TECHNO-ECONOMIC ANALYSIS AND LIFE CYCLE ASSESSMENT OF ALGAL TURF SCRUBBERS TREATING ANAEROBIC LAGOON EFFLUENT FOR NUTRIENT RECOVERY AND RENEWABLE DIESEL PRODUCTION

Abstract

High-nutrient wastewater sources, such as anaerobic dairy lagoon effluent, contribute to nitrogen (N) and phosphorus (P) overapplication, groundwater contamination, and surface-water impairment. Algal turf scrubbers (ATS) can recover these nutrients while producing harvestable biomass for bioproducts, but the economic feasibility of treatment remains unexplored. This study presents the first national-scale techno-economic and life cycle assessment of a modular ATS system for treating dairy anaerobic lagoon effluent across the contiguous United States, using a county-level model informed by 2022 dairy census data, manure-management datasets, and process wastewater criteria. Nutrient removal was simulated using an experimentally validated framework integrating Monod-based biokinetics and light-use-efficiency-based biomass productivity. Harvested biomass was routed to centralized state-level hydrothermal liquefaction facilities for renewable diesel production. Results show that ATS-derived renewable diesel remained economically challenging, with fuel selling prices exceeding the U.S. average fuel selling price of $0.98 LGE-1 across all cost assumptions. However, to reach economic parity, the required nutrient credits were below conventional treatment cost benchmarks for 30-96% of locations for N and 65-96% for P, depending on cost assumptions. For wastewater treatment alone, lower cultivation-cost assumptions allowed 94% of evaluated locations to fall below a $1.61 m-3 treatment benchmark. Life-cycle results showed that most locations exceeded low-carbon fuel thresholds due to cultivation and biomass transportation burdens. Overall, while ATS-derived renewable diesel faces persistent economic and carbon-intensity barriers, lagoon-based ATS systems demonstrate strong potential as a nutrient-recovery technology with potential fuel co-production serving as a supplementary benefit rather than a primary value driver.