renewable energy in the form of biodiesel and digester biogas, remove polluting nutrients, and abate greenhouse gases. Research under the Department of Energy Aquatic Species Program during 1978-1996 concluded that cultivating algae for biofuels was cost prohibitive at that time and that an integrated approach should be studied that combined wastewater treatment with algal biofuel production. Nutrient removal, in particular nitrogen and phosphorus, from wastewater is a growing regulatory need and the use of algae cultivation could create a unique marriage between waste treatment and biofuel production. To investigate this possible synergy, bench-scale tests were conducted to determine potential algal lipid productivity with mixed-cultures of algae grown on anaerobically-pretreated dairy wastewater in batch mode. The total lipid content of the algae ranged from 8% to 29% of algal mass. Maximum biomass concentration reached 920 mg/L, measured as volatile suspended solids, on Day 13 of incubation. In contrast, maximum total lipid content was reached at Day 6, corresponding to a lipid productivity of 2.8 g/m/day, or 1,200 gallons/acre/year if scaled up. Nutrient removal over 12 days of incubation was nearly complete. Total ammonia (NH3+NH4) was reduced 96% to 1.1 mg/L as N, and phosphate (PO4) was reduced >99% from an initial concentration of 2.5 mg/L PO4 as P.