Abstract
Microalgae are a potential feedstock for a wide range of final products. However, the commercialization of simple process routes and multi-product biorefinery schemes is hindered by unsatisfactory or uncertain environmental and economic performances. Many life cycle assessment (LCA) studies have evaluated the environmental sustainability of microalgal systems, leading to controversial results. In most cases, they are affected by the use of lab-scale extrapolated or literature data, resulting in qualitative and unreliable projections.
This work presents a preliminary evaluation of the environmental profile of an industrial-scale plant by applying the LCA methodology with the use of primary data for the foreground inventory. The analyzed facility is installed in Caltagirone, Sicily (Italy). It has a capacity of 1200 kgDW year–1 (DW = dry weight biomass) cultivating Chlorella vulgaris in vertically stacked horizontal photobioreactors (VSt-PBRs) with a total volume of 40.4 m3. Demineralized water, produced via reverse osmosis of tap water, is used for cultivation and maintenance (cleaning). Centrifugation is used for dewatering the algal suspension from 2 gDW L–1 to ~200 gDW L–1. A cradle-to-gate assessment was performed using primary data on plant operation and poly(methyl methacrylate) (PMMA) usage (the main construction material for the PBRs). The LCA results highlight that (i) cultivation is by far the most impactful process step compared to cleaning and harvesting, and (ii) chemicals (nutrients for cultivation, and cleaning and sterilization agents) and electricity (pumping and agitation, thermoregulation, and LED lighting) are the flows that cause the main environmental hotspots. In contrast, PMMA usage and waste treatment provided lower relative contributions to generating potential impacts, while tap water consumption had negligible effects.
