Biodiversity Improves Life Cycle Sustainability Metrics in Algal Biofuel Production

Algal biofuel has yet to realize
its potential as a commercial
and sustainable bioenergy source, largely due to the challenge of
maximizing and sustaining biomass production with respect to energetic
and material inputs in large-scale cultivation. Experimental studies
have shown that multispecies algal polycultures can be designed to
enhance biomass production, stability, and nutrient recycling compared
to monocultures. Yet, it remains unclear whether these impacts of
biodiversity make polycultures more sustainable than monocultures.
Here, we present results of a comparative life cycle assessment (LCA)
for algal biorefineries to compare the sustainability metrics of monocultures
and polycultures of six fresh-water algal species. Our results showed
that when algae were grown in outdoor experimental ponds, certain
bicultures improved the energy return on investment (EROI) and greenhouse
gas emissions (GHGs) by 20% and 16%, respectively, compared to the
best monoculture. Bicultures outperformed monocultures by performing
multiple functions simultaneously (e.g., improved stability, nutrient
efficiency, biocrude characteristics), which outweighed the higher
productivity attainable by a monoculture. Our results demonstrate
that algal polycultures with optimized multifunctionality lead to
enhanced life cycle metrics, highlighting the significant potential
of ecological engineering for enabling future environmentally sustainable
algal biorefineries.