Microalgae cultivation using industrial CO2 emissions and fortuitous heat gains: Preliminary environmental assessment of an Industrial Symbiosis

Due to their photosynthetic metabolism, microalgae’s growth is based on their capacity to uptake CO2 while capturing energy from light (solar or artificial) and transforming it into chemical energy and molecules. Grown under... [ view full abstract ]

Due to their photosynthetic metabolism, microalgae’s growth is based on their capacity to uptake CO₂ while capturing energy from light (solar or artificial) and transforming it into chemical energy and molecules. Grown under specific process conditions in different reactor configurations (e.g. pH, light, temperature, nutrients), microalgae biomass contains proteins, carbohydrates, lipids and pigments, that can be valued in different industries such as energy production, pharmaceutics, food, cosmetics, construction materials, etc.

Compared to other terrestrial crops, microalgae exhibit higher surface productivity (Lardon et al., 2009). Consequently, several studies have focused in microalgae cultivation, especially for biodiesel production (Quinn and Davis, 2015). Some studies having evaluated the life cycle environmental impacts of microalgal biodiesel manufacture (Stephenson et al., 2010), have shown that the cultivation step may contribute significantly to the total energy consumption and to the global warming potential (GWP).

Besides, microalgae have shown the aptitude to grow on waste such as CO₂ from flue gases and wastewater (Mata et al., 2010). Additionally, Soratana and Landis, 2011 have evaluated the environmental impacts of microalgae cultivation when such industrial wastes (CO₂ from flue gas and wastewater) are integrated to the process. Results showed that GWP and eutrophication impacts were avoided.

Another industrial waste flow that could be incorporated into the microalgae’s cultivation process, in order to improve its environmental impact, is the industrial heat losses. In fact, for some microalgae strains, the optimal growth temperature needs to be maintained at close to 35ºC, which can lead to a significant energy demand and consequently affect the environmental life cycle of the cultivation process. 

In the context of a prospective study for the development of a sub-industrial platform, this work aims to evaluate, through a Life-Cycle Assessment (LCA), the environmental impact of using both CO₂ emissions and heat losses from an industrial site for the culture of microalgae in a raceway reactor. Life cycle inventory data were collected from life cycle inventory database and from gate to gate inventory models obtained from a microalgae producer. Infrastructure flows for the construction of the process facilities are included. The results allow identifying environmental benefits of setting up this industrial symbiosis compared to the conventional process without the use of industrial wastes.

The authors wish to thank the Algosource Group for providing the inventory data as well as the ADEME Agency and Région Pays de la Loire for their financial support to the Cimentalgue project.