Life cycle assessment of microalgae production in a raceway pond with alternative culture media

Abstract

Microalgae production is responsible for phycoremediation and the development of green products synthesis and for cleaning processes. Studies on the environmental impacts of this process are fundamental to make these systems feasible. In these studies, a life cycle assessment of the production of microalgae biomass is important. We performed this study considering the production in wastewater or NPK medium and different methods of biomass separation. The LCA model was developed for the production of 9 and 12 kg of Desmodesmus subspicatus microalgae biomass in 10 days, which represents the production in 8000 L of wastewater and NPK solution, respectively. The total volume corresponded to 4 tanks of 2000 L each. The growth system used was an open raceway pond with culture movement caused by an air-lift system or by paddle wheels. Flocculation with NaOH and electroflotation with Al and Fe were chosen as the methods of biomass separation. These methods were chosen because they facilitate the separation using filtration or centrifugation. The final step was drying, which can be conducted with the biomass after filtration (80% water) or centrifugation (40% water). Several scenarios were examined to identify a more environmentally friendly method for microalgae biomass production. There were no differences using air lift or paddle wheels, however it was identified impacts in all stages. Also, there were fewer impacts using wastewater than using NPK. Regarding the separation of the biomass, electroflotation caused fewer impacts when compared to flocculation with NaOH. Overall, the scenario with fewest impacts was the one configured using wastewater for microalgae cultivation, followed by centrifugation and drying.