Seasonal Treatment and Economic Evaluation of an Algal Wastewater System for Energy and Nutrient Recovery

Timothy Strathmann, Yalin Li, Sydney Slouka, Shanka Henkanatte-Gedera, Nagamany Nirmalakhandan

Research output: Contribution to journalArticlepeer-review

16 Scopus Citations


Algal systems have been proposed for treating wastewater while simultaneously recovering energy and nutrients. In this study, an integrated system with algal treatment of municipal wastewater followed by hydrothermal liquefaction (HTL) conversion and upgrading steps was evaluated. Pilot-scale treatment of primary clarified municipal wastewater effluent was evaluated in different seasons (cold, warm, and a transitional period in between) with different strains of algae selected for each season, and the warm season strain successfully met all local discharge regulations. The collected wastewater algae biomass was subjected to HTL at 300 and 350 degrees C and both energy and nutrient recoveries were much improved at the higher temperature. The transitional batch was found to have the highest biocrude oil yields, and its co-products had the highest nutrient (nitrogen and phosphorus) contents. Economic analysis of conversion processes informed by the observed HTL product yields was conducted. While this revealed that targeting biofuel products alone was not profitable, adding nutrient co-products (e.g., ammonium sulfate fertilizer), adjusting algae harvesting time, and incorporating component-specific conversion processes could substantially improve system economics. Overall, this study highlights connections between treatment and conversion processes, and demonstrates how these connections can be leveraged for more efficient resource recovery without compromising treatment operations.
Original languageAmerican English
Pages (from-to)1545-1557
Number of pages13
JournalEnvironmental Science: Water Research and Technology
Issue number9
StatePublished - 2019

NREL Publication Number

  • NREL/JA-5100-74863


  • algal treatment
  • hydrothermal liquefaction
  • municipal wastewater


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