Techno-economic analysis and life cycle assessment of algal turf scrubbers treating wastewater effluent for renewable diesel production

Abstract

Algal turf scrubbers (ATS) are a promising wastewater treatment technology that can simultaneously remove nutrients from effluent and generate algal biomass for conversion into renewable fuels. This study presents the first integrated techno-economic analysis (TEA) and life cycle assessment (LCA) of ATS systems treating effluent from point-source wastewater treatment plants across the continental United States. A regionally resolved process model was developed using watershed data to simulate nutrient removal and biomass production, with biomass subsequently routed to centralized biorefineries for conversion to renewable diesel via hydrothermal liquefaction. The analysis incorporates non-co-located infrastructure and average transportation distances to reflect real-word deployment logistics. Economic viability was evaluated using a discounted cash flow rate of return model, and environmental impacts were assessed using a well-to-wheels LCA framework. Moreover, the TEA incorporates differentiated nutrient credits for nitrogen and phosphorus removal, enabling a more accurate evaluation of water quality services. Results indicate that ATS systems are effective at nutrient removal, with 75% of modeled sites achieving cost competitiveness for fuel production (< $0.87 per liter gasoline equivalent) when nutrient credits of $42 kg-1 for nitrogen and $321 kg-1 for phosphorus removal are applied. However, only 29% of sites present lower life cycle greenhouse gas emissions below the renewable fuel standard (45 g CO2eq MJ-1), limiting locations of feasible deployment. Nonetheless, ATS systems exhibit lower energy and carbon intensity compared to conventional tertiary treatment technologies, offering a viable pathway toward integrated wastewater management and biofuel production.