Techno-economic Analysis and Life Cycle Assessment of an Integrated Wastewater-Derived Duckweed Biorefinery

Duckweeds are efficient aquatic plants for wastewater treatment due to their high nutrient uptake capabilities, growth rates, and resilience to severe environmental conditions. The high starch and cellulose contents of duckweed species make them an attractive feedstock for biofuels and biochemicals. Experimental studies have shown that sequential anaerobic bioprocessing of duckweed into ethanol, carboxylates, methane, and soil amendment in a biorefinery system is technically feasible. This study aims to identify challenges and opportunities for large-scale wastewater-derived duckweed biorefineries as a way to promote a circular bioeconomy. The most suitable end products from wastewater-derived duckweed biomass, determined in a series of previously reported laboratory batch experiments, were used to estimate the bioproduct yields during the hypothetical operation of a large-scale biorefinery. Techno-economic analysis (TEA) revealed a minimum duckweed selling price of $7.69 Mg-1 dry matter and a minimum ethanol selling price of $2.17/L or $8.23 gal-1. Duckweed pond construction and duckweed harvesting accounted for the largest share of capital (55.6%) and operating expenses (90.4%), respectively. A cradle-to-gate life cycle assessment (LCA) revealed that duckweed pond construction led to increased land use change impacts, but water-quality and eutrophication impacts could be significantly reduced with this integrated system through efficient nutrient upcycling.