Technologies for improving microalgae biomass production coupled to effluent treatment: A life cycle approach

Algal biomass production in wastewater is a promising value-adding alternative that should be coupled to the treatment system. The technical aspects of cultivation systems for improved biomass yield have been widely reported in the literature; yet, their environmental performance can still be further studied and compared. This study evaluated the environmental impacts associated with the production of 1 kg of biomass grown in high-rate ponds, with domestic effluent as culture media. Seven systems with three approaches to cultivation were modeled through the life cycle assessment method: using effluent pre-treated with ultraviolet disinfection; with supplementation from industrial CO2 and with exhaust gas from gasoline combustion; coupled with a biofilm reactor for biomass attached growth. Environmental impacts were also compared to a base cultivation using the ReCiPe method, for 13 impact categories. The environmental impacts were reduced at least 30% by using wastewater as a water and nutrient source, with systems reaching negative impact values. The only exception was eutrophication categories, with the highest normalized impacts along with toxicity-related categories. The system using CO2 supply from exhaust gas from gasoline combustion had the best performance in 11 categories, reducing impacts in at least 56% compared to a base cultivation scenario. The most impactful process was industrial CO2 supplementation, followed by biofilm. Coupling industrial CO2 supply and hybrid systems for increased biomass productivity did not compensate environmentally, increasing impacts up to 227%. Scenario evaluations were performed for increased and worsened performance of CO2 supply rates (+/- 40%) and biofilm reactor lifespan (+/- 20 days). Opportunities to improve lie in the use of recovered gas from different industries and different support materials for the attached growth of biomass in hybrid systems.