Advanced membrane photobioreactors in algal CO2 biofixation and valuable biomass production: Integrative life cycle assessment and sustainability analysis

This paper presents and discusses the life cycle assessment (LCA) of CO2 capture and of microalgae biomass production in an advanced membrane photobioreactor (mPBR) system for climate change mitigation and the generation of renewable energy carriers. The study aims to evaluate environment-relevant aspects and propose alternative solutions for optimization of the environmental sustainability of the biologically based technology. The mPBR biotechnology, composed by an adsorption column, coupled with a reactor with a self-forming dynamic membrane (SFDM) module inside, was used for the experimental activities. Four principal operational steps (cultivation, harvesting, cleaning and drying) at three different scenarios were investigated and evaluated in terms of energy demand and environmental impacts amongst the boundary conditions based on the “cradle-to-gate” model. The ReCiPe 2016 and the Cumulative Energy Demand (CED) methodologies were applied for the assessment. In addition, a sensitivity analysis has been conducted. The results showed that across the operational phases, algae cultivation and drying are the most phases that lead to greater environment-relevant aspects. Analysing different scenarios, the use of wastewater as a source of nutrients for algae (Chlorella vulgaris species), with respect to the use of synthetic nutrients with the same biomass productivity, resulted to be the most feasible and attractive alternative in terms of environmental impact. Finally, the sensitivity analysis highlighted how the environmental performance can be significantly improved by enhancing the productivity and the harvesting rate. The study provides important information to the different actors involved in the biotechnologies sectors, to be able to build and/or evaluate different production options with a holistic and proactive approach, in order to optimize the technologies with a view to maximize its environmental sustainability.