Study On Life Cycle “2E&W” Analysis Of Microalgal Biodiesel In China

Due to the overly dependence on the fossil energy, the world is facing several challenges including energy security, environmental pollution, global warming, and water scarcity. The development and utilization of new energy is becoming an important way to compensate the consumption of conventional fossil energy. Developing non-food biofuels is considered as an essential route of new energy structure diversification. Microalgae has been hailed as the third-generation biofuel due to its merits such as fast growth rate, high lipid content, and no land-competition with food crops. It is also considered as an important resource for the biomass developing project in China. However, a systematic review is required to assess the potential of biofuel production from microalgae, combining with the local resource features in China.This study established a model to evaluate the life cycle energy consumption, environmental emissions and water footprint. Firstly, the biodiesel production potential from microalgae was assessed based on the local resource and climate conditions in China. Secondly, a representative location was selected according to the distribution of biodieselyield. A comprehensive biorefinery plant with daily consumption of 34 ton dry algae was designed to further evaluate the life cycle energy consumption and environmental emissions. After that, a horizontal comparison analysis was conducted with the selected non-food biofuel pathways, from the perspective of life cycle water footprint.The potential of biodiesel production from microalgae was evaluated based on the local water resource and climate data. The algae growth rates in winter and summer were 9.1 and 15.6 g/m2/d in the outdoor open ponds, respectively. Algae could not grow well in northeastern China and most area of northern regions. The southeast coastal area and Hainan were suitable for the growth of microalgae. The annual biodiesel production from microalgae in these regions can reach 4200~5000 L/ha.The comprehensive biorefinery plant of microalgae contained high rate algal ponds, harvesting & dewatering units, lipid extraction units, anaerobic digestion units, etc. Results showed that the life cycle total energy and fossil energy consumption of microalgal biodieselwere 94.6% and 3.6% higher than those of diesel, respectively, while the petroleum consumption and the GHG emissions were 96.2% and 23.6% lower respectively. If the ratio of renewable electricity would be increased in the future, the GHG emissions of microalgal biodiesel would be further decreased. Harvesting & dewatering was found to be the most energy-intensive process, followed by lipid extraction and the culture of microalgae.From the net fossil energy ratios and greenhouse gas emissions in the selected regions, we can conclude that these two parameters were highly relevant to the local electricity mix and algae growth rate. The higher the ratio of thermal power, the more the fossil energy were required, and the more the greenhouse gas emitted. Hainan, Guangxi, Guangdong and Fujian were suitable for the development of microalgal biodiesel, both from the view of net fossil energy ratio and greenhouse gas emission.The life cycle water footprint of cassava based bioethanol, sweet sorghum based bioethanol, Jatropha seeds based biodiesel and microalgae based biodiesel were 3708, 17156, 5787, and 31361 m3/ton, respectively. Crop cultivation was the most water footprint-intensive stage for all the biofuel pathways. Compared with the blue and green water footprints, the grey water was the dominated water type for the three terrestrial crops. While for microalgae, the ratios of grey and blue water were 50.4% and 48.8%, respectively. The high grey water footprint was due to the large utilization of fertilizer during the growth of each crop. The water footprint of microalgal biodiesel can be decreased when wastewater was used to cultivate algae.Overall, the cultivation of microalgae in outdoor open ponds is feasible in China. Microalgal biodiesel is incomparable to conventional biodiesel from the view of life cycle total energy consumption, fossil energy consumption and water footprint. However, it has the potential to reduce the petroleum usage and GHG emissions.