Life Cycle Assessment for Carbon Balance of a Wastewater Treatment Integrated Microalgae Biofuel Production Process

Recent technology advances in carbon fixation via microalgae have shown increasing potentials in reducing net greenhouse gas emission. Carbon in the greenhouse gas is assimilated by photosynthesis in algal cell during the cultivation process, which can be carried out in wastewater environment as an alternative to conventional fertilizer feedstock-based processes. To improve the environmental performance of microalgae biofuel production process as well as increase the efficiency of nutrient biomass uptake in microalgae activities, the carbon balance is investigated by using the Life Cycle Assessment (LCA) for a separated nutrient delivery configuration in this study. In the proposed configuration, sewage sludge from wastewater treatment segment is reclaimed as supporting mediums to improve microalgae biogas production and a stream of pretreated nutrient-enriched wastewater is introduced to high rate algal ponds to satisfy the demand of microalgae-derived lipid productivities. Combined with the downstream process converting algal biomass into biofuel, the system termed as wastewater treatment integrated microalgae biofuel production process is formed. Our analysis showed the advantage of the separated nutrient delivery configuration in improving microalgae carbon fixation performance and the environmental impact of the biofuel production process. In the analysis, the mass and energy balances are achieved by process simulation, and the background data are taken from available databases and the literature. The LCA results show that the system proposed in this work can generate biofuel in energy self-sufficient condition with the carbon fixation effect.