Microalgae biomass production from cultivation in availability and limitation of nutrients: The technical, environmental and economic performance

Abstract

Microalgae cultivation offers the potential to produce different biomass compositions while preventing pollution, treating waste and recovering resources. However, the energy, environmental and economic performance of the production of microalgae biomass should be advantageous compared to that of conventional biomass sources. The goal of this research was to quantify the performance of energy demand, carbon footprint and financial cost of microalgae biomass production in cultivation with availability and limitation of nutrients. The product system is composed of microalgae cultivation in open raceway ponds with carbon dioxide injection and harvesting with settling, filtration and centrifugation. The average annual biomass productivity in the cultivation was 18 g (m2 day)−1 in the base scenarios with availability (S1) and limitation (S2) of nitrogen and phosphorus, which was changed to 8.5 g (m2 day)−1 in S1LOWER and S2 LOWER and 25 g (m2 day)−1 in S1HIGHER and S2HIGHER. The methods used in this study were attributional life cycle assessment (LCA) for energy demand (Cumulative Energy Demand – CED) in Megajoule (MJ) and carbon footprint (IPCC-2021, Global Warming Potential 100 years) in kilogram of carbon dioxide equivalent (kg CO2eq) and techno-economic analysis (TEA) for financial cost in United States dollar (USD). The energy demand, carbon footprint and financial cost, respectively, in S1 were 10 MJ kg−1, 0.48 kg CO2eq kg−1 and 0.59 USD kg−1 for a dewatered biomass in total solids, while those varied by: +30%, +24% and +72% in S1LOWER; −11%, −8.9% and −19% in S1HIGHER; −38%, −46% and −15% in S2; −6.1%, −20% and +62% in S2LOWER; and −50%, −56% and −36% in S2HIGHER compared to S1. The largest contribution of energy demand and carbon footprint, respectively, in S1 was the fertilizer supply (52% and 61%), while in S2 it was the electricity supply (51% and 48%). The use of residual N and P and photovoltaic electricity supply were considered in the sensitivity analysis, which showed a potential to reduce up to 61% in energy demand, 84% in carbon footprint and 37% in financial cost compared to S1. Therefore, limiting nutrients and using nutrients from residual sources in cultivation along with providing electricity from a cleaner and affordable source are strategies for commodity production from microalgae biomass.