Impacts of the Contradictory Factors in Algal Co2 Sequestration with Sustainable Biofuel Benefit

Abstract

Background The purpose would discover the impacts of the contradictory factors in application of algae in CO2 sequestration with sustainable biofuel benefit. The quantitively assessment model and approach have been established coupling upstream CO2 source and deliverables with downstream algal biofuel deliverables at the uniform algae level of Nannochloropsis oceanica, which would be benefit for algae biofuel deliverables choice. The functional units have been defined at energy consumption (MJ) per final mass product (algae, jet biofuels by three refining pathways, biodiesels by three refining pathways) and energy consumption (MJ) per final energy yield (algae, jet biofuels, biodiesels). Computational framework is classified into three sub-models, including CO2 source and deliverable model, algae cultivation and deliverable model, refining process and biofuel deliverable model. This life cycle assessment investigated the following impacts: transportation distances and purification modes with flue gas CO2 concentrations, lipid content with specific productivity and CO2 biofixation coupling the nutrient supply, final products including algae, jet biofuel and biodiesel.Results Coupling the influence of transportation distances and purification modes on the energy consumption, flue gas with a wide range of CO2 concentration was compared for two type deliverables including algal CO2, edible CO2. flue gas with low CO2 concentration is appropriate for on-site algal CO2 deliverable within 10km while flue gas with above 95% CO2 is flexible to transportation distance and appropriate for edible CO2 deliverable. Specific productivities and CO2 fixation both comply with negatively logarithmic relationship with lipid contents. Coupling the effects of algae specific productivity and CO2 evaporation loss, the total CO2 fixation efficiencies were investigated above 90% at below 28 % lipid but obviously decrease at above 40% lipid. The nutrient supply enhances specific productivity and protein content but with indirect energy consumption. The total energy consumptions of different target products with upstream CO2 source and algae to downstream biofuel were calculated quantitatively on edible algae and general algae.Conclusions Biodieselwet and HTL-HRJ jet biofuel performed the priorities in energy consumption. Lipid content and profile defined biofuel deliverables in quantity and quality. The LCA indicated that allocation is a crucial issue to balance energy, environment and economy decision on target product choice and by-products. Coupling solar energy utilization and by-product of bioactive nutrients effects, the positive energy gains have been investigated at a wide range of lipid contents despite of jet biofuel or biodiesel. The results would enhance the interests in both LCA and application of algae in CO2 sequestration with sustainable biofuel benefit.