Sustainable production of microalgae in raceways: Nutrients and water management as key factors influencing environmental impacts

Microalgae production has taken on importance for its ability to be more energy efficient than land crops, with low input requirements and a wide number of possible applications. This work aimed to evaluate the environmental impacts of the production of microalgae for use as bio-stimulants and aquaculture feeds. Inventory data from a real production facility of 1 ha located in Almería (Spain) were acquired, and LCA was applied to compare nine scenarios with alternative water bases (fresh, sea and waste), and nutrient sources (fertilizers, manure and wastewater), and the alternatives were also compared using a CO2 supply (commercial liquid) versus a default scenario (recovered flue gas). The LCA results outlined that the main inputs affecting environmental performance were electricity use, chemical fertilizer demand (N and P) and transport. Scenarios using recovered nutrients from slurry and wastewater showed reductions in the climate change category (kg CO2 eq.) of 80% and 20% respectively, compared to standard fertilizer use. The threshold of distance for manure transport was 40 km, beyond that value the scenarios using recovered nutrients performed worse than scenarios using chemical fertilizers. The multifunctionality of the process which included wastewater depuration, permitted compensation in most of the impact categories, yielding negative values in some (all of the toxicity categories).